WO2010041992A1

WO2010041992A1 - User terminal assisted out-of-synchronization detection

Info

Publication number: WO2010041992A1
Application number: PCT/SE2008/051132
Authority: WO
Inventors: Lei Xiao; Huaisong Zhu; Qingyu Miao
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2008-10-07
Filing date: 2008-10-07
Publication date: 2010-04-15
Also published as: CN102177666A; CN102177666B

Abstract

A control module, a computer readable medium and a method for determining when a first base station (BS1) in a telecommunication network (20) is out of synch with the network (20), the network (20) including at least a second base station (BS2) and a user terminal (26) configured to receive signals from the first and second base stations (BS1, BS2). The method includes receiving in a control module (28) of the network (20) a measuring report from the user terminal (26), where the measuring report includes a first time of arrival (Ta1) of a first signal from the first base station (BS1) to the user terminal (26) and a second time of arrival (Ta2) of a second signal from the second base station (BS2) to the user terminal (26); receiving a maximum of a travel time difference (max(T1 - T2)) between (i) a first travel time (T 1) of the first signal from the first base station (BS 1) to the user terminal (26), and (ii) a second travel time (T2) of the second signal from the second base station (BS2) to the user terminal (26); determining a minimum of a difference starting time (min(T0 - T0')), which corresponds to a time offset between a starting time (T0) of the first signal and a starting time (T0') of the second signal, as a difference between (i) a difference between the first time of arrival (Ta1) and the second time of arrival (Ta2), and (ii) the maximum travel time difference (max(T1 - T2)); comparing the determined minimum difference starting time (min(T0 - T0')) with a predetermined threshold; and identifying the pair of the first base station (BS1) and the second base station (BS2) as including one base station that lost the synch with the network, when the determined minimum difference starting time (min(T0-T0')) is larger than the predetermined threshold in the comparing step.

Description

USER TERMINAL ASSISTED OUT-OF-SYNCHRONIZATION DETECTION

TECHNICAL FIELD

[0001] The present invention generally relates to radio communication systems, devices, software and methods and, more particularly, to mechanisms and techniques for detecting base stations and/or cells that are out-of-synchronism with the telecommunication network.

BACKGROUND

[0002] During the past years, the interest in radio access technologies for providing services for voice, video and data has increased. There are various telecom technologies used in cellular communications. The most widespread radio access technology for mobile communication is digital cellular. Increased interest is shown in 3G (third generation) systems.

[0003] One such third generation system is Time Division-Synchronous Code

Division Multiple Access (TD-SCDMA), a 3G telecommunications standard that is being pursued in China. TD-SCDMA is based on spread spectrum technology. The standard has been adopted by 3GPP (3^rd Generation Partnership Project) since ReI- 4, known as "UTRA TDD 1.28Mcps Option," the entire content of which is included here by reference.

[0004] TD-SCDMA uses Time-Division Duplex (TDD), in contrast to the

Frequency-Division Duplex (FDD) scheme used by the Wideband Code Division Multiple Access (W-CDMA). By dynamically adjusting the number of timeslots used for downlink and uplink, the system can more easily accommodate asymmetric traffic with different data rate requirements on downlink and uplink than FDD schemes. Since it does not require paired spectrum for downlink and uplink, spectrum allocation flexibility is also increased. Also, using the same carrier frequency for uplink and downlink means that the channel condition is the same on both directions, and the base station can deduce the downlink channel information from uplink channel estimates, which is helpful to the application of beamforming techniques. [0005] TD-SCDMA also uses Time Division Multiple Access (TDMA) in addition to the CDMA used in WCDMA. This reduces the number of users in each timeslot, which reduces the implementation complexity of multiuser detection and beamforming schemes, but the non-continuous transmission also may reduce coverage (because of the higher peak power needed), and mobility (because of lower power control frequency).

[0006] The "S" in TD-SCDMA stands for "synchronous," which means that uplink signals are synchronized at the base station receiver, achieved by continuous timing adjustments. This reduces the interference between users of the same timeslot using different codes by improving the orthogonality between the codes, therefore increasing system capacity, at the cost of some hardware complexity in achieving uplink synchronization.

[0007] TD-SCDMA is a time-division system in which each sub-radio frame 10

(see Figure 1 ) may have two Uplink-Downlink switching points SP1 and SP2. In other words, as shown in Figure 1 , the sub-radio frame 10 may include a downlink traffic broadcasting time period DT followed by an uplink traffic time period UT followed by another DT. The first DT in Figure 1 may be configured to carry broadcasting control traffic, for example, the physical channel that carries the broadcast channel (PCCPCH). Because both the downlink and uplink traffic is taking place in the same sub-frame 10, the switching points SP1 and SP2 are used to delimitate the uplink traffic from the downlink traffic. When the downlink and uplink traffic of the neighboring cells is considered, then the sub-frames of the cells have to be synchronized (to be in synch) in time to avoid adjacent cell's downlink signal affect the uplink time period signal of the current cell illustrated in Figure 1. Thus, a mechanism to maintain the synchronization of the entire radio network is needed to avoid these problems.

[0008] Currently, this problem is solved in the following way. If one base station of a cell loses the synchronization with the other base stations of the network, this base station will exhibit downlink and uplink traffic that is not synchronized with the other cells, i.e., the traffic of the base station that lost synchronization may be broadcasted at the same time with neighbor cells that are in synch. Thus, this simultaneous transmission traffic on two or more adjacent base stations may generate large interference at the neighboring cells of the base station that lost the synch.

[0009] Due to this interference, these neighboring cells appear to be out of synch. The network operator that is controlling the base stations has no tool to determine which specific base station lost the synch and for this reason, all the neighboring cells that experience the interference produced by only one base station are taken out-of-service. Thus, the stability and reliability of the entire transmission network becomes less than satisfactory.

[0010] Accordingly, the network operator may set high requirements to be maintained for the base station's synchronization to not affect the capacity of the entire telecommunication network. Taking the Global Positioning System (GPS) synchronization as an example, if one base station loses the GPS signal for 24 hours, a corresponding time drifting should be kept within 1 μs, in order to maintain the desired reliability of the network. As this time drifting may be difficult to achieve after 24 hours without the GPS signal, the operator may configure the base station with the lost GPS signal to automatically shut down after 24 hours. In a real situation, the base station that lost the GSP signal may maintain the desired synchronization, and thus, the shutting down of this base station is unnecessary. However, the operator of the network does not have the capability to determine whether the base station with the lost GPS is still maintaining the synchronization and thus, this base station has to be shut down, which is undesirable in this case.

[0011] In this regard, it is noted that at the time of filing this patent application, the operators of the TD-SCDMA network, which is deployed in China, have no mechanism to actually measure and use the synchronization of the base stations with the rest of the network in real time. It is also noted that the TD-SCDMA configuration is different from other 3G cellular technologies, and thus, it is not obvious, based on the other existing 3G technologies, to modify an existing 3G technology to arrive at the TD-SCDMA configurations. [0012] To summarize the problems with the existing TD-SCDMA configuration, it is noted that the radio network does not have the capacity to continuously monitor the adjacent cells' timing difference capacity, especially when all these cells are in service. Thus, other problems may be generated by imposing on the base stations that lose their synchronism the strict hold-over time when their synchronization source, for example, the GPS signal is lost. In addition, this problem is exacerbated by the fact that even if, after the hold-over time, the timing differences between adjacent base stations are tolerable, the operating and maintenance (OAM) system is configured to shut down the dangerous base station to make the network "safe." Thus, many tolerable base stations may be forced to shut down although not necessary.

[0013] Further, when some hardware/software errors occur in a specific base station causing the base station to lose its synchronism with the network, and the operator or the base station itself fails to find out the timing error, the entire radio network may be affected and the operator may have no capability to fix this problem. [0014] All these problems may be present in the current TD-SCDMA radio network configuration. Accordingly, it would be desirable to provide devices, systems and methods for TD-SCDMA communication networks that avoid the afore- described problems and drawbacks.

SUMMARY

[0015] According to one exemplary embodiment, there is a method for determining when a first base station in a telecommunication network is out of synch with the network, the network including at least a second base station and a user terminal configured to receive signals from the first and second base stations. The method includes receiving in a control module of the network a measuring report from the user terminal, where the measuring report includes a first time of arrival of a first signal from the first base station to the user terminal and a second time of arrival of a second signal from the second base station to the user terminal; receiving a maximum of a travel time difference between (i) a first travel time of the first signal from the first base station to the user terminal, and (ii) a second travel time of the second signal from the second base station to the user terminal; determining a minimum of a difference starting time, which corresponds to a time offset between a starting time of the first signal and a starting time of the second signal, as a difference between (i) a difference between the first time of arrival and the second time of arrival, and (ii) the maximum travel time difference; comparing the determined minimum difference starting time with a predetermined threshold; and identifying the pair of the first base station and the second base station as including one base station that lost the synch, when the determined minimum difference starting time is larger than the predetermined threshold in the comparing step. [0016] According to another exemplary embodiment, there is a control module in a telecommunication network for determining when a first base station in the telecommunication network is out of synch with the network, the network including at least a second base station and a user terminal configured to receive signals from the first and second base stations. The control module includes an input interface configured to receive a measuring report from the user terminal, where the measuring report includes a first time of arrival of a first signal from the first base station to the user terminal and a second time of arrival of a second signal from the second base station to the user terminal; and a processor connected to the input interface and configured to receive a maximum of a travel time difference between (i) a first travel time of the first signal from the first base station to the user terminal, and (ii) a second travel time of the second signal from the second base station to the user terminal, determine a minimum of a difference starting time, which corresponds to a time offset between a starting time of the first signal and a starting time of the second signal, as a difference between (i) a difference between the first time of arrival and the second time of arrival, and (ii) the maximum travel time difference, compare the determined minimum difference starting time with a predetermined threshold, and identify the pair of the first base station and the second base station as including one base station that lost the synch, when the determined minimum difference starting time is larger than the predetermined threshold. [0017] According to still another exemplary embodiment, there is a computer readable medium including computer executable instructions, wherein the instructions, when executed by a processor in a control module of a telecommunication network, cause the processor to determine when a first base station in the telecommunication network is out of synch with the network, the network including at least a second base station and a user terminal configured to receive signals from the first and second base stations. The instructions include receiving in a control module of the network a measuring report from the user terminal, where the measuring report includes a first time of arrival of a first signal from the first base station to the user terminal and a second time of arrival of a second signal from the second base station to the user terminal; receiving a maximum of a travel time difference between (i) a first travel time of the first signal from the first base station to the user terminal, and (ii) a second travel time of the second signal from the second base station to the user terminal; determining a minimum of a difference starting time, which corresponds to a time offset between a starting time of the first signal and a starting time of the second signal, as a difference between (i) a difference between the first time of arrival and the second time of arrival, and (ii) the maximum travel time difference; comparing the determined minimum difference starting time with a predetermined threshold; and identifying the pair of the first base station and the second base station as including one base station that lost the synch, when the determined minimum difference starting time is larger than the predetermined threshold in the comparing step.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate one or more embodiments and, together with the description, explain these embodiments. In the drawings: [0019] Figure 1 is a schematic diagram of a sub-frame in a TD-SCDMA telecommunication network;

[0020] Figure 2 is a schematic diagram of a TD-SCDMA telecommunication network that includes at least two base stations and a user terminal; [0021] Figure 3 is a schematic diagram of a TD-SCDMA telecommunication network that includes at least two base stations and a user terminal according to an exemplary embodiment;

[0022] Figure 4 is flow diagram that illustrates steps performed by a control module to maintain the network in sync according to an exemplary embodiment;

[0023] Figure 5 is a schematic diagram of a control module or user terminal; and

[0024] Figure 6 is a schematic diagram of a part of the TD-SCDMA telecommunication network.

List of abbreviations

TD-SCDMA - Time Division-Synchronous Code Division Multiple Access

3GPP - 3^rd Generation Partnership Project

TDD - Time Division Duplex

FDD - Frequency Division Duplex

W-CDMA - Wideband Code Division Multiple Access

TDMA - Time Division Multiple Access

SP - switching point

DT - downlink traffic

UT - uplink traffic

PCCPCH - Primary Common Control Physical Channel

GPS - General Positioning System

OAM - Operating and Maintenance UE - User Terminal

BS - Base Station

CM - Control Module

MM - Management Module

DETAILED DESCRIPTION

[0025] The following description of the exemplary embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. The following embodiments are discussed, for simplicity, with regard to the terminology and structure of TD-SCDMA system described above. However, the embodiments to be discussed next are not limited to this system but may be applied to other existing telecommunications systems.

[0026] Reference throughout the specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the present invention. Thus, the appearance of the phrases "in one embodiment" or "in an embodiment" in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments. [0027] As shown in Figure 2, according to an exemplary embodiment, a general telecommunication system 20 may include plural cells C1 to C2 22, each cell having one or more base stations BS1 to BS2 24. In this exemplary embodiment, each cell is shown having only one base station 24. However, a cell may have more than one base station. A user terminal UE 26 may be served by base station BS1 of cell C1 but the user terminal may still be able to receive a signal from BS2, which is in the neighboring cell C2.

[0028] Thus, the user terminal UE may be capable of receiving a first transmission signal TxBSI from the first base station BS1 and a second transmission signal TxBS2 from the second base station BS2. The signals are sent at corresponding times TO and TO'. These times are identical for ideal base stations. However, the base stations are sending the signals with a small time difference, i.e., TO - TO'. The expected transmission times of base stations BS1 and BS2 may be known in advance by the user terminal UE. If the user terminal is able to determine/calculate a difference of the actual transmission times TO and TO' (the actual transmission times of the base stations may be different from the expected transmission times of the base stations), then, based on these actual times, the synchronism of the two base stations BS1 and BS2 may be calculated. For example, the operator of the network that includes both cells C1 and C2 knows in advance the expected transmission times and may compare these expected transmission times to the actually transmission times of the base stations. Based in part on this observation, the following exemplary embodiments disclose how the synchronism of the base stations is to be determined.

[0029] Next, the handover measurements in the TD-SCDMA system are briefly discussed. The handover measurements are related to the movement of the user terminal UE from cell C1 to cell C2 and how the cell C1 handovers the control of the transmission to the user terminal UE to cell C2. To support handover, especially a baton handover, which is a characteristic feature of TD-SCDMA (baton handover, similar to the procedure of handing over a baton in a relay race, is based mainly on mobile positioning capability provided by TD-SCDMA base stations), the user terminal UE may continuously detect a signal from the serving cell C1 and from the neighboring cell C2 (the PCCPCH channel may be monitored for receiving these signals in downlink traffic as shown for example in Figure 1 ). Based on these received signals, the user terminal UE may measure a timing difference of the received PCCPCH channels.

[0030] The 3GPP standard determines that the user terminal UE should support several kinds of measurements in the network, for example, a timing advance (the time taken by a signal to travel from the user terminal to the base station), etc., and all these measurements may be based on the timing difference of received PCCPCH channels.

[0031] The measurement accuracy requirement (predetermined threshold) for the timing difference of adjacent cells measurement is desirable to be around +/- 0.125chip (+/- 0.098μs). The radio network algorithm of each network may be configured to require these measurements in a periodic report from the user terminal UE, or only when a certain criterion is met. Thus, according to an exemplary embodiment, the user terminal measurements that are used by the network for handover may also be used to detect and calculate the timing difference between adjacent base stations as discussed next. [0032] As shown in the exemplary embodiment illustrated in Figure 3, a maximum travel time difference (transmission Tx delay) of two adjacent cells C1 and C2 may be determined in the TD-SCDMA system, during the network planning, as being equal to T1 - T2, in which T1 is the transmission delay corresponding to the transmission signal TxBSI travelling from the base station BS1 24 to the user terminal UE 26 and T2 is the transmission delay corresponding to the transmission signal TxBS2 travelling from the base station BS2 24 to the user terminal UE 26. The maximum travel time difference may be estimated, for example, by considering a signal transmitted from BS1 to BS2. More specifically, the maximum T1-T2 may be calculated as a maximum delay for plural user terminals which are located in a first cell and are ready to handover to a second cell or vice verse. In other words, the positions of the plural user terminals in the handover area are taken into consideration when calculating the maximum of T1 - T2. In this regard, there are various methods for determining the maximum T1 - T2, as disclosed for example in PCT/SE2007/050664, entitled XXX, the entire disclosure of which is incorporated here by reference. [Roger, could you please provide the title and authors for this patent application?] The maximum delay travel time difference may depend on the air environment between the base stations, for example, rural or urban medium, by the cell range, etc.

[0033] With further regard to Figure 3, a time difference measured by the user terminal UE 26 relative to the arrival of the transmission signals TxBSI and TxBS2 at the user terminal UE is equal to Ta1-Ta2, where Ta1 is the time of arrival at the user terminal UE of the transmission signal from base station BS1 and Ta2 is the time of arrival of the corresponding transmission signal from base station BS2. [0034] Thus,

Ta1 - Ta2 = TO + T1 - (TO' + 12) = (TO-TO') + (T1 - 12), (1 ) where the measured time Ta1 - Ta2 or/and each of measured Ta1 and Ta2 may be sent to a network control in a measuring report from the user terminal UE. [0035] Because the maximum travel time difference max(T1 - 12) of base station BS1 and base station BS2 may be evaluated based on the design of the network, and because the user terminal UE is capable of measuring the difference Ta1 - Ta2, a minimum of a difference starting time min(T0 - TO') (the difference in starting times for sending the PCCPCH signals from the two base stations) may be determined as discussed next. It is noted that the following relation holds: TO - TO' = Ta1 - Ta2 (received PCCPCH timing difference) - (T1 - 12) > (Ta 1 - Ta2) max(T1 - 12).

Thus, min(T0 - TO') = (Ta1 - Ta2) - max(T1 - 12).

[0036] According to an exemplary embodiment, based on the determined minimum TO - TO' delay, a timing error at one or more base stations may be cataloged as follows:

[0037] Case 1 : a specific base station error is present, for example the GPS hardware module does not work, failing to provide an accurate time to the base station. These errors are detected by this base station;

[0038] Case 2: a specific base station error is present, and the affected base station fails to find itself the error; and [0039] Case 3: the entire synchronization source is faulty, a large area of the service is impacted, the source cannot be detected.

[0040] For Case 1 , the operator needs to know when to shut down the base station to avoid a large timing difference in the system, which is undesirable. Based on equation (1 ) discussed above, the minimum timing difference TO - TO' of pairs of base stations is continuously (for example every time the user terminal experiences a handover) calculated in a preset control module CM 28 of the network, based on the measurements received from the user terminal UE. The control module CM may also receive similar measurements from other user terminals in the network so that all active base stations may be monitored. As soon as the control module CM determines that the minimum timing difference TO - TO' of any pair of base stations is larger than a certain predetermined threshold (which may be operator dependent), and based also on information received from the affected base station, the control module CM may inform the management module (MM) 30 of the network operator about the loss of synch, and the management module MM or the control module CM then forces the affected base station out-of-service to prevent the loss of synch in the other base stations.

[0041] For Case 2, because the base station that is experiencing the time delay is not aware of this fact, the network operator has to determine which base station is having difficulties, without relying on information from the affected base station as in Case 1. In this regard, in Case 1 , the affected base station was able to communicate with the network operator and inform the management module about its identity and the experienced error. As in the previous case, the network operator (that includes the control module 28 and the management module 30) monitors the minimum timing difference TO - TO' of pairs of base stations. To reduce the time required by the monitoring step, the network operator may monitor only adjacent pairs of base stations, where the adjacent base stations may be defined based on their corresponding cells being geographically adjacent.

[0042] When the network operator determines that a pair of base stations has a minimum timing difference TO - TO' larger than the predetermined threshold, and no other data is received from the respective base stations, the network operator has to identify which one of the two base stations is losing the synch. Because any base station in the network is likely to have more than one adjacent base station, the loss of synch should be manifest in other pairs of base stations that include the affected base station. Thus, the network operator may monitor base stations that are adjacent to at least one base station of the pair of base stations that appear to lose synch. After identifying another pair of base stations that are exhibiting signs of losing the synch, the network operator verifies if a common base station exists among the pairs of base stations that exhibit a loss of synch. [0043] According to an exemplary embodiment, the network operator may verify that the common base station has a same phase for each of the timing difference with the neighboring base stations, for positively identifying the common base station as the one that is losing the synch. Then, the network operator verifies the size of the timing difference, i.e., whether the timing difference is above a certain predetermined threshold, and based on this info, the network operator decides whether to shut down the affected base station. The implementation of an algorithm in the network for deciding the location of a base station that is affected by an error may be operator dependent, as various judgment rules may be used to determine which base station is experiencing the synch loss. For example, in one exemplary embodiment, the network operator may decide that a base station is affected by a timing problem if at least two neighboring base stations, when paired up with the suspected base station, are affected by this problem.

[0044] Case 3 is different from the previous cases because, in this case, each base station may have its own timing. Thus, according to an exemplary embodiment, a reference timing may be selected based on one or more of the existing base stations that lost their synchronization source. Once the reference timing is selected, the network operator may decide to follow Case 2 for deciding which other base stations are to be shut down. For example, the network operator may designate certain cells (which are considered to be important) as key cells, and these cells may have a high priority to be kept in service even when the entire network lost the synchronization source. The timing of the important cells is considered to be the reference timing and the remaining cells are verified, based on the method discussed above, whether are in synch with the important cells. [0045] The steps to be followed for operating the network as discussed above are exemplified, according to an exemplary embodiment, in Figure 4. In Figure 4, a method for determining when a first base station in a telecommunication network is out of synch with the network is illustrated. The network may include at least a second base station and a user terminal configured to receive signals from the first and second base stations. As shown in Figure 4, the method includes a step 400 of receiving in a control module of the network a measuring report from the user terminal, where the measuring report includes a first time of arrival of a first signal from the first base station to the user terminal and a second time of arrival of a second signal from the second base station to the user terminal, a step 402 of receiving a maximum of a travel time difference between (i) a first travel time of the first signal from the first base station to the user terminal, and (ii) a second travel time of the second signal from the second base station to the user terminal, a step 404 of determining a minimum of a difference starting time, which corresponds to a time offset between a starting time of the first signal and a starting time of the second signal, as a difference between (i) a difference between the first time of arrival and the second time of arrival, and (ii) the maximum travel time difference, a step 406 of comparing the determined minimum difference starting time with a predetermined threshold, and a step 408 of identifying the pair of the first base station and the second base station as including one base station that lost the synch, when the determined minimum difference starting time is larger than the predetermined threshold in the comparing step.

[0046] Some advantages to be achieved by one or more embodiments of this disclosure are discussed next. The network operator is now capable to locate a base station that generates a timing error by using measurements from the user terminal. Thus, according to one embodiment, no new requirements are demanded from the base station and/or the user terminal UE, and also no new requirement is demanded from the radio interface. Thus, the implementation of one or more embodiments will have no impact onto the current standard and also no impact onto the current base station and user terminals.

[0047] The network may have the capability to continuously detect (via the user terminal) the timing difference of adjacent cells for locating what kind of errors are present to specific base stations, without the need to modify the network to provide these measurements. In addition, the network may have the capability to identify a failed base station (from synch point of view) even if the base station is not aware of this problem. Further, the timing difference detection does not interrupt the normal work of the base station. Thus, the base station may be used when the radio network is in service. Furthermore, if a specific base station lost its synchronization source, the network operator may force this station out of service only when the timing difference drift is intolerable to the radio network, not just simply based on a certain hold-over time as discussed in the Background section. [0048] For purposes of illustration and not of limitation, an example of a representative user terminal system or control module capable of carrying out operations in accordance with the exemplary embodiments is illustrated in Figure 5. It should be recognized, however, that the principles of the present exemplary embodiments are equally applicable to standard networking systems. [0049] The exemplary user terminal arrangement 500 may include a processing/control unit 502, such as a microprocessor, reduced instruction set computer (RISC), or other central processing module. The processing unit 502 need not be a single device, and may include one or more processors. For example, the processing unit 502 may include a master processor and associated slave processors coupled to communicate with the master processor. [0050] The processing unit 502 may control the basic functions of the mobile terminal as dictated by programs available in the storage/memory 504. Thus, the processing unit 502 may execute the functions described in Figures 2 to 4. More particularly, the storage/memory 504 may include an operating system and program modules for carrying out functions and applications on the mobile terminal. For example, the program storage may include one or more of read-only memory (ROM), flash ROM, programmable and/or erasable ROM, random access memory (RAM), subscriber interface module (SIM), wireless interface module (WIM), smart card, or other removable memory device, etc. The program modules and associated features may also be transmitted to the user terminal arrangement 500 via data signals, such as being downloaded electronically via a network, such as the Internet. [0051] One of the programs that may be stored in the storage/memory 504 is a specific program 506. The specific program 506 may instruct various components of the user terminal to interact with adjacent base stations to perform measurements as discussed in the exemplary embodiments. The program 506 and associated features may be implemented in software and/or firmware operable by way of the processor 502. The program storage/memory 504 may also be used to store data 508, such as the various measurements performed by the user terminal, or other data associated with the present exemplary embodiments. In one exemplary embodiment, the programs 506 and data 508 are stored in non-volatile electrically- erasable, programmable ROM (EEPROM), flash ROM, etc. so that the information is not lost upon power down of the user terminal 500.

[0052] The processor 502 may also be coupled to user interface 510 elements associated with the user terminal. The user interface 510 of the user terminal may include, for example, a display 512 such as a liquid crystal display, a keypad 514, speaker 516, and a microphone 518. These and other user interface components are coupled to the processor 502 as is known in the art. The keypad 514 may include alpha-numeric keys for performing a variety of functions, including dialing numbers and executing operations assigned to one or more keys. Alternatively, other user interface mechanisms may be employed, such as voice commands, switches, touch pad/screen, graphical user interface using a pointing device, trackball, joystick, or any other user interface mechanism. [0053] The user terminal arrangement 500 may also include a digital signal processor (DSP) 520. The DSP 520 may perform a variety of functions, including analog-to-digital (A/D) conversion, digital-to-analog (D/A) conversion, speech coding/decoding, encryption/decryption, error detection and correction, bit stream translation, filtering, etc. The transceiver 522, generally coupled to an antenna 524, may transmit and receive the radio signals associated with a wireless device. [0054] The mobile computing arrangement 500 of Figure 5 is provided as a representative example of a user terminal in which the principles of the present exemplary embodiments may be applied. From the description provided herein, those skilled in the art will appreciate that the present invention is equally applicable in a variety of other currently known and future mobile and fixed computing environments. For example, the specific application 506 and associated features, and data 508, may be stored in a variety of manners, may be operable on a variety of processing devices, and may be operable in mobile devices having additional, fewer, or different supporting circuitry and user interface mechanisms. It is noted that the principles of the present exemplary embodiments are equally applicable to non-mobile terminals, i.e., landline computing systems.

[0055] The network servers or other systems for providing calculation and management in connection with the present exemplary embodiments may be any type of computing device capable of processing and communicating information. An example of a representative computing system capable of carrying out operations in accordance with the servers of the exemplary embodiments is illustrated in Figure 6. Hardware, firmware, software or a combination thereof may be used to perform the various steps and operations described herein. The structure 600 of Figure 6 is an example computing structure that may be used in connection with such a system. [0056] The example computing arrangement 600 suitable for performing the activities described in the exemplary embodiments may include a control module or server 601. Such a server 601 may also serve as the management module or the management module may have the same structure as server 601. The server 601 may include a central processor (CPU) 602 coupled to a random access memory (RAM) 604 and to a read-only memory (ROM) 606. The ROM 606 may also be other types of storage media to store programs, such as programmable ROM (PROM), erasable PROM (EPROM), etc. The processor 602 may communicate with other internal and external components through input/output (I/O) circuitry 608 and bussing 610, to provide control signals and the like. The bussing 610 may be, for example, an input interface unit that communicates with user terminals UE present in the network served by the arrangement 600. The processor 602 carries out a variety of functions as is known in the art, as dictated by software and/or firmware instructions.

[0057] The server 601 may also include one or more data storage devices, including hard and floppy disk drives 612, CD-ROM drives 614, and other hardware capable of reading and/or storing information such as DVD, etc. In one embodiment, software for carrying out the above discussed steps may be stored and distributed on a CD-ROM 616, diskette 618 or other form of media capable of portably storing information. These storage media may be inserted into, and read by, devices such as the CD-ROM drive 614, the disk drive 612, etc. The server 601 may be coupled to a display 620, which may be any type of known display or presentation screen, such as LCD displays, plasma display, cathode ray tubes (CRT), etc. A user input interface 622 is provided, including one or more user interface mechanisms such as a mouse, keyboard, microphone, touch pad, touch screen, voice-recognition system, etc.

[0058] The server 601 may be coupled to other computing devices, such as the landline and/or wireless terminals and associated applications, via a network. The server may be part of a larger network configuration as in a global area network (GAN) such as the Internet 628, which allows ultimate connection to the various landline and/or mobile devices. [0059] The disclosed exemplary embodiments provide a user terminal, a system, a method and a computer program product for determining a timing difference between pairs of base stations in a transmission network. It should be understood that this description is not intended to limit the invention. On the contrary, the exemplary embodiments are intended to cover alternatives, modifications and equivalents, which are included in the spirit and scope of the invention as defined by the appended claims. Further, in the detailed description of the exemplary embodiments, numerous specific details are set forth in order to provide a comprehensive understanding of the claimed invention. However, one skilled in the art would understand that various embodiments may be practiced without such specific details.

[0060] As also will be appreciated by one skilled in the art, the exemplary embodiments may be embodied in a wireless communication device, a telecommunication network, as a method or in a computer program product. Accordingly, the exemplary embodiments may take the form of an entirely hardware embodiment or an embodiment combining hardware and software aspects. Further, the exemplary embodiments may take the form of a computer program product stored on a computer-readable storage medium having computer-readable instructions embodied in the medium. Any suitable computer readable medium may be utilized including hard disks, CD-ROMs, digital versatile disc (DVD), optical storage devices, or magnetic storage devices such a floppy disk or magnetic tape. Other non-limiting examples of computer readable media include flash-type memories or other known memories. [0061] Although the features and elements of the present exemplary embodiments are described in the embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the embodiments or in various combinations with or without other features and elements disclosed herein. The methods or flow charts provided in the present application may be implemented in a computer program, software, or firmware tangibly embodied in a computer-readable storage medium for execution by a general purpose computer or a processor.

Claims

WHAT IS CLAIMED IS:

1. A method for determining when a first base station (24) in a telecommunication network (BS1 ) is out of synch with the network, the network (20) including at least a second base station (BS2) and a user terminal (26) configured to receive signals from the first and second base stations (BS1 , BS2), the method comprising: receiving in a control module (28) of the network (20) a measuring report from the user terminal (26), where the measuring report includes a first time of arrival (Ta1 ) of a first signal from the first base station (BS1 ) to the user terminal (26) and a second time of arrival (Ta2) of a second signal from the second base station (BS2) to the user terminal (26); receiving a maximum of a travel time difference (max(T1 - T2)) between (i) a first travel time (T 1 ) of the first signal from the first base station (BS 1 ) to the user terminal (26), and (ii) a second travel time (T2) of the second signal from the second base station (BS2) to the user terminal (26); determining a minimum of a difference starting time (min(T0 - TO')), which corresponds to a time offset between a starting time (TO) of the first signal and a starting time (TO') of the second signal, as a difference between (i) a difference between the first time of arrival (Ta1 ) and the second time of arrival (Ta2), and (ii) the maximum travel time difference (max(T1 - T2)); comparing the determined minimum difference starting time (min(T0 - TO')) with a predetermined threshold; and identifying the pair of the first base station (BS1 ) and the second base station (BS2) as including one base station that lost the synch with the network, when the determined minimum difference starting time (min(T0 - TO')) is larger than the predetermined threshold in the comparing step.

2. The method of Claim 1 , further comprising: receiving, at the control module, information from the first and second base stations regarding a self-identification of each base station with regard to a loss of synch.

3. The method of Claim 2, further comprising: identifying the one base station that lost the synch based on the self- identification information and a result of the identifying step; and deciding whether to shut down the one base station that lost the synch.

4. The method of Claim 1 , further comprising: repeating, when information from the first and second base stations regarding a self-identification of each base station with regard to a loss of synch is not available, the steps of Claim 1 for pairs including the first base station and a third base station, which is adjacent to the first base station, and pairs including the second base station and a fourth base station, which is adjacent to the second base station.

5. The method of Claim 4, further comprising: identifying pairs of base stations that have the minimum difference starting time above the predetermined threshold; and determining a common base station of the pairs and identifying the common base station as the one base station that lost the synch.

6. The method of Claim 5, further comprising: shutting down the one base station that lost the synch.

7. The method of Claim 4, further comprising: identifying pairs of base stations that have the minimum difference starting time above the predetermined threshold and corresponding phases of the minimum difference starting time having a same sign.

8. The method of Claim 1 , further comprising: selecting, when information from the first and second base stations regarding a self-identification of each base station with regard to a loss of synch is not available or there is more than one common base station in the calculated pairs of base stations that have the minimum difference starting time above the predetermined threshold, a number of base stations that are considered to maintain the synch.

9. The method of Claim 8, further comprising: determining whether other base stations, except the selected number of base stations, have lost the synch by repeating the steps of Claim 1.

10. The method of Claim 1 , further comprising: using the measuring report from the user terminal to determine a handover between adjacent base stations of the user terminal.

11. The method of Claim 1 , wherein the receiving step further comprises: calculating the maximum travel time difference based only on a design of the network.

12. A control module (28) in a telecommunication network (20) for determining when a first base station (BS1 ) in the telecommunication network (20) is out of synch with the network (20), the network (20) including at least a second base station (BS2) and a user terminal (26) configured to receive signals from the first and second base stations (BS1 , BS2), the control module (28) comprising: an input interface (610) configured to receive a measuring report from the user terminal (26), where the measuring report includes a first time of arrival (Ta 1 ) of a first signal from the first base station (BS1 ) to the user terminal (26) and a second time of arrival (Ta2) of a second signal from the second base station (BS2) to the user terminal (26); and a processor (602) connected to the input interface (610) and configured to receive a maximum of a travel time difference (max(T1 - T2)) between (i) a first travel time (T 1 ) of the first signal from the first base station (BS1 ) to the user terminal (26), and (ii) a second travel time (T2) of the second signal from the second base station (BS2) to the user terminal (26), determine a minimum of a difference starting time (min(T0 - TO')), which corresponds to a time offset between a starting time (TO) of the first signal and a starting time (TO') of the second signal, as a difference between (i) a difference between the first time of arrival (Ta1 ) and the second time of arrival (Ta2), and (ii) the maximum travel time difference (max(T1 - T2)), compare the determined minimum difference starting time (min(T0 - TO')) with a predetermined threshold, and identify the pair of the first base station (BS 1 ) and the second base station (BS2) as including one base station that lost the synch, when the determined minimum difference starting time (min(T0 - TO')) is larger than the predetermined threshold.

13. The control module of Claim 12, wherein the input interface is further configured to receive information from the first and second base stations regarding a self-identification of each base station with regard to a loss of synch.

14. The control module of Claim 13, wherein the processor is further configured to identify the one base station that lost the synch based on the self- identification information and a result of the step of identifying, and to decide whether to shut down the one base station that lost the synch.

15. The control module of Claim 12, wherein the processor is further configured to repeat, when information from the first and second base stations regarding a self-identification of each base station with regard to a loss of synch is not available, the processes of Claim 12 for pairs including the first base station and a third base station, which is adjacent to the first base station, and pairs including the second base station and a fourth base station, which is adjacent to the second base station.

16. The control module of Claim 15, wherein the processor is further configured to: identify pairs of base stations that have the minimum difference starting time above the predetermined threshold; and determine a common base station of these pairs and identifying the common base station as the one base station that lost the synch.

17. The control module of Claim 16, wherein the processor is further configured to: shut down the one base station that lost the synch.

18. The control module of Claim 15, wherein the processor is further configured to: identify pairs of base stations that have the minimum difference starting time above the predetermined threshold and corresponding phases of the minimum difference starting time having a same sign.

19. The control module of Claim 12, wherein the processor is further configured to: select, when information from the first and second base stations regarding a self-identification of each base station with regard to a loss of synch is not available or there is more than one common base station in the calculated pairs of base stations that have the minimum difference starting time above the predetermined threshold, a number of base stations that are considered to maintain the synch.

20. The control module of Claim 19, wherein the processor is further configured to: determine whether other base stations, except the selected number of base stations, have lost the synch by repeating the processes of Claim 12.

21. The control module of Claim 12, wherein the processor is further configured to: use the measuring report from the user terminal to determine a handover between adjacent base stations of the user terminal.

22. The control module of Claim 12, wherein the maximum travel time difference is calculated based only on a design of the network.

23. A computer readable medium including computer executable instructions, wherein the instructions, when executed by a processor (602) in a control module (28) of a telecommunication network (20), cause the processor (602) to determine when a first base station (BS1 ) in the telecommunication network (20) is out of synch with the network (20), the network (20) including at least a second base station (BS2) and a user terminal (26) configured to receive signals from the first and second base stations (BS1 , BS2), the instructions comprising: receiving in the control module (28) of the network (20) a measuring report from the user terminal (26), where the measuring report includes a first time of arrival (Ta 1 ) of a first signal from the first base station (BS1 ) to the user terminal (26) and a second time of arrival (Ta2) of a second signal from the second base station (BS2) to the user terminal (26); receiving a maximum of a travel time difference (max(T1 - T2)) between (i) a first travel time (T1 ) of the first signal from the first base station (BS1 ) to the user terminal (26), and (ii) a second travel time (T2) of the second signal from the second base station (BS2) to the user terminal (26); determining a minimum of a difference starting time (min(T0 - TO')), which corresponds to a time offset between a starting time (TO) of the first signal and a starting time (TO') of the second signal, as a difference between (i) a difference between the first time of arrival (Ta 1 ) and the second time of arrival (Ta2), and (ii) the maximum travel time difference (max(T1 - T2)); comparing the determined minimum difference starting time (min(T0 - TO')) with a predetermined threshold; and identifying the pair of the first base station (BS1 ) and the second base station (BS2) as including one base station that lost the synch with the network, when the determined minimum difference starting time (min(T0 - TO')) is larger than the predetermined threshold in the comparing step.