CN101488836A - Space-time coding method, communication system using the method - Google Patents

Abstract

The invention provides a space-time block coding and decoding method comprising: in a transmitting terminal performing digital modulation for signal and performing the space-time block coding for the modulated signals, wherein, adding more redundancies during coding and transmitting coded signals; in a receiving terminal, performing zero forcing detection for received signals and performing maximum ratio combination for the detected signals. According to the invention, the transmission bit rate caused by compensating coding redundancies from high-dimensional modulating angles is declined by utilizing the power gain. The coding method has good effects that, the sufficient coding gain can enable the power gain space-time coding to have better performance than the Alamounti space-time coding under the same frequency spectrum efficiency, especially under the low signal-noise ratio, the space-time coding with power gain has better performance than the Alamounti coding, but under the low signal-noise ratio, the performance improvement of the receiver is important for improving the integral performance of the receiver.

Description

Space-time coding method, use the communication system of this method

Technical field

The present invention relates to multiaerial system, particularly, relate to a kind of space-time coding/decoding method, use the communication system of this method.

Background technology

Be subjected to the driving of professional quick growth such as internet and multimedia, more and more higher to the demand of wireless communication capacity.And unlimited frequency spectrum resource is limited, and this has very high spectrum efficiency with regard to an urgent demand communication system from now on.

MIMO (multiple-input and multiple-output) multiaerial system has been utilized spatial reuse, can improve power system capacity.The vertical demixing time space technology that experiment showed, Bell Laboratory can provide the spectrum efficiency up to 42bit/s/Hz.Space Time Coding is a kind of effective means that realizes the multiaerial system capacity, and it is at different transmitting antennas and different time period combined codings.The Alamounti Space-Time Block Coding is the coding a kind of commonly used in Space Time Coding field.It adopts the mode of 1 reception antenna of 2 transmitting antennas, and this system provides coding gain and full transmit diversity, and transmission code rate is 1, does not reduce spectrum efficiency.Has advantages such as deciphering simply, be easy to realization in addition.

Traditional Alamounti Space Time Coding adopts the mode of 1 reception antenna of 2 transmitting antennas.Encoder is got two modulation symbol x in each encoding operation ₁And x ₂Be a grouping, and it be mapped to transmitting antenna according to following encoder matrix:

$[x_1,x_2]\→\left[\begin{array}{cc}{x}_1& -x_2^{*}\\ x_2& x_1^{*}\end{array}\right]---\left(1\right)$

The output of encoder is launched from two antennas at two continuous emission cycle t, t+T.In the first emission cycle, signal x ₁And x ₂Launch respectively from antenna 1 and antenna 2 simultaneously; In second emission cycle, signal-x ₂ ^*From antenna 1 emission, and signal x ₁ ^*From antenna 2 emissions.At receiving terminal, suppose that receiving terminal can estimate the state of channel fully, then can the maximum-likelihood decoding criterion, to x ₁And x ₂Independent decoding.

The advantage of Alamounti Space Time Coding is full emission diversity gain, and code rate is 1, and can obtain coding gain.

In addition, the Alamounti Space Time Coding is compared with the spatial reuse of MIMO, has the advantage of coding gain and transmit diversity, but has reduced the transmission rate and the spectrum efficiency of channel.

The Alamounti Space Time Coding has made full use of advantages such as transmit diversity, coding gain, but does not make full use of for power gain.In fact, according to the channel capacity theorem of Shannon: c=Blog2 (1+s/n), when the signal to noise ratio of signal increased, the corresponding increase of channel capacity if the power gain in the Space Time Coding fully is used, then can reach the purpose that improves channel capacity.

In the Alamounti Space Time Coding, the redundancy encoding of retransmitting has reduced the rate of information throughput, if but these redundancy encoding bits are converted into power gain, and the raising of power gain is used for the higher-dimension modulation, make the channel under same-sign speed can transmit more bits information, just can both utilize coding gain, utilize power gain again, reach the purpose of comprehensive raising efficiency of transmission and raising spectrum efficiency.

Summary of the invention

The objective of the invention is to be to provide a kind of space-time coding method that can improve power gain, utilize this Space Time Coding that coding gain and power gain more fully are provided.Channel capacity theorem according to Shannon: C=Blog2 (1+S/N) can be converted into power gain the advantage of spectrum efficiency, has saved bandwidth resources from another angle, and coding gain helps reducing the error rate fully.

According to an aspect of the present invention, a kind of space-time block coding/decoding method comprises step:

At transmitting terminal, signal is carried out digital modulation, and modulation signal is carried out space-time block code, wherein in coding, added more redundant, and emission coded signal;

At receiving terminal, carry out ZF to the received signal and detect, and detected signal is carried out the high specific merging.

According to a further aspect in the invention, a kind of communication system comprises:

Transmitting terminal, described transmitting terminal comprises modulator, and signal is carried out digital modulation; Encoder carries out space-time block code to modulation signal, more redundant has wherein added in coding; And radiating portion, the emission coded signal;

Receiving terminal, described receiving terminal comprises the ZF detector, carries out ZF to the received signal and detects; And maximal ratio combiner, carry out detected signal and carry out the high specific merging.

According to the present invention, utilize power gain, the decline of the transmitted bit speed that causes from higher-dimension modulation angle compensation coding redundancy.In addition, coding gain makes this power gain Space Time Coding under identical spectrum efficiency fully, and contrast Alamounti Space Time Coding has more performance.Particularly under low signal-to-noise ratio, the Space Time Coding of this band power gain is having more performance than the Alamounti coding, and the improvement of the receiver performance under the low signal-to-noise ratio is significant to improving the receiver overall performance.

Description of drawings

Fig. 1, according to power gain Space Time Coding transmitter block diagram of the present invention

Fig. 2, according to power gain Space Time Coding receiver block diagram of the present invention

Fig. 3, high specific merge schematic diagram

BER simulation result under Fig. 4, the awgn channel

BER simulation result under Fig. 5, the Rayleigh fading channel

Embodiment

Fig. 1 and Fig. 2 show the transmitting terminal of communication system and the schematic block diagram of receiving terminal according to the preferred embodiment of the invention respectively.

As shown in Figure 1, at transmitting terminal, comprise channel encoder, modulator and Space Time Coding device.Wherein, channel encoder carries out chnnel coding to the signal from information source, and will be to carry out the channel input modulator of chnnel coding, so that carry out digital modulation.With modulation signal input coding device, modulation signal is carried out space-time block code, wherein in coding, used according to space-time coding method of the present invention, more redundantly promptly added.At last, radiating portion is transmitted into receiving terminal with coded signal.

As shown in Figure 2, at receiving terminal, receive code signal from transmitting terminal.Described receiving terminal comprises the ZF detector, carries out ZF to the received signal and detects.And by and maximal ratio combiner detected signal carried out high specific merge.To describe in further detail according to Space Time Coding coding/decoding method of the present invention and communication system below.

In order to make the empty time-code of Alamounti have more power gain and coding gain, when the design Space Time Coding, introduce more redundancy encoding, make coding longer, and the significant bit number that reduces to transmit.According to the mapping mode of the Space-Time Block Coding encoder of the embodiment of the invention can for:

$[x_1,x_2]\→\left[\begin{array}{c}{x}_1-x_2{x}_1^{*}-x_2^{*}\\ x_2{x}_1{x}_2^{*}{x}_1^{*}\end{array}\right]---\left(2\right)$

Wherein, first antenna of first behavior is at the signal of time t, t+T, t+2T, t+3T emission, and second antenna of second behavior is at the signal of time t, t+T, t+2T, t+3T emission., from coded system as can be seen, symbol x ₁And x ₂3 redundant codes have been added in the back, cause code rate to drop to 0.5.Receiving terminal has adopted zero forcing algorithm to detect received signal in order to reduce detection complexity.

At time period t and t+T, the receiving terminal received signal is:

r ₁＝h ₁₁x ₁+h ₂₁x ₂+n ₁ (1)

r ₂＝-h ₁₂x ₂+h ₂₂x ₁+n ₂ (2)

At time period t+2T and t+3T, the receiving terminal received signal is:

$r_3=h_{13}{x}_1^{*}+h_{23}{x}_2^{*}+n_3---\left(3\right)$

$r_4={-h}_{14}{x}_2^{*}+h_{24}{x}_1^{*}+n_4---\left(4\right)$

Being write as matrix form is:

$\left[\begin{array}{c}{r}_1\\ r_2\\ r_3\\ {\mathrm{<figure-callout\; id="4"\; label="r"\; filenames="A200810002660E00131.png"\; state="\{\{state\}\}">r</figure-callout>}}_4\end{array}\right]=\left[\begin{array}{cc}{h}_{11}& h_{21}\\ h_{12}& h_{22}\\ h_{13}& h_{23}\\ h_{14}& h_{24}\end{array}\right]\&CenterDot;\left[\begin{array}{cccc}{x}_1& -x_2& x_1^{*}& -x_2^{*}\\ x_2& x_1& x_2^{*}& x_1^{*}\end{array}\right]+\left[\begin{array}{c}{n}_1\\ n_2\\ n_3\\ {\mathrm{<figure-callout\; id="4"\; label="n"\; filenames="A200810002660E00131.png"\; state="\{\{state\}\}">n</figure-callout>}}_4\end{array}\right]$

Wherein, n1, n2, n3, n4 are that average is 0, power spectral density is the multiple Gaussian random process of No=1.

Suppose that channel dashes and response length is known, then channel matrix can be write as:

$H=\left[\begin{array}{cc}{h}_{11}& h_{21}\\ h_{12}& h_{22}\\ h_{13}& h_{23}\\ h_{14}& h_{24}\end{array}\right]$

The order of H can not be 4, and when the order of H was not 4, channel was that equation is still separated under the situation of ill-condition matrix, thereby was applicable to any communication environments.

According to equation (1)～(4), receiving terminal adopts zero forcing algorithm to detect, with (1) and (4) simultaneous, (2) and (3) simultaneous, obtain successively separate equation separate into:

${\hat{x}}_1=\frac{h_{14}^{*}{r}_1+h_{21}{r}_4^{*}}{{{(h}_{14}h}_{11}^{*}+h_{21}^{*}{h}_{24})},$

${\hat{x}}_2=\frac{h_{24}^{*}{r}_1-h_{11}{\mathrm{<figure-callout\; id="4"\; label="r"\; filenames="A200810002660E00131.png"\; state="\{\{state\}\}">r</figure-callout>}}_4^{*}}{h_{24}^{*}{h}_{21}+h_{11}{\mathrm{<figure-callout\; id="14"\; label="h"\; filenames="A200810002660E00131.png"\; state="\{\{state\}\}">h</figure-callout>}}_{14}^{*}}$

${\hat{x}}_1^{\&prime;}=\frac{h_{12}{\mathrm{<figure-callout\; id="3"\; label="r"\; filenames="A200810002660E00131.png,A200810002660E00132.png"\; state="\{\{state\}\}">r</figure-callout>}}_3^{*}+h_{23}{r}_2}{h_{23}^{*}{h}_{22}+h_{12}{h}_{13}^{*}}$

${\hat{x}}_2^{\&prime;}=\frac{h_{22}{\mathrm{<figure-callout\; id="3"\; label="r"\; filenames="A200810002660E00131.png,A200810002660E00132.png"\; state="\{\{state\}\}">r</figure-callout>}}_3^{*}-h_{13}^{*}{r}_2}{h_{22}{h}_{23}^{*}+h_{13}^{*}{\mathrm{<figure-callout\; id="12"\; label="h"\; filenames="A200810002660E00131.png"\; state="\{\{state\}\}">h</figure-callout>}}_{12}}$

Detected the estimated value that sends symbol

And

With

After, will

With

Press maximum rate and merge, With

Press maximum rate and merge,, again power gain is converted into spectral efficiency gain to obtain the power gain that more redundancy encoding is brought.Concrete merging block diagram as shown in Figure 3.

Wherein, weighted factor is relevant with the channel impulse response size, and the weighted factor of estimated signal x1 and x1 is respectively:

$g_1=\frac{h_{14}{h}_{11}^{*}+h_{21}{h}_{24}}{{\left|h_{11}\right|}^2+{\left|{\mathrm{<figure-callout\; id="14"\; label="h"\; filenames="A200810002660E00131.png"\; state="\{\{state\}\}">h</figure-callout>}}_{14}\right|}^2+{\left|h_{21}\right|}^2+{\left|h_{24}\right|}^2}$

${\mathrm{<figure-callout\; id="2"\; label="g"\; filenames="A200810002660E00131.png"\; state="\{\{state\}\}">g</figure-callout>}}_2=\frac{h_{23}^{*}{h}_{22}+h_{12}{h}_{13}^{*}}{{\left|{\mathrm{<figure-callout\; id="12"\; label="h"\; filenames="A200810002660E00131.png"\; state="\{\{state\}\}">h</figure-callout>}}_{12}\right|}^2+{\left|h_{13}\right|}^2+{\left|h_{22}\right|}^2+{\left|h_{23}\right|}^2}$

Estimated signal

With

Weighted factor be respectively:

${\mathrm{<figure-callout\; id="3"\; label="g"\; filenames="A200810002660E00131.png,A200810002660E00132.png"\; state="\{\{state\}\}">g</figure-callout>}}_3=\frac{h_{24}^{*}{h}_{21}+h_{11}{\mathrm{<figure-callout\; id="14"\; label="h"\; filenames="A200810002660E00131.png"\; state="\{\{state\}\}">h</figure-callout>}}_{14}^{*}}{{\left|h_{11}\right|}^2+{\left|{\mathrm{<figure-callout\; id="14"\; label="h"\; filenames="A200810002660E00131.png"\; state="\{\{state\}\}">h</figure-callout>}}_{14}\right|}^2+{\left|h_{21}\right|}^2+{\left|h_{24}\right|}^2}$

${\mathrm{<figure-callout\; id="4"\; label="g"\; filenames="A200810002660E00131.png"\; state="\{\{state\}\}">g</figure-callout>}}_4=\frac{h_{22}{h}_{23}^{*}+h_{13}^{*}{\mathrm{<figure-callout\; id="12"\; label="h"\; filenames="A200810002660E00131.png"\; state="\{\{state\}\}">h</figure-callout>}}_{12}}{{\left|{\mathrm{<figure-callout\; id="12"\; label="h"\; filenames="A200810002660E00131.png"\; state="\{\{state\}\}">h</figure-callout>}}_{12}\right|}^2+{\left|h_{13}\right|}^2+{\left|h_{22}\right|}^2+{\left|h_{23}\right|}^2}$

After high specific merges, improve and separate the required PSNR power signal-to-noise ratio of timing, demodulation when high s/n ratio is applicable to many level modulation of higher-dimension, this from another angle compensation the too much redundancy of introducing during Space Time Coding, and the redundant code of introducing during coding is useful to improving coding gain.Actual emulation is the result also prove: under same frequency spectrum efficient situation, the Space Time Coding performance of band power gain is better than the Alamounti Space Time Coding.

Simulated conditions is as shown in table 1:

Table 1

	According to empty time-code of the present invention	The empty time-code of Alamounti
			Channel model	Rayleigh fading and AWGN	Rayleigh fading and AWGN
Modulation	16QAM and 64QAM	QPSK and 8PSK
			Chnnel coding	1/3Turbo	1/3Turbo
Radiation pattern	Receive for 21	Receive for 21
			Space Time Coding	Redundant empty time-code	The empty time-code of Alamounti
Power gain receives	High specific merges	Do not have
			Code rate	0.5	1

It is 1/3 turbo sign indicating number that chnnel coding has adopted code check, and interpretation method is the logMAP algorithm.

In order to compare performance, QPSK, 8PSK, 16QAM, 64QAM4 kind mode have been used in modulation, wherein, the 16QAM level number is 4 times of QPSK, 64QAM is 8 times of 8PSK, a 16QAM symbol with bit number be the twice of QPSK, a 64QAM symbol with bit number be the twice of 8PSK.

For the performance gain that proves that the present invention is obtained, the invention provides computer artificial result, simulated channel is Rayleigh decline and awgn channel model, the coded identification that the power gain space-time coding method provides, bit rate drop by half when more empty than Alamounti, but the modulation symbol level number is 1 times of the empty time-code of Alamounti, and the two spectrum efficiency is identical.And empty time-code of power gain and Alamounti sky time-code contrasted, drawn the contrast properties curve.Fig. 4 is empty time-code of power gain and the performance comparison of the empty time-code of Alamounti under awgn channel, and Fig. 5 is the two performance comparison under the Rayleigh fading channel.

As can be seen from Figure 4 and Figure 5, be compared to traditional Alamounti Space Time Coding, under same frequency spectrum efficient, the Space Time Coding of band power gain is when signal to noise ratio is lower than 12dB, code performance when decoding performance is better than the Alamounti sky, performance approximately can improve about 1dB, valuable is that its decoding complexity is not high yet, has good applicability, but under high s/n ratio, the performance of the empty time-code of power gain is not as the empty time-code of Alamounti, and in real system, care all be under low signal-to-noise ratio, the quality of receiver performance, receiver performance generally can be not very poor under the high s/n ratio, at least is the acceptable level yet.Obviously, the empty time-code of power gain has remarkable advantages.Because this power gain Space Time Coding is compared and the empty time-code of Alamounti, utilized coding gain more fully, and transmit diversity, in addition, also made full use of power gain.

The invention provides Space Time Coding and coding/decoding method that a kind of new band power gain receives, comprise following aspect: transmitting terminal is introduced more redundant Space Time Coding and many level modulation of higher-dimension mode; At receiving terminal, receiver will receive the symbol of a lot of redundancy encodings of this introducing, after decoding corresponding to the transmitting terminal space-time coding method, identical symbol be carried out high specific merge, separate the required high s/n ratio of timing with raising, the signal after merging is sent into the demodulator demodulation.The method of the invention can provide a kind of performance to be better than the Space Time Coding mode of the empty time-code of Alamounti.

Claims (16)

1. space-time block coding/decoding method comprises step:

At transmitting terminal, signal is carried out digital modulation, and modulation signal is carried out space-time block code, wherein in coding, added more redundant, and emission coded signal;

At receiving terminal, carry out ZF to the received signal and detect, and detected signal is carried out the high specific merging.

2. by the described method of claim 1, it is characterized in that, at transmitting terminal, at moment t, with the transmission symbol x on two transmitting antennas ₁And x ₂Encode according to following coded system:

$[x_1,x_2]\&RightArrow;\left[\begin{array}{c}{x}_1-x_2{x}_1^{*}-x_2^{*}\\ x_2{x}_1{x}_2^{*}{x}_1^{*}\end{array}\right]$

Wherein whenever classify the different symbols launched on antenna 1 and the antenna 2 constantly located as.

3. by the described method of claim 2, it is characterized in that at transmitting terminal, the modulation system in the Space Time Coding is 2 times of the empty time-code modulation system of Alamounti level number.

4. by the described method of claim 2, it is characterized in that,, adopt the zero forcing algorithm of 2 unknown numbers of 4 equation solutions to obtain detected symbol at receiving terminal:

r ₁＝h ₁₁x ₁+h ₂₁x ₂+n ₁

r ₂＝-h ₁₂x ₂+h ₂₂x ₁+n ₂

$r_3=h_{13}{x}_1^{*}+h_{23}{x}_2^{*}+n_3$

$r_4={-h}_{14}{x}_2^{*}+h_{24}{x}_1^{*}+n_4.$

5. by the described method of claim 4, it is characterized in that,, the power gain of diversity is concentrated, merge according to high specific detected symbol is carried out the power gain computing at receiving terminal.

6. by the described method of claim 5, it is characterized in that the weight coefficient that described high specific merges is respectively:

$g_1=\frac{h_{14}{h}_{11}^{*}+h_{21}{h}_{24}}{{\left|h_{11}\right|}^2+{\left|h_{14}\right|}^2+{\left|h_{21}\right|}^2+{\left|h_{24}\right|}^2}$

$g_2=\frac{h_{23}^{*}{h}_{22}+h_{12}{h}_{13}^{*}}{{\left|h_{12}\right|}^2+{\left|h_{13}\right|}^2+{\left|h_{22}\right|}^2+{\left|h_{23}\right|}^2}$

Estimated signal

With Weighted factor be respectively:

$g_3=\frac{h_{24}^{*}{h}_{21}+h_{11}{h}_{14}^{*}}{{\left|h_{11}\right|}^2+{\left|h_{14}\right|}^2+{\left|h_{21}\right|}^2+{\left|h_{24}\right|}^2}$

$g_4=\frac{h_{22}{h}_{23}^{*}+h_{13}^{*}{h}_{12}}{{\left|h_{12}\right|}^2+{\left|h_{13}\right|}^2+{\left|h_{22}\right|}^2+{\left|h_{23}\right|}^2}.$

7. by the described method of claim 5, it is characterized in that, carrying out the high s/n ratio signal that obtains being done the many level demodulation of higher-dimension after power gain concentrates.

8. by the described method of claim 1, it is characterized in that, when carrying out the emission of signal, carry out one of in such a way: sequential transmission on time orientation; On two antennas in space, adopt the spatial multiplexing mode emission; And on a plurality of antennas in space, adopt the space diversity mode to launch.

9. communication system comprises:

Transmitting terminal, described transmitting terminal comprises modulator, and signal is carried out digital modulation; Encoder carries out space-time block code to modulation signal, more redundant has wherein added in coding; And radiating portion, the emission coded signal;

Receiving terminal, described receiving terminal comprises the ZF detector, carries out ZF to the received signal and detects; And maximal ratio combiner, carry out detected signal and carry out the high specific merging.

10. by the described system of claim 9, it is characterized in that described encoder is at moment t, with the transmission symbol x on two transmitting antennas ₁And x ₂Encode according to following coded system:

$[x_1,x_2]\&RightArrow;\left[\begin{array}{c}{x}_1-x_2{x}_1^{*}-x_2^{*}\\ x_2{x}_1{x}_2^{*}{x}_1^{*}\end{array}\right]$

Wherein whenever classify the different symbols launched on antenna 1 and the antenna 2 constantly located as.

11., it is characterized in that when described encoder carried out Space Time Coding, modulation system was 2 times of the empty time-code modulation system of Alamounti level number by the described system of claim 10.

12., it is characterized in that described ZF detector adopts the zero forcing algorithm of 2 unknown numbers of 4 equation solutions to obtain detected symbol by the described system of claim 10:

r ₁＝h ₁₁x ₁+h ₂₁x ₂+n ₁

r ₂＝-h ₁₂x ₂+h ₂₂x ₁+n ₂

$r_3=h_{13}{x}_1^{*}+h_{23}{x}_2^{*}+n_3$

$r_4={-h}_{14}{x}_2^{*}+h_{24}{x}_1^{*}+n_4.$

13. by the described system of claim 12, it is characterized in that described maximal ratio combiner is concentrated the power gain of diversity, merge according to high specific detected symbol is carried out the power gain computing.

14., it is characterized in that the weight coefficient that described high specific merges is respectively by the described method of claim 13:

$g_1=\frac{h_{14}{h}_{11}^{*}+h_{21}{h}_{24}}{{\left|h_{11}\right|}^2+{\left|h_{14}\right|}^2+{\left|h_{21}\right|}^2+{\left|h_{24}\right|}^2}$

$g_2=\frac{h_{23}^{*}{h}_{22}+h_{12}{h}_{13}^{*}}{{\left|h_{12}\right|}^2+{\left|h_{13}\right|}^2+{\left|h_{22}\right|}^2+{\left|h_{23}\right|}^2}$

Estimated signal

With

Weighted factor be respectively:

$g_3=\frac{h_{24}^{*}{h}_{21}+h_{11}{h}_{14}^{*}}{{\left|h_{11}\right|}^2+{\left|h_{14}\right|}^2+{\left|h_{21}\right|}^2+{\left|h_{24}\right|}^2}$

$g_4=\frac{h_{22}{h}_{23}^{*}+h_{13}^{*}{h}_{12}}{{\left|h_{12}\right|}^2+{\left|h_{13}\right|}^2+{\left|h_{22}\right|}^2+{\left|h_{23}\right|}^2}.$

15. by the described system of claim 13, it is characterized in that receiving terminal also comprises demodulator, be used for carrying out the high s/n ratio signal that obtains being done the many level demodulation of higher-dimension after power gain concentrates.

16., it is characterized in that described radiating portion carries out one of in such a way: sequential transmission on time orientation by the described system of claim 9; On two antennas in space, adopt the spatial multiplexing mode emission; And on a plurality of antennas in space, adopt the space diversity mode to launch.

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