KR20100086431A - Method for transmitting reference signal in transmitter using multiple antennas - Google Patents

Abstract

PURPOSE: A method for transmitting a reference signal in a transmitter using a multi-antenna is provided to reduce the overhead caused by reference signals corresponding to each antenna and adaptively transmit the reference signals according to the performance of the terminal. CONSTITUTION: Control information for uplink transmission is received(S101), and the reference signals of each antenna is generated from the control information. The generated reference signals are transmitted(S103), and are arranged in different symbols in each slot of a subframe used in the upper link transmission. For the reference signals arranged at each symbol, a CDM(Code Division Multiplexing) is performed as the different sequences.

Description

Method for transmitting reference signal in transmitter using multiple antennas}

The present invention relates to wireless communication, and more particularly, to a method of transmitting a reference signal in a transmitter using multiple antennas.

Recently, multiple input multiple output (MIMO) systems have attracted attention in order to maximize performance and communication capacity of a wireless communication system. MIMO technology is a method that can improve the transmission and reception data transmission efficiency by adopting multiple transmission antennas and multiple reception antennas, away from the use of one transmission antenna and one reception antenna. The MIMO system is also called a multiple antenna system. MIMO technology is an application of a technique of gathering and completing fragmented pieces of data received from multiple antennas without relying on a single antenna path to receive one entire message. As a result, it is possible to improve the data transfer rate in a specific range or increase the system range for a specific data transfer rate.

MIMO techniques include transmit diversity (TxD), spatial multiplexing (SM), beamforming, and the like. Transmit diversity is a technique of increasing transmission reliability by transmitting the same data in multiple transmit antennas. Spatial multiplexing is a technology that allows high-speed data transmission without increasing the bandwidth of the system by simultaneously transmitting different data from multiple transmit antennas. Beamforming is used to increase the signal to interference plus noise ratio (SINR) of a signal by applying weights according to channel conditions in multiple antennas. In this case, the weight may be represented by a weight vector or a weight matrix, which is referred to as a precoding vector or a precoding matrix.

Spatial multiplexing includes spatial multiplexing for a single user and spatial multiplexing for multiple users. Spatial multiplexing for a single user is also referred to as Single User MIMO (SU-MIMO), and spatial multiplexing for multiple users is called SDMA (Spatial Division Multiple Access) or MU-MIMO (MU-MIMO). The capacity of the MIMO channel increases in proportion to the number of antennas. The MIMO channel can be broken down into independent channels. When the number of transmitting antennas is Nt and the number of receiving antennas is Nr, the number Ni of independent channels is Ni ≦ min {Nt, Nr}. Each independent channel may be referred to as a spatial layer. The rank may be defined as the number of non-zero eigenvalues of the MIMO channel matrix and the number of transmittable streams that can be multiplexed.

MIMO can be divided into a Peruvian MIMO and an Open Loop MIMO. The method of using precoding weight similar to the channel according to the channel situation is called closed-loop MIMO method, and the method of using precoding weight according to a certain rule regardless of the channel condition is open-loop. It is called MIMO method.

In a wireless communication system, it is necessary to estimate an uplink channel or a downlink channel for data transmission / reception, system synchronization acquisition, channel information feedback, and the like. Channel estimation refers to a process of restoring a transmission signal by compensating for distortion of a signal caused by a sudden environmental change due to fading. In general, a reference signal known to both the transmitter and the receiver is required for channel estimation.

In general, multiple antenna systems require as many reference signals as the number of transmit antennas. As a method for reducing the overhead of a conventional reference signal, a method of varying the amount of frequency / time resources to which a reference signal is allocated according to a rank in a multi-antenna system has been proposed. The conventional rank dependant reference signal has a pattern of TDM / FDM. However, as the rank increases, the overhead of the reference signal increases linearly. Overhead due to the reference signal may be defined as the ratio of the number of subcarriers transmitting the reference signal to the total number of subcarriers in the frequency domain. In the time domain, it may be defined as the ratio of the number of OFDM symbols (or SC-FDMA symbols) for transmitting a reference signal to the total number of OFDM symbols (or SC-FDMA symbols). As the overhead caused by the reference signal increases, the number of data subcarriers or OFDM symbols for transmitting actual data may be reduced, thereby reducing data throughput and decreasing spectrum efficiency of the wireless communication system.

There is a need for an efficient reference signal transmission method in a transmitter using multiple antennas.

An object of the present invention is to provide a method for efficiently transmitting a reference signal in a transmitter using multiple antennas.

In a transmitter using a multi-antenna, a method of transmitting a reference signal includes receiving control information for uplink transmission; And generating and transmitting a reference signal of each antenna from the control information, wherein the reference signal is arranged in different symbols in each slot of a subframe used for the uplink transmission and is arranged in each symbol. The reference signal is characterized in that the CDM in a different sequence.

In a multi-antenna system, overhead due to a reference signal corresponding to each antenna can be reduced, and the reference signal can be adaptively transmitted according to the performance of the terminal.

1 is a block diagram illustrating a wireless communication system.
2 shows a structure of a radio frame.
3 shows a resource grid for one downlink slot.
4 shows a structure of a downlink subframe.
5 is an exemplary diagram illustrating a resource grid for one uplink slot.
6 shows a structure of an uplink subframe.
7 is an exemplary diagram illustrating transmission of uplink data and DMRS.
8 shows an example of a transmitter for transmitting a precoded reference signal.
9 shows an example of a transmitter for transmitting a non-precoded reference signal.
10 shows a reference signal transmission method according to an embodiment of the present invention.
11 shows an example of radio resource allocation in transmission of a reference signal of a conventional CDM scheme.
12 shows resource allocation for a reference signal of the CDM / TDM scheme according to the first embodiment of the present invention.
13 shows resource allocation of a reference signal of a CDM / TDM scheme according to a second embodiment of the present invention.
14 shows resource allocation of a reference signal of a CDM / TDM scheme according to a third embodiment of the present invention.
15 shows resource allocation of a reference signal of a CDM / TDM scheme according to a fourth embodiment of the present invention.
16 shows resource allocation of a reference signal of a CDM / TDM scheme according to a fifth embodiment of the present invention.
17 shows resource allocation of a reference signal of a CDM / TDM scheme according to a sixth embodiment of the present invention.

1 is a block diagram illustrating a wireless communication system. This may be a network structure of an Evolved-Universal Mobile Telecommunications System (E-UMTS). The E-UMTS system may be referred to as a Long Term Evolution (LTE) system. Wireless communication systems are widely deployed to provide various communication services such as voice, packet data, and the like.

Referring to FIG. 1, an Evolved-UMTS Terrestrial Radio Access Network (E-UTRAN) includes a base station (BS) 20 that provides a control plane and a user plane.

The UE 10 may be fixed or mobile and may be called by other terms such as a mobile station (MS), a user terminal (UT), a subscriber station (SS), a wireless device, and the like. The base station 20 generally refers to a fixed station communicating with the terminal 10, and may be referred to as other terms such as an evolved-NodeB (eNB), a base transceiver system (BTS), and an access point. have. One base station 20 may provide a service for at least one cell. The cell is an area where the base station 20 provides a communication service. An interface for transmitting user traffic or control traffic may be used between the base stations 20. Hereinafter, downlink means transmission from the base station 20 to the terminal 10, and uplink means transmission from the terminal 10 to the base station 20.

The base stations 20 may be connected to each other through an X2 interface. The base station 20 is connected to an Evolved Packet Core (EPC), more specifically, a Mobility Management Entity (MME) / Serving Gateway (S-GW) 30 through an S1 interface. The S1 interface supports a many-to-many-relation between base station 20 and MME / S-GW 30.

Layers of the radio interface protocol between the terminal and the network are based on the lower three layers of the Open System Interconnection (OSI) model, which is well known in communication systems. It may be divided into a second layer L2 and a third layer L3. The first layer is a physical layer (PHY) layer. The second layer may be divided into a medium access control (MAC) layer, a radio link control (RLC) layer, and a packet data convergence protocol (PDCP) layer. The third layer is a Radio Resource Control (RRC) layer.

The wireless communication system may be an Orthogonal Frequency Division Multiplexing (OFDM) / Orthogonal Frequency Division Multiple Access (OFDMA) based system. OFDM uses multiple orthogonal subcarriers. OFDM uses orthogonality between inverse fast fourier transforms (IFFTs) and fast fourier transforms (FFTs). The transmitter performs IFFT on the data and transmits it. The receiver recovers the original data by performing an FFT on the received signal. The transmitter uses an IFFT to combine multiple subcarriers, and the receiver uses a corresponding FFT to separate multiple subcarriers.

The wireless communication system may be a multiple antenna system. The multiple antenna system may be a multiple-input multiple-output (MIMO) system. Alternatively, the multi-antenna system may be a multiple-input single-output (MISO) system or a single-input single-output (SISO) system or a single-input multiple-output (SIMO) system. May be a system. The MIMO system uses multiple transmit antennas and multiple receive antennas. The MISO system uses multiple transmit antennas and one receive antenna. The SISO system uses one transmit antenna and one receive antenna. The SIMO system uses one transmit antenna and multiple receive antennas.

Techniques using multiple antennas in multi-antenna systems include space-time coding (STC) such as Space Frequency Block Code (SFBC), Space Time Block Code (STBC), Cyclic Delay Diversity (CDD), and frequency switched (FSTD) in rank 1. transmit diversity), time switched transmit diversity (TSTD), or the like may be used. In Rank 2 or higher, spatial multiplexing (SM), Generalized Cyclic Delay Diversity (GCDD), Selective Virtual Antenna Permutation (S-VAP), and the like may be used. SFBC is a technique that efficiently applies selectivity in the spatial domain and frequency domain to secure both diversity gain and multi-user scheduling gain in the corresponding dimension. STBC is a technique for applying selectivity in the space domain and the time domain. FSTD is a technique for dividing a signal transmitted through multiple antennas by frequency, and TSTD is a technique for dividing a signal transmitted through multiple antennas by time. Spatial multiplexing is a technique to increase the data rate by transmitting different data for each antenna. GCDD is a technique for applying selectivity in the time domain and the frequency domain. S-VAP is a technique using a single precoding matrix. Multi-codeword (MCW) S, which mixes multiple codewords between antennas in spatial diversity or spatial multiplexing, and Single Codeword (SCW) S using single codeword. There is a VAP.

2 shows a structure of a radio frame.

Referring to FIG. 2, a radio frame may consist of 10 subframes, and one subframe may consist of two slots. Slots in a radio frame are numbered slots 0 through 19. The time taken for one subframe to be transmitted is called a transmission time interval (TTI). TTI may be referred to as a scheduling unit for data transmission. For example, one radio frame may have a length of 10 ms, one subframe may have a length of 1 ms, and one slot may have a length of 0.5 ms.

The structure of the radio frame is only an example, and the number of subframes included in the radio frame or the number of slots included in the subframe may be variously changed.

3 shows a resource grid for one downlink slot.

Referring to FIG. 3, the downlink slot includes a plurality of OFDM symbols in a time domain and includes N ^DL resource blocks (RBs) in a frequency domain. The number N ^DL of resource blocks included in the downlink slot depends on the downlink transmission bandwidth set in the cell. For example, in the LTE system, N ^DL may be any one of 60 to 110. One resource block includes a plurality of subcarriers in the frequency domain.

Each element on the resource grid is called a resource element. Resource elements on the resource grid may be identified by an index pair (k, l) in the slot. Where k (k = 0, ..., N ^DL x 12-1) is the subcarrier index in the frequency domain, and l (l = 0, ..., 6) is the OFDM symbol index in the time domain.

Here, an example of one resource block includes 7 × 12 resource elements including 7 OFDM symbols in the time domain and 12 subcarriers in the frequency domain, but the number of OFDM symbols and the number of subcarriers in the resource block is equal to this. It is not limited. The number of OFDM symbols and the number of subcarriers can be variously changed according to the length of a cyclic prefix (CP), frequency spacing, and the like. For example, the number of OFDM symbols is 7 for a normal CP and the number of OFDM symbols is 6 for an extended CP. The number of subcarriers in one OFDM symbol may be one of 128, 256, 512, 1024, 1536, and 2048.

4 shows a structure of a downlink subframe.

Referring to FIG. 4, the downlink subframe includes two consecutive slots. In the downlink subframe, the first 3 OFDM symbols of the first slot are a control region to which a PDCCH is allocated and the remaining OFDM symbols are a data region to which a PDSCH is allocated. In addition to the PDCCH, the control region may be allocated a control channel such as PCFICH and PHICH. The UE may read the data information transmitted through the PDSCH by decoding the control information transmitted through the PDCCH. Here, the control region includes only 3 OFDM symbols, and the control region may include 2 OFDM symbols or 1 OFDM symbol. The number of OFDM symbols included in the control region in the subframe can be known through the PCFICH.

Control information transmitted through the PDCCH is referred to as downlink control information (DCI). DCI includes uplink scheduling information, downlink scheduling information, system information, system information, uplink power control command, control information for paging, control information for indicating a random access response, etc. It includes.

The DCI format includes format 0 for PUSCH scheduling, format 1 for scheduling one physical downlink shared channel (PDSCH) codeword, and format 1A for compact scheduling of one PDSCH codeword. Format 1B for simple scheduling of rank-1 transmission of a single codeword in spatial multiplexing mode, format 1C for very simple scheduling of downlink shared channel (DL-SCH), format for PDSCH scheduling in multi-user spatial multiplexing mode 1D, format 2 for PDSCH scheduling in closed-loop spatial multiplexing mode, format 2A for PDSCH scheduling in open-loop spatial multiplexing mode, TPC of 2-bit power regulation for PUCCH and PUSCH Transmission power control) format 3, and format 3A for transmission of 1-bit power control TPC commands for PUCCH and PUSCH.

5 is an exemplary diagram illustrating a resource grid for one uplink slot.

Referring to FIG. 5, an uplink slot includes a plurality of SC-FDMA or OFDM A symbols in a time domain and includes a plurality of resource blocks (RBs) in a frequency domain. Here, one uplink slot includes 7 SC-FDMA symbols, and one resource block includes 12 subcarriers as an example, but is not limited thereto. The number N ^UL of resource blocks included in an uplink slot depends on an uplink transmission bandwidth set in a cell.

6 shows a structure of an uplink subframe.

Referring to FIG. 6, the uplink subframe is allocated a control region in which a physical uplink control channel (PUCCH) carrying uplink control information is allocated in a frequency domain and a physical uplink shared channel (PUSCH) carrying user data. It can be divided into data areas. The PUCCH for one UE is allocated to a resource block (RB) pair (51, 52) in a subframe, and the RBs 51 and 52 belonging to the RB pair occupy different subcarriers in each of two slots. do. This is said that the RB pair allocated to the PUCCH is frequency hopping at the slot boundary.

7 is an exemplary diagram illustrating transmission of uplink data and DMRS. Referring to FIG. 7, the UE monitors the PDCCH in a downlink subframe and receives DCI format 0 601, which is an uplink resource allocation, on the PDCCH. The uplink data and the DMRS 602 are transmitted on the PUSCH configured based on the uplink resource allocation. Demodulation reference signal (DMRS) will be described later. That is, the UE receives an uplink scheduling message (uplink resource allocation information, for example, DCI format information, etc.) in a downlink subframe, and then, in accordance with the uplink scheduling message, uplink data and Send DMRS.

Now, a method of transmitting a reference signal in a transmitter using multiple antennas will be described.

The reference signal may be classified into a common reference signal (CRS) or a sounding reference signal (SRS) used for CQI measurement, a precoding matrix selection, and a rank selection, and a demodulation reference signal (DRMS) used for demodulation of data. The CRS is a reference signal transmitted from the base station to the terminal and used to determine the state of the channel and is transmitted over the entire band. The CRS may be referred to as a cell-specific RS in that it is a reference signal transmitted to all UEs in a cell.

The SRS is a reference signal transmitted by the terminal to the base station and may be transmitted over the entire band to determine the state of the uplink channel. The base station estimates an uplink channel through the received SRS, and uses the estimated uplink channel for uplink scheduling. SRS is not combined with transmission of PUSCH or PUCCH.

DMRS is a reference signal used for demodulation of data transmitted in an assigned specific band. DMRS may be referred to as a dedicated reference signal or a user-specific reference signal. DMRS may be combined with transmission of PUSCH or PUCCH.

Reference signals are generally transmitted in sequence. As the reference signal sequence, any sequence may be used without particular limitation. The reference signal sequence may use a PSK-based computer generated sequence. Examples of PSKs include binary phase shift keying (BPSK) and quadrature phase shift keying (QPSK). Alternatively, the reference signal sequence may use a constant amplitude zero auto-correlation (CAZAC) sequence. Examples of CAZAC sequences are ZC-based sequences, ZC sequences with cyclic extensions, ZC sequences with truncation, etc. There is this. Alternatively, the reference signal sequence may use a pseudo-random (PN) sequence. Examples of PN sequences include m-sequences, computer generated sequences, Gold sequences, and Kasami sequences.

In addition, the reference signal sequence may use a cyclically shifted sequence.

는 기본 시퀀스이다. M_sc ^RS는 참조 신호 시퀀스의 길이이다.

이며, 1≤m≤N_RB ^{m ax, UL}이며, N_sc ^RB는 주파수 영역에서 부반송파의 수로 나타낸 자원 블록의 사이즈이다. N_RB ^{max , UL}는 N_sc ^RB의 배수로 나타낸 최대 상향링크 대역폭 구성(configuration)이다. 복수의 참조 신호 시퀀스는 단일 기본 시퀀스를 기반으로 α가 다양하게 변화함에 따라 정의될 수 있다.In Equation 1 α is a cyclic shift (cyclic shift),

Is the base sequence. M _sc ^RS is the length of the reference signal sequence.

Where 1 ≦ ^m ≦ N _RB ^{m ax and UL} , and N _sc ^RB is the size of a resource block represented by the number of subcarriers in the frequency domain. N _RB ^{max , UL} is the maximum uplink bandwidth configuration expressed in multiples of N _sc ^RB . A plurality of reference signal sequences may be defined as various α changes based on a single basic sequence.

The sequence r ^PUSCH of the DMRS for the ^PUSCH may be defined by Equation 2.

In Equation 2, m = 0,1, n = 0,... , M _sc ^{RS -1} and M _sc ^RS = M _sc ^PUSCH . M _sc ^PUSCH is a scheduled bandwidth for uplink transmission expressed by the number of subcarriers. R _{u , v} ^(α) (n) is a reference signal sequence. The r ^PUSCH may be mapped to a resource block used for PUSCH transmission. The r ^PUSCH may be mapped to the fourth (l = 3) OFDM symbol in front of the normal CP in each slot constituting the resource block and to the third (l = 2) OFDM symbol in the front in the case of the extended CP. DMRS may be transmitted through the mapped resource.

The number of reference signals required in a multi-antenna system varies depending on whether the reference signal is a precoded reference signal or a non-precoded reference signal.

8 shows an example of a transmitter for transmitting a precoded reference signal. 9 shows an example of a transmitter for transmitting a non-precoded reference signal.

8 and 9, the transmitter 100 includes an encoder (110-1, ..., 110-N), a mapper (120-1, ..., 120-N), and a hierarchical mapper. (layer mapper 130), precoder 140, resource element mapper 150-1, ..., 150-Nt and signal generator 160-1, ... 160-Nt It includes. The transmitter 100 includes Nt transmit antennas 170-1,..., 170 -Nt.

The encoders 110-1,..., And 110 -N encode the input data according to a predetermined coding scheme to form coded data (hereinafter, codewords). The number of codewords may be N. The mappers 120-1, ..., 120-N map the codewords to modulation symbols representing positions on signal constellations. The modulation scheme is not limited and may be m-Phase Shift Keying (m-PSK) or m-Quadrature Amplitude Modulation (m-QAM). For example, m-PSK may be BPSK, QPSK or 8-PSK. m-QAM may be 16-QAM, 64-QAM or 256-QAM.

The hierarchical mapper 130 defines a hierarchy of modulation symbols so that the precoder 140 can distribute antenna-specific symbols to the path of each antenna. The layer may be defined as an information path input to the precoder 140. The number of modulation symbols output through the layer mapper 130 may be determined according to the rank. The information path before the precoder 140 may be referred to as a virtual antenna or a layer.

The precoder 140 performs precoding on the modulation symbol to output an antenna specific symbol. The precoder 140 distributes antenna specific symbols to resource mappers 150-1, ..., 150-Nt of the path of the corresponding antenna. Each information path sent by the precoder 140 to one antenna is called a stream. This may be referred to as a physical antenna.

The precoded reference signal 801 passes through the same precoder as the data, and the non-precoded reference signal 901 does not go through the precoder. The conventional precoded reference signal 801 requires the same number of sequence resources as the rank of the multi-antenna system, and the non-precoded reference signal 901 has the same number of sequences as the number of antennas of the multi-antenna system. Resources are needed. However, according to the present invention, the number of sequence resources required for these reference signals can be reduced.

10 shows a reference signal transmission method according to an embodiment of the present invention.

The base station transmits control information for uplink transmission to the terminal, and the terminal receives such control information (S101). The control information may be transmitted through the PDCCH. Physical layer (L1) parameters for uplink transmission may be defined in DCI format 0. In DCI format 0, a cyclic shift value (DMRS) of a DMRS, a rank index (RI) indicating a rank for an uplink channel, and a precoding matrix index indicating a precoding matrix used in a codebook-based MIMO. (precoding matrix indicator, PMI), MCS indicator (MCS-RV) indicating MCS (modulation and coding scheme) applied when transmitting multiple codewords, new data indicator indicating new data when transmitting multiple codewords, etc. It may include.

The terminal resource-maps the reference signal of each antenna from the control information (S102). In this case, the terminal may resource-map the reference signal according to the rank of the multi-antenna system. The rank of the multi-antenna system can be known through the rank index included in the control information. The resource mapping process of the reference signal will be described later in detail.

The terminal transmits the reference signal generated by resource mapping to the base station (S103).

11 shows an example of radio resource allocation in transmission of a reference signal in the conventional CDM scheme.

Assume an example of a transmitter in which the rank of the wireless communication system is 1 and uses four transmit antennas. Depending on the MIMO transmission method, it may be necessary to know all channel states of the four transmit antennas. For example, a method of combining STBC and FSTD, a method of combining SFBC and FSTD, a method using FSTD, and a case of using transmit diversity using a large delay CDD or the like. In order to estimate a channel for each transmit antenna, the conventional CDM reference signal uses four sequence (S ₁ , S ₂ , S ₃ , S ₄ ) resources in the code domain as shown in FIG. 11. . In this manner, since the reference signal uses power of a transmitting antenna separately, degradation of channel estimation performance may occur, and as a result, degradation of data demodulation performance may occur. Therefore, in order to increase channel estimation performance, it is proposed to add a reference signal in a TDM scheme.

Hereinafter, a method of resource mapping a reference signal for a PUSCH, that is, DMRS, in uplink transmission in a terminal including a transmitter using multiple antennas will be described.

<For rank 1>

When the UE can know that the rank is 1 through the rank index of the control information, the UE may allocate resources to the DMRS by any one of the methods described below.

1. In the DMRS transmitted through the same precoder as the data, one sequence resource is used in an equivalent form to one transmission antenna.

2. In case of applying transmit diversity using two transmit antennas, two sequence resources are required so that the receiver side can know the channel state of the two transmit antennas.

3. In case of applying transmit diversity using four transmit antennas, a reference signal is added in the form of TDM, and sequence resources are transmitted by CDM in each reference signal. Hereinafter, the reference signal of the CDM / TDM scheme will be described.

12 shows resource allocation for a reference signal of the CDM / TDM scheme according to the first embodiment of the present invention.

Referring to FIG. 12, a reference signal is TDM arranged in different symbols in each slot of a subframe used for uplink transmission, and the reference signals arranged in each symbol may be CDM in different sequences. For example, the reference signal may be disposed in the fourth SC-FDMA symbol and the sixth SC-FDMA symbol of each slot. For convenience, the reference signal disposed in the preceding SC-FDMA symbol is referred to as a first reference signal, and the reference signal added and added in a later SC-FDMA symbol is referred to as a second reference signal. Then, in the first reference signal, two sequence resources S ₁ and S ₂ may be CDM to distinguish two antennas (eg, first and second antennas). In the second reference signal, two sequence resources S ₁ and S ₂ may be CDM to distinguish two antennas (eg, third and fourth antennas). Each reference signal requires two sequence resources.

13 shows resource allocation of a reference signal of a CDM / TDM scheme according to a second embodiment of the present invention.

Referring to FIG. 13, the first reference signal may be disposed in the fourth SC-FDMA symbol of each slot, and the second reference signal may be disposed in the sixth SC-FDMA symbol of each slot.

Four sequence resources S ₁ , S ₂ , S ₃ , and S ₄ may be CDM in the first reference signal. In addition, four sequence resources S ₁ , S ₂ , S ₃ , and S ₄ may be CDM in the second reference signal. That is, four sequences for distinguishing four antennas from the first reference signal are transmitted by CDM, and the additional second reference signal repeats this process in the same manner. This method can achieve SNR gain. Four sequence resources are allocated to each reference signal.

14 shows resource allocation of a reference signal of a CDM / TDM scheme according to a third embodiment of the present invention.

Referring to FIG. 14, the first reference signal and the second reference signal use the same sequence S ₁ , but cover a code orthogonal to the same sequence to distinguish four transmitting antennas. For example, the first reference signal may be covered with a Walsh code (1, 1), and the second reference signal may be covered with a Walsh code (1, -1). In this case, it can be seen that two sequence resources are allocated to each reference signal.

When two transmission antennas are combined to form one channel among four transmission antennas, a total of two channels need to be distinguished. In this type of MIMO transmission in a transmitter using multiple antennas, two channels may be distinguished using two sequence resources in a CDM manner.

<In the case of rank 2>

When the UE can know that the rank is 2 through the rank index of the control information, the UE may allocate resources to the DMRS by any one of the methods described below.

1. In the DMRS transmitted through the same precoder as data, two sequence resources are used to distinguish two layers.

2. In the case of spatial multiplexing using two transmit antennas, two sequence resources are used, whether a precoded reference signal or a non-precoded reference signal.

3. In case of applying spatial multiplexing using four transmit antennas, two sequence resources are used for the precoded reference signal. For non-coded reference signals, all four transmit antennas must be distinguished. Therefore, four sequence resources may be used, or a reference signal of the CDM / TDM scheme described in rank 1 may be used.

<In the case of rank 3>

When the UE can know that the rank is 3 through the rank index of the control information, the UE may allocate resources to the DMRS by any one of the methods described below. If you use four transmit antennas,

1. Since the precoded reference signal must distinguish three streams transmitted to three layers, three sequence resources are used. The precoded reference signal may be transmitted as a reference signal of a CDM / TDM scheme as in the fourth to sixth embodiments to be described later.

15 shows resource allocation of a reference signal of a CDM / TDM scheme according to a fourth embodiment of the present invention.

Referring to FIG. 15, three sequence resources are used for the first reference signal and three sequence resources are repeated for the second reference signal. SNR gain can be obtained by using three sequence resources in the same manner as the first reference signal in the second reference signal added by the TDM scheme.

16 shows resource allocation of a reference signal of a CDM / TDM scheme according to a fifth embodiment of the present invention.

Referring to FIG. 16, N (N <3, N is a natural number) CDM sequences may be transmitted to a first reference signal, and (3-N) sequences may be transmitted to a second reference signal. For example, two sequences S ₁ and S ₂ may be transmitted by CDM to the first reference signal, and one sequence S ₃ may be transmitted to the second reference signal.

17 shows resource allocation of a reference signal of a CDM / TDM scheme according to a sixth embodiment of the present invention.

Referring to FIG. 17, two sequences may be transmitted by CDM to a first reference signal, and one sequence and another sequence used by the first reference signal may be transmitted by CDM to a second reference signal. For example the first reference signal, the second reference transmission by the CDM S _1, S ₂ sequence, and signals can be transmitted by the CDM S _2, S ₃ sequence.

If it is necessary to estimate the channels for all four transmit antennas, the method of the first to third embodiments in the above rank 1 may be applied.

2. In the case of the non-precoded reference signal, since all four transmit antennas must be distinguished, four sequence resources may be used in one resource block or the method of the first to third embodiments in rank 1 may be applied. Can be.

<In the case of rank 4>

When the UE can know that the rank is 4 through the rank index of the control information, since all four transmit antennas must be distinguished, the UE uses four sequence resources in one resource block or uses the first to second ranks in the first rank. The method of the third embodiment can be applied.

Increasing the overhead of the reference signal reduces the throughput of the data. For example, in a system using two reference symbols and twelve data symbols in the time domain, when four reference symbol symbols are used to increase channel estimation performance, two symbols for data transmission are used for transmission of the reference signal. Used. Thus, a throughput reduction of about 14% occurs. ((10/14)-(8/14) * 100 = 14.3%)

Even if the base station selects a high rank through the SRS, it is more likely to obtain a lower frequency efficiency and a lower channel estimation performance than when a low rank is selected due to the reference signal overhead. For example, when a channel estimation is performed by transmitting a sequence divided according to a rank to a reference signal symbol having a fixed overhead, or when the overhead of the reference signal is increased to improve channel estimation performance.

Since it may be better to transmit at a lower rank than the selected rank, the rank may be limited to reduce unnecessary computation of the rank selection process. For example, when having four transmit antennas, the rank may be limited to any one, two, or four. That is, the base station may transmit the rank index to only one of 1, 2, and 4 values.

The cyclic shift value included in the control information transmitted by the base station may be added according to the rank. If the rank is various, the DCI format may also be variously changed. In this case, dynamic rank adaptation is difficult to apply and ambiguity may occur when searching for a DCI format. Thus, a fixed cyclic shift value can be allocated regardless of rank in multi-antenna transmission. For example, in a multi-antenna system supporting up to 4, the cyclic shift value indicated by the base station may be limited to two.

Tables 1 to 5 below show examples of the DCI format.

Table 1 may be used for SIMO transmit diversity. Table 2 can be used for transmit diversity. Table 3 can be used for rank 1 closed loop spatial multiplexing. Table 4 can be used for the Peruvian spatial multiplexing transmitting two or fewer codewords. Table 5 can be used for the Peruvian spatial multiplexing that transmits two codewords.

In Tables 1 to 5, the number belonging to each field represents the number of bits. The cyclic shift value for the DMRS (cyclic shift for DMRS) may be configured up to 6 bits. Since three bits represent one cyclic shift value, six bits may represent two cyclic shift values. The aforementioned DCI format indicates up to two cyclic shift values in a multi-antenna system supporting up to four ranks.

In the uplink transmission of the terminal by transmitting the SRS is performed channel estimation for the entire band. SRS should be designed to distinguish the channels of each transmit antenna.

When a reference signal transmitted by a terminal including a transmitter using N transmit antennas is an SRS and generates a reference signal by the CDM method, N cyclic shift values may be allocated. As such, when N cyclic shift values are used, simultaneous transmission may be difficult due to the limitation of sequence resources when simultaneously transmitting multiple users.

Therefore, when performing SRS transmission, it is possible to limit the number of transmit antennas that can be identified using CDM among the transmit antennas. For example, two antennas may be divided into two groups of four transmission antennas. The first antenna group may be divided using CDM, and the second antenna group may be divided by TDM / FDM.

The sequence resource used for the SRS may utilize a cyclic shift value allocated to the DMRS or may be transmitted through a higher layer signal such as RRC signaling.

10: terminal
20: base station
100: transmitter

Claims (11)

In a method of transmitting a reference signal in a transmitter using multiple antennas,
Receiving control information for uplink transmission; And
And generating and transmitting a reference signal of each antenna from the control information, wherein the reference signal is TDM arranged in different symbols in each slot of a subframe used for the uplink transmission and arranged in each symbol. Reference signal transmission method in a transmitter using multiple antennas, characterized in that the CDM in a different sequence. The multi-antenna according to claim 1, wherein when the reference signal is a demodulation reference signal (DMRS), the control information indicates up to two cyclic shift values for the DMRS. Method of transmitting reference signal in transmitter. The method of claim 1, wherein the rank of the transmitter is 1, the number of antennas is 4, and the reference signal is DMRS,
In the DMRS, a first reference signal or a second reference signal is disposed in a different symbol in each slot of a subframe used for the uplink transmission, and TDM is performed. A method of transmitting a reference signal in a transmitter using multiple antennas, characterized in that a CDM sequence distinguishes the four antennas. The method of claim 1, wherein the rank of the transmitter is 1, the number of antennas is 4, and the reference signal is DMRS,
In the DMRS, a first reference signal or a second reference signal is arranged in different symbols in each slot of a subframe used for uplink transmission, and each of the first reference signal and the second reference signal has four CDM sequences. The reference signal transmission method in a transmitter using multiple antennas characterized in that the four antennas are distinguished. The method of claim 1, wherein the rank of the transmitter is 1, the number of antennas is 4, and the reference signal is DMRS,
In the DMRS, a first reference signal or a second reference signal is disposed in a different symbol in each slot of a subframe used for the uplink transmission, and TDM is performed, and the first reference signal and the second reference signal are identical to each other. 2. A method of transmitting a reference signal in a transmitter using multiple antennas, wherein two sequences configured by spreading a sequence by an orthogonal code are CDMed to distinguish the four antennas. The method of claim 1, wherein the rank of the transmitter is 3, the number of antennas is 4, and the reference signal is DMRS,
In the DMRS, a first reference signal or a second reference signal is TDM arranged in different symbols in each slot of a subframe used for uplink transmission, and N sequences are CDMed in the first reference signal. The reference signal transmission method in a transmitter using multiple antennas, characterized in that 3-N sequences are CDMed to distinguish three streams transmitted through the four antennas. Where N is a natural number less than 3. The method of claim 1, wherein the number of antennas of the transmitter is four,
The control information includes a rank index indicating a rank during the uplink transmission, wherein the rank index is a reference signal transmission method in a transmitter using multiple antennas, characterized in that limited to any one. The method of claim 1, wherein the control information is received through a physical downlink control channel (PDCCH). The control information of claim 1, wherein the control information is a precoding matrix index indicating a coding matrix applied to the reference signal, a rank index indicating a rank during the uplink transmission, and a modulation-coding applied to the multi-codeword transmission. scheme) method for transmitting a reference signal in a transmitter using multiple antennas, characterized in that it further comprises at least one of the indicators. The method of claim 1, wherein the reference signal is a sounding reference signal (SRS). The antenna of claim 10, wherein the multi-antenna is composed of a first antenna group and a second antenna group, and an SRS for distinguishing antennas included in the first antenna group is classified as a CDM and is included in a second antenna group. SRS for distinguishing between the two signals are divided into TDM or FDM reference signal transmission method in a transmitter using multiple antennas.

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