KR101531687B1 - Muti-user multi-input multi-output communication system for constant modulus beamforming - Google Patents

Abstract

A terminal of a multi-user MIMO communication system calculates channel direction information and channel quality information in a zero forcing mode based on expected other user interference. In addition, the UE can calculate the channel direction information and the channel quality information in the PU2RC mode by reusing the channel direction information and the channel quality information in the zero forcing mode. In addition, the base station can design an optimized precoding vector based on the feedback information.

Multi-user, multiple input / output, MIMO, precoding, feedback, codebook, channel quality information

Description

[0001] MUTI-USER MULTI-INPUT MULTI-OUTPUT COMMUNICATION SYSTEM FOR CONSTANT MODULUS BEAMFORMING [0002]

The following embodiments are directed to a multi-user multi-input / multi-output communication system, and more particularly to a closed-loop multi-user multi-input / output communication system using a codebook of a limited size.

2. Description of the Related Art In recent years, researches for providing various services such as a multimedia service in a wireless communication environment and transmitting data at a high quality and at a high speed have been actively conducted. As a part of this research, a technology related to a multiple input multiple output (MIMO) communication system using a plurality of channels in a spatial domain is rapidly developing.

In a MIMO communication system, a base station can use a Spatial Division Multiplexing (SDM) scheme and a Spatial Division Multiplexing Access (SDMA) scheme. That is, the base station can simultaneously transmit a plurality of data streams through a plurality of antennas according to the SDM scheme, and can transmit a plurality of data streams to a plurality of users through a plurality of antennas according to the SDMA scheme.

In this case, in order for the base station to efficiently transmit a plurality of data streams using a plurality of antennas, channel information about downlink channels formed between the plurality of antennas of the base station and at least one user must be grasped. Thus, at least one user must feed channel information for downlink channels back to the base station, and users use a codebook of limited size for feedback.

A method of operating a terminal for a MIMO communication system according to an exemplary embodiment of the present invention includes: calculating expected user interference from an effective reception signal; Calculating channel direction information and channel quality information in a zero-forcing mode based on the expected other user interference; And feeding back the channel direction information and the channel quality information to the serving base station.

The step of calculating the channel direction information and the channel quality information in the zero-forcing mode uses the Jensen's inequality to estimate the signal to interference ratio (SNR) of the UE in the zero- plus Noise Ratio (SINR), and calculating the channel direction information and the channel quality information based on the calculated lower limit.

The step of calculating the channel direction information and the channel quality information in the zero-forcing mode includes generating the effective reception signal from the received signal in association with the calculation of the channel direction information and the channel quality information And calculating a combining vector to be used.

The step of calculating channel direction information and channel quality information in the zero-forcing mode may include zero-forcing the at least one neighboring base station of the serving base station, ) Mode and the channel quality information in the channel mode information.

The method of operating a terminal for a MIMO communication system according to an embodiment of the present invention includes calculating a channel direction information and channel quality information in the zero forcing mode with a first codebook corresponding to a zero- ; A second codebook corresponding to a Per User Unitary Rate Control (PU2RC) mode, and the second codebook is jointly designed with the first codebook. - Considering the channel quality information in the zero forcing mode and the PU2RC mode Generating intermediate information indicating a relationship between channel quality information in the channel quality information; And feeding back the intermediate information to the serving base station.

Wherein the step of calculating the channel direction information and the channel quality information in the PU2RC mode includes the step of reusing the channel direction information and the channel quality information in the zero forcing mode with the second codebook to determine channel direction information and channel quality information in the PU2RC mode, May be a step of calculating information.

The channel direction information in the PU2RC mode may be calculated by the base station based on channel direction information in the zero forcing mode and an angle or a chordal distance between the elements of the second codebook.

Wherein the step of calculating channel direction information and channel quality information in the PU2RC mode includes calculating channel direction information and channel quality information in the PU2RC mode based on channel direction information in the zero forcing mode and an angle or a chordal distance between elements of the second codebook. And calculating channel direction information in the channel information.

The intermediate information may be related to the difference between the channel quality information in the zero forcing mode and the channel quality information in the PU2RC mode.

The step of feeding back the intermediate information may further include feedback of channel direction information and channel quality information in the zero forcing mode.

The method of operating a terminal for a MIMO communication system may further include calculating the expected other user interference from a valid received signal.

The method of operating a terminal for a MIMO communication system may further include the step of feeding back an indicator indicating whether a dedicated reference signal is requested to the serving base station.

(

는 복소수)을 고려하여 대상 사용자를 위한 프리코딩 벡터 의 초기치를 설정하는 단계,

의 값에 따라 미리 정의된 적어도 두 개의 방식들 중 적어도 하나의 방식을 이용하여

(

는 대상 사용자의 채널임)를 계산하는 단계 및 상기 계산된

를 기초로 상기 프리코딩 벡터 를 최적화하는 단계를 포함한다.A method of operating a base station for a MIMO communication system in accordance with an embodiment of the present invention includes: recognizing channels between the at least two users and the base station based on feedback information transmitted from at least two users; Your Channel

(

Setting an initial value of a precoding vector for a target user in consideration of a complex number)

Using at least one of the at least two predefined schemes according to the value of < RTI ID = 0.0 >

(

Is a channel of the target user) and calculating

And optimizing the precoding vector based on the precoding vector.

를 계산하는 단계는 상기

의 값에 따라

및

를 이용하여 상기

를 계산하는 단계일 수 있다.remind

Wherein the step

Depending on the value of

And

Lt; / RTI >

. ≪ / RTI >

를 계산하는 단계는 상기

의 값에 따라

및

를 이용하여 상기

를 계산하는 단계일 수 있다.remind

Wherein the step

Depending on the value of

And

Lt; / RTI >

. ≪ / RTI >

를 계산하는 단계는 상기

의 값에 따라

및

을 이용하여 상기

를 계산하는 단계일 수 있다.remind

Wherein the step

Depending on the value of

And

Lt; / RTI >

. ≪ / RTI >

A method of operating a base station for a MIMO communication system according to an embodiment of the present invention includes: recognizing channels between the user k and user m and the base station based on feedback information transmitted from user k and user m;

(C는 코드북)에 따라

및

를 생성하는 단계 및 상기

및

를 이용하여 상기 사용자 k를 위한 프리코딩 벡터를

(

는 상기 코드북의 엘리먼트들 중 상기 사용자 k의 채널를 나타내는 엘리먼트임)로 결정하고, 상기 사용자 m을 위한 프리코딩 벡터를

(

는 상기 코드북의 엘리먼트들 중 상기 사용자 k의 채널를 나타내는 엘리먼트임)로 결정하는 단계를 포함한다.

(C is a codebook)

And

; And

And

Lt; RTI ID = 0.0 > k < / RTI >

(

Is an element indicating the channel of the user k among the elements of the codebook), and determines a precoding vector for the user m as

(

Is an element representing the channel of the user k among the elements of the codebook).

The method of operating a terminal for a MIMO communication system according to an embodiment of the present invention includes calculating a channel direction information and channel quality information in the zero forcing mode with a first codebook corresponding to a zero- ; And a second codebook corresponding to a Per User Unitary Rate Control (PU2RC) mode, wherein the second codebook is jointly designed with the first codebook. The channel direction information and the channel quality in the zero- And calculating channel direction information and channel quality information in the PU2RC mode by reusing the information.

Also, an operation method of a base station for a MIMO system according to an embodiment of the present invention includes channel direction information in the zero forcing mode generated based on a first codebook corresponding to a zero-forcing mode, Quality information or a second codebook corresponding to a Per User Unitary Rate Control (PU2RC) mode, the second codebook being jointly designed with the first codebook. And at least one of channel quality information; And calculating channel direction information and channel quality information in the PU2RC mode based on channel direction information and channel quality information in the zero forcing mode or calculating channel direction information and channel quality information in the PU2RC mode based on channel direction information and channel quality information in the PU2RC mode, And calculating channel direction information and channel quality information in the forcing mode.

The UE according to an embodiment of the present invention can efficiently calculate channel direction information and channel quality information in each of the zero forcing mode and the PU2RC mode.

The UE according to an exemplary embodiment of the present invention can support switching between the zero forcing mode and the PU2RC mode while minimizing the feedback overhead through the proposed feedback procedure.

The base station according to an exemplary embodiment of the present invention can design an optimized precoding vector or precoding matrix.

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

1 is a diagram illustrating an example of a multi-user MIMO communication system.

Referring to FIG. 1, a multi-user MIMO communication system includes one base station 110 and a plurality of users 120, 130, and 140. M transmission antennas are installed in the base station 110, and one or more reception antennas may be installed in each of the plurality of users 120, 130, and 140.

Channels (downlink channels or uplink channels) exist between the base station 110 and each of the plurality of users 120, 130 and 140, and the base station 110 and each of the plurality of users (120, 130, 140) transmit / receive signals through the channels.

The base station 110 may transmit a plurality of data streams to the plurality of users 120, 130, and 140 at the same time. At this time, the base station 110 can operate in various modes such as Spatial Division Multiplexing Access (SDMA), Zero-Forcing Beam Forming, and Per User Unitary Rate Control (PU2RC). Here, PU2RC is unitary precoding. In the PU2RC mode, the BS 110 schedules only users orthogonal to each other and precodes data streams. On the other hand, in the zero forcing mode, the base station 110 can simultaneously beam-form data streams to users that are not orthogonal to each other. Also, in the zero forcing mode, the base station 110 uses a precoding matrix or precoding vector that is properly designed so that the signal to other simultaneously scheduled users is zero (0).

At this time, the base station 110 has to grasp the channel information on the downlink channels in order to perform beamforming or to select at least one of the plurality of users 120, 130, and 140. Here, the channel information may include channel direction information, preferred precoding matrix information, channel quality information, and the like.

In particular, the base station 110 may transmit at least one of the plurality of users 120, 130, and 140 using various user selection algorithms such as GUS (Greedy User Selection, Semi-orthogonal User Selection) You can choose.

The base station 110 may transmit the pilot signals to the plurality of users 120, 130, and 140 via the downlink channel. Here, the pilot signal is a well-known signal to the base station 110 and the plurality of users 120, 130, and 140. At this time, each of the plurality of users 120, 130, and 140 may estimate the downlink channels formed between the base station 110 and the plurality of users 120, 130, and 140 using the pilot signal.

Also, each of the plurality of users 120, 130, and 140 feeds channel information for downlink channels back to the base station 110 based on the estimates for the downlink channels. Herein, the channel information fed back to the base station 110 by the plurality of users 120, 130, and 140 is referred to as feedback information.

In addition, the plurality of users 120, 130, and 140 use a codebook having a limited size to reduce feedback overhead. That is, the plurality of users 120, 130, and 140 may transmit information (e.g., index) related to at least one of the elements included in the codebook having a limited size based on the estimates of the downlink channels, The feedback overhead can be reduced.

It is assumed that M transmit antennas are installed in the base station 110 and there are K users. At this time, it is assumed that each of the K users includes Nr reception antennas, and each of the base station 110 and the K users uses a codebook including 2 ^B unit norm vectors. Here, the size of each unit vector is M x 1, and B is the number of feedback bits.

라고 하고, 기지국(110)이 사용자들의 서브 셋

를 스케쥴링한다고 가정한다. 제한된 피드백 환경에서, 각각의 사용자에게 할당되는 데이터 스트림의 최대 개수는 1로 고정된다고 가정한다. 멀티 셀 및 멀티 섹터 환경에서, 사용자들의 수신 신호는 하기 수학식 1과 같이 표현될 수 있다.Codebook

, And the base station 110 transmits a subset

. ≪ / RTI > In a limited feedback environment, it is assumed that the maximum number of data streams allocated to each user is fixed at one. In multi-cell and multi-sector environments, the received signals of users can be expressed as: < EMI ID = 1.0 >

[Equation 1]

사이의 채널 매트릭스이고, G는 전송 매트릭스, u는 데이터 스트림들을 의미한다. 또한, I는 인터 셀 간섭이고,

이고,

이다. 여기서,

의 생성 방법은 MU-MIMO 모드(예를 들어, SDMA 모드, ZF 모드)에 의존한다. 그리고,

는 스케쥴링된

명의 사용자들 각각에 의해 수신된 신호들의 벡터이고, n은 복소 가우시안 노이즈 벡터이다.Here, H denotes a base station 110 and a subset of users

G is the transmission matrix, u is the data stream. I is inter-cell interference,

ego,

to be. here,

MIMO mode (e.g., SDMA mode, ZF mode). And,

Lt; / RTI >

Lt; / RTI > is the vector of signals received by each of the users, and n is a complex Gaussian noise vector.

는 M 개의 전송 안테나들로부터

명의 사용자들로의 물리적인 채널의 채널 매트릭스이고,

는 사용자 k의 유효 채널을 의미한다. 여기서,

로서

는 1xM 사이즈의 벡터이고, 사용자 k의

은 수신 빔포밍 벡터 또는 결합 벡터이다.And,

RTI ID = 0.0 > M < / RTI &

Lt; / RTI > is the channel matrix of the physical channel to the users,

Means the effective channel of user k. here,

as

Is a vector of 1xM size, and the user k

Is a receive beamforming vector or a combine vector.

When a reception signal of user k as _k r, the effective received signal of user k can be expressed by Equation (2).

&Quot; (2) "

를 곱함으로써, 유효 수신 신호 y_k를 생성한다. 여기서,

는 r 번째 기지국 및 j 번째 빔으로부터 사용자 k로의 인터 셀 간섭을 나타내는 항목으로서,

이고,

이다.

는 r 번째 기지국으로부터 사용자 k로의 물리적 채널을 나타낸다. That is, the user and k is the received signal r _k

To generate an effective received signal y _k . here,

Denotes an inter-cell interference from the r-th base station and the j-th beam to the user k,

ego,

to be.

Represents the physical channel from the r < th > base station to user k.

의 방향을 양자화한다. 즉, 사용자 k의 유효 채널

의 방향은

로 양자화되며,

는 코드북 C에 포함된 복수의 엘리먼트들 중 선택된 단위 놈 벡터

이다.

명의 사용자들이 모두 그들의 유효 채널들을 양자화한 경우, 양자화된 유효 채널들은

로 표현될 수 있다. For zero-forcing beamforming, user k is a valid channel

The direction of the pixel is quantized. That is, the effective channel

The direction of

Lt; / RTI >

Among the plurality of elements included in the codebook C,

to be.

If all of the users have quantized their effective channels, the quantized effective channels

. ≪ / RTI >

Further, the zero-forcing transmission matrix can be expressed by the following equation (3).

&Quot; (3) "

는 파워 규준화 계수들의 벡터이고, 전송 신호의 파워 제한(constraint)을 강제한다. 선택된 사용자들에게 균등하게 파워를 할당하기 위해서는

이다. 여기서,

는 F(s)의 k 번째 컬럼을 의미한다.Where F (s) is the precoding matrix for the selected users,

Is a vector of power normalization coefficients and forces the power constraint of the transmitted signal. In order to allocate power evenly to selected users

to be. here,

Is the kth column of F (s).

2 is a conceptual diagram illustrating inter-cell interference and intra-cell interference.

Referring to FIG. 2, the terminal A can receive a transmission signal from the base station 2 to the terminal C. At this time, the transmission signal from the terminal A to the base station 2 acts as intercell interference.

In addition, internal cell interference may occur in the terminal A. That is, the base station 1 can simultaneously transmit signals to the terminal A and the terminal B by beamforming multiple streams using PU2RC, ZFBF, etc., and a signal corresponding to the beam for the terminal B among the beams formed by the base station 1, A, and a signal corresponding to the beam for the terminal A among the beams formed by the base station 1 acts on the terminal B as an internal cell interference.

3 is a flowchart illustrating an operation method of a terminal according to an embodiment of the present invention.

Referring to FIG. 3, a terminal previously selected by the base station calculates another user interference expected (S310). Here, the expected other user interference includes expected inter-cell interference or expected internal cell interference.

At this time, the expected intra-cell interference

을 통해 계산될 수 있으며, 기대 인터 셀 간섭은

을 통해 계산될 수 있다.

, And expected inter-cell interference

Lt; / RTI >

In addition, the UE computes E [SINR _k ] in the zero forcing mode considering the expected other user interference (S320). More specifically, the UE can compute E [SINR _k ] in zero forcing mode based on at least one of expected inter-cell interference or expected inter-cell interference.

At this time, the terminal can calculate E [SINR _k ] in zero-forcing mode by calculating the lower bound of E [SINR _k ] using Jensen's inequality. That is, the terminal can use Equation (4) below.

&Quot; (4) "

는 j 번째 인터 셀 간섭으로부터 사용자 k로의 물리적 채널을 의미한다.here,

Denotes the physical channel from the jth inter-cell interference to the user k.

In addition, the terminal calculates optimal channel direction information and channel quality information in a zero forcing mode (S330).

는 하기 수학식 5와 같이 정의될 수 있다.It is assumed that constant coefficient beamforming is used in neighboring cells and each transmit antenna of neighboring cells applies a maximum transmit power. In this case, since p _k is not known to the users, the channel quality information in the zero-forcing mode of the user k,

Can be defined by the following equation (5).

&Quot; (5) "

는 상수이고,

이다. 사용자 k의 기대 SINR에 대한 근사적인(approximated) 하한은 하기 수학식 6과 같이 다시 쓰여질 수 있다.here,

Is a constant,

to be. The approximated lower bound for the expected SINR of user k can be rewritten as: < EMI ID = 6.0 >

&Quot; (6) "

을 얻을 수 있다. 여기서,

이고,

,

이다.Through some matrix manipulation,

Can be obtained. here,

ego,

,

to be.

At this time, the following equation (7) can be defined.

&Quot; (7) "

및 최적의 양자화된 유효 채널

는 하기 수학식 8을 통하여 최적화될 수 있다.Also, the optimal joint vector for user k

And an optimal quantized effective channel

Can be optimized through the following equation (8).

&Quot; (8) "

이므로, 사용자 k는 상기 수학식 8을 이용하여 최적의

를 찾을 수 있으며, 최적의

및 상기 수학식 7을 이용하여 최적의 결합 벡터

를 찾을 수 있다. 결국, 사용자 k는 최적의

의 인덱스를 채널 방향 정보로 생성할 수 있으며, 상기 수학식 6 및 최적의

을 통해 계산되는 최적의

를 채널 품질 정보로 생성할 수 있다. In other words,

Therefore, the user k can calculate the optimal

You can find the optimal

And using Equation (7)

Can be found. As a result,

May be generated as channel direction information, and Equation (6) and the optimal

The optimal

As channel quality information.

Finally, the user k feeds channel direction information and channel quality information in the zero forcing mode to the base station (S340).

4 is a table showing channel direction information and channel quality information corresponding to each of the PU2RC mode and the ZF mode according to an embodiment of the present invention.

Prior to description with reference to FIG. 4, the multi-user MIMO communication system according to an embodiment of the present invention may adaptively use one of a zero forcing mode and a PU2RC mode. Here, the switching between the zero-forcing mode and the PU2RC mode can be dynamic or semi-static.

와 PU2RC 모드에서의 채널 방향 정보

를 파악할 수 있어야 한다. 뿐만 아니라, 기지국은 제로 포싱 모드에서의 채널 품질 정보

및 PU2RC 모드에서의 채널 품질 정보

를 파악할 수 있어야 한다.However, in order to support both the zero forcing mode and the PU2RC mode, as shown in the table of FIG. 4, the base station transmits channel direction information

And channel direction information in the PU2RC mode

. In addition, the base station transmits the channel quality information in the zero-

And channel quality information in the PU2RC mode

.

Hereinafter, control signaling of a multi-user MIMO communication system will be described.

Control signaling includes downlink control signaling carried on a physical downlink control channel (PDCCH) and uplink control signaling carried on a physical uplink control channel (PUCCH). do.

- Dynamic switching between zero forcing mode and PU2RC mode

Codebooks with at least two types for constant coefficient beamforming may be proposed. That is, a first codebook C1 having a large size can be used for the zero-forcing mode, and a second codebook C2 having a small size for the PU2RC mode can be used. Here, the second codebook C2 is designed in conjunction with the first codebook C1. For example, the second codebook C2 may be a subset of the first codebook C1.

및 채널 방향 정보

는 제1 코드북 C1을 가지고 상기 수학식 4 내지 8을 통해 계산될 수 있다. 이 때, PU2RC 모드에서의 채널 방향 정보

는 제로 포싱 모드에서의 채널 방향 정보

를 재활용함으로써, 계산될 수 있다. 그러나, PU2RC 모드에서의 채널 방향 정보

는 제2 코드북 C2를 가지고 계산되어야 하므로, 제2 코드북 C2를 가지고 uncorrelated 채널들에 대한 코달 거리를 기초로

는

로 맵핑될 수 있다. 즉, 상기 수학식 9를 통하여

가 계산될 수 있다.Channel quality information in zero forcing mode

And channel direction information

Can be calculated through Equations 4 to 8 with the first codebook C1. At this time, the channel direction information in the PU2RC mode

Channel direction information in the zero forcing mode

Lt; / RTI > However, the channel direction information in the PU2RC mode

Should be computed with the second codebook C2, and therefore, based on the covariance distance for the uncorrelated channels with the second codebook C2

The

Lt; / RTI > That is, through Equation (9)

Can be calculated.

&Quot; (9) "

사이의 각도를 기초로 상기 수학식 10을 이용하여

를 계산할 수 있다.In addition, the terminal may transmit the elements in the second codebook C2

Using the above equation (10) on the basis of the angle between

Can be calculated.

&Quot; (10) "

는

을 가지고 상기 수학식 4 내지 8을 통하여 계산될 수 있다.Also, the channel quality information of the user k in the PU2RC mode

The

Can be calculated through Equations 4 to 8 above.

, 채널 방향 정보

및

를 포함한다. 여기서,

는 제로 포싱 모드에서의 채널 품질 정보

와 PU2RC 모드에서의 채널 품질 정보

사이의 차와 관련된다. 즉,

으로 정의될 수 있다.Also, the contents of the feedback information in the PUCCH are channel quality information

, Channel direction information

And

. here,

The channel quality information in the zero forcing mode

And the channel quality information in the PU2RC mode

Lt; / RTI > In other words,

. ≪ / RTI >

, 채널 방향 정보

를 요구한다. 반대로, 기지국이 PU2RC 모드로 동작한다면, 기지국은

및

를 요구하므로, 단말은

를 기지국으로 피드백할 수 있으며,

대신에

를 기지국으로 피드백할 수도 있다. 이 때, 기지국은

를 통해

를 파악할 수 있다.If the base station supports two concurrently scheduled users, the base station transmits the channel quality information in the zero forcing mode for the zero forcing mode

, Channel direction information

. Conversely, if the base station is operating in the PU2RC mode,

And

, The terminal

To the base station,

Instead of

To the base station. At this time,

Through the

.

As a result, the base station receives the channel direction information and the channel quality information in the zero forcing mode generated based on the first codebook corresponding to the zero-forcing mode from the terminal, thereby obtaining the channel direction information in the PU2RC mode, It can be seen that the channel quality information can be calculated. The base station may calculate the channel direction information and the channel quality information in the zero forcing mode by receiving the channel direction information and the channel quality information in the PU2RC mode from the terminal. At this time, the base station calculates channel direction information and channel quality information in the PU2RC mode by recycling channel direction information and channel quality information in the zero forcing mode, or calculates channel direction information and channel quality information in the PU2RC mode, The channel direction information and the channel quality information in the zero forcing mode can be calculated. In particular, the base station may calculate channel direction information and channel quality information in the PU2RC mode, or may use the intermediate information to calculate channel direction information and channel quality information in the zero forcing mode.

When the base station overturns the feedback to the users, users may request a dedicated reference signal (DRS) for the demodulation phase reference. At this time, the multi-user MIMO communication system according to an embodiment of the present invention may use an indicator indicating whether a dedicated reference signal is required in the PDCCH. This directive can reduce DRS overhead. For example, an indication of 1 means that the DRS is switched on, and a value of 0 indicates that the DRS is switched off.

- Semi-static switching between zero forcing mode and PU2RC mode

및

는 제1 코드북 C1을 가지고 계산 된다. 그리고, 제로 포싱 모드에서 피드백 정보의 컨텐츠는

,

를 포함한다. 또한, 상술한 바와 같이, PU2RC 모드에서

및

는 제2 코드북 C2를 가지고 계산된다. PU2RC 모드에서 피드백 정보의 컨텐츠는

및

를 포함한다.As described above,

And

Is calculated with the first codebook C1. In the zero-forcing mode, the content of the feedback information is

,

. Further, as described above, in the PU2RC mode

And

Is calculated with the second codebook C2. In the PU2RC mode, the content of the feedback information is

And

.

Even in the semi-static switching between the zero forcing mode and the PU2RC mode, an indicator indicating whether a dedicated reference signal is required in the PDCCH can be used. This directive can reduce DRS overhead. For example, an indication of 1 means that the DRS is switched on, and a value of 0 indicates that the DRS is switched off.

5 is a table showing examples of contents of feedback information required in each of the zero forcing mode and the PU2RC mode in dynamic switching.

, 채널 방향 정보

를 포함한다. 만약, 제로 포싱 모드에서 PU2RC 모드로 스위칭되는 경우, 피드백 정보의 컨텐츠는 채널 품질 정보

, 채널 방향 정보

및 매개 정보

를 포함 한다.Referring to FIG. 5, in the zero forcing mode, the contents of the feedback information include channel quality information

, Channel direction information

. If switching from the zero forcing mode to the PU2RC mode, the content of the feedback information is channel quality information

, Channel direction information

And mediation information

.

6 is a flowchart illustrating an operation method of a base station according to an embodiment of the present invention.

로 계산될 수 있다. 다만, 파워 손실 페널티를 줄이기 위하여 이러한 일반적인

는 변경되어야 한다.Prior to describing the method of operation of the base station with reference to FIG. 6, the general transmission matrix in the zero-

Lt; / RTI > However, in order to reduce the power loss penalty,

Should be changed.

는

에 따라 수정되어야 한다. 하지만, 현실적인 MIMO 통신 시스템에서 더 엄격한 제한

이 적용될 필요가 있다. 기지국은

의 제한을 깨지 않도록 사용자 k로부터의 채널 품질 정보

를 수정한다.First, it is necessary to analyze the power loss penalty due to power imbalance. The channel quality information in the zero forcing mode of user k

The

. However, in a realistic MIMO communication system,

Needs to be applied. The base station

The channel quality information from the user < RTI ID = 0.0 > k < / RTI &

.

및

를 정의한다.

는

의 i 번째 원소이다. 사용자 k의 전체 파워 손실은

로 정의되며,

가 일정 계수인 경우,

이고,

가 일정 계수가 아닌 경우,

이다.Also,

And

.

The

Is the i-th element of. The total power loss of user k is

Lt; / RTI >

Is a constant coefficient,

ego,

Is not a constant coefficient,

to be.

The base station may design precoding vectors or precoding matrices in the zero-forcing mode according to various methods. Here are three techniques.

- First Method

이고,

라고 가정한다. 여기서,

이다. It is assumed that user k and user m are scheduled at the same time. Besides,

ego,

. here,

to be.

라고 가정한다(S610). 여기서,

이고,

이다. Referring to FIG. 6, assuming that v is a precoding vector for user i, the base station calculates v =

(S610). here,

ego,

to be.

를 가정한다(S620). 이 때, 단계 S620-S670은 i가 0 부터 N-1까지 반복된다.In addition,

(S620). At this time, steps S620-S670 repeat i from 0 to N-1.

가 -1인지 여부를 판단한다(S630).In addition,

Is -1 (S630).

가 -1이 아닌 경우,

및

를 계산한다(S641).In addition,

Is not -1,

And

(S641).

을 계산한다(S642).In addition,

(S642).

가 -1이 아닌 경우,

및

를 계산한다(S651). 그리고, 기지국은

를 계산한다(S652).In addition,

Is not -1,

And

(S651). Then, the base station

(S652).

가 -1인 경우,

를 정의한다(S661). 여기서, 단계 S661-단계 S662는 i는 0부터 N-1까지 반복된다.In addition,

Is -1,

(S661). Here, in steps S661 to S662, i is repeated from 0 to N-1.

를 계산한다(S662).In addition,

(S662).

，

，

을 계산한다(S670). 이 때, 기지국은

，

，

을 기초로 최적의 프리코딩 벡터인

를 계산한다.In addition, the base station calculates T = max (T1, T2, T3)

,

,

(S670). At this time,

,

,

The optimal precoding vector < RTI ID = 0.0 >

.

- second method

According to the second method, one restriction can be applied to the codebook C as shown in Equation (11) below.

&Quot; (11) "

라고 하고, 사용자 m을 위한 프리코딩 벡터를 f_m이라 하는 경우,

및 f_m는 하기 수학식 12와 같이 정의될 수 있다.The precoding vector for user k is

And a precoding vector for user m is f _m ,

And f _m can be defined as Equation (12).

&Quot; (12) "

는 상기 코드북의 엘리먼트들 중 상기 사용자 k의 채널을 나타내는 엘리먼트이고,

는 상기 코드북의 엘리먼트들 중 상기 사용자 k의 채널를 나타내는 엘리먼트이다. 또한,

이다.here,

Is an element representing the channel of the user k among the elements of the codebook,

Is an element representing the channel of the user k among the elements of the codebook. Also,

to be.

,

이고,

이므로, 사용자 k 및 사용자 m에 균등한 파워가 할당된다.And, the power normalization coefficient is

,

ego,

, So that an equal power is allocated to user k and user m.

,

은

및

과 비직교한다. 이 때,

이고,

인 경우,

는

로 결정된다. 여기서,

및

이다.Also, the second method can be easily extended even when the rank is larger than 2. For example, when the user is k, m, n, and the rank is 3, the number of non-orthogonal vectors is one. In other words,

,

silver

And

Lt; / RTI > At this time,

ego,

Quot;

The

. here,

And

to be.

- Third method

을 사용할 수도 있고,

를 사용할 수도 있다.A base station according to an embodiment of the present invention may combine the first method and the second method described above. That is,

, ≪ / RTI >

May be used.

는 첫 번째 방법에서의 파워 손실이고,

는 두 번째 방법에서의 파워 손실을 의미한다. 또한,

는 제로 포싱 모드에서 일반적인 전송 매트릭스를 사용하는 경우 파워 손실을 의미한다. 그리고,

은 임계값으로서, 1 이상이다.here,

Is the power loss in the first method,

Is the power loss in the second method. Also,

Means power loss when using a general transmission matrix in zero forcing mode. And,

Is a threshold value of 1 or more.

The above-described methods may be implemented in the form of program instructions that can be executed through various computer means and recorded in a computer-readable medium. The computer-readable medium may include program instructions, data files, data structures, and the like, alone or in combination. The program instructions recorded on the medium may be those specially designed and constructed for the present invention or may be available to those skilled in the art of computer software. Examples of computer-readable media include magnetic media such as hard disks, floppy disks and magnetic tape; optical media such as CD-ROMs and DVDs; magnetic media such as floppy disks; Magneto-optical media, and hardware devices specifically configured to store and execute program instructions such as ROM, RAM, flash memory, and the like. Examples of program instructions include machine language code such as those produced by a compiler, as well as high-level language code that can be executed by a computer using an interpreter or the like. The hardware devices described above may be configured to operate as one or more software modules to perform the operations of the present invention, and vice versa.

While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. This is possible.

Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined by the equivalents of the claims, as well as the claims.

1 is a diagram illustrating an example of a multi-user MIMO communication system.

2 is a conceptual diagram illustrating inter-cell interference and intra-cell interference.

3 is a flowchart illustrating an operation method of a terminal according to an embodiment of the present invention.

4 is a table showing channel direction information and channel quality information corresponding to each of the PU2RC mode and the ZF mode according to an embodiment of the present invention.

5 is a table showing examples of contents of feedback information required in each of the zero forcing mode and the PU2RC mode in dynamic switching.

6 is a flowchart illustrating an operation method of a base station according to an embodiment of the present invention.

Claims (22)

A method of operating a terminal for a MIMO communication system, Calculating other user interference expected from the valid received signal; Calculating channel direction information and channel quality information in a zero-forcing mode based on the expected other user interference; And Feedback the channel direction information and the channel quality information to the serving base station And outputting the received signal to the terminal. The method according to claim 1, The step of calculating channel direction information and channel quality information in the zero-forcing mode comprises: Calculating a lower-bound of a signal-interference plus noise ratio (SINR) of the UE in the zero-forcing mode using Jensen's inequality, and based on the calculated lower limit, And calculating the channel direction information and the channel quality information using the channel quality information. The method according to claim 1, The step of calculating channel direction information and channel quality information in the zero-forcing mode comprises: Calculating a combining vector used to generate the effective received signal from the received signal in connection with calculating the channel direction information and the channel quality information And outputting the received signal to the terminal. The method according to claim 1, The step of calculating channel direction information and channel quality information in the zero-forcing mode comprises: Calculating a channel direction information and channel quality information in a zero-forcing mode on the assumption that at least one neighboring base station of the serving base station has a maximum transmission power; Lt; / RTI > A method of operating a terminal for a MIMO communication system, Calculating channel direction information and channel quality information in the zero forcing mode with a first codebook corresponding to a zero-forcing mode; A second codebook corresponding to a Per User Unitary Rate Control (PU2RC) mode, and the second codebook is jointly designed with the first codebook. - Considering the channel quality information in the zero forcing mode and the PU2RC mode Generating intermediate information indicating a relationship between channel quality information in the channel quality information; And Feedback the intermediate information to the serving base station And outputting the received signal to the terminal. 6. The method of claim 5, Calculating channel direction information and channel quality information in the PU2RC mode with the second codebook The method comprising the steps of: The method according to claim 6, The step of calculating channel direction information and channel quality information in the PU2RC mode And calculating channel direction information and channel quality information in the PU2RC mode by reusing channel direction information and channel quality information in the zero forcing mode with the second codebook. 8. The method of claim 7, Wherein the channel direction information in the PU2RC mode is calculated by the base station based on channel direction information in the zero forcing mode and an angle or a chordal distance between elements of the second codebook, The method comprising: 8. The method of claim 7, The step of calculating channel direction information and channel quality information in the PU2RC mode Calculating channel direction information in the PU2RC mode based on channel direction information in the zero forcing mode and an angle or a chordal distance between elements of the second codebook And outputting the received signal to the terminal. 6. The method of claim 5, Wherein the intermediate information is related to a difference between channel quality information in the zero forcing mode and channel quality information in the PU2RC mode. 6. The method of claim 5, The step of feeding back the intermediate information And further feedbacking channel direction information and channel quality information in the zero forcing mode. 6. The method of claim 5, Calculating expected other user interference from the valid received signal The method comprising the steps of: 6. The method of claim 5, A step of feeding back an indicator indicating whether a dedicated reference signal is requested to the serving base station The method comprising the steps of: A method of operating a base station for a MIMO communication system, Recognizing channels between the at least two users and the base station based on feedback information sent from at least two users; Neighbor's channel

(

Setting an initial value of a precoding vector for a target user in consideration of a complex number);

Using at least one of the at least two predefined schemes according to the value of < RTI ID = 0.0 >

(

Is a channel of the target user); And The calculated

The step of optimizing the precoding vector / RTI > 15. The method of claim 14, remind

≪ / RTI > remind

Depending on the value of

And

Lt; / RTI >

≪ / RTI > 15. The method of claim 14, remind

≪ / RTI > remind

Depending on the value of

And

Lt; / RTI >

≪ / RTI > 15. The method of claim 14, remind

≪ / RTI > remind

Depending on the value of

And

Lt; / RTI >

≪ / RTI > A method of operating a base station for a MIMO communication system, Recognizing channels between user k and user m and the base station based on feedback information sent from user k and user m;

(C is a codebook)

And

≪ / RTI > And remind

And

Lt; RTI ID = 0.0 > k < / RTI >

(

Is an element indicating the channel of the user k among the elements of the codebook), and determines a precoding vector for the user m as

(

Is an element representing the channel of the user k among the elements of the codebook) Wherein the base station comprises a base station and a base station. Calculating channel direction information and channel quality information in the zero forcing mode with a first codebook corresponding to a zero-forcing mode; And A second codebook corresponding to a Per User Unitary Rate Control (PU2RC) mode, and the second codebook is jointly designed with the first codebook. - Considering channel direction information and channel quality information in the zero- Calculating channel direction information and channel quality information in the PU2RC mode by recycling And outputting the received signal to the terminal. A method of operating a base station for a MIMO communication system, Channel direction information and channel quality information in the zero forcing mode generated based on a first codebook corresponding to a zero-forcing mode or a second codebook corresponding to a PU2RC (Per User Unitary Rate Control) mode; Receiving at least one of channel direction information and channel quality information in the PU2RC mode generated considering considering a second codebook jointly designed with the first codebook; And Calculating channel direction information and channel quality information in the PU2RC mode based on the channel direction information and channel quality information in the zero forcing mode or calculating channel direction information and channel quality information in the PU2RC mode based on channel direction information and channel quality information in the PU2RC mode, Calculating channel direction information and channel quality information in a mode Wherein the base station comprises a base station and a base station. 21. The method of claim 20, Receiving intermediate information indicating a relationship between the channel quality information in the zero forcing mode and the channel quality information in the PU2RC mode Further comprising: Calculating channel direction information and channel quality information in the PU2RC mode based on the channel direction information and channel quality information in the zero forcing mode or calculating channel direction information and channel quality information in the PU2RC mode based on channel direction information and channel quality information in the PU2RC mode, The step of calculating channel direction information and channel quality information in the mode Calculates channel direction information and channel quality information in the PU2RC mode based on the channel direction information and the channel quality information in the zero forcing mode using the intermediate information, calculates channel direction information and channel quality information in the PU2RC mode, And calculating channel direction information and channel quality information in the zero forcing mode based on the calculated channel direction information and channel quality information. 21. The method of claim 20, Calculating channel direction information and channel quality information in the PU2RC mode based on the channel direction information and channel quality information in the zero forcing mode or calculating channel direction information and channel quality information in the PU2RC mode based on channel direction information and channel quality information in the PU2RC mode, The step of calculating channel direction information and channel quality information in the mode By calculating channel direction information and channel quality information in the PU2RC mode by recycling channel direction information and channel quality information in the zero forcing mode or by reusing channel direction information and channel quality information in the PU2RC mode, And calculating channel direction information and channel quality information in a zero forcing mode.

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