CN101378299A - Transmission diversity method base on null-frequency encode - Google Patents

Abstract

The invention discloses a transmission diversity method based on space-frequency coding, which is applicable to an MIMO-OPDM system with a sending antenna which is more than 2. The method takes a combination of the SFBC and pre-coding weighing switching as a diversity mode of SFBC+PVS, taking the objective factor into the account that the stronger the channel correlation is, the weaker the diversity effect is, and uses a weighted vector to remove the effect resulted by the inclination angle between antennae and the channel correlation between different antennae. The method comprises the following steps: step one, two paths of data streams are obtained by carrying out SFBC coding to an input bit stream; step two, two groups of pre-coding weighing vectors are selected; and step three, a coding matrix after pre-coding weighing switching is obtained after the pre-coding weighing vector is adopted to carry out weighing to an SFBC coding data block, and finally an in-time signal obtained by inverse fast Fourier transform is transmitted. By adopting the diversity method, the space diversity effect can be utilized better and the effect on coding gains can be reduced.

Description

A kind of emission diversity method based on space-frequency coding

Technical field

The present invention relates to the diversity technique of wireless telecommunication system, especially relate to a kind of employing based on space-frequency coding (Space Frequency Block Coding, the emission diversity method of multi-input multi-output-orthogonal frequency division multiplexing SFBC) (MIMO-OFDM) system.

Background technology

Follow-on wireless communication system will provide better speech quality, the faster data transmission rate.But, the time multipath transmission environment, limited bandwidth resources and the user that become make above-mentioned requirements implement very difficulty to the demand of service.Effective ways that address these problems are to adopt diversity technique.Diversity technique can be divided into time diversity, frequency diversity and space diversity etc. according to the difference that obtains the independent pathway signal method.With regard to time diversity, frequency diversity and space diversity three, because under the slow fading situation, time domain interweaves and can cause the bigger delay of signal, will introduce interference this moment, thereby the business of delay sensitive is not suitable for; And when the coherence bandwidth of channel greater than the delay expansion of apread spectrum bandwidth or signal relatively hour, it is just not too suitable to utilize spread spectrum to obtain frequency diversity; But in most of the cases, space diversity reception to communicate can obtain great diversity gain without the victim signal frequency bandwidth when guaranteeing message transmission rate

The empty time-code of Alamouti scheme is because of its simplicity of design, and decoding has conveniently obtained to use widely in mimo system.Agrawal etc. have proposed scheme-space-frequency coding (SFBC) that empty time-code and OFDM (OFDM) modulation technique are combined, thereby make system can obtain higher spectrum efficiency, transmission rate and communication quality.But have only when number of transmit antennas is 2, the Alamouti scheme just can be given full play to its advantage, satisfying encoder matrix quadrature and code rate simultaneously is one or two condition, when transmitting antenna greater than 2 the time, must be to select one among one just, and this all can reduce the performance of empty time-code in code rate quadrature and code rate.

Summary of the invention

Technical problem to be solved by this invention is, in conjunction with current design philosophy based on the SFBC diversity, at transmitting antenna greater than 2 MIMO-OFDM system, a kind of emission diversity method based on space-frequency coding is provided, can farthest utilize space diversity gain, time diversity gain and frequency diversity gain, overcome the Alamouti scheme and can only could bring into play the limitation of its advantage fully, improve diversity performance, reduced error performance at 2 system of transmit antennas.

For solving the problems of the technologies described above, the invention provides a kind of emission diversity method based on space-frequency coding, SFBC and precoding weighting are switched (Percoding Vector Switch, PVS) combination, diversity mode as SFBC+PVS, considering that correlation between channels is strong more, on the poor more objective factor of diversity, remove because the influence that correlation between channels causes diversity between angle of inclination between the antenna or different antennae with weighing vector, the effect of better utilization space diversity reduces the influence to coding gain.

A kind of emission diversity method based on space-frequency coding of the present invention may further comprise the steps:

The first step: the SFBC coding that carries out the Alamouti scheme through the data after chnnel coding and the planisphere mapping is obtained two paths of data stream:

$[S_1,S_2,S_3,S_4,\·\·\·S_{N-1},S_N]\→\left[\begin{array}{ccccc}{S}_1& -S_2^{*}& S_3& -S_4^{*}\·\·\·S_{N-1}& -S_N^{*}\\ S_2& S_1^{*}& S_4& S_3^{*}\·\·\·S_N& S_{N-1}^{*}\end{array}\right];$

Second step:, select two groups of precoding weight vectors according to the arrangement array and the polarization angle of antenna for base station:

$v_1=\left[\begin{array}{c}1\\ e^{-j{\mathrm{\θ}}_1}\end{array}\right],$ ? $v_2=\left[\begin{array}{c}{e}^{-j{\mathrm{\θ}}_2}\\ 1\end{array}\right],$ Wherein | θ ₁-θ ₂|=π;

The 3rd step:

Get $A_1=\left[\begin{array}{cc}{S}_1& -S_2^{*}\\ S_2& S_1^{*}\end{array}\right],A_2=\left[\begin{array}{cc}{S}_3& -S_4^{*}\\ S_4& S_3^{*}\end{array}\right],\·\·\·A_{\frac{N}{2}}=\left[\begin{array}{cc}{S}_{N-1}& -S_N^{*}\\ S_N& S_{N-1}^{*}\end{array}\right];$

With the precoding weight vector to through obtaining the encoder matrix after precoding weighting hand-off process after the weighting of SFBC coded data block, if A _i(the subscript odd number of 1≤i≤N/2) is then used v ₁The vector weighting is even number, then uses v ₂The vector weighting.

$B_1=A_1{v}_1=\left[\begin{array}{c}{A}_1\\ A_1{e}^{-j{\mathrm{\θ}}_1}\end{array}\right],B_2=A_2{v}_2=\left[\begin{array}{c}{A}_2{e}^{-j{\mathrm{\θ}}_2}\\ A_2\end{array}\right],\·\·\·B_{\frac{N}{2}}=A_{\frac{N}{2}}{v}_{\frac{N}{2}}=\left[\begin{array}{c}{A}_{\frac{N}{2}}\\ A_{\frac{N}{2}}{e}^{-j{\mathrm{\θ}}_1}\end{array}\right];$

In the formula,

When N/2 is odd number, $v_{\frac{N}{2}}=v_1,$ During for even number, then $v_{\frac{N}{2}}=v_2;$

Be written as $\left[\begin{array}{cc}{A}_1& A_2{e}^{-j{\mathrm{\θ}}_2}\\ A_1{e}^{-j{\mathrm{\θ}}_1}& A_2\end{array}\right],\·\·\·\left[\begin{array}{cc}{A}_{\frac{N}{2}-1}& A_{\frac{N}{2}}{e}^{-j{\mathrm{\θ}}_2}\\ A_{\frac{N}{2}-1}{e}^{-j{\mathrm{\θ}}_1}& A_{\frac{N}{2}}\end{array}\right],$ Passing through invert fast fourier transformation (IFFT) at last obtains time-domain signal and launches.

Beneficial effect of the present invention: adopt a kind of emission diversity method of the present invention based on space-frequency coding, promptly kept Alamouti scheme SFBC coding self simplicity of design, decoding is convenient, make system can obtain the characteristics of higher spectrum efficiency, transmission rate and communication quality, made full use of the best weight value that the array angular relationship design of transmitting terminal antenna adapts with it again, farthest utilize the effect of space diversity gain and coding gain, make bit error rate performance be significantly improved, and realize also fairly simple.

Description of drawings

Fig. 1 is the emitter junction composition of 4 antenna MIMO-OFDM systems of a kind of emission diversity method based on space-frequency coding of the present invention;

Fig. 2 is the diversity scheme discussed in a kind of emission diversity method based on space-frequency coding of the present invention and the performance comparison curves of other diversity modes.

Embodiment

Below in conjunction with accompanying drawing technical scheme of the present invention is described further:

The invention provides a kind of emission diversity method based on space-frequency coding, space-frequency coding is with simplicity of design, deciphering empty easily time-code combines with OFDM (OFDM) modulation technique, and system can be obtained higher spectrum efficiency, transmission speed and communication quality, in view of this advantage, with SFBC and the combination of precoding weighing vector, diversity mode as SFBC+PVS, considering that correlation between channels is strong more, on the poor more objective factor of diversity, to multiply each other with the precoding weight vector respectively through two branches of SFBC diversity, thereby realize the diversity of four antennas, remove because the influence that correlation between channels causes diversity between angle of inclination between the antenna or different antennae with weighing vector, the effect of better utilization space diversity, minimizing is to the influence of coding gain, and, can go up largely and improve diversity performance by the completely orthogonal weight vector of design.

As shown in Figure 1, adopt a kind of 4 antenna MIMO-OFDM systems of the emission diversity method based on space-frequency coding technical scheme of the present invention to be described as execution mode, a kind of emission diversity method of the present invention based on space-frequency coding, code stream to input carries out the SFBC coding, the value that obtains then obtains correlation matrix through the PVS coding again, obtain final time-domain signal through invert fast fourier transformation at last, specifically may further comprise the steps:

The first step: the SFBC coding that carries out the Alamouti scheme through the data after chnnel coding and the planisphere mapping is obtained two paths of data stream:

$[S_1,S_2,S_3,S_4,\·\·\·S_{N-1},S_N]\→\left[\begin{array}{ccccc}{S}_1& -S_2^{*}& S_3& -S_4^{*}\·\·\·S_{N-1}& -S_N^{*}\\ S_2& S_1^{*}& S_4& S_3^{*}\·\·\·S_N& S_{N-1}^{*}\end{array}\right];$

Code stream s to input carries out the SFBC coding, through the data format behind the coding is $\left[\begin{array}{cc}{s}_1& -s_2^{*}\\ s_s& s_1^{*}\end{array}\right];$

Second step: according to the arrangement array and the polarization angle of antenna for base station, two groups of precoding weight vectors of selection:

According to $v_1=\left[\begin{array}{c}1\\ e^{-j{\mathrm{\θ}}_1}\end{array}\right],$ ? $v_2=\left[\begin{array}{c}{e}^{-j{\mathrm{\θ}}_2}\\ 1\end{array}\right],$ Wherein | θ ₁-θ ₂| the principle of=π

Get ${\mathrm{\θ}}_1=\frac{\mathrm{\π}}{2},{\mathrm{\θ}}_2=-\frac{\mathrm{\π}}{2}$

Then obtain the precoding weight vector $v_1=\left[\begin{array}{c}1\\ -j\end{array}\right],v_2=\left[\begin{array}{c}j\\ 1\end{array}\right];$

The 3rd step:

Get $A_1=\left[\begin{array}{cc}{S}_1& -S_2^{*}\\ S_2& S_1^{*}\end{array}\right],$ ? $A_2=\left[\begin{array}{cc}{S}_3& -S_4^{*}\\ S_4& S_3^{*}\end{array}\right],$

With the precoding weight vector to through obtaining the encoder matrix after the precoding weighting is switched (PVS) and handled after the weighting of SFBC coded data block:

$B_1=A_1{v}_1=\left[\begin{array}{c}{A}_1\\ A_1{e}^{-j{\mathrm{\θ}}_1}\end{array}\right],$ ? $B_2=A_2{v}_2=\left[\begin{array}{c}{A}_2{e}^{-j{\mathrm{\θ}}_2}\\ A_2\end{array}\right];$

According to $\left[\begin{array}{cc}{A}_1& A_2{e}^{-j{\mathrm{\θ}}_2}\\ A_1{e}^{-j{\mathrm{\θ}}_1}& A_2\end{array}\right],$ If get ${\mathrm{\θ}}_1=\frac{\mathrm{\π}}{2},{\mathrm{\θ}}_2=-\frac{\mathrm{\π}}{2}$

Obtain after the processing $\left[\begin{array}{cccc}{S}_1& -S_2^{*}& j*S_3& -j{S}_4^{*}\\ S_2& S_1^{*}& j*S_4& j*S_3^{*}\\ -j*S_1& j*S_2^{*}& S_3& -S_4^{*}\\ -j*S_2& -j*S_1^{*}& S_4& S_3^{*}\end{array}\right],$ And then obtain time-domain signal and launch through invert fast fourier transformation (IFFT).

By top matrix encode as can be seen the back matrix first (three) OK, second (four) provisional capital is that the SFBC of quadrature encodes, and is quadrature between one, two and three, four.And one row and secondary series also be quadrature, this has just guaranteed that each reception data of organizing between former and later two subcarriers can not interfere with each other when receiving terminal is deciphered.

For other many antennas situations, can release by 4 antenna situations.

Be illustrated in figure 2 as, use based on the emission diversity method of space-frequency coding and the performance comparison curves of accurate quadrature SFBC+FSTD mode among the present invention, respectively following several diversity modes and this programme are compared in the simulation result.The channel model that adopts in the emulation is the SCME-C channel, and antenna configurations is 4*2, and the system bandwidth that adopts in the simulation process is 5MHz, and subcarrier spacing is 15KHz, and the duration of each symbol is 1/14ms.

In this emulation, adopt $\left[\begin{array}{cc}1& j\\ -j& 1\end{array}\right]$ As weighting matrix among the present invention, the diversity encoder matrix form that contrasts in the emulation is as follows:

$\left[\begin{array}{cccc}{S}_1& -S_2^{*}& j*S_3& -j{S}_4^{*}\\ S_2& S_1^{*}& j*S_4& j*S_3^{*}\\ -j*S_1& j*S_2^{*}& S_3& -S_4^{*}\\ -j*S_2& -j*S_1^{*}& S_4& S_3^{*}\end{array}\right]$

(1) a kind of encoder matrix of design according to the present invention

$\left[\begin{array}{cccc}{S}_1& -S_2^{*}& S_3& -S_4^{*}\\ S_2& S_1^{*}& S_4& S_3^{*}\\ S_3& -S_4^{*}& S_1& -S_2^{*}\\ S_4& S_3^{*}& S_2& S_1^{*}\end{array}\right]$

(2) accurate quadrature SFBC+FSTD

Can see from simulation result, the diversity scheme performance that adopts deversity scheme of the present invention to compare accurate quadrature SFBC coding will improve, the BER of deversity scheme of the present invention will reduce many than traditional deversity scheme, particularly along with the increase of the value of SNR, the value of BER significantly reduces, and has reflected that deversity scheme of the present invention has the low characteristics of the error rate, more than the increase of the value of SNR, performance difference increases thereupon, embodies deversity scheme of the present invention and has tangible performance advantage.

A kind of emission diversity method based on space-frequency coding of the present invention is not restricted to listed utilization in specification and the execution mode.Concerning the technology of the present invention those of ordinary skill in the field, can make various corresponding changes and distortion according to the present invention, and all these corresponding changes and distortion all belong to the protection range of claim of the present invention.

Claims (6)

1, a kind of emission diversity method based on space-frequency coding is applicable to that transmitting antenna greater than 2 MIMO-OPDM system, is characterized in that, may further comprise the steps:

The first step: the code stream to input carries out the SFBC coding;

Second step: according to the arrangement array and the polarization angle Selection precoding weight vector of antenna for base station;

The 3rd step: to through obtaining the encoder matrix after precoding weighting hand-off process after the weighting of SFBC coded data piece, obtain time-domain signal and emission by invert fast fourier transformation subsequently with the precoding weight vector.

As claim 1 emission diversity method based on space-frequency coding, it is characterized in that 2, the code stream of importing in the described first step is through the data after chnnel coding and the planisphere mapping.

As claim 1 emission diversity method based on space-frequency coding, it is characterized in that 3, the code stream to input in the described first step carries out the SFBC coding that the SFBC coding is based on the Alamouti scheme.

4, as claim 1 emission diversity method based on space-frequency coding, it is characterized in that, comprise the two paths of data stream that obtains behind the SFBC coding in the described first step:

$[S_1,S_2,S_3,S_4,\·\·\·S_{N-1},S_N]\→\left[\begin{array}{ccccc}{S}_1& -S_2^{*}& S_3& -S_4^{*}\·\·\·S_{N-1}& -S_N^{*}\\ S_2& S_1^{*}& S_4& S_3^{*}\·\·\·S_N& S_{N-1}^{*}\end{array}\right].$

5, as claim 1 emission diversity method based on space-frequency coding, it is characterized in that, comprise in described second step:

According to $v_1=\left[\begin{array}{c}1\\ e^{-j{\mathrm{\θ}}_1}\end{array}\right],$ $v_2=\left[\begin{array}{c}{e}^{-j{\mathrm{\θ}}_2}\\ 1\end{array}\right],$ Wherein | θ ₁-θ ₂| the principle of=π, select the precoding weight vector.

6, as claim 1 emission diversity method based on space-frequency coding, it is characterized in that, comprise in described the 3rd step:

Get $A_1=\left[\begin{array}{cc}{S}_1& -S_2^{*}\\ S_2& S_1^{*}\end{array}\right],$ $A_2=\left[\begin{array}{cc}{S}_3& -S_4^{*}\\ S_4& S_3^{*}\end{array}\right],$ ${\·\·\·A}_{\frac{N}{2}}=\left[\begin{array}{cc}{S}_{N-1}& -S_N^{*}\\ S_N& S_{N-1}^{*}\end{array}\right];$

$B_1=A_1{v}_1=\left[\begin{array}{c}{A}_1\\ A_1{e}^{-j{\mathrm{\θ}}_1}\end{array}\right],$ $B_2=A_2{v}_2=\left[\begin{array}{c}{A}_2{e}^{-j{\mathrm{\θ}}_2}\\ A_2\end{array}\right],$ $\·\·\·B_{\frac{N}{2}}=A_{\frac{N}{2}}{v}_{\frac{N}{2}}=\left[\begin{array}{c}{A}_{\frac{N}{2}}{e}^{-j{\mathrm{\θ}}_2}\\ A_{\frac{N}{2}}\end{array}\right];$

Be written as $\left[\begin{array}{cc}{A}_1& A_2{e}^{-j{\mathrm{\θ}}_2}\\ A_1{e}^{-j{\mathrm{\θ}}_1}& A_2\end{array}\right],$ $\·\·\·\left[\begin{array}{cc}{A}_{\frac{N}{2}-1}& A_{\frac{N}{2}}{e}^{-j{\mathrm{\θ}}_2}\\ A_{\frac{N}{2}-1}{e}^{-j{\mathrm{\θ}}_1}& A_{\frac{N}{2}}\end{array}\right],$ Obtaining time-domain signal through invert fast fourier transformation at last launches.

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