KR100934657B1 - Phase shift based precoding method and transceiver - Google Patents

Abstract

The present invention relates to a method for performing phase shift based precoding in a transmitting end of a multi-antenna system using a plurality of subcarriers, an extended phase shift based precoding method, and a transmission and reception apparatus supporting the methods. For example, a phase shift based precoding matrix can be obtained by determining a reference row corresponding to the first subcarrier in a predetermined precoding matrix, and phase shifting the reference row with a phase angle that increases in a predetermined unit to determine the remaining rows. The spatial multiplexing rate may be adjusted by selecting a specific column of the obtained precoding matrix. As another example, a phase shift based precoding matrix may be obtained by multiplying a diagonal matrix (a first matrix) having a constant phase shift interval and a second matrix satisfying a unitary matrix condition. You can adjust the spatial multiplexing rate or select a specific antenna.

Precoding, phase shift, OFDM, MIMO, unitary matrix

Description

Phase shift based precoding method and transceiver supporting the same

1 is a block diagram of an orthogonal frequency division multiplexing system having multiple transmit / receive antennas;

2 is a block diagram of a transmitter in a multiple antenna system using a conventional cyclic delay diversity scheme.

3 is a block diagram of a transmitter in a multiple antenna system using a conventional phase shift diversity scheme.

4 graphically illustrates two applications of a conventional phase shift diversity technique.

5 is a block diagram of a transmitting and receiving end of a multiple antenna system using a conventional precoding method.

FIG. 6 illustrates a process of performing a conventional phase shift diversity scheme in a system having four antennas and a spatial multiplexing ratio of 2. FIG.

FIG. 7 illustrates a process of performing a phase shift based precoding method of the present invention in the system of FIG. 6.

8 is a precoding matrix used for the phase shift based precoding method of the present invention in the system of FIG.

9 is a block diagram of a transceiver for supporting a phase shift based precoding method of the present invention.

FIG. 10 is a block diagram illustrating an SCW OFDM transmitter configured in the radio communication unit of FIG. 9; FIG.

FIG. 11 is a block diagram illustrating an MCW OFDM transmitter configured in the radio communication unit of FIG. 9; FIG.

12 is a graph comparing the performance difference when the phase shift based precoding technique and the conventional spatial multiplexing technique of the present invention are applied to an ML receiver and an MMSE receiver in a flat fading channel environment.

13A and 13B illustrate a case in which a phase shift based precoding scheme and a conventional spatial multiplexing scheme of the present invention are applied to an MMSE receiver according to coding rates in an ITU Pedestrian A (PedA) fading channel environment and a Physical Urban (TU) fading channel environment. Graph comparing performance differences.

14A to 14C illustrate a phase shift based precoding technique of the present invention and a conventional scheme for a system using SCW and MCW in a flat fading channel environment, an ITU Pedestrian A (PedA) fading channel environment, and a Typical Urban fading channel environment. Graph comparing performance differences when spatial multiplexing is applied.

FIG. 15 is a graph comparing performance differences between a case where a spatial multiplexing technique + a cyclic delay diversity scheme are applied to an MCS and a phase shift based precoding technique + a cyclic delay diversity scheme are applied to an MCS in a flat fading channel environment. FIG.

The present invention relates to a phase shift based precoding method in a multi-antenna system using a plurality of subcarriers, a phase shift based precoding method using the same, and a transceiver for supporting the same.

Recently, the demand for wireless communication services is rapidly increasing due to the generalization of information communication services, the appearance of various multimedia services, and the emergence of high quality services. To cope with this actively, it is necessary to increase the capacity of the communication system and increase the reliability of data transmission. In order to increase the communication capacity in a wireless communication environment, a method of finding new available frequency bands and increasing the efficiency of a given resource can be considered. Among them, the transceiver is equipped with a plurality of antennas to secure additional spatial area for resource utilization to obtain diversity gain, or transmit data in parallel through each antenna to increase transmission capacity. The so-called multi-antenna transmit and receive technology has recently been actively developed with great attention.

Referring to FIG. 1, a general structure of a multi-input multi-output (MIMO) system using orthogonal frequency division multiplexing (OFDM) among the multi-antenna transmission / reception techniques will be described below. same.

In the transmitting end, the channel encoder 101 attaches redundant bits to transmitted data bits to reduce the influence of the channel or noise, and the mapper 103 converts the data bit information into data symbol information. The serial-to-parallel converter 105 is responsible for parallelizing data symbols onto a plurality of subcarriers, and the multi-antenna encoder 107 converts the parallelized data symbols into space-time signals. The multiple antenna decoder 109, the parallel-to-serial converter 111, the de-mapper 113, and the channel decoder 115 at the receiving end are the multiple antenna encoder 107, the serial-to-parallel converter 105, the mapper ( 103 and the reverse function of the channel encoder 101, respectively.

In a multi-antenna OFDM system, various techniques are required for improving data transmission reliability. Specifically, Space-Time Code (STC), Cyclic Delay Diversity (CDD), and Antenna Selection (Antenna Selection); AS), antenna hopping (AH), spatial multiplexing (SM), beamforming (BF), precoding, and the like. Among the techniques listed above, the main techniques are described in more detail as follows.

Space-time code is a technique of obtaining a spatial diversity gain by continuously transmitting the same signal in a multi-antenna environment but transmitting it through different antennas in repeated transmission. The following determinant represents the most basic space-time code used in a system with two transmit antennas.

In the determinant, rows represent antennas and columns represent time slots.

Such a space-time coding technique requires a different form of space-time code as the antenna structure is different, and transmits data symbols repeatedly through a plurality of time slots to obtain a spatial diversity gain. There is a problem of increasing complexity, and since data is transmitted without using feedback information, the performance is relatively low compared to other techniques in a closed loop system. Table 1 shows that different space-time codes are required depending on the structure of the antenna.

 Space-time code  Spatial multiplexing rate  Number of antennas

 One  2

 2  2

 2  2

  One   4

  One   4

  2   4

Cyclic delay diversity is a technique in which a frequency diversity gain is obtained at a receiving end by transmitting an OFDM signal in a system having multiple transmitting antennas with all antennas having different delays or different sizes. 2 illustrates a configuration of a transmitter of a multiple antenna system using a cyclic delay diversity scheme.

After the OFDM symbol is separately transmitted to each antenna through a serial-to-parallel converter and a multi-antenna encoder, a Cyclic Prefix (CP) is added to the receiver to prevent interference between channels. At this time, the data sequence transmitted to the first antenna is transmitted to the receiving end as it is, but the data sequence transmitted to the next antenna is transmitted with a cyclic delay by a predetermined bit compared to the antenna of the previous sequence.

Meanwhile, if the cyclic delay diversity scheme is implemented in the frequency domain, the cyclic delay may be expressed as a product of a phase sequence. That is, as shown in FIG. 3, the data sequence in the frequency domain may be multiplied by a predetermined phase sequence (phase sequence 1 to phase sequence M) set differently for each antenna, and then may be transmitted to the receiver by performing fast inverse Fourier transform (IFFT). This is called a phase shift diversity technique.

According to the phase shift diversity scheme, a flat fading channel can be changed into a frequency selective channel and a frequency diversity gain or a frequency scheduling gain can be obtained through the channel code. That is, as shown in FIG. 4, in the case of generating a phase sequence using a large value of cyclic delay in the phase shift diversity scheme, the frequency selectivity period is shortened, so that the frequency selectivity is increased, and thus the channel code can obtain the frequency diversity gain. It is mainly used in open loop systems.

In addition, when a small value of the cyclic delay is used, the period of frequency selectivity becomes long, and thus, in a closed loop system, the frequency scheduling gain can be obtained by allocating resources to a region having the best channel. That is, as shown in FIG. 4, when the phase sequence is generated using a small value of the cyclic delay in the phase shift diversity scheme, the constant subcarrier region of the flat fading channel has a larger channel size, and the other subcarrier region has a smaller channel size. do. In this case, in an orthogonal frequency division multiple access (OFDMA) system that accommodates a large number of users, the signal-to-noise ratio can be increased by transmitting a signal through a subcarrier with a larger channel size for each user.

However, the above-described cyclic delay diversity scheme or phase shift diversity scheme has a problem in that the data transmission rate cannot be increased because the spatial multiplexing rate is 1 despite the above-mentioned advantages.

On the other hand, the precoding scheme includes a codebook based precoding scheme used when the feedback information is finite in a closed loop system, and a method of quantizing and feeding back channel information. The codebook-based precoding is a method of obtaining a signal-to-noise ratio (SNR) gain by feeding back an index of a precoding matrix known to the transmitter / receiver to the transmitter.

FIG. 5 illustrates a configuration of a transmitting and receiving end of a multiple antenna system using the codebook based precoding. Here, each of the transmitter and the receiver has finite precoding matrices ( P ₁ to P _L ), and the receiver feeds back the optimal precoding matrix index ( l ) to the transmitter using channel information. The precoding matrix corresponding to is applied to the transmission data ( χ ₁ ~ χ _{Mt )} .

This codebook-based precoding scheme has the advantage of effective data transmission through the feedback of the index, but it is not suitable for the mobile environment where channel change is severe because the stable channel must be secured for the feedback, and the uplink due to the feedback of the index Some loss occurs in the transmission rate, and there is a problem that memory usage increases because codebooks must be provided at both sides of the transmitting and receiving end.

The present invention has been proposed to solve the above problems, and has a lower complexity of the transceiver than the space-time coding scheme, supports various spatial multiplexing rates while maintaining the advantages of the phase shift diversity scheme, and compares the channel with the precoding scheme. The purpose of this paper is to propose a phase shift based precoding method that requires only a small amount of codebooks and is not sensitive to the problem.

Another object of the present invention is to provide a method for easily extending a matrix for performing the phase shift based precoding according to the number of antennas.

One aspect of the present invention for achieving the above object relates to a phase shift based precoding method in a multi-antenna system using a plurality of subcarriers, the reference row corresponding to the first subcarrier in a predetermined precoding matrix Determining a phase shift based precoding matrix and determining the remaining rows by phase shifting the reference row by a phase angle that increases by a predetermined unit. And performing a precoding of the transmission data using the method, selecting a number of columns corresponding to a predetermined spatial multiplexing rate in the determined phase shift based precoding matrix, and The method may further include reconfiguring the corresponding precoding matrix to include only selected columns.

In addition, another aspect of the present invention for achieving the above object relates to a transceiver of a multi-antenna system using a plurality of subcarriers, and to determine a reference row corresponding to the first subcarrier in a predetermined precoding matrix, Precoding matrix determination module for determining the remaining rows by phase shifting a reference row with a phase angle increasing by a predetermined unit and precoding for performing transmission of pre-transmission data using the determined phase shift based precoding matrix And a preselecting module for selecting a number of columns corresponding to a predetermined spatial multiplexing rate in the determined phase shift based precoding matrix, and reconstructing the corresponding precoding matrix to be composed of only the selected columns. The coding matrix reconstruction module may be further included.

On the other hand, an aspect of the present invention for achieving the above object relates to a phase shift based precoding method in a multi-antenna system using a plurality of subcarriers, and to satisfy the first matrix and unitary matrix conditions for the phase shift Determining a phase shift based precoding matrix by multiplying a second matrix, and performing precoding on subcarrier symbols using the determined phase shift based precoding matrix.

In this case, the phase shift based precoding method may further include selecting a number of columns corresponding to a spatial multiplexing rate in the second matrix, and reconstructing the second matrix to include only the selected columns. have. The method may further include reconfiguring the second matrix such that a specific antenna is selected from a plurality of transmit antennas.

In addition, another aspect of the present invention for achieving the object of the present invention relates to a transmission and reception apparatus of a multi-antenna system using a plurality of subcarriers, the second matrix for satisfying the first matrix and unitary matrix conditions for phase shift And a precoding matrix determining module for determining a phase shift based precoding matrix by multiplying and a precoding module for precoding a subcarrier symbol using the determined phase shift based precoding matrix.

In this case, a predetermined antenna among a plurality of transmit antennas or a precoding matrix reconstruction module for selecting a number of columns corresponding to a spatial multiplexing rate in the second matrix and reconstructing the second matrix to be made only of the selected columns A precoding matrix reconstruction module may be further included to reconstruct the second matrix to be selected. In addition, the first matrix may be a diagonal matrix in which the interval between phase shifts increases constantly.

Hereinafter, a phase shift based precoding method in two antenna systems and four antenna systems will be described, and a method of configuring a generalized phase shift based precoding matrix for extending it to N _t antenna systems will be described. .

Phase shift base Precoding  Way

When the phase shift based precoding matrix P proposed by the present invention is generalized and expressed as follows.

(i = 1,...,N_t, j = 1,...,R)는 부반송파 인덱스 k에 의해 결정되는 복소 가중치를 나타내고, N_t는 송신 안테나의 개수, R은 공간 다중화율을 각각 나타낸다. 여기서, 복소 가중치는 안테나에 곱해지는 OFDM 심볼 및 해당 부반송파의 인덱스에 따라 상이한 값을 가질 수 있다. 상기 복소 가중치는 채널 상황 및 피드백 정보의 유무 중 적어도 어느 하나에 따라 결정될 수 있다.here,

( i = 1, ..., N _t , j = 1, ..., R) represents a complex weight determined by the subcarrier index k, N _t represents the number of transmit antennas, R represents the spatial multiplexing rate, respectively. Here, the complex weight may have a different value depending on the OFDM symbol multiplied by the antenna and the index of the corresponding subcarrier. The complex weight may be determined according to at least one of channel conditions and presence or absence of feedback information.

Meanwhile, the precoding matrix P of Equation 1 is preferably designed as a unitary matrix to reduce the loss of channel capacity in the multi-antenna system. Here, the channel capacity of the multi-antenna system in order to find out the conditions for the unitary matrix configuration is represented as follows.

Here, H is a multi-antenna channel matrix of size N _r x N _t and N _r represents the number of receiving antennas. The phase shift based precoding matrix P is applied to Equation 2 as follows.

As shown in Equation 3, in order to avoid loss in channel capacity, PP ^H should be an identity matrix, so the phase shift based precoding matrix P should be a unitary matrix as follows.

In order for the phase shift based precoding matrix P to be a unitary matrix, two conditions, power constraints and quadrature constraints, must be satisfied at the same time. Here, the power constraint is to make the size of each column constituting the matrix to be 1, and the orthogonal constraint is to make orthogonal characteristics between each column of the matrix. Each of these expressions is expressed as follows.

Next, as an embodiment, a generalized equation of a 2 × 2 phase shift based precoding matrix will be presented, and the equations for satisfying the two conditions will be described. Equation 7 shows a general equation of a phase shift based precoding matrix having two transmit antennas and a spatial multiplexing rate of 2.

Here, α _i , β _i ( i = 1, 2) have a real value, θ _i (i = 1, 2, 3, 4) represents a phase value, and k represents a subcarrier index of an OFDM signal. In order to implement such a precoding matrix as a unitary matrix, power constraint conditions of Equation 8 and orthogonal constraints of Equation 9 must be satisfied.

Where the * symbol indicates a conjugate complex number. An embodiment of a 2 × 2 phase shift based precoding matrix that satisfies Equations 7 to 9 is as follows.

Here, θ ₂ and θ ₃ have the same relationship as in Equation 11 due to orthogonal constraint.

Meanwhile, the precoding matrix may be stored in a codebook form in memories of the transmitter and the receiver, and the codebook may include various precoding matrices generated through finite different θ ₂ values. In addition, the value of θ ₂ may be appropriately set depending on the channel condition and the presence or absence of feedback information. If θ ₂ is used when feedback information is used, θ ₂ is set high when feedback information is not used. Frequency diversity gain can be obtained.

On the other hand, even if a phase shift based precoding matrix is generated as shown in Equation 7, a spatial multiplexing rate may actually be set smaller than the number of antennas according to channel conditions. In this case, the phase shift based precoding matrix may be newly reconfigured by selecting a specific number of columns corresponding to the current spatial multiplexing rate (smaller spatial multiplexing rate) among the generated phase shift based precoding matrices. . That is, instead of creating a new precoding matrix applied to the system whenever the spatial multiplexing rate is different, the precoding matrix is selected by selecting a specific column of the precoding matrix as it is. Reconstruct

As an example, the precoding matrix of Equation 10 assumes that the spatial multiplexing rate is 2 in a multi-antenna system having two transmit antennas, but the spatial multiplexing rate may be lowered to 1 for some reason. have. In this case, the precoding may be performed by selecting a specific column from the matrix of Equation 10. The phase shift based precoding matrix when the second column is selected is represented by the following Equation 12. It has the same form as the cyclic delay diversity scheme of the two transmit antennas.

Herein, a system having two transmit antennas is taken as an example, but it may be extended to a system having four transmit antennas. That is, after generating the phase shift based precoding matrix in the case of four transmitting antennas, the precoding may be performed by selecting a specific column according to the varying spatial multiplexing rate. For example, FIG. 6 illustrates a case where conventional spatial multiplexing and cyclic delay diversity are applied to a multiple antenna system having four transmit antennas and a spatial multiplexing rate of 2. FIG. 7 Illustrates a case where the phase shift based precoding matrix of Equation 10 is applied to the multi-antenna system as described above.

) 및 제2 시퀀스(

가 전달되고, 제2 안테나 및 제4 안테나에는 소정 크기로 위상천이된 제1 시퀀스(

) 및 제2 시퀀스(

)가 전달된다. 따라서, 전체적으로는 공간 다중화율이 2가 됨을 알 수 있다.Referring to FIG. 6, the first and third antennas have a first sequence (

) And second sequence (

Is transmitted, and the second sequence and the fourth antenna have a first sequence phase shifted to a predetermined size (

) And second sequence (

) Is passed. Therefore, it can be seen that the spatial multiplexing ratio is 2.

가 전달되고, 제2 안테나에는

가 전달되며, 제3 안테나에는

가 전달되고, 제4 안테나에는

가 전달된다. 따라서, 상기 도 6의 시스템에 비해 프리코딩 방법의 장점을 가지면서도 단일한 프리코딩 행렬을 이용하여 4개의 안테나에 대해 순환지연(또는 위상천이)을 수행할 수 있으므로 순환지연 다이버시티 기법에 의한 장점까지 가질 수 있다.In contrast, the first antenna in FIG.

Is transmitted to the second antenna

Is transmitted to the third antenna.

Is transmitted to the fourth antenna

Is passed. Thus, the cyclic delay (or phase shift) can be performed for four antennas using a single precoding matrix while having the advantages of the precoding method compared to the system of FIG. 6. You can have until.

The phase shift based precoding matrix according to spatial multiplexing rates for the two antenna systems and the four antenna systems discussed above are summarized as follows.

Here, θ _i ( i = 1, 2, 3) is the phase angle according to the cyclic delay value, and K is the subcarrier index of OFDM. In Table 2, each of the four precoding matrices can be obtained by taking a specific portion of the precoding matrix for a multi-antenna system having four transmit antennas and a spatial multiplexing ratio of 2, as shown in FIG. Therefore, since there is no need to separately include each precoding matrix for the four cases in the codebook, the memory capacity of the transmitting end and the receiving end can be saved.

Generalized ( generalized Phase shift based Precoding  Way

In the above description, a process of configuring a phase shift based precoding matrix in the case of four transmitting antennas and a spatial multiplexing ratio of 2 has been described. However, in the phase shift based precoding method of the present invention, the number of antennas is N _t ( N _t is a natural number of 2 or more). ) And the spatial multiplexing rate is R ( R is a natural number of 1 or more). This may be extended in the same manner as described above, or may be generalized by the following equation (13).

을 만족하는 유니터리행렬이다. 후반부 행렬의 일 예로 신호대잡음비(SNR) 이득을 얻기 위한 소정의 프리코딩 행렬이 이용될 수 있으며, 특히 이러한 프리코딩 행렬로 왈쉬코드(Walsh code)가 사용되는 경우의 위상천이 기반 프리코딩 행렬(P) 생성식을 살펴보면 다음과 같다.Here, the first half matrix on the right side of the equal sign (等號. '=') Is a diagonal matrix for phase shifting, and the second half matrix U is a matrix used for a specific purpose.

Unitary matrix that satisfies As an example of the second half matrix, a predetermined precoding matrix for obtaining a signal-to-noise ratio (SNR) gain may be used, and in particular, a phase shift based precoding matrix (P) when Walsh code is used as the precoding matrix. ) The generation expression is as follows.

Equation (14) assumes a system having four transmit antennas and a spatial multiplexing rate of 4, wherein a specific transmission antenna is selected by appropriate reconstruction of the latter matrix, or the rate multiplexing is performed. can do. Equation (15) shows the reconstruction of the second half matrix to select two antennas in a system having four transmit antennas.

In addition, Table 3 below shows a method for reconstructing the second half matrix to match the multiplexing rate when the spatial multiplexing rate changes according to time or channel conditions.

In this case, Table 3 shows a case where the first column, the first to second columns, and the first to fourth columns of the second half matrix are selected according to the multiplexing rate, but the present disclosure is not limited thereto and the multiplexing rate is 1. Any one of the first, second, third, and fourth columns may be selected, and when the multiplexing rate is 2, any one of the first, second, second, third, third, and fourth columns may be selected.

Meanwhile, the latter half matrix may be provided in a codebook form at a transmitting end and a receiving end. In this case, the transmitting end receives feedback information of the codebook from the receiving end, selects a unitary matrix (second half matrix) of the corresponding index from its own codebook, and constructs a phase shift-based precoding matrix using Equation (13). do.

Phase shift base Precoding  Transceiver Supporting Method

9 is a block diagram illustrating a configuration of a transceiver for supporting the phase shift based precoding method of the present invention. In the embodiment of the transmitting and receiving apparatus, a case in which the second half matrix for forming the phase shift based precoding matrix is provided in the form of a codebook is described, but is not necessarily limited thereto.

The transceiver includes an input unit 901 for selecting a desired function or receiving information, a display unit 903 for displaying various information for operating the transceiver, and various programs and receivers required for the transceiver to operate. A memory unit 905 for storing data to be transmitted to the wireless communication unit; a wireless communication unit 907 for receiving an external signal and transmitting data to a receiving side; and converting and amplifying a digital voice signal into an analog voice signal to a speaker SP. And a sound processor 909 for outputting or amplifying the voice signal from the microphone MIC and converting the voice signal into a digital signal, and a controller 911 for controlling the overall driving of the transceiver.

Here, the configuration of the wireless communication unit 907 will be described in more detail. For reference, FIG. 10 is a block diagram illustrating a configuration of a SCW OFDM transmitter included in the wireless communication unit 907, and FIG. 11 is a diagram illustrating a configuration of a multi codeword OFDM transmitter. In addition, since the receiving unit corresponding to each transmitting unit is composed of components that perform the role of each component of the corresponding transmitting unit in reverse, a detailed description thereof will be omitted herein.

First, in the SCW OFDM transmitter, the channel encoder 1010 adds redundant bits to prevent the transmitted data from being distorted in the channel, and performs channel encoding using an encryption code such as a turbo code or an LDPC code. . Subsequently, the interleaver 1020 performs interleaving through code bit parsing to minimize loss due to instantaneous noise in the data transmission process, and the mapper 1030 converts the interleaved data bits into OFDM symbols. Such symbol mapping may be performed through a phase modulation technique such as QPSK, or an amplitude modulation technique such as 16QAM, 8QAM, 4QAM, or the like. Thereafter, the OFDM symbol passes through a precoder 1040 according to the present invention, and is then carried on a carrier in a time domain through a subchannel modulator (not shown) and a fast inverse Fourier transformer (IFFT) 1050. It is transmitted through a filter (not shown) and an analog converter 1060 to a wireless channel. Meanwhile, in the MCW OFDM transmitter, the OFDM symbols pass through the channel encoder 1110 and the interleaver 1120 in parallel with each channel, and the rest of the configurations 1130 to 1160 are the same.

The precoding matrix generation module 1041, 1141 determines a reference row corresponding to the first subcarrier in a predetermined precoding matrix, and phase shifts the reference row by a phase angle that increases by a predetermined unit. Decide on them. In the present invention, precoding is performed using a unitary matrix having a number of transmit antennas x spatial multiplexing rate, which is provided for each subcarrier index, and corresponds to a first index. Phase shift the unitary matrix to obtain the unitary matrix of the remaining indices.

That is, the precoding matrix generation modules 1041 and 1141 select an arbitrary first precoding matrix from a codebook previously stored in the memory unit 905. A second precoding matrix for the subcarrier at index 2 is generated by applying a phase shift of a predetermined magnitude to the first precoding matrix. In this case, the magnitude of the shifted phase may be variously set according to the current channel condition and / or whether there is feedback information from the receiver. A third precoding matrix for the subcarrier of the third index is obtained by performing phase shift on the second precoding matrix again. That is, the generation process of the second precoding matrix is repeated in the generation process of the third to last precoding matrix.

Precoding matrix reconstruction module 1042, 1142 selects the number of columns corresponding to a given spatial multiplexing rate in each precoding matrix generated by the precoding matrix generation module 1041, 1141, and other columns. Reconstructs the precoding matrix by deleting Here, a new precoding matrix composed of only the selected columns may be generated. On the other hand, selecting a specific column in the precoding matrix may be an arbitrary column may be selected, or a specific column may be selected according to a predetermined policy.

The precoding modules 1043 and 1143 substitute the OFDM symbols for the corresponding subcarrier in each of the determined precoding matrices to perform precoding.

Generalized ( generalized Phase shift based Precoding  Way

Hereinafter, the precoding matrix determination modules 1041 and 1141, the precoding matrix reconstruction modules 1042 and 1142, and the precoding modules 1043 and 1143 according to another embodiment of the present invention will be described.

The precoding matrix determination module 1041, 1141 selects a specific unitary matrix U (second half matrix) from the codebook with reference to the unitary matrix index fed back from the receiver, and selects the selected unitary matrix U in Equation 13. Substitution is performed to determine the phase shift based precoding matrix (P). Here, the phase shift value in the first half matrix of Equation 13 should be predetermined.

On the other hand, it may be necessary to change the channel condition to change the spatial multiplexing rate or to perform transmission by selecting a specific antenna from all the transmission antennas for various reasons. In this case, when the control unit 911 is notified of the change in the spatial multiplexing rate and / or the number of transmitting antennas, the precoding matrix reconstruction module 1042 or 1142 searches for a unitary matrix U corresponding to the situation from the codebook, Reconfigure the already selected unitary matrix (U) to suit the situation. In the former case, there is an advantage in that a desired phase shift based precoding matrix can be quickly obtained because no separate reconstruction procedure is required. However, since the codebooks for various cases must be provided, memory consumption increases. In addition, in the latter case, a load due to the reconfiguration procedure is generated, but the capacity of the codebook can be reduced. The reconstruction procedure of the unitary matrix according to the change of the spatial multiplexing rate or the number of transmitting antennas has been described above with reference to Equation 14 and Table 3.

The precoding modules 1043 and 1143 substitute the OFDM symbol for the corresponding subcarrier in the determined phase shift based precoding matrix to perform precoding.

The controller 911 notifies the precoding matrix reconstruction modules 1042 and 1142 of various pieces of information for reconstructing the precoding matrix such as the changed spatial multiplexing rate or the changed number of antennas to be used.

As a transmission / reception device according to the present invention, a PDA (Personal Digital Assistant), cellular phone, PCS (Personal Communication Service) phone, GSM (Global System for Mobile) phone, WCDMA (Wideband CDMA) phone, MBS (Mobile Broadband System) phone, etc. This can be used.

Finally, the performance difference between the phase shift based precoding scheme and the conventional spatial multiplexing scheme according to the present invention is applied to a multi-antenna OFDM open loop system using no feedback information. The parameters applied to the system in this experiment are shown in Table 4 below.

Parameters Parameter value Number of subcarriers 512 Number of guard band carriers 106 (left), 105 (right) Number of pilots 28 (perfect channel estimation) Types of MIMO Techniques Spatial Multiplexing (SM) and Phase-shift Precoding (PSP) MIMO receiver Minimum MeanSquared Error (MMSE), Minimum Likelihood (ML) Bandwidth 7.68 MHz Intermediate frequency 2 GHz Channel model Flat, PedA (ITU Pedestrian A), TU (Typical Urban), Mobility: 30 km / h, 250 km / h Number of OFDM symbols per frame 8 (localized) Modulation and Coding Set (MCS) Types QPSK (R = 1/4, R = 1/3, R = 1/2, R = 3/4) Channel coding type 3GPP Turbo (Max-log-MAP), 8 Iteration Transmit Antenna Count 2 Receive Antenna Count 2 Transceiver antenna correlation (0, 0)

FIG. 12 illustrates a phase-shift precoding (PSP) technique and a conventional spatial multiplexing (SM) technique of the present invention in a flat fading channel environment. Is a graph comparing the performance difference when applied to the MMSE (Minimum MeanSquared Error) receiver.

As shown in the figure, in the PSP system, a large gain is generally obtained in comparison with the conventional spatial multiplexing technique.In particular, in the ML receiver, the PSP can obtain more gain with a slightly smaller difference than the SM. In this case, it can be seen that the greater the signal-to-noise ratio (SNR), the greater the gain in the PSP.

13A and 13B illustrate a phase shift based precoding scheme and a conventional spatial multiplexing scheme of the present invention in an ITU Pedestrian A (PedA) fading channel environment and a TU (Typical Urban) fading channel environment, according to coding rates. Minimum MeanSquared Error) This is a graph comparing the performance difference when applied to the receiver.

As shown in the figure, the PSP increases the frequency selectivity while lowering the coding rate (R = 1/3, R = 1/4) in both the ITU Pedestrian A (PedA) fading channel environment and the Typical Urban (TU) fading channel environment. You can see that you can gain.

14A-14C illustrate a phase of the present invention for a system using a Single CodeWord (SCW) and a Multi CodeWord (MCW) in a flat fading channel environment, an ITU Pedestrian A (PedA) fading channel environment, and a Typical Urban fading channel environment. It is a graph comparing the performance difference between the transition-based precoding technique and the conventional spatial multiplexing technique.

In general, when the spatial multiplexing technique is used for the SCW, the channel code can additionally obtain the spatial diversity gain and the codeword can be increased to obtain the coding gain, so that the performance is higher than that of the MCW, but the reception complexity is relatively high. have. As shown in the figure, it can be seen that there is a big difference in the performance of the SCW and the MCW in the system to which the spatial multiplexing technique is applied. However, applying the phase shift based precoding scheme of the present invention can obtain a larger gain than the SCW of the system to which the spatial multiplexing scheme is applied. That is, in the figure, it can be seen that the case where the phase shift based precoding is applied has a much larger gain than the case where the conventional spatial multiplexing technique is applied to the MCW. It is clear that the improvement is made.

FIG. 15 shows the performance difference between the spatial multiplexing technique and the cyclic delay diversity technique applied to a modulation and coding set (MCS) in a flat fading channel environment, and the phase shift based precoding technique and the cyclic delay diversity technique according to the present invention. This is a graph comparing.

As shown in the figure, the phase shift based precoding scheme + cyclic delay diversity scheme of the present invention is applied to all coding rates (R = 1/2, 1/3, 1/4) according to the conventional spatial multiplexing scheme + cyclic scheme. It can be seen that the performance is better than that of the delay diversity scheme.

The present invention described above is capable of various substitutions, modifications, and changes without departing from the spirit of the present invention for those skilled in the art to which the present invention pertains. It is not limited by the drawings.

According to the phase shift based precoding method of the present invention, the complexity of the transceiver is lower than that of the space-time coding scheme, and it supports various spatial multiplexing rates while maintaining the advantages of the phase shift diversity scheme, and is more sensitive to the channel than the precoding scheme. It is possible to expect the advantage that only a small amount of codebook is required, and furthermore, through the generalized phase shift based precoding matrix, the phase shift based precoding can be easily applied regardless of the number of transmit antennas of the system.

Claims (26)

In the method for transmitting a signal using multiple antennas, Modulating a transmission signal to obtain at least one modulation symbol; Performing precoding comprising multiplying the obtained modulation symbol with a phase shift based precoding matrix composed of complex components having different phase angles for each row corresponding to each of the multiple antennas; And And transmitting the modulation symbol on which the precoding has been performed using the multiple antennas. The method of claim 1, The precoding step, To the obtained modulation symbol

Multiplying the diagonal matrix represented by: (k is an index used for the signal transmission, N _t is the number of transmit antennas, θ _j (j = 1, 2, ... Nt) represents the phase angle for each antenna) The method of claim 2, Wherein each row of the diagonal matrix has a complex value corresponding to a sequentially increasing phase angle. delete The method of claim 2, The phase angle applied to each row of the diagonal matrix is sequentially increased in a predetermined unit based on the first row. delete delete delete The method of claim 1, The phase shift based precoding matrix P

In this case, the phase shift based precoding matrix is First condition:

And Second condition:

The signal transmission method characterized in that it satisfies. (

Is the i th row and j th column components of the phase shift based precoding matrix corresponding to the index k used for signal transmission) The method of claim 1, And when the number of transmission paths used for the signal transmission decreases, the number of columns of the phase shift based precoding matrix decreases to correspond to the reduced number of transmission paths. The method of claim 1, The first phase shift based precoding matrix used when the number of transmission paths used for the signal transmission decreases may include columns of the second phase shift based precoding matrix used before the number of transmission paths used for the signal transmission decreases. And selecting a column corresponding to the reduced number of transmission paths. In the method for the receiving side receives a signal transmitted by the transmitting side using multiple antennas, Receiving a received signal using a receive antenna; Performing reverse processing of precoding using a phase shift based precoding matrix composed of complex components having different phase angles for each row corresponding to each of the multiple antennas to the received signal; And Demodulating the deprocessed signal. The method of claim 12, The reverse processing step of the precoding, To the received signal

Multiplying the diagonal matrix represented by: (k is an index used for the signal transmission, N _t is the number of transmit antennas, θ _j (j = 1, 2, ... Nt) represents the phase angle for each antenna) An apparatus for transmitting a signal using multiple antennas, A mapper for modulating the transmission signal to generate at least one modulation symbol; A precoder for performing precoding using a phase shift based precoding matrix composed of complex components having different phase angles for each row corresponding to each of the multiple antennas to the modulation symbol generated by the mapper; And And multiple antennas for transmitting the modulation symbols precoded by the precoder. The method of claim 14, The precoder is applied to the modulation symbol generated by the mapper.

And multiplying a diagonal matrix represented by: (k is the index used for the signal transmission, N _t is the number of transmit antennas, θ _j (j = 1, 2, ... Nt) represents the angle angle of each antenna) The method of claim 15, Wherein each row of the diagonal matrix has a complex value corresponding to a sequentially increasing phase angle. delete The method of claim 15, And a phase angle applied to each row of the diagonal matrix increases sequentially in a predetermined unit based on the first row. delete delete delete The method of claim 14, The phase shift based precoding matrix P

When expressed as The phase shift based precoding matrix is First condition:

And Second condition:

A signal transmission device characterized in that it satisfies.

Is the i th row and j th column components of the phase shift based precoding matrix corresponding to the index k used for signal transmission) The method of claim 14, And when the number of transmission paths used for the signal transmission decreases, the number of columns of the phase shift based precoding matrix decreases to correspond to the reduced number of transmission paths. The method of claim 14, The first phase shift based precoding matrix used when the number of transmission paths used for the signal transmission decreases may include columns of the second phase shift based precoding matrix used before the number of transmission paths used for the signal transmission decreases. And generating a column corresponding to the reduced number of transmission paths. A receiving antenna for receiving a signal transmitted using multiple antennas at a transmitting side; A precoder performing inverse processing of precoding using a phase shift based precoding matrix composed of complex components having different phase angles for each row corresponding to each of the multiple antennas to a signal received by the reception antenna. ; And And a demapper for demodulating the deprocessed signal. The method of claim 25, The precoder is adapted to a signal received through the receive antenna.

And multiplying the diagonal matrix represented by: (k is an index used for the signal transmission, N _t is the number of transmit antennas, θ _j (j = 1, 2, ... Nt) represents the phase angle for each antenna)

Images