KR101276838B1 - method for transmitting signals using space time code - Google Patents

Abstract

The present invention relates to a space-time code, and more particularly, to a space-time code in consideration of changes in channel environment including various channel coding methods.

In order to achieve the above object, the present invention provides a method for transmitting a signal using a space-time code, the method comprising a partial column and a Generalized Optimal Diversity (GOD) code of a linear transformation matrix of a spatial multiplexing scheme. Constructing a first matrix using some columns of the linear transformation matrix; Generating a linear transformation matrix by multiplying the constructed first matrix by a first unitary matrix; And transmitting the signal using the generated linear transformation matrix.

STC, Channel Sign, SM, GOD, Unitary Matrix

Description

Method for transmitting signals using space time code

1 is a result of displaying an error probability in a situation where a channel code is used for a conventional space-time code.

FIG. 2 is an example of a mobile communication system that performs optimal space-time encoding and closes channel coding by a closed loop.

3 is an example of a mobile communication system for performing space-time encoding and channel encoding according to the present embodiment.

4 to 6 are diagrams illustrating performances of different code rates in an IID (Independent and Identically Distributed) fast fading channel situation.

7 to 15 are diagrams illustrating performance by varying code rates in an OFDMA situation.

The present invention relates to a space-time code, and more particularly, to a space-time code in consideration of changes in channel environment including various channel coding methods.

The demand for communication services is rapidly increasing, including the generalization of information and communication services, the emergence of various multimedia services, and the emergence of high quality services. To cope with this actively, the capacity of the communication system must be increased. This demand is coming under greater pressure in wireless communications than in wired communications. In wireless communication, available frequency resources are basically limited, and they must be shared, and the demand is rapidly increasing due to the advantages of wireless communication. In order to increase the communication capacity in a wireless communication environment, there are methods of discovering available frequency bands and increasing efficiency of a given resource. The technology that has received great attention recently as a method of improving the efficiency of wireless resources and is actively promoting technological development is equipped with multiple antennas in the transceiver to secure additional spatial area for resource utilization, thereby improving diversity gain without increasing bandwidth. Space time code technologies are used to increase the transmission capacity through parallel transmission through space multiplexing or to increase the reliability of communication links.

The space-time code described above is designed to be suitable for a multiple input multiple output (MIMO) environment in which a plurality of transmit / receive antennas are used for communication. Equations 1 and 2 below are equations representing an example of a known space-time code in a transmission matrix.

The space-time code applied to the conventional MIMO system is designed in a situation where channel coding is not considered. Representative examples include a spatial multiplexing (SM) as shown in Equation 2, an orthogonal space time block code as referred to in Equation 1, and a `` OSTBC '', and a linear dispersion code as hereinafter. , Referred to as 'LDC'.

In the case of the LDC, pre-coding is performed on a data (S ₁ , S _2, etc.) using a linear transformation matrix, and the result of performing the pre-coding is specified to a specific antenna at a specific time. By way of transmission over, the special form of the LDC is the OSTBC. The OSTBC is a case where orthogonality exists between columns of a transmission matrix as shown in Equation (1).

Hereinafter, the characteristics of the above-described SM system, OSTBC system and LDC system will be described.

SM transmits different signals in each transmission antenna, and the transmission scheme is simple and the reception complexity is lower than that of the LDC. However, there is a disadvantage in that an error is more likely to occur in a received signal when the same signal-to-noise ratio (hereinafter referred to as 'SNR') is higher than that of the LDC.

In addition, OSTBC is designed to orthogonally space-time orthogonal symbols transmitted from multiple antennas, the maximum transmit and receive diversity (diversity) has the advantage of having a relatively constant performance even if the channel changes. In addition, the complexity is higher than SM but lower than LDC, and the probability of error due to SNR is lower than SM but higher than LDC.

The LDC is a method of linearly combining and transmitting transmission symbols to suit a MIMO channel environment. LDC has the advantage that the error is less likely to occur when the same SNR than SM and OSTBC by maximizing transmit and receive diversity and increase the sum of Euclidean distance in one block of STC by linear combination of transmit symbols. However, there is a disadvantage that the receiving method is complicated. Among the LDCs found so far, the best performance is the Golden code for two transmit / receive antennas and the Generalized Optimal Diversity (GOD) code that is generalized to be applicable even when the number of antennas increases.

An example of the above-described GOD code is shown in Equation 3 below.

1 is a result of displaying an error probability in a situation where a channel code is used for a conventional space-time code.

As shown in FIG. 1, when a channel code is used in a MIMO system, a change in a performance curve of a space-time code appears. For example, when a fast fading channel and two transmit / receive antennas are used, a low density parity check code (LDPC) code having a code rate of 1/2 is used. It shows a good performance curve, i.e. the probability of error occurring is lowest when the same SNR. Next, the God code shows good performance. Finally, the Alamouti code shown in Equation 1 has the worst performance curve.

As the code rate increases, the performance becomes more similar to that without the channel code, because it becomes more and more like the one without the channel code. For example, if the experiment environment is the same as the previous example, and the code rate of LDPC is changed to 2/3, the performance of SM and God codes is similar, and if the code rate is higher than 3/4, GOD code is SM method. It shows a better performance curve.

That is, the conventional space-time code has a problem that the performance is not constant according to the change of the communication environment such as the code rate.

The present invention aims to improve the above-mentioned problems of the prior art, and an object of the present invention is to propose a space-time encoding method with improved performance.

Another object of the present invention is to propose a space-time code with robust performance in various situations.

Another object of the present invention is to propose a space-time code having robust performance even with a change in channel code rate.

Summary of the Invention

In order to achieve the above object, the present invention provides a method for transmitting a signal using a space-time code, the method comprising a partial column and a Generalized Optimal Diversity (GOD) code of a linear transformation matrix of a spatial multiplexing scheme. Constructing a first matrix using some columns of the linear transformation matrix; Generating a linear transformation matrix by multiplying the constructed first matrix by a first unitary matrix; And transmitting the signal using the generated linear transformation matrix.

Preferably, the first matrix is generated by combining two columns of the linear transformation matrix of the SM scheme and two columns of the linear transformation matrix of the GOD code.

In addition, the present invention is a method of transmitting a signal using a space-time code, a partial column of the linear transformation matrix of the spatial multiplexing scheme and a partial column of the linear transformation matrix of the Generalized Optimal Diversity (GOD) code constructing a first matrix using a column; Constructing a second matrix by multiplying the constructed first matrix by a first unitary matrix; Multiplying the second matrix by a second unitary matrix; And transmitting the signal using the result of multiplying the second unitary matrix.

In addition, the transmitting apparatus according to the present invention uses a first column using a partial column of a linear transformation matrix of a spatial multiplexing scheme and a partial column of a linear transformation matrix of a generalized optimal diversity (GOD) code. A linear transformation matrix generation module configured to generate a linear transformation matrix by multiplying the constructed first matrix by a first unitary matrix; A space-time encoding module for performing space-time encoding on a signal transmitted to a receiver according to the generated linear transformation matrix; And a transmitting module for transmitting a result of the space-time encoding to the receiving device.

The transmission device according to the present invention is preferably a base station, a mobile terminal, or the like.

Invention Example

The present invention relates to a transceiver and a method using a space time code (STC) designed to be suitable for a multiple input multiple output (MIMO) environment when a channel code is used. The optimal performance of the STC depends on the code rate, the length change, and the channel condition, and therefore the transmission / reception apparatus used with the robust space time code (RSTC), which is robust in these various situations, is used. It is proposed in the present invention.

Specific configuration and operation of the RSTC proposed by the present invention will be further embodied by one embodiment of the present invention described below. Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

2 and 3 illustrate an example of a mobile communication system that performs an optimal space-time code and performs channel coding by a closed loop.

2 is an example of adaptive transmission by finding an STC having optimal performance according to a channel code and a change of a channel. As shown, the channel estimator 207 of the receiver estimates a channel value of a wireless channel using a preset reference signal lamp. The estimated channel value is input to the space-time decoder 205. The space-time decoder 205 performs space-time decoding using the estimated channel value. In addition, the result of the space-time decoding is output to the channel decoder 206. The channel decoder 206 performs channel decoding to output information bits before channel encoding. On the other hand, the SNR calculator 208 measures the SNR of the received signal using the received signal and transmits feedback information, that is, feedback information, for the transmitter to the transmitter. When the variable of the channel coding method and the space-time code of the transmitting apparatus needs to be changed so that the SNR can be increased from the perspective of the receiving apparatus, the receiving apparatus includes information necessary for the feedback information and feeds it back to the transmitting apparatus. The channel encoder 201 of the transmitting apparatus performs channel coding. The channel coding method or the channel code rate may be changed by the locus information fed back from the receiving apparatus. The channel encoding and modulation method selector 203 determines information on the type or code rate of channel encoding by using the information fed back from the receiving apparatus, and selects the method used for space-time encoding. In addition, when a variable variable value is used in space-time encoding, the space-time code adaptive variable determiner 204 may output the variable value to the space-time encoder 202 using information fed back. The space-time encoder 204 may perform optimal space-time encoding by using the information fed back from the receiving apparatus.

3 illustrates a case of using the RSTC proposed in this embodiment. The receiver of FIG. 3 includes the above-described space-time decoder 205, channel decoder 206, channel estimator 207, and SNR calculator 208. The RSTC also uses a variable that can control the feature of the encoding. The variable value is determined by the channel encoding and modulation selector 301 using information fed back from the receiving apparatus. Since RSTC shows robust performance in spite of a change in the code rate of a channel code, it is more preferable that the space-time encoder 202 uses only the RSTC but adjusts a variable value included in the RSTC to achieve optimal performance.

According to the structure of FIG. 3, a transmission / reception apparatus using RSTC having robust performance in the type, code rate, length of channel codes, and channel conditions can be designed.

The RSTC used in the transmission and reception apparatus proposed in this embodiment has a form obtained by multiplying a unitary matrix by a matrix having an LDC type and an SM type. By using a unitary matrix to linearly combine each symbol, that is, by sending a weighted sum for each symbol, it has an average Log Likelihood Ratio (LLR) of SM and LDC. This enables the design of a system with robust performance under any circumstances.

The linear transformation matrix C is defined as follows.

vec (A) means to arrange the A matrix as a column vector.

The model presented through Equation 4 is a transmission / reception signal model in a conventional MIMO system, and the model presented through Equation 5 is a model in which the information is arranged in a vector form, taking into account computational convenience. STC used in the MIMO transceiver refers to a linear transformation matrix C.

On the other hand, the linear transformation matrix C of the SM and GOD in the situation that there are two transmit and receive antennas, respectively, are represented as follows.

The contents of Equations 6 and 7 are shown through the linear transformation matrix C, respectively. In other words, equations (2) and (3) represent SM and GOD codes through a transmission matrix, and represent a space-time code through a transmission matrix indicating a time at which specific data is transmitted and a space (that is, an antenna) at which specific data is transmitted. do. On the other hand, the following equations (6) and (7) represent a space-time code as a precoding matrix for specific data.

A method of performing space-time encoding through the linear transformation matrix C will be described in detail with reference to Equation 7 (GOD code) as follows.

For example, suppose there are four data S ₁ , S ₂ , S ₃ , and S ₄ that need to be space-time encoded. When these four data are expressed by the column vector S, one new column vector can be obtained by multiplying the linear transformation matrix C of Equation 7 and the column vector S. When each component of the column vector thus obtained is transmitted in correspondence with a specific time and a specific antenna, space-time encoding is terminated.

That is, precoding is performed on the four data S ₁ , S ₂ , S ₃ , and S _{4 as} shown in Equation 8a.

The column vector is calculated using the components c ₁ to c ₄ as a result of Equation 8a. The column vector is transmitted through a specific transmission antenna at a specific transmission time according to a rule such as Equation 8b.

In Equation 8b, each column represents a transmission time and each row represents a transmission antenna. That is, the first column is transmitted at the first transmission time and the first row is transmitted through the first transmission antenna.

According to the above description, given a specific linear transformation matrix, space-time encoding can be easily performed using the given linear transformation matrix.

In a situation where there are two transmit / receive antennas, the form of RSTC used by the transmit / receive apparatus proposed in this embodiment is as follows.

As shown in Equation 9, the linear transformation matrix C proposed in this embodiment is a 4 * 4 matrix and transmits data through two transmission antennas. The matrix C can be obtained by combining a linear transformation matrix of the SM system and the GOD system.

More specifically, the matrix C uses the matrix of Equation 10a.

In the matrix of Equation 10a, the first column and the second column are columns used in the linear transformation matrix of GOD (Equation 7), and the third and fourth columns are columns used in the linear transformation matrix of SM (6). That is, the matrix of Equation 10a is a matrix combining the components of SM and GOD. The RSTC according to the present embodiment provides a space-time code that shows excellent performance even with various channel changes by using a matrix of SMs and GODs.

However, when combining the columns of SM and GOD as shown in Equation 10a, only one data (for example, one data s ₂ is transmitted by the second row of Equation 10a through a specific time and a specific antenna). Only one data s ₃ is transmitted by the third row), so that sufficient diversity cannot be obtained. Accordingly, the unitary matrix of Equation 10b is further multiplied so that the linear combination of the data is performed without changing the determinant value of Equation 10a.

인 경우, U를 유니터리 행렬이라 한다. When the result of multiplying a specific matrix and a hermit operation value for the matrix is an identity matrix, the specific matrix is called a unitary matrix. In other words,

If U is called a unitary matrix.

Precoding of data may be performed through the matrix C of Equation 9, and the precoded result is mapped to each antenna and transmission time according to Equation 8b.

The linear transformation matrix of Equation 9 proposed in this embodiment may be converted into various forms. That is, a new linear transformation matrix may be generated by multiplying a separate unitary matrix by Equation (9).

That is, a matrix C ′ different from the form of Equation 9 may be generated by multiplying the matrix C of Equation 9 by an arbitrary unitary matrix U ₁ having a size of 4 * 4. In other words, the result of multiplying the matrix of Equation 10a proposed in this embodiment by the first unitary matrix (matrices of Equation 10b) proposed in this embodiment is further multiplied by the second unitary matrix to generate a separate linear transformation matrix. can do. The result of multiplying the second unitary matrix described above is only a modification of Equation 9, and the result of multiplying the second unitary matrix is within the scope of the present invention.

In conclusion, using a linear transformation matrix multiplied by Equations 10a and 10b is performed by linearly combining each symbol using a unitary matrix, that is, a weighted sum for each symbol. Will be sent. This allows us to create a space-time code with the average Log Likelihood Ratio (LLR) of SM and LDC.

By using the present invention, robust performance can be maintained even in a channel code type, code rate, length change, and channel state. In addition, according to the various channel conditions as described above, the amount of feedback information can be reduced compared to the case of adaptive transmission of the STC.

Hereinafter, the performance of the RSTC will be described with reference to the accompanying drawings.

Performance curves of RSTC in various situations are as shown in FIGS. 4 to 16. In order to compare the performance of the LDC and SM mixed with the unitary matrix and the non-mixed, it is expressed as follows. In the simulation results below, Mix is simply a case of using a matrix consisting of SM and LDC as C, and A.mix is a case of multiplying unitary matrix by matrix C consisting of SM and LDC. In Equation (9), the r value was 0.613.

4 through 6 are diagrams illustrating performances of different code rates in an independent and identically distributed fast fading channel (IID) situation. 4 to 6 show cases where code rates are 1/2, 2/3, and 3/4. In Figures 4 to 6 'A. 'mix' or 'Robust' represents the performance of the space-time code proposed in this embodiment.

In the figure, k is the size of the information bits, and N is the size of the sum of the information bits and the parity bits. As shown, even if the code rate is different it can be seen that RSTC shows a constant performance.

7 to 16 are diagrams illustrating performance of different code rates in an OFDMA situation. First, as shown in FIG. 7 to FIG. 9 as a result of using the LDPC code, data included in four OFDM symbols is data generated by one LDPC operation. In the figure, 'Robust' represents the performance of the space-time code proposed in this embodiment.

As shown, each figure represents a different code rate, and RSTC shows good performance at each code rate.

10 to 15 illustrate a case where data included in eight OFDM symbols are data generated by one LDPC operation. 'Robust' represents the performance of the space-time code proposed in this embodiment.

As shown, each figure represents a different code rate, and RSTC shows good performance at each code rate.

As can be seen from the above-described drawings, it can be seen that the use of RSTC in various situations can achieve the same performance as using the optimal STC.

RSTC proposed in the present invention can also be adaptively transmitted by changing the r value according to the channel condition.

Those skilled in the art through the above description can be seen that various changes and modifications can be made without departing from the spirit of the present invention. Therefore, the technical scope of the present invention is not limited to the contents described in the detailed description of the specification but by the claims.

By using the present invention, robust performance can be maintained even in a channel code type, code rate, length change, and channel state. In addition, according to the various channel conditions as described above, the amount of feedback information can be reduced compared to the case of adaptive transmission of the STC.

Claims (12)

In the method for transmitting a signal using a space-time code, Constructing a first matrix using a partial column of a first linear transformation matrix of a spatial multiplexing scheme and a partial column of a second linear transformation matrix of a generalized optimal diversity (GOD) code; Generating a third linear transformation matrix by multiplying the constructed first matrix by a first unitary matrix; And Transmitting the signal using the generated third linear transformation matrix Method of transmitting a signal using a space-time code comprising a. The method of claim 1, The first linear transformation matrix of the spatial multiplexing scheme,

A method for transmitting a signal using a space-time code, characterized in that. The method of claim 1, The second linear transformation matrix of the GOD code is

A method for transmitting a signal using a space-time code, characterized in that. The method of claim 1, The first matrix, Using two columns of the first linear transformation matrix of the spatial multiplexing scheme and two columns of the second linear transformation matrix of the GOD code,

A method for transmitting a signal using a space-time code, characterized in that. The method of claim 1, The first unitary matrix,

A method for transmitting a signal using a space-time code, characterized in that. The method of claim 1, The third linear transformation matrix generated by multiplying the first unitary matrix,

A method for transmitting a signal using a space-time code, characterized in that. In the method for transmitting a signal using a space-time code, The first unitary matrix includes a first matrix including a partial column of a first linear transformation matrix of a spatial multiplexing scheme and a partial column of a second linear transformation matrix of a generalized optimal diversity (GOD) code. multiplying a unitary matrix to form a second matrix; Multiplying the second matrix by a second unitary matrix; And Transmitting the signal using a result of multiplying the second unitary matrix Method of transmitting a signal using a space-time code comprising a. The method of claim 7, wherein The second matrix,

A method for transmitting a signal using a space-time code, characterized in that. In the transmission device using a space-time code, A first matrix is constructed by using a partial column of the first linear transformation matrix of the spatial multiplexing scheme and a partial column of the second linear transformation matrix of the generalized optimal diversity (GOD) code. A third linear transformation matrix generation module for generating a linear transformation matrix by multiplying the constructed first matrix by a first unitary matrix; A space-time encoding module for performing space-time encoding on the signal transmitted to the receiver according to the generated third linear transformation matrix; And Transmission module for transmitting the result of the space-time encoding to the receiving device Consisting of Transmission device using space-time code 10. The method of claim 9, The first matrix, Using two columns of the first linear transformation matrix of the spatial multiplexing scheme and two columns of the second linear transformation matrix of the GOD code,

Characterized in that Transmission apparatus using space-time code. 10. The method of claim 9, The first unitary matrix,

Characterized in that Transmission apparatus using space-time code. 10. The method of claim 9, The third linear transformation matrix generated by multiplying the first unitary matrix,

Characterized in that Transmission apparatus using space-time code.

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