WO2011043411A1 - 基地局装置 - Google Patents
基地局装置 Download PDFInfo
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- WO2011043411A1 WO2011043411A1 PCT/JP2010/067628 JP2010067628W WO2011043411A1 WO 2011043411 A1 WO2011043411 A1 WO 2011043411A1 JP 2010067628 W JP2010067628 W JP 2010067628W WO 2011043411 A1 WO2011043411 A1 WO 2011043411A1
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- base station
- station apparatus
- synchronization
- information
- processing unit
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L5/00—Arrangements affording multiple use of the transmission path
- H04L5/0001—Arrangements for dividing the transmission path
- H04L5/0003—Two-dimensional division
- H04L5/0005—Time-frequency
- H04L5/0007—Time-frequency the frequencies being orthogonal, e.g. OFDM(A), DMT
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J11/00—Orthogonal multiplex systems, e.g. using WALSH codes
- H04J11/0023—Interference mitigation or co-ordination
- H04J11/005—Interference mitigation or co-ordination of intercell interference
- H04J11/0053—Interference mitigation or co-ordination of intercell interference using co-ordinated multipoint transmission/reception
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J11/00—Orthogonal multiplex systems, e.g. using WALSH codes
- H04J11/0023—Interference mitigation or co-ordination
- H04J11/005—Interference mitigation or co-ordination of intercell interference
- H04J11/0056—Inter-base station aspects
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L5/00—Arrangements affording multiple use of the transmission path
- H04L5/003—Arrangements for allocating sub-channels of the transmission path
- H04L5/0032—Distributed allocation, i.e. involving a plurality of allocating devices, each making partial allocation
- H04L5/0035—Resource allocation in a cooperative multipoint environment
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W56/00—Synchronisation arrangements
- H04W56/001—Synchronization between nodes
- H04W56/002—Mutual synchronization
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
- H04L27/2668—Details of algorithms
- H04L27/2681—Details of algorithms characterised by constraints
- H04L27/2688—Resistance to perturbation, e.g. noise, interference or fading
Definitions
- the present invention relates to a base station apparatus that performs wireless communication with a terminal apparatus.
- inter-base station synchronization may be performed to achieve synchronization of communication frame timing and the like among a plurality of base station apparatuses.
- Patent Document 1 discloses that inter-base station synchronization is performed using transmission signals from other base stations serving as synchronization sources.
- the base station apparatus when the base station apparatus tries to synchronize with another base station apparatus, the base station apparatus needs to receive the transmission signal that the other base station apparatus transmits to the terminal apparatus. Therefore, during the reception, since it can not perform transmission or reception with the terminal device, the communication quality with the terminal device may be affected to some extent. Therefore, if synchronization between base stations is frequently performed, although synchronization accuracy is improved, transmission signals from other base station devices are frequently received, so that it is possible between the base station device and the terminal device. The quality of the inherent communication that takes place is reduced. On the other hand, if the frequency of inter-base station synchronization is lowered, deterioration in communication quality with the terminal apparatus can be suppressed, but a situation may occur in which the synchronization accuracy is lowered.
- the above cell refers to an area in which the base station apparatus can communicate with the terminal apparatus.
- the transmission power is about 200 mW to 2 W
- a pico base station that forms a pico cell of about 100 m to 500 m the transmission power is about 20 to 200 mW, and a size of 100 m or less
- the femtocell formed by the femto base station apparatus is usually formed in a macrocell, so almost the entire area of the femtocell may overlap with the macrocell. Furthermore, the femto base station apparatus may be installed at any place in the macro cell by the user. Therefore, the downlink signal of the femto base station interferes with the terminal connected to the macro base station, and the uplink signal transmitted by the terminal connected to the femto base station interferes with the macro base station I sometimes give it. Further, there are also cases where a plurality of femto base station apparatuses adjacent to each other to form a femtocell and terminal apparatuses connected thereto give interference to each other.
- the radio frames of both base station apparatuses need to be synchronized with each other with high accuracy. Therefore, as described above, when there is a possibility that interference may occur in relation to the base station apparatus that is the synchronization source, it is preferable that synchronization between the base station apparatuses is more accurately synchronized.
- an object of this invention is to provide the base station apparatus which can perform appropriately the process accompanied with acquisition of the transmission signal from another base station apparatus. Also, another object of the present invention is to preferably avoid interference even when there is a possibility that interference may occur in relation to another base station apparatus that is a synchronization source in inter-base station synchronization. It is an object of the present invention to provide a base station apparatus capable of performing synchronization processing.
- a base station apparatus includes: a receiving unit that receives a transmission signal from another base station apparatus; a processing unit that acquires the transmission signal from the receiving unit and performs processing on the transmission signal; And / or a detection unit that detects a communication state with a terminal apparatus connected to the other base station apparatus, and the processing unit acquires the transmission signal based on the detection result of the detection unit. It is characterized by adjusting the timing to do.
- the processing unit adjusts the timing of acquiring the transmission signal based on the communication status with the terminal apparatus connected to itself and / or another base station apparatus.
- the processing can be performed at timing according to the necessity of the processing that changes depending on the communication status with the terminal device.
- processing accompanied by acquisition of transmission signals from other base station apparatuses can be appropriately performed.
- the processing unit adjusts timing so that the processing is periodically performed.
- the control unit may adjust the cycle of the processing based on the detection result of the detection unit.
- the communication status of a terminal apparatus connected to another base station apparatus can be grasped by confirming whether the downlink signal (transmission signal) of the other base station apparatus includes a signal directed to the terminal. can do. Therefore, the detection unit measures the reception power (reception level) of the received downlink signal of the other base station apparatus, and based on the reception power, the detection unit communicates with the terminal apparatus connected to the other base station apparatus. Communication status can be detected.
- the detection unit may measure the reception power of the downlink signal of the other base station apparatus for each minimum resource allocation unit in the downlink signal of the other base station apparatus, in this case The presence or absence of a signal directed to the terminal device can be grasped for each minimum unit, and the communication status of the terminal device can be detected in more detail.
- the communication condition which the said detection part detects is the number of the terminal devices specifically connected with self and / or the said other base station apparatus.
- the processing unit includes a synchronization processing unit that performs synchronization processing for achieving inter-base station synchronization with the other base station apparatus based on the transmission signal. Or a measurement processing unit that performs measurement processing for measuring the transmission signal.
- the processing timing can be adjusted so that the synchronization accuracy and the like can be maintained while suppressing the influence on the inherent communication.
- the synchronization processing unit adjusts the cycle of the synchronization processing to be longer as the number of terminal devices connected to the processing unit decreases. Further, it is preferable to adjust so that the period of the synchronization process becomes longer as the number of terminal devices connected to the other base station device is smaller. In this case, if the necessity of synchronization processing is low because the number of terminal devices connected to itself or the number of terminal devices connected to other base station devices is small, the frequency of the synchronization processing may be reduced. it can. As a result, synchronous processing can be performed without waste.
- the detection unit can detect the communication state using the measurement result of the measurement processing unit. In this case, the detection unit does not need to have a configuration for acquiring information on transmission signals of other base station apparatuses independently, which simplifies the configuration.
- a reception unit for receiving a transmission signal from another base station apparatus, the transmission signal obtained by the reception unit, and synchronization between base stations using the transmission signal A processing unit for performing synchronization processing to be performed, and the processing unit adjusts timing for performing the processing based on information indicating whether interference may occur due to the relationship between itself and the other base station apparatus It is characterized by
- the timing of performing synchronization processing is adjusted based on the information indicating whether or not interference may occur in the relationship between itself and the other base station apparatus that is the synchronization source. For example, if it can be determined that interference may occur in relation to another base station apparatus, the frequency of synchronization processing can be increased to effectively suppress interference, and the accuracy of inter-base station synchronization can be improved. be able to. As a result, even when there is a possibility that interference may occur due to the relationship with another base station apparatus that is the synchronization source, synchronization processing can be performed so that the interference can be suitably avoided.
- the information indicating whether interference may occur due to the relationship between itself and the other base station device is the terminal device connected to itself and / or the other base station device. Preferably it is a number.
- the accuracy of inter-base station synchronization between itself and another base station apparatus be high in order to effectively suppress interference. Therefore, the information indicating whether interference may occur in the relationship between itself and the other base station apparatus is information indicating a positional relationship between itself and the other base station apparatus, or It is preferable that the value be information affected by the positional relationship with another base station apparatus.
- the processing unit is based on the information indicating the positional relationship between itself and the other base station apparatus or the information whose value is affected by the positional relationship between itself and the other base station apparatus. .
- Adjust the timing of performing synchronization processing Therefore, for example, when it can be determined from the above information that the position between itself and another base station apparatus is relatively close and the possibility of interference is high, the synchronization processing is performed so that the frequency of synchronization processing becomes high. Timing can be adjusted. As a result, the accuracy of inter-base station synchronization can be enhanced, and interference generated with other base station apparatuses can be effectively suppressed.
- the timing of the synchronization process can be adjusted to reduce the frequency of the process. As a result, it is possible to prevent unnecessary synchronous processing.
- the timing at which synchronization processing is performed is adjusted based on the information indicating the positional relationship between itself and the other base station apparatus, thereby achieving inter-base station synchronization. Even when there is a possibility that interference may occur in relation to another base station apparatus that is the synchronization source, synchronization processing can be performed so that interference can be suitably avoided.
- the information whose value is affected by the positional relationship between itself and the other base station apparatus is information on the detection result when the transmission signal of the other base station apparatus is detected.
- the reception level of the transmission signal of the other base station apparatus, or the path loss value between the other base station apparatus and itself is information on the detection result when the transmission signal of the other base station apparatus is detected.
- the information on the detection result when the transmission signal of the other base station apparatus is detected is the number of times of detection of the other base station apparatus detected within a predetermined period, or the number of times of detection It is preferable that it is a detection rate which is a ratio of and the number of times of detection. Furthermore, the information on the detection result when the transmission signal of the other base station apparatus is detected is the time when the transmission signal of the other base station apparatus was last detected, or the current time from the time It may be an elapsed time until
- the information whose value is affected by the positional relationship between itself and the other base station apparatus is between itself and the other base station apparatus. It is preferable that the information is information on the number of handover attempts of a terminal device connected to the base station apparatus itself or the other base station apparatus, or information whose value is affected by the number of handover trials.
- the number of handover attempts is information indicating the positional relationship between itself and the other base station device, or information whose value is affected by the positional relationship between itself and the other base station device. is there. Therefore, also in this case, by adjusting the timing at which synchronization processing is performed based on the number of handover attempts, there is a possibility that interference may occur in relation to other base station apparatuses that are synchronization sources in inter-base station synchronization. Even in some cases, synchronization processing can be performed so that interference can be suitably avoided.
- the access mode defines the connection restriction of the terminal apparatus connected to another base station apparatus, and indicates the publicity of the other base station apparatus. For example, in the mode in which the degree of connection restriction of the terminal device is low, it indicates that the publicity is high and the possibility that a larger number of terminal devices are connected is high. Therefore, the more the access mode is the mode in which the connection restriction of the terminal device is low, the higher the possibility of giving interference.
- the information indicating whether interference may occur in the relationship between itself and the other base station device is information indicating the carrier frequency of the other base station device, and the other base station device is a macro base station Or information indicating the transmission power of the transmission signal, information indicating the access mode of the other base station apparatus to the terminal apparatus connected to the other base station apparatus, or It is preferable that it is an estimated number of terminal devices located in the vicinity and connected to the other base station device.
- the processing unit may further include information indicating whether or not the interference can be avoided. Based on this, the timing for performing synchronization processing may be adjusted, and in this case, interference can be suitably avoided with other base station apparatuses that may cause interference. More specifically, the information indicating whether the interference can be avoided is resource block allocation when the other base station apparatus performs resource allocation to a terminal apparatus connected to the other base station apparatus Preferably, the information is information indicating a format or information indicating whether inter-base station communication is possible between itself and the other base station apparatus.
- a reception unit for receiving a transmission signal from another base station apparatus, and the transmission signal obtained by the reception unit are used to perform inter-base station synchronization using the transmission signal.
- the information indicating the reception accuracy of the transmission signal from the other base station apparatus is preferably the reception level when the transmission signal is received, or SINR.
- the information affecting the reception accuracy of the transmission signal from the other base station apparatus according to the value is the information indicating the positional relationship between itself and the other base station apparatus, or It is preferable that the value be information affected by the positional relationship with another base station apparatus.
- the processing unit is based on the information indicating the positional relationship between itself and the other base station apparatus or the information whose value is affected by the positional relationship between itself and the other base station apparatus. , Adjust the timing of performing synchronization processing. Therefore, for example, based on the above information, it can be determined that the position of the base station apparatus is close to that of the base station apparatus itself and the reception accuracy of the transmission signal of the other base station apparatus is high enough to achieve high accuracy base station synchronization. In addition, since the accuracy of inter-base station synchronization can be maintained high without increasing the frequency of synchronization processing, the timing of synchronization processing can be adjusted so that the frequency of synchronization processing is relatively low.
- the timing of the synchronization process can be adjusted so that the frequency of the synchronization process is higher than when it can be determined. As a result, the accuracy of inter-base station synchronization can be enhanced, and interference generated with other base station apparatuses can be effectively suppressed.
- this base station apparatus information indicating the positional relationship between itself and the other base station apparatus, which is information affecting the reception accuracy of transmission signals of other base station apparatuses, etc.
- the information whose value is affected by the positional relationship between itself and the other base station apparatus is information on the detection result when the transmission signal of the other base station apparatus is detected. Is preferred.
- the information on the detection result when the transmission signal of the other base station apparatus is detected is the number of times of detection of the other base station apparatus detected within a predetermined period, or the number of times of detection It is preferable that it is a detection rate which is a ratio of and the number of times of detection. Furthermore, the information on the detection result when the transmission signal of the other base station apparatus is detected is the time when the transmission signal of the other base station apparatus was last detected, or the current time from the time It may be an elapsed time until
- the information whose value is affected by the positional relationship between itself and the other base station apparatus is between itself and the other base station apparatus. It is preferable that the information is information on the number of handover attempts of a terminal device connected to the base station apparatus itself or the other base station apparatus, or information whose value is affected by the number of handover trials.
- processing accompanied by acquisition of transmission signals from other base station apparatuses can be appropriately performed. Further, according to the base station apparatus of the present invention, interference can be suitably avoided even when there is a possibility that interference may occur in relation to other base station apparatuses that are synchronization sources in inter-base station synchronization. Synchronization processing can be performed.
- FIG. 1 is a schematic view showing a configuration of a wireless communication system according to a first embodiment of the present invention. It is a figure which shows the structure of each radio frame of uplink and downlink in LTE. It is a figure which shows the detailed structure of DL frame. It is a block diagram which shows the structure of a femto base station apparatus. It is a block diagram which shows the detail of RF section. It is a block diagram which shows the structure of the synchronous process part for performing the synchronous process which synchronizes between base stations between other base station apparatuses. It is a figure for demonstrating an example of the aspect of the synchronous process which a synchronous process part performs.
- FIG. 1 It is a figure which shows the aspect of the connection to the communication network of each BS. It is the sequence diagram which showed an example of the procedure at the time of the femto base station apparatus of 2nd embodiment acquiring measurement result information. It is a figure which shows an example of the neighboring cell information which a femto base station apparatus memorize
- (A) is a figure showing an example of a detection result of other base station devices detected when a femto base station device according to another example 2 of the second embodiment acquires measurement result information
- (A) is a figure showing an example of a detection result of other base station devices detected when a femto base station device according to another example 2 of the second embodiment acquires measurement result information
- (B) is a figure which shows an example of the adjacent cell information which the adjacent cell information generation part of this example produces
- It is a partial block diagram showing a part of internal configuration of a femto base station device concerning a third embodiment of the present invention.
- the femto base station apparatus of 3rd embodiment is a sequence diagram which shows an example of an aspect which acquires hand-over information in the hand-over performed with a terminal device. When a handover is performed in the procedure shown in FIG.
- FIG. 13 is a partial block diagram showing a part of the internal configuration of a femto base station device according to a fourth embodiment of the present invention. It is a figure which shows the content of the access mode set to a base station apparatus. It is a figure which shows an example of the neighboring cell information which the femto base station apparatus of 4th embodiment produces
- FIG. 13 is a partial block diagram showing a part of the internal configuration of a femto base station device according to a fourth embodiment of the present invention. It is a figure which shows the content of the access mode set to a base station apparatus. It is a figure which shows an example of the neighboring cell information which the femto base station apparatus of 4th embodiment produces
- FIG. 21 is a partial block diagram showing a part of the internal configuration of a femto base station device according to a fifth embodiment of the present invention. It is a figure which shows an example of the neighboring cell information which the femto base station apparatus of 5th embodiment produces
- FIG. 21 is a partial block diagram showing a part of the internal configuration of a femto base station device according to a sixth embodiment of the present invention. . It is a flowchart which shows the method of estimating the number of the terminal devices connected to the other base station apparatus located in the vicinity of a self-station apparatus. It is a figure which shows an example at the time of setting 1st PRACH and 2nd PRACH on a UL frame.
- FIG. 1 is a schematic view showing the configuration of a wireless communication system according to an embodiment of the present invention.
- the wireless communication system includes a plurality of base station devices 1 and a plurality of terminal devices 2 (mobile terminals: Mobile Stations) capable of performing wireless communication with the base station device 1.
- the plurality of base station devices 1 are, for example, a plurality of macro base station devices (Macro Base Station) 1a forming a communication area (macrocell) MC having a size of several kilometers, and several tens of meters installed in each macrocell MC.
- a plurality of femto base stations (Femto Base Stations) 1b that form relatively small femtocells FC.
- Each macro base station apparatus 1a (hereinafter, also referred to as macro BS1a) can perform wireless communication with the terminal apparatus 2 in the macro cell MC of its own (local apparatus).
- the femto base station apparatus 1b (hereinafter, also referred to as femto BS 1b) is disposed, for example, indoors or in a place where it is difficult to receive the radio wave of the macro BS 1a, and forms the femtocell FC.
- the femto BS 1b can perform wireless communication with the terminal device 2 (hereinafter also referred to as MS2) in the femtocell FC formed by itself (the own station device), and in this system, the radio wave of the macro BS 1a is
- MS2 terminal device 2
- the femto BS 1b forming a relatively small femtocell FC at a location where reception is difficult, etc., it is possible to provide a service with sufficient throughput to the MS2.
- the femto BS 1 b is installed in a macro cell MC formed by the macro BS 1 a after the macro BS 1 a is installed, and forms a femtocell FC in the macro cell MC. For this reason, there is a possibility that interference etc. may occur between the femto BS 1 b and the macro BS 1 a or the MS 2 etc. which are in communication with the macro BS 1 a.
- the femto BS 1b based on the function of monitoring (measurement processing) transmission conditions such as transmission power and used frequency in other base station apparatuses such as the macro BS 1a and other femto BSs 1b other than itself, the femto BS 1b and the result thereof It has a function of adjusting transmission conditions such as transmission power and used frequency so as not to affect communication in the macro cell MC.
- the femto BS 1 b can form the femtocell FC in the macrocell MC without affecting the communication of other base station apparatuses by this function.
- inter-base station synchronization is performed in which timings of communication frames are synchronized among a plurality of base station apparatuses including the macro BS 1 a and the femto BS 1 b.
- Inter-base station synchronization is performed by “air synchronization” in which another base station apparatus synchronizes by the base station apparatus serving as a parent (synchronization source) receiving a signal transmitted toward MS 2 in its own cell.
- the base station apparatus serving as the parent (synchronization source) may be capable of air synchronization with other base station apparatuses, or other than air synchronization, such as autonomously determining frame timing by a GPS signal.
- the frame timing may be determined by the following method.
- the macro BS 1a can be parented to another macro BS 1a, but can not be parented to the femto BS 1b.
- the femto BS 1 b can be parented to the macro BS 1 a or can be parented to another femto BS 1 b.
- the wireless communication system is, for example, a system for mobile phones to which LTE (Long Term Evolution) is applied, and communication based on LTE is performed between each base station apparatus and a terminal apparatus.
- LTE Long Term Evolution
- FDD frequency division duplex
- the communication system is not limited to the LTE, and is not limited to the FDD scheme, and may be, for example, a TDD (time division duplex) scheme.
- Uplink signals transmission signals from the terminal apparatus to the base station apparatus
- downlink signals transmission signals from the base station apparatus to the terminal apparatus
- Uplink communication and downlink communication are simultaneously performed by assigning different use frequencies to each other.
- FIG. 2 is a diagram showing the structure of uplink and downlink radio frames in LTE.
- the downlink frame (DL frame) and uplink frame (UL frame) in LTE each have a time length of 10 milliseconds for one radio frame, and are configured by 10 subframes from # 0 to # 9 .
- the DL frame and the UL frame are arranged in the time axis direction with their timings aligned.
- FIG. 3 is a diagram showing a detailed structure of a DL frame.
- the vertical axis direction indicates the frequency
- the horizontal axis direction indicates the time.
- the subframes forming the DL frame are each formed of two slots (for example, slots # 0 and # 1). Also, one slot is made up of seven (# 0 to # 6) OFDM symbols (in the case of Normal Cyclic Prefix).
- a resource block (RB: Resource Block), which is a basic unit (minimum unit) for data transmission, is defined by 12 subcarriers in the frequency axis direction and 7 OFDM symbols (1 slot) in the time axis direction. . Therefore, for example, when the frequency bandwidth of the DL frame is set to 5 MHz, 300 subcarriers are arrayed, and 25 resource blocks are arrayed in the frequency axis direction.
- a control channel for transmitting information necessary for downlink communication to the terminal apparatus by the base station apparatus is assigned to the beginning of each subframe.
- the control channel is allocated by symbols # 0 to # 2 (3 symbols at maximum) of a slot located on the top side in each subframe.
- DL control information, resource allocation information of the subframe, reception success notification (ACK: Acknowledgement) by hybrid automatic repeat request (HARQ: Hybrid Automatic Repeat Request), reception failure notification (NACK: Negative Acknowledgment) Etc are stored.
- a broadcast channel for notifying a terminal apparatus of a system bandwidth and the like by broadcast transmission is allocated to the first subframe # 0.
- the broadcast channel is arranged with four symbol widths at the positions of symbols # 0 to # 3 of the backward slot in the first subframe # 0 in the time axis direction, and the bandwidth of the DL frame in the frequency axis direction Is allocated at the middle position of 6 resource blocks wide (72 subcarriers).
- This broadcast channel is configured to be updated every 40 milliseconds by transmitting the same information over four frames.
- the broadcast channel stores main system information such as communication bandwidth, the number of transmitting antennas, and the structure of control information.
- each of the first (# 0) and sixth (# 5) subframes is a signal for identifying a base station apparatus or a cell.
- One synchronization signal and a second synchronization signal (P-SCH: Primary Synchronizaton Channel, S-SCH: Secondary Synchronizaton Channel) are allocated.
- the first synchronization signal is arranged with a single symbol width at the position of symbol # 6, which is the last OFDM symbol of the slot on the leading side in subframe # 0 and subframe # 5 in the time axis direction, in the frequency axis direction. , Are arranged at the center position of the bandwidth of the DL frame by six resource block widths (72 subcarriers).
- the first synchronization signal is information for the terminal device to identify each of a plurality of (three) sectors obtained by dividing the cell of the base station device, and three patterns are defined.
- the second synchronization signal is arranged with a single symbol width at the position of symbol # 5 which is the second OFDM symbol from the end of the slot on the head side of subframe # 0 and subframe # 5 in the time axis direction, Six resource block widths (72 subcarriers) are arranged at the center of the bandwidth of the DL frame in the frequency axis direction.
- the second synchronization signal is information for the terminal device to identify each of the communication areas (cells) of the plurality of base station devices, and is defined as 168 patterns.
- the first synchronization signal and the second synchronization signal are combined with each other to define 504 types (168 ⁇ 3) of patterns.
- the terminal apparatus can recognize in which sector of which base station apparatus the own terminal exists by acquiring the first synchronization signal and the second synchronization signal transmitted from the base station apparatus.
- a plurality of patterns that the first synchronization signal and the second synchronization signal can take are predetermined in the communication standard, and known in each base station apparatus and each terminal apparatus. That is, each of the first synchronization signal and the second synchronization signal is a known signal which can take a plurality of patterns.
- the first synchronization signal and the second synchronization signal are signals for inter-base station synchronization for synchronizing communication timing and / or frequency between base station devices as well as when the terminal device synchronizes with the base station device. Although this is also used as this, this point will be described later.
- DL shared channels Physical Downlink Shared Channel
- the DL shared channel is an area shared for communication by a plurality of terminal devices, and in addition to user data, control information and the like specific to each terminal device are also stored.
- the allocation of user data stored in the DL shared channel is defined by the resource allocation information in the control channel allocated at the beginning of each subframe, and the terminal apparatus is configured to It can be determined whether or not the data for itself is stored in the frame.
- FIG. 4 is a block diagram showing the configuration of the femto base station apparatus in FIG.
- the configuration of the femto BS 1 b will be described, the configuration of the macro BS 1 a is also substantially the same as that of the femto BS 1 b.
- the femto BS 1 b 1 performs processing for inter-base station synchronization as well as signal processing of transmission / reception signals exchanged between the antenna 3, the transmission / reception unit (RF unit) 4 to which the antenna 3 is connected, and the RF unit 4. And a signal processing unit 5 that performs measurement and the like.
- FIG. 5 is a block diagram showing the details of the RF unit 4.
- the RF unit 4 includes an upstream signal receiving unit 11, a downstream signal receiving unit 12, and a transmitting unit 13.
- the upstream signal receiving unit 11 is for receiving an upstream signal from the terminal device 2
- the downstream signal receiving unit 12 is for receiving a downstream signal from another macro BS 1a or another femto BS 1b. is there.
- the transmission unit 13 is for transmitting a downlink signal to the terminal device 2.
- the RF unit 4 also includes a circulator 14.
- the circulator 14 is for providing the reception signal from the antenna 3 to the upstream signal receiving unit 11 and the downstream signal receiving unit 12 and providing the transmission signal output from the transmission unit 13 to the antenna 3 side.
- the circulator 14 and the fourth filter 135 of the transmitter 13 prevent the reception signal from the antenna 3 from being transmitted to the transmitter 13 side.
- the circulator 14 and the first filter 111 of the upstream signal receiving unit prevent the transmission signal output from the transmitting unit 13 from being transmitted to the upstream receiving unit 11. Furthermore, the circulator 14 and the fifth filter 121 prevent the transmission signal output from the transmission unit 13 from being transmitted to the upstream signal reception unit 12.
- the upstream signal receiving unit 11 is configured as a super heterodyne receiver, and configured to perform IF (intermediate frequency) sampling. More specifically, the upstream signal receiving unit 11 includes a first filter 111, a first amplifier 112, a first frequency converter 113, a second filter 114, a second amplifier 115, a second frequency converter 116, and an A / A.
- a D conversion unit 117 is provided.
- the first filter 111 is for passing only an uplink signal from the terminal apparatus 2 is constituted by a band pass filter which passes only the frequency f u of an uplink signal.
- the received signal that has passed through the first filter 111 is amplified by the first amplifier (high frequency amplifier) 112 and converted from the frequency fu to the first intermediate frequency by the first frequency converter 113.
- the first frequency converter 113 is configured of an oscillator 113a and a mixer 113b.
- the output of the first frequency converter 113 is amplified again by the second amplifier (intermediate frequency amplifier) 115 through the second filter 114 which passes only the first intermediate frequency.
- the output of the second amplifier 115 is converted from the first intermediate frequency to the second intermediate frequency by the second frequency converter 116, and is further converted to a digital signal by the A / D converter 117.
- the second frequency converter 116 is also configured by the oscillator 116 a and the mixer 116 b.
- the output of the A / D conversion unit 117 (the output of the first receiving unit 11) is given to the signal processing unit 5 having a function as a demodulation circuit, and demodulation processing of the reception signal from the terminal device 2 is performed.
- uplink signal reception unit 11 a receiving unit configured to conform to the uplink signal frequency f u to receive an uplink signal from the terminal device, inherently required received as the base station apparatus It is a department.
- the transmission unit 13 receives the in-phase signal I and the quadrature signal Q output from the signal processing unit 5 and transmits the signal from the antenna 3 and is configured as a direct conversion transmitter.
- the transmission unit 13 includes D / A converters 131a and 131b, an orthogonal modulator 132, a third filter 133, a third amplifier (high power amplifier; HPA) 134, and a fourth filter 135.
- the D / A converters 131 a and 131 b perform D / A conversion on each of the in-phase signal I and the quadrature signal Q supplied from the signal processing unit 5.
- the outputs of the D / A converters 131a and 131b are supplied to an orthogonal modulator 132, which generates a transmission signal whose carrier frequency is f d (downlink signal frequency).
- the output of the quadrature modulator 132 passes through the third filter 133 which passes only the frequency f d , is amplified by the third amplifier 134, and further obtains the fourth filter 135 which passes only the frequency f d , and transmits from the antenna 3 And a down signal to the terminal device.
- the uplink signal receiving unit 11 and the transmitting unit 13 described above are functions required to perform intrinsic communication with the terminal device, but the base station device 1 of the present embodiment further includes the downlink signal receiving unit 12. Is equipped.
- the downlink signal receiving unit 12 is for receiving downlink signals transmitted by other base station apparatuses.
- the downlink signal of another base station apparatus received by the downlink signal receiving unit 12 is used for inter-base station synchronization processing and measurement of transmission conditions such as transmission power of another base station apparatus.
- the frequency of the downlink signal transmitted by the other base station apparatus is f d and is different from the frequency f u of the uplink signal, so that the other base station apparatus having only the uplink signal processing unit 11 Can not receive the downlink signal transmitted by the base station apparatus of
- the upstream signal reception unit 11 includes a first filter 111 for passing only the signal of the upstream signal frequency f u and a second filter 114 for passing only the first intermediate frequency converted from the frequency f u. Even if a signal of a frequency other than the frequency f u (the frequency f d of the downstream signal) is given to the first receiver 11, it can not pass through the upstream signal receiver 11.
- the upstream signal reception unit 11 is adapted to receive the signal of the upstream signal frequency f u by the filters 111 and 114 provided in the upstream signal reception unit 11, and signals of other frequencies (in particular, Down signal can not be received.
- the RF unit 4 of the present embodiment is provided with a downlink signal receiving unit 12 for receiving a downlink signal of frequency f d transmitted by another base station apparatus, separately from the uplink signal receiving unit 11.
- the downstream signal receiver 12 includes a fifth filter 121, a fourth amplifier (high frequency amplifier) 122, a third frequency converter 123, a sixth filter 124, a fifth amplifier (intermediate frequency amplifier) 125, and a fourth frequency converter 126. , And an A / D conversion unit 127.
- the fifth filter 121 is for passing only the downlink signal from another base station apparatus, and is configured by a band pass filter for passing only the frequency f d of the downlink signal.
- the reception signal that has passed through the fifth filter 121 is amplified by the fourth amplifier (high frequency amplifier) 122, and the output of the fourth amplifier 122 is transmitted from the downstream signal frequency f d to the first intermediate frequency by the third frequency converter 123.
- the third frequency converter 123 is configured of an oscillator 123a and a mixer 123b.
- the output of the third frequency converter 123 passes through the sixth filter 124 which passes only the first intermediate frequency output from the third frequency converter 123, and is amplified again by the fifth amplifier (intermediate frequency amplifier) 125.
- the output of the fifth amplifier 125 is converted by the fourth frequency converter 126 from the first intermediate frequency to the second intermediate frequency, and is further converted by the A / D converter 127 into a digital signal.
- the fourth frequency converter 126 is also configured by the oscillator 126a and the mixer 126b.
- the signal output from the A / D conversion unit 127 is supplied to a synchronization processing unit 5 b and a measurement processing unit 5 c (described later) included in the signal processing unit 5.
- the upstream signal receiving unit 11 and the downstream signal receiving unit 11 may be configured as a direct conversion receiver.
- the uplink and downlink symmetry in the downlink signal reception unit 11 and the transmission unit 13 be secured by antenna calibration.
- the antenna calibration can be performed by providing a gain / phase adjuster (not shown) in the downlink signal receiving unit 11 and / or the transmitting unit 13.
- the signal processing unit 5 has a function to perform signal processing of transmission / reception signals exchanged with the RF unit 4, and transmits various transmission data provided from the upper layer of the signal processing unit 5. And a modulation / demodulation unit 5a for performing processing to demodulate the reception signal supplied from the RF unit 4 into reception data.
- the modulation / demodulation unit 5a performs modulation / demodulation processing in a state in which the synchronization error is corrected based on the synchronization error (timing offset, frequency offset) calculated by the synchronization processing unit 5b described later.
- the signal processing unit 5 is provided with a frame counter (not shown) for determining the transmission timing for each radio frame of the transmission signal given to the RF unit 4.
- the signal processing unit 5 is a resource allocation control unit in addition to a synchronization processing unit 5b for performing synchronization processing to achieve synchronization between base stations with another base station apparatus, and a measurement processing unit 5c for performing measurement. 5 d and a terminal detection unit 5 e for detecting the communication status of the terminal devices connected to itself and other base station devices.
- the configuration of the synchronization processing unit 5b will be described below.
- FIG. 6 is a block diagram showing a configuration of a synchronization processing unit 5b for performing synchronization processing to achieve synchronization between base stations with another base station apparatus.
- each base station apparatus may be equipped with a GPS receiver, and synchronization may be performed by using GPS signals, or base stations may be connected by wire and synchronization may be performed.
- Inter base station synchronization by “air synchronization” in which synchronization is performed by (downlink signal) is adopted.
- the synchronization processing unit 5b acquires the downlink signal of another base station apparatus received by the downlink signal reception unit 12, and the first synchronization signal (P-SCH), which is a known signal included in the frame of the downlink signal, and Based on the second synchronization signal (S-SCH), synchronization processing is performed to synchronize the communication timing and communication frequency of the own base station apparatus 1 with other base station apparatuses.
- P-SCH first synchronization signal
- S-SCH second synchronization signal
- the synchronization processing unit 5b sets, in subframe units, the timing for acquiring the downlink signal of another base station apparatus, which is given from the downlink signal reception unit 12, so that the synchronization processing is performed in a predetermined cycle. Further, the synchronization processing unit 5b has a function of adjusting the timing at which the synchronization processing is performed by adjusting the cycle of the timing at which the downlink signal for synchronization processing is acquired according to the detection result of the terminal detection unit 5e. ing.
- the synchronization processing unit 5b starts synchronization processing by pausing transmission of the transmission signal by the transmission unit 13 in a sub-frame period corresponding to the timing (start timing of synchronization processing) for acquiring the downlink signal set by itself. Do.
- the synchronization processing unit 5b causes the downlink signal reception unit 12 to receive the downlink signal of another base station apparatus while acquiring the downlink signal while stopping transmission of the transmission signal. Thereafter, correction of its own frame timing and communication frequency is performed using this downlink signal, and synchronization processing is finished.
- the section in which the transmission of the transmission signal is paused can be set to a subframe corresponding to the timing of acquiring the downlink signal for synchronization processing and one or more subframes subsequent thereto. In addition to pausing transmission of the transmission signal, pausing reception of the upstream signal from the terminal device may also be performed.
- the synchronization processing unit 5b outputs synchronization timing information, which is information for specifying a subframe corresponding to a section in which transmission of the transmission signal is paused, to the resource allocation control unit 5d and the measurement processing unit 5c.
- the synchronization processing unit 5 b includes a synchronization error detection unit 14, a frame counter correction unit 15, a frequency offset estimation unit 16, a frequency correction unit 17, and a storage unit 18, and synchronizes frame transmission timing. It also has the function of making corrections.
- the synchronization error detection unit 14 detects a frame transmission timing of another base station apparatus using a known signal included in the downlink signal, and an error from the frame transmission timing in the own base station apparatus 1 (frame synchronization error; Communication timing offset) is detected.
- the transmission timing can be detected by detecting the timings of the first synchronization signal and the second synchronization signal, which are known signals (waveforms are also known) at predetermined positions in the frame of the received downlink signal.
- the synchronization error detection unit 14 applies the detected frame synchronization error to the storage unit 18 each time it is detected.
- the storage unit 18 accumulates these detected frame synchronization errors.
- the frame synchronization error detected by the synchronization error detection unit 14 is given to the frame counter correction unit 15.
- the frame counter correction unit 15 corrects the value of the frame counter that determines the transmission timing of the frame in accordance with the detected frame synchronization error.
- the femto BS 1b which is its own, can synchronize with other base station apparatuses.
- the frequency offset estimation unit 16 is based on the synchronization error detected by the detection unit 14, the clock frequency of the built-in clock generator (not shown) built in the base station apparatus itself which is the reception side, and others on the transmission side.
- the difference (clock frequency error) with the clock frequency of the built-in clock generator of the base station apparatus is estimated, and the carrier frequency error (carrier frequency offset) is estimated from the clock frequency error.
- the frequency offset estimation unit 16 is based on the frame synchronization error t1 detected in the previous air synchronization and the frame synchronization error t2 detected in the current air synchronization under a situation where air synchronization is periodically executed. Estimate the clock error.
- the previous frame synchronization error t1 can be acquired from the storage unit 18.
- the synchronization error (timing offset) after correction is 0 [msec].
- the synchronization error (timing offset) of 0.1 [msec] generated in 10 seconds is an accumulated value of an error between the clock cycle of another base station apparatus and the clock cycle of the own base station apparatus. That is, the following equation holds between the synchronization error (timing offset) and the clock cycle.
- the frequency offset estimation unit 16 estimates the clock frequency error as described above.
- the frequency offset estimation unit 16 can also estimate the carrier frequency error (carrier frequency offset) from the clock frequency error.
- the carrier frequency error estimated by the frequency offset estimation unit 16 is given to the frequency correction unit 17.
- the frequency correction unit 17 corrects the carrier frequency based on the carrier frequency error.
- the correction of the carrier frequency can be performed not only on the carrier frequency of the upstream signal but also on the carrier frequency of the downstream signal.
- the measurement processing unit 5c has a function for performing measurement (measurement processing) of the transmission status of downlink signals such as transmission power and used frequency in another base station apparatus, and the other signals received by the downlink signal reception unit 12
- the downlink signal of the base station apparatus is acquired, and the reception power (reception level) of the downlink signal is obtained.
- the measurement processing unit 5c sets, in subframe units, a timing at which a downlink signal is acquired in order to perform measurement processing. Furthermore, the measurement processing unit 5c has a function of adjusting the timing of performing the measurement process by setting and adjusting the timing of acquiring the downlink signal for the measurement process according to the detection result of the terminal detection unit 5e. ing.
- the measurement process is preferably performed immediately after the synchronization process, as described later. For this reason, the measurement processing unit 5c sets the timing at which the measurement processing is performed, in accordance with the synchronization timing information supplied from the synchronization processing unit 5b. For example, the measurement processing unit 5c specifies the subframe in which the synchronization process is started based on the received synchronization timing information, and performs the measurement process in the subframe belonging to the next wireless frame of the wireless frame to which the identified subframe belongs. Set to do.
- the measurement processing unit 5 c pauses the transmission of the transmission signal by the transmission unit 13 in the section of the subframe corresponding to the timing (the start timing of the measurement process) for acquiring the downlink signal for the measurement process set by itself. , Start the measurement process. While pausing transmission of the transmission signal, the measurement processing unit 5c causes the downlink signal reception unit 12 to receive the downlink signal of another base station apparatus, and acquires the received downlink signal. Thereafter, the received power of the downlink signal is measured, and the measurement process is finished.
- the section in which transmission of the transmission signal is paused can be set to a subframe corresponding to the timing of starting acquisition of the downlink signal and one or a plurality of subsequent subframes. In addition to pausing transmission of the transmission signal, pausing reception of the upstream signal from the terminal device may also be performed.
- the measurement processing unit 5c outputs, to the resource allocation control unit 5d, measurement timing information which is information for specifying a subframe corresponding to a section in which transmission of a transmission signal is to be paused.
- the measurement processing unit 5 c obtains an average value (power average value) of received power for each resource block from the downlink signal acquired from the downlink signal reception unit 12. From the acquired downlink signal, the measurement processing unit 5 c divides and extracts a portion estimated to be in resource block units in the time axis direction. Further, a portion for each frequency width of the resource block is extracted from each of the extracted portions, and the power of the portion for each frequency is determined as the power average value of the resource block. After obtaining the power average value, the measurement processing unit 5c outputs measurement result information indicating the power average value to the resource allocation control unit 5d, the terminal detection unit 5e, and the output control unit 5f.
- the measurement processing unit 5c obtains a downlink signal which is a signal (before demodulation) which has been quadrature modulated and obtained from the downlink signal receiving unit 12, and obtains an average power value for each resource block from this signal.
- the part estimated to be a resource block unit is divided and taken out in the time axis direction. For this reason, it is necessary to recognize the frame timing of another base station apparatus that is the transmission source of the downlink signal.
- the frame timing is synchronized between the other base station apparatus and itself, the frame timing of the other base station apparatus can be grasped from the frame timing of the other base station apparatus.
- the unit of resource blocks in the axial direction can be accurately estimated, and the power average value can be determined accurately. For this reason, it is preferable to perform measurement processing immediately after performing synchronization processing.
- the terminal detection unit 5e has a function of detecting a communication status with the MS 2 connected to itself and another base station apparatus. More specifically, the terminal detection unit 5e detects the current state and the number of MSs 2 connected to other base station apparatuses as the communication status.
- the MS 2 connected to another base station apparatus to be detected by the terminal detection unit 5 e is an MS 2 to which its own downlink signal may reach.
- the terminal detection unit 5 e acquires information on the number of MSs 2 connected to itself from the upper layer of the signal processing unit 5. On the other hand, the number of MSs 2 connected to another base station apparatus is estimated based on the measurement result information from the measurement processing unit 5c. Measurement processing is performed by receiving a downlink signal from another base station apparatus, and the other base station apparatus is located in the periphery of itself and is located within the reachable range of both downlink signals. It is a base station apparatus. Therefore, its own downlink signal may reach MS2 connected to the other base station apparatus. Therefore, the terminal detection unit 5e can detect the MS 2 to which the own downlink signal may reach, from the measurement result information on the downlink signal of the other base station apparatus as described above.
- the terminal detection unit 5e determines whether the MS 2 is connected to another base station apparatus based on the power average value for each resource block included in the measurement result information, and connects to the other base station apparatus. Estimate the number of MS2 to be That is, if another base station apparatus communicates with MS 2 in its own cell, user data directed to the MS 2 is assigned to the transmission signal, and the power of the part to which the data is assigned is Relative increase compared to unassigned data. Thus, the terminal detection unit 5e can determine whether the MS 2 is connected to the other base station apparatus based on the reception power of the transmission signal.
- the terminal detection unit 5e can estimate the number of MSs 2 connected to another base station apparatus from the assignment situation.
- the resource assignment control unit 5d has a function of assigning user data to be transmitted to each terminal device 2 to the DL shared channel in the wireless frame.
- the resource allocation control unit 5d allocates user data to subframes specified by the information. Restrict.
- the resource allocation control unit 5d determines the allocation of user data based on this information.
- the output control unit 5 f has a function of controlling the transmission power of the transmission unit 13 of the RF unit 4.
- the power control unit 5f connects to the other base station apparatus and the other base station apparatus based on the power average value. It adjusts its own transmission power to MS 2 so that its own transmission signal does not interfere.
- FIG. 7 is a diagram for explaining an example of the synchronization process performed by the synchronization processing unit.
- the frames transmitted by the macro BS 1a which is another base station apparatus and the femto BS 1b which is its own base station apparatus are shown on the same time axis, and the macro BS 1a which is a synchronization source is the femto BS 1b.
- the synchronization processing unit 5b of the femto BS 1b sets the timing for acquiring the downlink signal for synchronization processing as the subframe SF1
- the synchronization processing unit 5b determines the information for identifying the subframe SF1.
- the synchronization timing information that is included is output to the resource assignment control unit 5d and the measurement processing unit 5c. Note that, in the illustrated example, the section in which transmission of the transmission signal is paused is only in the section of the subframe SF1 corresponding to the start timing of the synchronization process.
- the synchronization processing unit 5b pauses the transmission of the transmission signal by the transmission unit 13 at the transmission timing of the sub-frame SF1, and causes the downlink signal reception unit 12 to receive the downlink signal of the macro BS 1a. , To obtain the received downlink signal. Then, the synchronization processing unit 5b detects the frame transmission timing of the macro BS 1a by using the first synchronization signal and the second synchronization signal included in the received downlink signal of the macro BS 1a, and detects the frame transmission timing of itself. Detect frame synchronization errors between
- the synchronization processing unit 5b stores in which timing the first synchronization signal and the second synchronization signal exist in the downlink signal of the macro BS 1a, and The transmission signal is set to be paused in an interval of a subframe corresponding to the timing.
- the resource allocation control unit 5d to which the synchronization timing information is given restricts the allocation of user data of the terminal apparatus 2 to the section of the subframe SF1, the transmission signal transmission is paused in this section.
- the terminal device 2 can not communicate with the femto BS 1b, the base station is not scanned needlessly or it is not recognized that some abnormality has occurred, and smooth communication can be maintained.
- the synchronization processing unit 5b synchronizes by correcting the start timing of the next radio frame of the radio frame to which the subframe SF1 belongs based on the detected frame synchronization error. For example, assuming that the beginning of the wireless frame before synchronization is at timing T3, the synchronization processing unit 5b sets the value of the frame counter so that the beginning of the wireless frame becomes timing T4 shifted from timing T3 by the above-mentioned error. to correct. As a result, the frame timing of the femto BS 1 b that is the self can be matched with the frame timing of the macro BS 1 a, and synchronization can be achieved. In the above, only the synchronization of the frame timing has been described, but the correction of the carrier frequency is similarly performed.
- FIG. 8 is a diagram for explaining an example of an aspect of measurement processing performed by the measurement processing unit 5c.
- the frames transmitted by the macro BS 1a as another base station and the femto BS 1b as its own base station are shown on the same time axis, and the femto BS 1b measures the downlink signal of the macro BS 1a.
- the aspect which processes is shown.
- the measurement processing unit 5c can specify the sub-frame corresponding to the start timing of the synchronization process by the synchronization processing unit 5b according to the synchronization timing information supplied from the synchronization processing unit 5b.
- the measurement processing unit 5 c is set to perform measurement processing in the next wireless frame of the wireless frame to which the subframe corresponding to the specified start timing of the synchronization processing belongs. That is, as shown in the figure, measurement processing is performed on the radio frame immediately after synchronization is achieved at timing T4.
- the measurement processing unit 5c sets the start timing of the measurement process as a subframe SF2 in the drawing. Then, measurement timing information including information for specifying a subframe corresponding to a section in which transmission of the transmission signal is paused for measurement processing is output to the resource assignment control unit 5d.
- the measurement processing unit 5c sets an interval in which transmission of the transmission signal is paused for measurement processing to three subframes up to two subframes subsequent to the subframe corresponding to the start timing. Therefore, as shown in the figure, the measurement processing unit 5c pauses transmission of the transmission signal in the section of the subframes SF2, SF3, and SF4. Therefore, the measurement processing unit 5c outputs measurement timing information including information for specifying the subframes SF2 to SF4 to the resource allocation control unit 5d.
- the measurement processing unit 5c pauses the transmission of the transmission signal by the transmission unit 13 at the transmission timing of the subframes SF2 to SF4, while the downlink signal reception unit 12 transmits the downlink signal of the macro BS 1a. It is made to receive and the received down signal is acquired. Then, the measurement processing unit 5c obtains an average power value for each resource block from the acquired downlink signal.
- FIG. 9 is a diagram showing an example of a result of obtaining the power average value for each resource block, which is obtained by the measurement processing unit 5c.
- the horizontal axis indicates each resource block aligned in the frequency direction
- the vertical axis indicates the power average value.
- the measurement processing unit 5c obtains data as shown in FIG. 9 from the acquired downlink signal for each time width that can be estimated as each resource block width in the symbol direction, and the power for each resource block included in the acquired downlink signal Get the average value.
- the resource allocation control unit 5d to which the measurement timing information is given restricts the allocation of the user data of the terminal apparatus 2 to the section of the subframes SF2 to SF4, and therefore the transmission signal transmission is suspended in this section. By doing this, even if the terminal device 2 can not communicate with the femto BS 1b, smooth communication can be maintained as in the case of synchronization processing.
- the measurement processing unit 5c After obtaining the power average value for each resource block, the measurement processing unit 5c outputs measurement result information including these to the resource allocation control unit 5d, the terminal detection unit 5e, and the output control unit 5f.
- the resource allocation control unit 5d to which the measurement result information is given, and the output control unit 5f perform the processing that the resource allocation control unit 5d performs itself so as to suppress the occurrence of interference with other base station apparatuses based on the measurement result information. Run.
- the measurement result information includes the power average value for each resource block in the downlink signal from the other base station apparatus, and the other base station apparatus is currently mainly used in communication with MS 2
- the frequency band can be recognized. For example, as shown in FIG. 9, since no user data for MS 2 is allocated to the frequency band where the power average value appears low, other base station apparatuses are not currently using this band. It can be guessed.
- the resource allocation control unit 5d allocates its own user data so as to preferentially use a band estimated to be unused by another base station apparatus. As a result, the band used by itself can be avoided as much as possible from overlapping with the band used by another base station apparatus, and interference is caused to MS2 connected to another base station apparatus or the other base station apparatus. It can be suppressed to occur.
- the output control unit 5 f estimates the transmission power of the other base station apparatus from the power average value obtained by the measurement result information, and adjusts its own transmission power based on the transmission power of the other base station apparatus. Do. For example, when it is determined that the transmission power of its own is relatively large with respect to the transmission power of another base station apparatus to cause interference, the power control unit 5 f may lower its transmission power. adjust.
- FIG. 10 is a diagram showing timing when synchronization processing and measurement processing are performed.
- FIG. 10 shows the arrangement of a radio frame F1 including subframes on which synchronization processing is performed and a radio frame F2 including subframes on which measurement processing is performed among a plurality of radio frames aligned in the time axis direction.
- the synchronization processing unit 5b sets the timing at which the synchronization processing is performed so that the synchronization processing is performed in a constant cycle. Further, the measurement processing unit 5c sets the measurement processing to be performed in the subframe included in the wireless frame F2 following the wireless frame F1 on which the synchronization processing unit 5b performs the synchronization processing.
- FIG. 10 shows the case where synchronization processing is set to be performed with five radio frames as one cycle.
- the synchronization processing unit 5b adjusts the timing at which the synchronization processing is performed by adjusting the cycle of the start timing of the synchronization processing in accordance with the detection result of the terminal detection unit 5e.
- the terminal detection unit 5e estimates the number of MSs 2 connected to another base station apparatus from the measurement result information obtained by the measurement process performed in the radio frame F2 before the synchronization process is performed. In addition, after the measurement process, the terminal detection unit 5e acquires, from the upper layer, information on the number of MSs 2 connected to itself until the next frame in which the synchronization process is performed. The terminal detection unit 5e gives information on the estimated number of MSs 2 connected to other base station apparatuses and the number of MSs 2 connected to itself to the synchronization processing unit 5b as a detection result. The synchronization processing unit 5b to which the information is given adjusts the cycle of the start timing of the synchronization process according to the estimated number of MSs 2 connected to other base station apparatuses and the number of MSs 2 connected to itself.
- FIG. 11 is a flowchart showing adjustment of the cycle of performing synchronization processing, which is performed by the synchronization processing unit 5b.
- the synchronization processing unit 5b stores a longest cycle that can be set as a cycle of synchronization processing and a cycle group including a plurality of cycles shorter than the longest cycle.
- the synchronization processing unit 5b performs period adjustment by selecting any one of the plurality of periods included in each period group and the longest period as the period for performing the synchronization process.
- the longest cycle is set to the maximum cycle at which the accuracy of inter-base station synchronization can be maintained at a minimum.
- the synchronization processing unit 5b When receiving the detection result from the terminal detection unit 5e, the synchronization processing unit 5b first determines whether there is an MS 2 connected to itself or another base station apparatus (step S101). If it is determined that there is no MS 2 connected to itself or another base station apparatus, the synchronization processing unit 5 b selects and sets the longest period, which is the longest period that can be set, as the period for performing synchronization processing (step S 102). ), Finish the process. If it is determined in step S101 that there is an MS 2 connected to itself or another base station apparatus, the synchronization processing unit 5b determines whether there is an MS 2 connected to itself (step S103). . If it is determined that there is no MS2 connected to itself, it can be determined that only the MS2 connected to another base station apparatus exists.
- the synchronization processing unit 5b selects one cycle out of a plurality of cycles included in the cycle group according to the number of MSs 2 connected to another base station apparatus based on a preset reference. , And set as a cycle of synchronization processing (step S104), and the processing is ended.
- the synchronization processing unit 5b determines whether there is an MS 2 connected to another base station apparatus (step S105). If it is determined that there is no MS2 connected to another base station apparatus, it can be determined that only the MS2 connected to itself exists. In this case, the synchronization processing unit 5b selects one cycle out of a plurality of cycles included in the cycle group according to the number of MSs 2 connected to itself based on a preset reference, and performs synchronization processing. The cycle is set (step S106), and the process ends.
- step S105 If it is determined in step S105 that there is an MS2 connected to another base station apparatus, it can be determined that both the MS2 connected to itself and the MS2 connected to another base station apparatus exist.
- the synchronization processing unit 5b determines a plurality of cycles included in the cycle group according to the number of MSs 2 connected to itself and the number of MSs 2 connected to other base station apparatuses based on a preset reference. One cycle is selected from among the above, and set as a cycle of synchronization processing (step S107), and the process is ended.
- the synchronization processing unit 5b selects a longer cycle if the number of MSs 2 is small. That is, when there is no MS 2 connected to itself or another base station apparatus, the synchronization processing unit 5 b selects the longest cycle, and if the number of MS 2 increases, the cycle of synchronization processing is further shortened.
- the measurement processing unit 5c sets the cycle of measurement processing according to the cycle of synchronization processing.
- the synchronization processing unit 5b determines the start timing of the synchronization process (for the synchronization process) based on the number of MSs 2 as the communication status of the MS 2 connected to itself and other base station apparatuses. Since the timing at which the signal is acquired is adjusted, for example, the processing can be performed at a timing according to the necessity of the synchronization processing which changes depending on the communication status with the MS 2 or the like. As a result, processing accompanied by acquisition of transmission signals from other base station apparatuses can be appropriately performed.
- the base station apparatus synchronizes with another base station apparatus, thereby suppressing interference with the MS 2 at the time of cooperative transmission by each BS, or performing space multiplexing transmission.
- the base station apparatus is set to perform synchronization processing at a fixed cycle, synchronization processing is performed at a fixed cycle even if MS2 does not exist and the necessity for synchronization is low. Low quality processing is performed relatively frequently, resulting in waste.
- the synchronization processing unit 5b may reach its own downlink signal by connecting to the MS 2 connected to itself and to another base station apparatus.
- the period of the synchronization process can be adjusted according to the number of MS2s. That is, when the necessity of synchronization processing is low due to the absence of MS 2 connected to itself and other base station apparatuses, the self and / or other base station apparatuses are selected to set the longest cycle, etc.
- the synchronization cycle period to be longer as the number of connected terminal devices decreases, the frequency at which the synchronization process is performed can be reduced according to the necessity of the synchronization process, and a process without waste can be performed. It becomes.
- the measurement processing unit 5c exemplifies a case where the measurement processing cycle is set according to the synchronization processing cycle adjusted by the synchronization processing unit 5b. However, regardless of the synchronization processing cycle, it is necessary. Accordingly, it is possible to set the timing for performing the measurement process at its own discretion. In this case, the measurement processing unit 5c sets the timing at which the measurement process is performed based on the detection result of the terminal detection unit 5e, as in the synchronization processing unit 5b.
- the present invention is not limited to the above embodiments. Although the case where synchronous processing is performed periodically was illustrated in the above-mentioned embodiment, according to the detection result of terminal detection part 5e, you may set up the timing of synchronous processing each time.
- the synchronization processing unit 5b exemplifies a case where the period of synchronization processing is set according to the number of MSs 2 connected to itself and other base stations, but only the number of MSs 2 connected to itself is set. It may be set according to the number of MSs 2 connected to another base station apparatus.
- the cycle of synchronization processing may be set according to the total number.
- the synchronization deviation is corrected at the head of the radio frame immediately after stopping the transmission signal and after receiving the downlink signal of another base station apparatus, for example, the head of the radio frame
- the out-of-synchronization may be corrected at the beginning of subframes other than the above.
- the section in which the transmission signal is paused can be arbitrarily set as needed.
- FIG. 12 is a partial block diagram showing a part of the internal configuration of the femto BS 1b according to the second embodiment of the present invention.
- the configuration of the macro BS 1 a is also substantially the same as that of the femto BS 1 b.
- the difference between the present embodiment and the first embodiment resides in that the measurement result information acquisition unit for acquiring measurement result information indicating measurement results of downlink signals of other base station devices 1 other than the own station device 1b1. 41. Based on the measurement result information acquired by the measurement result information acquisition unit 41, generation of adjacent cell information in which measurement result information of another cell (another base station apparatus 1) adjacent to the own station apparatus 1 is registered On the basis of the measurement result information included in the adjacent cell information, in that the synchronization processing unit 5b includes the adjacent cell information generation unit 42 and the cell information storage unit 43 for storing the generated adjacent cell information. The point is to adjust the cycle of synchronization processing.
- the measurement result information acquisition unit 41 transmits a measurement start request for causing the MS 2 that performs communication connection to the own station device 1 b 1 to measure the downlink signal of another base station device 1 via the modem unit 5 a and the transmission unit 13. Have the ability to send to Moreover, the measurement result information acquisition part 41 has a function to acquire measurement result information from the measurement result which MS2 which measured based on the said measurement start request transmits. Furthermore, the measurement result information acquisition unit 41 has a function of measuring the downlink signal of the other base station apparatus 1 received by the downlink signal reception unit 12 and acquiring measurement result information from the measurement result.
- the adjacent cell information generation unit 42 generates adjacent cell information based on the measurement result information acquired by the measurement result information acquisition unit 41, and outputs the adjacent cell information to the cell information storage unit 43.
- the adjacent cell information includes measurement result information such as the reception level of the downlink signal of the other base station device 1 and the carrier frequency. More specifically, as the neighboring cell information is registered with the unique cell ID given to each of the other base station devices 1, the reception level of the downlink signal of the other base station device 1 included in the measurement result information And the carrier frequency and the cell ID of the corresponding other base station apparatus 1 are generated as a table in association with each other.
- the cell information storage unit 43 has a function of storing the adjacent cell information output by the adjacent cell information generation unit 42 and updating the new adjacent cell information each time it is output.
- the synchronization processing unit 5b of this embodiment When executing the synchronization process, the synchronization processing unit 5b of this embodiment first refers to the neighboring cell information stored in the cell information storage unit 43. Then, the synchronization processing unit 5b selects another base station device 1 as a synchronization source from among the other base station devices 1 registered in the neighboring cell information. Furthermore, based on the measurement result information of the selected other base station apparatus 1, the synchronization processing unit 5b determines a cycle of performing synchronization processing. Then, the synchronization processing unit 5b periodically performs synchronization processing using the downlink signal of another base station apparatus 1 selected as the synchronization source. The synchronization process is performed according to the same procedure as the first embodiment.
- FIG. 13 is a view showing an arrangement example of the femto BS 1b in the radio communication system according to the present embodiment.
- two macro BSs 1 a 1 and 1 a 2 and two femto BSs 1 b 1 and 1 b 2 are arranged.
- Both femto BSs 1 b 1 and 1 b 2 form femto cells FC 1 and FC 2 in a macro cell MC 1 formed by the macro BS 1 a 1.
- the two femtocells FC1 and FC2 are formed without overlapping regions.
- the femtocell FC1 is formed so as to overlap in a region where the macrocell MC1 and the macrocell MC2 overlap each other.
- FIG. 14 is a diagram showing an aspect of connection of each BS to a communication network.
- Each macro BS 1 a is connected to the communication network 31 of the wireless communication system via an MME (Mobility Management Entity) 30.
- the MME 30 is a node that manages the position of each MS 2 and the like, and performs processing for mobility management by handover of each MS 2 and the like.
- Each femto BS 1 b is connected to the MME 30 via the gateway 32 (GW).
- the gateway 32 has a function of relaying communication performed between each femto BS 1 b and the MME 30 and between each femto BS 1 b.
- the MME 30 and each macro BS 1 a, the MME 30 and the gateway 32, and the gateway 32 and the femto BS 1 b are connected by a line 33 by a communication interface called an S1 interface.
- each macro BS 1a is connected by a line 34 by an inter-base station communication interface called an X2 interface, and inter-base station communication for exchanging information directly between base station apparatuses is enabled.
- the gateway 32 is also connected to the macro BS 1 a by the line 34 by the X2 interface.
- the X2 interface is provided for the purpose of exchanging information and the like on mobility management such as handover in each MS 2 moving between base station apparatuses.
- an X2 interface is provided to communicate between the base station apparatuses.
- Communication between base station apparatuses using the X2 interface can be performed by a plurality of methods such as a method of directly connecting base station apparatuses and a method of connecting base station apparatuses via a gateway.
- the femto BS 1 b is not provided with a communication line by the X2 interface directly with the other base station apparatus 1. Therefore, in the present embodiment, the femto BS 1b performs inter-base station apparatus communication with the other base station apparatus 1 with the other base station apparatus 1 via the communication line 33 and the gateway 32 with the S1 interface connecting up to the gateway 32. Take a method.
- the macro BS 1 a directly connected to the MME 30 may be referred to as an eNB (Evolved Node B), the gateway 32 may be referred to as a Home-eNB Gateway, and the femto BS 1 b may be referred to as a Home-eNB.
- eNB evolved Node B
- the gateway 32 may be referred to as a Home-eNB Gateway
- the femto BS 1 b may be referred to as a Home-eNB.
- the femto BS 1b of the present embodiment acquires the measurement result information and generates or updates adjacent cell information.
- focusing on the femto BS 1 b 1 in FIG. 13, its function and operation will be described.
- FIG. 15 is a sequence diagram showing an example of a procedure when the femto BS 1 b 1 of the present embodiment acquires measurement result information.
- the case where femto BS1b1 performs measurement of the downlink signal of the base station apparatus 1 adjacent to MS2 (1) is shown in FIG.
- the femto BS 1 b 1 that has decided to obtain measurement result information sets the measurement target of MS 2 (1) (step S 10).
- the femto BS 1 b 1 causes the MS 2 (1) to perform a full frequency search when the own station device 1 b 1 does not have the neighboring cell information, such as when the own station device 1 b 1 is activated.
- the MS 2 when the MS 2 (1) first establishes an RRC (Radio Resource Control) connection with the femto BS 1 b 1 after activation of the femto BS 1 b 1, ie, completes processing for establishing communication connection with the femto BS 1 b 1
- the femto BS 1 b 1 causes the MS 2 to perform a full frequency search.
- the full frequency search means measuring the reception level of the downlink signal from the other base station apparatus 1 for all types (full band) of carrier frequencies set in the wireless communication system. Therefore, when the femto BS 1 b 1 does not have the neighboring cell information, the femto BS 1 b 1 sets the measurement target to all frequencies in step S 10.
- the downlink signal of another base station apparatus specified by the adjacent cell information can be measured, or all frequencies Can also be measured.
- the femto BS 1 b 1 transmits, to the MS 2 (1), a measurement start request to cause the MS 2 (1) to measure the downlink signal of the set other base station device 1 (step S 11).
- the measurement start request includes the frequency to be measured, the information of the base station apparatus, and the like.
- the MS 2 (1) receives the measurement start request from the femto BS 1 b 1 and performs downlink signal measurement on the measurement target indicated by the measurement start request (step S12).
- the MS 2 (1) detects the downlink signal of the other base station apparatus 1 and measures the carrier frequency of the detected downlink signal and the reception level. Furthermore, the cell ID of the base station apparatus 1 that is the transmission source of the detected downlink signal is acquired.
- the MS 2 (1) transmits a measurement result notification including the detected downlink signal carrier frequency, its reception level, and the corresponding cell ID, which are the measurement result, to the femto BS 1 b 1 (steps S13).
- the femto BS 1 b 1 Upon receiving the measurement result notification from the MS 2 (1), the femto BS 1 b 1 acquires measurement result information based on the measurement result notification (step S14). Then, when the femto BS 1b1 does not have the neighboring cell information, the femto BS 1b1 generates neighboring cell information based on the acquired measurement result information (step S15). When the femto BS 1b1 has the neighboring cell information, the femto BS 1b1 updates the neighboring cell information stored based on the measurement result information (step S15).
- the femto BS 1 b 1 periodically or periodically performs acquisition of the measurement result information described above. Also, the femto BS 1 b 1 executes this also when performing a handover, which will be described later.
- FIG. 16 is a diagram illustrating an example of neighboring cell information stored by the femto BS 1 b 1.
- the cell ID of macro BS1a1 is “1a1”
- the carrier frequency is “f1”
- the cell ID of macro BS1a2 is “1a2”
- the carrier frequency is "f2”
- the cell ID of femto BS1b2 is “1b2”
- the carrier frequency Indicates the case where "f2" is given.
- the adjacent cell information the cell ID of the detected other base station apparatus 1 (cell) is registered, and the carrier frequency and the reception level which are the respective measurement result information are associated with the cell ID Is registered.
- the macro BS 1 a 1, the macro BS 1 a 2, and the femto BS 1 b 2 exist around the femto BS 1 b 1. Therefore, when the femto BS 1 b 1 acquires measurement result information, the MS 2 (1) may detect these downlink signals. Therefore, when the cell IDs of the macro BS1a1, the macro BS1a2, and the femto BS1b2 are respectively set as described above, the femto BS1b acquires measurement result information including the cell ID, the carrier frequency, and the reception level. . Further, the femto BS 1 b 1 reflects the carrier frequency and the reception level of the downlink signal included in the measurement result information on the neighboring cell information as shown in FIG.
- the synchronization processing unit 5b of the femto BS 1b1 selects another base station apparatus 1 (hereinafter referred to as “synchronization source” among other base station apparatuses 1 registered in the neighboring cell information). , Synchronization source base station apparatus 1). Furthermore, the synchronization processing unit 5b determines the cycle of synchronization processing based on the measurement result information of the synchronization source base station device 1, and periodically performs synchronization processing. More specifically, if the reception level included in the measurement result information of the synchronization source base station device 1 is relatively large, the synchronization processing unit 5b determines so that the period of the synchronization process becomes short.
- the downlink signal of one base station apparatus 1 causes interference to the MS 2 connected to the other base station apparatus 1.
- the possibility is high.
- the reception level of the downlink signal of the other base station device 1 acquired by the femto BS 1b1 of the present embodiment is larger, there is a possibility that the other base station device 1 is positioned closer to the femto BS 1b1. It shows that it is high. That is, the information on the reception level of the other base station device 1 constitutes the information whose value is influenced by the positional relationship between the own station device 1 b 1 and the other base station device 1.
- the synchronization processing unit 5 b of the femto BS 1 b 1 selects the macro BS 1 a 1 as the synchronization source base station device 1.
- the reception level of the macro BS 1a1 is "8" and is larger than the macro BS 1a2 (reception level "3") and the femto BS 1b2 (reception level "2")
- the position of the macro BS 1a1 is relative It can be determined that the possibility of interference is the highest.
- the synchronization processing unit 5b adjusts the period (timing) of the synchronization process to be shorter than when the macro BS 1b 2 and the femto BS 1b 2 are selected as the synchronization source base station device 1. This relatively increases the frequency of synchronization processing. As a result, the accuracy of inter-base station synchronization can be enhanced, and interference occurring with the synchronization source base station apparatus 1 can be effectively suppressed.
- the synchronization processing unit 5b selects the macro BS 1a2 as the synchronization source base station device 1, the position of the macro BS 1a2 is relatively far from the reception level, and the possibility of interference is low. It can be judged. In this case, there is little need to improve the accuracy of inter-base station synchronization, and the synchronization processing unit 5b adjusts the period of synchronization processing to be longer compared to the case where the macro BS 1b1 is selected as the synchronization source base station device 1. As a result, it is possible to prevent unnecessary synchronous processing.
- the timing at which synchronization processing is performed is adjusted based on the reception level of the downlink signal of the synchronization source base station device 1, in relation to the synchronization source base station device 1. Even in the case where there is a possibility that interference may occur, synchronization processing can be performed so that interference can be suitably avoided.
- the synchronization processing unit 5b adjusts the cycle of synchronization processing based on the reception level of the downlink signal of the synchronization source base station apparatus 1 among the measurement result information included in the adjacent cell information, For example, as another example of the present embodiment, the synchronization processing unit 5b sets the cycle of synchronization processing according to the carrier frequency of the downlink signal of the synchronization source base station apparatus 1 among the measurement result information included in the adjacent cell information. It can also be configured to adjust.
- the synchronization processing unit 5b has a frequency of synchronization processing compared to the case where both carrier frequencies are different.
- the period of the synchronization process is adjusted to be shorter to be higher.
- the carrier frequencies used by the two base station apparatuses 1 are different from each other, there is a low possibility that interference will occur between them, but when the carrier frequencies used by each other are identical, the downlinks of both base station apparatuses 1 There is a high possibility that each signal causes interference to each MS 2 connected to both base station devices 1. That is, the carrier wave frequency of another base station apparatus 1 constitutes information indicating whether interference may occur due to the relationship between the own station apparatus 1 b 1 and the synchronous base station apparatus 1.
- the carrier frequency of the femto BS 1b1 is "f1" and the neighboring cell information of the femto BS 1b1 is as shown in FIG. 16, it is assumed that the synchronization processing unit 5b of the femto BS 1b1 selects the macro BS1a1 as the synchronization source base station device 1. .
- the carrier frequency of the macro BS 1a1 and the carrier frequency of the local station apparatus 1b1 are both “f1” and the same. Therefore, it can be judged that femto BS 1 b 1 is highly likely to cause interference in relation to macro BS 1 a 1.
- the synchronization processing unit 5b adjusts the cycle (timing) of the synchronization processing to a shorter time than when the macro BS 1b2 having different carrier frequencies is selected as the synchronization source base station device 1. This relatively increases the frequency of synchronization processing. As a result, the accuracy of inter-base station synchronization can be enhanced, and interference occurring with the synchronization source base station apparatus 1 can be effectively suppressed.
- the synchronization processing unit 5 b selects the macro BS 1 a 2 as the synchronization source base station device 1.
- the femto BS 1b1 can determine that the possibility of occurrence of interference is low.
- the synchronization processing unit 5b adjusts the period of synchronization processing to be longer compared to the case where the macro BS 1b1 is selected as the synchronization source base station device 1.
- the synchronization processing unit 5b Since the frequency of the synchronization process is higher than when it can be determined that it can not occur, the accuracy of inter-base station synchronization can be improved. As a result, it is possible to effectively suppress the interference with the other base station device 1. Therefore, also in this example, the accuracy of inter-base station synchronization can be adjusted as necessary, and synchronization processing can be appropriately performed.
- the measurement result information acquisition unit 41 acquires measurement result information including the detection results of the other base station apparatuses 1, and the synchronization processing unit 5b acquires the measurement result information as the measurement result information. According to the detection result of the base station device 1, the period of the synchronization process may be adjusted.
- FIG. 17A is a diagram illustrating an example of a detection result of another base station apparatus 1 detected when the femto BS 1b according to another example 2 of the present embodiment performs acquisition of measurement result information.
- FIG. 17B is a diagram showing an example of the neighboring cell information generated by the neighboring cell information generation unit 42 of the present example based on the detection result of FIG. 17A.
- the measurement result information acquiring unit 41 of this example counts the number of times of detection of the other base station apparatus 1 detected based on the measurement result notification transmitted for each downlink signal measurement performed by the MS 2, and , And the detection rate as measurement result information.
- the adjacent cell information generation unit 42 is an adjacent cell in which the number of times of detection and the detection rate included in the measurement result information are associated with the cell ID of the corresponding other base station device 1. Generate information.
- the measurement result information acquisition unit 41 receives, from the MS 2, a measurement result notification including cell IDs of other base station apparatuses 1 detected by downlink signal measurement each time the measurement result information is acquired.
- the measurement result information acquisition unit 41 executes acquisition of measurement result information four times at a predetermined timing, and the detection results of the other base station apparatus 1 by downlink signal measurement at the time of each execution are shown in FIG. Suppose that it is shown.
- the measurement result information acquiring unit 41 receives, from the MS2, a measurement result notification including the detected cell IDs of the macro BS1a1, the macro BS1a2, and the femto BS1b2.
- the measurement result information acquisition unit 41 receives the notification including the detection results of the other base station device 1.
- the measurement result information acquisition unit 41 can recognize that the base station device 1 of the cell ID included in the measurement result information is detected as a result of the downlink signal measurement. Therefore, the measurement result information acquiring unit 41 counts, for each base station apparatus, the number of detections of the other base station apparatus 1 detected each time the acquisition of the measurement result information is performed. Furthermore, the measurement result information acquisition unit 41 obtains a ratio of the number of detections to the number of measurements of the downlink signal measurement as a detection rate. For example, as shown in FIG. 17A, the macro BS 1a1 is detected in all four downlink signal measurements. Therefore, the measurement result information acquisition unit 41 obtains measurement result information in which the number of times of detection of the macro BS 1 a 1 is “4” and the detection rate is “1.00”. The measurement result information acquiring unit 41 obtains the number of times of detection of the other detected cells and the detection rate in the same manner as described above.
- the adjacent cell information generation unit 42 generates the adjacent cell information shown in FIG. 17B by receiving the measurement result information obtained by the measurement result information acquisition unit 41.
- the synchronization processing unit 5b adjusts the cycle of synchronization processing based on at least one of the number of detections or the detection rate of the synchronization source base station device 1 included in the neighboring cell information. More specifically, if the number of times of detection of the synchronization source base station apparatus 1 is relatively large, the synchronization processing unit 5b determines so that the cycle of synchronization processing becomes short.
- the larger the number of times of detection the higher the possibility that the other base station device 1 corresponding to the number of times of detection is present at a position closer to the own station device 1b1. That is, the number of times of detection of another base station apparatus 1 constitutes information whose value is influenced by the positional relationship between the own station apparatus 1 b 1 and the other base station apparatus 1. Also, as described above, as the positions of the two base station devices 1 adjacent to each other are closer, the downlink signal of one of the base station devices 1 is compared with the MS 2 connected to the other base station device 1. Interference is likely to occur.
- the synchronization processing unit 5 b of the femto BS 1 b 1 selects the macro BS 1 a 1 as the synchronization source base station device 1.
- the position of the macro BS1a1 is relative to the position of the macro BS1a1. It can be determined that the possibility of interference is the highest.
- the synchronization processing unit 5b of the femto BS 1b1 that selects the macro BS 1a1 as the synchronization source base station device 1 has a cycle (timing) of synchronization processing than when the macro BS 1b2 and the femto BS 1b2 are selected as the synchronization source base station device 1.
- the synchronization processing unit 5b selects the macro BS1a2 as the synchronization source base station device 1
- the position of the macro BS1a2 is relatively far from the number of times of detection and the possibility of interference is low. It can be judged. In this case, there is little need to improve the accuracy of inter-base station synchronization, and the synchronization processing unit 5b adjusts the period of synchronization processing to be longer compared to the case where the macro BS 1b1 is selected as the synchronization source base station device 1. As a result, it is possible to prevent unnecessary synchronous processing.
- the accuracy of inter-base station synchronization can be adjusted as necessary, and there is a possibility that interference may occur in relation to the synchronization source base station apparatus 1. Also, synchronization processing can be performed so that interference can be suitably avoided.
- the detection rate is the same as the number of times of detection, the larger the value, the higher the possibility that the other base station device 1 corresponding to the detection rate is located closer to the own station device 1b1. ing. Therefore, in the above example, although the case where the synchronization processing unit 5b adjusts the cycle of synchronization processing in accordance with the number of times of detection is illustrated, the detection rate included in the measurement result information of the synchronization source base station device 1 The cycle of the synchronization process may be adjusted according to
- the measurement result information acquiring unit 41 acquires measurement result information including the detection time at which another base station device 1 is detected, and the synchronization processing unit 5 b acquires the synchronization source base station device 1.
- the period of the synchronization process may be adjusted according to the detected detection time.
- FIG. 18A is a diagram illustrating an example of a detection result of another base station apparatus 1 detected when the femto BS 1b according to another example 2 of the present embodiment performs acquisition of measurement result information.
- FIG. 18B is a diagram showing an example of neighboring cell information generated by the neighboring cell information generation unit 42 of this example based on the detection result of FIG. 18A.
- the measurement result information acquiring unit 41 of this example measures the final detection time of each of the other base station apparatuses 1 and the elapsed time thereof based on the measurement result notification transmitted for each downlink signal measurement performed by the MS 2. It is configured to get as.
- the adjacent cell information generation unit 42 is an adjacent cell in which the last detection time and the elapsed time included in the measurement result information are associated with the cell ID of the corresponding other base station device 1 Generate cell information.
- the measurement result information acquisition unit 41 executes acquisition of the measurement result information
- the measurement result notification including the cell ID of the other base station apparatus 1 detected by the downlink signal measurement every measurement and the measurement time at the time of detection is Receive from MS2.
- the measurement result information acquisition unit 41 executes acquisition of measurement result information four times at a predetermined timing, and the detection results of the other base station apparatus 1 by downlink signal measurement at the time of each execution are shown in FIG. Suppose that it is shown.
- the measurement result information acquiring unit 41 detects the cell ID of the detected macro BS 1 a 1, macro BS 1 a 2, femto BS 1 b 2, and the measurement time at that time “September 15, 2010 14
- the measurement result notification including “10 minutes” is received from MS2.
- the measurement result information acquisition unit 41 receives the notification including the detection results of the other base station device 1.
- the measurement result information acquisition unit 41 can recognize that the base station device 1 of the cell ID included in the measurement result information is detected as a result of the downlink signal measurement. Moreover, the measurement time at that time can also be recognized. Therefore, the measurement result information acquiring unit 41 updates, for each base station apparatus, the last time at which each of the other detected base station apparatuses 1 was detected each time the acquisition of the measurement result information is performed. Furthermore, the measurement result information acquisition unit 41 obtains an elapsed time from the last time to the current time. For example, assuming that the current time is "12:20 on September 16, 2010", the measurement time at which the macro BS1a1 was last detected is the same as the current time, as shown in FIG. 18 (a). It is "12:20 on September 16, 2010".
- the measurement result information acquiring unit 41 obtains measurement result information in which the final detection time of the macro BS 1a1 is "12:20 on September 16, 2010" and the elapsed time is "00:00".
- the measurement result information acquisition unit 41 obtains the final detection time and elapsed time of the other detected cells in the same manner as described above.
- the adjacent cell information generation unit 42 generates the adjacent cell information shown in FIG. 18B by receiving the measurement result information obtained by the measurement result information acquisition unit 41.
- the synchronization processing unit 5b adjusts the cycle of synchronization processing based on at least one of the final detection time of the synchronization source base station apparatus 1 or the elapsed time included in the neighboring cell information. More specifically, the synchronization processing unit 5b adjusts the cycle of synchronization processing to be shorter as the elapsed time of the synchronization source base station apparatus 1 registered in the neighboring cell information is shorter.
- the longer the elapsed time the longer the position of the other base station device 1 is, and the higher the possibility that the other base station device 1 is not present in the vicinity of the own station device 1b1. If the elapsed time is long, it is conceivable that the target other base station apparatus 1 has moved from the vicinity of the own station apparatus 1b1, or that the power is turned off and not activated. Conversely, the shorter the elapsed time, the higher the possibility of being present in the vicinity of the own station apparatus 1b1.
- the synchronization processing unit 5 b of the femto BS 1 b 1 selects the macro BS 1 a 1 as the synchronization source base station device 1.
- the elapsed time of the macro BS 1 a 1 is “0 minutes” and is shorter than the macro BS 1 a 2 (elapsed time “5 hours 50 minutes”) and the femto BS 1 b 2 (elapsed time “16 hours”), the femto BS 1 b 1 It can be determined that it is present around BS1a1 and that interference is likely to occur.
- the synchronization processing unit 5b adjusts the period (timing) of the synchronization process to be shorter than when the macro BS 1b 2 and the femto BS 1b 2 are selected as the synchronization source base station device 1. This relatively increases the frequency of synchronization processing. As a result, the accuracy of inter-base station synchronization can be enhanced, and interference occurring with the synchronization source base station apparatus 1 can be effectively suppressed.
- the synchronization processing unit 5 b selects the macro BS 1 a 2 as the synchronization source base station device 1, the position of the macro BS 1 a 2 is relatively far from the elapsed time and the possibility of interference is low. It can be judged. In this case, there is little need to improve the accuracy of inter-base station synchronization, and the synchronization processing unit 5b adjusts the period of synchronization processing to be longer compared to the case where the macro BS 1b1 is selected as the synchronization source base station device 1.
- the synchronization processing unit 5b adjusts the period of the synchronization process according to the elapsed time. However, the period may be adjusted according to the final detection time.
- the femto BS 1b performs measurement of the downlink signal of the other base station apparatus 1 adjacent to MS 2 (1) to obtain measurement result information, but the femto BS 1b 1
- the downlink signal of the other base station apparatus 1 may be measured by the downlink signal receiving unit 12 of the own station apparatus 1b1, and measurement result information may be acquired from the measurement result.
- the synchronization source base station device 1 there is a high possibility that interference occurs with the synchronization source base station device 1 by the reception level which is information indicating the positional relationship between the own station device 1b1 and the synchronization source base station device 1.
- each base station device 1 can grasp the position of the own station device 1 by providing the GPS function etc.
- the BS 1 b 1 can also acquire position information indicating the position of the other base station device 1 directly from the other base station device 1 and adjust the cycle of synchronization processing based on this.
- the femto BS 1 b 1 can acquire position information of another base station apparatus 1 by inter-base station communication.
- the base station apparatuses 1 can communicate with each other through the X2 interface, it is easy to exchange information such as position information and carrier frequency, so that interference can be avoided. Processing can be suitably performed. Therefore, information indicating whether or not the own station device 1b1 can perform inter-base station communication via the X2 interface between the own station device 1b1 and the other base station device 1 from the other base station device 1. And may generate neighboring cell information in which this information is registered. In this case, when the synchronization processing unit 5b of the femto BS 1b1 selects another base station device 1 capable of inter-base station communication with the own station device 1b1 via the X2 interface as the synchronization source, inter-base station communication is performed.
- the femto BS 1b1 can preferably perform the process for avoiding interference with the synchronization source base station apparatus 1, the cycle of the synchronization process can be relatively shortened to avoid interference. Processing can be performed more effectively.
- the information indicating whether communication between base stations via the X2 interface is possible between the own station device 1b1 and another base station device 1 is the same as the own station device 1b1 and another base station device. The information is configured to indicate whether or not the interference caused in relation to 1 can be avoided.
- FIG. 19 is a partial block diagram showing a part of the internal configuration of the femto BS 1b according to the third embodiment of the present invention.
- the configuration of the macro BS 1 a is also substantially the same as that of the femto BS 1 b.
- the femto BS 1b1 includes a handover information acquisition unit 44 that acquires handover information that is information related to the handover performed in the MS 2 that communicatively connects to the own station device 1b1.
- the adjacent cell information generation unit 42 generates and updates adjacent cell information in which the handover information is associated with the cell ID of another base station apparatus 1 of the handover destination, and the synchronization processing unit 5 b generates handover information. The point is to adjust the cycle of synchronization processing based on the above.
- the handover information includes the number of handover attempts, the number of successful handovers, and the handover success rate when the MS 2 connected to the femto BS 1 b 1 performs a handover.
- FIG. 20 is a sequence diagram showing an example of an aspect in which the femto BS 1 b 1 of the present embodiment acquires handover information in a handover performed with the MS 2. Note that FIG. 20 shows a case where the MS 2 (1) connected to the femto BS 1 b 1 in FIG. 13 hands over to the macro BS 1 a 1.
- the femto BS 1 b 1 causes the MS 2 (1) to perform downlink signal measurement by executing the above-described acquisition of the measurement result information. Therefore, the femto BS 1 b 1 sets the measurement target of MS 2 (1) (step S 20). Here, the femto BS 1 b 1 sets the measurement target to the downlink signal of another base station apparatus 1 registered in the neighboring cell information. Next, the femto BS 1 b 1 transmits, to the MS 2 (1), a measurement start request for causing the MS 2 (1) to measure the set downlink signal of the measurement target (step S 21).
- the measurement start request includes the frequency to be measured, the information of the base station apparatus, and the like.
- the MS 2 (1) receives the measurement start request from the femto BS 1 b 1 and performs downlink signal measurement on the measurement target indicated by the measurement start request (step S22).
- the MS 2 (1) transmits a measurement result notification including the reception level of the detected downlink signal and the corresponding cell ID, which is the measurement result, to the femto BS 1 b 1 (step S23).
- the MS 2 (1) also transmits the reception level of the downlink signal of the femto BS 1 b 1 to the femto BS 1 b 1.
- the femto BS 1 b 1 Upon receiving the measurement result notification from the MS 2 (1), the femto BS 1 b 1 determines whether the MS 2 (1) should be handed over based on the measurement result notification. If the femto BS 1 b 1 determines that the MS 2 (1) should perform handover, the femto BS 1 b 1 refers to the neighboring cell information to determine a handover destination, and transmits a handover request to the macro BS 1 a 1 (step S 24). In the example shown in the figure, the case where the handover destination is determined to be the macro BS1a1 is shown.
- the determination as to whether or not to perform handover and the determination of the handover destination are performed by comparing the reception level of the downlink signal of the currently connected base station apparatus 1 with the reception level of the other base station apparatus 1. Furthermore, the determination as to whether or not to perform handover and the determination of the handover destination may be made by the MS 2 (1). In this case, the femto BS 1 b 1 transmits a handover request according to the determination and determination of MS 2 (1).
- the femto BS 1 b 1 can recognize to which base station apparatus 1 the MS 2 (1) has attempted to perform a handover by transmitting the handover request.
- the handover information acquisition unit 44 acquires information indicating that the handover is attempted and the determined handover destination (step S25).
- the macro BS 1a1 having received the handover request transmits a handover response to the handover request to the femto BS 1b1 (step S26).
- the femto BS 1 b 1 having received the handover response transmits an RRC connection re-establishment instruction to the MS 2 (1) (step S 27).
- MS 2 (1) transmits an RRC connection establishment notification to macro BS 1 a 1 (step S 28).
- the macro BS 1a1 having received the RRC connection establishment notification transmits a handover completion notification to the femto BS 1b1 (step S29).
- the femto BS 1 b 1 having received the handover completion notification releases the information on the MS 2 (1) and finishes the handover.
- the femto BS 1b1 can recognize that the handover is successful by receiving the handover completion notification.
- the handover information acquisition unit 44 acquires information on the result of the handover (step S30).
- the macro BS 1a1 transmits a handover failure notification in step S29.
- transmission and reception of handover request, handover response, and handover completion notification which are performed between the femto BS 1 b 1 and the macro BS 1 a 1, are performed through higher-level devices such as the MME 30 and the gateway 32, but through the X2 interface It may be performed by communication between base stations.
- the handover information acquiring unit 44 is handover information for each of the other base station apparatuses 1 based on the information on the determined handover destination and the information on the result of the handover that the handover has been attempted in the above steps S25 and S30. , The number of handover attempts, the number of handover successes, and the handover success rate.
- the handover success rate can be obtained by dividing the number of successful handovers by the number of handover trials.
- the handover information acquisition unit 44 outputs the acquired handover information to the adjacent cell information generation unit 42.
- the adjacent cell information generation unit 42 associates the number of handover attempts, the number of handover successes, and the handover success rate included in the handover information with the cell ID of the other base station apparatus 1 of the handover destination based on the handover information. Generate and update information.
- FIG. 21 is a diagram showing an example of the aspect in which the femto BS 1 b 1 updates adjacent cell information when handover is performed according to the procedure shown in FIG.
- a sequence diagram of the operation process of handover is shown on the right side of the drawing, and adjacent cell information corresponding to the operation process of handover is shown on the left of the drawing.
- the femto BS 1 b 1 is attempted to handover nine times within a certain specific period. That is, the adjacent cell information of the femto BS 1 b 1 at this stage indicates that the handover from the femto BS 1 b 1 to the macro BS 1 a 1 has been tried five times in the past and succeeded five times in the past. Therefore, the handover success rate is “1.00”. Also, it is shown that the handover from the femto BS 1 b 1 to the macro BS 1 a 2 has been attempted three times and succeeded once.
- the handover success rate is “0.33”. It is shown that the handover from the femto BS 1 b 1 to the femto BS 1 b 2 has been attempted three times and succeeded once. Therefore, the handover success rate is “0.33”.
- the femto BS 1b1 attempts a handover to the macro BS 1a1 as a handover destination for the MS 2 (1) connected to the local station apparatus 1b1.
- the femto BS 1 b 1 updates the number of handover attempts of the macro BS 1 a 1 in the neighboring cell information from “5” to “6” (FIG. 21 (b)).
- the femto BS 1b1 updates the number of successful handovers of the macro BS 1a1 in the neighboring cell information from "5" to "6" (FIG. 21 (c)). In this case, the handover success rate is maintained as it is because it does not change.
- FIG. 22 is a diagram illustrating another example of an aspect in which the femto BS 1 b 1 updates neighboring cell information when handover is performed.
- the femto BS 1 b 1 in the stage before the femto BS 1 b 1 transmits the handover request (FIG. 22 (a)), the neighboring cell information having the same content as that in FIG. 21 is obtained.
- the femto BS 1b1 tries a handover to the macro BS 1a2 as a handover destination for the MS 2 (1) connected to the local station apparatus 1b1.
- the femto BS 1 b 1 updates the number of handover attempts of the macro BS 1 a 2 in the neighboring cell information from “3” to “4” (FIG. 22 (b)).
- the femto BS 1 b 1 receives a handover failure notification from the macro BS 1 a 2. Thereby, the femto BS 1 b 1 maintains the number of successful handovers of the macro BS 1 a 2 in the neighboring cell information as “1”, and updates the handover success rate from “0.33” to “0.25” (FIG. 22 (c )).
- the handover source in the femto BS 1b1 when it is possible to recognize the handover source in the femto BS 1b1, not only the information of the handover destination but also the neighboring cell information may be generated using the information of the handover source.
- the synchronization processing unit 5b of the femto BS 1b1 adjusts the period of the synchronization process based on the handover information. More specifically, if the number of handover attempts is relatively large among the pieces of handover information, the synchronization processing unit 5b adjusts the cycle of synchronization processing to be short.
- the reason that the MS 2 connected to the own station device 1b 1 needs to be handed over with high probability is that the reception level of the other adjacent base station device 1 is in a relatively large state.
- the reception level is relatively large, it indicates that the other base station apparatus 1 is highly likely to be located near the femto BS 1 b 1.
- the number of handover trials of MS 2 performed with another base station device 1 constitutes information whose value is influenced by the positional relationship between the own station device 1 b 1 and the other base station device 1.
- the two base station apparatuses 1 adjacent to each other cause interference to the MS 2 connected to the other base station apparatus 1 with the downlink signal of one base station apparatus 1 as the positions of the two base stations become closer. The possibility is high.
- the synchronization processing unit 5 b of the femto BS 1 b 1 selects the macro BS 1 a 1 as the synchronization source base station device 1.
- the femto BS1b1 is not the macro BS1a1. It can be determined that the position is relatively close and interference is most likely to occur.
- the synchronization processing unit 5b adjusts the period (timing) of the synchronization process to be shorter than when the macro BS 1b 2 and the femto BS 1b 2 are selected as the synchronization source base station device 1. This relatively increases the frequency of synchronization processing. As a result, the accuracy of inter-base station synchronization can be enhanced, and interference occurring with the synchronization source base station apparatus 1 can be effectively suppressed.
- the synchronization processing unit 5b selects the macro BS1a2 as the synchronization source base station device 1
- the position of the macro BS1a2 may be relatively far from the number of handover attempts, and interference may occur. It can be judged low. In this case, there is little need to improve the accuracy of inter-base station synchronization, and the synchronization processing unit 5b adjusts the period of synchronization processing to be longer compared to the case where the macro BS 1b1 is selected as the synchronization source base station device 1.
- the accuracy of inter-base station synchronization can be adjusted as necessary, and there is a possibility that interference may occur in relation to the synchronization source base station apparatus 1,
- a synchronization process can be performed to preferably avoid interference.
- the cycle of synchronization processing is considered in consideration of the number of handover successes or the handover success rate. It may be configured to adjust the
- the handover information acquisition unit 44 can acquire a time interval (handover interval) at which handover for each other base station apparatus 1 is attempted, the cycle of synchronization processing is adjusted according to the handover interval. May be This is because the shorter the handover interval, the higher the number of handover attempts per unit time.
- the staying time is from time t1 at which the handover for MS2 to the local station apparatus 1b1 is performed to time t2 at which the handover for MS2 to another base station apparatus 1 is performed. It is a time interval (t2-t1). If the stay time is short, it indicates that the handover is frequently performed, and the short stay time is an index similar to the number of handovers.
- the staying time is also information whose value is affected by the number of handovers.
- the staying time may be a time during which the MS 2 stays in another cell adjacent to the own cell. That is, as the staying time, from time t1 when the handover for MS2 to connect from the own station apparatus 1b1 to the first other base station apparatus 1 is performed, the MS2 is the first other base station apparatus 1 From the time interval until the time t2 when the handover for connecting to the second other base station apparatus 1 or the own station apparatus 1b1 is performed (the residence time of the first other base station apparatus 1 in the cell) It may be.
- the staying time from time t1 when the handover for connecting MS2 from the first other base station apparatus 1 to the second other base station apparatus 1 is performed, that MS2 is the first other one.
- the time from the base station device 1 to the time t2 when the handover for connecting to the own station device 1b1 is performed may be the time (the staying time of the second other base station device 1 in the cell).
- FIG. 23 is a partial block diagram showing a part of the internal configuration of the femto BS 1b according to the fourth embodiment of the present invention.
- the configuration of the macro BS 1 a is also substantially the same as that of the femto BS 1 b.
- the femto BS 1b1 includes an attribute information acquisition unit 45 that acquires attribute information indicating an attribute related to communication connection of another base station apparatus 1, adjacent cells
- the attribute information acquisition unit 45 is a downlink signal of another base station apparatus 1 received by the downlink signal reception unit 12 or a measurement result notification transmitted from an MS 2 connected to the local station apparatus 1 b 1 by acquiring measurement result information. Receive and obtain attribute information based on the information included in the downlink signal or the measurement result notification.
- the attribute information includes access mode information indicating an access mode set in another base station apparatus 1 and a cell for identifying whether the other base station apparatus 1 is a macro base station or a femto base station. Information on the form and information indicating the allocation form of resource blocks of the other base station apparatus 1 are included.
- FIG. 24 is a diagram showing the contents of the access mode set in the base station device 1.
- the access mode is a mode for the base station apparatus to define the restriction of communication connection with the MS 2.
- the base station apparatus 1 is set to any of these three different access modes.
- the open access mode is a mode connectable to all MSs.
- the macro BS 1 a installed by the communication company or the like is normally set in the open access mode because it has high publicity.
- the closed access mode is a mode in which connection is permitted only to the MS 2 registered in the base station apparatus 1 set in this mode.
- the hybrid mode is basically a mode in which connection with all MSs 2 is possible, but there may be cases where registered MS 2 may be favored for allocation of communication resources, etc., compared to MS 2 not registered.
- the femto BS 1 b is set to any one of the above three modes.
- the femto BS 1 b is installed by an individual or company in its own building or specific space, and the individual or company installing the femto BS 1 b wants to restrict MS 2 connected to the femto BS 1 b to only a specific MS 2 There is a case. In such a case, the femto BS 1b is configured to be able to select and set any one of the above three modes in accordance with the situation.
- Distributed transmission is a format in which the resources of each MS 2 are equally distributed over a predetermined frequency bandwidth for transmission, and localized transmission is when the resources of each MS 2 are in the frequency direction within a specific bandwidth range. It is a form of allocating to continuous resource blocks and transmitting one MS2 resource in a predetermined narrow band range.
- FIG. 25 (a) is a diagram showing an example of neighboring cell information generated by the femto BS 1b1 of the present embodiment.
- the attribute information acquisition unit 45 acquires access mode information indicating that the femto BS 1 b 2 is in the hybrid mode.
- the macro BS1a1 and the macro BS1a2 in FIG. 13 are in the open access mode as described above. Therefore, the attribute information acquisition unit 45 acquires access mode information indicating that the macro BS1a1 and the macro BS1a2 are in the open access mode.
- the adjacent cell information generation unit 42 associates the access mode information, the information on the cell configuration, and the information indicating the allocation format of resource blocks of the other base station apparatus 1 with the cell information ID, as shown in FIG.
- the synchronization processing unit 5b adjusts the cycle of synchronization processing based on the attribute information of the synchronization source base station device 1 included in the adjacent cell information. More specifically, when the access mode set in the synchronization source base station apparatus 1 is the open access mode, the synchronization processing unit 5b adjusts the period of the synchronization process shorter than in the other modes, Thereafter, adjustment is made so that the period of the synchronization process is sequentially extended in the order of the hybrid mode and the closed access mode.
- the open access mode without limitation of the connectable MSs 2 is the most public, and there is a high possibility that more MSs 2 are connected.
- the closed access mode is the least public and has a relatively small number of connected MSs 2. Since the femto BS 1 b 1 has the possibility of giving interference to the MSs 2 connected to the other base station apparatuses 1, the possibility of giving interference is high when the number of MSs 2 connected to the other base station apparatuses 1 is large. Become.
- the synchronization processing unit 5 b of the femto BS 1 b 1 selects the macro BS 1 a 1 as the synchronization source base station device 1.
- the access mode of the macro BS 1 a 1 is “open”, the femto BS 1 b 1 can determine that the possibility of occurrence of interference is high.
- the synchronization processing unit 5b adjusts the period (timing) of the synchronization process to be shorter than when the femto BS 1b2 whose access mode is "hybrid" is selected as the synchronization source base station device 1. This relatively increases the frequency of synchronization processing. As a result, the accuracy of inter-base station synchronization can be enhanced, and interference occurring with the synchronization source base station apparatus 1 can be effectively suppressed.
- the synchronization processing unit 5 b of the femto BS 1 b 1 selects the femto BS 1 b 10 as the synchronization source base station device 1.
- the access mode of the femto BS 1 b 10 is “closed”, the femto BS 1 b 1 can determine that the possibility of occurrence of interference is low.
- the synchronization processing unit 5b selects the femto BS 1 b 11 (access mode “open”) and the femto BS 1 b 12 (access mode “hybrid”) as the synchronization source base station apparatus 1.
- the cycle (timing) of the synchronization process is adjusted to be longer than in the case where As a result, the frequency of synchronization processing can be relatively lowered, and wasteful synchronization processing can be prevented.
- the synchronization processing unit 5 b of the femto BS 1 b 1 selects the femto BS 1 b 12 as the synchronization source base station device 1. Since the access mode of the femto BS 1 b 12 is “hybrid”, the femto BS 1 b 1 can be determined to be more likely to cause interference than the femto BS 1 b 10 but less likely to cause interference than the femto BS 1 b 11.
- the synchronization processing unit 5 b synchronizes the femto BS 1 b 10 (access mode “closed”) with a longer cycle of synchronization processing than when the femto BS 1 b 11 (access mode “open”) is selected as the synchronization source base station device 1.
- the period of the synchronization process is adjusted to be shorter than in the case where it is selected as the original base station device 1.
- the accuracy of inter-base station synchronization can be adjusted according to the access mode, and interference is preferably generated even when there is a possibility that interference may occur in relation to the synchronization source base station apparatus 1.
- the synchronization process can be performed so that it can be avoided.
- the period of the synchronization process is adjusted based on the information on the cell configuration for identifying whether it is a macro base station or a femto base station.
- the synchronization processing unit 5 b adjusts the cycle of synchronization processing to be shorter than when using the femto BS 1 b as the synchronization source base station apparatus 1.
- the information on a cell form for identifying whether another base station apparatus 1 is a macro base station or a femto base station it is directly determined whether it is a macro base station or a femto base station.
- the information which shows the transmission power of a downlink signal other than the information to show is also included.
- the transmission power of the downlink signal of the macro base station is set to a very large value as compared to that of the femto base station forming the narrow femtocell FC. Therefore, by referring to the information indicating the transmission power of the downlink signal, it is possible to identify whether it is a macro base station or a femto base station.
- the transmission power of the downlink signal is relatively small to form a narrow range cell, it can be determined that the transmission source of the downlink signal is the femto base station. Also, if the transmission power of the downlink signal is a large value that can be recognized to form a wide range of cells, it can be determined that the transmission source of the downlink signal is the macro base station. Therefore, the cycle of the synchronization process may be adjusted to be shorter as the transmission power of the downlink signal is larger, and the cycle of the synchronization process may be adjusted to be longer as the transmission power of the downlink signal is smaller.
- the period of the synchronization process may be adjusted based on the allocation format of the resource block of the synchronization source base station device 1.
- the synchronization processing unit 5b adjusts the period of synchronization processing to be longer so that the frequency of synchronization processing becomes lower than in the case of localized. Is preferred. If the assignment type is localized, then the resources of MS 2 are assigned to a specific frequency bandwidth range as described above. Therefore, in order to suppress interference between the local station apparatus 1b1 and the other base station apparatus 1, it is possible to allocate resources so as not to overlap in the frequency direction.
- the information indicating the assignment format constitutes information indicating whether interference with another base station apparatus 1 can be avoided.
- the synchronization processing unit 5 b of the femto BS 1 b 1 selects the macro BS 1 a 1 as the synchronization source base station device 1.
- the femto BS 1 b 1 can determine that the interference with the macro BS 1 a 1 can be avoided.
- the synchronization processing unit 5b adjusts the period (timing) of the synchronization process to be shorter than when the macro BS1a2 whose allocation type is “distributed” is selected as the synchronization source base station device 1. This relatively increases the frequency of synchronization processing. As a result, the accuracy of inter-base station synchronization can be enhanced, and interference occurring with the synchronization source base station apparatus 1 can be effectively suppressed.
- the synchronization processing unit 5 b selects the macro BS 1 a 2 as the synchronization source base station device 1
- the femto BS 1 b 1 may determine from the assignment format that interference with the macro BS 1 a 2 is difficult to avoid. it can.
- the synchronization processing unit 5b adjusts the period of synchronization processing to be longer compared to the case where the macro BS 1b1 is selected as the synchronization source base station device 1.
- FIG. 26 is a partial block diagram showing a part of the internal configuration of the femto BS 1b according to the fifth embodiment of the present invention.
- the configuration of the macro BS 1 a is also substantially the same as that of the femto BS 1 b.
- the femto BS 1b1 includes a path loss value acquisition unit 47 for acquiring a path loss value with another base station apparatus 1, an adjacent cell information generation unit 42 generates and updates adjacent cell information in which the path loss value is associated with the cell ID of the corresponding other base station device 1, and the synchronization processing unit 5b uses the path loss value of the synchronization source base station device 1 as the path loss value. Accordingly, the cycle of synchronization processing is adjusted.
- the path loss value acquiring unit 47 is a downlink signal of another base station apparatus 1 received by the downlink signal receiving unit 12 or a measurement result notification transmitted from an MS 2 connected to the own station apparatus 1 b 1 by acquiring measurement result information. Based on the information contained in the downlink signal or the measurement result notification, a path loss value between the own station apparatus 1b1 and another base station apparatus 1 is obtained.
- the path loss value acquisition unit 47 acquires path loss values of other base station apparatuses 1 as follows. That is, the path loss value acquiring unit 47 previously acquires the transmission power of the other base station apparatus 1 from the downlink signal of the other base station apparatus 1 received by the downlink signal receiving unit 12 or the measurement result notification from MS2. Keep it. Then, the path loss value acquiring unit 47 receives the reception level of the downlink signal of the other base station device 1 by the downlink signal of the other base station device 1 received by the downlink signal receiving unit 12 or the measurement result notification from MS2. get. The path loss value acquisition unit 47 acquires the path loss value from the transmission power of the downlink signal of the other base station apparatus 1 acquired as described above and the reception level.
- FIG. 27 is a diagram illustrating an example of neighboring cell information generated by the femto BS 1b1 according to the present embodiment.
- the path loss value acquiring unit 47 acquiring path loss values of other base station apparatuses 1
- the path loss value of the macro BS1a1 shown in FIG. 13 is 5 dBm
- the path loss value of the macro BS1a2 is 10 dBm
- the path loss value of the femto BS1 b2 is 72 dBm.
- the path loss value acquisition unit 47 outputs the information indicating the path loss value to the adjacent cell information generation unit 42.
- the adjacent cell information generation unit 42 generates adjacent cell information shown in FIG. 27 by associating the path loss value with the cell information ID.
- the synchronization processing unit 5b of the femto BS 1b1 of the present embodiment adjusts the cycle of synchronization processing according to the path loss value of the synchronization source base station device 1 as described above. More specifically, if the value of the path loss value of the synchronization source base station device 1 is relatively small, the synchronization processing unit 5b adjusts so that the period of the synchronization process becomes smaller.
- the path loss values of the other base station apparatuses 1 constitute information whose values are influenced by the positional relationship between the own station apparatus 1 b 1 and the other base station apparatuses 1. Also, as described above, as the positions of the two base station devices 1 adjacent to each other are closer, the downlink signal of one of the base station devices 1 is compared with the MS 2 connected to the other base station device 1. Interference is likely to occur.
- the synchronization processing unit 5 b of the femto BS 1 b 1 selects the macro BS 1 a 1 as the synchronization source base station device 1.
- the path loss value of the macro BS 1 a 1 is “5 dBm”, which is smaller than that of the macro BS 1 a 2 (path loss value “10 dBm”) and the femto BS 1 b 2 (path loss value “72 dBm”), so the position of the macro BS 1 a 1 is relative It can be determined that the possibility of interference is the highest.
- the synchronization processing unit 5b adjusts the period (timing) of the synchronization process to be shorter than when the macro BS 1b 2 and the femto BS 1b 2 are selected as the synchronization source base station device 1. This relatively increases the frequency of synchronization processing. As a result, the accuracy of inter-base station synchronization can be enhanced, and interference occurring with the synchronization source base station apparatus 1 can be effectively suppressed.
- the synchronization processing unit 5b selects the macro BS 1a2 as the synchronization source base station device 1, the position of the macro BS 1a2 is relatively far from the reception level, and the possibility of interference is low. It can be judged. In this case, there is little need to improve the accuracy of inter-base station synchronization, and the synchronization processing unit 5b adjusts the period of synchronization processing to be longer compared to the case where the macro BS 1b1 is selected as the synchronization source base station device 1. As a result, it is possible to prevent unnecessary synchronous processing.
- the accuracy of inter-base station synchronization can be adjusted as necessary, and there is a possibility that interference may occur in relation to the synchronization source base station apparatus 1,
- a synchronization process can be performed to preferably avoid interference.
- FIG. 28 is a partial block diagram showing a part of the internal configuration of the femto BS 1b according to the sixth embodiment of the present invention.
- the configuration of the macro BS 1 a is also substantially the same as that of the femto BS 1 b.
- the difference between this embodiment and the second embodiment resides in the number-of-terminals estimation unit 46 for estimating the number of MSs 2 connected to another base station apparatus 1 where the femto BS 1b1 is located in the vicinity of the own station apparatus 1b1.
- the adjacent cell information generation unit 42 generates and updates adjacent cell information in which the estimated number of terminals is associated with the cell ID of the corresponding other base station apparatus 1, and the synchronization processing unit 5b The period of the synchronization process is adjusted according to the estimated number of terminals.
- the terminal number estimation unit 46 estimates the number of MSs 2 connected to another base station apparatus 1 located in the vicinity of the own station apparatus 1b1 as follows.
- the terminal number estimation unit 46 of the femto BS 1b1 first acquires downlink reception signals of other base station apparatuses 1 (step S40). Among the system information of the other base station apparatus 1 among the downlink received signals, the number-of-terminals estimation section 46 assigns allocation information of PRACH (PRACH: Physical Random Access Channel) in the other base station apparatus 1, and RAP. Control information necessary for transmitting a RAP directed to another base station apparatus 1, such as information on the format of (connection request signal; Random Access Preamble), is acquired (step S41).
- PRACH Physical Random Access Channel
- the femto BS 1b1 transmits to the other base station apparatus 1 in addition to the first PRACH for receiving the RAP of the MS 2 attempting to connect to the own station apparatus 1b 1 based on the assignment information of the PRACH obtained in step S41.
- the second PRACH for intercepting the RAP of the MS 2 to be connected is set in the UL frame of the own station apparatus 1b1 (step S42).
- FIG. 30 is a diagram illustrating an example in which a first PRACH and a second PRACH are set on a UL frame.
- both PRACHs are set to have a bandwidth of 72 subcarriers in the frequency axis direction and a range of one subframe width in the time axis direction.
- the RAP transmitted using this second PRACH is intercepted and acquired, and another base is within the reach of the RAP to the local station apparatus 1b1. It recognizes that there is an MS 2 connected to the station apparatus 1 (step S43). At this time, by using the information on the format of the RAP acquired in step S41, the MS 2 connected to the other base station device 1 can acquire the RAP transmitted to the other base station device 1.
- the number-of-terminals estimation unit 46 counts the number N of recognized MS2 devices within the time width T that has been obtained in the past by the time T from the present time (step S44), and the number N Are acquired as information indicating the presence status of the MS 2 connected to the other base station device 1 located in the vicinity of the own station device 1 b 1. That is, the device number N is a value obtained by counting MS2 located in the range where the RAP reaches the own station device 1b1 as being located near the own station device 1b1.
- the number-of-terminals estimation unit 46 estimates the number of MSs 2 connected to another base station device 1 located in the vicinity of the own station device 1b1 from the above-described number N of devices.
- the adjacent cell information generation unit 42 generates adjacent cell information in which the estimated number of MS2 is associated with each cell information ID.
- the synchronization processing unit 5b may generate interference.
- the period of the synchronization process is adjusted to be shorter so that the frequency of the synchronization process is higher than when it can be determined that As a result, the accuracy of inter-base station synchronization can be enhanced, and interference generated with the synchronization source base station apparatus 1 can be effectively suppressed.
- the accuracy of inter-base station synchronization can be adjusted as necessary, and there is a possibility that interference may occur in relation to the synchronization source base station apparatus 1, A synchronization process can be performed to preferably avoid interference.
- the local station apparatus 1b1 and the synchronization source base station apparatus 1 can be determined to such an extent that the possibility of causing interference is high. If the position between them is close, the case where the period of the synchronization process is adjusted to be short is illustrated. On the other hand, if the position between the own station apparatus 1b1 and the other base station apparatus 1 is close and the reception accuracy of the downlink signal from the other base station apparatus 1 is high, one synchronization process is performed with high accuracy. It may be possible to synchronize between base stations.
- the timing at which the synchronization process is performed may be adjusted based on In this case, for example, if the reception accuracy of the downlink signal from the other base station apparatus 1 that is the synchronization source is high enough to allow high-precision inter-base station synchronization, compared to the case where the reception accuracy is lower than that.
- the period of the synchronization process can be adjusted relatively long.
- the synchronization processing unit 5 b can use the reception level or the signal-to-interference and noise power ratio (SINR) as the reception accuracy of the downlink signal from the other base station device 1.
- SINR signal-to-interference and noise power ratio
- the synchronization processing unit 5b uses the position relationship between the own station device 1b1 and the synchronization source base station device 1 as information that affects the reception accuracy of the downlink signal from the synchronization source base station device 1 according to the value. Or information whose value is affected by the positional relationship between the local station apparatus 1 b 1 and the synchronization source base station apparatus 1.
- the synchronization processing unit 5b uses the information indicating the positional relationship between the local station apparatus 1b1 and the synchronization source base station apparatus 1, or the value according to the positional relationship between the local station apparatus 1b1 and the synchronization source base station apparatus 1. Adjust the timing of performing synchronization processing based on the information that is affected. Therefore, for example, based on the above information, the positions of the local station apparatus 1b1 and the synchronization source base station apparatus 1 are close, and the reception accuracy of the transmission signal of the synchronization source base station apparatus 1 is high enough to enable high accuracy inter-base station synchronization.
- the accuracy of inter-base station synchronization can be maintained high without increasing the frequency of synchronization processing, so the timing of synchronization processing is adjusted so that the frequency of synchronization processing becomes relatively low. be able to. As a result, it is possible to maintain high inter-base station synchronization accuracy without wastefully performing synchronization processing, and it is possible to effectively suppress interference with the synchronization source base station apparatus 1.
- the timing of synchronization processing can be adjusted so that the frequency of synchronization processing is higher than when it can be determined that the reception accuracy is high. As a result, the accuracy of inter-base station synchronization can be enhanced, and interference generated with the synchronization source base station apparatus 1 can be effectively suppressed.
- the positional relationship between the self-station device 1 b 1 and the synchronization source base station device 1, which is information affecting the reception accuracy of the transmission signal of the synchronization source base station device 1, is obtained.
- the timing at which the synchronization process is performed based on the information or the like to be shown, the synchronization process can be performed such that the interference can be suitably avoided.
- the positional relationship between self-station apparatus 1b1 and synchronization source base station apparatus 1 that is close enough that it can be determined that the reception accuracy of the transmission signal of synchronization source base station apparatus 1 is high enough to enable high accuracy inter-base station synchronization. Is the case where the cell of the local station apparatus 1b1 is located closest to the synchronization source base station apparatus 1, and so on. That is, when it is determined that the reception accuracy of the transmission signal of synchronization source base station device 1 is high, the range determined by the positional relationship between self station device 1 b 1 and synchronization source base station device 1 is determined to be highly likely to cause interference.
- the femto BS 1 b 1 adjusts the synchronization processing period to a short time to increase the accuracy of inter-base station synchronization.
- the information whose value is affected by the positional relationship between the local station apparatus 1b1 and the synchronization source base station apparatus 1 is information related to the detection result when the transmission signal of the synchronization source base station apparatus 1 is detected.
- the information on the detection result when the transmission signal of the synchronization source base station device 1 is detected is the number of times of detection of the synchronization source base station device 1 detected within a predetermined period, or the detection It is preferable that the detection rate is a ratio of the number of times and the number of times of detection.
- the information on the detection result when the transmission signal of synchronization source base station apparatus 1 is detected is the time when the transmission signal of synchronization source base station apparatus 1 was last detected, or the current time from the time It may be an elapsed time until
- information whose value is affected by the positional relationship between the local station apparatus 1b1 and the synchronization source base station apparatus 1 is synchronized with the local station apparatus 1b1 performed between the local station apparatus 1b1 and the synchronization source base station apparatus 1. It may be information on the number of handover attempts of a terminal device connected to the original base station device 1, or information whose value is affected by the number of handover attempts.
- each of the above information is information whose value is affected by the positional relationship between the local station apparatus 1 b 1 and the synchronization source base station apparatus 1 as described in the above respective embodiments.
- the synchronization processing unit 5b which adjusts the frequency, for example, increases the frequency of synchronization processing in order to effectively suppress interference when it can be determined that interference may occur in relation to another base station apparatus, for example. Can improve the accuracy of inter-base station synchronization. As a result, even when there is a possibility that interference may occur due to the relationship with the other base station apparatus 1 that is the synchronization source, synchronization processing can be performed so that the interference can be suitably avoided.
- the synchronization processing unit 5b uses the number of terminal devices connected to itself and / or the other base station device as information indicating whether interference may occur due to the relationship between the own station device 1b1 and the synchronization source base station device 1. Can be used. Further, the synchronization processing unit 5 b is information indicating the carrier frequency of the synchronization source base station device 1 as information indicating whether interference may occur in the relationship between the own station device 1 b 1 and the synchronization source base station device 1, synchronization source Information that can identify whether the base station device 1 is a macro base station or a femto base station, information indicating the transmission power of the downlink signal of the synchronization source base station device 1, the synchronization source base to the MS 2 connected to the synchronization source base station device 1 It is possible to use information indicating the access mode of the station device 1 or the estimated number of MSs 2 that are located in the vicinity of the own station device 1 b 1 and connected to the synchronization source base station device 1.
- the position of the synchronization source base station device 1 is closer, there is a high possibility that the downlink signals of the own station device 1b1 and the synchronization source base station device 1 may cause interference to MSs 2 connected to both base station devices 1, respectively. Become.
- the accuracy of inter-base station synchronization between the self-station apparatus 1 b 1 and the synchronization source base station apparatus 1 be high.
- the information indicating whether interference can occur in the relationship between the own station device 1b1 and the synchronization source base station device 1 is information indicating the positional relationship between the own station device 1b1 and the synchronization source base station device 1
- the value be information affected by the positional relationship between the local station apparatus 1b1 and the synchronization source base station apparatus 1.
- the synchronization processing unit 5b uses the information indicating the positional relationship between the local station apparatus 1b1 and the synchronization source base station apparatus 1, or the value according to the positional relationship between the local station apparatus 1b1 and the synchronization source base station apparatus 1. Adjust the timing of performing synchronization processing based on the information that is affected. Therefore, for example, when it can be determined from the above information that the positions of the own station device 1b1 and the synchronization source base station device 1 are relatively close and there is a high possibility of interference, the frequency of synchronization processing is increased. The timing of the synchronization process can be adjusted.
- the accuracy of inter-base station synchronization can be enhanced, and interference generated with the synchronization source base station apparatus 1 can be effectively suppressed.
- the timing of the synchronization process can be adjusted so that the frequency of the synchronization process is lower than in the case. As a result, it is possible to prevent unnecessary synchronous processing.
- inter-base stations are adjusted by adjusting the timing at which synchronization processing is performed based on information indicating the positional relationship between the local station 1 b 1 and the synchronization source base station 1. Even when there is a possibility that interference may occur in relation to the other base station apparatus 1 that is the synchronization source in synchronization, synchronization processing can be performed so that the interference can be suitably avoided.
- the synchronization processing unit 5 b can use position information acquired by the GPS function as information indicating the positional relationship between the own station device 1 b 1 and the synchronization source base station device 1.
- the synchronization processing unit 5b detects when the transmission signal of the synchronization source base station device 1 is detected as the information whose value is affected by the positional relationship between the own station device 1b1 and the synchronization source base station device 1. Information on the result, the reception level of the transmission signal of synchronization source base station apparatus 1, or the path loss value between synchronization source base station apparatus 1 and own station apparatus 1b1 can be used.
- the synchronization processing unit 5b detects the number of times of detection of the synchronization source base station device 1 within the predetermined period, and the number of detections. And the detection rate, which is the ratio of the number of times detection was performed, the time when the downlink signal of the synchronization source base station was last detected (final detection time), or the elapsed time from the last detection time to the current time Time can be used.
- the synchronization processing unit 5b is performed between the own station apparatus 1b1 and the other base station apparatus 1 as information whose value is affected by the positional relationship between the own station apparatus 1b1 and the synchronization source base station apparatus 1. It is possible to use information whose value is affected by the number of MS2 handover attempts or the number of handover attempts. Further, the synchronization processing unit 5b can use the number of successful handovers and the successful handover rate obtained based on the number of handover trials as information whose value is affected by the number of handover trials.
- the synchronization processing unit 5b is added to the information indicating whether the interference can be avoided or not.
- the timing at which synchronization processing is performed may be adjusted based on this, and in this case, interference can be suitably avoided with the synchronization source base station apparatus 1 that may cause interference.
- the information indicating whether or not the interference can be avoided is the resource block allocation format when the synchronization source base station device 1 performs resource allocation to the MS 2 connected to the synchronization source base station device 1 Or information indicating whether inter-base station communication via the X2 interface is possible between the own station device 1b1 and the synchronization source base station device 1, for example.
- the synchronization processing unit 5b is information indicating the reception accuracy of the downlink signal from the synchronization source base station device 1, or information that affects the reception accuracy of the transmission signal from the other base station device according to the value thereof.
- the timing at which the synchronization process is performed may be adjusted based on the above, and in this case, if the reception accuracy of the downlink signal from the synchronization source base station device 1 is high enough to enable high accuracy inter-base station synchronization, synchronization may be performed.
- the synchronization accuracy can be kept high without increasing the frequency of processing. As a result, synchronization processing can be performed so that interference can be suitably avoided.
- the information indicating the reception accuracy of the downlink signal from synchronization source base station apparatus 1 is preferably the reception level at the time of reception of the downlink signal or SINR.
- the synchronization processing unit 5b determines the positional relationship between the self station apparatus 1b1 and the synchronization source base station apparatus 1 as information affecting the reception accuracy of the transmission signal from the synchronization source base station apparatus 1 according to the value. Or information whose value is affected by the positional relationship between the local station apparatus 1 b 1 and the synchronization source base station apparatus 1.
- the synchronization processing unit 5b relates to the detection result when the transmission signal of the synchronization source base station device 1 is detected as information whose value is affected by the positional relationship between the local station device 1b1 and the synchronization source base station device 1.
- a detection rate which is a ratio of the number of times of detection of the synchronization source base station device 1 detected within a predetermined period, the number of times of detection, and the number of times of detection The time when the transmission signal of the base station apparatus 1 was last detected, or the elapsed time from the time to the current time can be used.
- the synchronization processing unit 5b is performed between the own station device 1b1 and the synchronization source base station device 1 as information whose value is affected by the positional relationship between the own station device 1b1 and the synchronization source base station device 1.
- Information on the number of handover attempts of the MS 2 connected to the own station device 1 b 1 and the synchronization source base station device 1 or information whose value is affected by the number of handover attempts can be used.
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Abstract
Description
例えば、特許文献1には、同期元となる他の基地局装置からの送信信号を用いて基地局間同期を行うことが開示されている。
このような問題に対処するには、定期的に同期をとり直すことが考えられる。これにより、経時的に同期誤差が生じたとしても、同期がとり直されるため、基地局間同期をほぼ維持することができる。
従って、基地局間同期を頻繁に行うと、同期精度は良好になるものの、他の基地局装置からの送信信号の受信を頻繁に行うこととなるため、基地局装置と端末装置との間で行われる本来的な通信の品質が低下する。一方、基地局間同期の頻度を低くすると、端末装置との通信品質の低下は抑制できるものの、同期精度が低下するといった事態が発生する。
また、上記のような事態は、基地局間同期の場合に限らず、他の基地局装置からの送信信号を定期的に取得して行う処理に共通して生じる。
また、小型基地局としては、送信電力が200mW~2W程度であり、100m~500m程度の大きさのピコセルを形成するピコ基地局や、送信電力が20~200mW程度であり、100m以下の大きさのフェムトセルを形成するフェムト基地局がある。
このため、フェムト基地局装置の下り信号が、マクロ基地局装置に接続する端末装置に干渉を与えたり、フェムト基地局装置に接続する端末装置が送信する上り信号が、マクロ基地局装置に干渉を与えたりすることがある。
また、互いに隣接してフェムトセルを形成する複数のフェムト基地局装置及びそれに接続する端末装置が、相互に干渉を与える場合もある。
従って、上記のように、同期元である基地局装置との関係で、干渉が生じうる可能性のある場合、より精度よく基地局装置間同期がとれていることが好ましい。
また、本発明の他の目的は、基地局間同期における同期元である他の基地局装置との関係で干渉が生じ得る可能性のある場合にも、好適に干渉を回避することができるように同期処理を行うことができる基地局装置を提供することを目的とする。
(5)なお、前記検知部が検出する通信状況は、具体的には、自己及び/又は前記他の基地局装置に接続する端末装置の数である。
この場合、本来的な通信に与える影響を抑えつつ同期精度等をも維持できるように処理のタイミングを調整することができる。
この場合、自己に接続する端末装置の数、又は、他の基地局装置に接続する端末装置の数が少ないことで同期処理の必要性が低い場合には、当該同期処理の頻度を下げることができる。この結果、無駄なく同期処理を行うことができる。
従って、自己と前記他の基地局装置との関係で干渉を生じ得るか否かを示す前記情報は、自己と前記他の基地局装置との間の位置関係を示す情報、又は、自己と前記他の基地局装置との位置関係によってその値が影響を受ける情報であることが好ましい。
一方、上記情報から、自己と他の基地局装置との位置が相対的に遠く、干渉が生じる可能性が低いと判断できる場合には、干渉が生じる可能性が高いと判断できる場合よりも同期処理の頻度が低くなるように同期処理のタイミングを調整することができる。この結果、無駄に同期処理を行うのを防止できる。
以上のように、この基地局装置によれば、自己と前記他の基地局装置との間の位置関係を示す情報等に基づいて同期処理を行うタイミングを調整することで、基地局間同期における同期元である他の基地局装置との関係で干渉が生じ得る可能性のある場合にも、好適に干渉を回避することができるように同期処理を行うことができる。
さらに、前記他の基地局装置の送信信号が検出されたときの検出結果に関する情報は、前記他の基地局装置の送信信号が最後に検出されたときの時刻、又は、前記時刻から現在の時刻までの経過時間であってもよい。
つまり、このハンドオーバの試行数は、自己と前記他の基地局装置との間の位置関係を示す情報、又は、自己と前記他の基地局装置との位置関係によってその値が影響を受ける情報である。
従って、この場合においても、ハンドオーバの試行数に基づいて同期処理を行うタイミングを調整することで、基地局間同期における同期元である他の基地局装置との関係で干渉が生じ得る可能性のある場合にも、好適に干渉を回避することができるように同期処理を行うことができる。
また、自己の近傍に位置しかつ他の基地局装置に接続する端末装置が多ければ多いほど、自己は、他の基地局装置に接続する端末装置に干渉を与える可能性が高くなる。
他の基地局装置がマクロ基地局の場合、フェムト基地局である場合と比較して、より多数の端末装置が接続している可能性が高い。よって、他の基地局装置が、マクロ基地局である場合の方が干渉を生じさせる可能性が高くなる。
さらに、アクセスモードは、他の基地局装置に接続する端末装置の接続制限に関して規定するものであり、他の基地局装置の公共性を示している。例えば、端末装置の接続制限の度合が低いモードであれば、公共性が高く、より多数の端末装置が接続している可能性が高いことを示している。よって、アクセスモードが端末装置の接続制限の低いモードであればあるほど干渉を与える可能性が高くなる。
より具体的に、前記干渉が回避可能であるか否かを示す前記情報は、前記他の基地局装置が当該他の基地局装置に接続する端末装置にリソース割り当てを行う際のリソースブロックの割り当て形式を示す情報、又は、自己と前記他の基地局装置との間で基地局間通信が可能であるか否かを示す情報であることが好ましい。
この場合、他の基地局装置からの送信信号の受信精度が、高精度の基地局間同期が可能な程度に高い場合、同期処理の頻度を高めずとも、同期の精度を高く維持することができる。この結果、好適に干渉を回避することができるように同期処理を行うことができる。
よって、その値に応じて前記他の基地局装置からの送信信号の受信精度に影響を与える情報は、自己と前記他の基地局装置との間の位置関係を示す情報、又は、自己と前記他の基地局装置との位置関係によってその値が影響を受ける情報であることが好ましい。
一方、上記情報から、自己と他の基地局装置との位置が相対的に遠く、他の基地局装置の送信信号の受信精度が相対的に低いと判断できる場合には、前記受信精度が高いと判断できる場合よりも同期処理の頻度が高くなるように同期処理のタイミングを調整することができる。この結果、基地局間同期の精度が高めることができ、他の基地局装置との間で生じる干渉を効果的に抑制することが可能となる。
以上のように、この基地局装置によれば、他の基地局装置の送信信号の受信精度に影響を与える情報である、自己と前記他の基地局装置との間の位置関係を示す情報等に基づいて同期処理を行うタイミングを調整することで、好適に干渉を回避することができるように同期処理を行うことができる。
さらに、前記他の基地局装置の送信信号が検出されたときの検出結果に関する情報は、前記他の基地局装置の送信信号が最後に検出されたときの時刻、又は、前記時刻から現在の時刻までの経過時間であってもよい。
また本発明の基地局装置によれば、基地局間同期における同期元である他の基地局装置との関係で干渉が生じ得る可能性のある場合にも、好適に干渉を回避することができるように同期処理を行うことができる。
〔1. 第一の実施形態〕
〔通信システムの構成〕
図1は、本発明の一実施形態に係る無線通信システムの構成を示す概略図である。
この無線通信システムは、複数の基地局装置1と、この基地局装置1との間で無線通信を行うことができる複数の端末装置2(移動端末;Mobile Station)とを備えている。
複数の基地局装置1は、例えば数キロメートルの大きさの通信エリア(マクロセル)MCを形成する複数のマクロ基地局装置(Macro Base Station)1aと、各マクロセルMC内に設置され数十メートル程度の比較的小さなフェムトセルFCを形成する複数のフェムト基地局装置(Femto Base Station)1bとを含んでいる。
また、フェムト基地局装置1b(以下、フェムトBS1bともいう)は、例えば、屋内等、マクロBS1aの無線波を受信し難い場所等に配置され、上記フェムトセルFCを形成する。フェムトBS1bは、自己(自局装置)が形成するフェムトセルFC内にある端末装置2(以下、MS2ともいう)との間で無線通信が可能であり、本システムでは、マクロBS1aの無線波が受信し難い場所等においても、その場所に比較的小さいフェムトセルFCを形成するフェムトBS1bを設置することで、MS2に対して十分なスループットでのサービスの提供を可能にする。
このため、フェムトBS1bは、マクロBS1aや自己以外の他のフェムトBS1bといった、他の基地局装置における送信電力や使用周波数といった送信状況をモニタリング(メジャメント処理)を行う機能、及びその結果に基づいて、マクロセルMCにおける通信に対して影響を与えないように送信電力や使用周波数等の送信条件を調整する機能を有している。フェムトBS1bは、この機能によって他の基地局装置の通信に影響を与えることなく、マクロセルMC内にフェムトセルFCを形成することができる。
基地局間同期は、親(同期元)となる基地局装置が、自己のセル内のMS2に向けて送信した信号を、別の基地局装置が受信することで同期をとる「エア同期」によって実行される。
親(同期元)となる基地局装置は、さらに他の基地局装置との間でエア同期をとるものであってもよいし、GPS信号によってフレームタイミングを自律的に決定する等、エア同期以外の方法によってフレームタイミングを決定するものであってもよい。
ただし、マクロBS1aは、他のマクロBS1aを親とすることはできるが、フェムトBS1bを親とすることはできない。フェムトBS1bは、マクロBS1aを親とすることもできるし、他のフェムトBS1bを親とすることもできる。
本実施形態の通信システムが準拠するLTEにおいて採用可能なFDD方式においては、上り信号(端末装置から基地局装置への送信信号)と、下り信号(基地局装置から端末装置への送信信号)との間で、互いに異なる使用周波数を割り当てることで、上り通信と下り通信とを同時に行う。
DLフレームを構成するサブフレームは、それぞれ2つのスロット(例えば、スロット♯0,♯1)により構成されている。また、1つのスロットは、7個(♯0~♯6)のOFDMシンボルにより構成されている(Normal Cyclic Prefixの場合)。
また、図中、データ伝送の上での基本単位(最小単位)であるリソースブロック(RB:Resource Block)は、周波数軸方向に12サブキャリア、時間軸方向に7OFDMシンボル(1スロット)で定められる。従って、例えば、DLフレームの周波数帯域幅が5MHzに設定されている場合、300個のサブキャリアが配列されるので、リソースブロックは、周波数軸方向に25個配置される。
同報チャネルには、通信帯域幅や、送信アンテナ数、制御情報の構造等の主要なシステム情報が格納される。
第二同期信号は、時間軸方向において、サブフレーム♯0及びサブフレーム♯5それぞれの先頭側のスロットの最後から2番目のOFDMシンボルであるシンボル♯5の位置に1つのシンボル幅で配置され、周波数軸方向において、DLフレームの帯域幅の中央の位置に6リソースブロック幅分(72サブキャリア)で配置されている。この第二同期信号は、端末装置が、複数の基地局装置の通信エリア(セル)それぞれを識別するための情報であり、168パターン定義されている。
第一同期信号及び第二同期信号がとり得る複数のパターンは、通信規格において予め定められており、各基地局装置及び各端末装置において既知である。つまり、第一同期信号及び第二同期信号は、それぞれ、複数のパターンをとり得る既知信号である。
DL共有チャネルに格納されるユーザデータの割り当てについては、各サブフレームの先頭に割り当てられている上記制御チャネル内のリソース割当情報により規定されており、端末装置は、このリソース割当情報によって、そのサブフレーム内に自己に対するデータが格納されているか否かを判断できる。
図4は、図1中、フェムト基地局装置の構成を示すブロック図である。なお、ここでは、フェムトBS1bの構成について説明するが、マクロBS1aの構成も、フェムトBS1bとほぼ同様である。
フェムトBS1b1は、アンテナ3と、アンテナ3が接続された送受信部(RF部)4と、RF部4との間で授受が行われる送受信信号の信号処理の他、基地局間同期についての処理や、メジャメント等を行う信号処理部5とを備えている。
図5は、RF部4の詳細を示すブロック図である。RF部4は、上り信号受信部11、下り信号受信部12、及び送信部13を備えている。上り信号受信部11は、端末装置2からの上り信号を受信するためのものであり、下り信号受信部12は、他のマクロBS1a又は他のフェムトBS1bからの下り信号を受信するためのものである。送信部13は、端末装置2へ下り信号を送信するためのものである。
このように、上り信号受信部11は、端末装置からの上り信号を受信するために上り信号周波数fuに適合して構成された受信部であって、基地局装置として本来的に必要な受信部である。
直交変調器132の出力は、周波数fdだけを通過させる第3フィルタ133を経て、第3増幅器134によって増幅され、さらに周波数fdだけを通過させる第4フィルタ135を得て、アンテナ3から送信され、端末装置への下り信号となる。
この下り信号受信部12は、第5フィルタ121、第4増幅器(高周波増幅器)122、第3周波数変換部123、第6フィルタ124、第5増幅器(中間周波増幅器)125、第4周波数変換部126、及びA/D変換部127を備えている。
信号処理部5は、RF部4との間で授受が行われる送受信信号の信号処理を行うための機能を有しており、当該信号処理部5の上位レイヤから与えられる各種送信データを送信信号に変調するとともに、RF部4から与えられる受信信号を受信データに復調する処理を行う変復調部5aを備えている。変復調部5aでは、後述の同期処理部5bによって算出された同期誤差(タイミングオフセット、周波数オフセット)に基づき、同期誤差を補正した状態で変復調の処理が行われる。
さらに、信号処理部5は、RF部4に与える送信信号についての無線フレームごとの送信タイミングを決定するためのフレームカウンタ(図示せず)を備えている。
また、信号処理部5は、他の基地局装置との間で基地局間同期をとる同期処理を行うための同期処理部5b、メジャメントを行うためのメジャメント処理部5cの他、リソース割当制御部5dと、自己及び他の基地局装置に接続する端末装置の通信状況を検知するための端末検知部5eとを備えている。
以下、同期処理部5bの構成について説明する。
図6は、他の基地局装置との間で基地局間同期をとる同期処理を行うための同期処理部5bの構成を示すブロック図である。
基地局間同期は、各基地局装置がGPS受信機を備えて、GPS信号によって同期をとったり、基地局間を有線で接続して同期をとったりしてもよいが、本実施形態では、無線信号(下り信号)によって同期を行う「エア同期」による基地局間同期を採用している。
また、同期処理部5bは、端末検知部5eの検知結果に応じて、同期処理のための下り信号を取得するタイミングの周期を調整することで、同期処理を行うタイミングを調整する機能を有している。
また、上記送信信号の送信の休止のほか、端末装置からの上り信号の受信の休止も行っても良い。
なお、送信タイミングの検出は、受信した下り信号のフレーム中の所定位置にある既知信号(波形も既知)である、第一同期信号及び第二同期信号のタイミングを検出することで行える。
また、同期誤差検出部14は、検出したフレーム同期誤差をフレームカウンタ補正部15の他、検出される度に記憶部18に与える。記憶部18は、これら検出されたフレーム同期誤差を蓄積する。
すなわち、同期誤差(タイミングオフセット)とクロック周期の間には以下の等式が成り立つ。
同期元基地局のクロック周期:同期先基地局のクロック周期=T:(T+T2)=10:(10+0.0001)
(同期元基地局のクロック周波数-同期先基地局のクロック周波数)
=同期元基地局のクロック周波数×T2/(T+T2)
≒同期元基地局のクロック周波数×0.00001
となる。
周波数補正部17は、このキャリア周波数誤差に基づいて、キャリア周波数の補正を行う。なお、キャリア周波数の補正は、上り信号のキャリア周波数だけでなく、下り信号のキャリア周波数についておこなうことができる。
次に、メジャメント処理部5cの機能について説明する。
メジャメント処理部5cは、他の基地局装置における送信電力や使用周波数といった下り信号の送信状況の測定(メジャメント処理)を行うための機能を有しており、下り信号受信部12が受信する他の基地局装置の下り信号を取得して、当該下り信号の受信電力(受信レベル)を求める。
例えば、メジャメント処理部5cは、受け取った同期タイミング情報に基づいて同期処理が開始されるサブフレームを特定し、その特定したサブフレームが属する無線フレームの次の無線フレームに属するサブフレームでメジャメント処理を行うように設定する。
また、上記送信信号の送信の休止のほか、端末装置からの上り信号の受信の休止も行っても良い。
メジャメント処理部5cは、取得した下り信号から、リソースブロック単位であると推定される部分を時間軸方向に分けて取り出す。さらに取り出した部分それぞれから、リソースブロックの周波数幅ごとの部分を取り出し、その周波数ごとの部分の電力をリソースブロックの電力平均値として求める。
メジャメント処理部5cは、上記電力平均値を求めると、この電力平均値を示すメジャメント結果情報を、リソース割当制御部5d、端末検知部5e、及び出力制御部5fに出力する。
ここで、他の基地局装置と自己との間でフレームタイミングの同期がとれていれば、自己のフレームタイミングから、他の基地局装置のフレームタイミングを把握できるので、メジャメント処理部5cは、時間軸方向におけるリソースブロックの単位を精度よく推定でき、精度よく電力平均値を求めることができる。このため、メジャメント処理は、同期処理を行った直後に行うことが好ましい。
端末検知部5eは、自己及び他の基地局装置に接続するMS2との間の通信状況を検知する機能を有している。
より具体的には、端末検知部5eは、通信状況として、現状、自己及び他の基地局装置に接続しているMS2の数を検知する。
なお、ここで、端末検知部5eの検出対象となる他の基地局装置に接続しているMS2は、自己の下り信号が到達する可能性のあるMS2である。
一方、他の基地局装置に接続するMS2の数については、メジャメント処理部5cからのメジャメント結果情報に基づいて推定する。
メジャメント処理は、他の基地局装置からの下り信号を受信して行われるものであり、他の基地局装置は、自己の周辺に位置することで双方の下り信号が到達可能な範囲に位置する基地局装置である。よって、この他の基地局装置に接続するMS2に対して、自己の下り信号が到達する可能性がある。
従って、端末検知部5eは、上記のような他の基地局装置の下り信号についてのメジャメント結果情報から、自己の下り信号が到達する可能性のあるMS2を検出することができる。
リソース割当制御部5dは、無線フレーム中のDL共有チャネルに、各端末装置2に送信するためのユーザデータを割り当てる機能を有している。
また、リソース割当制御部5dは、前記同期タイミング情報、及び、前記メジャメントタイミング情報が、同期処理部5b及びメジャメント制御部5fから与えられると、これら情報により特定されるサブフレームにユーザデータの割り当てを制限する。さらに、リソース割当制御部5dは、メジャメント処理部5cからメジャメント結果情報が与えられると、この情報に基づいて、ユーザデータの割り当てを決定する。
図7は、同期処理部が行う同期処理の態様の一例を説明するための図である。図7では、他の基地局装置であるマクロBS1a、及び自己の基地局装置であるフェムトBS1bそれぞれが送信するフレームを同一の時間軸上で示しており、フェムトBS1bが、同期元であるマクロBS1aの下り信号に対して同期を行う態様を示している。
図7において、タイミングT4より前の区間で、マクロBS1aの無線フレームと、フェムトBS1bの無線フレームとの間で互いにサブフレームの先頭にタイミングのずれが生じ、フレーム送信タイミングにずれが生じている状態を示している。
そして、同期処理部5bは、受信したマクロBS1aの下り信号に含まれる第一同期信号及び第二同期信号を利用して当該マクロBS1aのフレーム送信タイミングを検出するとともに、自己のフレーム送信タイミングとの間のフレーム同期誤差を検出する。
なお、上記では、フレームタイミングの同期についてのみ説明したが、キャリア周波数の補正についても同様に行われる。
図8は、メジャメント処理部5cが行うメジャメント処理の態様の一例を説明するための図である。図8では、他の基地局装置であるマクロBS1a及び自己の基地局装置であるフェムトBS1bそれぞれが送信するフレームを同一の時間軸上で示しており、フェムトBS1bが、マクロBS1aの下り信号についてメジャメント処理を行う態様を示している。
メジャメント処理部5cは、特定した同期処理の開始タイミングに対応するサブフレームが属する無線フレームの次の無線フレームにおいて、メジャメント処理を行うように設定する。つまり、図に示すように、タイミングT4で同期がとられた直後の無線フレームにおいてメジャメント処理を行う。
本実施形態では、メジャメント処理部5cは、メジャメント処理のために送信信号の送信を休止させる区間を、開始タイミングに対応するサブフレームに続く二つのサブフレームまでの三つのサブフレーム分に設定する。よって、メジャメント処理部5cは、図に示すように、サブフレームSF2,SF3,SF4の区間について送信信号の送信を休止させる。
従って、メジャメント処理部5cは、このサブフレームSF2~SF4を特定するための情報を含むメジャメントタイミング情報を、リソース割当制御部5dに出力する。
そして、メジャメント処理部5cは、取得した下り信号から、リソースブロックごとの電力平均値を求める。
図に示すように、各リソースブロックにおいて、電力平均値が高く現れるものと低く現れるものがあり、電力平均値が高く現れるリソースブロックにおいては、ユーザデータが割り当てられていることが判る。
メジャメント処理部5cは、図9に示すようなデータを、取得した下り信号から、シンボル方向におけるリソースブロック幅ごとと推定できる時間幅ごとに求め、取得した下り信号に含まれる各リソースブロックごとの電力平均値を得る。
メジャメント結果情報が与えられたリソース割当制御部5d、及び出力制御部5fは、このメジャメント結果情報に基づいて、他の基地局装置との干渉が生じるのを抑制されるように自己が行う処理を実行する。
例えば、図9に示すように、電力平均値が低く現れている周波数帯域には、MS2に対するユーザデータが割り当てられていないので、他の基地局装置は、この帯域については、現状使用していないと推測することができる。
リソース割当制御部5dは、他の基地局装置が使用していないと推測される帯域を優先的に使用するように、自己のユーザデータの割り当てを行う。これによって、自己が使用する帯域が、他の基地局装置が使用する帯域と重複するのを極力回避でき、他の基地局装置や当該他の基地局装置に接続するMS2に対して、干渉が生じるのを抑制することができる。
図10は、同期処理及びメジャメント処理が行われるタイミングを示す図である。図10では、時間軸方向に並ぶ複数の無線フレームの内、同期処理が行われるサブフレームを含む無線フレームF1及びメジャメント処理が行われるサブフレームを含む無線フレームF2の配置を示している。
ここで、同期処理部5bは、端末検知部5eの検知結果に応じて、同期処理の開始タイミングの周期を調整することで、同期処理を行うタイミングを調整する。
端末検知部5eは、他の基地局装置と接続するMS2の推定数と、自己に接続するMS2の数についての情報を検知結果として、同期処理部5bに与える。
これら情報が与えられた同期処理部5bは、他の基地局装置と接続するMS2の推定数、及び、自己に接続するMS2の数に応じて、同期処理の開始タイミングの周期を調整する。
本実施形態において、同期処理部5bは、同期処理の周期として設定しうる最長の周期と、最長周期よりも短い周期を複数含んでいる周期群を記憶している。同期処理部5bは、周期群それぞれに含まれる複数の周期、及び最長周期の内、いずれかを同期処理を行う周期として選択することで、周期調整を行う。なお、上記最長周期は、基地局間同期の精度を最低限維持することができる最大の周期に設定される。
ステップS101において、自己及び他の基地局装置に接続するMS2が存在していると判定された場合、同期処理部5bは、自己に接続するMS2が存在するか否かを判定する(ステップS103)。自己に接続するMS2が存在しないと判定された場合、他の基地局装置に接続するMS2のみが存在していると判断できる。この場合、同期処理部5bは、予め設定された基準に基づき、他の基地局装置に接続するMS2の数に応じて、周期群に含まれる複数の周期の中から、一の周期を選択し、同期処理の周期として設定し(ステップS104)、処理を終える。
つまり、同期処理部5bは、自己及び他の基地局装置に接続するMS2が存在しない場合には、最長周期を選択し、MS2の数が増加すれば、より同期処理の周期を短くするように設定する。
その一方、基地局装置が一定の周期で同期処理を行うように設定されている場合、MS2が存在せず、同期をとる必要性が低くても、一定の周期で同期処理を行うので、必要性の低い処理を比較的高い頻度で行うこととなり無駄が生じる。
上記実施形態では、同期処理を周期的に行う場合を例示したが、端末検知部5eの検知結果に応じて、その都度ごとに同期処理のタイミングを設定してもよい。
また、上記実施形態では、同期処理部5bは、自己及び他の基地局装置に接続するMS2の数に応じて同期処理の周期を設定する場合を例示したが、自己に接続するMS2の数のみに応じて設定してもよいし、他の基地局装置に接続するMS2の数のみに応じて設定してもよい。
さらに、上記実施形態では、まず、自己に接続するMS2の数と、他の基地局装置に接続するMS2の数とを把握した後、それぞれのMS2の数について個別的に評価し、同期処理の周期を設定したが、自己及び他の基地局装置に接続するMS2の総数のみに着目し、その総数に応じて、同期処理の周期を設定してもよい。
図12は、本発明の第二の実施形態に係るフェムトBS1bの内部構成の一部を示す部分ブロック図である。なお、マクロBS1aの構成も、フェムトBS1bの場合とほぼ同様である。
また、測定結果情報取得部41は、前記測定開始要求に基づいて測定を行ったMS2が送信する測定結果から測定結果情報を取得する機能を有している。さらに、測定結果情報取得部41は、下り信号受信部12が受信した他の基地局装置1の下り信号を測定しその測定した結果から測定結果情報を取得する機能を有している。
セル情報記憶部43は、隣接セル情報生成部42が出力する上記隣接セル情報を記憶するとともに、新たな隣接セル情報が出力されるごとに更新する機能を有している。
各フェムトBS1bは、ゲートウェイ32(GW)を介してMME30に接続されている。ゲートウェイ32は、各フェムトBS1bと、MME30との間、及び各フェムトBS1b間で行われる通信を中継する機能を有している。
MME30と各マクロBS1aとの間、MME30とゲートウェイ32との間、ゲートウェイ32とフェムトBS1bとの間は、それぞれS1インターフェースと呼ばれる通信インターフェースによる回線33によって接続されている。
このX2インターフェースは、各基地局装置間で移動する各MS2におけるハンドオーバ等の移動管理についての情報等を交換する目的で設けられている。なお、このような機能はMME30の機能と重複するが、MME30が各マクロBS1aに接続するMS2についての移動管理を一元的に行うと処理が集中に膨大な処理量となる点、及び、移動管理について、基地局装置間で行った方がより効率的である点といった理由から、基地局装置間で通信を行うためのX2インターフェースが設けられている。
フェムトBS1bには、図14に示すように、他の基地局装置1との間で、直接的にX2インターフェースによる通信回線が設置されていない。よって、本実施形態では、フェムトBS1bは、ゲートウェイ32までを接続するS1インターフェースによる通信回線33及びゲートウェイ32を経由し、他の基地局装置1との間でX2インターフェースによる基地局装置間通信を行う方法を採る。
図15は、本実施形態のフェムトBS1b1が測定結果情報を取得する際の手順の一例を示したシーケンス図である。なお、図15では、図13中、フェムトBS1b1がMS2(1)に隣接する基地局装置1の下り信号の測定を実施させる場合を示している。
ここで、フェムトBS1b1は、自局装置1b1の起動時等、自局装置1b1が隣接セル情報を有していない場合、MS2(1)に対して全周波数検索を行わせる。例えば、LTEでは、フェムトBS1b1の起動後、最初にMS2(1)が、フェムトBS1b1とのRRC(Radio Resource Control)コネクションを確立したとき、すなわち、フェムトBS1b1と通信接続するための処理を完了したときに、フェムトBS1b1は、当該MS2に対して全周波数検索を行わせる。全周波数検索とは、無線通信システムにおいて設定された全ての種類(全帯域)の搬送波周波数について、他の基地局装置1からの下り信号の受信レベルを測定することを意味する。
従って、フェムトBS1b1が隣接セル情報を有していない場合、当該フェムトBS1b1は、ステップS10において、測定対象を全周波数に設定する。
MS2(1)は、ステップS12において、他の基地局装置1の下り信号の検出を行い、検出された下り信号の搬送波周波数、及び受信レベルを測定する。さらに、検出された下り信号の送信元の基地局装置1についてのセルIDを取得する。
MS2(1)は、下り信号測定を終えると、その測定結果である、検出された下り信号の搬送波周波数、その受信レベル、及び対応するセルIDを含む測定結果通知をフェムトBS1b1へ送信する(ステップS13)。
そして、フェムトBS1b1は、隣接セル情報を有していない場合、取得した測定結果情報に基づいて、隣接セル情報の生成を行う(ステップS15)。また、フェムトBS1b1は、隣接セル情報を有している場合、この測定結果情報に基づいて記憶している隣接セル情報の更新を行う(ステップS15)。
図16のように、隣接セル情報は、検出された他の基地局装置1(セル)のセルIDが登録されるとともに、それぞれの測定結果情報である搬送波周波数及び受信レベルがセルIDに対応付けられて登録されている。
従って、マクロBS1a1、マクロBS1a2、及び、フェムトBS1b2のセルIDがそれぞれ上記のように設定されている場合、フェムトBS1bは、これらのセルID、搬送波周波数、及び受信レベルを含む測定結果情報を取得する。
さらに、フェムトBS1b1は、測定結果情報に含まれる搬送波周波数及び下り信号の受信レベルを、図16に示すように、隣接セル情報に反映させる。
より具体的には、同期処理部5bは、同期元基地局装置1の測定結果情報に含まれる受信レベルが相対的に大きければ、同期処理の周期が短くなるように決定する。
また、本実施形態のフェムトBS1b1が取得する他の基地局装置1の下り信号の受信レベルは、大きければ大きいほど、当該他の基地局装置1がフェムトBS1b1の近くに位置している可能性が高いことを示している。つまり、他の基地局装置1の受信レベルに関する情報は、自局装置1b1と他の基地局装置1との位置関係によってその値が影響を受ける情報を構成している。
この場合、基地局間同期の精度を高める必要性が低く、同期処理部5bは、マクロBS1b1を同期元基地局装置1として選択した場合と比べて、同期処理の周期を長く調整する。この結果、無駄に同期処理を行うのを防止できる。
また、本実施形態では、同期処理部5bは、隣接セル情報に含まれる測定結果情報の内、同期元基地局装置1の下り信号の受信レベルに基づいて、同期処理の周期を調整したが、例えば、本実施形態の他の例として、同期処理部5bが、隣接セル情報に含まれる測定結果情報の内、同期元基地局装置1の下り信号の搬送波周波数に応じて、同期処理の周期を調整するという構成とすることもできる。
この場合、基地局間同期の精度を高める必要性が低く、同期処理部5bは、マクロBS1b1を同期元基地局装置1として選択した場合と比べて、同期処理の周期を長く調整する。
よって、本例においても、基地局間同期の精度を必要に応じて調整することができ、同期処理を適切に行うことができる。
図17(a)は、本実施形態の他の例その2に係るフェムトBS1bが測定結果情報の取得を行ったときに検出された他の基地局装置1の検出結果の一例を示す図であり、図17(b)は、図17(a)の検出結果に基づいて、本例の隣接セル情報生成部42が生成する隣接セル情報の一例を示す図である。
本例の測定結果情報取得部41は、MS2により行われる下り信号測定毎に送信される測定結果通知に基づいて、検出された他の基地局装置1の検出回数をカウントし、その検出回数と、検出率とを測定結果情報として取得するように構成されている。
また、隣接セル情報生成部42は、図17(b)に示すように、測定結果情報に含まれる検出回数及び検出率と、対応する他の基地局装置1のセルIDとを関連付けた隣接セル情報を生成する。
例えば、測定結果情報取得部41が測定結果情報の取得を4回所定のタイミングで実行し、それぞれの実行時の下り信号測定による他の基地局装置1の検出結果が、図17(a)に示すものであったとする。この場合、1回目の下り信号測定では、測定結果情報取得部41は、検出されたマクロBS1a1、マクロBS1a2、及びフェムトBS1b2のセルIDを含む測定結果通知をMS2から受信する。2回目以降も同様に、測定結果情報取得部41は、他の基地局装置1の検出結果を含む通知を受信する。
例えば、マクロBS1a1は、図17(a)のように、4回の下り信号測定の全てで検出されている。よって、測定結果情報取得部41は、マクロBS1a1の検出回数が「4」、検出率が「1.00」である測定結果情報を得る。測定結果情報取得部41は、他の検出されたセルの検出回数、検出率についても、上記と同様にして得る。
より具体的には、同期処理部5bは、同期元基地局装置1の検出回数が相対的に多ければ、同期処理の周期が短くなるように決定する。
また、上述したように、互いに隣接する二つの基地局装置1は、互いの位置が近ければ近いほど、一方の基地局装置1の下り信号が、他方の基地局装置1に接続するMS2に対して干渉を生じさせる可能性が高くなる。
この場合、基地局間同期の精度を高める必要性が低く、同期処理部5bは、マクロBS1b1を同期元基地局装置1として選択した場合と比べて、同期処理の周期を長く調整する。この結果、無駄に同期処理を行うのを防止できる。
従って、上記例では、同期処理部5bが検出回数に応じて同期処理の周期を調整する場合を例示したが、同期処理部5bが、同期元基地局装置1の測定結果情報に含まれる検出率に応じて同期処理の周期を調整するものであってもよい。
また、さらに他の例として、測定結果情報取得部41が、他の基地局装置1が検出された検出時刻を含む測定結果情報を取得し、同期処理部5bが、同期元基地局装置1を検出した検出時刻に応じて、同期処理の周期を調整するという構成とすることもできる。
本例の測定結果情報取得部41は、MS2により行われる下り信号測定毎に送信される測定結果通知に基づいて、他の基地局装置1それぞれの最終検出時刻、及びその経過時間を測定結果情報として取得するように構成されている。
また、隣接セル情報生成部42は、図18(b)に示すように、測定結果情報に含まれる最終検出時刻及び経過時間と、対応する他の基地局装置1のセルIDとを関連付けた隣接セル情報を生成する。
例えば、測定結果情報取得部41が測定結果情報の取得を4回所定のタイミングで実行し、それぞれの実行時の下り信号測定による他の基地局装置1の検出結果が、図18(a)に示すものであったとする。この場合、1回目の下り信号測定では、測定結果情報取得部41は、検出されたマクロBS1a1、マクロBS1a2、フェムトBS1b2のセルID、及びそのときの測定時刻である「2010年9月15日14時10分」を含む測定結果通知をMS2から受信する。2回目以降も同様に、測定結果情報取得部41は、他の基地局装置1の検出結果を含む通知を受信する。
例えば、現在の時刻が、「2010年9月16日12時20分」であるとすると、マクロBS1a1が最後に検出された測定時刻は、図18(a)のように、現在の時刻と同じ「2010年9月16日12時20分」である。よって、測定結果情報取得部41は、マクロBS1a1の最終検出時刻が「2010年9月16日12時20分」、経過時間が「00:00」である測定結果情報を得る。測定結果情報取得部41は、他の検出されたセルの最終検出時刻、及び経過時間についても、上記と同様にして得る。
より具体的には、同期処理部5bは、隣接セル情報に登録されている同期元基地局装置1の経過時間が短ければ短いほど同期処理の周期が短くなるように調整する。
逆に、経過時間は、短ければ短いほど、自局装置1b1の周辺に存在している可能性が高いことを示している。
この場合、基地局間同期の精度を高める必要性が低く、同期処理部5bは、マクロBS1b1を同期元基地局装置1として選択した場合と比べて、同期処理の周期を長く調整する。
なお、上記例では、同期処理部5bが経過時間に応じて同期処理の周期を調整する場合を例示したが、最終検出時刻に応じて周期を調整してもよい。
なお、上記実施形態では、フェムトBS1bが、MS2(1)に隣接する他の基地局装置1の下り信号の測定を実施させて、測定結果情報を取得する場合を例示したが、フェムトBS1b1が、自局装置1b1の下り信号受信部12によって他の基地局装置1の下り信号の測定を行い、その測定した結果から測定結果情報を取得してもよい。
この場合、各基地局装置1は、互いにX2インターフェースを介した基地局間通信が可能なので、フェムトBS1b1は、基地局間通信によって、他の基地局装置1の位置情報を取得することができる。
従って、自局装置1b1が、他の基地局装置1から、自局装置1b1と他の基地局装置1との間でX2インターフェースを介した基地局間通信が可能であるか否かを示す情報を取得し、この情報が登録された隣接セル情報を生成してもよい。
この場合、フェムトBS1b1の同期処理部5bは、自局装置1b1とX2インターフェースを介した基地局間通信が可能な他の基地局装置1を同期元として選択した場合、基地局間通信を行うことができない他の基地局装置1を選択した場合よりも、同期処理の周期が短くなるように調整する。これにより、フェムトBS1b1は、同期元基地局装置1との間で、干渉を回避するための処理を好適に行うことができる場合には、同期処理の周期を相対的に短くし、干渉回避のための処理をより効果的に行うことができる。
このように、自局装置1b1と他の基地局装置1との間でX2インターフェースを介した基地局間通信が可能であるか否かを示す情報は、自局装置1b1と他の基地局装置1との関係で生じる干渉が回避可能であるか否かを示す前記情報を構成している。
図19は、本発明の第三の実施形態に係るフェムトBS1bの内部構成の一部を示す部分ブロック図である。なお、マクロBS1aの構成も、フェムトBS1bの場合とほぼ同様である。
次に、フェムトBS1b1は、設定した測定対象の下り信号をMS2(1)に測定させるための測定開始要求をMS2(1)へ送信する(ステップS21)。この測定開始要求には、測定対象となる周波数および基地局装置の情報等が含まれている。
MS2(1)は、下り信号測定を終えると、その測定結果である、検出された下り信号の受信レベル及び対応するセルIDを含む測定結果通知をフェムトBS1b1へ送信する(ステップS23)。また、このとき、MS2(1)は、フェムトBS1b1の下り信号の受信レベルもフェムトBS1b1へ送信する。
MS2(1)からの測定結果通知を受信すると、フェムトBS1b1は、この測定結果通知に基づいて、MS2(1)がハンドオーバすべきか否かを判断する。フェムトBS1b1は、MS2(1)がハンドオーバすべきと判断すると、隣接セル情報を参照してハンドオーバ先を決定し、ハンドオーバ要求をマクロBS1a1へ送信する(ステップS24)。なお、図例では、ハンドオーバ先をマクロBS1a1に決定した場合を示している。
また、ハンドオーバするか否かの判断、及びハンドオーバ先の決定は、現在接続する基地局装置1の下り信号の受信レベルと他の基地局装置1の受信レベルとを比較することにより行われる。
さらに、ハンドオーバするか否かの判断、及びハンドオーバ先の決定は、MS2(1)が行うこともある。この場合、フェムトBS1b1は、MS2(1)の判断及び決定に応じてハンドオーバ要求を送信する。
ハンドオーバ応答を受信したフェムトBS1b1は、MS2(1)へRRCコネクション再確立指示を送信する(ステップS27)。
RRCコネクション確立通知を受信したマクロBS1a1は、フェムトBS1b1へハンドオーバ完了通知を送信する(ステップS29)。
ハンドオーバ完了通知を受信したフェムトBS1b1は、MS2(1)に関する情報を開放し、ハンドオーバを終える。また、フェムトBS1b1は、ハンドオーバ完了通知を受信することで、ハンドオーバが成功したことを認識することができる。ここで、ハンドオーバ情報取得部44は、ハンドオーバの結果に関する情報を取得する(ステップS30)。
また、フェムトBS1b1と、マクロBS1a1との間で行われる、ハンドオーバ要求や、ハンドオーバ応答、ハンドオーバ完了通知の送受信は、MME30や、ゲートウェイ32等の上位の機器を介して行われるが、X2インターフェースを介した基地局間通信によって行われる場合もある。
フェムトBS1b1は、ハンドオーバ要求をマクロBS1a1へ送信すると、隣接セル情報中のマクロBS1a1のハンドオーバ試行数を「5」から「6」に更新する(図21(b))。
図22では、フェムトBS1b1がハンドオーバ要求を送信する前の段階(図22(a))では、図21と同じ内容の隣接セル情報となっている。
フェムトBS1b1は、ハンドオーバ要求をマクロBS1a2へ送信すると、隣接セル情報中のマクロBS1a2のハンドオーバ試行数を「3」から「4」に更新する(図22(b))。
より具体的には、同期処理部5bは、ハンドオーバ情報の内、ハンドオーバ試行数が相対的に多ければ、同期処理の周期が短くなるように調整する。
さらに、互いに隣接する二つの基地局装置1は、互いの位置が近ければ近いほど、一方の基地局装置1の下り信号が、他方の基地局装置1に接続するMS2に対して干渉を生じさせる可能性が高くなる。
この場合、基地局間同期の精度を高める必要性が低く、同期処理部5bは、マクロBS1b1を同期元基地局装置1として選択した場合と比べて、同期処理の周期を長く調整する。
自局装置1b1と他の基地局装置1との位置関係によってその値が影響を受ける情報として、上述のハンドオーバ試行数、ハンドオーバ成功数、又はハンドオーバ成功率以外に、自局装置1b1に接続するMS2が自セル内に滞在する滞在時間(平均値など)も利用できる。ここで、滞在時間とは、MS2が自局装置1b1に接続するためのハンドオーバが行われた時間t1から、そのMS2が他の基地局装置1に接続するためのハンドオーバが行われる時間t2までの時間間隔(t2-t1)である。滞在時間が短ければ、ハンドオーバが頻繁に行われていることを示しており、滞在時間の短さは、ハンドオーバの回数の多さと同様の指標となる。つまり、滞在時間は、ハンドオーバ回数によって、その値が影響を受ける情報でもある。
なお、滞在時間としては、自セルに隣接する他セル内に、MS2が滞在する時間であってもよい。つまり、滞在時間としては、MS2が自局装置1b1から第1の他の基地局装置1に接続するためのハンドオーバが行われた時間t1から、そのMS2が、第1の他の基地局装置1から、第2の他の基地局装置1又は自局装置1b1に接続するためのハンドオーバが行われる時間t2までの時間間隔(第1の他の基地局装置1のセル内での滞在時間)であってもよい。
また、滞在時間としては、MS2が第1の他の基地局装置1から第2の他の基地局装置1に接続するためのハンドオーバが行われた時間t1から、そのMS2が、第1の他の基地局装置1から、自局装置1b1に接続するためのハンドオーバが行われる時間t2までの時間(第2の他の基地局装置1のセル内での滞在時間)であってもよい。
図23は、本発明の第四の実施形態に係るフェムトBS1bの内部構成の一部を示す部分ブロック図である。なお、マクロBS1aの構成も、フェムトBS1bの場合とほぼ同様である。
アクセスモードとは、基地局装置がMS2との間における通信接続の制限を規定するためのモードである。アクセスモードには、図24に示すように、オープンアクセスモード、クローズドアクセスモード、及び、ハイブリッドモードの3種類がある。基地局装置1は、これら3種類の異なるアクセスモードのいずれかに設定されている。
クローズドアクセスモードとは、このモードに設定されている基地局装置1に登録されているMS2のみに接続が許容されるモードである。
ハイブリッドモードとは、基本的に全てのMS2と接続可能であるが、登録されているMS2が、登録されていないMS2と比べて通信リソースの割り当て等で優遇される場合があるモードである。
フェムトBS1bは、上記3つのモードの内、いずれか一つのモードに設定されている。
フェムトBS1bは、個人又は企業等が自己の建物や特定の空間内に設置するものであり、フェムトBS1bを設置する個人や企業等が、当該フェムトBS1bに接続するMS2を特定のMS2のみに制限したい場合がある。このような場合に、フェムトBS1bは、その状況に応じて上記3つのモードの内、いずれか一つのモードを選択し設定することができるように構成されている。
例えば、図13に示すフェムトBS1b2がハイブリッドモードに設定されているとすると、属性情報取得部45は、フェムトBS1b2がハイブリッドモードであることを示すアクセスモード情報を取得する。また、図13中のマクロBS1a1及びマクロBS1a2は、上述のようにオープンアクセスモードである。よって、属性情報取得部45は、マクロBS1a1及びマクロBS1a2がオープンアクセスモードであることを示すアクセスモード情報を取得する。
隣接セル情報生成部42は、上記アクセスモード情報、セル形態に関する情報、及び、他の基地局装置1のリソースブロックの割り当て形式を示す情報を、セル情報IDと関連付けることで、図25(a)に示す隣接セル情報を生成する。
より具体的には、同期処理部5bは、同期元基地局装置1に設定されているアクセスモードが、オープンアクセスモードである場合、同期処理の周期を他のモードの場合よりも短く調整し、以下、ハイブリッドモード、クローズドアクセスモードの順で同期処理の周期が順次長くなるように調整する。
フェムトBS1b1は、他の基地局装置1に接続するMS2に干渉を与える可能性を有しているため、他の基地局装置1に接続するMS2の数が多いと、干渉を与える可能性が高くなる。
この場合、同期処理部5bは、フェムトBS1b11(アクセスモード「オープン」)を同期元基地局装置1として選択した場合よりも、同期処理の周期を長く、フェムトBS1b10(アクセスモード「クローズド」)を同期元基地局装置1として選択した場合よりも、同期処理の周期を短く調整する。
よって、同期処理部5bは、マクロBS1aを同期元基地局装置1とする場合、フェムトBS1bを同期元基地局装置1とする場合よりも、同期処理の周期を短く調整する。
この場合、同期処理部5bは、同期元基地局装置1の割り当て形式がディストリビューテッドである場合、ローカライズドである場合よりも同期処理の頻度が低くなるように同期処理の周期を長く調整することが好ましい。
割り当て形式がローカライズドである場合、MS2のリソースは、上述のように、特定の周波数帯域幅の範囲に割り当てられる。よって、自局装置1b1と他の基地局装置1との間で、干渉を抑制するために、周波数方向で重複しないようにリソースを割り当てることが可能である。
一方、ディストリビューテッドである場合、各MS2のリソースを、所定の周波数帯域幅全域に均等に分配して送信するので、自局装置1b1と他の基地局装置1との間で、重複しないようにリソースを割り当てることが困難である。よって、同期処理の周期を長く調整することで、無駄に同期処理を行うのを防止できる。
つまり、上記割り当て形式を示す情報は、他の基地局装置1との間の干渉が回避可能であるか否かを示す情報を構成している。
この場合、基地局間同期の精度を高める必要性が低く、同期処理部5bは、マクロBS1b1を同期元基地局装置1として選択した場合と比べて、同期処理の周期を長く調整する。この結果、無駄に同期処理を行うのを防止できる。
図26は、本発明の第五の実施形態に係るフェムトBS1bの内部構成の一部を示す部分ブロック図である。なお、マクロBS1aの構成も、フェムトBS1bの場合とほぼ同様である。
次いで、パスロス値取得部47は、他の基地局装置1の下り信号の受信レベルを、下り信号受信部12が受信する他の基地局装置1の下り信号、又は、MS2からの測定結果通知によって取得する。
パスロス値取得部47は、上記のようにして取得した、他の基地局装置1の下り信号の送信電力、及び、受信レベルからパスロス値を取得する。
例えば、パスロス値取得部47が他の基地局装置1のパスロス値を取得した結果、図13に示すマクロBS1a1のパスロス値が5dBm、マクロBS1a2のパスロス値が10dBm、フェムトBS1b2のパスロス値が72dBmであったとする。パスロス値取得部47は、これらパスロス値を示す情報を隣接セル情報生成部42に出力する。
隣接セル情報生成部42は、上記パスロス値を、セル情報IDと関連付けることで、図27に示す隣接セル情報を生成する。
より具体的には、同期処理部5bは、同期元基地局装置1のパスロス値の値が相対的に小さければ、同期処理の周期が小さくなるように調整する。
また、上述したように、互いに隣接する二つの基地局装置1は、互いの位置が近ければ近いほど、一方の基地局装置1の下り信号が、他方の基地局装置1に接続するMS2に対して干渉を生じさせる可能性が高くなる。
この場合、基地局間同期の精度を高める必要性が低く、同期処理部5bは、マクロBS1b1を同期元基地局装置1として選択した場合と比べて、同期処理の周期を長く調整する。この結果、無駄に同期処理を行うのを防止できる。
図28は、本発明の第六の実施形態に係るフェムトBS1bの内部構成の一部を示す部分ブロック図である。なお、マクロBS1aの構成も、フェムトBS1bの場合とほぼ同様である。
端末数推定部46は、このように第一及び第二PRACHを設定することで、自局装置1b1に接続しようとするMS2が送信するRAPを受信しつつ、他の基地局装置1に接続しようとするMS2が送信するRAPを確実に傍受することが可能となる。
端末数推定部46は、上記装置数Nから、自局装置1b1の近傍に位置する、他の基地局装置1に接続したMS2の数を推定する。
このように、本実施形態によれば、基地局間同期の精度を必要に応じて調整することができ、同期元基地局装置1との関係で干渉が生じ得る可能性のある場合にも、好適に干渉を回避することができるように同期処理を行うことができる。
なお、上記第二の実施形態、第三の実施形態、及び第五の実施形態では、干渉を生じさせる可能性が高いと判断できる程度に、自局装置1b1と同期元基地局装置1との間の位置が近ければ、同期処理の周期を短く調整する場合を例示した。
これに対して、自局装置1b1と他の基地局装置1との間の位置が近く、当該他の基地局装置1からの下り信号の受信精度が高ければ、一回の同期処理で精度よく基地局間同期をとることができる場合がある。このため、他の基地局装置1からの下り信号の受信精度が、高精度の基地局間同期が可能な程度に高い場合、同期処理の周期を短くせずとも、同期の精度を高く維持することができる。この結果、好適に干渉を回避することができるように同期処理を行うことができる。
この場合、例えば、同期元である他の基地局装置1からの下り信号の受信精度が、高精度の基地局間同期が可能な程度に高い場合、それよりも受信精度が低い場合よりも、同期処理の周期を相対的に長く調整することができる。
同期処理部5bは、他の基地局装置1からの下り信号の受信精度として、受信レベル、又は、SINR(Signal-to-Interference and Noise power Ratio)を用いることができる。
よって、同期処理部5bは、その値に応じて同期元基地局装置1からの下り信号の受信精度に影響を与える情報として、自局装置1b1と同期元基地局装置1との間の位置関係を示す情報、又は、自局装置1b1と同期元基地局装置1との位置関係によってその値が影響を受ける情報を用いることができる。
以上のように、このフェムトBS1b1によれば、同期元基地局装置1の送信信号の受信精度に影響を与える情報である、自局装置1b1と同期元基地局装置1との間の位置関係を示す情報等に基づいて同期処理を行うタイミングを調整することで、好適に干渉を回避することができるように同期処理を行うことができる。
従って、同期元基地局装置1の送信信号の受信精度が高いと判断できる両基地局装置の位置関係から、互いにより遠ざかった位置となると、高精度の基地局間同期が可能な程度に同期元基地局装置1の送信信号の受信精度が得られなくなるが、互いの基地局装置間で干渉が生じる可能性が高いと判断される位置関係となる。この場合、フェムトBS1b1は、干渉を効果的に抑制するために、同期処理の周期を短く調整することで基地局間同期の精度を高める。
さらに、同期元基地局装置1の送信信号が検出されたときの検出結果に関する情報は、同期元基地局装置1の送信信号が最後に検出されたときの時刻、又は、前記時刻から現在の時刻までの経過時間であってもよい。
また、同期処理部5bは、自局装置1b1と同期元基地局装置1との関係で干渉を生じ得るか否かを示す情報として、同期元基地局装置1の搬送波周波数を示す情報、同期元基地局装置1がマクロ基地局かフェムト基地局かを識別可能な情報、同期元基地局装置1の下り信号の送信電力を示す情報、同期元基地局装置1に接続するMS2に対する当該同期元基地局装置1のアクセスモードを示す情報、又は、自局装置1b1の近傍に位置しかつ同期元基地局装置1に接続するMS2の推定数を用いることができる。
従って、自局装置1b1と同期元基地局装置1との関係で干渉を生じ得るか否かを示す前記情報は、自局装置1b1と同期元基地局装置1との間の位置関係を示す情報、又は、自局装置1b1と同期元基地局装置1との位置関係によってその値が影響を受ける情報であることが好ましい。
一方、上記情報から、自局装置1b1と同期元基地局装置1との位置が相対的に遠く、干渉が生じる可能性が低いと判断できる場合には、干渉が生じる可能性が高いと判断できる場合よりも同期処理の頻度が低くなるように同期処理のタイミングを調整することができる。この結果、無駄に同期処理を行うのを防止できる。
以上のように、このフェムトBS1b1によれば、自局装置1b1と同期元基地局装置1との間の位置関係を示す情報等に基づいて同期処理を行うタイミングを調整することで、基地局間同期における同期元である他の基地局装置1との関係で干渉が生じ得る可能性のある場合にも、好適に干渉を回避することができるように同期処理を行うことができる。
また、同期処理部5bは、ハンドオーバ試行数によってその値が影響を受ける情報として、ハンドオーバ試行数に基づいて求められるハンドオーバ成功数、及びハンドオーバ成功率を用いることができる。
より具体的に、前記干渉が回避可能であるか否かを示す情報は、同期元基地局装置1が当該同期元基地局装置1に接続するMS2にリソース割り当てを行う際のリソースブロックの割り当て形式を示す情報、又は、自局装置1b1と同期元基地局装置1との間で、例えば、X2インターフェースを介した基地局間通信が可能であるか否かを示す情報であることが好ましい。
同期処理部5bは、自局装置1b1と同期元基地局装置1との位置関係によってその値が影響を受ける情報として、前記同期元基地局装置1の送信信号が検出されたときの検出結果に関する情報を用いることができ、より詳細には、所定の期間内で検出された同期元基地局装置1の検出回数、前記検出回数と、検出を実行した回数との割合である検出率、同期元基地局装置1の送信信号が最後に検出されたときの時刻、又は、前記時刻から現在の時刻までの経過時間を用いることができる。
Claims (27)
- 他の基地局装置からの送信信号を受信する受信部と、
前記受信部による前記送信信号を取得し当該送信信号についての処理を行う処理部と、
自己及び/又は前記他の基地局装置に接続する端末装置との間の通信状況を検知する検知部と、を備え、
前記処理部は、前記検知部の検知結果に基づいて、前記送信信号を取得するタイミングを調整することを特徴とする基地局装置。 - 前記処理部は、前記処理が周期的に行われるようにタイミングを調整するとともに、前記検知部の検知結果に基づいて、前記処理の周期を調整する請求項1に記載の基地局装置。
- 前記検知部は、受信した前記他の基地局装置の送信信号の受信電力を測定し、前記受信電力に基づいて前記他の基地局装置に接続する端末装置との間の通信状況を検知する請求項1又は2に記載の基地局装置。
- 前記検知部は、前記他の基地局装置の下り信号におけるリソース割り当て最小単位ごとに、前記他の基地局装置の下り信号の受信電力を測定する請求項3に記載の基地局装置。
- 前記検知部が検出する通信状況は、自己及び/又は前記他の基地局装置に接続する端末装置の数である請求項1~4のいずれか一項に記載の基地局装置。
- 前記処理部は、前記送信信号に基づいて前記他の基地局装置との間で基地局間同期をとるための同期処理を行う同期処理部を含む請求項1~5のいずれか一項に記載の基地局装置。
- 前記同期処理部は、自己に接続する端末装置の数が少ないほど前記同期処理の周期が長くなるように調整する請求項6に記載の基地局装置。
- 前記同期処理部は、前記他の基地局装置に接続する端末装置の数が少ないほど前記同期処理の周期が長くなるように調整する請求項6又は7に記載の基地局装置。
- 前記処理部は、前記送信信号を測定するメジャメント処理を行うメジャメント処理部を含む請求項1~8のいずれか一項に記載の基地局装置。
- 前記検知部は、前記メジャメント処理部による測定結果を用いて通信状況の検知を行う請求項9に記載の基地局装置。
- 他の基地局装置からの送信信号を受信する受信部と、
前記受信部による前記送信信号を取得し当該送信信号を用いて基地局間同期を行う同期処理を行う処理部と、を備え、
前記処理部は、自己と前記他の基地局装置との関係で干渉を生じ得るか否かを示す情報に基づいて、同期処理を行うタイミングを調整することを特徴とする基地局装置。 - 自己と前記他の基地局装置との関係で干渉を生じ得るか否かを示す前記情報は、自己及び/又は前記他の基地局装置に接続する端末装置の数である請求項11に記載の基地局装置。
- 自己と前記他の基地局装置との関係で干渉を生じ得るか否かを示す前記情報は、自己と前記他の基地局装置との間の位置関係を示す情報、又は、自己と前記他の基地局装置との位置関係によってその値が影響を受ける情報である請求項11に記載の基地局装置。
- 自己と前記他の基地局装置との位置関係によってその値が影響を受ける前記情報は、前記他の基地局装置の送信信号が検出されたときの検出結果に関する情報、前記他の基地局装置の送信信号の受信レベル、又は、前記他の基地局装置と自己との間のパスロス値である請求項13に記載の基地局装置。
- 前記他の基地局装置の送信信号が検出されたときの検出結果に関する情報は、所定の期間内で検出された前記他の基地局装置の検出回数、又は、前記検出回数と、検出を実行した回数との割合である検出率である請求項14に記載の基地局装置。
- 前記他の基地局装置の送信信号が検出されたときの検出結果に関する情報は、前記他の基地局装置の送信信号が最後に検出されたときの時刻、又は、前記時刻から現在の時刻までの経過時間である請求項14に記載の基地局装置。
- 自己と前記他の基地局装置との位置関係によってその値が影響を受ける前記情報は、自己と当該他の基地局装置との間で行われる自己又は前記他の基地局装置に接続する端末装置のハンドオーバの試行数に関する情報、又は、前記ハンドオーバの試行数によってその値が影響を受ける情報である請求項13に記載の基地局装置。
- 自己と前記他の基地局装置との関係で干渉を生じ得るか否かを示す前記情報は、前記他の基地局装置の搬送波周波数を示す情報、前記他の基地局装置がマクロ基地局かフェムト基地局かを識別可能な情報、前記送信信号の送信電力を示す情報、前記他の基地局装置に接続する端末装置に対する当該他の基地局装置のアクセスモードを示す情報、又は、自己の近傍に位置しかつ前記他の基地局装置に接続する端末装置の推定数である請求項11に記載の基地局装置。
- 前記処理部は、自己と他の基地局装置との関係で干渉を生じ得るか否かを示す前記情報に加え、前記干渉が回避可能であるか否かを示す情報に基づいて、同期処理を行うタイミングを調整する請求項11に記載の基地局装置。
- 前記干渉が回避可能であるか否かを示す前記情報は、前記他の基地局装置が当該他の基地局装置に接続する端末装置にリソース割り当てを行う際のリソースブロックの割り当て形式を示す情報、又は、自己と前記他の基地局装置との間で基地局間通信が可能であるか否かを示す情報である請求項19に記載の基地局装置。
- 他の基地局装置からの送信信号を受信する受信部と、
前記受信部による前記送信信号を取得し当該送信信号を用いて基地局間同期を行う同期処理を行う処理部と、を備え、
前記処理部は、前記他の基地局装置からの送信信号の受信精度を示す情報、又は、その値に応じて前記他の基地局装置からの送信信号の受信精度に影響を与える情報に基づいて、同期処理を行うタイミングを調整することを特徴とする基地局装置。 - 前記他の基地局装置からの送信信号の受信精度を示す情報は、前記送信信号を受信したときの受信レベル、又は、SINRである請求項21に記載の基地局装置。
- その値に応じて前記他の基地局装置からの送信信号の受信精度に影響を与える前記情報は、自己と前記他の基地局装置との間の位置関係を示す情報、又は、自己と前記他の基地局装置との位置関係によってその値が影響を受ける情報である請求項21に記載の基地局装置。
- 自己と前記他の基地局装置との位置関係によってその値が影響を受ける前記情報は、前記他の基地局装置の送信信号が検出されたときの検出結果に関する情報である請求項23に記載の基地局装置。
- 前記他の基地局装置の送信信号が検出されたときの検出結果に関する情報は、所定の期間内で検出された前記他の基地局装置の検出回数、又は、前記検出回数と、検出を実行した回数との割合である検出率である請求項24に記載の基地局装置。
- 前記他の基地局装置の送信信号が検出されたときの検出結果に関する情報は、前記他の基地局装置の送信信号が最後に検出されたときの時刻、又は、前記時刻から現在の時刻までの経過時間である請求項24に記載の基地局装置。
- 自己と前記他の基地局装置との位置関係によってその値が影響を受ける前記情報は、自己と当該他の基地局装置との間で行われる自己又は前記他の基地局装置に接続する端末装置のハンドオーバの試行数に関する情報、又は、前記ハンドオーバの試行数によってその値が影響を受ける情報である請求項23に記載の基地局装置。
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JPWO2011043411A1 (ja) | 2013-03-04 |
CN102550099A (zh) | 2012-07-04 |
US20120184312A1 (en) | 2012-07-19 |
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