WO2015084051A1

WO2015084051A1 - Csi feedback method and apparatus in multiple antenna system

Info

Publication number: WO2015084051A1
Application number: PCT/KR2014/011771
Authority: WO
Inventors: 리지안준
Original assignee: 주식회사 아이티엘
Priority date: 2013-12-03
Filing date: 2014-12-03
Publication date: 2015-06-11
Also published as: KR102168637B1; KR20150064383A

Abstract

The present invention relates to a method for supporting full dimension (FD) multiple-input multiple-output (MIMO) in a multiple antenna system in which a horizontal domain and a vertical domain each comprise four antenna ports (APs), the method comprising a codebook having unitary properties, wherein the codebook is based on a DFT beam vector and uses all possible orthogonal beams, and comprises the same number of orthogonal beams between code words, considering code word layer mapping.

Description

CSI feedback method and apparatus in a multi-antenna system

The present invention relates to wireless communications, and more particularly, to a method and apparatus for channel state information (CSI) feedback in a multi-antenna system.

The mobile communication system can support eight transmit antennas for beamforming operation. In particular, in a multi-user multiple input multiple output (MIMO) operation, the same physical resource block (PRB) may be scheduled or allocated to up to four user equipments (UEs). have. Regarding the configuration of the antenna in this next generation mobile communication system, a closely-spaced X-polarized antenna is considered, for example, from 0.5λ to 0.7λ.

However, the current mobile communication system only considers the antenna arrangement in the horizontal direction for beamforming operation. Meanwhile, in order to further improve MIMO performance, it is necessary to introduce a full dimension (MID) MIMO supporting both a horizontal direction and a vertical direction.

Meanwhile, the next generation mobile communication system aims to support up to 64 transmit antennas in a two-dimensional antenna configuration with respect to a closed loop (CL) MIMO operation. As a first step, 8 APs FD MIMO scheme supporting 8 antenna ports (AP) based on a 2D array should be supported.

In this regard, CSI feedback for stably supporting FD MIMO including up to eight transmit antennas is an important issue, and a new precoding codebook design for eight APs is required.

One example of the present invention is to provide a CSI feedback method and apparatus in a multiple antenna system.

Another example of the present invention is to provide an apparatus and method for designing a codebook for supporting FD MIMO.

Another example of the present invention is to provide an apparatus and method for designing a codebook in consideration of two-dimensional beamforming or layer mapping.

According to an aspect of the present invention, there is provided a method of supporting a full dimension (FD) multiple-input multiple-output (MIMO) by a terminal in a multi-antenna system. The method includes Channel State Information (CSI) including Precoding Matrix Index (PMI) 1 corresponding to the horizontal domain, PMI 2 corresponding to the vertical domain, and Rank Indication (RI) indicating the number of layers for downlink transmission. Transmitting the precoded data from the base station based on the detected precoding matrix based on the PMI1, the PMI2, and the RI, wherein the precoding matrix is the RI. It is included in the codebook defined according to the number of layers indicated by the codebook, characterized in that based on the Discrete Fourier Transform (DFT) beam vector.

According to another aspect of the present invention, there is provided a method for supporting FD MIMO in a multi-antenna system. The method may further include receiving, from the terminal, a CSI including a PMI1 corresponding to the horizontal domain, a PMI2 corresponding to the vertical domain, and an RI indicating a number of layers related to downlink transmission, based on the RI. Determining a codebook according to the number of times, detecting a precoding matrix in the codebook based on the PMI1 and the PMI2, and generating precoded data based on the detected precoding matrix; And transmitting the precoded data to the terminal, wherein the codebook is based on a DFT beam vector.

According to another aspect of the present invention, a terminal supporting FD MIMO in a multi-antenna system is provided. The terminal receives a CSI-RS (Channel State Information Reference Signal) through the four antenna ports for the horizontal domain and the four antenna ports for the vertical domain from the base station, based on the CSI-RS A processor unit for generating a CSI including a PMI1 corresponding to the horizontal domain, a PMI2 corresponding to the vertical domain, and an RI indicating a number of layers for downlink transmission, and transmitting the generated CSI to the base station A transmitter, wherein the processor detects a codebook based on a DFT beam vector and a precoding matrix included in the codebook based on the PMI1, the PMI2, and the RI, and the receiver based on the detected precoding matrix Receiving precoded data from the base station.

In implementing MIMO operation using up to 8 transmit antennas or APs that can be implemented in the next generation mobile communication system, a codebook optimized for 2D beamforming or FD MIMO in consideration of codeword layer mapping is provided. To provide an advantage. Thus, system throughput performance can be improved.

1 shows a wireless communication system to which the present invention is applied.

2 and 3 illustrate a CSI-RS pattern according to an example of the present invention.

4 illustrates a multiple antenna system according to an example of the present invention.

5 shows an example of codeword layer mapping for 5 layer transmission.

6 shows an example of codeword layer mapping for 6 layer transmission.

7 shows an example of codeword layer mapping for 7 layer transmission.

8 shows an example of codeword layer mapping for 8 layer transmission.

9 is an example of an explanatory diagram showing a precoding method in an FD MIMO system according to an embodiment of the present invention.

10 is an example of a block diagram illustrating a terminal and a base station according to an embodiment of the present invention.

Hereinafter, some embodiments will be described in detail with reference to the accompanying drawings. In adding reference numerals to the components of each drawing, it should be noted that the same reference numerals are assigned to the same components as much as possible even though they are shown in different drawings. In addition, in describing the embodiments of the present specification, when it is determined that a detailed description of a related well-known configuration or function may obscure the gist of the present specification, the detailed description thereof will be omitted.

In addition, the present specification describes a wireless communication network, the operation performed in the wireless communication network is performed in the process of controlling the network and transmitting data in the system (for example, the base station) that is in charge of the wireless communication network, or the corresponding wireless Work may be done at the terminal coupled to the network.

According to embodiments of the present invention, 'transmitting a channel' may be interpreted as meaning transmitting information through a specific channel. Here, the channel is a concept including both a control channel and a data channel, and the control channel may be, for example, a physical downlink control channel (PDCCH) or a physical uplink control channel (PUCCH). The data channel may be, for example, a Physical Downlink Shared CHannel (PDSCH) or a Physical Uplink Shared CHannel (PUSCH).

Referring to FIG. 1, the wireless communication system 10 is widely deployed to provide various communication services such as voice and packet data. The wireless communication system 10 includes at least one base station 11 (evolved-NodeB, eNB). Each base station 11 provides a communication service for

specific cells

15a, 15b, and 15c. One base station may be responsible for multiple cells. In the present invention, the base station 11 refers to a transceiver for performing information and control information sharing with the terminal for cellular communication, and includes a base station (BS), a base transceiver system (BTS), an access point (Access Point), Other terms, such as a femto base station, a home node B, a relay, and the like, may be called. A cell is meant to encompass all of the various coverage areas such as megacell, macrocell, microcell, picocell, femtocell, and the like.

The UE 12 may be fixed or mobile and may have a mobile station (MS), a mobile terminal (MS), a mobile terminal (MT), a user terminal (UT), a subscriber station (SS), a wireless device, or a PDA. (personal digital assistant), wireless modem (wireless modem), a handheld device (handheld device) may be called other terms.

Hereinafter, downlink refers to a transmission link from the base station 11 to the terminal 12, and uplink refers to a transmission link from the terminal 12 to the base station 11. it means. In downlink, the transmitter may be part of the base station 11 and the receiver may be part of the terminal 12. In uplink, the transmitter may be part of the terminal 12 and the receiver may be part of the base station 11. There is no limitation on the multiple access scheme applied to the wireless communication system. Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Orthogonal Frequency Division Multiple Access (OFDMA), Single Carrier-FDMA (SC-FDMA), OFDM-FDMA, OFDM-TDMA For example, various multiple access schemes such as OFDM-CDMA may be used. The uplink transmission and the downlink transmission may use a time division duplex (TDD) scheme that is transmitted using different times, or may use a frequency division duplex (FDD) scheme that is transmitted using different frequencies.

Layers of a radio interface protocol between the terminal 12 and the base station 11 are based on the lower three layers of the Open System Interconnection (OSI) model, which is well known in communication systems. The layer L1 may be divided into a second layer L2 and a third layer L3. Among them, the physical layer belonging to the first layer provides an information transfer service using a physical channel.

There are several physical channels used in the physical layer. First, as a downlink physical channel, a physical downlink control channel (PDCCH) is a hybrid automatic repeat request (HARQ) related to resource allocation and DL-SCH of a paging channel (PCH) and a downlink shared channel (DL-SCH) to the terminal 12. Information. The PDCCH may carry an uplink grant that informs the terminal 12 of resource allocation of uplink transmission. The DL-SCH is mapped to a physical downlink shared channel (PDSCH). The Physical Control Format Indicator Channel (PCFICH) informs the terminal 12 of the number of OFDM symbols used for PDCCHs and is transmitted every subframe. PHICH (Physical Hybrid ARQ Indicator Channel) is a downlink channel, and carries a HARQ ACK / NACK signal that is a response of uplink transmission.

Next, as an uplink physical channel, HARQ (Hybrid Automatic Repeat reQuest) ACK (Non-acknowledgement) / NACK (Non-acknowledgement), channel status information (CSI) indicating the downlink channel status, for example, Channel Quality Indicator (CQI) ) And uplink control information such as a precoding matrix index (PMI), a precoding type indicator (PTI), and a rank indication (RI). PUSCH (Physical Uplink Shared Channel) carries the UL-SCH (Uplink Shared Channel). Physical Random Access Channel (PRACH) carries a random access preamble.

The CQI provides information on link adaptive parameters that the terminal 12 can support for a given time. The CQI may indicate a data rate that can be supported by the downlink channel in consideration of characteristics of the receiver of the terminal 12 and signal to interference plus noise ratio (SINR). The base station 11 may determine the modulation (QPSK, 16-QAM, 64-QAM, etc.) and coding rate to be applied to the downlink channel using the CQI. CQI can be generated in several ways. For example, a method of quantizing and feeding back a channel state as it is, a method of calculating a feedback to a signal to interference plus noise ratio (SINR), and a method of notifying a state that is actually applied to a channel such as a modulation coding scheme (MCS) may be used. have. When the CQI is generated based on the MCS, the MCS includes a modulation scheme, a coding scheme, a coding rate, and the like.

PMI provides information about the precoding matrix in the codebook based precoding. PMI is associated with multiple-input multiple-output (MIMO). Feedback of PMI in MIMO is called CL MIMO (closed loop MIMO).

RI is information about a rank (ie, number of layers) recommended by the terminal 12. That is, RI represents the number of independent streams used for spatial multiplexing. The RI is fed back only when the terminal operates in the MIMO mode using spatial multiplexing. RI is always associated with one or more CQI feedback. In other words, the fed back CQI is calculated assuming a specific RI value. Since the rank of the channel generally changes slower than the CQI, the RI is fed back fewer times than the CQI. The transmission period of the RI may be a multiple of the CQI / PMI transmission period. RI is given for the entire system band and frequency selective RI feedback is not supported.

The wireless communication system 10 may be a multiple antenna system. Multiple antenna systems may be referred to as MIMO systems. 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.

Multiple antenna transmit / receive schemes used for the operation of multiple antenna systems include frequency switched transmit diversity (FST), Space Frequency Block Code (SFBC), Space Time Block Code (STBC), and Cyclic Delay Diversity (CDD). TSTD (time switched transmit diversity) may be used.

The wireless communication system 10 needs to estimate an uplink channel or a downlink channel for data transmission / reception, system synchronization acquisition, channel information feedback, and the like. The process of restoring a transmission signal by compensating for distortion of a signal caused by a sudden change in channel environment is called channel estimation. In addition, it is also necessary to measure the channel state (channel state) for the cell to which the terminal 12 belongs or other cells. In general, a reference signal (RS) known to each other is used by the terminal 12 and the base station 11 for channel estimation or channel state measurement.

Since the terminal 12 knows the information of the reference signal, it is possible to accurately obtain the data sent from the base station 11 by estimating the channel and compensating the channel value based on the received reference signal. If p is the reference signal transmitted from the base station 11, h is channel information experienced by the reference signal during transmission, n is thermal noise generated at the terminal 12, and y is the signal received at the terminal 12, y = h. It can be expressed as p + n.

In this case, since the reference signal p is already known to the terminal 12, when the LS (Least Square) method is used, the channel information (p.

) Can be estimated.

Equation 1

Here, the channel estimate estimated using the reference signal p

Is

Depends on the value, so to get an accurate estimate of

You need to converge to zero. By using a large number of reference signals

The channel can be estimated by minimizing the effects of

The reference signal may be allocated to all subcarriers or may be allocated between data subcarriers for transmitting data. In a method in which the reference signals are allocated to all subcarriers, a signal of a specific transmission timing is composed of only a reference signal such as a preamble in order to obtain a gain of channel estimation performance. According to a method in which reference signals are allocated between data subcarriers, the amount of data transmission can be increased. In a multi-antenna system, resource elements used by one antenna to transmit a reference signal are not used by another antenna. This is to avoid interference between antennas.

The downlink reference signal includes a channel state information (CSI) reference signal (CSI-RS) and a DMRS.

Channel State Information Reference Signal (CSI-RS) may be used for estimation of channel state information. The CSI-RS is placed in the frequency domain or time domain. CQI, PMI, RI, etc. may be reported from the terminal 12 to the base station 11 as channel state information when necessary through estimation of the channel state using the CSI-RS.

The wireless communication system 10 may operate in accordance with various transmission modes. For example, transmission mode 0 may be a mode that supports only a single antenna port, whereas transmission modes 9 and 10 may be a mode that can support up to eight antenna ports. Here, the definition of the antenna port is as follows.

When a first symbol (or signal) is carried over a first channel and a second symbol (or signal) is carried over a second channel, the first channel can be inferred by the second channel. An antenna port is defined such that the channel over which a symbol on the antenna port is conveyed can be inferred from the channel over which another symbol on the same antenna port is conveyed).

There is one resource grid unique to one antenna port. Each element in the resource grid for antenna port p is called a resource element (RE), and each resource element is identified by an index pair (k, l) in every slot. Where k = 0, ..., N ^DL _RB N ^RB _sc -1, l = 0, ..., N ^DL _symb-1 , k is a subcarrier index in the frequency domain, and l is time The symbol index in the region. The resource element represents the smallest frequency-time unit to which the modulation symbol of the data channel or the modulation symbol of the control channel is mapped. If there are M subcarriers on one OFDM symbol, and one slot includes N OFDM symbols, one slot includes a total of M × N resource elements.

In the multi-antenna system, different antenna ports may be mapped to each physical antenna. For example, antenna ports 0 to 3 may be sequentially mapped to each of four physical antennas.

The number of antenna ports and the unique resource grid of each antenna port are determined depending on the reference signal configuration in the cell. For example, when the total number of physical antennas is 64, the number of antenna ports supporting CSI-RS is {1, 2, 4, 8 according to the configuration of the CSI-RS and the arrangement of the CSI-RS ports in the physical antenna. , 16, 32, 64}, and each antenna port may have a unique pattern for carrying a CSI-RS as shown in FIG. 2 or 3. Hereinafter, a unique pattern in which an antenna port carries a CSI-RS or a pattern in which a CSI-RS is mapped to a resource element is called a CSI-RS pattern.

2 and 3 illustrate a CSI-RS pattern according to an example of the present invention. 2 illustrates an example in which a CSI-RS is mapped to a resource element in the case of a normal cyclic prefix, and FIG. 3 illustrates an example in which a CSI-RS is mapped to a resource element in the case of an extended CP. It is shown schematically.

2 and 3, Rp represents a resource element used for CSI-RS transmission at the antenna port P. For example, R ₁₅ means CSI-RS transmitted from antenna port 15. When one antenna port is supported in FIG. 2, the CSI-RS pattern is one in which CSI-RSs are mapped to resource elements (2, 5) and (2, 6) of antenna port 15. Alternatively, in FIG. 2, when eight antenna ports are supported, the CSI-RS pattern is mapped to resource elements (2, 5) and (2, 6) of antenna ports 15 and 16, and that antenna ports 17 and Mapped to resource elements (8, 5) and (8, 6) of 18, mapped to resource elements (3, 5) and (3, 6) of antenna ports 19 and 20, and resource elements of antenna ports 21 and 22 Maps to (9, 5) and (9, 6).

As described above, each antenna port has a unique CSI-RS pattern. 2 and 3 illustrate a total of eight antenna ports 15 to 22 transmitting CSI-RS in a wireless communication system equipped with eight physical antennas. However, this is only an example, and in the case of a wireless communication system having 64 physical antennas, up to 64 antenna ports may be supported, and in this case, antenna ports transmitting CSI-RS may be extended to antenna ports 15 to 63.

Referring to FIG. 4, the multi-antenna system 400 includes a base station 410 having a plurality of antennas and a terminal 420 having a plurality of antennas. Unlike the prior art, which supports one, two, four, eight antenna ports, the base station 410 supports a two-dimensional antenna array having eight or more antenna ports. For example, eight or more antenna ports supported by the base station 410 may be a corresponding number of any one of {16, 32, 64} as an example. That is, the base station 410 may support an antenna port corresponding to a multiple of eight. Here, when the base station 410 supports a multi-user MIMO (MU-MIMO) operation, for example, 10 terminals may be simultaneously supported.

The base station 410 may transmit the CSI-RS to the terminal 420 for CSI feedback. For example, the base station 410 may transmit the CSI-RS to the terminal 420 in the horizontal antenna port (s) and vertical antenna port (s).

Meanwhile, the terminal 420 feeds back two PMIs to the base station 410 based on the CSI-RS. In this case, for example, PMI1 may correspond to the horizontal antenna port and PMI2 may correspond to the vertical antenna port. That is, PMI1 may be for beamforming in the horizontal direction, and PMI2 may be for beamforming in the vertical direction. Of course, as an example, PMI1 may correspond to the vertical antenna port, and PMI2 may correspond to the vertical antenna port. Hereinafter, it is assumed that PMI1 corresponds to the horizontal antenna port and PMI2 corresponds to the vertical antenna port.

The number of antenna ports for CSI-RS transmission in each direction, whether horizontal or vertical, is one of 2, 4, and 8.

Codebooks for the two and four antenna ports are designed based on independent spatial channels. In contrast, the codebook for the eight antenna ports is designed based on the x-polarized antenna configuration. For all antennas, if x polarized antennas are not used, the optimized codebook is redesigned and no co-phasing part is needed. Based on an original codebook, embodiments of the present invention can design a codebook as a combination of discrete fourier transform (DFT) beam and beam selection.

In the embodiment of the present invention, a new codebook design for a new 8 APs FD MIMO is proposed in consideration of the following criteria.

(1) Keep codebook as unitary. That is, each column of the matrix in the codebook is orthogonal to each other.

(2) Reuse the DFT beam for 4 APs.

(3) Double beam selection operation for two dimensions by two different PMI indexes through two different PMIs. This can be done by using different DFT beam vectors for different columns of the matrix in the codebook. Different DFT beam vectors may be obtained based on two different PMI indexes.

(4) Eliminate coping operation. The co-phasing operation which is replaced by beam selection. In other words, in the existing codebook design, the phase part φ _n (φ _n = e ^{jπn / 2} ) is used in some cases in the second row of the matrix, but in the design according to the present invention, the phase part is removed and the angle of the matrix is removed. Rows are used for beam selection based on different DFT beam vectors.

(5) Consideration optimization on codebook size. In other words, the design according to the present invention maintains the codebook size according to each existing rank, thereby minimizing the effect on the system.

(6) Consideration optimization on beam direction selection and configuration. To this end, orthogonal vectors and zero vectors are used in the design according to the invention.

In view of the above criteria, a codebook for 8 APs can be designed as follows.

First, to design a codebook for 8 APs, the 4 APs DFT beam vector v _m and / or v _n can be used.

Equation 2

Referring to Equation 2, a vector v _m having a size of 4 is designed in such a manner that the phase is sequentially changed from the first element 1 to the fourth element e ^{j6πm / 32} . [] ^T means a transpose matrix, m is an integer of 0 to 31. Thus, the vector v _m has a total of 32 beam directions. When the variable m is replaced with the variable n in Equation 2, a DFT beam vector v _n may be obtained.

According to an example of the present invention, a codebook design to be described below may be configured by selecting a specific beam direction among the 32 beam directions.

First Embodiment: One Layer Codebook

For codebooks for one layer (ie rank 1 codebook), only one beam direction selection is required. This is because in FD MIMO, for the rank 1 codebook, one beam direction must be selected for each of the horizontal domain and the vertical domain. In this case, two PMIs corresponding to each of the horizontal domain and the vertical domain may be used. In order to maintain the codebook size defined in the current standard, each PMI may have 4 bits. Thus only 16 beam directions can be selected in this case. In order to fully use the 32 beam directions, a delta value may be added to a parameter regarding each horizontal and vertical domain of a codebook, which may be represented as shown in Table 1 below.

Table 1

Table 1 shows an example of a codebook for 1-layer CSI reporting using 8 antenna ports (numbers 15 to 22). Referring to Table 1, W ⁽¹⁾ _{m, n} is a codebook for one layer for FD MIMO. v _m , v _n are the beam vectors of the horizontal domain and the vertical domain, respectively, i ₁ represents the value of PMI1 (e.g., PMI corresponding to the horizontal domain), and i ₂ corresponds to PMI2 (e.g., vertical domain) PMI) value. And d ₁ and d ₂ are delta values for beam direction selection for the horizontal domain and the vertical domain, respectively. And d ₁ and d ₂ have a value of 0 or 1. According to Table 1, m = 2i ₁ + d ₁ , n = 2i ₂ + d ₂ , and i ₁ and i ₂ each have a value of 0 to 15, and thus m and n may each have 32 values. have.

The d ₁ and d ₂ may be determined according to, for example, the following alternatives Alt.

For example, in case of Alt 1, the d ₁ and the d ₂ may be configured through RRC signaling. That is, the d ₁ and the d ₂ may be changed to semi statically.

As another example, in the case of Alt 2, the d ₁ and the d ₂ depend on a CSI subframe set. For example, d ₁ and d ₂ may be determined as in

Equations

3 and 4, respectively.

Equation 3

Equation 4

Here, C _{CSI, 0} , C _{CSI, 1} represent subframe sets, and are configured by a higher layer. For example, if C _{CSI, 0} , C _{CSI, 1} is configured by a higher layer, resource-restricted CSI measurements are configured in the terminal.

If only one subframe set of C _{CSI, 0} , C _{CSI, 1} is configured, both d ₁ and d ₂ are set to zero.

Considering that the two subframe sets were originally designed for Inter-Cell Interference Coordination (ICIC), it can be seen that each subframe set has a different interference condition, and therefore, RI of the two subframe sets If is equal, it is advantageous for the precoding operation of the base station.

Meanwhile, as another example, according to Alt 3, the d ₁ and the d ₂ may be determined according to a CSI process. Multiple CSI processes may be configured in a transmission mode (TM) 10, and thus, UEs supporting TM 10 may be configured with two different CSI processes. Therefore, the d ₁ and the d ₂ can be determined according to each CSI process.

For example, it may be determined that d ₁ = 0 and d ₂ = 0 for one CSI process and d ₁ = 1 and d ₂ = 1 for another CSI process.

Second Embodiment: Two Layer Codebook

For codebooks for two layers (ie rank 2 codebook), the selection of two beam directions is required. That is, two beam directions should be selected for each of the horizontal domain and the vertical domain. In this case, as described above, two PMIs corresponding to the horizontal domain and the vertical domain are used. In order to reduce the interference between these two layers, the direction difference of the two beams should be maximum. Among the 32 directions in total, there are 16 cases in which the beams of each layer have a direction perpendicular to each other (that is, v _{m (n),} v _{m (n) +16} ). have. Each PMI may have 4 bits to maintain the Rank 2 codebook size defined in the current standard. The rank 2 codebook may be represented as in the following table.

TABLE 2

Table 2 shows an example of a codebook for two-layer CSI reporting using eight antenna ports (numbers 15 to 22). Referring to Table 2, W ⁽²⁾ _{m, n} is a codebook for two layers for FD MIMO. v _m , v _n are the beam vectors of the horizontal domain and the vertical domain, respectively, i ₁ represents the value of PMI1 (e.g., PMI corresponding to the horizontal domain), and i ₂ corresponds to PMI2 (e.g., vertical domain) PMI) value is as described above. The same applies to the following. The columns of the matrix included in the codebook correspond to the number of layers.

Third Embodiment: Three Layer Codebook

For codebooks for three layers (ie rank 3 codebook), the selection of three beam directions is required. That is, three beam directions should be selected for each of the horizontal domain and the vertical domain. In this case, as described above, two PMIs corresponding to the horizontal domain and the vertical domain are used. In order to reduce the interference between these three layers, the direction difference of the three beams should be maximum. There are 16 cases in which the direction difference between the three beams is the largest among the 32 directions. Each PMI may have 4 bits to maintain the Rank 3 codebook size defined in the current standard. The rank 3 codebook may be represented as the following table.

TABLE 3

Table 3 shows an example of a codebook for 3 layer CSI reporting using 8 antenna ports (numbers 15 to 22). Referring to Table 3, W ⁽³⁾ _{m, n} is a codebook for three layers for FD MIMO.

Fourth Embodiment: Four Layer Codebook

For codebooks for four layers (ie rank 4 codebook), the selection of four beam directions is required. That is, four beam directions should be selected for each of the horizontal domain and the vertical domain. In this case, as described above, two PMIs corresponding to the horizontal domain and the vertical domain are used. In order to reduce the interference between the four layers, there are eight cases where the direction difference of the four beams is maximized. Each PMI may have 3 bits to maintain the Rank 4 codebook size defined in the current standard. The rank 4 codebook may be represented as the following table.

Table 4

Table 4 shows an example of a codebook for 4-layer CSI reporting using eight antenna ports (numbers 15 to 22). Referring to Table 4, W ⁽⁴⁾ _{m, n} is a codebook for four layers for FD MIMO.

Fifth Embodiment: Five-Layer Codebook

For codebooks for five layers (ie rank 5 codebook), the selection of five beam directions is required. That is, five beam directions should be selected for each of the horizontal domain and the vertical domain based on the two PMIs. However, according to the 4 APs based DFT beam vector described above in Equation 2, the number of orthogonal beams that can be selected is up to four. In order to maintain the unitary characteristics of the codebook, an orthogonal structure between columns of the matrix included in the codebook must be maintained. In order to design a codebook comprising a matrix with an orthogonal structure, codeword to layer mapping should be considered. Accordingly, the following rules may be followed for rank 5 codebook design.

Table 5

(1) Each column of the matrix in the codebook is orthogonal to each other. (2) All possible orthogonal beams are used. (3) Maintain codeword balance. That is, another codeword has the same number of orthogonal beams in both the horizontal and vertical domains.

When designing a rank 5 codebook according to the above rules, first, four orthogonal DFT beams may be selected from the rank 4 codebook.

Then, since there are up to four orthogonal beams for the rank 5 codebook, share four beams for the five layers. That is, four beams are allocated to five layers for both the horizontal domain and the vertical domain. In this case, each layer includes at least one beam.

Here, for rank 5 codebook design, codeword layer mapping should be considered important. The following codeword layer mapping may be applied for 5 layer transmission.

5 shows an example of codeword layer mapping for 5 layer transmission.

Referring to FIG. 5, codeword 0 is mapped to layer 1 and layer 2, and codeword 1 is mapped to layer 3, layer 4, and layer 5. In this case, the same number of beams are assigned to codeword 0 and codeword 1. That is, two beams may be shared for each domain (or dimension) of layer 1 and layer 2, and two beams may be shared for each domain (or dimension) for layer 3 and layer 5.

On the other hand, when one layer does not have a beam in a vertical domain or a horizontal domain, a zero vector may be inserted.

Reflecting the above method, the rank 5 codebook may be represented as follows.

Table 6

Table 6 shows an example of a codebook for 5-layer CSI reporting using 8 antenna ports (numbers 15 to 22). W ⁽⁵⁾ _{m, n} is a codebook for 5 layers for FD MIMO. Where for each domain orthogonal vectors of v _{m (n)} , v _{m (n) +8} , v _{m (n) +16} , v _{m (n) +24} , and 0 Vectors can be used.

On the other hand, the codebook of Table 6 has a problem that the power applied to the layers are different, so that the rank 5 codebook can be represented as follows so that all the layers have the same power.

TABLE 7

Table 7 shows another example of a codebook for 5-layer CSI reporting using eight antenna ports (numbers 15 to 22).

On the other hand, the codebook of Table 7 has a problem that the above-described codeword layer mapping is not considered. If horizontal beamforming is applied to one codeword and vertical beamforming is applied to another codeword, the codebook may be designed. That is, the rank 5 codebook to which domain (or dimension) based codeword division is applied may be represented as follows.

Table 8

Table 8 shows another example of a codebook for 5-layer CSI reporting using eight antenna ports (numbers 15 to 22).

In addition, when optimizing codeword layer mapping in terms of diversity, the rank 5 codebook may be represented as follows.

Table 9

Table 9 shows another example of a codebook for 5-layer CSI reporting using 8 antenna ports (numbers 15 to 22).

Sixth Embodiment: Six-Layer Codebook

For codebooks for six layers (ie rank 6 codebook), the selection of six beam directions is required. That is, six beam directions should be selected for each of the horizontal domain and the vertical domain based on the two PMIs. The design rules of Table 5 described above may be applied for the rank 6 codebook.

The following codeword layer mapping may be applied for rank 6 (ie, six layer transmission).

6 shows an example of codeword layer mapping for 6 layer transmission.

Referring to FIG. 6, codeword 0 is mapped to layer 1, layer 2, and layer 3, and codeword 1 is mapped to layer 4, layer 5, and layer 6. In this case, the same number of beams are assigned to codeword 0 and codeword 1. That is, layers 1 to 3 may share two beams for each domain (or dimension), and layers 4 to layer 6 may share two beams for each domain (or dimension). On the other hand, when one layer does not have a beam in a vertical domain or a horizontal domain, a zero vector may be inserted.

Reflecting the above method, the rank 6 codebook may be represented as follows.

Table 10

Table 10 shows an example of a codebook for six-layer CSI reporting using eight antenna ports (numbers 15 to 22). W ⁽⁶⁾ _{m, n} is a codebook for 6 layers for FD MIMO.

On the other hand, the codebook of Table 10 has a problem that the power applied to the layers are different, so that the rank 6 codebook can be represented as follows so that all the layers have the same power.

Table 11

Table 11 shows another example of a codebook for six-layer CSI reporting using eight antenna ports (numbers 15 to 22).

Meanwhile, when optimizing in terms of codeword layer mapping, the rank 6 codebook may be represented as follows.

Table 12

Table 12 shows another example of a codebook for six-layer CSI reporting using eight antenna ports (numbers 15 to 22).

Seventh Embodiment: Seven-Layer Codebook

For codebooks for seven layers (ie rank 7 codebook), the selection of seven beam directions is required. That is, seven beam directions should be selected for each of the horizontal domain and the vertical domain based on the two PMIs. The design rules of Table 5 described above may be applied for the rank 7 codebook.

The following codeword layer mapping may be applied for rank 7 (ie, seven layer transmission).

7 shows an example of codeword layer mapping for 7 layer transmission.

Referring to FIG. 7, codeword 0 is mapped to layer 1, layer 2, and layer 3, and codeword 1 is mapped to layer 4, layer 5, layer 6, and layer 7. In this case, the same number of beams are assigned to codeword 0 and codeword 1. That is, layers 1 to 3 may share two beams for each domain (or dimension), and layers 4 to layer 7 may share two beams for each domain (or dimension). On the other hand, when one layer does not have a beam in a vertical domain or a horizontal domain, a zero vector may be inserted.

Reflecting the above method, the rank 7 codebook may be represented as follows.

Table 13

Table 13 shows an example of a codebook for 7-layer CSI reporting using 8 antenna ports (numbers 15 to 22). W ⁽⁷⁾ _{m, n} is a codebook for 7 layers for FD MIMO.

On the other hand, the codebook of Table 13 has a problem that the power applied to the layers are different, in order to ensure that all the layers have the same power, the rank 7 codebook can be represented as follows.

Table 14

Table 14 shows another example of a codebook for 7-layer CSI reporting using eight antenna ports (numbers 15 to 22).

If horizontal beamforming is applied to one codeword and vertical beamforming is applied to another codeword, the rank 7 codebook may be represented as follows.

Table 15

Table 15 shows another example of a codebook for 7-layer CSI reporting using eight antenna ports (numbers 15 to 22).

Meanwhile, when optimizing in terms of codeword layer mapping, a rank 7 codebook may be represented as follows.

Table 16

Table 16 shows another example of a codebook for 7-layer CSI reporting using 8 antenna ports (numbers 15 to 22).

Eighth Embodiment: Eight Layer Codebook

For codebooks for 8 layers (ie, rank 8 codebook), selection of eight beam directions is required. That is, eight beam directions should be selected for each of the horizontal domain and the vertical domain based on the two PMIs. The design rules of Table 5 described above may be applied to the rank 8 codebook.

The following codeword layer mapping may be applied for rank 8 (ie, 8 layer transmission).

8 shows an example of codeword layer mapping for 8 layer transmission.

Referring to FIG. 8, codeword 0 is mapped to layer 1, layer 2, layer 3, and layer 4, and codeword 1 is mapped to layer 5, layer 6, layer 7, and layer 8. In this case, the same number of beams are assigned to codeword 0 and codeword 1. That is, layers 1 to layer 4 may share two beams for each domain (or dimension), and layers 5 to layer 8 may share two beams for each domain (or dimension). On the other hand, when one layer does not have a beam in a vertical domain or a horizontal domain, a zero vector may be inserted.

Reflecting the above method, the rank 8 codebook may be represented as follows.

Table 17

Table 17 shows an example of a codebook for 8-layer CSI reporting using 8 antenna ports (numbers 15 to 22). W ⁽⁸⁾ _{m, n} is a codebook for 8 layers for FD MIMO.

If horizontal beamforming is applied to one codeword and vertical beamforming is applied to the other codeword, the rank 8 codebook may be represented as follows.

Table 18

Table 18 shows another example of a codebook for 8-layer CSI reporting using 8 antenna ports (numbers 15 to 22).

9 is an example of an explanatory diagram showing a precoding method in an FD MIMO system according to the present invention. In the present invention, for eight antenna ports, a codebook designed for the antenna configuration as shown in FIG. 5 is used.

Referring to FIG. 9, the terminal transmits a CSI report including a PMI1 corresponding to horizontal APs, a PMI2 corresponding to vertical APs and an RI indicating the number of layers to the base station (S900). PMI1 and PMI2 provide information about the precoding matrix in the codebook based precoding. The RI provides information on rank (ie, number of layers) recommended by the UE. PMI1 may correspond to CSI-RS of APs of the horizontal domain, and PMI2 may correspond to CSI-RS of APs of the vertical domain. Such dual PMI may support beamforming in the horizontal direction (or domain or dimension) and in the vertical direction (or domain or dimension).

When the base station receives the CSI report from the terminal, the base station determines a codebook according to the number of layers based on the RI, and detects the precoding matrix in the corresponding codebook based on the PMI1 and PMI2 (S910). In this case, the base station may use one of the codebooks according to the layers described above in Tables 1 to 4 and Tables 6 to 18. In this case, i ₁ corresponds to PMI1 and i ₂ corresponds to PMI2 in each table as described above.

The base station transmits the precoded data to the terminal based on the detected precoding matrix (S920).

According to an embodiment of the present invention, in implementing FD MIMO operation using up to eight transmit antennas that can be implemented in a next generation mobile communication system, it is optimized for two-dimensional beamforming in consideration of codeword layer mapping. By providing customized codebooks, system throughput performance can be improved.

10 is an example of a block diagram illustrating a terminal and a base station according to the present invention. The terminal and the base station according to the present invention can use the antenna configuration as shown in FIG. In addition, the base station according to the present invention may use four antenna ports for each of the horizontal direction and the vertical direction.

Referring to FIG. 10, the terminal 1000 includes a terminal memory 1005, a terminal processor 1010, and a terminal transceiver 1020. The terminal memory 1005 is connected to the terminal processor 1010 and stores various information for driving the terminal processor 1010. The terminal transceiver 1020 is connected to the terminal processor 1010 to transmit and receive radio signals. The terminal processor 1010 implements a proposed function, process, and / or method for performing an operation according to the present invention In the above-described embodiments, the operation of the terminal is controlled by the terminal processor 1010. It can be implemented by.

The terminal transceiver 1020 receives the CSI-RS from the base station 1050. In this case, the terminal transceiver 1020 receives the CSI-RS through APs in the horizontal domain (or direction) of the base station 1050 and APs in the vertical domain (or direction).

The terminal processor 1010 includes a channel estimator 1011 and a CSI processor 1012.

The channel estimator 1011 performs channel estimation based on the CSI-RS, and the CSI processing unit 1012 is vertical (or horizontal) with the PMI1 corresponding to the horizontal (or vertical) APs based on the result of the channel estimation. Red) The RI indicating the PMI2 and the number of layers corresponding to the APs may be determined.

The CSI processor 1012 generates the PMI1, the PMI2, and the RI and sends the generated PMI1, the PMI2, and the RI to the terminal transceiver unit 1020. Then, the terminal transceiver 1020 transmits the CSI report including the PMI1, PMI2, and RI to the base station 1050. PMI1 corresponds to APs of the horizontal domain, and PMI2 corresponds to APs of the vertical domain.

The base station 1050 includes a base station memory 1055, a base station processor 1060, and a base station transceiver 1070. The base station memory 1055 is connected to the base station processor 1060 and stores various information for driving the base station processor 1060. The base station transceiver 1070 is connected to the base station processor 1060 and transmits and / or receives a radio signal. Base station processor 1060 implements the proposed functions, processes and / or methods for performing operations in accordance with the present invention. In the above-described embodiments, the operation of the base station may be implemented by the control of the base station processor 1060.

The base station processor 1060 includes a reference signal processor 1061, a CSI processor 1062, and a data processor 1063.

The reference signal processor 1061 generates a reference signal including the CSI-RS.

The base station transceiver 1070 transmits the reference signal including the CSI-RS to the terminal 1000.

The base station transceiver 1070 receives the CSI report from the terminal 1000. The CSI report includes PMI1, PMI2 and RI. Here, PMI1 corresponds to APs of the horizontal domain, and PMI2 corresponds to APs of the vertical domain.

When the base station transceiver 1070 receives the CSI report from the terminal 1000, the CSI processor 1062 determines a codebook according to the number of layers based on the RI, and based on the PMI1 and PMI2, The precoding matrix can be detected.

Specifically, for example, a codebook having the following characteristics may be determined or used by the CSI processing unit 1062.

(1) The unitary characteristics of the codebook are maintained. That is, each column of the matrix in the codebook is orthogonal to each other.

(2) DFT beams for 4 APs are reused.

(3) Two double beam selection operations for two dimensions are performed through two different PMIs. This can be done by using different DFT beam vectors for different columns of the matrix in the codebook. Different DFT beam vectors may be obtained based on two different PMI indexes.

(4) The coping operation is eliminated. The coping operation is replaced by the beam selection operation. In other words, in the existing codebook design, the phase part φ _n (φ _n = e ^{jπn / 2} ) is used in some cases in the second row of the matrix, but in the design according to the present invention, the phase part is removed and the angle of the matrix is removed. Rows are used for beam selection based on different DFT beam vectors.

(5) Optimization of codebook size is considered. In other words, in the design according to the present invention, the codebook size according to each rank is maintained, thereby minimizing the influence on the system.

(6) Beam direction selection and optimization of the configuration are considered. To this end, orthogonal vectors and zero vectors were used in the design according to the present invention.

In this case, the CSI processing unit 1062 may use one of the codebooks according to the layers described above in Tables 1 to 4 and Tables 6 to 18. In this case, i ₁ corresponds to PMI1 and i ₂ corresponds to PMI2 in each table as described above.

The data processor 1063 generates precoded data based on the detected precoding matrix, and transmits the precoded data to the terminal 1000 through the base station transceiver 1070.

In the present invention, the processor may include an application-specific integrated circuit (ASIC), another chipset, logic circuit and / or data processing device. The memory may include read-only memory (ROM), random access memory (RAM), flash memory, memory card, storage medium and / or other storage device. The transceiver may include a baseband circuit for processing a radio signal. When an embodiment is implemented in software or a program, the technique according to the present invention may be implemented as a module (process, function, etc.) for performing a corresponding function. The module may be stored in memory and executed by a processor. The memory may be internal or external to the processor and may be coupled to the processor by various well known means.

The above description is merely illustrative of the technical idea of the present invention, and those skilled in the art to which the present invention pertains may make various modifications and changes without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention but to describe the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The protection scope of the present invention should be interpreted by the following claims, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of the present invention.

Claims

A method for feeding back channel state information in a multi-antenna system,

A first precoding matrix index corresponding to the horizontal domain, a second precoding matrix index corresponding to the vertical domain, and a rank indication for the number of layers for downlink transmission by the terminal. Transmitting channel state information (CSI) to a base station; And

Receiving precoded data from the base station according to the detected precoding matrix based on the channel state information;

The precoding matrix is included in a codebook defined according to the number of layers indicated by the RI, the codebook applies a different beam vector for each column of the matrix, and the beam vector is the first precoding matrix index and the The feedback method of the terminal, characterized in that obtained based on the second precoding matrix index.
The method of claim 1, wherein the beam vector,

Based on a Discrete Fourier Transform (DFT) beam vector, up to four beams orthogonal to each other are selected for the first precoding matrix index and the second precoding matrix index. Feedback method.
The method of claim 2,

If the number of layers represented by the RI is 1, the codebook is a feedback method of a terminal, characterized in that the following table (T1),

(T1)

Where W (1) m, n is the codebook for one layer for FD MIMO, v m , v n are the beam vectors of the horizontal and vertical domains respectively, i 1 represents the PMI1 value, and i 2 Represents a PMI2 value, and d 1 and d 2 are delta values for beam direction selection for a horizontal domain and a vertical domain, respectively, wherein d 1 and d 2 have a value of 0 or 1.
The method of claim 3, wherein d 1 and d 2 are

Changed to semi statically, determined based on the CSI subframe set, or based on the CSI process, characterized in that the feedback method of the terminal.
The method of claim 2

When the number of layers represented by the RI is 5 or more, the four beams are shared for all layers.

Codeword 0 is mapped to some layers, codeword 1 is mapped to the remaining layers, and the number of beams transmitted through each codeword is two.
The method of claim 5,

When the beam is not allocated in the vertical domain or the horizontal domain with respect to any one of the layers, a zero vector is allocated to a corresponding beam vector of the codebook.
The method of claim 2

When the number of layers indicated by the RI is 5 or more, horizontal beamforming is applied to one codeword and vertical beamforming is applied to the other codeword.
In the method for receiving channel state information in a multi-antenna system,

Channel state information (CSI) including a first precoding matrix index corresponding to the horizontal domain, a second precoding matrix index corresponding to the vertical domain, and a rank indication (RI) for the number of layers for downlink transmission Receiving a) from the terminal;

Determining a codebook in consideration of the number of layers recommended by the terminal based on the RI;

Detecting a precoding matrix in the determined codebook based on the first precoding matrix index and the second precoding matrix index;

Precoding downlink data based on the detected precoding matrix and transmitting the downlink data to the terminal,

The codebook applies a different beam vector for each column of the matrix, and the beam vector is obtained based on the first precoding matrix index and the second precoding matrix index.
The method of claim 8, wherein the beam vector,

Based on a Discrete Fourier Transform (DFT) beam vector, up to four beams are selected that are orthogonal to each other with respect to the first precoding matrix index and the second precoding matrix index. How to receive information.
The method of claim 8,

When the number of layers is 1, the codebook is as shown in the following table (T2), channel state information receiving method,

(T2)

Where W (1) m, n is the codebook for one layer for FD MIMO, v m , v n are the beam vectors of the horizontal and vertical domains respectively, i 1 represents the PMI1 value, and i 2 Represents a PMI2 value, and d 1 and d 2 are delta values for beam direction selection for a horizontal domain and a vertical domain, respectively, wherein d 1 and d 2 have a value of 0 or 1.
The method of claim 10, wherein d 1 and d 2 are

A method for receiving channel state information, characterized in that changed to semi statically, determined based on a CSI subframe set, or determined based on a CSI process.
The method of claim 8

If the number of layers is 5 or more, the four beams are shared for all layers,

Codeword 0 is mapped to some layers, Codeword 1 is mapped to the remaining layers, and the number of beams transmitted through each codeword is two.
The method of claim 12,

And when the beam is not allocated in the vertical domain or the horizontal domain with respect to any one of the layers, a zero vector is assigned to a corresponding beam vector of the codebook.
An apparatus for transmitting channel state information in a multi-antenna system,

A receiver which receives a channel state information reference signal (CSI-RS) through four antenna ports for the horizontal domain and four antenna ports for the vertical domain;

A rank indication (RI) for a first precoding matrix index corresponding to the horizontal domain, a second precoding matrix index corresponding to the vertical domain, and the number of layers for downlink transmission based on the CSI-RS A processor unit for generating a CSI including; And

It includes a transmission unit for transmitting the generated CSI to a data transmission device,

The processor determines a precoding matrix of a codebook defined according to the number of layers indicated by the RI of the channel state information, and estimates a channel for reconstructing data transmitted from the data transmission apparatus using the precoding matrix. The apparatus for transmitting channel state information, further comprising a unit.