KR20210067762A - Method and apparatus for precoding downlink data in multi input multi output system - Google Patents

Abstract

A method for precoding downlink data in a multi-antenna system and a device thereof are provided. The present invention precodes a downlink pilot signal, transmits the precoded downlink pilot signal to a user terminal, and receives selective path gain information from a user terminal. The present invention can precode downlink data by using selective path gain information.

Description

Method and apparatus for precoding downlink data in a multi-antenna system {METHOD AND APPARATUS FOR PRECODING DOWNLINK DATA IN MULTI INPUT MULTI OUTPUT SYSTEM}

The present disclosure provides a method and apparatus for precoding downlink data in a multi-antenna system.

In a large-scale multiple input/output system, the base station precodes and transmits data to achieve a high data rate. In this case, precoding requires downlink channel information.

In a frequency division duplex (FDD) system, which is the most used in the existing cellular system, since different frequency resources are allocated and used in uplink and downlink, the base station downlinks to the user terminal to obtain downlink channel information. Transmit a link pilot signal.

The user terminal estimates a downlink channel using the received downlink pilot signal, and feeds back quantized downlink channel information to the base station. The base station pre-codes data based on the feedback downlink channel information and transmits it to the user terminal.

Recently, there is a need for reducing pilot overhead and feedback overhead in a large-capacity antenna system.

Korean Patent Registration: KR 10-1669857 B1 (Announcement Date: 2016.10.27)

An object of the present invention is to provide a method and apparatus for precoding downlink data in a multi-antenna system. Another object of the present invention is to provide a computer-readable recording medium in which a program for executing the method in a computer is recorded. The technical problem to be achieved by the present embodiment is not limited to the technical problems as described above, and other technical problems may be inferred from the following embodiments.

As a technical means for achieving the above technical problem, a first aspect of the present disclosure provides a method for precoding downlink data in a multi-antenna system, the method comprising: precoding a downlink pilot signal; transmitting the precoded downlink pilot signal to a user terminal and receiving selective path gain information from the user terminal; Precoding downlink data by using the selective path gain information; may include a method.

The receiving of the selective path gain information includes transmitting the precoded downlink pilot signal to a user terminal and receiving quantized selective path gain information from the user terminal. can do.

The method further comprising: receiving an uplink pilot signal from the user terminal, and estimating angle information of a downlink pilot signal based on angle information of the uplink pilot signal; The step may include precoding downlink data using the angle information of the downlink pilot signal and the selective path gain information.

A second aspect of the present disclosure provides an apparatus for precoding downlink data in a multi-antenna system, comprising: a memory in which at least one program is stored; and a processor for driving the apparatus by executing the at least one program, wherein the processor precodes a downlink pilot signal, transmits the precoded downlink pilot signal to a user terminal, and It is possible to provide an apparatus that receives selective path gain information and pre-codes downlink data using the selective path gain information.

A third aspect of the present disclosure provides a multi-antenna system for transmitting data, comprising: a base station; and a user terminal transmitting and receiving data with the base station, wherein the base station precodes a downlink pilot signal, transmits the precoded downlink pilot signal to the user terminal, and selects a path from the user terminal It is possible to provide a system that receives gain information and pre-codes downlink data using the selective path gain information.

In addition, the user terminal receives the downlink pilot signal precoded from the base station, estimates selective path gain information using the precoded downlink pilot signal, and quantizes the estimated selective path gain information. and to transmit the quantized selective path gain information to the base station, it is possible to provide a system.

In addition, the base station receives an uplink pilot signal from the user terminal, estimates angle information of a downlink pilot signal based on angle information of the uplink pilot signal, and determines the angle information of the downlink pilot signal and the It is possible to provide a system for precoding downlink data using selective path gain information.

In addition, the user terminal may provide a system that quantizes the selective path gain information estimated using a codebook, and the selective path gain information includes a codeword and an index.

A fourth aspect of the present disclosure may provide a computer-readable recording medium in which a program for executing the method of the first aspect is recorded on a computer.

According to the above-described problem solving means of the present disclosure, the base station can directly estimate the downlink angle information from the uplink pilot signal of the user terminal by using the characteristic that the channel angle information is similar in the uplink and the downlink. Accordingly, the user terminal feeds back only the path gain information among the multipath elements of the channel, thereby reducing pilot overhead.

In addition, according to the above-described problem solving means of the present disclosure, the base station pre-codes and transmits a downlink pilot signal to receive a selective path gain vector rather than the entire channel vector of the user terminal. Accordingly, the vector estimated and fed back by the user terminal is not a channel vector in the dimension of the number of antennas, but a path gain vector in a dimension much smaller than this. As a result, the pilot resource for estimating the path gain vector and the feedback resource for feeding back the path gain vector are no longer proportional to the number of transmit antennas, but are proportional to the number of selected paths, so feedback overhead is reduced in a large capacity antenna system. do.

1 is a diagram for explaining a multi-antenna system according to an embodiment.
2 is an exemplary diagram illustrating a data transmission flow between a base station and a user terminal according to an embodiment.
3 is an exemplary diagram for explaining a technique for precoding downlink data using selective path gain information according to an embodiment.
4 is a flowchart illustrating a method of precoding downlink data in a multi-antenna system according to an embodiment.
5 is a block diagram illustrating a hardware configuration of an apparatus for precoding downlink data in a multi-antenna system according to an embodiment.

The appearances of the phrases "in some embodiments" or "in one embodiment" in various places in this specification are not necessarily all referring to the same embodiment.

Some embodiments of the present disclosure may be represented by functional block configurations and various processing steps. Some or all of these functional blocks may be implemented in various numbers of hardware and/or software configurations that perform specific functions. For example, the functional blocks of the present disclosure may be implemented by one or more microprocessors, or by circuit configurations for a given function. Also, for example, the functional blocks of the present disclosure may be implemented in various programming or scripting languages. The functional blocks may be implemented as an algorithm running on one or more processors. Also, the present disclosure may employ prior art for electronic configuration, signal processing, and/or data processing, and the like. Terms such as “mechanism”, “element”, “means” and “configuration” may be used broadly and are not limited to mechanical and physical components. In addition, terms such as "... unit", "... module", etc. described in the specification mean a unit that processes at least one function or operation, which is implemented as hardware or software, or a combination of hardware and software. can be

In addition, the connecting lines or connecting members between the components shown in the drawings only exemplify functional connections and/or physical or circuit connections. In an actual device, a connection between components may be represented by various functional connections, physical connections, or circuit connections that are replaceable or added.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

1 is a diagram for explaining a multi-antenna system according to an embodiment.

Referring to FIG. 1 , the multi-antenna system includes a base station 110 and a user terminal 120 .

The user terminal 120 may be fixed or mobile, and may be referred to by other terms such as a mobile station (MS), a user terminal (UT), a subscriber station (SS), and a wireless device.

The base station 110 generally refers to a fixed station that communicates with the user terminal 120, and other terms such as Node-B, Base Transceiver System (BTS), and Access Point. may be referred to as One or more cells may exist in one base station 110 .

Downlink (DL) means communication from the base station 110 to the user terminal 120 , and uplink (UL) means communication from the user terminal 120 to the base station 110 . In the downlink, the transmitter may be part of the base station 110 and the receiver may be part of the user terminal 120 . In the uplink, the transmitter may be part of the user terminal 120 and the receiver may be part of the base station 110 .

The user terminal 120 and the base station 110 may perform wireless communication. The wireless communication system may be an Orthogonal Frequency Division Multiplexing (OFDM)/Orthogonal Frequency Division Multiple Access (OFDMA) based system. OFDM uses multiple orthogonal subcarriers. OFDM uses an orthogonality characteristic between an inverse fast Fourier transform (IFFT) and a fast Fourier transform (FFT). The transmitter performs IFFT on the data and transmits it. The receiver restores original data by performing FFT on the received signal. The transmitter uses the IFFT to combine the multiple subcarriers, and the receiver uses the corresponding FFT to separate the multiple subcarriers.

The multi-antenna system may be a multiple-input multiple-output (MIMO) system. Alternatively, the multi-antenna system may be a multiple-input single-output (MISO) system or a single-input single-output (SISO) system or a single-input multiple-output (SIMO) system. ) can also be a system. A 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.

2 is an exemplary diagram illustrating a data transmission flow between a base station and a user terminal according to an embodiment.

Hereinafter, a large-capacity antenna system including a base station 210 having N linear antenna systems uniformly arranged and K user terminals 220 having a single antenna is assumed.

는, 수학식 1과 같이 P개의 경로로 이루어진 다중경로채널 모델을 사용하여 표현할 수 있다. Downlink channel between the base station 210 and the user terminal k

, can be expressed using a multi-path channel model consisting of P paths as shown in Equation (1).

는 i번째 경로의 경로이득을 나타내고,

는 i번째 경로의 각도를 나타낸다.

는 아래의 수학식 2와 같이 정의된 방향 벡터를 나타낸다.In Equation 1 above

represents the path gain of the i-th path,

denotes the angle of the i-th path.

denotes a direction vector defined as in Equation 2 below.

는 방향 벡터

를 이용하여 수학식 3과 같이 정의된다. 또한,

는 경로이득 벡터로서 수학식 4와 같이 정의된다. direction matrix

is the direction vector

It is defined as in Equation 3 using Also,

is a path gain vector and is defined as in Equation (4).

는 상향링크와 하향링크에서 유사하므로, 기지국(210)은 하향링크의 각도 정보를 사용자 단말(220)로부터 피드백 받지 않고, 사용자 단말(220)의 상향링크 파일럿 신호로부터 하향링크의 각도 정보를 추정할 수 있다. 이에 따라, 사용자 단말(220)은 경로이득만을 기지국(210)에 피드백하게 된다.On the other hand, angle information

Since is similar in uplink and downlink, the base station 210 estimates downlink angle information from the uplink pilot signal of the user terminal 220 without receiving feedback of downlink angle information from the user terminal 220 can Accordingly, the user terminal 220 feeds back only the path gain to the base station 210 .

However, the number of propagation paths is 2 to 8 in the mmwave band of 6 GHz or higher, and 10 to 20 in the sub-6 GHz band, which is set in the 3GPP channel model. have. In the present invention, feedback overhead can be reduced by allowing the user terminal 220 to feed back only L path gains, which are a part of the total P path gains.

를 추정하고 기지국에 피드백할 수 있다. 선택적 경로이득 정보를 피드백하는 구체적인 과정은 도 3에서 후술하기로 한다.User terminal k is the selective path gain vector of Equation 5

can be estimated and fed back to the base station. A detailed process of feeding back the selective path gain information will be described later with reference to FIG. 3 .

3 is an exemplary diagram for explaining a technique for precoding downlink data using selective path gain information according to an embodiment.

Referring to FIG. 3 , the base station 310 may receive an uplink pilot signal from the user terminal k 320 .

As described above in FIG. 2 , since the uplink and downlink angle information are similar to each other, the base station 310 does not receive the downlink angle information from the user terminal k 320 , and does not receive feedback from the user terminal k 320 . Downlink angle information can be estimated from the uplink pilot signal.

The base station 310 may precode the downlink pilot signal for selective path gain estimation.

는 수학식 6과 같이 나타낼 수 있다.In general, a downlink pilot signal transmitted from the base station 310 at time t

can be expressed as Equation (6).

는 각 안테나 요소를 위한 파일럿 심볼 벡터를 나타낸다. 본 발명에서 제안하는 하향링크 파일럿 프리코딩 기술을 하향링크 파일럿 신호

에 적용하면, 시간 t에 기지국(310)에서 전송하는 하향링크 파일럿 신호

를 수학식 7과 같이 나타낼 수 있다.In Equation 6 above

denotes the pilot symbol vector for each antenna element. The downlink pilot precoding technique proposed in the present invention is used as a downlink pilot signal.

When applied to, the downlink pilot signal transmitted from the base station 310 at time t

can be expressed as in Equation 7.

는 파일럿 프리코딩 행렬을 나타낸다. 시간 t에 사용자 단말 k(320)가 수신하는 수신신호

는 수학식 8과 같이 나타낼 수 있다.In Equation 7 above

denotes the pilot precoding matrix. The reception signal received by the user terminal k (320) at time t

can be expressed as in Equation 8.

는 가우시안 노이즈를 나타낸다. 행렬-벡터 형태로 모은 사용자 단말 k(320)의 수신신호

는 수학식 9와 같이 나타낼 수 있다.In Equation 8 above

represents Gaussian noise. The received signal of the user terminal k (320) collected in a matrix-vector form

can be expressed as in Equation 9.

는 파일럿 심볼 행렬로서 수학식 10과 같이 나타낼 수 있고,

는 가우시안 노이즈 벡터로서 수학식 11과 같이 나타낼 수 있다.In Equation 9 above

is a pilot symbol matrix, and can be expressed as in Equation 10,

is a Gaussian noise vector and can be expressed as in Equation (11).

에 파일럿 심볼 행렬

를 곱한 값인 수학식 12의

를 수신한다.User terminal k (320) is a received signal

on the pilot symbol matrix

of Equation 12, which is a value multiplied by

receive

값만이 남게 된 것은, 아래 수학식 13에 제시된 파일럿 프리코딩 행렬의 직교성 때문이다.Finally, in Equation 12,

The reason that only the values remain is due to the orthogonality of the pilot precoding matrix shown in Equation 13 below.

를 적절히 디자인함으로써, 사용자 단말 k(320)가 실제 채널 벡터

가 아닌 선택적 경로이득 벡터

를 수신하도록 할 수 있다. That is, in the present invention, the pilot precoding matrix

By properly designing the user terminal k 320, the actual channel vector

An optional path gain vector that is not

can be received.

는, 채널 벡터

를 경로이득 벡터

로 줄이는 역행렬

와, 경로이득 벡터

를 선택적 경로이득 벡터

로 압축하는 압축행렬

를 포함한다. 역행렬

는 수학식 14와 같이 나타낼 수 있고, 압축행렬

는 수학식 15와 같이 나타낼 수 있다.pilot precoding matrix

is, the channel vector

is the path gain vector

the inverse matrix reduced to

with path gain vector

is an optional path gain vector

compression matrix to compress

includes inverse matrix

can be expressed as in Equation 14, and the compression matrix

can be expressed as in Equation 15.

는 수학식 16과 같이 나타낼 수 있다. Combining Equations 14 and 15 above, the downlink pilot precoding matrix

can be expressed as Equation (16).

는 수학식 17과 같이 나타낼 수 있다. When Equation 16 is applied to Equation 12, the reception signal received by the user terminal k 320

can be expressed as in Equation 17.

는 수학식 18과 같이 추정된다. If the linear least squares error estimation method is used, the selective path gain vector

is estimated as in Equation (18).

를 추정한 후,

를 양자화할 수 있다. 사용자 단말 k(320)는 코드북을 이용하여

를 양자화할 수 있다.The user terminal k (320) is a selective path gain vector through the above-described process.

After estimating

can be quantized. User terminal k (320) using the codebook

can be quantized.

가 주어졌을 때, 사용자 단말 k(320)가 기지국(310)으로 피드백하는 코드워드의 인덱스

는 수학식 19와 같이 나타낼 수 있다. Specifically, the B-bit codebook

When is given, the index of the codeword that the user terminal k 320 feeds back to the base station 310

can be expressed as in Equation 19.

를 피드백한다. When the codeword and the index are determined, the user terminal k 320 determines the index determined by the base station 310 .

feedback

를 피드백 받은 후,

를 이용하여 하향링크 데이터를 프리코딩할 수 있다.The base station 310 receives selective path gain information from the user terminal k 320 .

After receiving feedback,

can be used to precode downlink data.

에 기초하여 하향링크 데이터를 프리코딩하는 데이터 프리코딩 벡터

는 수학식 20과 같이 나타낼 수 있다.Specifically, selective path gain information

A data precoding vector for precoding downlink data based on

can be expressed as in Equation 20.

는 선택적 방향행렬로서, 수학식 21과 같이 나타낼 수 있다.At this time,

is an optional direction matrix, and can be expressed as Equation (21).

를 이용하여 송신신호 x를 전송할 수 있다. 송신신호 x는 수학식 22와 같이 나타낼 수 있다. Base station 310 data precoding vector

can be used to transmit a transmission signal x. The transmission signal x can be expressed as in Equation 22.

는 사용자 단말 j를 위한 데이터 심볼이다. 사용자 단말 k(320)의 수신신호

는 수학식 23과 같이 나타낼 수 있다.In Equation 22 above

is a data symbol for user terminal j. Received signal of user terminal k (320)

can be expressed as in Equation 23.

는 가우시안 노이즈를 나타낸다. In Equation 23 above

represents Gaussian noise.

4 is a flowchart illustrating a method of precoding downlink data in a multi-antenna system according to an embodiment.

Referring to FIG. 4 , in step 410, the base station may precode a downlink pilot signal.

Also, the base station may receive the uplink pilot signal from the user terminal and estimate angle information of the downlink pilot signal based on the angle information of the uplink pilot signal. That is, the base station can estimate the downlink angle information from the uplink pilot signal of the user terminal without receiving feedback of the downlink angle information from the user terminal. Accordingly, the user terminal feeds back only the path gain to the base station.

In step 420, the base station may transmit a precoded downlink pilot signal to the user terminal and receive selective path gain information from the user terminal.

The base station may transmit a precoded downlink pilot signal to the user terminal and receive quantized selective path gain information from the user terminal.

Specifically, when the base station transmits the precoded downlink pilot signal to the user terminal, the user terminal can estimate selective path gain information using the precoded downlink pilot signal. The user terminal may quantize the estimated selective path gain information and transmit the quantized selective path gain information to the base station.

Meanwhile, the user terminal may quantize the estimated selective path gain information using a pre-stored codebook. The selective path gain information transmitted from the user terminal to the base station may include a codeword and an index.

In step 430, the base station may precode downlink data using the selective path gain information.

Also, the base station may precode downlink data using angle information and selective path gain information of the downlink pilot signal.

According to the present disclosure, the base station may pre-code and transmit the downlink pilot signal to receive the selective path gain vector rather than the entire channel vector of the user terminal. Accordingly, the vector estimated and fed back by the user terminal is not a channel vector in the dimension of the number of antennas, but a path gain vector in a dimension much smaller than this. As a result, the pilot resource for estimating the path gain vector and the feedback resource for feeding back the path gain vector are no longer proportional to the number of transmit antennas, but are proportional to the number of selected paths, so feedback overhead is reduced in a large capacity antenna system. can be

5 is a block diagram illustrating a hardware configuration of an apparatus for precoding downlink data in a multi-antenna system according to an embodiment.

Referring to FIG. 5 , the device 500 may include a processor 510 , a communication unit 520 , and a memory 530 . Only the components related to the embodiment are shown in the device 500 of FIG. 5 . Accordingly, it can be understood by those skilled in the art that other general-purpose components may be further included in addition to the components shown in FIG. 5 .

The apparatus 500 may be implemented as various types of devices, such as a personal computer (PC), a server device, a mobile device, and an embedded device. The apparatus 500 may be mounted on a base station.

The processor 510 may control a series of processes for precoding downlink data in the multi-antenna system described above with reference to FIGS. 1 to 4 .

The processor 510 serves to control overall functions for controlling the apparatus 500 . For example, the processor 510 generally controls the device 500 by executing programs stored in the memory 530 in the device 500 . The processor 510 may be implemented as a central processing unit (CPU), a graphics processing unit (GPU), an application processor (AP), etc. included in the device 500 , but is not limited thereto.

The communication unit 520 may include a short-range communication unit, a mobile communication unit, and a broadcast receiving unit. The communication unit 520 may obtain an output signal of each of the plurality of sub-arrays from the plurality of sub-arrays including the plurality of antennas. Alternatively, the communication unit 520 may include a plurality of antennas, and in this case, the communication unit 520 may directly receive a signal from the outside. For example, the communication unit 520 may receive an uplink pilot signal from a plurality of user terminals.

The memory 530 is hardware for storing various data processed in the device 500 . For example, the memory 530 includes data received from the communication unit 520 , data processed by the device 500 , and Data to be processed can be stored. Also, the memory 530 may store applications, drivers, and the like to be driven by the device 500 . The memory 530 is a random access memory (RAM), such as dynamic random access memory (DRAM), static random access memory (SRAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), CD- It may include ROM, Blu-ray or other optical disk storage, a hard disk drive (HDD), a solid state drive (SSD), or flash memory.

The present embodiments may be implemented in the form of an application stored in a recording medium readable by an electronic device that stores instructions and data executable by the electronic device. The instructions may be stored in the form of program code, and when executed by a processor, a predetermined program module may be generated to perform a predetermined operation. Further, the instruction, when executed by a processor, may perform certain operations of the disclosed embodiments.

The present embodiments may also be implemented in the form of a recording medium including instructions executable by a computer, such as a program module executed by a computer. Computer-readable media can be any available media that can be accessed by a computer and includes both volatile and nonvolatile media, removable and non-removable media. In addition, computer-readable media may include both computer storage media and communication media. Computer storage media includes both volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data. Communication media typically includes computer readable instructions, data structures, other data in modulated data signals, such as program modules, or other transport mechanisms, and includes any information delivery media.

Also, in this specification, "unit" may be a hardware component such as a processor or circuit, and/or a software component executed by a hardware component such as a processor.

The description of the present specification described above is for illustration, and those of ordinary skill in the art to which the content of this specification belongs will understand that it can be easily modified into other specific forms without changing the technical spirit or essential features of the present invention. will be able Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive. For example, each component described as a single type may be implemented in a dispersed form, and likewise components described as distributed may be implemented in a combined form.

The scope of the present embodiment is indicated by the claims to be described later rather than the detailed description, and it should be construed as including all changes or modifications derived from the meaning and scope of the claims and their equivalents.

Claims (11)

A method for precoding downlink data in a multi-antenna system, the method comprising:
precoding a downlink pilot signal;
transmitting the precoded downlink pilot signal to a user terminal and receiving selective path gain information from the user terminal;
precoding downlink data using the selective path gain information;
A method comprising The method of claim 1,
Receiving the selective path gain information comprises:
transmitting the precoded downlink pilot signal to a user terminal and receiving quantized selective path gain information from the user terminal;
A method comprising The method of claim 1,
The method is
receiving an uplink pilot signal from the user terminal and estimating angle information of a downlink pilot signal based on angle information of the uplink pilot signal;
further comprising,
The precoding of the downlink data comprises:
precoding downlink data using angle information of the downlink pilot signal and the selective path gain information;
A method comprising An apparatus for precoding downlink data in a multi-antenna system, the apparatus comprising:
a memory in which at least one program is stored; and
a processor for driving a device by executing the at least one program;
The processor is
precoding a downlink pilot signal;
Transmitting the precoded downlink pilot signal to a user terminal and receiving selective path gain information from the user terminal;
The apparatus of precoding downlink data by using the selective path gain information. 5. The method of claim 4,
The processor is
Transmitting the precoded downlink pilot signal to a user terminal and receiving quantized selective path gain information from the user terminal. 5. The method of claim 4,
The processor is
receiving an uplink pilot signal from the user terminal, and estimating angle information of a downlink pilot signal based on angle information of the uplink pilot signal;
and precoding downlink data using angle information of the downlink pilot signal and the selective path gain information. In the multi-antenna system for transmitting data,
base station; and
a user terminal for transmitting and receiving data to and from the base station;
including,
The base station is
precoding a downlink pilot signal;
transmitting the precoded downlink pilot signal to the user terminal and receiving selective path gain information from the user terminal;
The system of precoding downlink data by using the selective path gain information. 8. The method of claim 7,
The user terminal is
receiving the precoded downlink pilot signal from the base station;
estimating selective path gain information using the precoded downlink pilot signal;
quantizing the estimated selective path gain information,
and transmitting the quantized selective pathgain information to the base station. 8. The method of claim 7,
The base station is
receiving an uplink pilot signal from the user terminal, and estimating angle information of a downlink pilot signal based on angle information of the uplink pilot signal;
and precoding downlink data using the angle information of the downlink pilot signal and the selective path gain information. 9. The method of claim 8,
The user terminal is
quantizing the estimated selective path gain information using a codebook,
The system of claim 1, wherein the optional pathgain information includes a codeword and an index. A computer-readable recording medium in which a program for executing the method of claim 1 in a computer is recorded.

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