WO2015065154A1 - 무선통신 시스템에서 신호를 전송하는 방법 및 장치 - Google Patents
무선통신 시스템에서 신호를 전송하는 방법 및 장치 Download PDFInfo
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- WO2015065154A1 WO2015065154A1 PCT/KR2014/010514 KR2014010514W WO2015065154A1 WO 2015065154 A1 WO2015065154 A1 WO 2015065154A1 KR 2014010514 W KR2014010514 W KR 2014010514W WO 2015065154 A1 WO2015065154 A1 WO 2015065154A1
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Classifications
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
- H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
- H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
- H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
- H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
- H04B7/0617—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal for beam forming
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- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
- H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
- H04B7/0413—MIMO systems
- H04B7/0452—Multi-user MIMO systems
-
- H—ELECTRICITY
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- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
- H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
- H04B7/0413—MIMO systems
- H04B7/0456—Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting
- H04B7/046—Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting taking physical layer constraints into account
- H04B7/0469—Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting taking physical layer constraints into account taking special antenna structures, e.g. cross polarized antennas into account
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- H—ELECTRICITY
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- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
- H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
- H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
- H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
- H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
- H04B7/0619—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal using feedback from receiving side
- H04B7/0621—Feedback content
- H04B7/0626—Channel coefficients, e.g. channel state information [CSI]
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- H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
- H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
- H04B7/0686—Hybrid systems, i.e. switching and simultaneous transmission
- H04B7/0691—Hybrid systems, i.e. switching and simultaneous transmission using subgroups of transmit antennas
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- H04B7/00—Radio transmission systems, i.e. using radiation field
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- H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
- H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
- H04B7/0686—Hybrid systems, i.e. switching and simultaneous transmission
- H04B7/0695—Hybrid systems, i.e. switching and simultaneous transmission using beam selection
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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
- H04L5/0014—Three-dimensional division
- H04L5/0023—Time-frequency-space
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- H04L5/00—Arrangements affording multiple use of the transmission path
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- H04L5/0048—Allocation of pilot signals, i.e. of signals known to the receiver
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W72/00—Local resource management
- H04W72/20—Control channels or signalling for resource management
- H04W72/21—Control channels or signalling for resource management in the uplink direction of a wireless link, i.e. towards the network
Definitions
- the present invention relates to a wireless communication system. More specifically, the present invention relates to a signal using analog beamforming and digital bumpforming in a wireless access system supporting MU-MIM0 (mult i user-multiple input and multiple output). It is about the transmission method and the device supporting it.
- MU-MIM0 mult i user-multiple input and multiple output
- Multi-Input Multi-Out put (MIMO) technology improves the efficiency of data transmission and reception by using multiple transmit antennas and multiple receive antennas, eliminating the use of one transmit antenna and one receive antenna. It is a technique to let. If a single antenna is used, the receiving side receives data through a single antenna path, but if multiple antennas are used, the receiving end receives data through several paths. Therefore, the data transmission speed and the transmission amount can be improved, and the coverage can be increased.
- a single user-MIMO (SU-MIM0) scheme in which one terminal receives a downlink signal in one cell and two or more terminals perform one
- the cell may be divided into a multi-user-MIMO (MU-MIM0) scheme for receiving a downlink signal from a cell.
- SU-MIM0 single user-MIMO
- MU-MIM0 multi-user-MIMO
- Channel estimation refers to a process of restoring a received signal by compensating for distortion of a signal generated by fading.
- fading refers to a phenomenon in which a signal strength fluctuates due to multipath—time delay in a wireless communication system environment.
- a reference signal known to both the transmitter and the receiver is required.
- the reference signal may simply be referred to as a pilot (Pi lot) according to a reference signal (RS) or a standard applied.
- the downlink reference signal is a coherent signal such as a Physical Downlink Shared CHannel (PDSCH), a Physical Control Format Indicator CHannel (PCFICH), a Physical Hybrid Indicator CHannel (PHICH), and a Physical Downlink Control CHannel (PDCCH). Pilot signal for coherent demodulation.
- the downlink reference signal is applied to all stages in the cell. There is a common reference signal (CRS) shared by a word and a dedicated reference signal (DRS) for a specific terminal only.
- LTE-based systems with extended antenna configurations e.g. LTE-supporting 8 transmit antennas
- conventional communication systems supporting 4 transmit antennas e.g., systems according to the LTE release 8 or 9 standard).
- DRS-based data demodulation is considered to support efficient reference signal operation and advanced transmission scheme. That is, in order to support data transmission through an extended antenna, DRSs for two or more layers may be defined. Since the DRS is precoded by the same precoder as the data, the receiver does not need to precode the data. Channel information for demodulation can be easily estimated.
- the system according to the LTE-A standard may define a reference signal, that is, CSI-RS, for acquiring channel state information (CSI) at the receiving side.
- CSI-RS channel state information
- the present invention proposes a method and apparatus for transmitting a signal in a wireless communication system.
- a method for transmitting a signal by a base station in a wireless access system supporting MU-MIMO (mul ti user-mul t iple input and mul t iple output) according to an embodiment of the present invention is analog bump forming. Generating a beam for a subgroup including a plurality of terminals by using; Distinguishing a signal transmitted to each terminal belonging to the subgroup using digital beamforming; And transmitting a signal generated based on the analog beamforming and the digital bumpforming to the terminal, wherein a weight of the analog bumpforming is determined based on channel state information obtained using an uplink reference signal. Can be.
- a base station transmitting a signal in a wireless access system that supports multi-user input and multiple output (MU-MIMO) includes: a radio frequency (RF) unit; And a processor, wherein the processor is configured to generate a category for a subgroup including a plurality of terminals using analog bump forming, and to output a signal transmitted to each terminal belonging to the sub group using digital bump forming. Discriminate and transmit a signal generated based on the analog bumpforming and the digital beamforming to the terminal, and the weight of the analog beamforming is based on channel state information obtained using an uplink reference signal. Can be determined.
- RF radio frequency
- a transmission period of the uplink reference signal may be determined by adding a guard time to a time obtained by dividing a data symbol period.
- the uplink reference signal may be generated by maintaining a sampling frequency of a data symbol and increasing a subcarrier space.
- the uplink reference signals continuously transmitted may be partially overlapped with each other on the time axis.
- the uplink reference signal may be transmitted at the same time as another control signal or data signal.
- the method may further include transmitting transmission period information of the uplink reference signal to the terminal.
- the uplink reference signal may be based on a sequence having similar correlation characteristics in frequency and time.
- 1 illustrates a structure of a downlink radio frame.
- 2 shows an example of a resource grid for one downlink slot.
- 3 is a diagram illustrating a structure of a downlink subframe.
- FIG. 5 is a configuration diagram of a wireless communication system having multiple antennas.
- FIG. 6 is a diagram illustrating a pattern of a conventional CRS and a DRS.
- FIG. 7 illustrates an example of a DM RS pattern.
- FIG. 8 is a diagram illustrating examples of a CSI-RS pattern.
- FIG. 9 is a diagram for describing an example of a method in which a CSI-RS is periodically transmitted.
- FIG. 10 is a diagram for explaining an example of a method in which a CSI-RS is transmitted aperiodically.
- FIG. 11 illustrates an example of an RF receiver used in a wireless access system.
- FIG. 12 illustrates an example of an RF transmitter used in a wireless access system.
- FIG. 13 shows an example of a duplex texturer.
- FIG. 14 shows an example of a duplexer in a frequency band.
- 15 and 16 illustrate examples of a transmitter and a receiver that can perform digital bump forming.
- 17 and 18 show examples of a transmitter and a receiver that can perform analog bump forming.
- Figure 19 shows an example of the structure of an individual antenna using one transceiver and one PA.
- FIG. 20 shows an example of the structure of an individual antenna using one transceiver and a plurality of PS / PAs.
- FIG. 21 shows an example of a structure of a shared antenna using one transceiver and a plurality of PS / PAs.
- FIG. 22 shows an example of a structure using an individual antenna using one transceiver and a plurality of PS / PAs.
- FIG. 23 shows an example of a shared antenna structure using one transceiver and a plurality of PS / PAs. 24 illustrates a first embodiment of distinguishing multiple users in hybrid beamforming according to the present invention.
- FIG. 25 illustrates a second embodiment of discriminating multiple users in hybrid beamforming according to the present invention.
- 26 shows an example of an antenna arrangement structure according to the present invention.
- FIG 27 shows another example of an antenna array structure according to the present invention.
- 29 illustrates an example in which a plurality of short OFDM symbols are longer than one conventional OFDM symbol period.
- FIG. 30 shows an example of a method of transmitting the OFDM symbols so that they overlap.
- Figure 31 illustrates a base station and a terminal that can be applied to an embodiment of the present invention.
- each component or feature may be considered optional unless stated otherwise.
- Each component or feature may be implemented in a form not combined with other components or features.
- some of the components and / or features may be combined to form an embodiment of the present invention.
- the order of the operations described in the embodiments of the present invention may be changed. Some configurations or features of one embodiment may be included in another embodiment, or may be replaced with other configurations or features of another embodiment.
- Embodiments of the present invention will be described with reference to the relationship between data transmission and reception between a base station and a terminal.
- the base station has a meaning as a terminal node of the network that directly communicates with the terminal.
- the specific operation described as performed by the base station in this document may be performed by an upper node of the base station in some cases.
- a 'base station ion (BS)' may be replaced by terms such as fixed station ion, Node B, eNode B (eNB), and access point (AP).
- Repeater Relay Node (RN), Relay It may be replaced by a term such as Station (RS).
- RS Station
- terminal may be replaced with terms such as UE Jser Equiment (Mob), Moble Station (MS), Moleb Subscriber Station (MSS), and Subscriber Station (SS).
- the present invention and embodiments may be supported by standard documents disclosed in at least one of IEEE 802 systems, 3GPP systems, 3GPP LTE and LTE-Advanced (LTE-A) systems, and 3GPP2 systems, which are wireless access systems. That is, steps or parts which are not described to clearly reveal the technical spirit of the present invention among the embodiments of the present invention may be supported by the above documents. In addition, all the terms disclosed in this document can be described by the standard document.
- CDMA code division multiple access
- FDMA frequency division multiple access
- TDMA time division multiple access
- SC single carrier frequency division
- Multiple Access such as Multiple Access
- CDMA may be implemented with radio technologies such as UTRA Universal Terrestrial Radio Access) or CDMA2000.
- TDMA may be implemented in a wireless technology such as Global System for Mobile Communication (GSM) / General Packet Radio Service (GPRS) / Enhanced Data Rates for GSM Evolution (EDGE).
- GSM Global System for Mobile Communication
- GPRS General Packet Radio Service
- EDGE Enhanced Data Rates for GSM Evolution
- 0FDMA may be implemented with wireless technologies such as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX) ⁇ IEEE 802-20, Evolved UTRA (E-UTRA), and the like.
- UTRA is part of UMTS Jniversal Mobile Telecommunications System.
- 3rd Generation Partnership Project (3GPP) long term evolution (LTE) is part of Evolved UMTS (E-UMTS) using E-UTRA, and employs 0FDMA in downlink and SC-FDMA in uplink.
- LTE-A Advanced
- WiMAX is an IEEE 802.16e specification (WirelessMAN-OFDMA Reference System) and an advanced IEEE 802.16m specification. This can be explained by the WirelessMAN-OFDMA Advanced system. For clarity, the following description focuses on the 3GPP LTE and LTE-A standards, but the technical spirit of the present invention is not limited thereto.
- a structure of a downlink radio frame will be described with reference to FIG. 1.
- uplink / downlink data packet transmission is performed in units of subframes, and one subframe is defined as a certain time interval including a plurality of OFDM symbols.
- the 3GPP LTE standard supports a type 1 radio frame structure applicable to FD! XFrequency Division Duplex (FD! X) and a type 2 radio frame structure applicable to time division duplex (TDD).
- FIG. 1 is a diagram illustrating a structure of a type 1 radio frame.
- a downlink radio frame consists of 10 subframes, and one subframe consists of two slots in the time domain.
- the time it takes for one subframe to be transmitted is called a TTKtransmission interval (TK).
- TK TTKtransmission interval
- the length of one subframe may be 1 ms and the length of one slot may be 0.5 ms.
- One slot includes a plurality of 0FDM symbols in the time domain and a plurality of resource blocks (RBs) in the frequency domain.
- RBs resource blocks
- the 0FDM symbol represents one symbol period.
- the 0FDM symbol may also be referred to as an SC-FDMA symbol or symbol period.
- a resource block (RB) is a resource allocation unit and may include a plurality of consecutive subcarriers in one slot.
- the number of 0FDM symbols included in one slot may vary according to the configuration (conf igurat ion) of Cyclic Pref ix (CP).
- CPs include extended CPs and normal CPC normal CPs.
- the number of 0FDM symbols included in one slot may be seven.
- the 0FDM symbol is configured by the extended CP, since the length of one 0FDM symbol is increased, the number of 0FDM symbols included in one slot is smaller than that of the normal CP.
- the number of 0FDM symbols included in one slot may be six.
- an extended CP may be used to further enjoy inter-symbol interference.
- one slot includes 7 OFDM symbols, so that one subframe includes 14 OFDM symbols.
- the first two or three OFDM symbols of each subframe may be allocated to a physical downl ink control channel (PDCCH), and the remaining OFDM symbols may be allocated to a physical downl ink shared channel (PDSCH).
- PDCCH physical downl ink control channel
- PDSCH physical downl ink shared channel
- the structure of the radio frame is merely an example, and the number of subframes included in the radio frame, the number of slots included in the subframe, and the number of symbols included in the slot may be variously changed.
- FIG. 2 is an exemplary diagram illustrating an example of a resource grid for one downlink slot. This is the case in which an OFDM symbol consists of a normal CP.
- the downlink slot includes a plurality of OFDM symbols in the time domain and includes a plurality of resource blocks in the frequency domain.
- one downlink slot includes 7 OFDM symbols and one resource block includes 12 subcarriers as an example, but the present invention is not limited thereto.
- Each element on the resource grid is called a resource element (RE).
- the resource element a (k, l) becomes a resource element located in the k th subcarrier and the 1 st OFDM symbol.
- one resource block includes 12 X 7 resource elements (in the case of an extended CP, it includes 12 X 6 resource elements). Since the interval of each subcarrier is 15 kHz, one resource block includes about 180 kHz in the frequency domain.
- NDL is the number of resource blocks included in a downlink slot. The value of NDL may be determined according to the downlink transmission bandwidth set by the scheduling of the base station.
- FIG. 3 is a diagram illustrating a structure of a downlink subframe.
- Up to three 0FDM symbols in the front of the first slot in one subframe correspond to the control region to which the control channel is allocated.
- the remaining 0FDM symbols correspond to a data area to which a Physical Downlink Shared Channel (PDSCH) is allocated.
- the basic unit of transmission is one subframe. That is, PDCCH and PDSCH are allocated over two slots.
- Downlink control channels used in the 3GPP LTE system include, for example, a physical control format indicator channel (PCFICH), a physical downlink ink control channel (PDCCH), physical HARQ indicator channel (Physical Hybrid Automatic Repeat Request Indicator Channel; PHICH).
- PCFICH physical control format indicator channel
- PDCCH physical downlink ink control channel
- HARQ indicator channel Physical Hybrid Automatic Repeat Request Indicator Channel
- the PCFICH is transmitted in the first 0FDM symbol of a subframe and includes information on the number of 0FDM symbols used for control channel transmission in the subframe.
- PHICH is a response to uplink transmission.
- HARQ ACK / NACK signal as a.
- Control information transmitted through the PDCCH is referred to as Downlink Control Information (DCI).
- the DCI includes uplink or downlink scheduling information or an uplink transmit power control command for a certain terminal group.
- PDCCH is a resource allocation and transmission format of the DL-SCH, resource allocation information of the UL-SCH, paging information of the paging channel (PCH), system information on the DL-SCH, and PDSCH Resource allocation of upper layer control messages, such as random access responses, sent to the user, a set of transmit power control commands for individual terminals in a given terminal group, transmit power control information, and activation of voice over IP (VoIP) And the like.
- a plurality of PDCCHs may be transmitted in the control region.
- the terminal may monitor the plurality of PDCCHs.
- the PDCCH is transmitted in a combination of one or more consecutive Control Channel Elements (CCEs).
- CCEs Control Channel Elements
- the CCE is a logical allocation unit used to provide a PDCCH at a coding rate based on the state of a radio channel.
- the CCE processes multiple resource element groups.
- the format of the PDCCH and the number of available bits are determined according to the correlation between the number of CCEs and the coding rate provided by the CCEs.
- the base station determines the PDCCH format according to the DCI transmitted to the terminal, and adds a Cyclic Redundancy Check (CRC) to the control information.
- CRC is masked with an identifier called Radio Network Temporary Ident if ier (RNTI) according to the owner or purpose of the PDCCH.
- RNTI Radio Network Temporary Ident if ier
- the cel l-RNTI (C-RNTI) identifier of the UE may be masked on the CRC.
- C-RNTI cel l-RNTI
- a paging indicator identifier P-RNTI
- the PDCCH is for system information (more specifically, system information block (SIB))
- SIB system information block
- RNTKSI-RNTI random access -RNTKRA-RNTI
- the uplink subframe may be divided into a control region and a data region in the frequency domain.
- the control region is allocated a Physical Uplink Control Channel (PUCCH) including uplink control information.
- a physical uplink ink shared channel (PUSCH) including user data is allocated to the data area.
- PUCCH Physical Uplink Control Channel
- PUSCH physical uplink ink shared channel
- one UE does not simultaneously transmit a PUCCH and a PUSCH.
- PUCCH for one UE is allocated to an RB pair in a subframe. Resource blocks belonging to a resource block pair occupy different subcarriers for two slots. This resource block pair allocated to the PUCCH is said to be frequency-hopped at the slot boundary.
- the MULT (Mul t iple Input Mult iple Output) system is a system that improves the transmission / reception efficiency of data by using multiple transmit antennas and multiple receive antennas. independence, a plurality of data pieces received through a plurality of antennas may be combined to receive the entire data.
- the MIM0 technique includes a spatial diversity scheme and a spatial mult iplexing technique.
- Spatial diversity scheme can increase the transmission reliability (rel iabi l i ty) or widen the cell radius through diversity gain, which is suitable for data transmission for a mobile terminal moving at high speed.
- Spatial multiplexing can increase the data rate without increasing the bandwidth of the system by simultaneously transmitting different data.
- FIG. 5 is a configuration diagram of a wireless communication system having multiple antennas.
- the theoretical channel is proportional to the number of antennas, unlike when only a plurality of antennas are used in a transmitter or a receiver.
- the transmission capacity is increased. Therefore, the transmission rate can be improved and the frequency efficiency can be significantly improved.
- the transmission rate may theoretically increase as the rate of increase rate Ri multiplied by the maximum transmission rate Ro when using a single antenna.
- the transmission information may be expressed as follows.
- Each transmission information>, ' ", 3 ⁇ 4 may have different transmission powers. If each transmission power is ' , ⁇ ,', transmission information with adjusted transmission power may be expressed as follows. .
- S may be expressed as follows using the diagonal matrix P of the transmission power.
- W is also called 31 recording matrix.
- the transmission signal X may be considered in different ways depending on two cases (for example, spatial diversity and spatial multiplexing).
- spatial multiplexing different signals are multiplexed and the multiplexed signal is transmitted to the receiver, so that the elements of the information vector (s) have different values.
- spatial diversity the same signal is repeatedly transmitted through a plurality of channel paths so that the elements of the information vector (s) have the same value.
- a combination of spatial multiplexing and spatial diversity techniques can also be considered. That is, the same signal may be transmitted according to a spatial diversity scheme through three transmission antennas, for example, and the remaining signals may be spatially multiplexed and transmitted to a receiver.
- the received signals, 3 ⁇ 4, ' ", and 1 ⁇ 4 « of each antenna may be expressed as vectors as follows.
- channels may be classified according to transmit / receive antenna indexes.
- the channel from the transmitting antenna j to the receiving antenna i will be denoted by. Note that at 3 ⁇ 4, the order of the index is the receive antenna index first, followed by the index of the transmit antenna.
- FIG. 5 (b) shows a channel from NT transmit antennas to receive antenna i.
- the channels may be bundled and displayed in the form of a vector and a matrix.
- a channel arriving from a total of NT transmit antennas to a receive antenna i may be represented as follows.
- all channels arriving from the NT transmit antennas to the NR receive antennas may be expressed as follows.
- the real channel is added with white noise (AWGN) after passing through the channel matrix H.
- AWGN white noise
- the white noise, 2, ' '' ,% 3 ⁇ 4 added to each of the NR receive antennas can be expressed as
- the received signal may be expressed as follows.
- the number of rows and columns of the channel matrix H indicating the channel state is determined by the number of transmit / receive antennas.
- the number of rows is equal to the number of receiving antennas NR
- the number of columns is equal to the number of transmitting antennas NT. That is, the channel matrix H is NRXNT matrix.
- the rank of a matrix is defined as the minimum number of rows or columns independent of each other. Thus, the tank of the matrix cannot be larger than the number of rows or columns.
- the tank (ra «(H)) of the channel matrix H is limited as follows.
- 'rank' indicates the number of paths that can independently transmit a signal
- 'number of layers' indicates the number of signal streams transmitted through each path.
- the transmitting end transmits a number of layers corresponding to the number of tanks used for signal transmission, unless otherwise specified, a tank has the same meaning as the number of layers.
- a signal When a packet is transmitted in a wireless communication system, a signal may be distorted in the transmission process because the transmitted packet is transmitted through a wireless channel. In order to properly receive the distorted signal at the receiver, the distortion must be corrected in the received signal using the channel information. In order to find out the channel information, a signal known to both the transmitting side and the receiving side is transmitted, and a method of finding the channel information with the degree of distortion when the signal is received through the channel is mainly used. The signal is referred to as a pilot signal or a reference signal.
- RSs can be classified into two types according to their purpose.
- One is RS used for channel information acquisition, and the other is RS used for data demodulation. Since the former is an RS for allowing the terminal to acquire downlink channel information, the former should be transmitted over a wide band, and a terminal that does not receive downlink data in a specific subframe should be able to receive and measure the corresponding RS.
- Such RS is also used for measurement such as handover.
- the latter is an RS that is transmitted together with the corresponding resource when the base station transmits a downlink, and the terminal can estimate the channel by receiving the corresponding RS, thus demodulating the data. This RS should be transmitted in the area where data is transmitted.
- 3GPP LTE Long Term Evolution
- DRS dedicated RS
- the CRS is used for obtaining information about channel state, measuring for handover, and the like, and may be referred to as cell-specific RS.
- DRS is used for data demodulation and may be called UE-specific RS.
- DRS is used only for data demodulation, and CRS can be used for both purposes of channel information acquisition and data demodulation.
- the CRS is a cell-specific RS and is transmitted every subframe for a wideband.
- the CRS may be transmitted for up to four antenna ports according to the number of transmit antennas of the base station. For example, if the number of transmitting antennas of the base station is two, CRSs for antenna ports 0 and 1 are transmitted, and for four, CRSs for antenna ports 0 to 3 are transmitted.
- FIG. 6 shows a pattern of CRS and DRS on one resource block (12 subcarriers on 14 OFDM symbols X frequencies in time in case of a normal CP) in a system in which a base station supports four transmit antennas. It is a figure which shows.
- resource elements RE denoted by 'R0', 'R1', 'R2' and * R3 ' indicate positions of CRSs with respect to antenna port indexes 0, 1, 2, and 3, respectively.
- the resource element denoted as 'D' in FIG. 6 indicates the location of the DRS defined in the LTE system.
- RS for up to eight transmit antennas should also be supported. Since the downlink RS in the LTE system is defined only for up to four antenna ports, the RS for these antenna ports is additionally defined when the base station has four or more up to eight downlink transmit antennas in the LTE-A system. Should be. As RS for up to eight transmit antenna ports, both RS for channel measurement and RS for data demodulation should be considered.
- Backward compatibility means that the existing LTE terminal supports to operate correctly even in LTE-A system. From the point of view of RS transmission, the time when CRS defined in LTE standard is transmitted in every subframe in full band. When adding RSs for up to eight transmit antenna ports in the frequency domain, the RS overhead becomes too large. Therefore, in designing RS for up to 8 antenna ports, consideration should be given to reducing RS overhead.
- RS newly introduced in LTE-A system can be classified into two types. One of them is RS, channel state information-reference signal for channel measurement for selection of transmission tank, modulation ion and coding scheme (MCS), precoding matrix index (PMI), etc.
- MCS modulation ion and coding scheme
- PMI precoding matrix index
- CSI-RS Channel State Informat ion RS
- DM RS demodulation-reference signal
- CSI-RS for channel measurement purposes is for the purpose of channel measurement, unlike CRS in the existing LTE system used for data demodulation at the same time as channel measurement, handover measurement, etc. There is a feature to be designed.
- the CSI-RS may also be used for the purpose of measuring handover. Since the CSI-RS is transmitted only for obtaining channel state information, unlike the CRS in the existing LTE system, the CSI-RS does not need to be transmitted every subframe. Thus, to reduce the overhead of the CSI-RS, the CSI-RS may be designed to be transmitted intermittently (eg, periodically) on the time axis.
- a dedicated DM RS is transmitted to a terminal scheduled for data transmission.
- the DM RS dedicated to a specific terminal may be designed to be transmitted only in a resource region in which the terminal is scheduled, that is, in a time-frequency region in which data for the terminal is transmitted.
- FIG. 7 is a diagram illustrating an example of a DM RS pattern defined in an LTE-A system.
- a position of a resource element in which a DM RS is transmitted on one resource block (12 subcarriers on 14 0FDM symbol X frequencies in time in case of a normal CP) in which downlink data is transmitted is shown.
- the DM RS may be transmitted for four antenna ports (antenna port indexes 7, 8, 9, and 10) which are additionally defined in the LTE-A system.
- DM RSs for different antenna ports can be distinguished by being located in different frequency resources (subcarriers) and / or different time resources (0 FDM symbols) (ie, can be multiplexed in FDM and / or TDM schemes). .
- DM RSs for different antenna ports located on the same time-frequency resource may be distinguished from each other by orthogonal codes (ie, may be multiplexed by CDM).
- CDM multiplexed by CDM
- DM RS CDM group 1 in the example of FIG.
- DM RSs for antenna ports 7 and 8 may be located and they may be multiplexed by orthogonal codes.
- DM RSs for antenna ports 9 and 10 may be located in resource elements indicated as DM RS group 2 in the example of FIG. 7, which may be multiplexed by an orthogonal code.
- FIG. 8 is a diagram illustrating examples of a CSI-RS pattern defined in an LTE-A system.
- FIG. 8 shows the location of a resource element on which a CSI-RS is transmitted on one resource block in which downlink data is transmitted (12 subcarriers on 14 OFDM symbols X frequencies in time in the case of a general CP).
- one of the CSI-RS patterns of FIGS. 8 (a) to 8 (e) may be used.
- the CSI-RS may be transmitted for eight antenna ports (antenna port indexes 15, 16, 17, 18, 19, 20, 21, and 22) that are additionally defined in the LTE-A system.
- CSI-RSs for different antenna ports can be distinguished by being located in different frequency resources (subcarriers) and / or different time resources (OFDM symbols) (i.e., can be multiplexed in FDM and / or TDM schemes). .
- CSI-RSs for different antenna ports located on the same time-frequency resource may be distinguished from each other by orthogonal codes (ie, may be multiplexed by the CDM scheme).
- CSI-RSs for antenna ports 15 and 16 may be located in resource elements (REs) indicated as CSI-RS CDM group 1, which may be multiplexed by an orthogonal code.
- REs resource elements
- CSI-RSs for antenna ports 17 and 18 may be located in resource elements indicated as CSI-RS CDM group 2, which may be multiplexed by an orthogonal code.
- CSI-RSs for antenna ports 19 and 20 may be located in resource elements indicated as CSI-RS CDM group 3, which may be multiplexed by an orthogonal code.
- CSI-RSs for antenna ports 21 and 22 may be located, and they may be multiplexed by an orthogonal code.
- the RS patterns of FIGS. 6 to 8 are merely exemplary and are not limited to a specific RS pattern in applying various embodiments of the present invention. That is, even when RS patterns different from those of FIGS. 6 to 8 are defined and used, various embodiments of the present invention may be equally applied.
- CSI-RS configuration (conf igurat ion)
- one CSI-RS resource for signal measurement and one interference measurement resource (IMR) for interference measurement are associated with one (associat ion) CSI processes can be defined.
- CSI information derived from different CSI processes is fed back to a network (eg, a base station) with independent periods and subframe offsets (subframe of fset).
- each CSI process has an independent CSI feedback setting.
- the CSI-RS resource, IMR resource associ at ion information, and CSI feedback configuration may be informed by the base station to the UE through higher layer signaling such as RRC for each CSI process. For example, it is assumed that the UE receives (sets) three CSI processes as shown in Table 1 below.
- CSI-RS 0 and CSI-RS 1 indicate CSI-RSs received from cell 2, which is a neighboring cell participating in coordination with CSI-RSs, which are each received from cell 1, which is a serving cell of a terminal. If it is assumed that the IMR set for each CSI process of Table 1 is set as shown in Table 2,
- IMR 0 cell 1 performs mut ing and cell 2 performs data transmission, and the terminal is configured to measure interference from other cells except cell 1 from IMR 0.
- cell 2 performs muting and cell 1 performs data transmission, and the UE is configured to measure interference from cells other than cell 2 from IMR 1.
- both the cell 1 and the cell 2 perform muting in IMR 2
- the terminal is configured to measure interference from cells other than cell 1 and cell 2 from IMR 2.
- Table 1 and Table 2 CSI information of CSI process 0 represents optimal RI, PMI, and CQI information when data is received from cell 1.
- CSI information of CSI process 1 represents optimal RI, PMI, and CQI information when data is received from cell 2.
- CSI information of CSI process 2 represents optimal RI, PMI, and CQI information when data is received from cell 1 and no interference is received from cell 2.
- a plurality of CSI processes configured (configured) for one UE share a mutually dependent value. For example, in the case of joint transit (JT) in cell 1 and cell 2, the channel in CSI process 1 and cell 2 that treats cell 1 as the signal part is considered as the signal part. If the considered CSI process 2 is configured (set) for one UE, the tanks of the CSI process 1 and the CSI process 2 and the selected subband index should be the same to facilitate JT scheduling.
- JT joint transit
- the period or pattern in which the CSI-RS is transmitted may be configured by the base station (conf igurat ion).
- the UE In order to measure CSI-RS, the UE must know the CSI—RS configuration (conf igurat ion) for each CSI-RS antenna port of the cell to which the UE belongs.
- the CSI-RS configuration includes a downlink subframe index in which the CSI-RS is transmitted and a time-frequency position of the CSI-RS resource element (RE) in the transmission subframe (for example, FIGS.
- CSI-RS sequence (a sequence used for CSI-RS purposes, and pseudo-random according to a predetermined rule based on slot number, cell ID, CP length, etc.). May be generated). That is, a plurality of CSI-RS configuration (conf igurat ion) can be used in any (given) base station, the base station can inform the CSI-RS configuration to be used for the terminal (s) in the sal among the plurality of CSI-RS configuration have.
- the CSI-RSs for each antenna port may be multiplexed in FDM, TDM and / or CDM scheme using orthogonal frequency resources, orthogonal time resources, and / or orthogonal code resources. Can be.
- the base station informs UEs in a cell of information about CSI-RS (CSI-RS configuration)
- information about a time-frequency to which CSI-RS is mapped to each antenna port is mapped.
- the time information includes subframe numbers in which the CSI-RS is transmitted, period in which the CSI-RS is transmitted, subframe offset in which the CSI-RS is transmitted, OFDM symbol number through which the CSI-RS resource element (RE) of a specific antenna is transmitted.
- the information on the frequency may include a frequency spacing through which the CSI-RS resource element (RE) of a specific antenna is transmitted, an offset or shift value of the RE on the frequency axis, and the like.
- the CSI-RS may be periodically transmitted with an integer multiple of one subframe (for example, 5 subframe periods, 10 subframe periods, 20 subframe periods, 40 subframe periods, or 80 subframe periods). have.
- FIG. 9 illustrates that one radio frame includes 10 subframes (subframe numbers 0 to 9).
- subframe numbers 0 to 9 for example, before the CSI-RS of the base station
- the offset value may have a different value for each base station so that CSI-RS of several cells may be evenly distributed in time.
- the offset value may have one of 0 to 9.
- the offset value may have one of 0 to 4,
- the offset value When the CSI-RS is transmitted in a period of 15 ms, the offset value may have one of 0 to 19. When the CSI-RS is transmitted in a period of 40 ms, the offset value may have one of 0 to 39. For example, when the CSI-RS is transmitted in a period of 80 ms, the offset value may have one of 0 to 79. This offset value indicates the value of the subframe where the base station transmitting the CSI-RS in a predetermined period starts the CSI-RS transmission. When the base station informs the transmission period 0 and the offset value of the CSI-RS, the terminal may receive the CSI-RS of the base station at the corresponding subframe location using the value.
- the terminal may measure the channel through the received CSI-RS, and as a result, may report information such as CQI, PMI, and / or RI (Rank Indicator) to the base station. Except where CQI, PMI, and RI are distinguished from each other in this document, these may be collectively called CQI (or CSI).
- CQI or CSI
- the CSI-RS transmission period and offset may be separately specified for every 5 CSI-RS configuration (conf igurat ion).
- one radio frame includes 10 subframes (subframe numbers 0 to 9).
- the subframe in which the CSI-RS is transmitted may appear in a specific pattern.
- the CSI-RS transmission pattern may be configured in units of 10 subframes 0, and 1 bit indicating whether to transmit the CSI-RS in each subframe. Can be specified as a ruler.
- 10 illustrates a CSI-RS pattern transmitted at subframe indexes 3 and 4 within 10 subframes (subframe indexes 0 to 9). Such an indicator may be provided to the terminal through higher layer signaling.
- the configuration for CSI-RS transmission may be configured in various ways as described above.
- the base station may perform CSI-RS. It is necessary to inform the terminal of the setting. Embodiments of the present invention for informing the UE of the CSI-RS configuration will be described below.
- FIG. 11 shows an example of an RF receiver used in a wireless access system.
- an antenna 1101 receives an electromagnetic wave signal in the air and transmits it as an electrical change on a wire.
- the band select filter (Band select f lter, 1102) performs band pass filtering to amplify only a desired frequency band. If multiple channels are used, the band select filter must pass all channels (in-band). If the same antenna is used, the duplexer can serve as a band select f i ter.
- the LNA Low Noise Ampl i ier 1103 allows the signal to be amplified while suppressing the amplification to the noise when amplifying a reception signal that is buried in the air.
- the IRF lmage reject filter (1104) performs bandpass filtering once again to prevent the fatal image frequency from being amplified in the LNA. In addition, it improves the stability of receiver by removing spurious frequencies and separating RF stage and IF stage.
- the RF down mixer 1105 down-converts the frequency of the low noise amplified RF signal to the IF band.
- the RF Local Oscillator (RF L0, 1106) supplies the L0 frequency for frequency synthesis to the RF down mixer.
- channel selection can be made by changing the L0 frequency.
- phase locked loop (PLL) 1107 holds the output frequency of the RF L0 so that it can be fixed at a constant frequency without being shaken. That is, RF L0 through Control input It precisely adjusts the voltage of VC0, which is used for frequency tuning, to move and fix the RF L0 output frequency to the desired frequency.
- the signals converted to the IF frequency include several channels, and the channel select filter (Channel select f i ter, 1108) selects only the desired channels by bandpass filtering. Since the spacing between the channels is mostly narrow, a filter having good skirt characteristics is required.
- the IF amplifier (ampl i ier) 1109 arbitrarily adjusts the gain of the IF AMP, such as VGA or AGC.
- the IF Down mixer finishes channel selection and amplification at the IF stage and removes the carrier frequency to change to a baseband, which is a frequency band containing the original signal. In other words, downconversion mixing is performed.
- the IF Local Oscillator (IF L0) supplies the L0 frequency to the IF Mixer for converting IF to baseband.
- An additional IF PLL can be used to lock the L0 frequency.
- FIG. 12 illustrates an example of an RF transmitter used in a wireless access system.
- the driving amplifier (Drive Ampl i ier, DA, 1201) will be described.
- the Tx stage has a constant input signal unlike the Rx stage.
- PA Power Amp
- PA Power Amp
- the input signal must also have some level of power.
- Drive AMP solves the lack of gain of power amp and at the same time plays a role to make enough input power to PA.
- BSF Bit Select Filter
- the power amplifier (Power Ampl if ier, PA, 1203) is the most important configuration in the RF, Tx section.
- the PA performs power amplification so that a signal with sufficient power can be sent out at the final stage.
- the isolator will be described.
- the transmitting end is not the receiving end, since there is a possibility of the signal flowing back through the antenna, it is necessary to fix the echo of the signal so that the signal can be transmitted only in a specific direction. Signal flows in the output direction, and the signal coming in the reverse direction is terminated so that the signal is not transmitted in reverse. In other words, it is possible to prevent the PA from being damaged by preventing the signal from flowing back and disturbing the impedance of the PA output terminal.
- BSF Bit Select Filter, 1205
- nonlinear spurious frequency components may appear at the rear of the nonlinear amplifier.
- bandpass filtering is performed to cut them out and release only the desired frequency band to the outside.
- Duplexer can play this role if the system shares antenna with receiver.
- the antenna 1206 serves to radiate the change of the electrical signal on the lead to electromagnetic waves in the air.
- Multiplex refers to a configuration in which multiple signals are shared and distributed, and a multiplexer sends multiple signals through a single line and collects or distributes them again. .
- Duplex is to share two signals in one path.
- two signals usually refer to two types of transmission signals and received signals.
- TDD and FDD may be mentioned in a manner in which transmission and reception signals are shared together using one transmission line or an antenna.
- a duplexer is needed to arrange the transmission, reception, and three stages of the antenna to flow only as desired without mixing with each other. That is, the duplexer branches the transmitter and the receiver while using the same antenna. By using a duplexer, it is possible to share the antenna efficiently by extinguishing the transmitting and receiving end with one antenna.
- the duplexer may be configured by attaching a BPF (Bandpass Filter) which passes only a transmitting end frequency and a BPF which passes only a receiving end frequency, and then properly matches the middle with an antenna.
- BPF Bandpass Filter
- S21 and S13 represent power transfer from antenna port 1 to port 2 and port 3. Each by filter characteristics It can have a high pass at the BPF pass frequency of.
- S23 means power transfer between the transmitting end and the receiving end. It is suppressed to the lowest in both the transmit and receive frequency bands.
- a Diplexer refers to branching between a transmitting end and a receiving end using the same antenna.
- the diplexer can be configured using LPF and HPF. For example, when a signal is transmitted and received using a wired path, it may be used when only two transmission signals and a reception signal exist in the shielded line without other frequencies. In addition, it can be used to simultaneously digest Celular CDMA of 800MHz and PCS CDMA of 8GHz in Mul t-band terminal.
- a phase shifter is a change in phase of a signal in an electrical or mechanical manner. It can be used in RF analog signal processing stages such as pan control and phase modulation of a phased array antenna.
- the first method of changing the phase is to mechanically change the length of the track. For example, in a structure where two metal coaxial lines overlap, one can coaxially insert and remove one coaxial pipe. This method can be phase shifted continuously and has the advantage of low loss. On the other hand, mechanically, it takes a long time to change phase and has a large size.
- the second method of changing the phase is a line conversion method.
- This is one of the phase shifting methods of electrically changing the length.
- a plurality of transmission lines having different lengths can be arranged, and the path can be changed by a switch.
- This method can be miniaturized and has a very short phase shift time.
- the 4-bit phase shifter of the line conversion method can change the phase shift in units of 22.5 from 0 to 337.5.
- the third method of changing the phase is reflection. Reflective use is likewise one of the phase shifting methods of electrically changing length. Similar to the principle that when light strikes somewhere, it is reflected and the phase shifts, and the electrical signal changes phase by reflecting at the point where impedance changes. Specifically, the insertion phase can be adjusted according to the value of the device connected in the middle of the transmission line. This method has the disadvantage that the insertion loss is deteriorated and the impedance characteristic is also deteriorated.
- the fourth method of changing the phase is a Loaded Line Type or a Hybrid Coupled Type. These are also one of the phase shifting methods of electrically changing the length. It is often used as a digital stomach acid transition.
- Loaded Line Type is used for phase shifter with 45 ⁇ or less phase shift.
- Hybrid Coupled Type is used for phase shifter with 45 or more s phase shift.
- the phase can be varied using the reactance change when the PIN diode is turned on / of f.
- the fifth method of changing the phase is the vector modulator phase shifter, which adjusts orthogonal magnitudes of two orthogonal components according to a desired phase so that the synthesizer meets them to obtain a signal having the required phase. to be.
- 15 and 16 illustrate examples of a transmitter and a receiver that can perform digital bump forming.
- the digital beamforming technique applies a signal processing technique at the baseband stage to change the phase and size for beamforming for each antenna port.
- Such a digital beamforming technique has an advantage of enabling independent panforming and sophisticated beamforming for each frequency band. Therefore, the digital bumpforming technique requires an independent baseband signal processing block for each antenna port.
- 17 and 18 show examples of a transmitter and a receiver that can perform analog bump forming.
- the analog beamforming technique is characterized by forming a band by changing a phase and a magnitude value of each antenna element of a signal transmitted from a baseband in an RF stage. Because the shaping is done at the RF stage, the baseband hardware complexity is reduced by using a relatively small number of baseband signal processing blocks. On the other hand, the analog bumpforming technique has variable beamforming on the time axis and the same panforming on the entire frequency band has low beamforming freedom and low accuracy.
- Massive MIM0 based wireless communication has advantages such as improved signal quality performance, energy efficiency, and multi-user interference by applying multiple antennas. As the number of antennas increases, many advantages can be obtained. On the other hand, as the number of antennas increases, the number of baseband signal processing blocks also increases, which increases signal processing and hardware complexity.
- a hybrid beamforming method that combines a digital bumping method and an analog beamforming method has been proposed to reduce the hardware complexity and maintain the gain of the Massive MIM0.
- the digital panforming method has a high magnetic induction capable of different panforming for each frequency band.
- the analog bump forming method that forms the same band in the frequency band used is combined with the digital bump forming method, the degree of freedom for beamforming is lowered than when only the digital bump forming method is used. This lowers the degree of freedom of multi-user transmission and at the same time results in lower multi-user gains that can be obtained through Massive MIM0.
- a first embodiment of the present invention relates to a hybrid bump forming method for multi-user transmission.
- Hybrid beamforming is characterized in that simultaneously performing analog beamforming and digital beamforming.
- it is important to maintain the beam's resolved ion and the freedom of massive multi-user transmission.
- a hybrid bump forming method for satisfying two requirements is described.
- Analog beamforming uses RF with phase shi fter.
- Analog beamforming concentrates energy in a specific direction by overlapping beams radiated by a plurality of antenna elements to make a sharp beam (donut shape or pencil shape).
- the pan shaping direction can be adjusted by changing the value of the phase shi ft.
- Analog beamforming applies a phase change to one analog signal to transmit or receive through multiple antennas.
- Analog bumpforming allows for variable phase changes over time.
- N independent phase shi fters are used for analog bump forming, N independent beams that can be spatially distinguished can be formed at the same time.
- N beams formed independently can be assigned to one user to form N paths, and N users can also be assigned to N multi-users for multi-user transmission.
- N independent basebands are required to transmit N different data through N beams.
- a broad beam emitted by a plurality of passive antennas is superimposed by digital processing to concentrate energy in a specific direction so as to be a sharp beam.
- Sharp beams generated by beamforming are generated in the azimuth range in which the broad beam formed by the passive antenna is transmitted.
- Digital beamforming in a MIMO system using a passive antenna combines beams formed by the passive antenna using digital domain processing to give direction. This directivity can be performed independently by narrowband.
- digital beamforming adjusts coefficients in the digital domain, it is possible to form a beam having good resolut ion.
- J-MIM0 transmission using a passive antenna generates a plurality of sharp beams by superimposing Digital Processing on broad beams formed by a plurality of passive antennas. Thereafter, when transmitting to specific users, simultaneous transmission is performed by selectively using orthogonal beams as much as possible in order to reduce indirect among users.
- the beam of the analog domain is not spatially distinguished when multi-user is transmitted, but spatially is distinguished using the beam generated by the digital beamformer.
- the degree of freedom for beamforming weight calculation in hybr id beamforming has the analog domain as well as the digital domain.
- RF with variable phase shifter and power amplifier is introduced into the antenna element.
- Hybrid beamforming that can simultaneously perform digital beamforming and analog beamforming can be implemented.
- the existing techniques related to hybrid beamforming focus mainly on determining the optimal weight of hybrid beamforming from a single user perspective.
- methods for calculating the optimal weight by considering the weight of the digit domain and the analog domain are proposed. These studies focus on calculating the optimal weight from a single user's perspective.
- the mult iple beam generation in the analog domain is used for the purpose of collecting energy of multipath transmission, the optimal beamforming weight is calculated.
- FIG. 19 shows an example of the structure of an individual antenna using one transceiver and one PA.
- K N
- N TRX tolerance iver
- Each TRX is mapped with one antenna element, and each TRX has one PA.
- Ful l digital beamforming may be performed using N antenna elements.
- FIG. 20 illustrates an example of a structure of an individual antenna using one transceiver and a plurality of PS / PAs.
- FIG. 20 shows an example of a structure of a shared antenna using one transceiver and a plurality of PS / PAs.
- K > N antenna elements and N TRXs are used, and antennas are shared between TRXs.
- Each TRX is mapped with M antenna elements, and each TRX has M PS / PAs.
- Analog beamforming is performed using M antenna elements and digital beamforming is performed using N TRXs.
- a plurality of analog beamforming may be performed through one antenna.
- FIG. 22 illustrates an example of a structure using one transceiver and a plurality of PS / PAs and using an individual antenna.
- K > N antenna elements, N TRXs, and independent antennas for each TRX are used.
- Each TRX is mapped with M antenna elements, and each TRX has M PS / PAs.
- the transmitter has a Mul t iple PS / PA while the receiver has a single RF receiver.
- Analog beamforming is performed using M antenna elements in the TX stage, and digital beamforming is performed using N TRXs.
- In the RX stage fixed beamforming is performed, and digital beamforming is performed using N TRXs.
- FIG. 23 shows an example of a shared antenna structure using one transceiver and a plurality of PS / PAs.
- K (> N) antenna elements and N TRXs are used to share antennas between TRXs.
- Each TRX is mapped with M antenna elements, and each TRX has M PS / PAs.
- the transmitter has a Mul t iple PS / PA, while the receiver has a single RF receiver.
- Analog beamforming is performed using ⁇ antenna elements at the Tx end, and digital beamforming is performed using N TRXs.
- a plurality of analog beamforming may be performed through one antenna.
- fixed beamforming is performed, and digital beamforming is performed using N TRXs.
- Embodiment 1-1 according to the present invention relates to a method for distinguishing multiple users using hybrid bump forming.
- FIG. 24 illustrates a first embodiment for distinguishing multiple users in hybrid bump forming according to the present invention.
- antenna elements are bundled to form a subgroup.
- antenna elements may be configured as subgroups in the same manner as in FIGS. 20 and 22.
- analog beamforming is performed for each subgroup.
- “Analog Beams, which are formed in subgroups, are wide, wide, and wide.”
- a beam is formed in various directions in order to be able to distinguish several spaces.
- the signal processor of the digital domain allows multiple beams created by subgroups to be synthesized. Weights for synthesizing multiple beams can be generated by using the independent spatial channel characteristics of each user in the space of the analog beam. This can be used to distinguish multiple users.
- four independent radio channels may be formed.
- Four radio channels are mapped to four antenna ports.
- Multiple stream transmission is performed using a transmission precoder supporting four antenna ports. .
- 25 illustrates a second embodiment of distinguishing multiple users in hybrid bump forming according to the present invention.
- signals generated from a plurality of Phase Shifter (PS) I Power Amp (PA) are synthesized and transmitted through one antenna element.
- Analog beamforming is performed for each PS / PA, and beams are formed in various directions to distinguish the space. That is, when multiple PS / PAs are used, beams can be formed in various directions at the same time.
- a plurality of PS / PAs may be configured in each antenna subgroup.
- a plurality of beams may be formed for each antenna subgroup.
- the signal processor of the digital domain can generate a signal for each PS / PA so that waveforms generated from the DAC can be transmitted as different analog signals (independent signals).
- Precoding of the digital beamformer plays a role of synthesizing the analog beams generated from the antenna subgroup and the plurality of PS / PAs.
- Embodiments 1-2 of the present invention relate to an analog bump forming method for hybrid bump forming effectively in multi-user transmission.
- 20 and 22 have a degree of freedom of beam generation in each subgroup so that beams of different directions are simultaneously transmitted in each subgroup.
- 21 and 23 may have a degree of freedom of beam generation in each PS / PA so that beams of different directions may be simultaneously transmitted in each PS / PA.
- the structure of FIG. 25 allows beam generation in each subgroup and each PS / PA so that beams of different directions can be simultaneously transmitted in each subgroup and each PS / PA.
- Analog beams are characterized by concentrating energy in a specific direction to improve the state of the channel. In other words, the channel condition is good and bad in areas where energy is concentrated and areas that are not.
- SDMA and TDMA can be applied to transmit signals to users in the area covered by the transmission point using the beamforming technique.
- Embodiments 1-3 illustrate an analog beamforming method for effective hybr id beamforming in multi-user transmission.
- a plurality of beams are formed at the same time. If the beams that concentrate energy in different directions are transmitted at the same time, different beams can be used to transmit signals with less interference to users in different regions. But many If many beams are used in different directions at the same time in a subgroup, the narrower the distance between beams, the more likely the interference between beams will occur. In this case, it is effective to reduce the interference by taking a method of avoiding the interference between beams, because beams having a long distance between beams are selected and transmitted rather than transmitting different beams for each subgroup.
- At least two subgroups generate beams in the same direction as a first method for selectively transmitting beams having a long distance between beams while subgroups simultaneously transmit beams.
- Each PS / PA in a subgroup forms an independent beam.
- signals of subgroups forming beams in the same direction are distinguished from multiple users by using digital beamforming.
- the spread of good and bad channel conditions in the area covered by the transmission point is greater than that of using an omni antenna.
- the beam can be transmitted independently for each subgroup, and the direction of the beam transmitted by each subgroup can be set differently according to time.
- you change the direction of the beam every hour the measurement and reporting becomes complicated.
- the transmission beam direction may be changed based on a subframe (base unit of time in scheduling).
- a time unit for performing the same measurement can be specified in order to reflect the channel state change according to the change in the transmission beam direction.
- a subframe set that performs the same measurement can be defined using a bit map, and can be indicated by a higher layer signal.
- subgroups that generate beams in the same direction can maintain a combination of subgroups that perform the same beamforming even when the beam changes over time.
- Embodiments 1-3 of the present invention relate to a digital bump forming method for effectively performing hybrid bump forming in multi-user transmission.
- the characteristics of the antenna port are described first in terms of transmission and channel measurement.
- the channel of the antenna port (for example, A antenna port 5 in LTE, AP 7-14, etc.) used for signal transmission is changed according to the transmission precoding weight applied to the frequency and time.
- the antenna port (eg AP 15-22 defined in LTE) used for measurement has only time-varying channel characteristics by Doppler.
- the hybrid BF may be considered as a MIM0 transmission method (Digital BF) having a plurality of antenna ports generated by analog beamforming.
- the difference from the antenna port of the existing MIM0 system is that the channel state can be changed by analog beamforming.
- the channel may be changed by the number of antenna subgroups, a method of configuring a subgroup, a beamforming method applied to the subgroup, or the like.
- the shape and value of a precoding weight applied to digital beamforming in hybrid beamforming are first used for analog beamforming. It depends on the number of transmission beams generated and the precoding weight applied. For example, if the number of transmission beams is four, a transmission precoder having four antenna ports is used. In this case, the transmission precoding weight is selected in consideration of the transmission precoding weight used for analog beamforming. If the precoding weight of analog beamforming is maintained and changed for a certain time, the precodng weight of digital beamforming should be changed at least when the precoding of analog beamforming is changed.
- digital beamforming may serve to compensate for the phase difference between the N channels generated by the A-Beam.
- Digital beamforming may also be performed in narrowband units.
- a transmission precoder is configured to transmit M independent signals.
- Embodiment 1-4 relates to a scheduling method for supporting multi-user transmission in hybrid beamforming.
- a set of target users is generated according to the analog beamforming weight.
- users are distinguished by digital beamforming using a short term. Users who use analog beams directed in a similar direction are classified into beams made by synthesizing multiple analog beams through digital processing.
- a second embodiment according to the present invention relates to a method of applying antenna subgrouting for efficient hybrid beamforming.
- a training sequence for analog beamforming is transmitted.
- the RF stage applies phase and magnitude values for each antenna element, and a training sequence for selecting an appropriate phase / size value is left.
- analog beamforming is performed for each antenna subgroup.
- analog beamforming may be performed in units of subgroups.
- analog beamforming may be performed independently for each subgroup. For example, when one antenna subgroup includes four antenna elements, beamforming may be performed by applying independent phase and magnitude values to the four antenna elements. There is a degree of freedom for beamforming in different directions for each of the 16 subgroups.
- the antenna subgroup is a set of antenna elements.
- the antenna subgroup may be a basic unit for performing analog beamforming by performing a bundle of antenna elements (AEs).
- AEs antenna elements
- PS phase shifters
- PA Power Ampl if ier
- signal synthesizers are built into the AS. It can be designed to transmit / receive signals through one antenna and generate multiple analog beams in one AS.
- AS may be performed in various combinations.
- There are various arrangements such as Linear Array, Planar Array, Circular Array, etc. according to the method of arranging antennas.
- UPA Uniform Planar Array
- Various combinations can be considered depending on how many AEs are used as Vertical Domain (V-D) and Horizontal Domain OH)) to form a subgroup.
- V-D Vertical Domain
- H-D Horizontal Domain
- a massive antenna having 64 AEs is assumed.
- four combinations (1, 2, 4, 8) are obtained in each domain, and the subgroup has 16 combinations.
- the AS configuration (the number of AEs of V-D * the number of AEs of H-D) is expressed as a multiple of 2 including the number of AEs of V-D and H-D as follows.
- (1x1), (1x2), (1x4), (1x8), (2x1), (2x2), (2x4), (2x8), (4x1), (4x2), (4x4) ), (4x8), (8x1), (8x2), (8x4), and (8x8) AS combinations can be derived.
- the first method according to the second embodiment of the present invention is to apply the same subgrouping pattern to at least one antenna subgroup. Furthermore, all antenna subgroups may apply the same subgrouting pattern.
- the complexity for calculating the precoding weight of analog beamforming can be reduced.
- the use of analog beamforming precoding weights having the same phase increments / magnitude increments of antenna subgroups has the advantage of reducing the complexity and overhead of reporting to perform beamforming.
- At least one antenna subgroup among the antenna subgroups to which the same subgrouping pattern is applied applies an analog beamforming precoding weight having the same phase increment / magnitude increment.
- all the antenna subgroups to which the same subrouting pattern is applied may apply analog beamforming precoding weights having the same phase increment / size increment.
- the AS may apply different subgrouping patterns over time. Changing the subgrouping pattern means that the channel state changes. Considering the time relationship of measuring and applying channels, the subgrouping pattern should be maintained for at least the time that channel information is reported and used for data transmission. For example, when the CSI reporting period is 5ms, the subgrouping pattern is maintained for at least 10ms.
- a time durat ion to which a plurality of subgrouping patterns is applied can be set as a single t set.
- the set is maintained for at least one period of reporting.
- M subgrouping patterns to change dynamically during N t ime, and keep the minimum time dynamically changing (for example, 10 subframe time intervals) as one cycle.
- the same subgrouping scheme is applied to a selected antenna subgroup pattern for a predetermined time.
- Information about a subgroup may be provided through higher layer signaling. For example, it may be provided as RRC signal ing. This may be terminal specific information or cell specific It may be information. Subgrouping can be set with several candidate methods and specified using indicators. The subgrouping method specified by the indicator is equally applied to one or more antenna subgroups.
- the antenna subgroup is set to a block for generating an independent channel for signal transmission.
- the AS may be defined as a block that creates an independent channel through which several signal sequences among a plurality of signal sequences generated in the baseband can be transmitted.
- N ASs forming K analog beams
- M independent signal strings are generated in the baseband
- M independent signals are converted into analog through Digital-Analog-Converter (DAC).
- DAC Digital-Analog-Converter
- the method of measuring the channel and finding the precoding weight depends on the configuration of the antenna subgroup or the number of beams transmitted in the subgroup. If the UE measures the channel of the antenna elements and finds and reports an analogue beamforming precoding weight suitable for each subgroup, the UE finds and reports a weight value corresponding to the pattern of the subgroup, and for this purpose, a weight set used for each subgroup is defined. Can be. For example, in the configuration of (4 * 2) and (2 * 2), different weights should be applied.
- the weight set applied depends on the antenna subgroup conf igurat ion. Further, when the UE measures and reports the appropriate weight to report the channel, it can be found in the weight value for the applied antenna subgrouping.
- a weight set for antenna subgrouping may be indicated or may be defined by tie with an antenna subgrouping pattern.
- a third embodiment of the present invention relates to channel state information for hybrid beamforming. Specifically, in the third embodiment, a channel state reporting method for supporting hybr id beamforming that performs digital beamforming after analog beamforming is performed will be described.
- the coarse beam uses a beam having broad width and directs the beam in a spatially rough direction.
- the fine beam is characterized by being able to accurately point the user's point using a sharp beam.
- a beam width of 2Tx is wider than a beam of 16Tx.
- the 3dB beamwidth point is defined as a point directed by different beams, the distance between the beams is wider between beams of the 16Tx antenna.
- the beamforming weight value changes according to the change in the channel condition. The amount of change in the beamforming weight for the coarse beam is less sensitive to the change in the channel condition than the fine beam.
- the resolut ion of beamforming may be determined according to characteristics of devices such as phase shifter and power amplifier iier.
- red beamforming is possible depending on the situation of the UE, there is a limit to performing sophisticated beamforming due to the limitation of the device. Therefore, it is appropriate to use analog beamforming for generating a coarse beam.
- digital beamforming is suitable for use in generating fine beam because it has the freedom to control the change of phase and amplitude in baseband in various ranges.
- channel state information for analog beamforming is reported as a long term I wideband.
- the channel state information for the digital beamforming has the same period as the analog beamforming state information or reports at a faster period.
- channel state information for digital beamforming may be reported as wideband or subband.
- the UE selects and reports a precoding weight for analog beamforming
- information on the weight of the analog beamforming is reported using a small amount of bit intermittently, but based on the reported weight, the precoding to be used for future transmission is reported.
- the robustness of reporting is important because it is determined, the method of using very low MCS as a method of robustly reporting the information of analog beamforming, and attaching CRC You can use this method to check for errors.
- a transmission resource it may be reported through an uplink control channel or may use part of an uplink data channel.
- the uplink control channel can be transmitted at a low coding rate to the QPSK modul at ion.
- the precoding weight of analog beamforming is coded and transmitted separately from other channel state information, feedbcak information such as Hybr id ARQ A / N, and information such as SRS request.
- a specific indi cator may be defined, which may be to indicat ion a value reflecting spatial information of a horzontal or verticacal domain.
- precoding weight information for analog beamforming is measured and reported by a terminal. This information may be reported through a part of an uplink control channel or an uplink data sharing channel.
- the channel state information for analog beamforming and the channel state information for digital beamforming are classified and reported according to the types of reporting information and the timing of reporting the information. For example, channel state information for analog beamforming is reported as long-term. On the other hand, channel state information for digital beamforming is reported as a short-term.
- the channel state information for analog beamforming may be obtained by a terminal report or by using a signal (eg, an SRS) transmitted upward.
- a signal eg, an SRS
- the precoding used for analog beamforming is applied for a longer period than the period for applying digital beamforming.
- channel state information for digital beamforming may be obtained by defining a channel formed by analog beamforming as an antenna port.
- the channel state information thus obtained is reported through an uplink control channel or an uplink data sharing channel.
- a synthesized channel formed by analog beamforming is defined as an antenna port, and a channel is measured by using a reference signal for the corresponding antenna port to perform digital beamforming. Calculate the CSI.
- Channel state information for digital beamforming is reported through an uplink control channel or an uplink data sharing channel.
- the measurement and reporting information of channel state information for performing digital beamforming depends on the beam pattern selected by analog beamforming . Is determined.
- the number of beams generated by analog beamforming may be variable, and even if N beams are generated, the synthesis channel is changed when the beamforming weight is changed.
- N beams are transmitted by analog beamforming
- channels of N antenna ports are measured for digital beamforming, and an element is selected and reported in Precoding Mat ix for N antenna ports.
- the precoding weight generated in analog beamforming is variable, multiple channels must be measured for digital beamforming.
- a plurality of reference signal transmission instructions (including antenna port number, frequency / time / code resource allocation information, etc.) message is indicated to the terminal.
- the number of antenna ports for measuring channels for digital beamforming is also variable.
- a plurality of reference signal transmission instructions (including antenna port number, frequency / time / code resource allocation information, etc.) message is indicated to the terminal.
- channel state measurement and reporting information for digital beamforming is determined according to a beamforming method of analog beamforming.
- the transmission request calculates a CSI for performing digital beamforming by measuring a channel from a reference signal corresponding to the antenna port.
- CSI feedback for digital beamforming is defined as a PUSCH / PUCCH repor ng mode.
- codebook for performing digital beamforming may be changed according to the beam pattern selected by analog beamforming.
- Hybr id beamforming is characterized by performing analog beamforming and digital beamforming at the same time.
- the radiation pattern generated by analog beamforming determines signal transmission coverage.
- a degree of freedom for adjusting the tilting angle of the antenna by analog beamforming is given. If the tilting angle is changed according to the distribution of users in Cel l, the system performance and energy efficiency can be improved.
- the UE measures the channel and reports it to the base station, and the base station can be divided into a method of determining based on the reported information and a method of determining and measuring the uplink signal by the base station.
- the terminal reports only one value of the RSRP measurement.
- the base station In a first method, the base station generates a plurality of analog beams, and the terminal measures and reports the synthesized channel generated by beamforming to the base station.
- the channel information to be measured by the UE is designated as an antenna port, and RSRP measurement is performed on a plurality of antenna ports.
- a plurality of RSRP information measured by the terminal is reported through the associated reporting channel.
- RSRP information may be reported together with antenna port information.
- it may be considered to report only some RSRP of the information measured by the terminal.
- the RSRP information and the related indicator are reported together.
- the antenna port index may be listed in order, and the method of turning on the bi t f lag of the corresponding antenna port selected in the bi t column may be used.
- channel information to be measured by the UE is designated as an antenna port, and RSRP measurement is performed on one antenna port.
- the unit for performing measurement can be defined as a time unit. For example, specify the time unit to be measured through the upper signal, and report the information measured in the time unit.
- a plurality of time units can be set. The measured information is reported in the order of reporting determined by time unit. If reported simultaneously, the order of the information can be specified. If reported from individual resources, it can be set per resource.
- the UE synthesizes a channel using a promised analog beamforming set, measures a synthesized channel, and reports the synthesized channel to a base station.
- the base station transmits an RS for an antenna element on which analog beamforming is not performed. Instructs the UE to perform a set of analog beamforming, and the UE combines the antenna element and the beamforming weight using the indicated set. do. RSRP measurement is performed based on the synthesized channel.
- the terminal may report all the measured channel information to the base station. Alternatively, only some set information preferred by the terminal may be reported in order to compress the information.
- the above-described methods may be performed according to the instructions of the base station or the capability of the terminal.
- the terminal reports its capacity to the base station.
- the base station may instruct the terminal having Capabi l ty to use the above-described reporting method.
- the terminal may perform a new measurement method according to the indicator of the base station.
- the third method relates to a method of measuring and determining by a base station. Specifically, the base station measures the channel state through the uplink signal and determines the weight of analog beamforming for downlink signal transmission.
- the base station may determine the weight for performing analog beamforming through the receiving end. This may be performed in various forms by a hardware structure or a signal processing method for uplink signal processing. When multiple terminals simultaneously transmit signals, signals and channels for various purposes are synthesized in the received signals. Among them, a reference signal for channel measurement is divided to perform channel measurement for uplink transmission.
- the analog beamforming weight is determined using a reference signal for data transmission.
- the reference signal for data transmission is characterized by performing digital domain beamforming.
- Various analog beamforming may be performed to find an optimal analog beamforming value.
- a reference signal for data transmission of a corresponding user is extracted from a plurality of analog beamformed signals.
- the channel state of the data transmission reference signal on which a plurality of analog beamforming is performed is measured, and an analog beamforming weight is selected based on the channel state.
- a weight for performing analog beamforming may be determined by collecting received signals for each antenna element in uplink.
- a reference signal for measuring a channel state of the terminal may be extracted from the received signal and used.
- An analog beamforming weight for downlink transmission is determined based on the selected analog beamforming weights through the above examples.
- the downlink transmission analog beamforming weight may change in units of time. Depending on the weight changing in time
- the downlink synthesis channel also changes, requiring an RSRP measurement method.
- the base station may designate a time unit for performing RSRP measurement to the terminal.
- a fourth embodiment according to the present invention relates to a method for compensating for phase difference between narrow bands.
- an unwanted beam is transmitted due to a phase difference between a high frequency and a low frequency in broadband transmission.
- the basic concept of analog beamforming is to adjust the phase of the signal in the desired direction by varying the time at which the signal is transmitted (or received) according to the direction in which the signal is transmitted (or received) based on the multiple antenna columns. . Since the sin wave changes in phase with time, the transmission (or reception) delay can be synonymous with the phase change in the signal. However, the phase change due to the transmission (or reception) delay depends on the frequency used for transmission (or reception). In the same delay situation, low frequencies produce less phase change, while high frequencies produce large phase changes.
- Analog beamforming has a feature of multiplying weights in an analog domain for transmission or reception of multiple antennas.
- the beamforming weights are equally used in the transmission band.
- the difference in phase change between the high frequency and the low frequency within the band is small, but when the transmission band is wide, the difference may occur greatly.
- the difference in phase change in the transmission band is small when the center frequency used for transmission is low, while the difference may occur when the center frequency is high.
- Hybr id beamforming is used in wideband transmission or high frequency band transmission.
- the existing Cel lular system (ex. LTE) is mainly designed to transmit at a maximum bandwidth of 20 MHz in the vicinity of the 2 GHz band. Is being considered.
- the basic principle of beamforming is to generate linear phase rotation between antennas so that transmit and receive signals have the same phase to achieve maximum gain when synthesized.
- the linear phase rotation value that must be applied between antennas varies from band to band.
- the linear phase value that is applied to the antennas differs from band to band.
- maximum gain is not achieved.
- the signal may be synthesized in a direction to attenuate the signal according to the amount of phase change.
- Beam di rect ion mi smatch by phase difference may appear more sensitive as the beam becomes sharper.
- Broad beams on the other hand, may be less sensitive to beam direct ion mismatch due to phase difference.
- Massive MIMO can produce extremely sharp beams by synthesizing energy using many antennas. Therefore, in Massive MIMO, it is sensitive to the beam direct ion mismatch caused by the phase difference method 1.
- phase difference occurs when the same phase rotation is applied to the broadband. In this case, the sharper the beam width, the higher the sensitivity. On the other hand, if the same phase is applied to the narrow band, less phase difference occurs, and the sensitivity of the phase di fference to the beam can be broadly lowered.
- an embodiment of the present invention proposes an antenna configuration method and a Precoder configuration and application method of the digital beamformer for this purpose.
- a broad beam is generated in an analog domain and a phase rotation is applied to a narrow band in a digit domain.
- the number of elements performing beamforming in the analog domain is reduced to generate a broad beam, thereby lowering the sensitivity to beam di rect ion change due to phase difference.
- phase difference occurring in the antenna elements is averaged in the synthesized channel. Digitized beamforming synthesized channels including the average phase difference is formed to form a sharp beam in a desired direction.
- Embodiment 4-2 relates to an antenna array structure. Specifically, antenna subgrouping is performed in a row or column having two or more antenna elements.
- Analog beamforming changes the phase and amplitude of the antenna element.
- Subgroups of the antenna elements may be configured, and analog beamforming may be performed for each subgroup.
- analog beamforming is performed using a small number of antenna elements. To this end, two or more antenna subgroups are configured.
- 26 illustrates an example of an antenna array structure according to the present invention.
- two subgroups may be obtained by forming a subgroup by combining five antenna elements.
- two beams having a beamwidth wider than the beamwidth generated using the ten antenna elements are generated.
- the beam generated in the subgroup is more robust against phase error than the beams of 10 antenna elements.
- FIG 27 shows another example of an antenna array structure according to the present invention.
- a fourth embodiment of the present invention relates to a method for compensating for the narrow band phase difference caused when analog beamforming is applied to a wide band.
- a method of applying a beamforming weight having the same phase change between weights applied to each element may be applied.
- W [WO Wl W2 W3 W4].
- W1 and W2 are as follows.
- Wl and W2 have the same phase change amount of precoding weight applied to each element as expj (a).
- W1 to W4 are as follows.
- W4 [expj ( ⁇ + ⁇ ) ex j ( ⁇ + ⁇ + a) expj ( ⁇ + ⁇ + 2 ⁇ ) expj ( ⁇ + ⁇ + 3 ⁇ ) expj (Y + ⁇ +4 a)]
- a fourth embodiment of the present invention describes performing digital beamforming on a narrow band basis.
- a new channel is formed through an analog beam.
- Phase difference between channels created in each subgroup may occur. Compensate for phase difference by using digital domain precoder. If the channel is severely changed, the channel correlation of the subgroup is low, or the transmission band is wide, the phase difference between the channels of the subgroup may be different for each narrow band.
- the digital beamformer corrects the phase between subgroups, and the digital domain precoding is performed in a narrow band. For example, it is assumed that a channel of Subband k generated by analog beamforming of Subgroup n is called Ch n (k), and that the phase of Ch n (k) is z—Ch n (k).
- the channel of each antenna element may be approximated by a linear phase change. If the difference in phase shift between the antenna elements in the subband 1 and 2 channels is 2 ⁇ , the subband 1 and 2 channels may be expressed as follows.
- [344] H (l) x [l exp j ( ⁇ - ⁇ ) expj (2 a-2 6) ex j (3 a -3 ⁇ ) expj (4 a -4 ⁇ ) expj (5 a -5 ⁇ ) expj (6 a -6 ⁇ ) expj (7 a -7 ⁇ ) expj (8 a -8 ⁇ ) expj (9 a -9 ⁇ )]
- [346] H (2) x [l expj (a + ⁇ ) expj (2 a +2 ⁇ ) expj (3 a +3 ⁇ ) expj (4 a +4 ⁇ ) expj (5 a +5 ⁇ ) expj (6 a +6 ⁇ ) expj (7 a +7 ⁇ ) expj (8 a +8 ⁇ ) expj (9 a +9 ⁇ )]
- a fourth exemplary embodiment of the present invention is a method for channel state reporting for supporting digital beamforming.
- channel state information In order to support downlink digital beamforming, channel state information should be reported.
- Channel status information can be reported directly using the Impl i feedback method (eg Rank Indicat ion I Precoding Matix ix Indicat ion I Channel Qual Inty cat ion, etc.) that reports the value converted into the promised Index.
- Impl i feedback method eg Rank Indicat ion I Precoding Matix ix Indicat ion I Channel Qual Inty cat ion, etc.
- Expl i ci t feedback method In both cases, channel information measured in narrowband is reported to the base station. In this case, it means channel state information estimated based on channel information synthesized by analog beamforming for each subgroup.
- the UE may find and report a weight suitable for beamforming by measuring channel states of antenna elements of a subgroup.
- the beamforming weight to be applied to the subgroup is reported to the base station.
- the beamforming weight is assumed to be commonly applied to the transmission bandwidth, and then selected and reported.
- a fifth embodiment of the present invention relates to a training sequence transmission method for analog BF in Hybr id BF.
- the base station In order to form downlink, the base station should acquire downlink channel information. As a method for this, the base station measures (1) the downlink channel measured by the terminal and reports (2) the uplink channel measured by the base station for downlink transmission. How to use can be used.
- An embodiment of the present invention describes a reference signal transmission method and a physical signal structure for the UE to measure a downlink channel in downlink Hybr id beamforming.
- a reference signal of the digital configuration method is designed to obtain channel information of each antenna port by allocating orthogonal resources (frequency, time, code, etc.) between antenna ports.
- the reference signal defined as the antenna port is not suitable for classifying and estimating channels of the antenna elements.
- N antenna ports are N When mapped to TRX and each TRX is transmitted through M antenna elements, orthogonal resources allocated for one antenna port are transmitted through M antenna elements, and signals of M antenna elements are synthesized at a receiving end. It is received as a signal of one antenna port.
- a transmission method of a downlink reference signal according to the present invention is described as follows.
- An antenna element specifi c resource is allocated as a first method of transmitting reference signals for antenna elements in a digit domain. This method can apply the same time transmission or different time transmission. At this time, the phase of the reference signal for the antenna element may be reversed in consideration of analog beam forming.
- a beam speci f i c resource may be allocated.
- a reference signal generator may generate a reference signal sequence and synthesize the reference signal sequence with the signal generated by the TRX. 28 is an example of a reference signal generator structure according to an embodiment of the present invention.
- a resource (n X M) classified for each antenna element may be used.
- a resource M for classifying M elements may be used.
- a reference signal may be synthesized and transmitted using antenna switching.
- a channel of each antenna element can be estimated.
- a training sequence for each antenna element is transmitted.
- the physical structure uses a block to generate a reference signal that is distinct from the signal transmitted from the TRX.
- the sequence indicates a sequence orthogonal between antenna elements.
- it can be divided into frequency resources / code resources.
- the sequence can be transmitted simultaneously with the data signal.
- the antenna port refers to a signal synthesized by analog beamforming
- the antenna element refers to a unit for performing analog beamforming.
- channel measurement of antenna elements is required.
- various methods of transmitting a reference signal may be considered.
- Reference signals for the antenna element may be transmitted in the digital domain or in the analog domain.
- the fifth embodiment of the present invention relates to a method in which analog beamforming is not performed while a reference signal is transmitted when a reference signal is transmitted in a digital domain.
- a specific resource is allocated to each antenna element.
- the resource means time, frequency, code, and the like.
- the reference signal may be transmitted at different times for each antenna element.
- the time is at least an OFDM symbol durat ion.
- a reference signal for one antenna element is transmitted during one OFDM symbol durat ion, and a reference signal for another antenna element is transmitted at the next Durat ion.
- a signal branched to each antenna element is a signal generated in one TRX. If each element transmits the same signal at the same time, it is difficult for the receiving end to obtain a reference signal corresponding to each antenna element.
- the antenna turn on / of f method may be applied as a method of transmitting reference signals by time for each antenna element. For example, by lowering the gain of the power ampl if ier in the antenna element, the signal transmitted from the antenna element may be raised or lowered. At a certain point in time, the PA of a specific antenna element is increased and the PA of other antenna elements is lowered. This operation is performed in turn for each antenna element. Even if the same reference signal is transmitted from each antenna element, the antenna signal is turned on and off so that the reference signal is transmitted only from one antenna.
- time orthogonal reference signal resources may be allocated among antenna elements included in the antenna subgroup, and frequency orthogonal or code resources may be allocated between antenna elements between antenna subgroups.
- antenna element transmission is distinguished by time since the same reference signal is transmitted to each antenna element.
- different reference signals can be transmitted. Therefore, subgroups can be allocated by transmitting reference signals with different frequency orthogonal or code resources. In addition, the reference signal may be transmitted by using different time resources.
- a fifth embodiment of the present invention relates to a method for transmitting an analog beamformed reference signal when a reference signal is transmitted in a digital domain. For this purpose, a specific resource is allocated to each analog beam.
- the transmission of a reference signal on which analog beamforming has been performed means that a reference signal for distinguishing a set with respect to a possible analog beamforming weight set is allocated.
- a structure capable of independently allocating resources for each beamforming execution unit may be introduced to allocate a reference signal for distinguishing beamforming. Compared to a complexi ty for measuring precoding weight for performing analog beamforming by measuring channels for each antenna element, there is an advantage of having a significantly lower complexi ty.
- a fifth embodiment of the present invention relates to a method of transmitting a reference signal for an antenna element in an analog domain.
- a reference signal sequence is generated and synthesized with the signal generated by the TRX.
- the reference signal may be allocated to a specific resource for each antenna element. For example, when allocating resources orthogonal to time, independent time resources are used for each antenna element. In this case, the length of the time resource may be designed to have a length smaller than one OFDM symbol.
- a code resource may be allocated. Use different code resources for each antenna element It is possible to distinguish each antenna channel. In the case of using the ZC sequence, signals can be distinguished by using different cyc lic shi ft values.
- N * M resources divided by antenna elements may be used. If a reference signal is used for distinguishing signals of each antenna element in the TRX, a method of sharing antenna element resources among the TRXs and independently assigning antenna element resources in the TRX may be used.
- a training sequence allocated to each antenna element may be transmitted.
- orthogonal resources separated in time for each antenna element may be allocated. In such a case, a very long time may be required for channel estimation of corresponding antenna elements for performing analog beamforming.
- the training sequence is transmitted at a time different from the time when the signals for data transmission are transmitted due to the nature of the analog signal, the time for data transmission is shortened and system performance may be degraded.
- the training sequence when transmitting a training sequence in the analog domain, may be transmitted while maintaining a data rate.
- a training sequence for analog beamforming and an existing signal may be synthesized and transmitted in an analog domain.
- the two signals are combined to overlap, and the synthesized signals are transmitted simultaneously.
- Training sequences or existing signals are transmitted repeatedly, each covered by an orthogonal code.
- h_n (t) means channel impulse response at time t.
- s_k (t) denotes a training sequence transmitted through the k-th antenna element, and r—k (t) denotes an existing signal transmitted through the k-th antenna element.
- t + N the channel and the received signal are represented by t + N.
- a signal of one OFDM symbol may be repeated over two OFDM symbol intervals.
- a signal may be repeatedly transmitted in one OFDM symbol period.
- the repetitive synthesis of the signal in the analog domain can be determined in conjunction with the period of generating and repeating the signal in the digital domain.
- the synthesized and transmitted signal may be restored to a desired signal through a simple sum / difference.
- Y (t) + y (t + N) h_k (t) ® (s_k (t) + r (t) + s_k (t) -r_k (t)) + n (t) + n (t + N)
- signals of each antenna element may be distinguished using orthogonality of time orthogonal resources or code resources.
- a sixth embodiment of the present invention relates to an uplink reference signal for hybrid beamforming.
- a training sequence for selecting a weight vector for performing downlink beamforming for multiple users in the UL is transmitted.
- the feature of uplink received analog beamforming is that the base station selects an appropriate beamforming device for performing analog beamforming from the received signal. To this end, the base station needs a function of selecting an analog beamforming weight.
- the analog beamforming weight selector selects an appropriate beamforming vector by applying a beamforming weight vector for performing signal word 1 analog beamforming received from each antenna element.
- the base station may use the signals transmitted from the terminal, PRACH, SRS, DMRS, PUSCH, PUCCH, etc. may be candidates. It is preferable to select a precoding weight using a signal after t iming and frequency synchronizat ion of the transmission signal are performed. This is because t iming / Frequency synchronizat ion influences the precoding weight selection. Therefore, it is not preferable to use PRACH.
- SRS may be used as a first example that is easy to apply.
- the SRS is used as information for MCS for uplink transmission, transmission precoding determination, and band allocation by acquiring channel state information of the UE. It is also used as information for determining downlink transmission precoding.
- Channel information is obtained from the SRS to perform digital beam forming.
- a channel estimated through the SRS is obtained by signal processing of the digit domain.
- the existing SRS is transmitted through one OFDM symbol, and allocates frequency and code resources in one OFDM symbol to obtain a multi-user channel and a single-user multi-antenna channel.
- the frequency resources are divided into clusters (groups of contiguous subcarriers), and then re-allocated into inter leaved (odd or even subcarriers) in clustered frequency resources.
- clusters groups of contiguous subcarriers
- inter leaved odd or even subcarriers
- Analog beamforming plays a role of collecting or lowering energy of a signal transmitted or received in a specific direction by using transmission or reception weights to the antenna element.
- the weight may be selected based on channel state information. All.
- the channel state information may be measured at the receiver and may be used for reception beamforming and transmission beamforming.
- channel state information may be obtained from an uplink signal transmitted by the terminal, and a weight for reception may be calculated. This weight can be used as the transmission beamforming weight after proper calibrat ion. Multi-user interference is an important problem in acquiring channel state information through uplink signals transmitted by the terminal.
- channel state information is obtained by training a signal at an analog stage.
- the analog signal is characterized in that it is processed in the time domain.
- the multi-user signals are distinguished by the orthogonality of the transmission sequence.
- users performing digital beamforming in a system based on 0FDMA or SC-FDMA are able to accommodate a relatively large number of users because they are allocated resources for frequency domain.
- the resource in the time domain may be divided and transmitted as an uplink reference signal.
- the capacity of the multi-user classification is assumed to be N.
- N the capacity of the multi-user classification
- the signal distortion occurs due to the mult i-path of the spatial channel. Therefore, the guard guard should be set appropriately even if the signal cycle is short.
- the divided time resources when dividing a plurality of time resources in an existing OFDM symbol durat ion, may also have a structure having guard time.
- the eighth-first embodiment of the present invention relates to a method of dividing a plurality of time resources by designing a Durat ion shorter than an OFDM symbol durat ion.
- the symbol durat ion consists of (Nf ft + Ncp) samples
- the short OFDM symbol durat ion can consist of (Nfft + Ncp) / M samples. Or (Nfft / M) + (Ncp) 'smaple. That is, a signal having a durat ion of about Nf ft / M is generated and a short period of OFDM symb having a sample of Ncp / M or (Ncp) 'is formed.
- the sampling frequency is the same as that of the existing OFDM symbol (to equal the sampling time), and the subcarrier spacing is increased by M times.
- the UE increases the subcarrier spacing and generates an uplink reference signal by setting the same Samp 1 ing frequency, and converts the generated reference signal into an analog signal by DAC converting and transmits the RF signal by calling RF. .
- a sixth embodiment of the present invention is a method of designing a signal having a short period of OFDM symbol durat ion to have a short period of CP.
- the CP length is preferably based on the CP length applied to the existing OFDM symbol.
- the plurality of short OFDM symbols is one existing OFDM symbol period.
- 29 shows an example in which a plurality of short OFDM symbols are longer than one conventional OFDM symbol period.
- Embodiment 6-3 proposes a method of transmitting an OFDM symbol so that it overlaps.
- M signals having a short OFDM symbol period each is assigned to different users.
- 30 shows an example of a method of transmitting so that OFDM symbols overlap.
- the preceding short period OFDM symbol is assigned to user A and the subsequent short period OFDM symb is assigned to user B.
- User A transmits a short of dm symbol according to the existing OFDM symbol transmission time
- user B transmits a short OFDM symbol slightly earlier than the conventional OFDM symbol transmission time.
- the short OFDM symbol transmitted by user A will be received in accordance with the start time when the existing OFDM symbols are received, and the short period OFDM symbol transmitted by user B will be received according to the last time received in the existing OFDM symbol. .
- the base station can appropriately set the time window to minimize the interference between symbols.
- a training sequence for performing analog BF is composed of a short period of OFDM symbol.
- a sequence mapped to each subcarrier may use a sequence (eg, a ZC sequence) having similar correlat ion characteristics in frequency and time. Signals made by mapping such sequences are advantageous in performing de-spreading in the time domain because the frequency and time domain characteristics are similar.
- the embodiment 6-5 relates to a method of transmitting a reference signal or training sequence for analog beamforming at a time different from a time interval in which an existing signal is transmitted.
- the time for transmitting the training sequence may be performed according to the indicator given to the terminal by the base station.
- the base station transmits the training sequence that the terminals should transmit.
- the indicator can be distinguished from the transmission signal of another signal.
- the training sequence is set to be transmitted separately from the existing SRS transmission cycle.
- the terminal does not simultaneously transmit other signals at the time of transmitting the training sequence. For example, when a data signal or a RACH black control channel is to be transmitted at the time when the training sequence is transmitted, priority is given to the transmission of the training sequence.
- a sixth embodiment of the present invention relates to a method for performing analog beamforming by dividing a multi-user signal in a digital domain.
- a block capable of purely extracting a signal from an antenna element and designing a block for digital processing is estimated and estimated for each antenna element.
- Weight is determined to perform analog beamforming based on the channel.
- the terminal transmits a reference signal according to the instruction of the base station.
- the base station makes a signal received from each antenna element into a digital signal and extracts a reference signal from the generated digital signal. Analog beamforming is performed based on the channel state of each antenna element obtained from the reference signal.
- Such a block is distinguished from a block for data demodulat ion.
- Data demodulat ion performs demodulat ion based on a signal obtained after performing analog beamforming, while a block for obtaining channel state information processes a signal based on signals extracted directly from an antenna element.
- weights for performing analog beamforming are determined by collecting reference signals on which analog beamforming is performed.
- a reference signal is extracted from the signals for which the analog beamforming is performed.
- Signals transmitted from single users are subjected to multiple analog beamforming, and reference signals of the corresponding users are extracted from the multiple analog beamfogging signals.
- Signal strengths of the extracted reference signals are measured to compare signal strengths according to analog beamforming values. By comparing the signal strength, the appropriate analog beamforming weight is monitored. Try to select analog beamforming weight for many users in the same way And stores the selected beamforming weight value. Group users who have selected the same weight and use it when receiving and transmitting data.
- Figure 31 illustrates a base station and a terminal that can be applied to an embodiment of the present invention.
- the relay When the relay is included in the wireless communication system, communication is performed between the base station and the relay in the backhaul link, and communication is performed between the relay and the terminal in the access link. Therefore, the base station or the terminal illustrated in the figure may be replaced with a relay according to the situation.
- a wireless communication system includes a base station 3110 and a terminal 3120.
- Base station 3110 includes a processor 3113, a memory 3114, and a Radio Frequency (RF) unit 3111, 3112.
- the processor 3113 may be configured to implement the procedures and / or methods proposed in the present invention.
- the memory 3114 is connected with the processor 3113 and stores various information related to the operation of the processor 3113.
- the RF unit 3116 is connected with the processor 3113 and transmits and / or receives a radio signal.
- the terminal 3120 includes a processor 3123, a memory 3124, and an RF unit 3121, 1422. Processor 3123 may be configured to implement the procedures and / or methods proposed in the present invention.
- the memory 3124 is connected with the processor 3123 and stores various information related to the operation of the processor 3123.
- the RF units 3121 and 3122 are connected to the processor 3123 and transmit and / or receive radio signals.
- the base station 3110 and / or the terminal 3120 may have a single antenna or multiple antennas.
- a specific operation described as performed by a base station may be performed by an upper node in some cases. That is, in a network consisting of a plurality of network nodes including a base station for communication with the terminal Obviously, the various operations performed may be performed by a base station or other network nodes other than the base station.
- a base station may be replaced by terms such as fixed station, Node B, eNodeB (eNB), access point, and the like.
- an embodiment according to the present invention may be implemented by various means, for example, hardware, firmware, software, or a combination thereof.
- an embodiment of the present invention may include one or more ASICs, pp icat ion speci f ic integrated circuits, DSPs (digi tal signal processors), DSPDs (digi tal signal processing devices), PLDs (programmable). logic devices, FPGAs programmable gate arrays, processors, controllers, microcontrollers, microprocessors, and so on.
- an embodiment of the present invention may be implemented in the form of modules, procedures, functions, etc. that perform the functions or operations described above.
- the software code may be stored in a memory unit and driven by a processor.
- the memory unit may be located inside or outside the processor, and may exchange data with the processor by various known means.
- the present invention can be used in a wireless communication device such as a terminal, a relay, a base station, and the like.
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KR1020167006604A KR102290759B1 (ko) | 2013-11-04 | 2014-11-04 | 무선통신 시스템에서 신호를 전송하는 방법 및 장치 |
US15/029,194 US10084521B2 (en) | 2013-11-04 | 2014-11-04 | Method and apparatus for transmitting signal in wireless communication system |
JP2016522771A JP6673824B2 (ja) | 2013-11-04 | 2014-11-04 | 無線通信システムにおいて信号を送信する方法及び装置 |
EP14858304.0A EP3068060A4 (en) | 2013-11-04 | 2014-11-04 | Method and apparatus for transmitting signal in wireless communication system |
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- 2014-11-04 US US15/032,036 patent/US20160261325A1/en not_active Abandoned
- 2014-11-04 KR KR1020167006604A patent/KR102290759B1/ko active IP Right Grant
- 2014-11-04 US US15/029,194 patent/US10084521B2/en active Active
- 2014-11-04 EP EP14858304.0A patent/EP3068060A4/en not_active Withdrawn
- 2014-11-04 WO PCT/KR2014/010515 patent/WO2015065155A1/ko active Application Filing
- 2014-11-04 WO PCT/KR2014/010519 patent/WO2015065158A1/ko active Application Filing
- 2014-11-04 JP JP2016522771A patent/JP6673824B2/ja active Active
- 2014-11-04 CN CN201480060402.9A patent/CN105684323B/zh active Active
- 2014-11-04 WO PCT/KR2014/010517 patent/WO2015065157A1/ko active Application Filing
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US10644781B2 (en) | 2015-12-28 | 2020-05-05 | China Academy Of Telecommunications Technology | Analog channel measurement method and base station |
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WO2017194028A1 (zh) * | 2016-05-13 | 2017-11-16 | 中兴通讯股份有限公司 | 信道状态信息的测量方法及装置 |
Also Published As
Publication number | Publication date |
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JP6673824B2 (ja) | 2020-04-01 |
EP3068060A1 (en) | 2016-09-14 |
CN105684323B (zh) | 2020-02-07 |
WO2015065155A1 (ko) | 2015-05-07 |
WO2015065156A1 (ko) | 2015-05-07 |
JP2016539541A (ja) | 2016-12-15 |
WO2015065152A1 (ko) | 2015-05-07 |
US20160261325A1 (en) | 2016-09-08 |
US20160241323A1 (en) | 2016-08-18 |
KR102290759B1 (ko) | 2021-08-18 |
US10084521B2 (en) | 2018-09-25 |
CN105684323A (zh) | 2016-06-15 |
WO2015065158A1 (ko) | 2015-05-07 |
WO2015065157A1 (ko) | 2015-05-07 |
KR20160082235A (ko) | 2016-07-08 |
EP3068060A4 (en) | 2017-11-01 |
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