KR101427420B1 - Method and apparaus for transmission in a multiple input multiple output comunication system - Google Patents

Abstract

A method for transmitting data in a MIMO communication system, the method comprising: calculating a performance reduction amount of a first transmission method and a performance reduction amount of a second transmission method according to a variable; Selecting a transmission method having a smaller amount of performance reduction by comparing the performance reduction amount of the second transmission method; and transmitting a probing signal for channel estimation of the base station when the transmission method is selected, And transmitting data according to the scheduling information. In the antenna selection method and the transmission beamforming method using a codebook according to the criteria proposed in the present invention in an environment with a limited feedback amount, By choosing a transmission method, it is possible to adaptively transmit There is an effect capable of implementing the method. It is also possible to predict which of the two transmission methods has higher performance with respect to a given feedback amount with respect to each of the number of transmission antennas, thereby enabling effective data transmission.

MIMO, Antenna Selection, Trnasmit Beamforming, Feedback

Description

TECHNICAL FIELD [0001] The present invention relates to a method and apparatus for transmitting data in a MIMO communication system,

The present invention relates to a method and apparatus for transmitting data according to a limited amount of feedback in a MIMO communication system.

In the next generation communication system, a high data rate is required, and efficient data transmission techniques based on a Multiple Input Multiple Output (MIMO) system for multiple users are actively researched. In particular, as the amount of traffic required for downlink as well as uplink has increased recently, it is necessary to study an efficient transmission technique for the uplink.

Hereinafter, an FDD (Frequency Division Duplex) based uplink MIMO system will be described.

1 is a block diagram of a general MIMO system.

개의 송신안테나 들을 포함하고,

개의 단말들(110-1~K)은 각각

개의 수신안테나들을 포함한다.1, the base station 100 includes a packet scheduler 102,

Lt; / RTI > transmit antennas,

The terminals 110-1 to 110-K are

Lt; / RTI > receive antennas.

개의 단말들(110-1~K) 각각은 프로빙(proving) 신호를 상기 기지국(100)으로 전송한다. 상기 기지국(100)의 패킷 스케쥴러(102)는 순시 채널 정보 즉, 수신한 프로빙 신호를 바탕으로 채널을 추정하여 각 단말들(110-1~K)에 대한 스케줄링 된 결과를 해당 단말들에게 궤환(feedback)한다. 이때, 상기 궤환량이 제한된다.remind

Each of the UEs 110-1 to 110-K transmits a proving signal to the base station 100. The packet scheduler 102 of the base station 100 estimates a channel on the basis of the instantaneous channel information, i.e., the received probing signal, and feeds the scheduled result for each of the terminals 110-1 to K to the corresponding terminals feedback. At this time, the feedback amount is limited.

The present invention considers an antenna selection method and a transmit beamforming method for transmitting a single stream for each terminal in order to efficiently transmit data through a limited amount of feedback. The antenna selection method selects antennas that can have the maximum sum capacity among transmit antennas that each terminal has based on channel estimation for each of the terminals in the base station. In the transmission beamforming method, a base station calculates a beamforming vector maximizing a performance sum through channel information for each UE, and feeds the calculated beamforming vector to the corresponding UEs.

The feedback of the antenna selection method is advantageous in that the feedback amount can be reduced because the base station transmits only the order of the antennas selected for the corresponding terminal in the base station, but there is a disadvantage in that there is no SNR gain obtained from the transmission beamforming method.

On the other hand, in the case of the transmission beamforming method, the SNR gain can be obtained by applying the beamforming method. However, in order to accurately obtain the SNR gain, the beamforming vector calculated by the base station must be completely fed back to the respective terminals, . Therefore, by applying the codebook technique to the calculated beamforming vector in an environment where the feedback amount is limited, the index of the representative beamforming vector having the most similar characteristics to the given beamforming vector is fed back to each terminal, Can be obtained.

The antenna selection method and the transmission beamforming method using a codebook have different performance depending on environments such as the number of transmit / receive antennas, the number of users, and the allowable feedback amount.

Therefore, in order to efficiently transmit data in an actual environment with a limited amount of feedback, the antenna selection method and the transmission beamforming method using a codebook are adaptively selected and applied, and a criterion for selection is required.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention, which is designed to solve the problems of the prior art that operates as described above, to provide an antenna transmission method and a transmission beamforming method using a codebook in a MIMO communication system with a limited feedback amount, A method and apparatus for transmitting data.

Another object of the present invention is to provide a criterion for adaptively selecting the antenna selection method and a transmission beamforming method using a codebook.

According to an aspect of the present invention, there is provided a method of transmitting data in a MIMO communication system, the method comprising: Selecting a transmission method having a smaller amount of performance reduction by comparing a performance reduction amount of the first transmission method with a performance reduction amount of the second transmission method when the transmission method is selected; Transmitting a probe signal for channel estimation of a base station, receiving scheduling information from the base station, and transmitting data according to the scheduling information.

According to another embodiment of the present invention, there is provided a method of scheduling data in a MIMO communication system, the method comprising: calculating a performance reduction amount of the first transmission method and a performance reduction amount of the second transmission method according to a variable; Selecting a transmission method having a smaller amount of decrease, and generating a scheduling information according to the selected transmission method after receiving a probing signal from the terminal and transmitting the generated scheduling information to the terminal.

An apparatus according to an embodiment of the present invention calculates a reduction amount of performance of a first transmission method and a performance reduction amount of a second transmission method according to a variable in a transmission apparatus of data in a MIMO communication system, A transmission method selecting unit for selecting a transmission method having a smaller performance reduction amount by comparing a performance reduction amount of the first transmission method with a performance reduction amount of the second transmission method; And a transmitter for receiving scheduling information from the base station and transmitting data according to the scheduling information.

An apparatus according to another embodiment of the present invention is an apparatus for scheduling data in a multi-input / output communication system, the apparatus comprising: calculating a performance reduction amount of the first transmission method and a performance reduction amount of the second transmission method according to a variable; A transmission method selecting unit selecting a transmission method having a smaller amount of decrease in the transmission rate than the first transmission method when the selected transmission method is the first transmission method after receiving the probing signal from the terminal; And a scheduling unit configured to generate scheduling information according to the second transmission method when the selected transmission method is the second transmission method after receiving the probing signal from the terminal And a second transmission method scheduler for transmitting to the terminal.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. It will be clear to those who have.

The present invention is based on the fact that when selecting an antenna selection method and a transmission method with a smaller capacity loss among a transmission beamforming system using a codebook according to the criteria proposed in the present invention when there is a limited amount of feedback, An adaptive selection mode having a sum of the performance can be implemented. It is also possible to predict which of the two transmission methods has higher performance with respect to a given feedback amount with respect to each of the number of transmission antennas, thereby enabling effective data transmission.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. First, it should be noted that, in the drawings, the same components or parts have the same reference numerals as much as possible. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted so as to avoid obscuring the subject matter of the present invention.

First, an antenna selection method and a transmission beam method, which are transmission methods used in the present invention, will be described in detail.

1) Antenna Selection Technique

개의 사용자 안테나를 선택한다. 다음으로 스케줄링을 통해 선택된

개의 사용자에 대한 안테나 순번은 궤환 채널을 통해 해당 단말에게 전송된다. 이후, 각 단말은 기지국으로부터 수신한 선택된 순번에 해당하는 안테나를 이용하여 데이터를 송신한다.In the antenna selection method, a terminal belonging to a base station network first transmits a proving signal for channel estimation to a base station, and the base station estimates a channel state between the terminals using the proving signal. In this case, when the number of terminals capable of simultaneously transmitting is limited to the number of base station antennas, the packet scheduler of the base station can maximize the sum of the channel capacities based on the estimated channel information

Select user antennas. Next, through scheduling,

The antenna sequence numbers of the users are transmitted to the corresponding UE through the feedback channel. Then, each terminal transmits data using an antenna corresponding to the selected sequence number received from the base station.

개의 단말이 존재할 때 각각의 단말은

개의 송신 안테나를 구비하고, 기지국은

개의 수신 안테나를 가지는 도 1의 시스템을 예로 들어 설명한다.

번째 단말과 기지국 간 채널이

인 채널 행렬

로 표시할 때, 각 단말에 대한 송신 안테나의 채널 벡터를

와 같이 재배열한다. 여기서, 모든 단말에 대한 채널 행렬

는

의 행렬이며 계수(Rank)는

으로 나타낸다. 따라서,

에 비해

이 작다는 가정 하에 이 채널의 자유도(Degree of Freedom)는 수신안테나 수로 제한된다. 이 경우, MMSE-SIC(Minimum Mean Square Error with Successive Interfiernece Cancellation) 수신기 구조에서 도달할 수 있는 최대 성능합은 하기 <수학식 1>과 같다.Specifically,

When there are two terminals, each terminal

, And a base station

1 < / RTI > having a plurality of receive antennas will be described as an example.

Lt; th &gt;

Channel matrix

, The channel vector of the transmission antenna for each terminal is represented by

. Here, a channel matrix for all terminals

The

And the Rank is

Respectively. therefore,

Compared to

The degree of freedom of this channel is limited to the number of receiving antennas. In this case, the maximum performance sum that can be reached in the MMSE-SIC (Minimum Mean Square Error with Successive Interference Cancellation) receiver structure is expressed by Equation (1).

는 채널 벡터의 집합(

)에서

명의 단말이 동시에 선택되었을 경우, 가능한 모든 송신 안테나 벡터들의 집합 중 채널용량을 최대화시킬 수 있는 송신 안테나 벡터들의 집합을 선택한 스케줄링 결과를 나타낸다.remind

Is a set of channel vectors (

)in

The UE selects a set of transmit antenna vectors that maximize the channel capacity among the set of all possible transmit antenna vectors.

개의 단말들에 안테나 순번을 결정하고, 이를 궤환 채널(feedback channel)을 통해서 해당 단말들에게 전송한다. 이때, 각 사용자 별로 사용되는 궤환 량은 송신 안테나

에 대하 여

비트로 나타낼 수 있다.Thereafter, the base station can maximize the above Equation (1)

Determines the antenna order number for the UEs, and transmits the determined order to the UEs through a feedback channel. At this time, the amount of feedback used for each user is determined by the transmission antenna

about

Lt; / RTI &gt;

2) transmission beamforming method

개의 단말들을 선택하고, 상기 선택된 단말들에 대한 빔포밍 벡터를 계산한다. 이때, 기지국과 단말들 사이에서는 허용 가능한 궤환량에 따른 코드북이 미리 설계되어 있다. 상기 코드북을 바탕으로 기지국은 계산된 빔포밍 벡터에 상응하는 코드북으로, 상기 코드북 내에서 가장 상관성이 높은 코드북 인덱스를 선택하여 해당 단말에게 궤환한다. 이후, 상기 단말은 상기 코드북 인덱스에 상응하는 빔포밍 벡터를 이용하여상기 기지국으로 데이터를 송신한다.The transmission beamforming method transmits a pudbling signal for channel estimation to a base station to which the terminal belongs. When the number of terminals that can be simultaneously transmitted is limited to the number of base station antennas, the packet scheduler of the base station can maximize the sum of the channel capacities based on the channel information estimated through the probing signal

Selects the UEs, and calculates a beamforming vector for the selected UEs. At this time, a codebook according to an allowable feedback amount is designed in advance between the base station and the terminals. Based on the codebook, the base station selects a codebook index having the highest correlation within the codebook as a codebook corresponding to the calculated beamforming vector, and feeds back the selected codebook index to the corresponding terminal. Then, the terminal transmits data to the base station using a beamforming vector corresponding to the codebook index.

개이고,

개의 송신 안테나 가지고 있는

개의 단말이 존재하는 도 1의 경우를 예로 들어 설명한다.

번째 단말과 기지국간 채널은

행렬

로 나타낼 수 있다. 또한

번째 단말에 대한 송신 빔포밍 벡터는

이고

인

인 벡터로 나타낸다. 이때 각각의 단말은 데이터 송신에 앞서서 모든 송신 안테나들에 대해서 프로빙 신호를 상기 기지국으로 전송하고, 이를 바탕으로 상기 기지국은 각 단말들의 채널을 고려하여

개의 안테나를 통해서 동시에 데이터를 송신할 수 있는 단말들의 집합 중에서 채널 용량 합이 최대화될 수 있도록 스케줄링을 수행한다. 이후, 상기 스케쥴링을 통해서 선택된 집합에 포함된 단말들에 대한 빔포밍 벡터를 해당 궤환 채널을 통하여 상기 단말들에게 알려준다.Specifically, the receiving antenna of the base station

And,

Having a transmitting antenna

1 in which there are two UEs will be described as an example.

The channel between the &lt; RTI ID = 0.0 &gt;

procession

. Also

The transmit beamforming vector for the &lt; RTI ID = 0.0 &gt;

ego

sign

. At this time, each of the UEs transmits a probing signal to all of the transmit antennas to the Node B prior to data transmission, and based on this, the Node B considers the channel of each UE

Scheduling is performed so that the sum of the channel capacities can be maximized among the sets of terminals capable of simultaneously transmitting data through the antennas. Thereafter, a beamforming vector for the UEs included in the selected set through the scheduling is notified to the UEs through the corresponding feedback channel.

Specifically, when the number of terminals capable of receiving data transmitted simultaneously by the base station is limited to the number of receiving antennas, the received signal vector is expressed by Equation (2).

는 총

개의 단말들 중에서 실제 데이터 전송을 수행한

개의 단말들에 대한 집합을 나타낸다. 또한,

는

인

수신 신호 벡터이고,

는 선택된 사용자들의 집합

에 대하여

번째로 선택된 사용자의 신호를 의미한다.

은 가우시안 잡음이며, 잡음 분산 행렬은

이다.Here,

Gun

The UE performs the actual data transmission among the UEs

&Lt; / RTI &gt; Also,

The

sign

Is the received signal vector,

Lt; RTI ID = 0.0 &gt;

about

Means the signal of the second selected user.

Is the Gaussian noise, and the noise variance matrix is

to be.

에 대하여

번째로 선택된 사용자의 채널과 이때 형성된 빔포밍 벡터를 통해 실효 채널 벡터(Effective Channel Vector)

가 생성되고 선택된

개의 단말들의 실효 채널 벡터를 통해

인 실효 채널 행렬(Effective Channel Matrix)

을 구할 수 있다. 상기 실효 채널 행렬을 통해서 채널과 빔포밍 벡터를 고려한 채널 용량 합은 하기 <수학식3>과 같이 나타내어 진다.remind

about

The effective channel vector is obtained through the channel of the user selected first and the beamforming vector formed at this time,

Is created and selected

Through the effective channel vector of the UEs

Effective Channel Matrix < RTI ID = 0.0 >

Can be obtained. The channel capacity sum considering the channel and the beamforming vector through the effective channel matrix is expressed by Equation (3).

개의 단말들이 동시에 전송 가능하고 각각 송신 빔포밍을 사용할 때 도달할 수 있는 채널 용량 합을 나타낸다. 이때, 시스템이 최대 채널 용량 합을 갖기 위해서는 각각의 단말들이 할당된 전력 을f모두 사용한다는 조건 하에 반복 해(iterative solution) 방식을 통해 MMSE-SIC 빔포밍 벡터를 통해서 결정할 수 있다. 하기 <표 1>은 반복 해 방식을 통한 MMSE-SIC 가중치 벡터 계산을 설명한 표이다.Equation (3) is obtained from the MMSE-SIC receiving end

Indicates the sum of the channel capacities that can be reached when the UEs can simultaneously transmit and use the transmission beamforming, respectively. At this time, in order to have the maximum channel capacity sum, the system can determine through the MMSE-SIC beamforming vector through an iterative solution scheme that all the terminals use the allocated power f. Table 1 below is a table describing the calculation of the MMSE-SIC weight vector by the iterative method.

Repeat  Way MMSE - SIC Beam forming  Calculate vector and channel capacity

개의 채널 집합

에 대하여

개의 단말들에 대한 채널 집합

을 구성한다.
b. 채널 집합

에 대하여 하기 절차를 수렴할 때까지 반복한다.

c. a,b절차를 통해서 획득한 빔포밍 벡터를 이용하여 채널 용량 C를 하기와 같이 계산한다.

a. gun

Channel set

about

A set of channels for the UEs

.
b. Channel set

Until the following procedure converges.

c. The channel capacity C is calculated as follows using the beamforming vector obtained through the procedures a and b.

개의 단말들 중

개의 단말들을 선택한 모든 조합을 고려하여 각각의 경우에 해당하는 단말 집합에 대해 반복해 방식을 통해서 빔포밍 벡터를 계산하여 채널 용량을 계산한 후, 계산된 채널 용량이 최대값을 가지는 사용자 집합이 선택된다.As a result of the above scheduling,

Of the terminals

Considering all the combinations of UEs selected, a beamforming vector is calculated through an iterative method for each set of UEs, and a channel capacity is calculated. Then, a user set having a calculated maximum channel capacity is selected do.

인 궤환량을 요구하는 반면, 송신 빔포밍 방법의 경우 계산된 빔포밍 벡터의 원소들이 복소값(complex value)을 가지므로 해당 단말들로 궤환해 줄 때 많은 양의 궤환 채널이 요구된다. 따라서, 본 발명에서는 실제 구현 가능성을 고려하여 궤환 량에 제한을 두고, 코드북을 적용한다. 예를 들어, 허용되는 궤환 비트가

일 때

가지의 대표되는 빔포밍 벡터를 이용하여 코드북을 만들고 실제 계산된 빔포밍 벡터와 가장 유사한 성능을 갖는 코드북의 인텍스만을 단말에게 알려준다. 그러나, 궤환 량이 제한된 환경하에서는 송신 빔포밍 방법이 안테나 선택 방법에 비해서 항상 좋은 성능을 나타내지 않는다. 즉, 주어진 궤환량이나 송/수신 안테나의 개수에 따라 그 성능의 우열 관계가 뒤바뀌게 된다. 따라서, 본 발명은 각 사용자별로 단일 스트림을 전송한다고 가정할 때, 주어진 환경을 고려하여 상기 안테나 선택 방법과 코드북을 이용한 송신 빔포밍 방법을 선택하는 기준(criterion)을 제안한다. 이때, 단말과 기지국은 상기 기준을 결정하기 위한 변수들을 미리 알고 있고, 각각 상기 변수들에 따른 기준을 계산하여 최적의 송신 방법을 선택한다.As described above, in the case of the antenna selection method

In the case of the transmission beamforming method, since the elements of the calculated beamforming vector have a complex value, a large amount of feedback channel is required for feedback to the corresponding terminals. Therefore, in the present invention, a codebook is applied with a limitation on the feedback amount in consideration of the practical feasibility. For example, if the allowable feedback bit is

when

A codebook is generated using representative beamforming vectors of branches and only the index of the codebook having the performance similar to the actual calculated beamforming vector is notified to the UE. However, under an environment where the feedback amount is limited, the transmission beamforming method does not always exhibit a better performance than the antenna selection method. That is, the performance relation of the performance is reversed depending on the given feedback amount or the number of transmitting / receiving antennas. Therefore, the present invention proposes a criterion for selecting a transmission beamforming method using the antenna selection method and a codebook considering a given environment, assuming that a single stream is transmitted for each user. At this time, the terminal and the base station know the parameters for determining the reference in advance, and calculate the criterion according to the parameters, respectively, to select the optimal transmission method.

및 각 단말별 SNR(Signal Noise Ratio)등을 통해서 결정된다.The criterion is a parameter that affects the channel capacity sum of the antenna selection method and the transmission beamforming method

And signal-to-noise ratio (SNR) for each terminal.

이라는 가정 하에 채널 용량 합 전송률에 가장 큰 영향을 미치는 채널 벡터는

이며, 총

개의 단말이 기지국으로 데이터를 동시에 송신한다고 가정하자. 이때, 상기 <수학식1>과 같이 나타내어지는 채널 용량을 하기 <수학식4>와 같이 나타내어지는 증가(Growth rate)율

로 근사화된다.In the case of the antenna selection method,

The channel vector having the greatest influence on the channel capacity sum rate is

And total

Let's assume that the terminals transmit data to the base station at the same time. At this time, the channel capacity expressed by Equation (1) can be expressed as Equation (4)

.

이 카이 제곱 분포를 따를 때 극값 이론(Extreme Value Theorem)에 의해 상기

은

의 스케줄링 이득을 갖는다. 따라서, 상기 <수학식4>의

는 다시 하기 <수학식5>와 같이 근사화된다.Here,

When this chi-square distribution is followed, the extreme value theory (Extreme Value Theorem)

silver

Lt; / RTI &gt; Therefore, in Equation (4)

Is approximated again as Equation (5).

2A is a graph illustrating a total data rate and a channel capacity increase rate in an antenna selection method according to an embodiment of the present invention.

를 나타낸 것이다. 상기

는 증가율을 근사화하여 나타낸 것이므로, 절대적인 값에는 큰 차이가 존재하지만 사용자 수에 따른 총 전송율 증감과의 개형은 거의 일치함을 확인할 수 있다.Referring to FIG. 2A, as the number of users is increased,

. remind

Is an approximation of the rate of increase, it can be seen that there is a large difference in the absolute value, but it is almost the same with the increase and decrease of the total transmission rate according to the number of users.

및 각 단말별 SNR 등의 변수들이 어떤 형태로 증감을 나타내는지를 근사화하였다.Similar to the antenna selection method, in the transmission beamforming method,

And the SNR of each terminal.

이라는 가정 하에 채널 용량 합에 가장 큰 영향을 미치는 단말의 최대 고유값을

이라 할 때,

명이 동시에 전송된다고 가정하였으므로, 상기 <수학식3>의 채널 용량 합은 증가율

으로 하기 <수학식6>과 같이 근사화된다.In other words,

The maximum eigenvalue of the terminal which has the greatest influence on the channel capacity sum

In other words,

Are simultaneously transmitted, the channel capacity sum of Equation (3)

Is approximated as Equation (6).

,

인 범위의 카이 제곱 분포를 따르므로

은

와 같은 스케줄링 이득을 얻는다.remind

,

Lt; RTI ID = 0.0 &gt;

silver

Lt; / RTI &gt;

의 기대값(Expectation)은 하기 <수학식7>을 이용하여 계산된다.remind

Is calculated using Equation (7) below. &Quot; (7) &quot;

는 하기 <수학식8>과 같이 근사화된다.Therefore, by using Equations (6) to (7)

Is approximated as Equation (8) below.

2B is a graph illustrating a total data rate and a channel capacity increase rate in a transmission beamforming method according to an embodiment of the present invention.

를 나타낸 것이다. 상기

는 증가율을 근사화하여 나타낸 것이므로 절대적인 값에는 큰 차이가 존재하지만 사용자 수에 따른 총 전송율 증감과의 개형은 거의 일치함을 확인할 수 있다. 송신 빔포밍 시스템에서 상기 <수학식8>의

는 궤환량이 무한할 때의 경우이다. 따라서, 실제 궤환량이 제한된 환경에서의 성능 감소가 반영되어야 한다. 따라서, 본 발명에서는 송신 빔 벡터 방법에 단일 사용자 MIMO 환경에서 최적으로 알려진 그래스매니안(Grassmannian) 코드북이 적용된 송신 빔포밍 벡터 방법을 사용한다. 궤환량의 제한 없이 최적의 빔포밍 벡터를 사용할 때에 비해, 궤환량이 제한된 단일 사용자 환경에서 코드북을 적용한 빔포밍 벡터 방법의 성능 저하는, SNR 측면에서 하기 <수학식9>와 같이 나타난다. 즉, 무한한 궤환 량이 존재한다는 가정 하에 빔포밍 벡터를 통해 얻을 수 있는 SNR 이득값인

와 코드북을 이용할 때 얻게 되는 SNR 이득값의 차이를 나타낸 것이다.Referring to FIG. 2B, as the number of users is increased,

. remind

Is an approximation of the rate of increase, so there is a large difference in the absolute value, but it can be seen that the number of users is almost the same as that of the total transmission rate. In the transmission beamforming system,

Is the case when the feedback amount is infinite. Therefore, performance reduction in an environment where the actual feedback amount is limited should be reflected. Therefore, in the present invention, a transmit beamforming vector method using a Grassmannian codebook that is best known in a single user MIMO environment is used for the transmit beam vector method. The degradation of the beamforming vector method employing the codebook in a single user environment with limited feedback amounts, as compared with the case of using the optimal beamforming vector without limitation of the feedback amount, is expressed by Equation (9) in terms of SNR. That is, assuming that there is an infinite amount of feedback, the SNR gain value obtained through the beamforming vector

And the SNR gain value obtained by using the codebook.

가 궤환 비트일 때,

이고,

는 코드북이고,

은 코드북 내의 빔 벡터를 의미한다.in this case,

Is a feedback bit,

ego,

Is a codebook,

Denotes a beam vector in the codebook.

), 이러한 성능 저하는 절대적으로 정확한 값은 아니지만 성능 저하의 증감이 각 변수들에 따라 어떤 경향을 따르는지를 반영한다.Using the above Equation (9), the reduction amount of performance according to the limited feedback amount in the multi-user environment is defined as Equation (10). That is, the effect of decreasing performance decreases as the feedback amount is limited,

), This performance degradation is not absolutely accurate, but it reflects the tendency of the performance degradation to follow each variable.

In the case of the transmission beamforming method, the size of the codebook can be increased in accordance with the allowable feedback amount. Therefore, the codebook size is determined according to the maximum feedback amount allowed in the system, and the performance according to the size of the determined codebook is determined. On the other hand, in the antenna selection method, the feedback amount allocated to each terminal is determined by the number of transmission antennas, and the performance is determined according to the determined feedback amount.

FIG. 3 is a graph illustrating a comparison of performance of a transmission rate according to a variation of a variable according to an embodiment of the present invention.

=12), 기지국의 안테나가 6개(

=6)인 상황에서 각 단말의 송신안테나(

)의 개수를 2,3,4,5,6개씩 늘려감에 따른 송신률을 나타낸 것이다. 궤환량이

만큼 허용된다고 할 때, 주어진 송신 안테나의 개수에 대하여 동일한 궤환량의 코드북을 적용한 송신 빔포밍 방법에 비해 안테나 선택 방법의 성능이 항상 좋은 성능을 나타냄을 확인할 수 있다.Referring to FIG. 3, when the SNR per terminal is 7 dB and a total of 12 terminals exist

= 12), the antenna of the base station is 6

= 6), the transmission antenna of each terminal

4, 5, and 6, respectively. Feedback amount

The performance of the antenna selection method is always better than that of the transmission beamforming method in which the codebook of the same amount of feedback is applied to a given number of transmission antennas.

에 비해 더 크면, 송신 빔포밍 방법은 더 큰 코드북을 사용함으로써 더 높은 성능을 나타낼 수 있다. 따라서, 단말 혹은 기지국 각각은 안테나 선택 방법과 송신 빔포밍 방법 중 제한된 궤환 정보의 양에 따라 더 높은 송신률을 낼 수 있는 송신 방법을 선택하는 적응적 방법 전환을 한다. 즉, 상기 단말 혹은 기지국은 각각 주어진 변수

및

에 대하여 상기 <수학식11> 내지 하기<수학식12>와 같이 정의되는 기준을 통해서, 상기 안테나 선택 방법과 송신 빔포밍 방법 간의 적응적 방법 중 하나를 선택한다.On the other hand, while the feedback information amount of the antenna selection method is fixed by the number of transmission antennas,

, The transmit beamforming method can exhibit higher performance by using a larger codebook. Accordingly, each of the UEs and the BSs performs an adaptive method of selecting a transmission method capable of achieving a higher transmission rate according to the amount of limited feedback information among the antenna selection method and the transmission beamforming method. That is, the terminal or the base station transmits a given variable

And

An adaptive method between the antenna selection method and the transmission beamforming method is selected through a criterion defined by Equation (11) to Equation (12).

는

을,

는

로 나타낸다.

은 상수 값으로 실험적인 결과로써

= 8~10인 범위를 갖는 임의의 값으로 설정할 수 있다.here,

The

of,

The

Respectively.

Is an experimental result with a constant value

= 8 to 10, as shown in FIG.

인 경우는 안테나 선택 방법을 선택하고,

인 경우는 송신 빔포밍 기법을 선택한다.Equation (11) represents a performance reduction rate in a transmission beamforming system according to a limited amount of feedback in comparison with an infinite feedback amount, and Equation (12) represents a maximum channel capacity of a transmission beamforming system in an infinite feedback amount This shows the difference in the channel capacity increase rate when the antenna selection technique is applied to the agreement increase rate. Accordingly, the UE or the BS compares Equations (11) to (12)

The antenna selection method is selected,

The transmission beamforming technique is selected.

Table 2 is a table comparing the actual value of the performance reduction in the environment shown in FIG. 2 and the ratio of the performance reduction based on the criterion, and Table 3 shows a system environment Table 1 compares the ratio between the actual value of the performance reduction of the antenna selection method and the transmission beamforming method and the performance reduction ratio applied by the reference. Here, A and T mean the antenna selection method and the transmission beamforming method, respectively, and the numbers indicate feedback bits for the respective terminals.

First, when the number of transmit antennas is given, the magnitude of the actual value is obtained through actual experiments on the performance reduction between the antenna selection method and the transmission beamforming method using the codebook according to a given feedback bit. Thereafter, the increase rate corresponding to the actual value is calculated using Equations (11) to (12), and the magnitude relation of the actual value and the magnitude of the increase rate corresponding to the actual value are compared, .

For example, in Table 2, when the transmission antenna is 3, the antenna selection technique A2 requiring only 2-bit feedback amount has a capacity loss compared to the transmission beamforming technique T2 using a 2-bit codebook, And it can be confirmed that this has a larger capacity loss than the transmission beamforming scheme T3 when the feedback amount is 3 bits. As a result, if the feedback bit is 2 bits, the antenna selection method has higher performance. If there is more than 3 bits of the allowable feedback bit, the system using the transmission beamforming method has higher performance.

라 가정한다.4 is a configuration diagram of a MIMO system according to an embodiment of the present invention. Here, the allowable feedback bits are

.

의 수신 안테나와, 송신 방법 선택부(402)와, 송신 빔포밍 방법 적용 스케쥴러(404) 및 안테나 선택 방법 적용 스케쥴러(406)를 포함한다.

개의 단말들(410-1~K)은 각각

개의 송신 안테나와, 송신 방법 선택부(412~422) 및 송신부(414~424)를 각각 포함한다. 상기 기지국(400)과 상기 단말들(410~420)은 송신 방법 선택을 위한 변수인

및

를 서로 알고 있다고 가정한다.Referring to FIG. 4, the base station 400

A transmission method selection unit 402, a transmission beamforming method application scheduler 404, and an antenna selection method application scheduler 406. [

The terminals 410-1 to 410-K are

Transmission method selection units 412 to 422, and transmission units 414 to 424, respectively. The base station 400 and the UEs 410 to 420 receive a variable &lt; RTI ID = 0.0 &gt;

And

Are known to each other.

및

에 따른 최적의 송신 방법을 각각 선택하여 알고 있다.The transmission method selection unit 402 of the base station 400 and the transmission method selection units 412 and 422 of the terminals 410-1 to 410-K use the Equations (11) to (12) And selects a transmission method most suitable for the variable among the antenna selection method and the transmission beamforming method. That is, each of the base station 400 and the terminals 410-1 to 410-

And

Respectively, are selected and known.

Each of the terminals 410-1 to 410-K transmits a probing signal for channel estimation according to a transmission method selected from the transmission method selecting units 412 to 422 to the base station 400.

When the transmission method selected through the transmission method selection unit 402 is a transmission beamforming method, the scheduling unit 404 applies the transmission beamforming method to the transmission of a selected one of the terminals 1 to K (410-1 to K) And feed back an index to the beamforming vector. When the transmission method selected through the transmission method selection unit 402 is an antenna selection method, the antenna selection application scheduler 406 calculates an antenna index for the selected one of the terminals 1 to K (410-1 to K) .

Each of the transmitters 414 to 424 of the UEs 410-1 to 410-K transmits data based on the feedback information received from the transmit beamforming method applying scheduler 404 or the antenna selection method applying scheduler 406, .

이 6이고,

는 12이고, SNR은 7dB이다.5A and 5B are graphs illustrating performance comparisons of an adaptive transmission method according to an embodiment of the present invention. here,

Is 6,

Is 12, and the SNR is 7 dB.

Referring to FIGS. 5A and 5B, when the transmission method is applied as an adaptive selection method, the performance is always maintained as compared with the case where the antenna selection method and the transmission beamforming method are applied alone.

Referring to FIG. 5A, the available feedback bits for each user terminal are 3 bits. In this case, when the number of antennas is 4 or less, the transmission beamforming method exhibits greater performance, and when the number of antennas is larger than 4, the antenna selection method exhibits greater performance. That is, it is possible to adaptively convert the transmission method according to the number of antennas, thereby selecting a transmission method exhibiting higher performance in a given system environment.

가 4비트이다. 이때, 안테나 개수가 5개 이하일 경우 송신 빔포밍 방법이 더 큰 성능을 나타내고, 안테나 개수가 5개보다 클 경우 안테나 선택 방법이 더 큰 성능을 나타낸다. 즉, 송신 방법을 안테나의 수에 따라 적응적으로 변환하여 주어진 시스템 환경에서 더 높은 성능을 나타내는 송신 방법을 선택할 수 있다.Referring to FIG. 5B, a feedback bit usable for each user terminal

Is 4 bits. In this case, the transmission beamforming method exhibits greater performance when the number of antennas is less than five, and the antenna selection method exhibits greater performance when the number of antennas is greater than five. That is, it is possible to adaptively convert the transmission method according to the number of antennas, thereby selecting a transmission method exhibiting higher performance in a given system environment.

1 is a block diagram of a general MIMO system;

FIG. 2A is a graph showing a total transmission rate and a channel capacity increase rate in an antenna selection method according to an embodiment of the present invention; FIG.

FIG. 2B is a graph showing a total transmission rate and a channel capacity increase rate in a transmission beamforming method according to an embodiment of the present invention; FIG.

FIG. 3 is a graph illustrating a comparison of performance of a transmission rate according to a variation of a variable according to an embodiment of the present invention. FIG.

4 is a configuration diagram of a MIMO system according to an embodiment of the present invention;

5A and 5B are graphs illustrating performance comparisons of an adaptive transmission method according to an embodiment of the present invention.

Claims (27)

A method for transmitting data in a MIMO communication system, Calculating a performance reduction amount of the first transmission method and a performance reduction amount of the second transmission method according to a variable; Selecting a transmission method having a smaller amount of performance reduction by comparing a performance reduction amount of the first transmission method with a performance reduction amount of the second transmission method; Receiving a scheduling information from the base station after transmitting a probe signal for channel estimation of the base station when the transmission method is selected; and transmitting data according to the scheduling information. 2. The method of claim 1, wherein the scheduling information comprises: Wherein the base station is configured to calculate a performance reduction amount of the first transmission method and a performance reduction amount of the second transmission method, The first transmission method is a method of selecting a combination of transmit antennas that maximizes a sum rate, and the second transmission method is a method of selecting a user having a maximum transmission rate by applying a beamforming scheme for maximizing the sum rate Wherein the data transmission method comprises the steps of: 3. The method of claim 2, Number of receive antennas (

), The number of user terminals (

), The number of transmit antennas of each user terminal (

) And a signal-to-noise ratio (SNR), an allowable feedback bit (

And a value previously known between the base station and the user terminal. 4. The method of claim 3, wherein the reduced amount of performance of the first transmission method comprises: Is calculated using the following equation (13).

remind

The

ego,

The

ego,

Is a constant,

Is the gain value of SNR

Lt; / RTI &gt; range. 5. The method of claim 4, Wherein a performance difference when the feedback amount of the base station is limited in performance when the feedback amount of the base station is infinite is calculated using the following equation (14).

here,

Is a feedback bit,

ego,

Is a codebook,

Denotes a beam vector in the codebook,

Is a channel vector between the BS and the corresponding MS, remind

Is expressed by the following equation (15).

6. The method of claim 5, wherein the reduced amount of performance of the second transmission method comprises: (16): &quot; (16) &quot;

here,

to be. A method for scheduling data in a MIMO communication system, Calculating a performance reduction amount of the first transmission method and a performance reduction amount of the second transmission method according to a variable and selecting a transmission method having the calculated performance reduction amount smaller; And generating scheduling information according to the selected transmission method and transmitting the generated scheduling information to the terminal after receiving the probing signal from the terminal. 8. The method of claim 7, wherein the transmitting comprises: Selecting a combination of transmit antennas that maximizes a total data rate among transmit antennas of the user equipment when the selected transmission method is a first transmission method; And transmitting an index of transmission antennas included in the combination to the MS as the scheduling information. 8. The method of claim 7, wherein the transmitting comprises: And transmitting a codebook index for a beamforming vector of the UE to the MS as the scheduling information if the selected transmission method is the second transmission method. 10. The method of claim 9, Number of receive antennas (

), The number of user terminals (

), The number of transmit antennas of each user terminal (

) And a signal-to-noise ratio (SNR), an allowable feedback bit (

Wherein the data scheduling method comprises: 11. The method of claim 10, (17). &Lt; EMI ID = 17.0 &gt;

remind

The

ego,

The

ego,

Is a constant,

Is the gain value of SNR

Lt; / RTI &gt; range. 12. The method of claim 11, wherein the reduced amount of performance of the second transmission method comprises: Wherein a performance difference when the feedback amount of the base station is limited in performance when the feedback amount of the base station is infinite is calculated using Equation (18) below.

here,

Is a feedback bit,

ego,

Is a codebook,

Denotes a beam vector in the codebook,

Is a channel vector between the base station and the corresponding terminal,

Is expressed by the following equation (19).

13. The method of claim 12, (20). &Lt; EMI ID = 20.0 &gt;

here,

to be. In a data transmitting apparatus in a multi-input / output communication system, The performance reduction amount of the first transmission method and the performance reduction amount of the second transmission method according to the variable are calculated and the performance reduction amount of the first transmission method is compared with the performance reduction amount of the second transmission method, A transmission method selection unit for selecting a transmission method, And a transmitter for transmitting a probing signal for channel estimation of a base station and receiving scheduling information from the base station and transmitting data according to the scheduling information when the transmission method is selected. 15. The method of claim 14, Wherein the base station is configured to calculate a performance reduction amount of the first transmission method and a performance reduction amount of the second transmission method, The first transmission method is a method of selecting a combination of transmission antennas that maximizes a sum rate, and the second transmission method is a method of selecting a user having a maximum transmission rate by applying a beamforming scheme to maximize the sum rate And the data transmission device. 16. The method of claim 15, Number of receive antennas (

), The number of user terminals (

), The number of transmit antennas of each user terminal (

) And a signal-to-noise ratio (SNR), an allowable feedback bit (

And a value previously known between the base station and the user terminal. 17. The method of claim 16, wherein the reduced amount of performance of the first transmission method comprises: Is calculated using the following equation (21).

remind

The

ego,

The

ego,

Is a constant,

Is the gain value of SNR

Lt; / RTI &gt; range. 18. The method of claim 17, wherein the reduced amount of performance of the second transmission method comprises: Wherein a performance difference when the feedback amount of the base station is limited in performance when the feedback amount of the base station is infinite is calculated using the following equation (22).

here,

Is a feedback bit,

ego,

Is a codebook,

Denotes a beam vector in the codebook,

Is a channel vector between the base station and the corresponding terminal,

Is expressed by the following equation (23).

19. The method of claim 18, (24): &quot; (24) &quot;

here,

to be. An apparatus for scheduling data in a MIMO communication system, A transmission method selecting unit for calculating a performance reduction amount of the first transmission method and a performance reduction amount of the second transmission method according to a variable and selecting a transmission method having the calculated performance reduction amount smaller, A first transmission method scheduler for generating scheduling information corresponding to the first transmission method and transmitting the generated scheduling information to the terminal when the selected transmission method is the first transmission method after receiving a probing signal from the terminal; And a second transmission method scheduler for generating scheduling information according to the second transmission method when the selected transmission method is the second transmission method after receiving the probing signal from the terminal and transmitting the generated scheduling information to the terminal, Device. 21. The method of claim 20, The first transmission method is a method of selecting a combination of transmission antennas that maximizes a sum rate, and the second transmission method is a method of selecting a user having a maximum transmission rate by applying a beamforming scheme to maximize the sum rate Wherein the data scheduling apparatus comprises: 22. The method of claim 21, wherein the first transmission method scheduler comprises: Selects a combination of transmit antennas for maximizing the sum rate among transmit antennas of the UE and transmits indexes of transmit antennas included in the combination to the UE as the scheduling information. 22. The method of claim 21, wherein the second transmission method scheduler comprises: And transmits a codebook index for the beamforming vector of the UE to the MS as the scheduling information. 21. The method of claim 20, Number of receive antennas (

), The number of user terminals (

), The number of transmit antennas of each user terminal (

) And a signal-to-noise ratio (SNR), an allowable feedback bit (

And a scheduling unit for scheduling the scheduling of the data. 25. The method of claim 24, Is calculated using Equation (25). &Lt; EMI ID = 25.0 &gt;

remind

The

ego,

The

ego,

Is a constant,

Is the gain value of SNR

Lt; / RTI &gt; range. 26. The method of claim 25, wherein the reduced amount of performance of the second transmission method comprises: Wherein a performance difference when the feedback amount of the base station is limited in performance when the feedback amount of the base station is infinite is calculated using the following equation (26).

remind

Is a feedback bit,

ego,

Is a codebook,

Denotes a beam vector in the codebook,

Is a channel vector between the BS and the corresponding MS, remind

Is expressed by Equation (27) below.

27. The method of claim 26, (28). &Lt; EMI ID = 28.0 &gt;

here,

to be.

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