KR102168637B1 - Method and apparatus of csi feedback in multiple antenna system - Google Patents

Abstract

The present invention is a method of supporting a full dimension (FD) multiple-input multiple-output (MIMO) in a multi-antenna system including four antenna ports (APs) in a horizontal domain and a vertical domain, respectively, and is unitary. Includes a codebook having characteristics The codebook is based on a DFT beam vector, and uses all possible orthogonal beams, but includes the same number of orthogonal beams between codewords in consideration of codeword layer mapping. According to the present invention, in implementing a MIMO operation using eight transmit antennas that can be implemented in a next-generation mobile communication system, system throughput performance can be improved by providing a codebook optimized for 2D beamforming or FD MIMO. have.

Description

CSI feedback method and apparatus in a multi-antenna system {METHOD AND APPARATUS OF CSI FEEDBACK IN MULTIPLE ANTENNA SYSTEM}

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

Existing mobile communication systems can support eight transmit antennas for a beamforming operation. In particular, in a multi-user (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. In relation to the configuration of an antenna in such a next-generation mobile communication system, a closely-spaced X-polarized antenna, for example, from 0.5 to 0.7λ is considered. However, in the current long term evolution (LTE) Release 10, only antenna arrangements in a horizontal direction are considered for a beamforming operation. In order to further improve MIMO performance, a full dimension (FD) MIMO supporting both horizontal and vertical directions should be introduced.

On the other hand, next-generation mobile communication systems such as LTE (long term evolution) Release 12 aim to support up to 64 transmit antennas with a two-dimensional antenna configuration in relation to closed loop (CL) MIMO operation. Are doing. As a first step, an 8 APs FD MIMO scheme supporting 8 antenna ports (APs) based on a 2D array should be supported. CSI feedback for stably supporting FD MIMO including up to 8 transmit antennas is a very important issue, and a new precoding codebook design for 8 APs is required.

An object of the present invention is to provide a CSI feedback method and apparatus in a multi-antenna system.

Another technical problem of the present invention is to provide a codebook design for supporting FD MIMO.

Another technical problem of the present invention is to provide a codebook design optimized for 2D beamforming.

Another technical problem of the present invention is to provide a codebook design in consideration of layer mapping of codewords.

Another technical problem of the present invention is to provide an 8 APs codebook design.

According to an aspect of the present invention, in a multi-antenna system, FD (Full Dimension) MIMO (multiple dimensional) performed by a terminal is performed for a base station including four antenna ports (APs) for a horizontal domain and a vertical domain, respectively. -input multiple-output) support method is provided. The method is CSI (Channel State Information) including a Precoding Matrix Index (PMI) 1 corresponding to the horizontal domain, a PMI2 corresponding to the vertical domain, and a rank indication (RI) indicating the number of layers related to downlink transmission. Transmitting to the base station, and receiving precoded data from the base station based on the precoding matrix detected based on the PMI1, the PMI2, and the RI, wherein the precoding matrix is the RI It is included in a codebook defined according to the number of layers indicated by, and the codebook is characterized by being based on a Discrete Fourier Transform (DFT) beam vector.

According to another aspect of the present invention, there is provided a method of supporting FD MIMO performed by a base station including four antenna ports (APs) for a horizontal domain and a vertical domain in a multi-antenna system. The method includes receiving a CSI from the terminal including a PMI1 corresponding to the horizontal domain, a PMI2 corresponding to the vertical domain, and an RI indicating the number of layers for downlink transmission from the terminal, the layer based on the RI Determining a codebook according to the number of, detecting a precoding matrix in a corresponding codebook based on the PMI1 and the PMI2, 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 for a base station including four antenna ports for a horizontal domain and a vertical domain in a multi-antenna system is provided. The terminal is a receiver configured to receive a Channel State Information Reference Signal (CSI-RS) through four antenna ports for the horizontal domain and four antenna ports for the vertical domain from the base station, based on the CSI-RS PMI1 corresponding to the horizontal domain, PMI2 corresponding to the vertical domain, and a processor unit for generating a CSI including RI indicating the number of layers for downlink transmission, and transmitting the generated CSI to the base station A transmission unit, wherein the processor unit 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 receiving unit is based on the detected precoding matrix. It is characterized in that the precoded data is received from the base station.

According to the present invention, in implementing MIMO operation using up to 8 transmit antennas that can be implemented in a next-generation mobile communication system, it is optimized for 2D beamforming or FD MIMO in consideration of codeword to layer mapping. By providing a codebook, 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 shows a multi-antenna system according to an example of the present invention.
5 shows an example of codeword to layer mapping for 5-layer transmission.
6 shows an example of codeword to layer mapping for 6-layer transmission.
7 shows an example of codeword to layer mapping for 7 layer transmission.
8 shows an example of codeword to 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 the present invention.
10 is an example of a block diagram showing a terminal and a base station according to the present invention.

Hereinafter, some embodiments will be described in detail through exemplary drawings in the present specification. In adding reference numerals to elements of each drawing, it should be noted that the same elements are assigned the same numerals as possible even if they are indicated on different drawings. In addition, in describing an embodiment of the present specification, if it is determined that a detailed description of a related known configuration or function may obscure the subject matter of the present specification, a detailed description thereof will be omitted.

In addition, this specification describes a wireless communication network, and the work performed in the wireless communication network is performed in the process of controlling the network and transmitting data in a system (for example, a base station) that governs the wireless communication network, or The work can be done at a terminal coupled to the network.

According to embodiments of the present invention, the meaning of “transmitting a channel” may be interpreted as meaning that information is transmitted 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).

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

Referring to FIG. 1, a 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 (evolved-NodeB, eNB) 11. Each base station 11 provides a communication service for a specific cell (15a, 15b, 15c). One base station can serve multiple cells. In the present invention, the base station 11 refers to a transmitting/receiving terminal that shares information and control information with a terminal for cellular communication, and includes a base station (BS), a base transceiver system (BTS), an access point, and It may be called a different term such as a femto base station, a home base station (Home nodeB), and a relay. Cell is meant to encompass all of a variety of coverage areas such as megacells, macrocells, microcells, picocells, and femtocells.

The terminal 12 (user equipment, UE) may be fixed or mobile, and may be a mobile station (MS), a mobile terminal (MT), a user terminal (UT), a subscriber station (SS), a wireless device, and a PDA. (personal digital assistant), wireless modem (wireless modem), handheld device (handheld device) can be referred to as 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 a part of the base station 11 and the receiver may be a part of the terminal 12. In the uplink, the transmitter may be a part of the terminal 12 and the receiver may be a part of the base station 11. There are no restrictions on multiple access techniques applied to wireless communication systems. 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 , OFDM-CDMA, such as various multiple access techniques can be used. For uplink transmission and downlink transmission, a Time Division Duplex (TDD) scheme transmitted using different times may be used, or a Frequency Division Duplex (FDD) scheme transmitted using different frequencies may be used.

The layers of the radio interface protocol between the terminal 12 and the base station 11 are first based on the lower three layers of the Open System Interconnection (OSI) model, which is widely known in communication systems. It may be divided into a layer (L1), a second layer (L2), and a third layer (L3). Among them, a 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, the PDCCH (Physical Downlink Control Channel) allocates resources of a Paging Channel (PCH) and a Downlink Shared Channel (DL-SCH) to the terminal 12 and a Hybrid Automatic Repeat Request (HARQ) related to the DL-SCH. ) Informs information. The PDCCH may carry an uplink grant that informs the UE 12 of resource allocation for uplink transmission. The DL-SCH is mapped to the PDSCH (physical downlink shared channel). The PCFICH (Physical Control Format Indicator Channel) informs the terminal 12 of the number of OFDM symbols used for PDCCHs, and is transmitted every subframe. The PHICH (Physical Hybrid ARQ Indicator Channel) is a downlink channel and carries a HARQ ACK/NACK signal that is a response of an uplink transmission.

Next, as an uplink physical channel, HARQ (Hybrid Automatic Repeat Request) ACK (Acknowledgement) / NACK (Non-acknowledgement), channel status information (CSI) indicating downlink channel status, for example, Channel Quality Indicator (CQI) ), 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 an UL-SCH (Uplink Shared Channel). PRACH (Physical Random Access Channel) carries a random access preamble.

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 the characteristics of the UE 12 receiver and signal to interference plus noise ratio (SINR). The base station 11 may determine a modulation (QPSK, 16-QAM, 64-QAM, etc.) and a coding rate to be applied to the downlink channel using CQI. CQI can be generated in several ways. For example, a method of quantizing the channel state as it is and providing feedback, a method of calculating and feeding back a signal to interference plus noise ratio (SINR), a method of indicating a state that is actually applied to a channel such as a Modulation Coding Scheme (MCS). have. When the CQI is generated based on the MCS, the MCS includes a modulation method, a coding method, and a corresponding coding rate.

PMI provides information on a precoding matrix in codebook-based precoding. PMI is related to multiple-input multiple-output (MIMO). PMI feedback in MIMO is referred to as CL MIMO (closed loop MIMO).

RI is information on a rank recommended by the terminal 12 (ie, the number of layers). That is, RI represents the number of independent streams used for spatial multiplexing. RI is fed back only when the UE operates in the MIMO mode using spatial multiplexing. RI is always associated with more than one CQI feedback. That is, the CQI fed back 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 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. The multi-antenna system can be referred to as a MIMO system. Alternatively, a multi-antenna system is 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.

The multi-antenna transmission/reception scheme used for operation of a multi-antenna system is FSTD (frequency switched transmit diversity), SFBC (Space Frequency Block Code), STBC (Space Time Block Code), and CDD (Cyclic Delay Diversity). , TSTD (time switched transmit diversity), or the like may be used.

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

)를 추정할 수 있다.Since the terminal 12 knows the information of the reference signal, it is possible to accurately obtain data sent from the base station 11 by estimating a channel based on the received reference signal and compensating for the channel value. If the reference signal transmitted from the base station 11 is p, the channel information experienced by the reference signal is h, the thermal noise generated by the terminal 12 is n, and the signal received by the terminal 12 is y, y = h. It can be expressed as p + n. At this time, since the reference signal p is already known to the terminal 12, when using the LS (Least Square) method, channel information (

) Can be estimated.

는

값에 의존하게 되므로, 정확한 h값의 추정을 위해서는

이 0에 수렴시킬 필요가 있다. 많은 개수의 참조 신호를 이용함으로써

의 영향을 최소화하여 채널을 추정할 수 있다. Here, the channel estimate value estimated using the reference signal p

Is

Depends on the value, so for accurate estimation of h

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

The channel can be estimated by minimizing the influence of.

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

Downlink reference signals include a channel state information (CSI) reference signal (CSI-RS) and a DMRS.

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

The wireless communication system 10 may operate according to various transmission modes. For example, transmission mode 0 may be a mode supporting only a single antenna port, while transmission modes 9 and 10 may be a mode capable of supporting 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, carrying a symbol (or signal) and the second symbol (or signal) together. which another symbol on the same antenna port is conveyed).

One unique resource grid exists in one antenna port. Each element in the resource grid for the antenna port p is called a resource element (RE), and each resource element is identified by an index pair (k,l) in every slot. Here, 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 the time This is the symbol index in the region. The resource element represents the smallest frequency-time unit to which a modulation symbol of a data channel or a modulation symbol of a 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 MxN resource elements.

In a 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 the four physical antennas.

The number of antenna ports and the unique resource grid of each antenna port are determined depending on a reference signal configuration in a 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 depending on the configuration of the CSI-RS and the arrangement of the CSI-RS ports to the physical antennas. , 16, 32, 64}, and each antenna port may have a unique pattern carrying CSI-RS as shown in FIG. 2 or 3. Hereinafter, a 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 referred to as a CSI-RS pattern.

2 and 3 illustrate a CSI-RS pattern according to an example of the present invention. 2 is an example in which a CSI-RS is mapped to a resource element in the case of a normal CP (cyclic prefix), and FIG. 3 is 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 an antenna port P. For example, R ₁₅ refers to a CSI-RS transmitted through the antenna port 15. When one antenna port is supported in FIG. 2, the CSI-RS pattern is that the CSI-RS is mapped to resource elements (2, 5) and (2, 6) of the antenna port 15. Or, assuming that 8 antenna ports are supported in FIG. 2, the CSI-RS pattern is mapped to resource elements (2, 5) and (2, 6) of the antenna ports 15 and 16, and the CSI-RS pattern is It is mapped to resource elements (8, 5) and (8, 6) of 18, and is mapped to resource elements (3, 5) and (3, 6) of antenna ports 19 and 20, and resource elements of antenna ports 21 and 22 It is mapped to (9, 5) and (9, 6).

In this way, each number of antenna ports has a unique CSI-RS pattern. 2 and 3, in a wireless communication system equipped with 8 physical antennas, a total of 8 antenna ports 15 to 22 for transmitting CSI-RS are defined. 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, the antenna ports transmitting CSI-RS may be extended to antenna ports 15 to 63.

4 shows a multi-antenna system according to an example of the present invention.

Referring to FIG. 4, a 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 that supports 1, 2, 4, and 8 antenna ports, the base station 410 supports a two-dimensional antenna array having 8 or more antenna ports. For example, the number of eight or more antenna ports supported by the base station 400 may be any one of {16, 32, 64}. That is, the base station 400 may support an antenna port corresponding to a multiple of 8. Here, when the base station 400 supports multi-user MIMO (MU-MIMO) operation, for example, 10 terminals may be simultaneously supported.

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

Meanwhile, the terminal 830 feeds back two PMIs to the base station 410 based on the CSI-RS. In this case, for example, PMI1 may correspond to a horizontal antenna port, and PMI2 may correspond to a vertical antenna port. That is, PMI1 may be for beamforming in a horizontal direction, and PMI2 may be for beamforming in a vertical direction. Of course, as an example, it is natural that PMI1 may correspond to a vertical antenna port and PMI2 may correspond to a 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 supported in each direction, whether in a horizontal or vertical direction, is one of 2, 4, and 8.

Codebooks for two and four antenna ports are designed based on an independent spatial channel. On the other hand, the codebook for the eight antenna ports is designed based on an x-polarized antenna configuration. For all antennas, if the x polarized antenna is not used, the optimized codebook is redesigned, and the co-phasing part is not required. When based on an original codenook, an embodiment of the present invention can design a codebook by a combination of a discrete fourier transform (DFT) beam and beam selection.

In an 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) Maintain the unitary characteristics of the codebook. That is, each column of the matrix in the codebook is orthogonal to each other.

(2) Reuse the DFT beam for 4 APs.

(3) Two double beam selection operations for 2D are performed through two different PMIs.

(4) Eliminate co-phasing motion. The co-paging operation is replaced by a beam selection operation.

(5) Optimization of the codebook size is considered.

(6) Beam direction selection and optimization of configuration are considered.

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

First, in order to design a codebook for 8 APs, a 4 APs DFT beam vector v _m as shown in the following equation may be used.

Referring to Equation 2, a vector υ _m of size 4 is designed in a form in which the phase is sequentially changed from the 1st element 1 to the 4th element e ^{j6 πm/32} . The [] ^T means a transposition matrix, and m is an integer of 0 to 31. Therefore, the vector v _m has a total of 32 beam directions. The codebook design to be described later according to the present invention may be configured by selecting a specific beam direction from among the 32 beam directions.

First Example : One Layer Codebook ( layer codebook)

For a codebook for one layer (ie, rank 1 codebook), only one beam direction is required to be selected. 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. Each PMI may have 4 bits to maintain the codebook size defined in the current standard. Therefore, in this case, only 16 beam directions can be selected. In order to fully use the 32 beam directions, a delta value may be added to a parameter for each horizontal and vertical domain of the codebook, which may be represented as in Table 1 below.

Table 1 is 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 and v _n are beam vectors of the horizontal domain and the vertical domain, respectively, i ₁ represents the PMI1 (e.g., PMI corresponding to the horizontal domain), and i ₂ represents the PMI2 (e.g., the vertical domain). PMI) value. And, d ₁ and d ₂ are delta values for selecting a beam direction for a horizontal domain and a vertical domain, respectively. The d ₁ and d ₂ have a value of 0 or 1. According to Table 1 above, m=2i ₁ +d ₁ , n=2i ₂ +d ₂ , and i ₁ and i ₂ each have values from 0 to 15, so m and n can 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 the case of Alt 1, d ₁ and d ₂ may be configured through RRC signaling. That is, the d ₁ and d ₂ may be semi statically changed.

As another example, in the case of Alt 2, d ₁ and d ₂ depend on a CSI subframe set (depend on). For example, d ₁ and d ₂ may be determined as in Equation 3 and Equation 4 below, respectively.

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} are configured by an upper layer, resource-restricted CSI measurements are configured in the UE.

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

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

Meanwhile, as another example, in the case of Alt 3, the d ₁ and d ₂ may be determined according to the CSI process. In LTE Rel 11, a multiple CSI process may be configured in a transmission mode (TM) 10, and thus, a terminal supporting TM 10 may be configured with two different CSI processes. Accordingly, d ₁ and d ₂ may be determined according to each CSI process. For example, d ₁ =0 and d ₂ =0 for one CSI process, and d ₁ =1 and d ₂ =1 for the other CSI process.

Second Example : 2 Layer Codebook

For a codebook for 2 layers (ie, rank 2 codebook), 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 respectively corresponding to the horizontal domain and the vertical domain are used. In order to reduce the interference between the two layers, the difference in direction of the two beams should be maximized. Among a total of 32 directions, 16 cases in which the beams of each layer have a direction orthogonal to each other (i.e., v _{m (n),} v _{m (n) +16} ) are have. Each ?PMI may have 4 bits to maintain the rank 2 codebook size defined in the current standard. The rank 2 codebook can be represented as shown in the following table.

Table 2 is an example of a codebook for 2-layer CSI reporting using 8 antenna ports (numbers 15 to 22). Referring to Table 2, W ⁽²⁾ _m,n is a codebook for 2 layers for FD MIMO. v _m and v _n are beam vectors of the horizontal domain and the vertical domain, respectively, i ₁ represents the PMI1 (e.g., PMI corresponding to the horizontal domain), and i ₂ represents the PMI2 (e.g., the vertical domain). The PMI) value is as described above. The same is the case below. The columns of the matrix included in the codebook correspond to the number of layers.

Third Example : 3 Layer Codebook

For a codebook for 3 layers (ie, rank 3 codebook), 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 respectively corresponding to the horizontal domain and the vertical domain are used. In order to reduce the interference between the three layers, the difference in direction of the three beams should be maximized. There are 16 cases in which the difference in the direction of the three beams becomes the maximum 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 can be represented as shown in the following table.

Table 3 is 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 3 layers for FD MIMO.

Fourth Example : 4 Layer Codebook

For a codebook for 4 layers (ie, rank 4 codebook), selection of 4 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 respectively 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 in which the difference in the directions of the four beams becomes maximum. Each PMI may have 3 bits to maintain the rank 4 codebook size defined in the current standard. The rank 4 codebook can be represented as shown in the following table.

Table 4 is an example of a codebook for 4-layer CSI reporting using 8 antenna ports (numbers 15 to 22). Referring to Table 4, W ⁽⁴⁾ _m,n is a codebook for 4 layers for FD MIMO.

No. 5 Example : 5 Layer Codebook

For a codebook for 5 layers (ie, rank 5 codebook), selection of 5 beam directions is required. That is, five beam directions should be selected for each of the horizontal and vertical domains based on two PMIs. However, according to the 4 APs-based DFT beam vector described in Equation 2, the number of orthogonal beams that can be selected is a maximum of 4. In order to maintain the unitary characteristic of the codebook, an orthogonal structure between columns of a matrix included in the codebook must be maintained. To design a codebook including a matrix having an orthogonal structure, codeword to layer mapping must be considered. Therefore, the following rules can be followed for the rank 5 codebook design.

(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 up to 4 orthogonal beams exist for the rank 5 codebook, 4 beams are shared for 5 layers. That is, 4 beams are allocated to 5 layers for both the horizontal domain and the vertical domain. In this case, each layer includes at least one beam.

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

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

Referring to FIG. 5, codeword 0 is mapped to layers 1 and 2, and codeword 1 is mapped to layers 3, 4, and 5. In this case, beams of the same number are allocated 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) of layers 3 to 5.

On the other hand, when no one layer has a beam in a vertical domain or a horizontal domain, a 0 vector may be inserted.

Reflecting the above method, the rank 5 codebook can be expressed as follows.

Table 6 is 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.

Meanwhile, the codebook of Table 6 has a problem in that the power applied to the layers is different, and the rank 5 codebook may be expressed as follows in order to ensure that all layers have the same power.

Table 7 is another example of a codebook for 5-layer CSI reporting using 8 antenna ports (numbers 15 to 22).

Meanwhile, the codebook of Table 7 has a problem in 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 can be designed. That is, a rank 5 codebook to which domain (or dimension)-based codeword division is applied may be expressed as follows.

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

In addition, when the codeword layer mapping is optimized in terms of diversity, the rank 5 codebook can be expressed as follows.

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

No. 6 Example : 6 Layer Codebook

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

For rank 6 (ie, 6 layer transmission), the following codeword layer mapping may be applied.

6 shows an example of codeword to 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, beams of the same number are allocated 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 6 may share two beams for each domain (or dimension). On the other hand, when no one layer has a beam in a vertical domain or a horizontal domain, a 0 vector may be inserted.

Reflecting the above method, the rank 6 codebook can be expressed as follows.

Table 10 is an example of a codebook for 6-layer CSI reporting using 8 antenna ports (numbers 15 to 22). W ⁽⁶⁾ _m,n is a codebook for 6 layers for FD MIMO.

Meanwhile, the codebook of Table 10 has a problem in that the power applied to the layers is different from each other, and the rank 6 codebook may be expressed as follows in order to ensure that all layers have the same power.

Table 11 is another example of a codebook for 6-layer CSI reporting using 8 antenna ports (numbers 15 to 22).

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

Table 12 is another example of a codebook for 6-layer CSI reporting using 8 antenna ports (numbers 15 to 22).

No. 7 Example : 7 Layer Codebook

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

For rank 7 (ie, 7 layer transmission), the following codeword layer mapping may be applied.

7 shows an example of codeword to 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, beams of the same number are allocated 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 7 may share two beams for each domain (or dimension). On the other hand, when no one layer has a beam in a vertical domain or a horizontal domain, a 0 vector may be inserted.

Reflecting the above method, the rank 7 codebook can be expressed as follows.

Table 13 is 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.

Meanwhile, the codebook of Table 13 has a problem in that the power applied to the layers is different, and the rank 7 codebook can be expressed as follows in order to ensure that all layers have the same power.

Table 14 is another example of a codebook for reporting layer 7 CSI using 8 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 can be expressed as follows.

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

Meanwhile, when optimizing in terms of codeword layer mapping, the rank 7 codebook can be expressed as follows.

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

No. 8 Example : 8 Layer Codebook

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

For rank 8 (ie, 8 layer transmission), the following codeword layer mapping may be applied.

8 shows an example of codeword to 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, beams of the same number are allocated to codeword 0 and codeword 1. That is, layers 1 to 4 may share two beams for each domain (or dimension), and layers 5 to 8 may share two beams for each domain (or dimension). On the other hand, when no one layer has a beam in a vertical domain or a horizontal domain, a 0 vector may be inserted.

Reflecting the above method, the rank 8 codebook can be expressed as follows.

Table 17 is an example of a codebook for reporting 8-layer CSI 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 another codeword, the rank 8 codebook can be expressed as follows.

Table 18 is 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.

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

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 a 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 in Tables 1 to 4 and Tables 6 to 18. In this case, in each table, i ₁ corresponds to PMI1 and i ₂ corresponds to PMI2 as described above.

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

According to the present invention, in implementing an FD MIMO operation using up to eight transmit antennas that can be implemented in a next-generation mobile communication system, a codebook optimized for 2D beamforming is prepared in consideration of codeword to layer mapping. By providing, system throughput performance can be improved.

10 is an example of a block diagram showing a terminal and a base station according to the present invention. The terminal and the base station according to the present invention may use the antenna configuration as shown in FIG. 5 described above. In addition, the base station according to the present invention may use four antenna ports for each of the horizontal and vertical directions.

Referring to FIG. 10, the terminal 1000 includes a terminal receiving unit 1005, a terminal processor 1010, and a transmitting unit 1020.

The terminal receiver 1005 receives a CSI-RS from the base station 1050. In this case, the terminal receiving unit 1005 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 may perform channel estimation based on the CSI-RS, and, as a result, may determine PMI1 corresponding to horizontal APs, PMI2 corresponding to vertical APs, and RI indicating the number of layers.

The terminal processor 1010 generates the PMI1, PMI2, and RI and sends them to the transmission unit 1020. Then, the terminal transmission unit 1020 transmits the CSI report including the PMI1, PMI2 and RI to the base station 1050. PMI1 corresponds to APs in the horizontal domain, and PMI2 corresponds to APs in the vertical domain.

The base station 1050 includes a base station transmitting unit 1055, a base station receiving unit 1060, and a base station processor 1070.

The base station transmission unit 1055 transmits a reference signal including a CSI-RS to the terminal 1000.

The base station receiver 1060 receives a CSI report from the terminal 1000. The CSI report includes PMI1, PMI2 and RI. Here, PMI1 corresponds to APs in the horizontal domain, and PMI2 corresponds to APs in the vertical domain.

When the base station receiving unit 1060 receives the CSI report from the terminal 1000, the base station processor 1070 determines a codebook according to the number of layers based on the RI, and free in the corresponding codebook based on the PMI1 and PMI2. It is possible to detect the coding matrix. In this case, the base station processor 1070 may use one of the codebooks according to the layers described in Tables 1 to 4 and Tables 6 to 18. In this case, in each table, i ₁ corresponds to PMI1 and i ₂ corresponds to PMI2 as described above.

In addition, the base station processor 1070 generates precoded data based on the detected precoding matrix, and transmits the precoded data to the terminal 1000 through the base station transmission unit 1055.

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

Claims (20)

A method of supporting full dimension (FD) multiple-input multiple-output (MIMO) by a terminal performed for a base station including four antenna ports (APs) for a horizontal domain and a vertical domain in a multi-antenna system to,
The base station provides Channel State Information (CSI) including a Precoding Matrix Index (PMI) 1 corresponding to the horizontal domain, a PMI2 corresponding to the vertical domain, and a rank indication (RI) indicating the number of layers for downlink transmission. Transferring to; And
Receiving from the base station precoded data based on the precoding matrix detected based on the PMI1, the PMI2, and the RI,
The precoding matrix is included in a codebook defined according to the number of layers indicated by the RI, and the codebook is based on a Discrete Fourier Transform (DFT) beam vector,
A method of supporting FD MIMO, characterized in that up to four beams orthogonal to each other are selected for each of the horizontal domain and the vertical domain based on the DFT beam vector. delete The method of claim 1,
When the number of layers indicated by the RI is 1, the codebook is an FD MIMO support method, characterized in that as shown in Table (T1),

(T1)
Here, W ⁽¹⁾ _m,n is a codebook for 1 layer for FD MIMO, v _m and v _n are beam vectors of horizontal and vertical domains, respectively, i ₁ represents a PMI1 value, and i ₂ Denotes a PMI2 value, d ₁ and d ₂ are delta values for selecting a beam direction for a horizontal domain and a vertical domain, respectively, and d ₁ and d ₂ have values of 0 or 1. The method of claim 3,
The d ₁ and d ₂ are characterized in that the semi-statically (semi statically) is changed, FD MIMO support method. The method of claim 4,
Receiving the d ₁ and the d ₂ from the base station through RRC (Radio Resource Control) signaling, characterized in that the FD MIMO support method. The method of claim 3,
The d ₁ and d ₂ are characterized in that it depends on the CSI subframe set (set), FD MIMO support method. The method of claim 3,
The d ₁ and d ₂ are determined based on a CSI process, FD MIMO supporting method. The method of claim 1
When the number of layers indicated 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 other layers, and the number of beams transmitted through each codeword is 2, FD MIMO support method The method of claim 8,
When the beam is not allocated in a vertical domain or a horizontal domain for any one of the layers, a 0 vector is assigned to a corresponding beam vector of the codebook. The method of claim 1
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 another codeword. A method for supporting FD MIMO performed by a base station including four antenna ports (APs) for a horizontal domain and a vertical domain in a multi-antenna system,
Receiving a CSI from a terminal including a PMI1 corresponding to the horizontal domain, a PMI2 corresponding to the vertical domain, and an RI indicating the number of layers for downlink transmission;
Determining a codebook according to the number of layers based on the RI;
Detecting a precoding matrix in a corresponding codebook based on the PMI1 and the PMI2;
Generating precoded data based on the detected precoding matrix; And
Including the step of transmitting the precoded data to the terminal,
The codebook is based on the DFT beam vector,
A method of supporting FD MIMO, characterized in that up to four beams orthogonal to each other are selected for each of the horizontal domain and the vertical domain based on the DFT beam vector. delete The method of claim 11,
When the number of layers is 1, the codebook is an FD MIMO support method, characterized in that as shown in Table (T2),

(T2)
Here, W ⁽¹⁾ _m,n is a codebook for 1 layer for FD MIMO, v _m and v _n are beam vectors of horizontal and vertical domains, respectively, i ₁ represents a PMI1 value, and i ₂ Denotes a PMI2 value, d ₁ and d ₂ are delta values for selecting a beam direction for a horizontal domain and a vertical domain, respectively, and d ₁ and d ₂ have values of 0 or 1. The method of claim 13,
The d ₁ and d ₂ are characterized in that the semi-statically (semi statically) is changed, FD MIMO support method. The method of claim 14,
The method further comprising the step of transmitting the d ₁ and the d ₂ to the terminal through RRC signaling, FD MIMO support method. The method of claim 13,
The d ₁ and d ₂ are characterized in that it depends on the CSI subframe set (set), FD MIMO support method. The method of claim 13,
The d ₁ and d ₂ are determined based on a CSI process, FD MIMO supporting method. The method of claim 11
When 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 other layers, and the number of beams transmitted through each codeword is 2, FD MIMO support method The method of claim 18,
When the beam is not allocated in a vertical domain or a horizontal domain for any one of the layers, a 0 vector is assigned to a corresponding beam vector of the codebook. A terminal supporting FD MIMO for a base station including 4 antenna ports for a horizontal domain and a vertical domain in a multi-antenna system,
A receiver configured to receive a Channel State Information Reference Signal (CSI-RS) from the base station through four antenna ports for the horizontal domain and four antenna ports for the vertical domain;
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 the number of layers for downlink transmission based on the CSI-RS; And
Including a transmission unit for transmitting the generated CSI to the base station,
The processor unit 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,
The receiving unit receives precoded data from the base station based on the detected precoding matrix,
The terminal, characterized in that up to four beams orthogonal to each other are selected for each of the horizontal domain and the vertical domain based on the DFT beam vector.

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