CN101295989B - Space-time and space-frequency block encoding method for orthogonal frequency division multiplexing - Google Patents

Abstract

The invention provides a decoding method used for an orthogonal frequency division multiplexing space-time and space-frequency block and n is the number of transmitting antennas. The generation of the encoding matrix G includes the following steps: (a) the first column of G is x1, x2, ellipsis, xn and the value is the one corresponding to a constellation point after signal modulation; the first mvalues of the first row of the G are x1, -x2, ellipsis -x m and m is greater than n and the value of m is determined by code rate; (b) the first m columns of the matrix G is generated according to orthogonality criterion and the first m elements from the second row to the nth row of the matrix G are obtained by the re-arrangement of x1, x2, ellipsis, xn or by adding minus signs to the related elements after the re-arrangement; furthermore, the first element from the second row to the nth row is x2, ellipsis x n respectively and the diagonal lines of the first n rows and n columns of the matrix G are symmetrical and the signs of the symmetrical elements are opposite to each other; (c) the first column to the mth column of the matrix G are conjugated to respectively obtain the (m+1)th column to the (2m)th column of the matrix G to finally obtain the matrix G containing 2m columns.

Description

A kind of when being used for OFDM space and the Space Frequency Block Coding method

Technical field

The present invention relates to a kind of OFDM (OFDM) space-time block coding (Space TimeBlock Code:STBC) and Space Frequency Block Coding (Space Frequency Block Code:SFBC) method of being used for, relate in particular to the technology that the OFDM in OFDM field combines with MIMO space diversity (STBC/SFBC).

Background technology

STBC and SFBC are essentially different, and OFDM combines with STBC, utilization be space, time bidimensional, that is to say that ST coding is the encoding symbols of different antennae to adjacent moment; OFDM combines with SFBC, utilization be space, frequency bidimensional, that is to say that SF coding is that different antennae is encoded to adjacent sub-carrier.

The encoder matrix of STBC/SFBC is identical, and the position in ofdm system is also identical, is example with two transmit antennas, its encoder matrix (subscript * represents to get complex conjugate) as follows:

$\left[\begin{array}{cc}{c}_1& c_2\end{array}\right]\⇒\left[\begin{array}{cc}{c}_1& -c_2^{*}\\ c_2& c_1^{*}\end{array}\right]$

One of block encoding design criterion is exactly that the block encoding matrix satisfies orthogonality condition, and simultaneously, the design of block code also will be satisfied order criterion and determinant criterion, and is specific as follows:

The quadrature criterion: the block encoding matrix satisfies orthogonality condition, and the traditional mathematics structure of orthogonal design can be used for constructing the transmitting antenna of block code to any amount, and the popularization of orthogonal design can provide the real number and the constellation of complex figure of block code.

The order criterion: in order to obtain maximum diversity gain nm, (c is e) for a pair of different code word c and e should be full ranks arbitrarily for matrix B.

The determinant criterion: to all different code word c and e, should make matrix A (c, e)=B (c, e) B ^*(c, the determinant absolute value sum of all r e) * r rank principal minor should be big as far as possible.

At present, be a new focus for the research of STBC/SFBC, but all do not have to propose to generate particularly the method for encoder matrix, just propose some criterions; Decoding generally all is to adopt maximum likelihood method.Design a quadrature and encoder matrix that speed is higher difficult, and in ofdm system, can not use STBC sometimes, for example under OFDM symbol situation, these shortcomings need improvement.

Summary of the invention

The technical problem to be solved in the present invention provides a kind of when being used for OFDM space and the empty coding method of piece frequently.

In order to solve the problems of the technologies described above, the invention provides a kind ofly when being used for OFDM space and the Space Frequency Block Coding method, n is the number of transmitting antenna, the generation of its encoder matrix G comprises following steps:

(a) first of G classify x as ₁, x ₂... x _n, its value be transmit the modulation after the constellation point value corresponding; Preceding m value of first row of G is x ₁,-x ₂...-x _m, m is more than or equal to n, and the value of m is determined by code check;

(b) according to the preceding m row of quadrature criterion generation G matrix, G matrix the 2nd walks to preceding m capable element of n by x ₁, x ₂... x _mReset the back and obtain, and described the 2nd to n first capable element is respectively x at coherent element interpolation negative sign ₂... x _n, the capable n row of the preceding n diagonal symmetry and the symmetry elements opposite in sign of G matrix; Described quadrature criterion is any two row quadratures of matrix, refers to any two row quadratures in the preceding m row of G matrix herein;

(c) G matrix the 1st row to m row are got conjugation, the m+1 that obtains the G matrix respectively is listed as the row to 2m, finally obtains the G matrix and comprises the 2m row.

Further, said method also can have following characteristics, and described transmitting when being an OFDM symbol only used Space Frequency Block Coding SFBC coded system.

Further, said method also can have following characteristics, and is described when transmitting to a plurality of OFDM symbol, adopts SFBC or space-time block coding STBC coded system.

The coding method that the present invention proposes, compared with prior art, the generation of its encoder matrix is simple and convenient, has saved design time.

Description of drawings

Fig. 1 is the ofdm system transmitter architecture figure that adopts STBC/SFBC;

Fig. 2 is the ofdm system receiver structure figure that adopts STBC/SFBC;

Fig. 3 is a STBC/SFBC coding flow chart of the present invention;

Fig. 4 is a STBC/SFBC decoding flow chart of the present invention.

Embodiment

Of the present invention when empty and its encoder matrix structure of Space Frequency Block Coding method as follows:

The first step: a given orthogonal design matrix G, the first row all elements all is a positive sign here;

1. can be sure of that first of G classifies x as ₁, x ₂... x _n, its value be transmit the modulation after the constellation point value corresponding, n is the number of transmitting antenna.

2.G preceding n value of first row be x ₁,-x ₂...-x _m, the value of m determines that by code check m is more than or equal to n.

In second step, the preceding m that generates the G matrix is listed as;

Generate the preceding m row of G matrix according to the quadrature criterion, described quadrature criterion is any two row quadratures of matrix, refers to any two row quadratures in the preceding m row of G matrix herein.

G matrix the 2nd walks to preceding m capable element of n by x ₁, x ₂... x _mRearrangement obtains, or obtains at coherent element interpolation negative sign after resetting, and described the 2nd to n first capable element is respectively x ₂... x _n

Wherein, the preceding m row of G matrix have following characteristics:

1. matrix element is with diagonal symmetry or local symmetry;

The difference that diagonal symmetry and local symmetry are meant code check is and distinguishing, and 1 encoder matrix that is for code check is a square formation, so be with diagonal symmetry (local symmetrical special case);

Code check is not that 1 encoder matrix is not a square formation, so be local symmetry.The element of the capable n row of the preceding n of G matrix is the diagonal symmetry, and whole relatively G matrix is local symmetry.

2. the symmetry elements opposite in sign of its preceding n row.

The 3rd step, the 1st row to m row are got conjugation, the m+1 that obtains the G matrix respectively is listed as to 2m and is listed as.

Finally obtain the G matrix and comprise the 2m row, its m+1 row～2m row are respectively the conjugation of 1 row～m row.

Be without loss of generality, can suppose that G has this character.As:

To two transmit antennas, its encoder matrix

As follows:

$G_2^C=\left(\begin{array}{cc}{x}_1& -x_2^{*}\\ x_2& x_1^{*}\end{array}\right)$

Two transmit antennas are a kind of special circumstances (a unique code check are 1 situation), also meet orthogonality, but two transmit antennas also can write out the encoder matrix of code check 1/2 according to the method for the invention, but generally can adopt the encoder matrix of high code check.

Corresponding to 4 transmit antennas, its encoder matrix

As follows:

$G_4^C=\left(\begin{array}{cccccccc}{x}_1& -x_2& -x_3& -x_4& x_1^{*}& -x_2^{*}& {-x}_3^{*}& {-x}_4^{*}\\ x_2& x_1& x_4& {-x}_3& x_2^{*}& x_1^{*}& x_4^{*}& {-x}_3^{*}\\ x_3& {-x}_4& x_1& x_2& x_3^{*}& {-x}_4^{*}& x_1^{*}& x_2^{*}\\ x_4& x_3& -x_2& x_1& x_4^{*}& x_3^{*}& {-x}_2^{*}& x_1^{*}\end{array}\right)$

The 4th step: judge and use concrete coded system

1. if transmit is an OFDM symbol, can only use SFBC;

For example control channel is only used an OFDM symbol, and an OFDM symbol has only a time point, but different frequencies is arranged, so can only use SFBC.

2. if transmit is two or more OFDM symbols, can use STBC/SFBC;

For example control channel is with two OFDM symbols, and two the OFDM symbols that mean of Biao Daing just have two time points here, and also have different frequencies, so can use STBC/SFBC.

For surpassing under the situation of two OFDM symbols, the rest may be inferred, so long as there is the odd number time point just can not STBC, can only use SFBC.

Below by an example the present invention is described in further detail.

Fig. 1 is the ofdm system transmitter architecture figure that the present invention adopts STBC/SFBC.At first the constellation point behind the signal normalization to be sent is mapped on the subcarrier, selects the respective coding matrix, encode according to the number of transmitting antenna.

Fig. 2 is the ofdm system receiver structure figure that adopts STBC/SFBC.At first judge the number of emission and reception antenna, according to emission and the different combining form of reception antenna number, decipher accordingly then.

Fig. 3 is described to be STBC/SFBC coding flow chart.The concrete steps of coding are:

To two transmit antennas, at first define two data blocks of input and output, take out two adjacent symbol x then ₁And x ₂, second symbol x ₂Former state is moved, second symbol x ₂The real part negate, first symbol x ₁Get conjugation and move, again two data blocks are merged, finish coding.

To other number transmitting antennas, according to the structure of encoder matrix of the present invention, can adopt similar method, finish coding.

Fig. 4 is described to be STBC/SFBC decoding flow chart, specific implementation process: at first estimate channel response, carry out corresponding complex multiplication and complex addition again, finish decoding.

2*2 illustrates with antenna configurations

The emission symbol $G_2^C=\left(\begin{array}{cc}{x}_1& -x_2^{*}\\ x_2& x_1^{*}\end{array}\right),$ Channel matrix $H=\left(\begin{array}{cc}{h}_{11}& h_{12}\\ h_{21}& h_{22}\end{array}\right),$ Receiving symbol $R=\left(\begin{array}{cc}{r}_1& r_2\\ r_3& r_4\end{array}\right),$ Symbol to be translated ${\tilde{r}}_1=h_{11}^{*}{r}_1+h_{12}{r}_2^{*}+h_{21}^{*}{r}_3+h_{22}{r}_4^{*}$

${\tilde{r}}_2=h_{12}^{*}{r}_1-h_{11}{r}_2^{*}+h_{22}^{*}{r}_3-h_{21}{r}_4^{*}$

The scale equation ${\hat{c}}_1=\arg \underset{c_1}{\min }\left|\right|{\tilde{r}}_1-\mathrm{\ρ}{c}_1\left|\right|$

${\hat{c}}_2=\arg \underset{c_2}{\min }\left|\right|{\tilde{r}}_2-\mathrm{\ρ}{c}_2\left|\right|$

C1, c2 are the symbol of emission.

Generally speaking: r _m=H _mC+n _n

$\hat{c}=\arg \underset{c}{\min }\underset{m=1}{\overset{M}{\mathrm{\Σ}}}{\left|\right|{\tilde{r}}_m-\mathrm{\ρc}\left|\right|}^2$

To sum up, adopt the method for the invention, compared with prior art, reached the simple effect of generation encoder matrix, saved design time.

Claims (3)

1. one kind when being used for OFDM space and the Space Frequency Block Coding method, n is the number of transmitting antenna, and the generation of its encoder matrix G comprises following steps:

(a) first of G classify x as ₁, x ₂... x _n, its value be transmit the modulation after the constellation point value corresponding; Preceding m value of first row of G is x ₁,-x ₂...-x _m, m is more than or equal to n, and the value of m is determined by code check;

(b) according to the preceding m row of quadrature criterion generation G matrix, G matrix the 2nd walks to preceding m capable element of n by x ₁, x ₂... x _mReset the back and obtain, and described the 2nd to n first capable element is respectively x at coherent element interpolation negative sign ₂... x _n, the capable n row of the preceding n diagonal symmetry and the symmetry elements opposite in sign of G matrix; Described quadrature criterion is any two row quadratures of matrix, refers to any two row quadratures in the preceding m row of G matrix herein;

(c) G matrix the 1st row to m row are got conjugation, the m+1 that obtains the G matrix respectively is listed as the row to 2m, finally obtains the G matrix and comprises the 2m row.

2. the method for claim 1 is characterized in that: described transmitting when being an OFDM symbol, only use Space Frequency Block Coding SFBC coded system.

3. the method for claim 1 is characterized in that: described when transmitting to two or more OFDM symbols, adopt SFBC or space-time block coding STBC coded system.

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