KR101415417B1 - Multi user data transmitting method using multiple antennas and transmitter - Google Patents

Abstract

A method for transmitting a multi-user data using multiple antennas is provided. A combination of users for which the sum of the performance indices of the respective streams is maximized for a plurality of streams to be transmitted to multiple users and precoding is performed for a stream to be transmitted to each user belonging to the user combination, And transmits the performed signal. A plurality of streams can be efficiently scheduled and transmitted by precoding, thereby improving transmission performance.

Scheduler, transmission performance, multiple antennas, interference line deduction, DPC, precoding

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a multi-

1 is a block diagram illustrating a transmitter having multiple antennas.

2 is a block diagram illustrating a receiver having multiple antennas.

3 is an exemplary diagram illustrating a model of a communication system for one receiving antenna.

4 is a flowchart showing a method of implementing DPC.

5 is a flowchart illustrating a method of implementing DPC at a fixed data rate.

6 is a flowchart illustrating a method of implementing DPC under fixed power.

7 is a flowchart of a data transmission method according to an embodiment of the present invention.

8 is a flowchart of a data transmission method according to an embodiment of the present invention.

9 is an example of generating a transmission combination in the data transmission method according to an embodiment of the present invention.

10 is an example of generating a transmission combination in the data transmission method according to an embodiment of the present invention.

DESCRIPTION OF REFERENCE NUMERALS OF THE MAIN PARTS OF THE DRAWINGS

100: transmitter 110: scheduler

 200: receiver

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to wireless communication, and more particularly, to a multi-user data transmission method using multiple antennas.

The demand for communication services such as the universalization of information communication services, the appearance of various multimedia services, and the emergence of high quality services are rapidly increasing. Various wireless communication technologies are being investigated in various fields to satisfy this demand.

Multiple input multiple output (MIMO) technology is attracting attention as a technology for enhancing link reliability and interference prevention with high frequency efficiency. In the MIMO technique, the signals transmitted through the multiple transmission antennas have independency, thereby increasing the diversity gain.

In a MIMO system with multiple antennas in a transceiver, orthogonal resources may be allocated to one user in order to avoid interference to other users, thereby increasing a transmission rate or reducing a packet error probability. Alternatively, multiple users may be allocated to one orthogonal resource to increase the transmission rate. In the MIMO system, each user's data is stored in a virtual spatial layer through a spatial multiplexing technique, which transmits user data to each antenna, and precoding. There is a sending mechanism.

A MIMO system can be divided into a point-to-point communication system such as single-user MIMO and a point-to-multipoint communication system such as multi-user MIMO. In recent point-to-multipoint communications such as multi-user MIMO, an interference presubtraction method in a transmitter has recently attracted attention. Sending a signal u ₁ for the first user when sending the signal u ₂ for the second user, the transmitter subtracted from the u ₁ u ₂ line. At this time, the receiver of the second user can receive only u ₂ as if interference does not exist. This eliminates the need for separate interference cancellation at the receiver, greatly reducing the complexity of the receiver. One such scheme is referred to as dirty paper coding (DPC). DPC is described in M. Costa, "Writing on Dirty Paper ", IEEE Trans. on Inf. Theory, vol. IT-239, No. 2 3, May 1983, incorporated herein by reference. In this paper, Costa showed that the channel capacity under the transmission power limitation through DPC is the same as the case where there is no interference.

However, methods and apparatuses for effectively implementing DPC in one-to-many communication are not disclosed. In addition, although the MIMO scheme can achieve a high data rate, it is difficult to find an example using the DPC. Therefore, a technique for improving the performance of the system by combining MIMO and DPC is needed.

In addition, in data transmission, it is difficult to control a data rate when there are a plurality of data streams due to the complexity of the MIMO encoding method and the like. Or it may be necessary to transmit the data stream only to some of the multiple users. Therefore, it is necessary to efficiently distribute and transmit a plurality of data streams within a limited radio resource.

SUMMARY OF THE INVENTION The present invention provides a data transmission method that efficiently schedules a plurality of streams and transmits the streams to multiple users using multiple antennas.

According to an aspect of the present invention, there is provided a data transmission method for selecting at least one transport stream from N (N is an integer of 1 or more) candidate streams and transmitting the transport stream. A data transmission method includes: obtaining a performance index for each candidate stream; selecting a candidate stream having a maximum performance index among the performance indexes as a first transport stream; and selecting one or more candidate streams from the first transport stream and the remaining candidate streams A candidate stream having a maximum sum of the performance indices of each stream is selected as a second transport stream, and the first stream and the second stream are subjected to DPC and transmitted.

According to another aspect of the present invention, there is provided a method of transmitting multi-user data using multiple antennas. A data transmission method includes: obtaining a user combination having a maximum sum of the performance indexes of a plurality of streams to be transmitted to multiple users, precoding the stream to be transmitted to each user belonging to the user combination, Lt; / RTI >

A transmitter according to another aspect of the present invention includes an antenna, a scheduler for obtaining a user combination using a performance index of each stream for multiple streams to be transmitted to multiple users, and a scheduler for obtaining a combination of the performance And a preprocessor for performing precoding using the index and transmitting the precoded data through the antenna.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Like reference numerals designate like elements throughout the specification.

The following techniques can be used in various communication systems. Communication systems are widely deployed to provide various communication services such as voice, packet data, and the like. This technique can be used for a downlink or an uplink. The downlink means communication from a base station (BS) to a user equipment (UE), and the uplink means communication from a terminal to a base station. A base station generally refers to a fixed station that communicates with a terminal and may be referred to by other terms such as a node-B, a base transceiver system (BTS), an access point, and the like. A terminal may be fixed or mobile and may be referred to by other terms such as a mobile station (MS), a user terminal (UT), a subscriber station (SS), a wireless device,

1 is a block diagram illustrating a transmitter having multiple antennas.

1, a transmitter 100 includes a scheduler 110, channel encoders 120-1, ..., and 120-K, mappers 130-1 through 130-K, 140-1, ..., 140-K, and a multiplexer 150. [ The transmitter 100 includes Nt (Nt > 1) transmit antennas 190-1, ..., 190-Nt. The transmitter 100 may be part of a base station (BS). A base station generally refers to a fixed station that communicates with a terminal and may be referred to by other terms such as a node-B, a base transceiver system (BTS), an access point, and so on.

The scheduler 110 receives data from N users and outputs K streams to be transmitted at one time. The scheduler 110 determines the users to transmit to the available resources and the transmission rate using the channel information of each user. The scheduler 110 extracts channel information from the feedback data and selects a code rate, a modulation and coding scheme (MCS).

The channel information may include channel state information (CSI), channel quality information (CQI), or user priority information. The channel state information includes a channel matrix between the transceivers, a channel correlation matrix, a quantized channel matrix, or a quantized channel correlation matrix. The channel quality information includes signal to noise ratio (SNR), signal to interference and noise ratio (SINR), and the like between the transceivers. The user priority information is information having a priority for the user according to the level or the like of each user.

The available resources allocated by the scheduler mean resources used in data transmission in the communication system. For example, in a time division multiple access (TDMA) system, each time slot is a resource. In a code division multiple access (CDMA) system, each code and time slot is a resource. Orthogonal frequency division multiple access ) System, each subcarrier and time slot are resources. Each resource can be defined orthogonally in time, code or frequency domain so as not to cause interference to other users in the same cell (Cell) or sector (Sector).

It is possible to transmit data at a different transmission rate to each user according to the channel information for each user. The transmission rate for each user is determined by the size of the constellation symbol (e.g., BPSK, QPSK, 16-QAM, 64-QAM, etc.) and the code rate (e.g., 1/3, 1/2, May be determined by adjusting the MIMO encoding scheme.

The channel encoders 120-1, ..., and 120-K encode the input stream according to a predetermined coding scheme to form coded data. The mappers 130-1,..., 130-K map the coded data into symbols representing positions on the signal constellation. The modulation scheme is not limited and may be m-Phase Shift Keying (m-PSK) or m-Quadrature Amplitude Modulation (m-QAM).

The preprocessors 140-1 to 140-K perform precoding on the input information symbol u to generate an input symbol x . The information symbol u is a symbol for channel coding and constellation mapping of data to be transmitted to each user. Pre-coding is a technique of performing preprocessing on an information symbol u to be transmitted. Of these precoding schemes, RBF (random beamforming), ZFBF (zero) generating a input symbol x by applying a weight vector or a precoding matrix to the information symbol u , forcing beamforming). In addition, precoding includes a DPC technique for applying weight vectors or weight matrices to symbols performed by modulo arithmetic after limiting multi-user interference.

The multiplexer 150 allocates the input symbol x to an appropriate subcarrier, and multiplexes the input symbol x according to the user. The multiplexed symbols are modulated and transmitted through the transmit antennas 190-1, ..., 190-Nt.

2 is a block diagram illustrating a receiver having multiple antennas.

2, the receiver 200 includes a demodulator 210, a channel estimator 220, a post processor 230, a demapper 240, a channel decoder 245 and a controller 260. One receiver 200 is shown, but a plurality of receivers 200 can be arranged in the system. The receiver may correspond to K users, respectively. The receiver 200 may be part of a user equipement (UE). A terminal may be fixed or mobile and may be referred to by other terms such as a mobile station (MS), a user terminal (UT), a subscriber station (SS), a wireless device, The downlink means communication from the base station to the terminal, and the uplink means communication from the terminal to the base station.

The signal received from the receiving antenna 290 is demodulated by the demodulator 210. [ The channel estimator 220 estimates the channel, and the post-processor 230 performs post-processing corresponding to the preprocessors 140-1, ..., and 140-K. The demapper 240 demaps the input symbols into the encoded data, and the channel decoder 250 decodes the encoded data to recover the original data. The controller 260 returns valuable data including the channel state information (CSI), the channel quality information (CQI), or the user priority information to the transmitter 100.

Hereinafter, a transmission method using the communication system will be described. A transmission method using DPC (Dirty Paper Coding) will be described as an example of a multi-user transmission method using multiple antennas.

3 is an exemplary diagram illustrating a model of a communication system for one receiving antenna.

Referring to FIG. 3, the preprocessor 140 performs DPC on an input information symbol u to generate an input symbol x . The preprocessing unit 140 includes a modulo arithmetic unit 142 and a feedback unit 145. The modulo arithmetic operation unit 142 performs a modulo operation and the feedback unit 145 returns the output of the modulo arithmetic operation unit 142 to the input side of the modulo arithmetic operation unit 142, do. The vector w is multiplied by a transmit antenna matrix B by a modulo operation to generate an input symbol x and transmitted through a transmit antenna.

The post-processor 230 of the receiver 200 processes the reception antenna matrix v _i ^H with respect to the reception signal input from the reception antenna 290 and sends it to the modulo arithmetic operation unit 235. In the following, (·) ^H is a Hermitian matrix. The output of the modulo arithmetic unit 250 becomes an estimation symbol, demapped, channel-decoded, and restored as original data.

The input information symbol vector u = {u ₁ , ..., u _K } includes the information symbols of the users 1 to k. I information symbol of user u _i has the constellation size (constellation size) that is determined by the rate Rate _i of user i. (-L _i, L _i] is defined as the interval (interval) between that contains the aqueous phase. For example, with the aqueous phase from the size of the transmission rate per channel is referred to as a 4-bit 16-QAM, the coordinates of sex shops {± 1, ± 3} and L _i = 4.

The matrix I - G fed back by the feedback unit 145 is an upper triangular matrix. In accordance with the given encoding order, I - G deducts multiuser interference. Hereinafter, the order of encoding is from user K to user 1 in that order.

The values to be deducted are used to generate a vector w through a modulo operation. The vector w is expressed by the following equation (1).

Where w _i is the ith element of vector w , and g _ij is the (i, j) th element of matrix G.

이 된다. 모듈로 연산으로 인해 w_i와 w_j는 i≠j 에 대해 상관되어 있지 않다(uncorrelated). 따라서, R _w = E[ww ^H] = diag(σ_w1 ², ... , σ_wK ²) 라 한다. The modulo operation is to reduce transmission power while maintaining the distinguishability of stores. That is, the output w of the pre-processor 140 through a modulo operation is a finite interval (-L _i, are bound into the L _i]. If the power of the signal that is fed back is greater than the power of the information symbol vector w is a distance (-L _i , L _i ], where σ _wi ² is the power of w _i ,

. Due to the modulo operation, w _i and w _j are uncorrelated to i ≠ j. ^{_{Thus, R w = E [ww H}} ] = diag (σ w1 2, ..., σ wK 2) is referred to.

Hereinafter, a return matrix G is obtained. The return matrix G is designed to remove interference from previously encoded users.

The operation of the preprocessor 140 of the transmitter 100 may be said to be substantially equivalent to a decision feedback equalizer (DFE) that may be implemented in the receiver 200. Therefore, the matrix G can be obtained as a DFE in the receiver 200.

Received signal y _i of the receiver 200 of user i is equal to the following expression (2).

Here, h _i is Nt × 1 channel information from the transmitter 100 to the i-th receiver 200, and n _i is noise for the _i -th receiver 200.

The types of linear DFE (Decision Feedback Equalizer) are ZF (zero-forcing) DFE and MME (minimum mean square error) DFE.

를 i-번째 사용자에 대해 추정된 송신 신호라 할 때, 다음 수학식 3과 같이 나타낼 수 있다.First, we obtain the filter matrix G for the ZF DFE. The filter matrix G may first remove the interference of the encoded user.

Is the estimated transmission signal for the i-th user, the following equation (3) can be obtained.

)은 다음 수학식 4와 같다.When the noise is ignored, the output of the ZF DFE for the (K-1) th user

Is expressed by the following equation (4).

이어야 한다. 이와 같은 방법으로 전개하면 행렬 G의 (i,j)번째 원소인 g_ij는 다음 수학식 5와 같이 나타낼 수 있다.Here,? ₁ and? ₂ are arbitrary constants. To eliminate the interference of the K-th user from the K-th user

. In this way, the (i, j) th element g _ij of the matrix G can be expressed by the following equation (5).

In the case of the MMSE DFE, partial interfering precession is performed. In this case, g _{ij, which} is the (i, j) th element of the matrix G , can be expressed by Equation (6).

Here, β _i can be selected as shown in the following Equation (7).

In one embodiment of performing DPC, DPC can be performed by applying singular value decomposition (SVD). SVD can decompose an arbitrary matrix H into unitary matrices U and V and a diagonal matrix Λ as shown in the following mathematical expression.

Here, if H is assumed to be channel information known to each other in the transceiver, the transmitter processes the weight matrix on the transmission signal and the receiver can increase the channel capacity by appropriate signal processing.

And the transmission signal x = Bw, may generate a covariance matrix E [xx ^H] = B B _w R ^H using a x. Here, R _w = E [ ww ^H ] = diag (σ _w1 ² , ..., σ _wK ² ), which is a diagonal matrix. When the corresponding equation (8) on the covariance matrix (E [xx ^H]), the unitary matrix of the equation (8) U and V corresponds to the transmitting antenna matrix B, and the diagonal matrix Λ of Equation (8) corresponds to R _w.

The transmit covariance matrix for user i is σ _wi ² b _i b _i ^H. On the other hand, if S _i is a transmission covariance matrix for user i, S _i = λ _i m _i m _i ^H can be defined. Where λ _i is the eigenvalue of S _i and m _i is the unit-norm eigenvector. lambda _i is the optimal power allocation for user i, and m _i is the transmit beamforming vector. Therefore, the following equation (9) can be obtained.

Here, b i is a vector multiplied by i-th user data in the transmission antenna matrix B.

Hereinafter, a conversion for outputting a covariance matrix from a transmitter to a receiver having the same data rate for a receiver-transmitter covariance matrix will be described. This is based on the duality between the DPC region of one of the many downlink channels and the capacity region of the many-to-one uplink channel. That is, the sum of the possible transmission rates in the uplink under the power limit is equal to the sum of the transmission rates in the downlink under the power limit. This can be easily proved for multiple transmit antennas and multiple receive antennas. S. Vishwanath et al., &Quot; Duality, Achievable Rates and Sum-Rate Capacity of Gaussian MIMO Broadcast Channels ", IEEE Trans. on Inf. Theory, Vol.49, No.10, Oct. 2003. < / RTI >

The receiver 200 is said to have a decoding order in which user 1 is first decoded and the next user is sequentially decoded. The matrices A i and D i for the i-th user are defined by the following equations (10) and (11), respectively.

Here, P _i is the power of the i-th user in the uplink.

The rate _i ^UPLINK for the user i in the uplink is ^expressed by Equation (12).

Here, D _i represents the interference experienced by the user i in the uplink. | I + AD | = | I + DA | And A _j ^-1/2 A ^1/2 _j = I , the rate ^U _i can be expressed by Equation (13).

Now consider the rate _i ^DOWNLINK of the user i in the downlink with the encoding order opposite to the decoding order. That is, the encoding order for encoding user K first and sequentially encoding the previous user.

Here, A _i represents the interference experienced by the user i in the downlink. If S _i is selected as: Rate _i ^UPLINK = Rate _i ^DOWNLINK .

S _i is S _1, ..., S _{i -1,} so dependent only S _i can be obtained sequentially. The covariance matrix in the downlink having the same data rate as that in the uplink can be obtained by performing the process on all K users. In this case, B _i ^-1/2 h _i ^H A _i ^-1/2 = F _i Λ _i G _i ^H , The covariance matrix of the i-th user can be obtained by the following equation (16). &Quot; (16) "

Hereinafter, a method of obtaining the power of the user i in the transmitter 100 will be described. Here we provide user i with the minimum transmission power for a given rate R _i and maximum bit error rate (BER).

The transmission rate R _i that can be achieved for the user i in the multi-user downlink channel is given by Equation 17, considering the encoding order in which the user K is first encoded and the user 1 is later encoded.

Therefore, the problem of minimizing the downlink power becomes a problem of obtaining the minimum power P under the transmission rate limitation satisfying the above-mentioned equation (17). Here, the P = Σtr (S _i). tr (·) is the sum of the diagonal elements of the matrix.

인데, 모듈로 연산에 의해

가 된다. 따라서,

이 되므로 Γ_PM을 찾을 때 이를 고려해야 한다. 예를 들어, Pe = 10^-6을 만족하기 위해서는 QAM의 경우 5×10^-7의 차이(gap)를 이용해야 하고, 16-QAM의 경우 7.5×10^-7, 64-QAM의 경우 8.75×10^-7의 차이를 이용해야 한다.Γ _SH and Γ _PM are the SNR differences due to the actual modulation and DPC. Γ _SH is a shaping loss, which is the loss due to modulo operation. This is due to the uniform distribution of w . This can lead to a loss of about 1.53 dB at high SNRs. Γ _PM also has power loss and modulo loss due to loss due to modulo operation. The power loss is caused by the fact that the power of w is larger than u , resulting in a loss of about m / (m-1) in m-QAM, and the size becomes larger as the constellation size becomes smaller. 1.2494 dB for QAM, 0.2803 dB for 16-QAM, and 0.0684 dB for 64-QAM. The loss due to the modulo is due to the increase of the nearest surrounding symbols by the modulo operation. More specifically, the m-QAM

By modulo operation

. therefore,

, So you have to take this into account when looking for Γ _PM . For example, to satisfy Pe = 10 ^-6 , a gap of 5 × 10 ^-7 for QAM should be used, 7.5 × 10 ^{-7 for} 16-QAM, and 8.75 × 10 ^-7 for 64-QAM ^You should use a difference of ^-7 .

Equation (17) is a function that is neither convex nor concave with respect to the covariance matrix S _i . According to this, it is very difficult to find the DPC region which satisfies the power limitation when the general optimization algorithm is used.

The virtual rate is defined by the following equation (18).

로 계산할 수 있다.Using the virtual transmission rate, the required transmission rate and the required SINR for the BER

.

As described above, the DPC region of the MIMO downlink channel having the given power limit is equal to the capacity region of the MIMO uplink channel having the power limit sum. If user 1 is first decoded and complete interference cancellation is achieved, then the possible rate at the virtual uplink is: < EMI ID = 19.0 >

Since Equation 19 is a convex function for Pj, a general optimization algorithm can be applied.

As a result, the power of the user i can be obtained by Equation (20) if the receiver 200 has one receiving antenna 290 (Nr = 1).

4 is a flowchart showing a method of implementing DPC.

Referring to FIG. 4, a transmission power P _i satisfying a given transmission rate is obtained for each user (S 110). This can be obtained according to Equation (20).

A matrix D _i is obtained according to the transmission power P _i (S120). The matrix D _i is defined as Equation (11).

S _i and A _i are obtained in order from the user 1 using the matrix D _i (S130). S _i and A _i can be obtained by Equations (16) and (10).

B _i is obtained using the covariance matrix S i (S140). b _i can be obtained as shown in Equation (9).

b _i is used to obtain a return matrix G (S140). G can be obtained according to the ZF or MMSE scheme. In the case of ZF, MMSE can be obtained from Equation (5) by Equation (6).

In this way, all the parameters determined by the DPC unit 150 and the transmission processing unit 160 are determined, and the transmitter 100 processes the information symbol u , converts it into a transmission signal x , and transmits it to each user.

In another embodiment for performing DPC, DPC may be performed by applying QR decomposition. In the transmission antenna matrix B , a vector for multiplying the data of user i, b _i , can be obtained by using a QR decomposition. The transmitter collects the channel information from the K receivers and generates a stacking matrix H _s as shown in the following equation.

는 i-번째 수신기에 대한 채널 벡터이며, 스택 행렬(H _s)은 K 수신기의 채널 벡터(

)를 스택(Stacking)하여 생성되는 행렬이다. 스택 행렬(H _s)의 허미션 행렬(

)은 수학식 10과 같이 QR 분해에 의해 유니터리 행렬(Unitary matrix; Q)과 상삼각 행렬(Upper triangular matrix; R)로 분리될 수 있다.here,

Is the channel vector for the i-th receiver, and the stack matrix ( H _s ) is the channel vector of the K receiver

) Is stacked. The Hermitian matrix of the stack matrix ( H _s )

) Can be separated into a unitary matrix ( Q ) and an upper triangular matrix ( R ) by QR decomposition as shown in Equation (10).

로 표현 된다. 유니터리 행렬(Q)에 전송 안테나 행렬(B)을 대입하면, 다음의 수학식이 얻어진다.Therefore,

Lt; / RTI > When the transmission antenna matrix B is substituted for the unitary matrix Q , the following equation is obtained.

Therefore, after processing the transmit antenna matrix B in the stack matrix H _s , a lower triangular matrix R ^H can be obtained. Since the interference of the user encoded first is removed by the preprocessor, each user is in a state of no interference from other users.

The vector b _i , in which the data of the user i is multiplied, in the transmission antenna matrix B can be obtained by the following equation.

Where P _i is the transmit power for the receiver of user i and q _i is the i-th column vector of the unitary matrix Q.

5 is a flowchart illustrating a method of implementing DPC at a fixed data rate.

Referring to FIG. 5, when a user i is transmitted at a fixed rate (Rate _i ) with respect to a receiver, the downlink transmission rate can be calculated by the following equation.

Once the transmission rate for each user is determined, the transmission power P _i allocated to each user can be obtained by the following equation (S200).

The transmission power P _i for the receiver of the user i is calculated, and then b _i is calculated by the equation (24) (S210). b _i after the calculation calculates the matrix G (S220). The matrix G can be obtained according to the ZF or MMSE scheme, where ZF can be obtained from Equation (5) and MMSE can be obtained from Equation (6).

The transmitter 100 processes the information symbol u , converts the information symbol into a transmission signal x , and transmits the transmission signal x to each user.

6 is a flowchart illustrating a method of implementing DPC under fixed power. And DPC is performed when the transmission power P _i is determined for the user i's receiver. Referring to FIG. 6, a transmission rate for each user under a fixed transmission power is obtained by Equation 25 (S300). When the transmission rate is determined, b _i is calculated by the equation (24) (S310). b _i after the calculation calculates the matrix G (S320).

Transmitter 100 processes transmission symbol u by DPC and transmits it to each user.

In Equations 25 and 26, Γ _mod and Γ _THP are losses caused by modulation and DPC. Γ _mod is a loss due to modulation. Generally, Γ _mod = 8.8 dB is required to satisfy Pe = 10 ^-6 in uncoded situations.

Γ _THP is the loss due to implementation of DPC. Losses such as shaping loss, power loss and modulo loss can occur if the ideal DPC is not used. Shaping loss is a loss due to modulo operation and occurs because w _i is uniformly distributed. At high SNR, a loss of about 1.53dB may occur. The power loss is a loss due to a modulo operation and occurs when the power increases. The power loss is caused by the fact that the power of w is larger than u , resulting in a loss of about m / (m-1) in m-QAM, and the size becomes larger as the constellation size becomes smaller. 1.2494 dB for QAM, 0.2803 dB for 16-QAM, and 0.0684 dB for 64-QAM. Modulo loss is caused by the increase of nearest neighboring symbols by modulo operation.

7 is a flowchart of a data transmission method according to an embodiment of the present invention.

Referring to FIG. 7, the case where the number of streams to be transmitted by the transmitter is k will be described. First, L may be designated as a basic number of streams transmitted from the transmitter (S400). L is an arbitrary positive integer. For example, when L = 1, one transport stream is designated.

When the number of streams is designated, a maximum index indicating optimum performance is given in a given number of streams (S410). At this time, channel information can be used to obtain the performance index of each stream.

The transmitter can collect channel information for the receiver and determine a metric for each receiver. The channel information is information on the channel state for each receiver, and may include, for example, a channel matrix, a channel vector or a noise variance. The transmitter can receive channel information from each receiver or extract channel information using feedback data transmitted from each receiver.

A Modulation and Coding Scheme (MCS) can be determined based on the channel information. In addition, the SINR (Signal to Interference plus Noise Ratio) can be known, and a performance index such as a transmission rate or a throughput with respect to a stream transmitted from a transmitter can be obtained.

When the number of transport streams is selected, sum indices (Sm) are obtained by obtaining performance indices for each stream using channel information. Sum sum (Sm) is a value obtained by summing the figure of merit when transmitted for a user combination S and expressed by one index, and can be expressed by the following equation.

Here, m _ij ^s is a figure of merit for the j-th stream of the i-th user when transmitting for a user combination of S. k _i represents the number of streams for the _i -th user.

Sum sum (Sm) can be expressed by the following equation by multiplying the performance index of each user by the priority (ρ _i ).

The summation exponent of Equation (28) reflects the weights of the users in the figure of merit for each user, thereby giving a high weight to users with high priorities.

the summation exponent of Equation (27) or Equation (28) may be changed according to a method of allocating k streams to each user. The transmitter may generate a k-max exponent (M _k ) indicating a possible sum exponent for a limited number of streams by the following equation (S410).

Here, the maximum exponent represents a maximum value of the sum exponent when k streams are transmitted, and S _k denotes a transmission combination in which k streams are allocated when the maximum exponent is used.

Alternatively, it is possible to select the _k -largest exponent (M _k ) which is the maximum among the combinations of the equation (28) representing the sum index reflecting the user's weight to the performance index for each user (S410).

After selecting the _k -max exponent (M _k ), the number of streams to be transmitted by the transmitter is incremented by n (n is an arbitrary integer) (S420). For example, if n is an integer 1, k increases by one in the number of previous streams, and if n is an integer 5, the number of streams to be transmitted increases by five. However, only the case of increasing the number of streams to be transmitted is mentioned, but the present invention can also be applied to the case of reducing the number of streams. In other words, if n is -1, the number of streams can be reduced by one.

After the number of transport streams is increased, a maximum exponent is generated from the sum exponent when transmitting k streams increased by applying Equation (29) or (30) (S430). The performance index for each stream is obtained using the channel information to generate the maximum index. When the number of streams is increased, it can be transmitted to more users by an increased number of streams, or more streams can be allocated to one user. For these various combinations, a sum exponent is generated and a k-max exponent (M _k ), which is the maximum exponent having a maximum value, is generated.

The step of comparing the _k -max index (M _k ) with the kn maximum index (M _{k -n} ) in the previous step is performed (S440). When the k-max index (M _k ) is increased compared to the kn max index (M _{k -n} ) in the previous step, the number of streams is increased by n and the maximum index is generated again.

If the k-max index (M _k ) does not increase or decrease with respect to the kn max index (M _{k -n} ), the data is transmitted without increasing the number of streams further (S450). In other words, if the maximum index indicating the transmission performance increases while increasing the number of streams, the number of streams is continuously increased. However, if the maximum index is decreased, the number of streams is not increased any more.

Since we can transmit a large number of streams according to the maximum exponent, where the kn max maximum exponent (M _{k -n} ) is highest when there are kn stream quantities in the above, the combination satisfying the kn max exponent (M _{k -n} ) A plurality of streams can be transmitted. Or may transmit a plurality of streams for a combination that satisfies the _k -max exponent (M _k ) when there are k streams.

Encodes the stream for each user according to the maximum exponent, and generates a constellation symbol by the mapper. DPC is performed by a preprocessor and data is transmitted through a transmission antenna. As described above, the user combination according to the maximum index is determined and the user data can be transmitted by performing the DPC according to the performance index, which is the transmission rate or the yield of the stream to be transmitted to each user.

8 is a flowchart of a data transmission method according to an embodiment of the present invention.

Referring to FIG. 8, a performance index for each candidate stream is generated for N (one or more integers) candidate streams (S500). Here, the candidate stream refers to N streams to be transmitted by the transmitter. The figure of merit is an index representing the performance for one stream, for example, a data rate or a yield rate.

A performance index is generated for each candidate stream, and a candidate stream having a maximum performance index which is the maximum value among the performance indexes is selected as the first transport stream (S510). When the number of streams is one, the maximum figure of merit becomes the maximum figure.

 When the first transport stream is selected, a combination including one or more candidate streams among the first stream and the remaining candidate streams may be generated (S520). These combinations can be generated in various combinations according to the number of candidate streams, and each combination includes a first transmission stream.

Therefore, the performance index of each stream included in the combination is obtained, and the sum of the performance indices is obtained as a sum index. For each combination, a sum exponent of the sum of the performance indices of each stream included in the corresponding combination is generated, and a maximum exponent having a maximum value is generated. In the combination satisfying the maximum exponent, the second transport stream is selected as the stream excluding the first transport stream (S530). Therefore, the combination including the first transport stream and the second transport stream is a combination that satisfies the maximum exponent.

The maximum index is a measure of the transmission performance. As the maximum index increases, the transmission performance increases. Therefore, it is determined whether the maximum index is increased or not (S540).

When the transmission performance is increased, a candidate stream is added again to generate a plurality of combinations. A sum exponent is calculated for each of the generated combinations, a maximum exponent having a maximum value is generated, and a third transport stream excluding the first transport stream and the second transport stream is selected.

However, if the transmission performance is not increased, the DPC is transmitted to the selected stream without adding the candidate stream any more (S550).

As described above, a combination of streams is obtained in which the transmission performance is maximized while increasing the number of streams in the candidate streams. Therefore, a combination in which a plurality of streams are transmitted and transmission performance is maximized can be obtained. A plurality of streams can be transmitted to multiple users by performing DPC on the selected combination.

9 is an example of generating a transmission combination in the data transmission method according to an embodiment of the present invention. Referring to FIG. 9, a case where a maximum of one stream is allocated to one user and transmitted is described.

First, 1 is set to k in which the number of streams is specified as one. In the case where the number of streams is designated as one for five users, there are five cases in which a stream is assigned to each of five users. Therefore, the sum exponent is calculated for five cases to generate the first maximum exponent (M ₁ ). Here, the sum index is summed up with the performance index, and the performance index is applied as the transmission rate.

For example, assume that the transmission rate is 0.2 for user # 1, 0.3 for user # 2, 0.4 for user # 3, 1.0 for user # 4, and 1.2 for user # 5. In this case, the transmission performance can be maximized by transmitting data to the fifth user under a situation in which the transmission rate for the fifth user is maximized and one stream is given. Therefore, the first maximum exponent M ₁ is 1.2, and the combination S ₁ at this time is (5). Here, for the transmission rate, the unit is not specified simply to compare the relative sizes.

Increases the number of streams by one to send two streams. The combination for transmitting two streams includes transmitting one stream to user 5. And the case where the first maximum exponent is satisfied is a case where one stream is transmitted to the fifth user. Therefore, there is a combination of (5, 1), (5, 2), (5, 3) and (5, 4).

(5, 1) refers to transmitting the first stream to user # 5 and transmitting the second stream to user # 1. However, the first stream and the second stream are simply for distinguishing streams, and are not referred to as sequences. If the transmission rate is 1.0 for the user # 5 and the transmission rate is 0.3 for the user # 1, the sum exponent (here, the sum of the transmission rates) is 1.3.

(5, 2) transmits the first stream to user # 5, and transmits the second stream to user # 2. Here, if the transmission rate for user # 5 is 0.5 and the transmission rate for user # 2 is 0.9, the sum index is 1.4.

(5, 3) is to transmit one stream to user # 5 and user # 3. If the data rate for user # 5 is 0.9 and the data rate for user # 3 is 0.8, the summed index is 1.7.

(5, 4) is to transmit one stream to user # 5 and user # 4. If the transmission rate for user # 5 is 0.5 and the transmission rate for user # 4 is 0.3, the sum exponent is 0.8.

Therefore, the sum exponent is compared to select the combination having the best performance in transmission of the above four combinations. (5, 3) combinations with the maximum sum index being selected, and the sum of the transmission rates at this time is 1.7, the second maximum index (M ₂ ), and the combination S ₂ is (5, 3).

Since the second maximum index M ₂ is larger than the first maximum index M ₁ , the number of streams is increased by one again. When the number of streams is three, there are three combinations of (5, 3, 1), (5, 3, 2) and (5, 3, 4).

(5, 3, 1) refers to transmitting three streams one by one to user # 5, user # 3 and user # 1. If the transmission rate is 0.3 for user # 5, the transmission rate is 0.5 for user # 3, and the transmission rate is 0.5 for user # 1, the sum exponent (here, the sum of transmission rates) is obtained.

(5, 3, 2) transmits one stream to user # 5, user # 3, and user # 2. For the 5th user, the transmission rate is 0.7, for the 3th user, the transmission rate is 0.5, and for the 2th user, the transmission rate is 0.4.

(5, 3, 4) transmits one stream to user # 5, user # 3 and user # 4. For the fifth user, the transmission rate is 0.3, for the third user, the transmission rate is 0.4, and for the fourth user, the transmission rate is 0.8, the sum index is 1.5.

Therefore, in the above three combinations, 1.6, which is the maximum value of the sum of the transmission rates, becomes the third maximum index (M ₃ ). The combination S ₃ that becomes the third maximum index (M ₃ ) is (5, 3, 2). The third maximum index (M ₃ ) is compared with the second maximum index (M ₂ ). Since the third maximum exponent value is rather small compared to the second maximum exponent value, the step of increasing the number of more streams is not performed.

A plurality of streams can be transmitted according to the maximum index. Since the second maximum index (M ₂ ) is the highest when there are two streams in the above, for the combination S ₂ satisfying the second maximum index (M ₂ ) ≪ / RTI > streams. Therefore, the data can be transmitted at a transmission rate of 0.9 for user # 5 and at a transmission rate of 0.8 for user # 3. At this time, DPC is performed on the stream to be transmitted to each user and is transmitted.

Or when there are three streams it may be transmitted to the three streams for the combination of 3 satisfies the maximum index (M _3).

10 is an example of generating a transmission combination in the data transmission method according to an embodiment of the present invention. Referring to FIG. 10, a case where a plurality of streams can be transmitted to the same user will be described. Here, the sum index is summed up with the performance index, and the performance index is applied as the transmission rate.

First, the basic number of streams is taken as one and k = 1 is specified. If there are 5 users to receive data, there are five cases where one stream is sent to each user when there are one stream. When transferring to the user # 1 rate (r ₁₁₎ is 1.0, the case of transmitting to the user # 2 rate (r ₂₁₎ when transmitting to the user the 1.2 and 3 rate (r ₃₁₎ is sent to the 0.5 and 4 users (R ₄₁ ) is 0.4, and the transmission rate (r ₅₁ ) is 0.2 when the transmission is performed to the user 5. Here, r _ij is the transmission rate of the j-th stream for the i-th user. Therefore, the first maximum index M ₁ is 1.2, which is the transmission rate when one stream is transmitted to the second user, and the combination S ₁ is (2). Here, for the transmission rate, the unit is not specified simply to compare the relative sizes.

The number of streams is increased by one to designate k = 2. And a combination of transmitting one stream to the second user when the number of streams is two. This is because the combination S ₁ that represents the maximum performance when transmitting one stream is (2). (2, 2), (2, 3), (2, 4), and (2) , 5). Here, (2, 2) means that the first stream is also allocated to the second user, and the second stream is also allocated to the second user, that is, two streams are allocated to the second user. However, the first and second streams are simply for distinguishing streams, and are not referred to as sequences.

Therefore, the transmission rate is examined for each combination of the above five cases. (R ₂₁ ) of the first stream is 0.7 for the second stream (2, 1), and the sum exponent (sum of the transmission rates) is 1.3 when the second stream r ₁₁ is 0.6. (R ₂₁ ) for the first stream is 0.5, and the transmission rate (r ₂₂ ) for the second stream is 0.6, the sum exponent is 1.1 for the combination of (2, 2). In addition, for the combination (2, 3), the second user's transmission rate (r ₂₁ ) for the first stream is 0.4, and the transmission rate (r ₃₁ ) for the third user for the second stream is 0.5, 0.9. (R ₂₁ ) for the first stream is 0.7 and the transmission rate (r ₄₁ ) for the third user is 1.0 for the second stream, the sum exponent is 1.4 do. (R ₂₁ ) for the first stream is 0.3 and the transmission rate (r ₅₁ ) for the fifth stream is 0.4 for the second stream, the sum exponent is 0.7 for the combination of (2, 5) .

Therefore, the maximum value among the sum of the transmission rates for the combination is 1.7, which is the sum index for the combination of (2, 4). And has a second maximum index (M ₂ ) in the case of a combination of S ₂ transmitted to the second user and the fourth user transmitted in the two streams.

The second maximum index (M ₂ ) is compared with the first maximum index (M ₁ ). Since the second maximum index (M ₂ ) is larger than the first maximum index (M ₁ ), the number of streams is increased again and the calculation of the transmission rate is repeated.

Increase the number of streams by one to specify k = 3. And a combination of transmitting streams one by one to users # 2 and # 4 when the number of streams is three. (2, 4, 1), (2, 4, 2), (2, 4, 3) ), (2, 4, 4) and (2, 4, 5).

When a stream is allocated to users # 2, # 4 and # 1, the first stream is transmitted to the second user, the second stream is transmitted to the fourth user, and the third stream is transmitted to the first user, (r ₂₁ , r ₄₁ , r ₁₁ ) is (0.4, 0.3, 0.4). The sum index is 1.1.

(2, 4, 2), two streams are assigned to the second user and one stream is assigned to the fourth user. (R ₂₁ , r ₄₁ , r ₂₂ ) is (0.4, 0.5) when the first stream is transmitted to the second user, the second stream is transmitted to the fourth user and the third stream is transmitted to the second user again. , 0.7). Here, since two streams are allocated to the second user, the transmission rate for the third stream can be represented by r ₂₂ . The sum exponent plus each rate is 1.6.

(2, 4, 3), the first stream is transmitted to the second user, the second stream is transmitted to the fourth user, and the third stream is transmitted to the third user. Let each transmission rate (r ₂₁ , r ₄₁ , r ₃₁ ) be (0.2, 0.5, 0.5). The sum index is 1.2.

(2, 4, 4), the first stream is transmitted to the second user and the second and third streams are transmitted to the fourth user. Let each transmission rate (r ₂₁ , r ₄₁ , r ₄₂ ) be (0.6, 0.4, 0.3). The sum index is 1.3.

(2, 4, 5), the first stream is transmitted to the second user, the second stream is transmitted to the fourth user, and the third stream is transmitted to the fifth user. Let each transmission rate (r ₂₁ , r ₄₁ , r ₅₁ ) be (0.7, 0.3, 0.4). The sum index is 1.4.

Therefore, the maximum value 1.6 of the sum of the transmission rates is the third maximum index (M ₃ ), and the combination S ₃ at this time is (2, 4, 2). When the third maximum index M ₃ and the second maximum index M ₂ are compared, the third maximum index M ₃ is smaller than the second maximum index M ₂ .

Therefore, the stream is transmitted without increasing the number of streams. In order to transmit a plurality of streams, a plurality of streams are encoded, and after mapping to constellation symbols, DPC is performed and transmitted through transmission antennas.

A plurality of streams can be transmitted according to the maximum index. Since the second maximum index (M ₂ ) is the highest when there are two streams in the above, for the combination S ₂ satisfying the second maximum index (M ₂ ) ≪ / RTI > streams. Therefore, the data is transmitted at a rate of 0.7 for the second user and a transmission rate of 1.0 for the fourth user, and DPC is performed on the stream to be transmitted to each user.

Or when there are three streams it may be transmitted to the three streams for the combination of 3 satisfies the maximum index (M _3).

As described above, the maximum index for maximizing the transmission performance is obtained while increasing the number of streams. Therefore, even when the number of streams is flexible, transmission performance can be maximized, which is advantageous for a variable wireless communication environment. In addition, by using the channel information, it is possible to control the transmission performance according to the state of the channel, thereby improving the data transmission performance in the time varying wireless communication system.

The present invention may be implemented in hardware, software, or a combination thereof. (DSP), a programmable logic device (PLD), a field programmable gate array (FPGA), a processor, a controller, a microprocessor, and the like, which are designed to perform the above- , Other electronic units, or a combination thereof. In software implementation, it may be implemented as a module that performs the above-described functions. The software may be stored in a memory unit and executed by a processor. The memory unit or processor may employ various means well known to those skilled in the art.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the invention. You will understand. Therefore, it is intended that the present invention covers all embodiments falling within the scope of the following claims, rather than being limited to the above-described embodiments.

As described above, according to the present invention, it is possible to efficiently schedule a plurality of streams to be transmitted to a user combination and transmit the streams by precoding or DPC, thereby improving data transmission performance. In addition, it is possible to realize high transmission performance by variously changing the number of variable streams and the combination of users to transmit them.

Claims (10)

A data transmission method for selecting a plurality of transport streams from N (N is an integer of 2 or more) candidate streams and transmitting the plurality of transport streams, Obtaining a transmission rate for each candidate stream when one candidate stream among the N candidate streams is transmitted; Selecting a candidate stream having a maximum value among the transmission rates for each candidate stream as a first transport stream; When a combination of the first transport stream and one of the remaining candidate streams is transmitted, a candidate stream included in the combination in which the sum of the transmission rates of the streams is the largest is selected as the second transport stream step; And And transmitting the first transport stream and the second transport stream. The method according to claim 1, A combination of the first transport stream, the second transport stream, and one of the remaining candidate streams is transmitted, a candidate stream included in the combination in which the sum of the transmission rates of the streams is maximum 3 < / RTI > transport stream. antenna; A scheduler for obtaining, for a plurality of candidate streams to be transmitted to multiple users, transport streams to be transmitted to a user combination using a rate of each candidate stream; And And a preprocessor for precoding the transmission streams to be transmitted to each user belonging to the user combination using the transmission rates of the candidate streams and transmitting the precoded streams through the antennas, Wherein the scheduler obtains a transmission rate for each candidate stream when one of the N candidate streams is transmitted and determines a candidate stream having a maximum value among the transmission rates for the respective candidate streams as a first transport stream Select, When a combination of the first transport stream and one of the remaining candidate streams is transmitted, a candidate stream included in the combination in which the sum of the transmission rates of the streams is the largest is selected as the second transport stream Lt; / RTI > The method of claim 3, Wherein the antenna is a plurality of antennas. The method of claim 3, Wherein the scheduler is configured to select, when a combination of the first transport stream, the second transport stream, and one of the remaining candidate streams is transmitted, And selecting the stream as the third transport stream. delete delete delete delete delete

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