CN100508507C - Adaptive equilibrium method of multi-input multi-output communication system - Google Patents

Abstract

This invention puts forward an adaptive interference cancel decision feed back balance method for a MIMO communication system under time-varying frequency selective decline channel characterizing in applying an adaptive decision feed back interference cancel balancer module to adaptively adjust the interference cancel coefficient among sub-flows, namely, a channel matrix is estimated then to equalize the balancer into a new prolonged one based on the channel matrix and the newly increased parameter is the tested interference cancel coefficient of the sub-flows, at the same time, the tested data sub-flows are taken as the related new input, its interference cancel coefficient is varied adaptively applying the recursive least square method based on the input data to follow the time varying channels.

Description

A kind of adaptive equilibrium method of multiple-input-multiple-output communication system

Technical field:

The invention belongs to mobile communication multiple-input and multiple-output (MIMO) antenna technical field, be particularly related under the time varying frequency Selective Fading Channel, vertical-as to handle the adaptive equalization technique that reduces average error sign ratio (SER) in (V-BLAST) system during dblast.

Background technology:

The V-BLAST receive-transmit system is present moving communicating field broad research, the effective ways that improve the transmission of radio links speed and the availability of frequency spectrum.Under the time varying frequency Selective Fading Channel, how better effectively to carry out channel equalization, be the key that improves systematic function.

" international electronics communicate by letter journal " (Layered Space Time Receivers forFrequency-Select ive Wireless Channels.IEEE Trans.on Comm. with The Institution of Electrical Engineers, 2002,50 (1): 65-73) introduced a kind of ordering based on minimum mean square error criterion (MMSE) interference cancellation decision feedback equalization method (0SIC-DFE) one by one, every grade solves a son stream and calculates and eliminate its interference at the channel matrix that the next stage utilization estimates.But because this method is based on quasi-static channel opens, think that just channel parameter does not change in a data block, so just can in a data block, insert one section training sequence earlier, estimate channel parameter, again it is used to calculate equalizer coefficients and carries out interference cancellation, so under time varying channel, this method is just no longer suitable.

" international electronics and The Institution of Electrical Engineers's signal processing journal " (Multi-input multi-output fadingchannel tracking and equalization using Kalman estimation.IEEE Transactions onSignal Processing, 2002,50 (5): 1065-1076) based on adaptive filtering theory, having proposed the adaptive channel in the mimo system estimates and equalization methods, at first by training sequence Initial Channel Assignment estimated value and equalizer coefficients, then with input data adaptive ground track channel change.But this method is to detect each substream of data simultaneously at receiving terminal, does not carry out interference cancellation so the space that can improve in addition on the performance.

Summary of the invention:

The present invention is directed to above-mentioned the deficiencies in the prior art, propose a kind of in the time varying frequency Selective Fading Channel adaptive interference cancellation decision feedback equalization algorithm, the expense that can save training sequence, and improve system's error sign ratio (SER) performance.

The present invention improves the adaptive equilibrium method of V-BLAST multi-input multi-output system performance under the time varying frequency Selective Fading Channel, comprising: the adaptive decision feedback equalizer module 6 based on recurrent least square method (RLS) detects the 1st way flow data; Adaptive interference cancellation decision feedback equalizer module 7 based on the recurrent least square method algorithm detects second respectively to a last way flow data;

It is characterized in that:

Adopt the adaptive interference cancellation decision feedback equalizer module 7 interference cancellation coefficient between adjustment stream adaptively, that is: second and later each stream on, estimate earlier that with one channel matrix is the equalizer of a new lengthening according to the DFF equivalence that channel matrix carries out interference cancellation again, the interference cancellation coefficient of the promptly detected son stream of its newly-increased parameter; Simultaneously detected substream of data is imported as corresponding increasing newly, the interference cancellation coefficient of this substream of data is used recursive least squares and is carried out adaptive variation to follow the tracks of time varying channel according to the input data.

The present invention at be the V-BLAST system of M * N, wherein M is a number of transmit antennas, N is the reception antenna number, becomes fading channel 4 times when frequency selectivity, received signal can be expressed as

$y\left(k\right)=\underset{p=0}{\overset{P}{\mathrm{\Σ}}}{H}_p\left(k\right)x(k-p)+n\left(k\right)---\left(1\right)$

Y (k)=[y wherein ₁(k) y ₂(k) ... y _N(k)] ^TThe signal phasor 11 that expression k receives constantly, x (k)=[x ₁(k) x ₂(k) ... x _M(k)] ^TThe signal phasor that expression k sends constantly, H _p(k) channel matrix of expression p footpath N * M, P+1 represents channel exponent number, the additive white Gaussian noise on n (k) the expression k moment reception antenna, it satisfies E[n (k) n ^H(k)]=σ ²I _N

In said system, when the present invention disturbs between elimination stream, with general estimate earlier the Channel Transmission matrix calculate the algorithm of interference cancellation coefficient different be, the equivalence of interference cancellation coefficient is the newly-increased parameter in the DFF of lengthening, makes it to change to follow the tracks of time varying channel according to input data adaptive ground.Concrete derivation is as follows:

The feedforward partial-length of supposing interference cancellation DFF 14 is N _f, feedback fraction length is N _b, the judgement time delay is a Δ, then to m son stream, solves because 1～m-1 son flows, so can eliminate the interference of preceding m-1 the son stream that has solved by following expression.

$y(k-\mathrm{\Δ})=y(k-\mathrm{\Δ})-\underset{i=1}{\overset{m-1}{\mathrm{\Σ}}}{\left(H_0\left(k\right)\right)}_i{\hat{x}}_i(k-\mathrm{\Δ})$

$y(k-\mathrm{\Δ}+1)=y(k-\mathrm{\Δ}+1)-\underset{i=1}{\overset{m-1}{\mathrm{\Σ}}}{\left(H_1\left(k\right)\right)}_i{\hat{x}}_i(k-\mathrm{\Δ})---\left(2\right)$

$\begin{array}{cc}\·& \·\\ \·& \·\\ \·& \·\end{array}$

$y(k-\mathrm{\Δ}+P)=y(k-\mathrm{\Δ}+P)-\underset{i=1}{\overset{m-1}{\mathrm{\Σ}}}{\left(H_P\left(k\right)\right)}_i{\hat{x}}_i(k-\mathrm{\Δ})$

Wherein, (H _j(k)), the expression k moment, the i row of j footpath channel parameter matrix.

Adaptive interference cancellation DFF equalizer module 7 output results 15 are

${\tilde{x}}_m(k-\mathrm{\Δ})=q_m\left(k\right)u\left(k\right)=w_m\stackrel{\‾}{y}\left(k\right)+b_m\widehat{\stackrel{\‾}{x}}(k-\mathrm{\Δ}-1)---\left(3\right)$

Wherein u (k) is equalizer input, y (k)=[y ^T(k) ... y ^T(k-N _f+ 1)] ^TExpression equalizer input feedforward part 13, $\widehat{\stackrel{\‾}{x}}(k-\mathrm{\Δ}-1)={[{\hat{x}}^T(k-\mathrm{\Δ}-1)...{\hat{x}}^T(k-\mathrm{\Δ}-N_b)]}^T$ Expression equalizer input feedback fraction 23.

With (2) substitution (3),,

${\tilde{x}}_m(k-\mathrm{\Δ})$

$=w_m\stackrel{\‾}{y}\left(k\right)+b_m\widehat{\stackrel{\‾}{x}}(k-\mathrm{\Δ}-1)-(w_{m,k-\mathrm{\Δ}}\·\underset{i=1}{\overset{m-1}{\mathrm{\Σ}}}{\left(H_0\left(k\right)\right)}_i{\hat{x}}_i(k-\mathrm{\Δ})+...+w_{m,k-\mathrm{\Δ}+P}\·\underset{i=1}{\overset{m-1}{\mathrm{\Σ}}}{\left(H_P\left(k\right)\right)}_i{\hat{x}}_i(k-\mathrm{\Δ}))$

$=w_m\stackrel{\‾}{y}\left(k\right)+b_m\widehat{\stackrel{\‾}{x}}(k-\mathrm{\Δ}-1)-(\underset{p=0}{\overset{P}{\mathrm{\Σ}}}{w}_{m,k-\mathrm{\Δ}+p}{\left(H_p\left(k\right)\right)}_1{\hat{x}}_1(k-\mathrm{\Δ})+...+\underset{p=0}{\overset{P}{\mathrm{\Σ}}}{w}_{m,k-\mathrm{\Δ}+P}{\left(H_p\left(k\right)\right)}_{m-1}{\hat{x}}_{m-1}(k-\mathrm{\Δ}))$

$=w_m\stackrel{\‾}{y}\left(k\right)+b_m\widehat{\stackrel{\‾}{x}}(k-\mathrm{\Δ}-1)+c_1{\hat{x}}_1(k-\mathrm{\Δ})+...+c_{m-1}{\hat{x}}_{m-1}(k-\mathrm{\Δ})$

$=\left[w_m{b}_m{c}_m\right]\·\stackrel{\·}{u}\left(k\right)={\stackrel{\·}{q}}_m\left(k\right)\·{\stackrel{\·}{u}}_m\left(k\right)$

(4)

Wherein, w _{M, k-Δ+p}Expression and y (the equalizer coefficients vector of k-Δ+p) multiply each other, p=0...P

By (4) formula as can be seen, the length of band interference cancellation is N * N _f+ M * N _bEqualizer can equivalence be N * N for length _f+ M * N _bThe new equalizer of+m-1, interference cancellation coefficient are then as newly-increased equalizer coefficients, and each detected son stream is as the newly-increased input of equalizer accordingly.So, to m son stream, can be expressed as based on the adaptive interference cancellation decision feedback equalization algorithm of RLS algorithm:

$k_m\left(k\right)=\frac{P_m(k-1){\stackrel{\·}{u}}_m\left(k\right)}{\mathrm{\λ}+{{\stackrel{\·}{u}}_m}^H\left(k\right)P_m(k-1){\stackrel{\·}{u}}_m\left(k\right)}---\left(5\right)$

${\stackrel{\·}{q}}_m\left(k\right)={\stackrel{\·}{q}}_m(k-1)+(\hat{x}(k-\mathrm{\Δ})-{\stackrel{\·}{q}}_m(k-1){\stackrel{\·}{u}}_m\left(k\right)){k_m}^H\left(k\right)---\left(6\right)$

$P_m\left(k\right)={\mathrm{\λ}}^{-1}{P}_m(k-1)-{\mathrm{\λ}}^{-1}{k}_m\left(k\right){\stackrel{\·}{u}}_m\left(k\right)P_m(k-1),m=1...M---\left(7\right)$

Wherein: ${\stackrel{\·}{u}}_m\left(k\right)={[y^T\left(k\right)...y^T(k-N_f+1){\hat{x}}^T(k-\mathrm{\Δ}-1)...{\hat{x}}^T(k-\mathrm{\Δ}-N_b){\hat{x}}_1(k-\mathrm{\Δ})...{\hat{x}}_{m-1}(k-\mathrm{\Δ})]}^T$ Be N * N _f+ M * N _bThe equalizer input column vector of+m-1 dimension, back m-1 item flows for preceding m-1 of having detected is sub declares 9-10 as a result firmly,

Be N * N _f+ M * N _b+ m-1 ties up row vector, represents the upward coefficient of adaptive equalizer 14 of m way stream.

Compare with general mimo system decision-feedback interference cancellation equalization algorithm,, can utilize the track channel change of input data adaptive, thereby save the expense of training sequence owing to the present invention is based on the theory of adaptive-filtering.

Compare with general mimo system adaptive decision-feedback equalization algorithm, the present invention is owing to adopted the method for adaptive interference cancellation in equalization algorithm, can utilize the interference of the substream of data that detected of elimination of input data adaptive, thereby improve balanced its error sign ratio performance.

Description of drawings:

Fig. 1 is an adaptive interference cancellation decision feedback equalization method system schematic

Adaptive interference cancellation decision feedback equalization method and general adaptive decision-feedback equalization method performance comparison diagram under the smooth fading channel condition that flattens when Fig. 2 is.

Fig. 3 is an adaptive interference cancellation decision feedback equalization method and general adaptive decision-feedback equalization method performance comparison diagram under the time varying frequency Selective Fading Channel condition.

Embodiment:

Below in conjunction with the description of drawings embodiments of the invention.

Embodiment 1:

Present embodiment is with a M transmitting antenna, and the V-BLAST system of N reception antenna is that example describes.As shown in Figure 1: send data 1 through string and modular converter 2, radio frequency processing module 3 by transmitting antenna sends to wireless channel 4, channel 4 is the time varying frequency Selective Fading Channel, sends signal and receives by the radio frequency processing module 5 that is received antenna after the channel 4, and received signal can be expressed as

$y\left(k\right)=\underset{p=0}{\overset{P}{\mathrm{\Σ}}}{H}_p\left(k\right)x(k-p)+n\left(k\right)---\left(1\right)$

Y (k)=[y wherein ₁(k) y ₂(k) ... y _N(k)] ^TThe signal phasor 11 that expression k receives constantly, x (k)=[x ₁(k) x ₂(k) ... x _M(k)] ^TThe signal phasor that expression k sends constantly, H _p(k) channel matrix of expression p footpath N * M, P+1 represents channel exponent number, the additive white Gaussian noise on n (k) the expression k moment reception antenna, it satisfies E[n (k) n ^H(k)]=σ ²I _N

Received signal vector 11 is imported into adaptive decision feedback equalizer module 6 and adaptive interference cancellation decision feedback equalizer module 7, obtains the detection data 8-10 of each height stream.

Among the present invention, adopt adaptive interference cancellation decision feedback equalizer module 7, k received signal vector y (k) 11 constantly is input in the feed-forward process module 12, obtain equalizer input feedforward part y (k)=[y ^T(k) ... y ^T(k-N _f+ 1)] ^T13, will go up detected transmission signal phasor of a moment

(k-Δ-1) 21 is input in the feedback processing modules 22, obtains equalizer input feedback fraction $\widehat{\stackrel{\‾}{x}}(k-\mathrm{\Δ}-1)={[{\hat{x}}^T(k-\mathrm{\Δ}-1)...{\hat{x}}^T(k-\mathrm{\Δ}-N_b)]}^{T}23,$ With detected sub-flow data

As the newly-increased part and 13,23 of equalizer input input adaptive equalizer 14 together, obtain the equalizer output result on the m way stream

Obtain detected m way stream by hard decision module 16 Subtract each other with equalizer output result 15 and to obtain error signal 17, input adaptive equalizer 14 is adjusted equalizer coefficients with the RLS algorithm, suc as formula (8)-(10).

$k_m\left(k\right)=\frac{P_m(k-1){\stackrel{\·}{u}}_m\left(k\right)}{\mathrm{\λ}+{{\stackrel{\·}{u}}_m}^H\left(k\right)P_m(k-1){\stackrel{\·}{u}}_m\left(k\right)}---\left(8\right)$

${\stackrel{\·}{q}}_m\left(k\right)={\stackrel{\·}{q}}_m(k-1)+(\hat{x}(k-\mathrm{\Δ})-{\stackrel{\·}{q}}_m(k-1){\stackrel{\·}{u}}_m\left(k\right)){k_m}^H\left(k\right)---\left(9\right)$

$P_m\left(k\right)={\mathrm{\λ}}^{-1}{P}_m(k-1)-{\mathrm{\λ}}^{-1}{k}_m\left(k\right){\stackrel{\·}{u}}_m\left(k\right)P_m(k-1),m=1...M---\left(10\right)$

In order to specify advantage of the present invention, it is as follows to provide computer artificial result: analogue system adopts two transmitting antennas, the V-BLAST system of four reception antennas.System determination time-delay Δ=P-1, the feedforward length N _f=Δ+1, feedback length N _b=Δ-1, each son stream modulation system is QPSK, parameter lambda in the RLS algorithm=0.95, the data block size is 500 sampled points.Wireless channel adopts the JAKES model in the emulation, and parameter satisfies $E\left(\underset{p=0}{\overset{P}{\mathrm{\Σ}}}{\left|h_P(n,m)\right|}^2\right)=1,$ Channel variation parameter f _d/ f _sExpression, wherein f _dBe Doppler frequency, f _sBe sample frequency, receiving terminal average received signal to noise ratio is defined as $\mathrm{SNR}=10\log \left(\frac{P_T}{{\mathrm{\σ}}^2}\right),$ P wherein _TTotal emitted energy for transmitting terminal.

The time flatten (P=0) under the smooth fading channel environment, the mimo system adaptive interference cancellation decision-feedback RLS equalization algorithm (RLS-IC-DFE) that the present invention proposes and general mimo system self-adaptive decision feedback RLS equalization algorithm (RLS-DFE) and be applicable under the quasi-static channel opens interference cancellation decision feedback equalization algorithm (MIMO-OSIC-DFE) systematic function more as shown in Figure 2.The reception average signal-to-noise ratio of abscissa for representing with dB among the figure, ordinate is the average error sign ratio of received signal.Among the figure, curve A, B are respectively that the MIMO-OSIC-DFE method is in the channel variation parameter f _d/ f _s=1/500 and f _d/ f _sSER performance curve under=1/1000 the time varying channel; Curve C, E do not carry out the general mimo system self-adaptive decision feedback RLS equalization algorithm (RLS-DFE) of interference cancellation at f _d/ f _s=1/500 and f _d/ f _sUnder=1/1000 channel variation parameter performance curve; Curve D, F are respectively that the mimo system adaptive interference cancellation decision-feedback RLS equalization algorithm (RLS-IC-DFE) that proposes of the present invention is at f _d/ f _s=1/500 and f _d/ f _sUnder=1/1000 channel variation parameter performance curve.From as can be seen: under time varying channel with upper curve, the MIMO-OSIC-DFE algorithm is no longer suitable, and the RLS-IC-DFE that the present invention proposes can be applied to time varying channel and than general RLS-DFE under different channels pace of change situation, better mistake symbol performance can both be provided.

Under time varying frequency Selective Fading Channel environment (P=2), the adaptive interference cancellation decision-feedback RLS equalization algorithm (RLS-IC-DFE) that the present invention proposes and general self-adaptive decision feedback RLS equalization algorithm (RLS-DFE) and be applicable under the quasi-static channel opens interference cancellation decision feedback equalization algorithm (MIMO-OSIC-DFE) systematic function more as shown in Figure 3.Among the figure, curve G, H are respectively that the MIMO-OSIC-DFE method is in the channel variation parameter f _d/ f _s=1/500 and f _d/ f _sSER performance curve under=1/1000 the time varying channel; Curve I, K do not carry out the general mimo system self-adaptive decision feedback RLS equalization algorithm (RLS-DFE) of interference cancellation at f _d/ f _s=1/500 and f _d/ f _sUnder=1/1000 channel variation parameter performance curve; Curve J, L are respectively that the mimo system adaptive interference cancellation decision-feedback RLS equalization algorithm (RLS-IC-DFE) that proposes of the present invention is at f _d/ f _s=1/500 and f _d/ f _sUnder=1/1000 channel variation parameter performance curve.From as can be seen: when frequency selectivity, become under the fading channel with upper curve, the MIMO-OSIC-DFE algorithm is equally no longer suitable, and the RLS-IC-DFE that the present invention proposes still can be applied to time varying channel and than general RLS-DFE under different channels pace of change situation, better mistake symbol performance can both be provided.

Claims (1)

1, a kind of adaptive equilibrium method that improves V-BLAST multi-input multi-output system performance under the time varying frequency Selective Fading Channel comprises: the adaptive decision feedback equalizer module based on recurrent least square method detects the 1st way flow data; Adaptive interference cancellation decision feedback equalizer module based on the recurrent least square method algorithm detects second respectively to a last way flow data; It is characterized in that: employing adaptive interference cancellation decision feedback equalizer module is adjusted the interference cancellation coefficient between son stream adaptively, that is: second and later each stream on, estimate earlier that with one channel matrix is the equalizer of a new lengthening according to the DFF equivalence that channel matrix carries out interference cancellation again, the interference cancellation coefficient of the promptly detected son stream of its newly-increased parameter; Simultaneously detected substream of data is imported as corresponding increasing newly, the interference cancellation coefficient of this substream of data is used recursive least squares and is carried out adaptive variation to follow the tracks of time varying channel according to the input data.

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