CN1972175A - Code design method and demodulation method for reducing complexity of space-time grid code decoding - Google Patents

Abstract

This invention relates to one codes design method and demodulation method to lower space codes complexity in wireless communication middle space coding technique, which comprises the following steps: introducing time and space fix relationship to emission signal to make the first judgment to induce backward part signals; when emission days is 2 or 3, designing two codes; in receive end demodulation, using time judged signals as feedback to induce current time part signal to offset current remaining signal test.

Description

Reduce the code word method for designing and the demodulation method of space-time grid code decoding complexity

Technical field

What the present invention relates to is a kind of method for designing and corresponding demodulation method of communication code technical field, specifically is a kind of code word method for designing and demodulation method that reduces the space-time grid code decoding complexity.

Background technology

Multiple-input and multiple-output (MIMO) technology has significantly improved the availability of frequency spectrum by increasing the antenna amount of transmitting terminal and receiving terminal.Under desirable propagation conditions, the potential availability of frequency spectrum and the antenna amount of multi-input multi-ouput channel are linear.Space Time Coding (STC) technology then is to reach or have potentiality, the high new technology of feasibility near multi-input multi-output system capacity a kind of, and it can utilize space, time and frequency diversity fully, reduces the error rate of reception information greatly.At present, the empty time-code of ingenious, the superior performance of existing a variety of designs.The empty time-code that has is pursued maximum spatial multiplexing gain, during as dblast (BLAST), obtained the high rate of information throughput, and the empty time-code of other is to realize that maximum diversity gain is a target, as Space-Time Block Coding (STBC) and space-time grid code (STTC), higher diversity gain makes the error performance of system that significant improvement arranged.

Space-time grid code is proposed by people such as Tarokh the earliest, and different with Space-Time Block Coding is that space-time grid code has the feature of convolution code, has considered the relevance between the input information of front and back, also has very high coding gain when obtaining higher diversity gain.Specifically, when transmitting terminal was encoded, the input data bit flow after the Trellis-coded modulation of multi-system, formed a plurality of parallel signal flows, and launches simultaneously on each transmitting antenna respectively according to the transmission requirement of reality.By the signal after the Channel Transmission, separate mediation decoding at receiving terminal.The method that demodulation is adopted is the maximum-likelihood sequence estimation (MLSE) based on Viterbi soft-decision algorithm, with Euclidean distance between the signal phasor square is the tolerance in path, in grid, carry out maximum likelihood searching, and select to have the path of minimum degree value as final output sequence.

Though, space-time grid code all has error performance preferably in various channels, but, space-time grid code adopts best maximum-likelihood sequence estimation because separating timing at receiving terminal, when number of transmit antennas fixedly the time, its computation complexity can be exponential growth along with the constraint length of Trellis-coded modulation device and the increase of information emission rate, can be expressed as with formula:

η _MLSE≈l×N _s×2 _n×N _t×N _r (1)

Wherein, η _MLSEThe computation complexity of expression maximum-likelihood sequence estimation, l is a frame length, N _sBe the status number in the grid chart, the constraint length of it and Trellis-coded modulation device is exponential relationship, and n represents is to read n bit to encode and modulate N at every turn _tAnd N _rBe respectively number of transmit antennas and reception antenna number.In order to obtain higher coding gain, people usually suitably increase constraint length, and from (1) as can be seen, computation complexity also will be exponential increase with the increase of constraint length.High judgement computation complexity becomes the widely used main reason of restriction space-time grid code.Therefore, how research reduces the focus that the decoding complexity of space-time grid code is domestic and international concern always.

Find through literature search prior art, Triolo, A.A., Liberti, J.C. and Hoerning, the document that T.R. three people deliver on MILCOM 2002 (2002 annual military communication meeting) " OFDM space-timetrellis coded MIMO systems with experimental results " (adopting the multi-input multi-output system and the experimental result thereof of OFDM and space-time grid coding) was also once done the research that reduces aspect the space-time grid code decoding complexity.The method that they propose is the fusion, compromise to existing space-time grid code and hierarchical space-time code (LST), with original bit stream grouping earlier, carries out independently Trellis-coded modulation then separately, respectively organizes signal at last and launches simultaneously.Receiving terminal then relies on the distinctive continuous interference cancellation method of hierarchical space-time code earlier each grouping to be separated the maximum-likelihood sequence estimation in organizing again.Because people's such as Triolo scheme is not done any change to the coding and decoding method of space-time grid code inherence, all the time to carry out maximum-likelihood sequence estimation, its overall demodulated complex degree still with the constraint length exponent function relation of Trellis-coded modulation device, thereby the reduction degree of complexity limited (particularly when number of transmit antennas is smaller, even not having the effect that reduces complexity).

Summary of the invention

The present invention is directed to the high shortcoming of space-time grid code decoding complexity, a kind of code word method for designing and demodulation method that reduces the space-time grid code decoding complexity proposed, guaranteeing under the constant situation of the availability of frequency spectrum, make receiving terminal only carry out maximum likelihood (ML) judgement separating timing to the minority signal, replace traditional maximum-likelihood sequence estimation method, significantly reduced the demodulated complex degree of space-time grid code.In addition, the performance of space-time grid code system applies when correlated channels of using traditional coding and decoding scheme is always not as the performance under the non-correlation channel, and coding method of the present invention and demodulation method are insensitive to correlation between channels, and it is the same that transmission performance keeps during still with channel independence.

The present invention is achieved by the following technical solutions:

The invention provides a kind of code word method for designing that reduces the space-time grid code decoding complexity,, can know its follow-up part signal by inference by paid-in signal to the signal introducing time of emission and the fixed correlation on the space.Specific as follows:

A. be 2 multi-input multi-output system to number of transmit antennas, can adopt the method that postpones diversity, obtain the code word of full diversity gain.The signal that previous moment can be launched on second antenna postpones an emission cycle, launches (perhaps the two forms fixing mapping relations) once more by first antenna.

B. on the basis of a, can design number of transmit antennas more than 2 multi-input multi-output system code word.For example, number of transmit antennas is 3 o'clock, the signal that can make previous moment on the 3rd antenna, launch, and postponing an emission cycle reappears on first antenna, and second antenna can be fixed as a certain signal or form fixing combination with the 3rd antenna.In like manner analogize, obtain number of transmit antennas more than 3 multi-input multi-output system code word.

Follow code word method for designing proposed by the invention, designed and be applicable to that number of transmit antennas is 2 and 3 the STTC code word code word of 2 transmit antennas and 3 transmit antennas (is suitable for each two kinds).Wherein preceding two kinds of code words are methods of setting forth according among the top a, the signal that previous moment is launched on second antenna, remain untouched or be mapped as, launch by first antenna again the signal that becomes former point symmetry on the planisphere with it (signal on reference axis needn't be done mapping).The back is applicable to that number of transmit antennas is that 3 code word is on the basis of preceding two kinds of code words for two kinds, and the signal on the middle transmit antennas is fixed as 0 or lead the signal of second and third root antenna emission to form fixing 00,12,23,31 4 kind of combination.In sum, these four kinds of code words all have same characteristics, and the signal on a certain moment first transmit antennas is always stayed close adjacent previous moment N _tThere is relation one to one in signal on the transmit antennas.If there is not interference of noise, in case to previous moment N _tAfter signal on the transmit antennas is finished judgement, just can determine the signal on this moment first transmit antennas immediately.

The present invention is based on the code word method for designing of above-mentioned space-time grid code, a kind of corresponding demodulation method also is provided, that is: separate timing at receiving terminal, the signal that previous time has been adjudicated is as feedback, know the part signal of current time by inference, and in current demand signal, offset, be used for detection to residual signal.Do like this and can not use maximum-likelihood sequence estimation, and only need several signals (number is less than number of transmit antennas) are carried out the maximum likelihood demodulation independently.According to the characteristics of this demodulation method, the present invention is referred to as feedback-Interference Cancellation and detects (FICD).Though maximum-likelihood sequence estimation best performance but complexity is also the highest, and the poor slightly feedback-Interference Cancellation of performance detects time, the spatial correlation that has made full use of between signal, has greatly reduced amount of calculation.The concrete steps that feedback-Interference Cancellation detects are:

A. the initial condition of decoder is set to the encoder initial condition (generally the two all be changed to zero) of transmitting terminal, and contrast coding grid, learns first signal that first antenna of receiving terminal receives.

B. this signal is deducted the received signal vector that obtains revising from current received signal vector.

C. the received signal vector of revising is used maximum likelihood decision, obtain the decision value of the signal launched on all the other antennas.

D. according to this moment N _tThe decision value of the signal that transmit antennas is launched and the corresponding relation of coding in the grid obtain next decision value of the signal launched of first transmit antennas constantly.

E. repeat the b～d of front, up to whole received signals all demodulation finish.

In Computer Simulation, carried out emulation to three kinds in four kinds of code words.Be applicable to that number of transmit antennas is two kinds of code words of 2, closely similar in coding and demodulation, thereby only wherein a kind of carried out emulation.From the contrast of running time of emulation experiment, can find intuitively that the present invention is in the advantage that reduces on the decoding complexity.In addition, consider channel relevancy to the having a strong impact on of traditional space-time grid code frame error rate, the present invention has carried out emulation at correlated channels especially.Simulation result shows that code word method for designing proposed by the invention and feedback-Interference Cancellation detects and guaranteed that the frame error rate performance of system is not influenced by any of channel relevancy.

Description of drawings

Fig. 1,2,3,4 follows code word method for designing proposed by the invention and the space-time grid code code word designed.Wherein the code word of Fig. 1 (claiming that its code word is STTC-I) and Fig. 2 is applicable to that number of transmit antennas is 2 situation, and the then suitable number of transmit antennas of Fig. 3 (claiming that its code word is STTC-II) and Fig. 4 (claiming that its code word is STTC-III) is 3 multi-input multi-output system.

The relative computation complexity that Fig. 5 is three kinds of space-time grid code code words under maximum-likelihood sequence estimation and feedback-Interference Cancellation detection scheme.

What Fig. 6 showed is to work as N _t=N _r=2 o'clock, the comparison of the frame error rate of STTC-I under maximum-likelihood sequence estimation and feedback-Interference Cancellation detection scheme.

Fig. 7 is N _t=N _r=3 o'clock, STTC-II and the STTC-III frame error rate performance under maximum-likelihood sequence estimation and feedback-Interference Cancellation detection scheme relatively.

Fig. 8 shows is coefficient correlation ρ when getting different value, the frame error rate curve of STTC-I code word under the detection of feedback-Interference Cancellation.

Embodiment

Provide specific embodiment below in conjunction with technical scheme body of the present invention:

Multi-input multi-output system is modeled as with matrix operation

r _t＝Hc _t+n _t (2)

Wherein, r _tBe t received signal vector constantly, and $r_t={\left[\begin{array}{cccc}{r}_t^1& {\mathrm{<figure-callout\; id="2"\; label="r\; t"\; filenames="A20061011727600131.png"\; state="\{\{state\}\}">r</figure-callout>}}_t^{}& ...& r_t^{N_r}\end{array}\right]}^T,$ [-] ^TThe transposition of representing matrix.H is N _r* N _tChannel matrix, c _tBe the t vector that transmits constantly, $c_t={[\begin{array}{cccc}{c}_t^1& {\mathrm{<figure-callout\; id="2"\; label="c\; t"\; filenames="A20061011727600131.png"\; state="\{\{state\}\}">c</figure-callout>}}_t^{}& ...& c_t^{N_t}\end{array}]}^T,$ $n_t={[\begin{array}{cccc}{n}_t^1& {\mathrm{<figure-callout\; id="2"\; label="n\; t"\; filenames="A20061011727600131.png"\; state="\{\{state\}\}">n</figure-callout>}}_t^{}& ...& n_t^{N_r}\end{array}]}^T$ What represent is that multiple Gauss's additive white noise is in t sampled value constantly.

The code word method for designing that proposes among the present invention is by to the suitable screening of trellis encoder (at present, all being by exhaustive mode to the searching of space-time grid code word), guarantees c _t ^NtAnd c _T+T ¹(T is the emission cycle of signal) exists the relation of mapping one by one, introduces to the vector that transmits and determines constant time, the heavy relevance of Space Double.In case to c _t ^NtAfter the correct judgement, just available c _t ^NtDecision value obtain c indirectly _T+T ¹Decision value.

According to this method, work as N _t, can use simple delay diversity method to obtain as illustrated in fig. 1 and 2 code word at=2 o'clock.But, at N _t, seek out suitable code word and just be not a task easily at 〉=3 o'clock.The present invention has provided N here _tTwo kinds of code words of=3 o'clock.Need to prove that in these listed four kinds of code words, three kinds (seeing Fig. 1,3,4) are arranged is to exist $c_t^{N_t}=c_{t+\mathrm{<figure-callout\; id="1"\; label="T"\; filenames="A20061011727600131.png"\; state="\{\{state\}\}">T</figure-callout>}}^1$ Relation of identity, though another kind of (see figure 2) does not have this relation of identity to set up c _t ^NtAnd c _T+T ¹Between exist one to one relation (concrete corresponding relation can be obtained easily by grid chart).

Adopt feedback-Interference Cancellation to detect at receiving terminal and carry out demodulation, its concrete execution mode is as follows:

I. as shown in Figure 1 (STTC-I):

This is a kind of space-time grid code code word that postpones the diversity scheme design of utilizing, and is applicable to that number of transmit antennas is 2 multi-input multi-output system, and has obtained the full diversity gain, and the coder state number is 4, adopts the QPSK modulation.As can be seen from Figure 1, the burst of first transmit antennas emission is the burst through second antenna behind the lasting cycle delay of a signal.The specific implementation process that feedback-Interference Cancellation detects is:

The received signal that is located on the moment t reception antenna j is r _t ^j(1≤j≤N _r), the capable i column element of the j h in the channel matrix H _{J, i}(1≤j≤N _r, 1≤i≤N _t) the fading channel factor of expression from transmitting antenna i to reception antenna j.Receiving terminal correctly rules out the signal on the t moment second antenna ${\hat{c}}_{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="A20061011727600131.png"\; state="\{\{state\}\}">t</figure-callout>}}^2\text{=}{\mathrm{<figure-callout\; id="2"\; label="c\; t"\; filenames="A20061011727600131.png"\; state="\{\{state\}\}">c</figure-callout>}}_t^{},$ So, for the signal on the t+T moment first antenna Can have ${\hat{c}}_{t+\mathrm{<figure-callout\; id="1"\; label="T"\; filenames="A20061011727600131.png"\; state="\{\{state\}\}">T</figure-callout>}}^1={\hat{c}}_{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="A20061011727600131.png"\; state="\{\{state\}\}">t</figure-callout>}}^2.$ From received signal r _T+T ^j(1≤j≤N _r) in balance out Interference,

${\tilde{r}}_{t+T}^j=r_{t+T}^j-h_{j,1}{\hat{c}}_{t+T}^1---\left(3\right)$

Again by revising

Right

Adjudicate, from set of signals S, find out and to satisfy following formula As judgement output

${\hat{c}}_{t+\mathrm{<figure-callout\; id="2"\; label="T"\; filenames="A20061011727600131.png"\; state="\{\{state\}\}">T</figure-callout>}}^2=\begin{array}{cc}\arg & \underset{{\stackrel{-}{c}}_{t+\mathrm{<figure-callout\; id="2"\; label="T"\; filenames="A20061011727600131.png"\; state="\{\{state\}\}">T</figure-callout>}}^2\&Element;S}{\min }\end{array}\underset{j=1}{\overset{N_r}{\mathrm{\&Sigma;}}}{|{\tilde{r}}_{t+T}^j-h_{j,2}{\stackrel{-}{c}}_{t+\mathrm{<figure-callout\; id="2"\; label="T"\; filenames="A20061011727600131.png"\; state="\{\{state\}\}">T</figure-callout>}}^2|}^2---\left(4\right)$

By that analogy, can realize the judgement of whole burst.This scheme only needs individual signals is carried out maximum likelihood decision, compares with the Viterbi soft-decision of maximum-likelihood sequence estimation, and complexity greatly reduces.But when individual signals was adjudicated, the signal to noise ratio of receiving terminal had reduction.After the interference of feedback signal was cancelled, actual signal to noise ratio only be original 1/2 on the reception antenna, so works as N _t=2 o'clock, the detection of feedback-Interference Cancellation can cause the snr loss of nearly 3dB.

II. code word is as shown in Figure 2 also utilized the delay diversity method design, and the coder state number is 8, uses the 8PSK modulation.Though this code word is not just like among the STTC-I $c_{t+\mathrm{<figure-callout\; id="1"\; label="T"\; filenames="A20061011727600131.png"\; state="\{\{state\}\}">T</figure-callout>}}^1={\mathrm{<figure-callout\; id="2"\; label="c\; t"\; filenames="A20061011727600131.png"\; state="\{\{state\}\}">c</figure-callout>}}_t^{}$ Permanent establishment of relation, but c _T+T ¹And c _t ²Between exist one to one relation, in case obtain correct judgement It is well-determined to utilize corresponding relation to learn

Still can use feedback-Interference Cancellation to detect to the code word of this full diversity, concrete steps and STTC-I are much the same, do not repeat them here.

III. as shown in Figure 3 (STTC-II):

The coder state number is 4, adopts the QPSK modulation, can be used for number of transmit antennas and be 3 multi-input multi-output system.In the encoding scheme of STTC-II, the signal of first antenna emission is the same with last one signal of launching on the 3rd antenna constantly, and the signal of launching on second antenna is always fixed.Therefore, can detect demodulation with feedback-Interference Cancellation, concrete steps are referring to the I part.And because c _t ²Immobilize, right The judgement accuracy can be than higher.Similarly, right When carrying out independent judgement, signal to noise ratio has the loss of about 4.77dB.

IV. as shown in Figure 4 (STTC-III):

It is 3 multi-input multi-output system that STTC-III is equally applicable to number of transmit antennas, and the coder state number is 4, and modulation system is QPSK.In this encoding scheme, the signal of launching on the 3rd antenna of signal and previous moment of first antenna emission is the same, and coded identification that each moment launches from second and third root antenna only has four kinds of combined situation, and promptly 00,12,23,31.At the signal that balances out first antenna emission Back (seeing (3) formula) can be to remaining two signals on the antenna

With

Carry out the maximum likelihood cascading judgement, promptly

$\&lang;{\hat{c}}_{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="A20061011727600131.png"\; state="\{\{state\}\}">t</figure-callout>}}^2,{\hat{c}}_{\mathrm{<figure-callout\; id="3"\; label="t"\; filenames="A20061011727600131.png"\; state="\{\{state\}\}">t</figure-callout>}}^3\&rang;=\arg \underset{{\stackrel{-}{c}}_{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="A20061011727600131.png"\; state="\{\{state\}\}">t</figure-callout>}}^2,{\stackrel{-}{c}}_{\mathrm{<figure-callout\; id="3"\; label="t"\; filenames="A20061011727600131.png"\; state="\{\{state\}\}">t</figure-callout>}}^3\&Element;S}{\min }\underset{j=1}{\overset{N_r}{\mathrm{\&Sigma;}}}{|{\tilde{r}}_t^j-h_{j,2}{\stackrel{-}{c}}_t^2-h_{j,3}{\stackrel{-}{c}}_{\mathrm{<figure-callout\; id="3"\; label="t"\; filenames="A20061011727600131.png"\; state="\{\{state\}\}">t</figure-callout>}}^3|}^2---\left(5\right)$

Two signals are being carried out cascading judgement when decoding, the loss of the nearly 1.76dB of signal to noise ratio.

Detect as can be seen from top four kinds of grid coding structures and feedback-Interference Cancellation, coding and decoding scheme of the present invention has made full use of the room and time relevance between the signal on the different transmit antennas, to follow-up signal decision the time, had certain feedback input, thereby made the number of signals of each judgement less than N _t, complexity is much smaller than the maximum-likelihood sequence estimation based on viterbi algorithm.

The comparison of demodulated complex degree:

Be the comparison of convenient two kinds of demodulation scheme complexities, rewrite (1) formula as follows

η _MLSE≈l×N _s×2 ⁿ×N _t×N _r

Traditional space-time grid code demodulation scheme can reflect its computation complexity η with this general expression formula, and therefrom finds out the constraint length exponent function relation of computation complexity and encoder.In order to obtain better frame error rate performance, people usually can suitably increase the constraint length of encoder, and this consequence of thereupon bringing is the exponential growth of demodulated complex degree.

And for the computation complexity that feedback-Interference Cancellation detects, can change slightly because of the difference of encoding scheme.Here the complexity that the feedback of STTC-I, STTC-II, STTC-III and Fig. 2 code word-Interference Cancellation is detected is derived, and the expression formula of deriving is representative, can be generalized to the code word that other can use feedback-Interference Cancellation detection at an easy rate.The amount of calculation η of Interference Cancellation and judgement during feedback-Interference Cancellation detects _FICDCan be represented by the formula

η _FICD≈l×N _r×(N _t-m)+l×N _r×m×2 ⁿ

In the formula, what m represented is each the signal number that need adjudicate constantly. concerning the code word of STTC-I, STTC-II and Fig. 2, and m=1; For STTC-III, m=2.First amount of calculation when being Interference Cancellation in the right, second amount of calculation when being maximum likelihood decision.η _FICDWith N _sIrrelevant, thereby can not change along with the increase of encoder constraint length.Fig. 5 has provided four kinds of code words relating among the present invention and has detected relative computation complexity down in maximum-likelihood sequence estimation with feedback-Interference Cancellation, and therefrom the complexity of feedback-Interference Cancellation detection only is about 1/10 of a maximum-likelihood sequence estimation as can be seen.In addition, the expression formula of the two computation complexity shows clearly that also under the bigger situation of encoder constraint length, it will be more obvious that feedback-Interference Cancellation detects with respect to the advantage of maximum-likelihood sequence estimation.

Fig. 6 and 7 is the frame error rate simulation results to STTC-I, STTC-II and three kinds of code words of STTC-III.The prerequisite of emulation is, supposes that channel is the quasistatic flat fading, and separate between each parallel channel, can obtain desirable channel condition information at receiving terminal, and transmitting terminal is unknown fully to the state of channel.Noise is independent Gauss's additive white noise again.Each frame is made up of 130 symbols of every antenna emission, and in the beginning and ending place of each frame, the state of Trellis-coded modulation device all returns to 0 state.As can be seen from the figure, though the performance that feedback-Interference Cancellation detects is not so good as maximum-likelihood sequence estimation, its advantage on complexity is that maximum-likelihood sequence estimation is incomparable.

Fig. 8 is under the relevant situation of transmitting antenna, adopts feedback-Interference Cancellation to detect the system's frame error rate curve that obtains.In emulation, reception antenna is separate, emission correlation matrix R _tHas exponential form

$R_t=\begin{array}{c}\left[\begin{array}{cccc}1& \mathrm{\&rho;}& ...& {\mathrm{\&rho;}}^{(N_t-1)}\\ .& .& .& .\\ .& .& .& .\\ .& .& .& .\\ {\mathrm{\&rho;}}^{(N_t-1)*}& {\mathrm{\&rho;}}^{(N_T-1)*}& ...& 1\end{array}\right]\end{array}\begin{array}{}\end{array}$

When channel was relevant, maximum-likelihood sequence estimation can cause system's frame error rate that bigger deterioration (Ama, A.G. are arranged; Navarro, M.; Tarable, A.; " Robust space-time trellis codes on correlatedchannels ", Vehicular Technology Conference, 2004.VTC2004-Fall.2004 IEEE60th Volume 4,26-29 Sept.2004 Page (s): 2457-2461 Vol.4), and coefficient correlation ρ is big more, and the frame error rate performance loss must be severe more.And Fig. 8 has clearly reacted, and feedback-Interference Cancellation detects has very strong decorrelation ability, and the frame error rate performance of system because of the variation of ρ any weakening does not take place.

In sum, traditional space-time grid code uses and carries out demodulation based on the maximum-likelihood sequence estimation of Viterbi soft-decision, and its computation complexity is quite high.For reducing the demodulated complex degree of space-time grid code, the present invention proposes a kind of encoding scheme and designed corresponding feedback-Interference Cancellation detection method.The theory analysis and the simulation result of Fig. 1～4 four kind of code word all show, the method that the present invention proposes is when obtaining better frame error rate performance, reduced the decoding complexity of space-time grid code significantly, and the correlation to antenna is insensitive, can have relatively high expectations or there is the occasion utilization of correlation in channel in real-time.

Claims (3)

1, a kind of code word method for designing that reduces the space-time grid code decoding complexity is characterized in that: to the signal introducing time of emission and the fixed correlation on the space, know its follow-up part signal by inference by paid-in signal, specific as follows:

A. to number of transmit antennas 2 multi-input multi-output system: adopt the method that postpones diversity, obtain the code word of full diversity gain, signal with previous moment is launched on second antenna postpones an emission cycle, is launched once more or the two forms fixing mapping relations by first antenna;

B. designing the multi-input multi-output system code word of number of transmit antennas on the basis of a: when number of transmit antennas is 3 more than 2, the signal that makes previous moment on the 3rd antenna, launch, postponing an emission cycle reappears on first antenna, and second antenna is fixed as a certain signal or forms fixing combination with the 3rd antenna; In like manner analogize, obtain number of transmit antennas more than 3 multi-input multi-output system code word.

2, the code word method for designing of reduction space-time grid code decoding complexity according to claim 1, it is characterized in that, the resulting number of transmit antennas that is applicable to is that 2 and 3 code word respectively has two kinds, these four kinds of code words all have same characteristics, there is relation one to one in the signal that signal on a certain moment first transmit antennas is always stayed close on the adjacent previous moment Nt transmit antennas, if there is not interference of noise, in case after the signal on the previous moment Nt transmit antennas finished judgement, just can determine this signal on first transmit antennas constantly immediately.

3, a kind of demodulation method based on the described code word method for designing of claim 1 is characterized in that, concrete steps are:

A. the initial condition of decoder is set to the encoder initial condition of transmitting terminal, and contrast coding grid, learns first signal that first antenna of receiving terminal receives;

B. this signal is deducted the received signal vector that obtains revising from current received signal vector;

C. the received signal vector of revising is used maximum likelihood decision, obtain the decision value of the signal launched on all the other antennas;

D. the corresponding relation in the decision value of the signal of being launched according to this moment Nt transmit antennas and the coding grid obtains next decision value of the signal launched of first transmit antennas constantly;

E. repeat the b～d of front, up to whole received signals all demodulation finish.

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