KR101322643B1 - Multi-input multi-output communication method and multi-input multi-output communication system of enabling the method - Google Patents

Abstract

Disclosed are a multiple input / output communication system and a multiple input / output communication method. The multiple input / output communication system uses an antenna number determination unit that determines the number of one or more active antennas transmitting the transmission signal among the transmission antennas in consideration of the power of the transmission signal and channel information fed back from the user terminals. It includes a beam forming unit for generating the transmission signal corresponding to the number of the active antenna.

Multiple I / O, MIMO, Beamforming, Zero Forcing, Active Antenna, Feedback

Description

MULTI-INPUT MULTI-OUTPUT COMMUNICATION METHOD AND MULTI-INPUT MULTI-OUTPUT COMMUNICATION SYSTEM OF ENABLING THE METHOD}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to multi-user multi-input / output communication, and more particularly, to a multi-input / output communication system and method for controlling a transmission antenna in consideration of power of a transmission signal.

Recently, researches are being actively conducted to provide various multimedia services including voice services in a wireless communication environment and to support high quality and high speed data transmission. As a part of this research, a technology for a multi-input multi-output (MIMO) system using a plurality of channels in a spatial domain is rapidly developing.

MIMO technology is a technique for providing a high data rate by increasing the number of channel bits within a limited frequency resource by using multiple antennas. The MIMO technique provides the channel capacity that is theoretically proportional to the small number of antennas of the transmission and reception antennas by using the multiple transmission / reception antennas in a scattering-rich channel environment.

In a multi-user environment in which one base station supports multiple terminals, studies are being actively conducted to increase the overall channel capacity of a MIMO system considering a multi-user.

In the uplink of the MIMO system considering the multi-user, the multi-user transmits data toward the same base station, and in the downlink, the base station transmits data to the multi-user. In addition, the lack of coordination between multiple users is different from a single user-based MIMO system.

In multi-user based MIMO, the user terminal generally feeds back information about the quantized channel to the base station. In addition, when the base station transmits a precoded signal based on the feedback channel information, there is a difference between the actual channel vector and the channel vector corresponding to the channel information. Therefore, an error occurs during precoding due to the difference. This error is a cause of reducing the data rate when the signal is transmitted at a high power, due to the noise due to the error.

However, in order to reduce such an error, ideally, a large number of bits of channel information should be fed back. As the number of bits of the channel information to be fed back increases, overhead that affects the communication system also increases.

Therefore, there is a need for a multiple input / output communication system and method capable of achieving a high data rate without increasing the number of bits of feedback channel information.

The present invention provides a multi-input / output communication system and a multi-input / output communication method capable of transmitting data more effectively by variably determining a transmit antenna in consideration of transmit signal power.

The present invention also provides a multi-input / output communication system and a multi-input / output communication method capable of achieving a high data rate even under high power of a transmission signal.

The present invention also provides a multi-input / output communication system and a multi-input / output communication method capable of transmitting data more efficiently by using a smaller number of transmit antennas even if the signal-to-noise ratio of the transmitted signal is high.

The present invention also provides a multi-input / output communication system and a multi-input / output communication method capable of using less hardware resources by achieving a high data rate using fewer transmit antennas.

The present invention also provides a multi-input / output communication system and a multi-input / output communication method capable of achieving a high data rate in consideration of the power of a transmission signal and the number of user terminals even if the number of bits of channel information to be fed back is limited.

The present invention also provides a multiple input / output communication system and a multiple input / output communication method capable of providing a communication environment with less interference by generating a transmission signal using a zero-forcing algorithm.

In the multiple input / output communication system according to an embodiment of the present invention, an antenna number determination unit and user terminals for determining the number of one or more active antennas transmitting the transmission signal among the transmission antennas in consideration of the power of the transmission signal. And a beam forming unit generating the transmission signal corresponding to the number of the active antennas using the channel information fed back from the channel information.

In addition, the multiple input and output communication system according to an embodiment of the present invention is a beam forming unit for generating a transmission signal using the channel information fed back from the user terminal and the transmission signal of the transmission antennas in consideration of the power of the transmission signal And an antenna selector for selecting one or more active antennas for transmitting the data.

In addition, in the multiple input / output communication method according to an embodiment of the present invention, determining the number of one or more active antennas transmitting the transmission signal among the transmission antennas in consideration of the power of the transmission signal and from user terminals Generating the transmission signal corresponding to the number of the active antennas using the feedback channel information.

In addition, in the multiple input / output communication method according to an embodiment of the present invention, generating a transmission signal using channel information fed back from user terminals and transmitting the transmission signal among transmission antennas in consideration of the power of the transmission signal. Selecting one or more active antennas.

According to the present invention, data can be transmitted more effectively by selecting a transmit antenna in consideration of transmit signal power.

In addition, the present invention can achieve a high data rate even in a situation where the power of the transmission signal is high.

In addition, the present invention can transmit data more efficiently by using a smaller number of transmit antennas even if the signal-to-noise ratio of the transmitted signal is high.

In addition, the present invention can use less hardware resources by achieving higher data rates using fewer transmit antennas.

In addition, the present invention can achieve a high data rate in consideration of the power of the transmission signal and the number of user terminals even if the number of bits of the channel information to be fed back is limited.

In addition, the present invention can provide a communication environment with less interference by generating a transmission signal using a zero-forcing algorithm.

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 multiple input / output communication system according to the present invention.

Referring to FIG. 1, the base station 110 includes M transmit antennas and there are K user terminals.

A channel for data communication is formed between the antennas of the base station 110 and the user terminals. In general, the formed channel may be represented by a channel matrix, and it is assumed here that the channel matrix is H. At this time, a relationship as shown in Equation 1 is established between the signal received at the user terminal side and the signal transmitted at the transmit antenna side.

Here, Y is a vector for signals received at the user terminal side, X is a vector for signals transmitted at the transmitting antenna side, and N is noise.

At this time, if the transmitting end knows the information on the channel matrix in advance, the transmission signal X can be efficiently transmitted to the user terminal. That is, if the data stream S precoded transmission signal X is generated using Equation 2, the user terminals can more efficiently receive the data stream S without interference with each other.

In this case, Equation 1 may be expressed as Equation 2 below.

를 이용하여 프리코딩된다. 여기서, D는

의 크기를 정규화(normalize)하기 위한 대각 행렬이다. That is, if the data stream to be transmitted is called S, the data stream S is

Precoded using Where D is

Diagonal matrix for normalizing the size of.

At this time, since the state of the channel formed between the base station 110 and the user terminal changes over time and space, the base station 110 should periodically find out information about the channel.

At this time, the user terminals periodically grasp channel information through a pilot signal, and then feed back the determined channel information to the base station 110. Thus, the base station 110 precodes the data stream S using the channel information fed back from the user terminals. However, if the user terminal calculates a channel vector by itself and feeds back the entire channel vector calculated by the base station 110, the number of bits of data to be fed back may be too large.

In this case, the user terminal may store a plurality of vectors in advance, and the user terminal may select a vector closest to the direction of the calculated channel vector among the prestored vectors after calculating the channel vector. At this time, the user terminal may feed back information about the selected vector.

In this case, the user terminals may feed back only the index of the selected vector among the pre-stored vectors to the base station 110. Therefore, the number of bits of data fed back by the user terminal can be greatly reduced.

개의 벡터들을 미리 저장해 둘 수 있다. Here, it is assumed that the number of bits of data fed back from the user terminals to the base station 110 is B. At this time, since the user terminals can feed back B bits of data.

Vectors can be stored in advance.

개의 벡터들 중 계산된 채널 벡터와 가장 근접한 벡터를 선택할 수 있고, 선택된 벡터에 대한 인덱스만을 기지국(110)으로 피드백할 수 있다. 이에 따라, 기지국(110)은 피드백된 상기 인덱스를 이용하여 상기 인덱스에 상응하는 채널 벡터를 미리 준비된 벡터들 중에서 선택하고, 이를 기초로 빔포밍 벡터를 생성할 수 있다.At this time, if the user terminal calculates a channel vector through a pilot signal or the like, the user terminal is prepared in advance.

It is possible to select a vector closest to the calculated channel vector among the vectors, and to feed back only the index for the selected vector to the base station 110. Accordingly, the base station 110 may select a channel vector corresponding to the index from previously prepared vectors by using the fed back index, and generate a beamforming vector based on this.

Through the above-described process, the base station 110 can generate the transmission signal X beamforming the data stream S, and the user terminal can efficiently feed back channel information with a small number of bits.

In this case, the channel matrix H may be represented by Equation 3 below.

Here, when the number of transmit antennas of the base station is M and the number of user terminals is K, H may be a matrix having a size of K × M.

Although the present specification describes a case in which the user terminal has one antenna, the present invention is not limited to the case in which the user terminal has one antenna. In particular, in the case of a system in which a user terminal has a plurality of antennas and outputs a scalar by incorporating a linear filter and a vector received by these antennas, the effective channel is the same as the case in which the user terminal has one antenna. This may apply equally.

는 M x 1 사이즈를 갖는 채널 벡터일 수 있다. 즉,

는 채널 매트릭스의 전각 매트릭스(transpose matrix)인 H^T의 i 번째 열 벡터(column vector)일 수 있다. Also, a vector for a channel formed with the i th user terminal.

May be a channel vector having an M × 1 size. In other words,

May be an i th column vector of H ^T , which is a transpose matrix of the channel matrix.

, 송신 안테나가 송신하는 전송 신호를

라고 가정한다. 이 때,

는 하기 수학식 4와 같이 표현될 수 있다. At this time, the i-th user terminal receives a signal

The transmit signal transmitted by the transmit antenna

. At this time,

May be expressed as Equation 4 below.

(i=1, 2, 3,..., K)

(i = 1, 2, 3, ..., K)

는 i 번째 유저 단말기에서 발생되는 잡음(noise)을 나타낸다. here,

Denotes noise generated in the i-th user terminal.

는 i 번째 유저 단말기와 형성되는 채널에 대한 채널 벡터와 송신 안테나에서 송신되는 전송 신호(x)를 곱한 값에 잡음(

)을 더한 값과 같게 된다. That is, the signal received at the i th user terminal

Is a value obtained by multiplying a channel vector for a channel formed with an i-th user terminal by a transmission signal (x) transmitted from a transmission antenna.

) Is equal to the sum of

는 기지국(110)의 송신 안테나들과 유저 단말기 사이에 형성되는 채널을 통해 상기 수학식 4의 관계를 가지고 유저 단말기에게 전송된다. Transmission signal transmitted via transmission antennas

Is transmitted to the user terminal with the relation of Equation 4 through a channel formed between the transmitting antennas of the base station 110 and the user terminal.

는 하기 수학식 5와 같이 표현될 수 있다. Transmission signal of Equation 4

May be expressed as Equation 5 below.

는 데이터 스트림(s)을 프리코딩하여 생성될 수 있다. 여기서,

는 매트릭스

의 j 번째 열(column)벡터로서 빔포밍 벡터이다. That is, the transmission signal

May be generated by precoding the data stream s. here,

The matrix

It is the beamforming vector as the j-th column vector of.

는 하기 수학식 6과 같이 나타낼 수 있다. At this time, using the equation (5) and the equation (4)

Can be expressed as in Equation 6 below.

In this case, Equation 6 may be expressed by Equation 7 below.

는 i 번째 유저 단말기의 입장에서는 잡음으로 해석될 수 있다. here,

May be interpreted as noise from the perspective of the i-th user terminal.

를 제로(zero, 0)로 만들 수 있다면, 간섭과 잡음은 n_i로 줄어들게 된다. 이 때, i 번째 단말기로 형성되는 채널 매트릭스와 직교하는(orthogonal)는

가 선택될 수 있다. 즉,

와

가 직교한다면,

는 제로가 되어 간섭이 최소화된다. 즉, 기지국이 i 번째 단말기에게 데이터 스트림을 전송하고자 하는 경우 i 번째 단말기와 형성되는 채널 이외의 모든 채널과 직교하는 빔포밍 벡터

로 데이터 스트림을 프리코딩하는 것을 제로 포싱 빔포밍(zero forcing beam forming)이라고 한다. if

If can be made zero, interference and noise will be reduced to n _i . At this time, orthogonal to the channel matrix formed by the i-th terminal is

Can be selected. In other words,

Wow

If is orthogonal,

Is zero to minimize interference. That is, when the base station wants to transmit a data stream to the i th terminal, the beamforming vector orthogonal to all channels other than the channel formed with the i th terminal

Precoding the raw data stream is referred to as zero forcing beam forming.

도 유저 단말기로부터 피드백된 채널 정보를 이용하여 생성된다. 즉, 유저 단말기들에는 채널 벡터 혹은 채널 방향 벡터가 될 수 있는 다수의 벡터들이 미리 저장될 수 있다. 이상적인 경우로서, 기지국이 모든 유저들의 채널 방향 벡터를 정확히 알고 있다면, 기지국에서 제로 포싱 빔포밍을 통해 계산한 i 번째 빔포밍 벡터는 i 번째 단말기 이외의 모든 단말기들의 채널들과 직교한다. 그러나 유저 단말기들은 미리 저장된 다수의 벡터들 중 자신의 채널 벡터 방향과 가장 근접한 벡터의 인덱스만을 기지국(110)으로 피드백하므로, 이 과정에서 오차가 발생한다. 이 때, 이러한 오차를 양자화 에러(quantization error)라고 한다. 채널 정보를 피드백하는 과정에서 발생하는 양자화 에러는 제로 포싱 빔포밍 과정에도 영향을 주므로 기지국에서 실제로 생성한 i 번째 빔포밍 벡터는 i 번째 단말기 이외의 채널들과 정확히 직교하지 않고 약간의 간섭을 일으킨다. However, at this time, the beamforming vector

It is also generated using the channel information fed back from the user terminal. That is, a plurality of vectors, which may be channel vectors or channel direction vectors, may be stored in the user terminals in advance. Ideally, if the base station knows the channel direction vectors of all users correctly, the i th beamforming vector calculated by the zero forcing beamforming at the base station is orthogonal to the channels of all terminals other than the i th terminal. However, since the user terminals feed back only the index of the vector closest to the direction of their channel vector among the plurality of vectors stored in advance, an error occurs in this process. At this time, such an error is called a quantization error. Since the quantization error generated during the feedback of the channel information also affects the zero forcing beamforming process, the i th beamforming vector actually generated by the base station causes little interference without being orthogonal to the channels other than the i th terminal.

The quantization error can be ignored when the signal is transmitted at low power, but the effect can not be ignored when the signal is transmitted at high power. However, the quantization error may be reduced by increasing the number of bits of data fed back by the user terminal. This is because as the number of bits of data increases, more vectors can be stored in the base station or the user terminal. In addition, as the number of bits of the feedback data increases, the total data rate of data transmitted from the transmitting antennas to the user terminals also increases. However, an increase in the number of bits of data fed back by the user terminal has a bad effect on the system as a whole, and changing the number of bits variably places a heavy burden on the design of the frame structure.

At this time, an equation such as Equation 8 is established between the number of bits B of data fed back by the user terminal, the number K of the user terminals, the number M of transmit antennas, and the power P of the transmission signal. In doing so, the loss due to quantization error can be kept below a certain level. That is, as the power P of the transmission signal increases, the number of feedback bits B must be continuously increased so that the loss due to the quantization error can be controlled. The power P of the transmission signal includes a signal-to-noise ratio of the transmission signal. As the power P of the transmission signal increases, the signal-to-noise ratio SNR of the transmission signal increases, and the power P of the transmission signal increases. As decreases, the signal-to-noise ratio (SNR) of the transmission signal decreases.

More specifically, when the number of feedback bits B is continuously increased according to the power P of the transmission signal as shown in Equation 8, the data rate in the ideal case (that is, the rate in which the base station knows the channel information correctly without quantization error) Contrast rate loss can be maintained within a certain level.

Where c is a constant.

Referring to Equation 8, even when B and K are constant, that is, even when the number of feedback bits B is kept constant, the transmission antenna is changed according to the change in the signal-to-noise ratio (SNR) or the power (P) of the transmission signal. It can be seen that the loss due to quantization error can be controlled by adjusting the number.

2 is a block diagram illustrating a multiple input / output communication system according to an embodiment of the present invention.

2, a multiple input / output communication system according to an embodiment of the present invention includes an antenna number determiner 210, a beam former 220, and an antenna switch 230.

The antenna number determiner 210 determines the number of one or more active antennas transmitting the transmission signal among the transmission antennas in consideration of the power of the transmission signal.

At this time, the power of the transmission signal may be set in advance at the transmitting end.

Again, referring to Equation 8, it is assumed that B, the number of bits fed back from the user terminals to the base station, is fixed. At this time, in order to achieve a high signal-to-noise ratio P, the number M of transmit antennas must be reduced.

Accordingly, the antenna number determiner 210 according to an embodiment of the present invention may reduce the number of active antennas as the power of the transmission signal increases. The higher the power of the transmitted signal, the higher data rate can be achieved by transmitting the transmitted signal with fewer active antennas. In particular, when the power of the transmission signal is higher than a certain level, by using fewer active antennas, the interference occurring between the active antennas can be reduced, so that a high data rate can be achieved.

In this case, the antenna number determiner 210 may determine the number of active antennas by further considering at least one of a signal to noise ratio of the transmission signal, the number of user terminals, and the number of bits of channel information. Here, the signal-to-noise ratio may be a concept included in the power of the transmission signal. This is because the signal-to-noise ratio means power when noise is normalized to some constant value. In addition, the antenna number determiner 210 may increase the number of active antennas as the number of bits of channel information is small. The antenna number determiner 210 may increase the number of active antennas as the number of user terminals increases.

In addition, the beam forming unit 220 generates a transmission signal corresponding to the number of active antennas using the channel information fed back from the user terminals.

At this time, it is assumed that there are four transmitting antennas. In this case, the antenna number determiner 210 may determine the number of active antennas from two of the four transmit antennas in consideration of the power of the transmission signal. In this case, a higher data rate may be achieved when a transmission signal is transmitted through two active antennas than when four transmission antennas are transmitted.

In addition, when the number of active antennas among the four transmit antennas is three, the beam forming unit 220 may generate a transmission signal as if the three transmit antennas are present. Furthermore, user terminals receiving transmission signals from three active antennas may feed back channel information as if the number of transmission antennas is three.

In this case, since the dimension of the beamforming vector may vary according to the number of active antennas, a plurality of codebooks may be stored in advance in the user terminals. For example, in case of 4, 3, 2, or 1 active antennas, A, B, C, and D codebooks for each case may be stored in advance in the user terminals. In this case, the vectors included in the A, B, C, and D codebooks may have dimensions of 4 x 1, 3 x 1, 2 x 1, 1 x 1, respectively, and the user terminals are A, B according to the number of active antennas. One of C, D, and C codebooks may be selected, and at least one of vectors included in the selected codebook may be selected. The user terminals may feed back channel information, which may include index information of the selected vector, to the base station.

That is, when the number of transmit antennas is M and the number of bits of channel information is B, the antenna number determiner 210 may determine the number of active antennas as M-L smaller than M in consideration of the power of the transmission signal. At this time, the beam forming unit 220 may generate a transmission signal having a dimension of M-L by using a beamforming vector having an antenna dimension of M-L so as to correspond to the determined number of active antennas (M-L). In this case, a part corresponding to the remaining L dimension in the transmission signal may be set to zero.

사이즈를 갖는 코드북을 사용한다. 다만, 본 발명의 일실시예에 따르면, 유저 단말기들은 액티브 안테나의 수와 상응하는 (M-L) x

사이즈를 갖는 코드북을 사용할 수 있다.Also, in general, when the number of transmit antennas is M and the number of bits of channel information is B, the user terminals are M x.

Use a codebook with a size. However, according to an embodiment of the present invention, the user terminals (ML) x corresponding to the number of active antennas

A codebook having a size can be used.

That is, the user terminal may select one active codebook from among a plurality of codebooks stored in advance according to the determined number of active antennas (M-L). At this time, the vectors included in the active codebook have a dimension of M-L. The user terminal may feed back channel information, which may include index information of at least one of the vectors included in the active codebook, to the base station.

In addition, the antenna number determiner 210 may determine the number of active antennas using the concept of a virtual antenna. At this time, the antenna number determiner 210 may determine the number of active antennas so that the effective channel state is maintained.

Assuming that there are M transmit antennas, using the virtual antenna concept, the number of active antennas is determined to be M, so that even if all M transmit antennas transmit a signal, the same effect as that of ML antennas transmit a signal may occur. have. In this case, each of the M-L antennas is called a virtual antenna.

That is, when all M transmit antennas are determined to be active antennas, it is assumed that a signal transmitted by the M transmit antennas is X _out , and a signal transmitted by the ML virtual antennas is X _in . Here, the dimension of X _out is M x 1 and the dimension of X _in is (ML) x 1. In this case, the relationship between X _out and X _in can be expressed by Equation 9 below.

X _out = PX _in

Referring to Equation 9, P is a matrix having a size of M x (M-L). In this case, the effective channel is equal to the product of the matrix P and the channel vector. Therefore, when the M active antennas transmit a signal through an actual channel and when the M-L virtual antennas transmit a signal through an effective channel, the user terminal receives the same signal.

That is, the technical idea according to an embodiment of the present invention includes an embodiment in which the same effect may be derived to a user terminal by varying the number of physically active antennas that actually transmit a signal using a virtual antenna technique. However, even if the number of physical active antennas is changed using the virtual antenna technique, the effective channel formed between the user terminal and the base station does not change.

In particular, when using the virtual antenna technique, the power allocated to each active antenna can be easily controlled, and each user terminal quantizes information about an effective channel and feeds back to the base station, thereby reducing the quantization error. In addition, the data rate may increase accordingly.

In this case, the beam forming unit 220 may generate a transmission signal using a zero forcing algorithm. That is, the beamformer 220 may generate a transmission signal using a zero forcing algorithm so as to match the determined number of active antennas. Since the zero forcing beamforming algorithm has been described with reference to FIG. 1, a description thereof will be omitted.

In this case, the fed back channel information may include channel state information or channel direction information. For example, when a transmission signal is generated by the zero-forcing beamforming method described above, the base station can determine the direction of the channel by receiving the feedback of the channel direction information. Accordingly, the base station can generate a beamforming vector orthogonal to the channel vector by identifying the direction of the channel.

In addition, if the antenna number determiner 210 determines M-L of the M transmit antennas as the active antenna, the terminal may feed back channel information on the channel formed from the M-L active antennas to the beam forming unit 220.

In this case, although not shown in FIG. 2, the beam forming unit 220 generates the transmission signal using the beamforming vector generator for generating a beamforming vector based on the channel information and the generated beamforming vector. It may include a transmission signal generator.

For example, the beamforming vector generator may generate a zero forcing beamforming vector based on the channel direction information included in the channel information. In addition, the transmission signal generator may generate a transmission signal using the generated beamforming vector and the data stream to be transmitted.

In this case, the channel information may include information regarding the index of the selected vectors among the plurality of vectors previously stored in the user terminals.

In this case, the channel information may be a predetermined number of bit information. For example, the user terminals may store a plurality of vectors in advance, and after identifying channel information, may feed back an index of vectors corresponding to the channel information to the base station. Accordingly, the base station can also generate a beamforming vector using channel information fed back from the user terminal with predetermined bit information.

In addition, the antenna switching unit 230 switches one or more active antennas of the transmitting antennas.

For example, if M-L of the M transmit antennas is determined as the number of active antennas, the beam forming unit 220 may generate a transmission signal having a dimension of M-L. At this time, the antenna switching unit 230 may switch the transmission antennas so that the M-L active antennas can transmit the transmission signals to the user terminals. At this time, only M-L active antennas turned on by the antenna switching unit 230 among the M transmit antennas may transmit the transmission signal.

That is, the present invention can efficiently transmit data without changing the number of bits of data fed back by variably adjusting the number of active antennas in consideration of the power of the transmission signal.

In addition, although not shown in FIG. 2, the multiple input / output communication system according to an embodiment of the present invention may further include a user terminal selecting unit for selecting a user terminal to participate in communication among a plurality of terminals using channel information. .

That is, among the plurality of terminals, the user terminal participating in the actual communication may be a part. For example, the user terminal selector may select only a terminal corresponding to a channel having a good channel state as the user terminal according to channel state information which is information about a channel state. In addition, the user terminal selector may select a user terminal using a semi-orthogonal user selection (SUS) and greedy user selection (GUS) algorithm. In this case, the user terminal selector may set a data rate of the transmission signal.

3 is a diagram illustrating a multiple input / output communication system according to another embodiment of the present invention.

Referring to FIG. 3, the user terminal selecting unit 310, the beam forming unit 320, the antenna selecting unit 330, the transmitting antennas ANT1, ANT2, ANT3, and ANT4 and the users (user 1, user 2, ..., user 4) is shown.

The user terminal selector 310 may select users (user 1, user 2, ..., user 4) participating in the communication using the channel information fed back from the plurality of users. In this case, the user terminal selector 310 may select the users in consideration of the channel state formed between the base station and the users.

When the base station uses M transmit antennas, up to M users may be selected to participate in communication at one time. At this time, if the number of active antennas is reduced to M-L in consideration of the power of the transmission signal, up to (M-L) users can participate in the communication.

The beam former 320 generates a transmission signal to be transmitted to the users who will participate in the communication by using the channel information fed back from the users. In this case, the beam former 320 may generate a transmission signal using the data stream and the precoding matrix. In addition, although described with reference to FIG. 2, the beam former 320 may generate a transmission signal using a beamforming vector corresponding to the number of active antennas.

In this case, the beam forming unit 320 may receive the channel information, which is information about the channel, from the users participating in the communication. The channel information may include channel direction information or channel state information about a channel vector formed between the base station and the users.

In this case, the beam former 320 may generate a transmission signal using a zero forcing algorithm. When a transmission signal is generated using a zero forcing algorithm, and the transmission signal is transmitted to users, ideally, noise due to interference between channels can be eliminated. However, since channel information fed back from users is information about a quantized channel vector, noise due to interference between channels may still exist. In particular, as power or signal-to-noise ratio of a transmission signal increases, noise due to interference between channels may increase.

In addition, the beamformer 320 may include a beamforming vector generator for generating a beamforming vector based on the fed back channel information, and a transmission signal generator for generating a transmission signal using the beamforming vector.

The antenna selector 330 selects one or more active antennas ANT1, ANT2, and ANT3 that transmit a transmission signal among the transmission antennas ANT1, ANT2, ANT3, and ANT4 in consideration of the power of the transmission signal. In this case, the antenna selector 330 may further consider the signal-to-noise ratio of the transmission signal as well as the power of the transmission signal.

That is, the antenna selector 330 reduces the number of active antennas from four to three when the power of the transmission signal is greater than or equal to a predetermined level. At this time, a higher data rate may be achieved than when the number of active antennas is three. That is, when the number of bits of the channel information to be fed back is constant, a higher data rate may be achieved by adjusting the number of active antennas. For example, when the power of the transmission signal is further increased, the antenna selector 330 may select the active antenna such that the active antennas are ANT1 and ANT2.

In addition, as described above, the antenna selector 330 may determine the number of active antennas to maintain the effective channel state using a virtual antenna technique.

4 is a flowchart illustrating a multiple input / output communication method according to an embodiment of the present invention.

Referring to FIG. 4, the multiple input / output communication method according to an embodiment of the present invention determines the number of one or more active antennas transmitting the transmission signal among the transmission antennas in consideration of the power of the transmission signal (S410).

In this case, the determining of the number of active antennas (S410) may determine the number of active antennas by further considering at least one of a signal to noise ratio of the transmission signal, the number of user terminals, or the number of bits of channel information. Can be.

In this case, the determining of the number of active antennas (S410) may reduce the number of active antennas as the power of a transmission signal increases.

In addition, the multiple input / output communication method according to an embodiment of the present invention generates a transmission signal corresponding to the number of active antennas by using channel information fed back from user terminals (S420).

In this case, in operation S420, the transmission signal may be generated by using a zero forcing algorithm.

In this case, the generating of the transmission signal (S420) may include generating a beamforming vector based on the channel information and generating a transmission signal using the generated beamforming vector.

In addition, according to an embodiment of the present invention, a multiple input / output communication method switches at least one active antenna among transmission antennas (S430).

In addition, although not shown in Figure 4, the multiple input and output communication method according to an embodiment of the present invention may further comprise the step of detecting the power of the transmission signal.

In addition, although not shown in FIG. 4, the multi-input / output communication method according to an embodiment of the present invention may further include selecting a user terminal participating in communication among a plurality of terminals using channel information.

In addition, although not shown in FIG. 4, the multi-input / output communication method according to an embodiment of the present invention selects one or more active antennas for transmitting the transmission signal among the transmission antennas in consideration of the power of the transmission signal and a user. Generating a transmission signal using the channel information fed back from the terminals.

In this case, the step of selecting the active antenna may determine the number of active antennas by further considering at least one of a signal to noise ratio of the transmission signal, the number of user terminals or the number of bits of channel information. In this case, the selecting of the active antenna may select the active antenna using a virtual antenna technique.

Content not described with respect to the steps illustrated in FIG. 4 is the same as described above with reference to FIGS.

5 is a block diagram illustrating a terminal device according to an embodiment of the present invention.

Referring to FIG. 5, the terminal device 510 according to an embodiment of the present invention includes a channel information generator 511, a channel information transmitter 512, and a transmission signal receiver 513.

The channel information generator 511 generates channel information on the channel formed with the base station 520 in consideration of the number of active antennas.

In this case, the channel information generator 511 may select an active codebook corresponding to the number of active antennas from one or more codebooks stored in advance, and generate channel information using the selected codebook.

In addition, the channel information generator 511 may select a vector corresponding to a channel formed with the base station 520 among the plurality of vectors included in the active codebook, and generate channel information including index information of the selected vector. .

That is, as described above, when the number of active antennas is variably adjusted, the size of the codebook or the size of the vectors included in the codebook should also change according to the number of active antennas. Therefore, according to an embodiment of the present invention, in case the number of active antennas is variously adjusted, one or more codebooks may be stored in the terminal device 510 corresponding to the number of active antennas.

The base station 520 informs the terminal device 510 of information related to the number of active antennas. In this case, the terminal device 510 may select an active codebook corresponding to information related to the number of active antennas among a plurality of prestored codebooks. The channel information generator 511 generates the channel information using the pilot signal received through the active codebook.

In particular, when the base station 520 uses a virtual antenna technique, the channel information generator 511 may estimate the effective channel, not the actual channel formed with the base station, and generate information related to the estimated effective channel as channel information. .

In addition, the channel information transmitter 512 feeds the generated channel information back to the base station 520. In this case, the channel information may include index information of a selected vector among a plurality of vectors included in the active codebook.

In addition, the transmission signal receiver 513 receives the transmission signal transmitted from the active antenna according to the channel information. That is, the base station 520 selects a beamforming vector using the fed back channel information, and generates a transmission signal based on the selected beamforming vector. At this time, the transmission signal is transmitted from the active antenna. In this case, the transmission signal received by the transmission signal receiver 513 may be provided to the user through an interference cancellation process, a decoding process, and the like.

6 is a flowchart illustrating a method of receiving a transmission signal according to an embodiment of the present invention.

Referring to FIG. 6, the method for receiving a transmission signal according to an embodiment of the present invention generates channel information on a channel formed with a base station in consideration of the number of one or more active antennas (S610).

At this time, the active antenna is selected by the base station among a plurality of transmit antennas in consideration of the power of the transmission signal.

In addition, the transmission signal reception method according to an embodiment of the present invention feeds back the channel information to the base station (S620).

In addition, the transmission signal transmitted from the active antenna is received according to the channel information (S630).

Although not shown in FIG. 6, the contents are not described below because they have been described with reference to FIGS. 1 to 5.

7 is a diagram illustrating terminal devices using a maximum non-coupling scheme or an antenna selection scheme according to an embodiment of the present invention.

Referring to FIG. 7, a base station 710 and a plurality of terminal devices 720, 730, and 740 are illustrated. Each of the plurality of terminal devices 720, 730, and 740 is provided with a plurality of receiving antennas, and each of the plurality of terminal devices 720, 730, and 740 receives the received signals from each of the plurality of receiving antennas.

In this case, each of the plurality of terminal devices 720, 730, and 740 may combine the received signals received from each of the plurality of receive antennas using various combining techniques.

In this case, the combining schemes include a maximum ratio combining (MRC) technique, at least one active receiving antenna among a plurality of receiving antennas, and combining received signals received from at least one active receiving antenna among the received signals. An antenna selective combining technique or a received signal non-combining technique that considers the received signals received from each of the plurality of receive antennas as independent signals.

Referring to FIG. 7, a maximum ratio combining (MRC) technique and an antenna selection combining technique will be described.

는 하기 수학식 10과 같이 표현될 수 있다.Received signal received from the l-th receive antenna of k-th terminal device 730

May be expressed as Equation 10 below.

는 하기 수학식 11과 같이 표현될 수 있다.In this case, when the number of receiving antennas of the k-th terminal device 730 is N, the received signals received from each of the N receiving antennas are combined.

May be expressed as in Equation 11 below.

는 k 번째 단말 장치(730)의 수신 가중치 벡터이고,

는

의 l 번째 원소이다.here,

Is a reception weight vector of the k-th terminal device 730,

The

Is the l th element of.

는 하기 수학식 12와 같이 나타낼 수 있다.At this time, the equation (11)

Can be expressed as in Equation 12 below.

는 k 번째 단말 장치(730)의 실효 채널 벡터이며,

는 k 번째 단말 장치(730)의 채널 매트릭스이다.In Equation (12)

Is the effective channel vector of the k-th terminal device 730,

Is the channel matrix of the k-th terminal device 730.

및 k 번째 단말 장치(730)가 기지국(710)으로 피드백하는 채널 정보가 달라진다.In this case, the reception weight vector according to the technique used by the k th terminal device 730 among various combination techniques.

And channel information fed back from the k-th terminal device 730 to the base station 710 is changed.

(1) When k th terminal device 730 uses Maximum Ratio Combining (MRC) scheme

는 하기 수학식 13과 같이 계산될 수 있다.If the k th terminal device 730 uses the maximum uncoupling scheme, the received weight vector

May be calculated as in Equation 13.

를 계산하고,

가 최대가 되는 m을 추출할 수 있다. 그리고, k 번째 단말 장치(730)는 추출된 m을 이용하여 수신 가중치 벡터

를 결정하고, 결정된 수신 가중치 벡터

를 이용하여 N 개의 수신 안테나들 각각으로부터 수신된 수신 신호들을 결합할 수 있다.That is, the k-th terminal device 730 changes i from 1 to 2 ^B

And calculate

We can extract m which is the maximum. The k th terminal device 730 receives the received weight vector using the extracted m.

And determine the received weight vector

The received signals received from each of the N receive antennas can be combined using the R-S sub-stage.

에 대하여 채널 매트릭스

가 가질 수 있는 특이값(singular value)들 중 최대의 특이값을 가질 수 있도록 코드북에 포함된 벡터들 중 어느 하나의 벡터를 선택할 수 있다. 더 나 아가, k 번째 단말 장치(730)는 양자화(quantization)된 정보인 선택된 벡터의 인덱스 정보를 채널 방향 정보로서 기지국(710)으로 피드백한다.In addition, the k-th terminal device 730 is a channel matrix

About the channel matrix

One of the vectors included in the codebook may be selected to have a maximum singular value among singular values that may be obtained. Furthermore, the k-th terminal device 730 feeds back index information of the selected vector, which is quantized information, to the base station 710 as channel direction information.

(2) When the k-th terminal device 730 uses the antenna selection technique

When the k-th terminal device 730 uses an antenna selection scheme, the k-th terminal device 730 selects at least one active receiving antenna from among the plurality of receiving antennas. The k-th terminal device 730 combines the received signal received from the active receive antenna among the received signals received from each of the plurality of receive antennas.

That is, the k-th terminal device 730 may calculate a quantization error with respect to the effective channel vector, and select an active reception antenna among a plurality of reception antennas so as to minimize the quantization error. In this case, the k-th terminal device 730 may select the active antenna using Equation 14 below.

(e is the index of the active antenna, f is the index of the selected vector among the vectors included in the codebook)

Referring to Equation 14, the k-th terminal device 730 is the index (e) of the active antenna and the index (f) of the vector selected from the vectors included in the codebook to minimize the quantization error for the effective channel vector ) Can be identified.

In this case, the k-th terminal device 730 feeds back the index (f) information of the selected vector among the vectors included in the codebook that is quantized information to the base station 710.

를 선택할 수 있다. 여기서, 설명의 편의를 위해 N은 2라고 가정한다.In addition, the k-th terminal device 730 receives the reception weight vector as shown in Equation 15 using the index e of the active antenna.

Can be selected. Here, for convenience of explanation, it is assumed that N is 2.

를 수신 가중치 벡터

로 선택하며, 액티브 안테나의 인덱스(e)가 2인 경 우,

를 수신 가중치 벡터

로 선택할 수 있다.That is, when the k th terminal device 730 has an index e of the active antenna of 1,

Receive weight vector

If the index (e) of the active antenna is 2,

Receive weight vector

.

As a result, the k-th terminal device 730 feeds back channel information to the base station 710 according to the antenna selection combining scheme, that is, the terminal device having a single receiving antenna selects any one of N x 2 ^B vectors. The same can be seen. Therefore, an effect such as substantially increasing the size of the codebook may occur.

8 is a diagram illustrating terminal devices using a received signal non-coupling scheme according to an embodiment of the present invention.

Referring to FIG. 8, a base station 810 and terminal devices 820, 830, and 840 are illustrated.

Each of the terminal devices 820, 830, and 840 feeds back channel information to the base station 810 according to a received signal non-coupling technique. Here, the received signal decoupling technique is a technique of considering received signals received from each of the plurality of receive antennas as independent signals.

That is, since the received signals received from each of the plurality of receive antennas are regarded as independent signals, each of the terminal devices 820, 830, and 840 may transmit channel information about a channel corresponding to each of all receive antennas. 810).

를 수신한다. 여기서, 설명의 편의를 위해 l은 0또는 1이라고 가정한다. 이 때, k 번째 단말 장치(830)는 첫 번째 수신 안테나에 상응하는 채널에 대한 채널 정보 및 두 번째 수신 안테나에 상응하는 채널에 대한 채널 정보를 기지국(810)으로 피드백한다.For example, the k-th terminal device 830 is from the l-th receiving antenna

. Here, for convenience of explanation, it is assumed that l is 0 or 1. At this time, the k-th terminal device 830 feeds back channel information on the channel corresponding to the first receiving antenna and channel information on the channel corresponding to the second receiving antenna to the base station 810.

Accordingly, according to the received signal non-coupling technique, the number of bits of channel information fed back by each of the terminal devices 820, 830, and 840 increases as the number of receive antennas increases. That is, when the number of receiving antennas of each of the terminal devices 820, 830, and 840 is N, the number of bits of channel information fed back by each of the terminal devices 820, 830, and 840 increases by N times. As a result, it can be seen that the number of receiving antennas of each of the terminal devices is N, and the performance of the communication system composed of K terminal devices is the same as that of the communication system composed of KxN terminal devices having a single receiving antenna. .

The multiple input / output communication method and the transmission signal reception method according to the present invention can be implemented in the form of program instructions that can be executed by various computer means and recorded in a computer readable medium. The computer readable medium may include program instructions, data files, data structures, etc. 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 recording media include magnetic media such as hard disks, floppy disks, and magnetic tape, optical media such as CD-ROMs, DVDs, and magnetic disks, 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 not only machine code generated by a compiler, but also high-level language code that can be executed by a computer using an interpreter or the like. The hardware device described above may be configured to operate as one or more software modules to perform the operations of the present invention, and vice versa.

As described above, the present invention has been described by way of limited embodiments and drawings, but the present invention is not limited to the above embodiments, and those skilled in the art to which the present invention pertains various modifications and variations from such descriptions. 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 multiple input / output communication system according to the present invention.

2 is a block diagram illustrating a multiple input / output communication system according to an embodiment of the present invention.

3 is a diagram illustrating a multiple input / output communication system according to another embodiment of the present invention.

4 is a flowchart illustrating a multiple input / output communication method according to an embodiment of the present invention.

5 is a block diagram illustrating a terminal device according to an embodiment of the present invention.

6 is a flowchart illustrating a method of receiving a transmission signal according to an embodiment of the present invention.

7 is a diagram illustrating terminal devices using a maximum non-coupling scheme or an antenna selection scheme according to an embodiment of the present invention.

8 is a diagram illustrating terminal devices using a received signal non-coupling scheme according to an embodiment of the present invention.

<Explanation of symbols for the main parts of the drawings>

210: antenna number determination unit

220: beam forming unit

230: antenna switching unit

Claims (25)

An antenna number determination unit determining the number of one or more active antennas transmitting the transmission signal among the transmission antennas in consideration of the power of the transmission signal; And Beam forming unit for generating the transmission signal corresponding to the number of the active antenna by using the channel information fed back from the user terminal Multiple input and output communication system comprising a. The method of claim 1, The multiple input and output communication system An antenna switching unit for switching one or more of the active antennas among the transmit antennas Multiple input and output communication system characterized in that it further comprises. The method of claim 1, The antenna number determination unit And determining the number of active antennas by further considering at least one of a signal to noise ratio of the transmission signal, the number of user terminals, and the number of bits of the channel information. The method of claim 1, The antenna number determination unit And the number of the active antennas decreases as the power of the transmission signal increases. The method of claim 1, The antenna number determination unit And determining the number of active antennas using a virtual antenna technique. The method of claim 5, The antenna number determination unit And determining the number of active antennas so that an effective channel state is maintained using a virtual antenna technique. The method of claim 1, The beam forming unit And generating the transmission signal using a zero forcing algorithm. The method of claim 1, The beam forming unit A beamforming vector generator configured to generate a beamforming vector based on the channel information; And A transmission signal generator for generating the transmission signal using the generated beamforming vector Multiple input and output communication system comprising a. An antenna selection unit for selecting one or more active antennas transmitting the transmission signals among the transmission antennas in consideration of power of the transmission signals; And A beam forming unit generating the transmission signal using the channel information fed back from user terminals Multiple input and output communication system comprising a. 10. The method of claim 9, The antenna selector And determining the number of active antennas by further considering at least one of a signal to noise ratio of the transmission signal, the number of user terminals, and the number of bits of the channel information. 10. The method of claim 9, The antenna selector And selecting the active antenna using a virtual antenna technique. Channel information generation unit for generating channel information about the channel formed with the base station in consideration of the number of one or more active antennas-The active antenna is selected from among the transmit antennas of the base station in consideration of the power of the transmission signal of the base station. -; A channel information transfer unit feeding back the channel information to the base station; And A transmission signal receiver for receiving the transmission signal transmitted from the active antenna according to the channel information Terminal device comprising a. The method of claim 12, The channel information generator And a plurality of receiving antennas, wherein the channel information is generated according to a combining technique for receiving signals received from each of the plurality of receiving antennas. 14. The method of claim 13, The combining scheme for the received signals may include a maximum ratio combining (MRC) scheme, an active receiving antenna selected from at least one of the plurality of receiving antennas, and the at least one active receiving antenna of the received signals. And an antenna selection combining technique for combining received received signals or a received signal non-combining technique for considering the received signals received from each of the plurality of receive antennas as independent signals. 14. The method of claim 13, The transmission signal receiving unit And combining the received signals using a reception weight vector corresponding to the combining technique for the received signals. The method of claim 12, The channel information generator And selecting an active codebook corresponding to the number of the active antennas from one or more codebooks stored in advance, and generating the channel information using the selected active codebook. 17. The method of claim 16, The channel information generator And selecting a vector corresponding to the channel among the vectors included in the active codebook, and generating the channel information including index information of the selected vector. Determining the number of one or more active antennas transmitting the transmission signal among the transmission antennas in consideration of the power of the transmission signal; Generating the transmission signal corresponding to the number of the active antennas using the channel information fed back from user terminals; And Switching the one or more active antennas of the transmit antennas Multiple input and output communication method comprising a. 19. The method of claim 18, Determining the number of active antennas And determining the number of active antennas by further considering at least one of a signal to noise ratio of the transmission signal, the number of user terminals, and the number of bits of the channel information.  19. The method of claim 18, Determining the number of active antennas And determining the number of active antennas using a virtual antenna technique. Selecting one or more active antennas transmitting the transmission signal among the transmission antennas in consideration of the power of the transmission signal; And Generating the transmission signal using channel information fed back from user terminals; Multiple input and output communication method comprising a. 22. The method of claim 21, Selecting the active antenna And determining the number of the active antennas by further considering at least one of a signal to noise ratio of the transmission signal, a number of the user terminals, and a number of bits of the channel information. 22. The method of claim 21, Selecting the active antenna And selecting the active antenna using a virtual antenna technique. Generating channel information on a channel formed with the base station in consideration of the number of one or more active antennas, wherein the active antenna is selected by the base station among transmission antennas in consideration of power of a transmission signal. -; Feeding back the channel information to the base station; And Receiving a transmission signal transmitted from the active antenna according to the channel information Transmission signal receiving method comprising a. 25. The method of claim 24, Generating the channel information And when the plurality of receive antennas are present, generating the channel information according to a combining scheme for the received signals received from each of the plurality of receive antennas.

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