CN101355541B - Blocking equalizing method for OFDM system under Quick-Change channel condition - Google Patents

Abstract

The invention provides a block balancing method for an orthogonal frequency division multiplexing (OFDM) system on the condition of a fast time variant channel. The method comprises the following: at a sending terminal, a bit signal subjected to cyclic redundancy codification is subjected to channel codification, interlacement, symbol map, serial/parallel conversion and IFFT conversion to be converted to a time domain signal; the time domain signal which is subjected to serial/parallel conversion and is inserted with a cyclic prefix is sent to a radio channel; at a receiving terminal, the signal is received by a traditional first-order frequency domain equalizer, and the signal guess value is checked after the signal is subject to serial/parallel conversion, demap, deinterlacement and signal path decoding; if the check is correct, the signal is outputted; if the check is not correct, the block balancing process is performed, during which, firstly, a time domain OFDM sending signal is restructured; secondly, the received time domain OFDM symbol is divided into a plurality of equilong signal receiving subblocks, the loop restructuring and the interference removing processes are performed by a time domain OFDM restructured signal; and finally, each subblock is subjected to frequency domain balance, the balanced guess values of sub blocks are merged to obtain the block balance output serving as the input of the serial/parallel conversion.

Description

Blocking equalizing method in the OFDM system under Quick-Change channel condition

Technical field

The invention belongs to OFDM (OFDM) mobile communication technology field.

Background technology

OFDM (OFDM, Orthogonal Frequency Division Multiplexing) technology is owing to reasons such as its availability of frequency spectrum is high, implementation complexity is low more and more receive people's attention.Since the eighties in 20th century, the OFDM technology not only is widely used in broadcast type DAB and video field, and has become the part of WLAN standard.Along with people's is to the enhancing of communication dataization, broadband, individualized and mobile demand, and the OFDM technology is applied at many high speed information transmission fields.At present, people are considering in the radio honeycomb GSM of future generation in future, to use the OFDM technology.Yet work in OFDM mobile system under high carrier frequency, the high rate travel condition field selectivity and frequency domain selectivity, i.e. double selectivity will cause channel to exist simultaneously the time.In this case; Become during channel quick and destroyed the orthogonality between subcarrier, thereby disturb (ICI) between causing carrying, traditional single order equalizer equalizes performance is affected; Even can't work, so the balancing technique of ofdm system becomes the focus of current research under the Quick-Change channel.

In order to improve the robustness that frequency-domain equalizer is worked in the time varying channel environment, can the interference cancellation techniques of cdma system Multiuser Detection be combined with frequency-domain equalization technology, utilize the means of iterative detection to reduce the influence of ICI to frequency-domain equalizer.Like people such as Wesheng Hou at " IEEE Trans.On Wireless Communications " vol.4; No.5, pp.2100-2110, September 2005 has delivered " ICI Cancellation for OFDM Communication Systems in Time-Varing Multipath Fading Channels " (IEEE radio communication journal in September, 2005; The 4th volume; The 5th phase, 2100 to 2110 pages, the time become carry in the ofdm communication system under the multidiameter fading channel between interference eliminated).To bring bigger processing delay to system but this method is introduced Interference Cancellation, the performance of its performance and the elementary detection of frequency-domain equalizer is closely related simultaneously, and has the error propagation problem.Another kind method be be used to improve when there is carrier wave frequency deviation in transceiver service behaviour the self-interference cancellation technology to be used under the time varying channel ofdm system balanced; Like people such as Yuping Zhao at " IEEE Trans.On Communications " vol.49; No.7, pp.1185-1191, July 2001 has delivered " Intercarrier Interference Self-Cancellation Scheme for OFDM Mobile Communication Systems " (ieee communication journal July calendar year 2001; The 49th volume; The 7th phase, 1185 to 1191 pages, disturb self elimination method between carrying in the mobile ofdm communication system).But this method need be carried out special precoding at transmitting terminal, has reduced the band efficiency of system.In addition, Philip Schniter is at " IEEE Trans.On Signal Processing " vol.52, no.4; Pp.1002-1011; April 2004 has delivered " Low-Complexity Equalization of OFDM in Doubly Selective Channels " (IEEE signal processing journal in April, 2004, the 52nd volume, the 4th phase; 1002 to 1011 pages; OFDM low complex degree equalization under the dual-selection channel), this method utilizes time-domain windowed that time varying channel is carried out filtering earlier, is utilizing iteration MMSE estimated signal; Its shortcoming is accurately to know the channel condition information of statistical information He each moment point of channel, and this channel estimator for actual ofdm system is to be difficult for realizing.People such as Li Wei propose in single-carrier frequency domain equalization system and ofdm system, to utilize the method antagonism time varying channel of piecemeal frequency domain equalization; But this method will receive signal simply and be divided into many sub-block and handle; Do not consider sub-inter-block-interference problem, cause equalization performance to descend.

Summary of the invention

The objective of the invention is to propose blocking equalizing method and device in the ofdm system under a kind of Quick-Change channel condition, to reduce because the performance loss that the time variation of channel brings.

The present invention realizes through following technical scheme:

1, blocking equalizing method in the ofdm system under a kind of Quick-Change channel condition is characterized in that:

At transmitting terminal, through the bit signal behind cyclic redundancy code stream b (n) channel encode, interweave, formation frequency domain orthogonal frequency-division multiplex singal behind sign map and the serial to parallel conversion, i frequency domain orthogonal frequency division multiplex ransmitting feed signals is expressed as s (i)=[s (i; 0), s (i, 1);, s (i, N-1)] ^T, N is a sub-carrier number, s (i) becomes time domain orthogonal frequency division multiplex ransmitting feed signals through contrary FFT

After, inserting length is the Cyclic Prefix of G, and behind parallel serial conversion, sends to wireless channel;

At receiving terminal, the first step: after removing Cyclic Prefix, serial to parallel conversion, i time domain orthogonal frequency division multiplexing receiving symbol $\tilde{r}\left(i\right)={[\tilde{r}(i,0),\tilde{r}(i,1),...,\tilde{r}(i,N-1)]}^T$ Can be expressed as:

$\tilde{r}\left(i\right)=H_t^i\tilde{s}\left(i\right)+\tilde{w}\left(i\right)=H_t^i{F}^{H}s\left(i\right)+\tilde{w}\left(i\right)$

Here Be channel matrix, Expression power is σ ²White Gaussian noise vector, F representes fourier transform matrix, () ^HThe operation of expression conjugate transpose; Balanced in order to carry out the single-order frequency domain equalization device, it is static earlier the channel hypothesis to be as the criterion, and promptly the variation of channel can be ignored in 1 OFDM symbol transmission time; Multipath channel is modeled as the FIR filter of constant finite impulse response when having the L-1 rank, uses h _l(i) expression l rank impulse response,

is a convolution matrix at this moment, can be expressed as

$H_t^i=F^H{\mathrm{\Λ}}^{i}F$

Here Λ ⁱBe diagonal matrix,

becomes frequency domain OFDM receiving symbol

to utilize the balanced frequency domain OFDM receiving symbol r (i) of single-order frequency domain equalization device through FFT, and the frequency domain orthogonal frequency-division multiplex singal estimated value

of equalizer output can be expressed as:

$\hat{s}\left(i\right)={\mathrm{\Λ}}^{\mathrm{iH}}{({\mathrm{\Λ}}^i{\mathrm{\Λ}}^{\mathrm{iH}}+{\mathrm{\σ}}^{2}I)}^{-1}r\left(i\right)$

Wherein I is the unit matrix of N * N,

is through parallel serial conversion; Separate mapping; Interweave, decoding obtains the estimated value of transmitting terminal bit signal stream

Second step: the transmitting terminal bit signal estimated value to obtaining is carried out CRC; If CRC is correct, then output; If CRC is incorrect, then carry out blocking equalizing, with the output of blocking equalizing input as parallel serial conversion in the first step,

Above-mentioned blocking equalizing method can be represented as follows:

A. the estimated value that the transmitting terminal bit signal that obtains in the first step is flowed

Carry out the chnnel coding identical, interweave, after the sign map, serial to parallel conversion, contrary FFT, obtain time domain orthogonal frequency division multiplexing reconstruction signal with transmitting terminal ${\tilde{s}}^{\′}\left(i\right)={[{\tilde{s}}^{\′}(i,0),{\tilde{s}}^{\′}(i,1),...,{\tilde{s}}^{\′}(i,N-1)]}^T,$

B. with each time domain orthogonal frequency division multiplexing symbol that receives

Be divided into M isometric reception signal subspace piece, sub-piece is counted M and is satisfied:

And be 2 integral number power, here

Expression rounds operation downwards, and the length of every sub-block is T=N/M, T＞L, and the k sub-block can be expressed as ${\tilde{r}}_k\left(i\right)={[{\tilde{r}}_k(i,0),{\tilde{r}}_k(i,1),...,{\tilde{r}}_k(i,T-1)]}^T={[\tilde{r}(i,\mathrm{KT}),\tilde{r}(i,\mathrm{KT}+1),...,\tilde{r}(i,(k+1)T-1)]}^T,$ { 0, M-1} in the time of every sub-block transmission, thinks that the time change of wireless channel can be ignored, promptly to k ∈

N=kT ..., (k+1) T-1, l ∈ 0, L-1},

Be the channel l rank impulse response of the time of k sub-block transmission, at this moment

Can be expressed as

${\tilde{r}}_k\left(i\right)=H_k^{\′}{\tilde{s}}_{k-1}\left(i\right)+H_k{\tilde{s}}_k\left(i\right)+{\tilde{w}}_k\left(i\right)$

Here ${\tilde{s}}_k\left(i\right)={[{\tilde{s}}_k(i,0),{\tilde{s}}_k(i,1),...,{\tilde{s}}_k(i,T-1)]}^T={[\tilde{s}(i,\mathrm{KT}),\tilde{s}(i,\mathrm{KT}+1),...,\tilde{s}(i,(k+1)T-1)]}^T,$

Characterized k-1 signal subspace piece the interblock that current k sub-block causes crosstalked,

The time domain of reconstruct is sent signal

Being divided into length is the sub-piece of T ${\tilde{s}}_k^{\′}\left(i\right)={[{\tilde{s}}_k^{\′}(i,0),{\tilde{s}}_k^{\′}(i,1),...,{\tilde{s}}_k^{\′}(i,T-1)]}^T={[{\tilde{s}}^{\′}(i,\mathrm{KT}),{\tilde{s}}^{\′}(i,\mathrm{KT}+1),...,{\tilde{s}}^{\′}(i,(k+1)T-1)]}^T,$ Utilize

Eliminate k-1 signal subspace piece the interblock that current k sub-block causes crosstalked,

${\tilde{r}}_k^{\′}\left(i\right)={\tilde{r}}_k\left(i\right)-H_k^{\′}{\tilde{s}}_{k-1}^{\′}\left(i\right)=H_k^{\′}({\tilde{s}}_{k-1}\left(i\right)-{\tilde{s}}_{k-1}^{\′}\left(i\right))+H_k{\tilde{s}}_k\left(i\right)+{\tilde{w}}_k\left(i\right)$

And carry out loop restructuring, and guaranteed the cycle characteristics of channel matrix, disturb between suppressing to carry,

${\tilde{r}}_k^{\′\′}\left(i\right)={\tilde{r}}_k^{\′}\left(i\right)+H_k^{\′}{\tilde{s}}_k^{\′}\left(i\right)=H_k^{\′}({\tilde{s}}_{k-1}\left(i\right)-{\tilde{s}}_{k-1}^{\′}\left(i\right))+H_k{\tilde{s}}_k\left(i\right)+H_k^{\′}{\tilde{s}}_k^{\′}\left(i\right)+{\tilde{w}}_k\left(i\right)$

If do not consider the error that reconstruct causes, promptly

then

${\tilde{r}}_k^{\′\′}\left(i\right)=H_{k,\mathrm{cir}}^{\′}{\tilde{s}}_k\left(i\right)+{\tilde{w}}_k\left(i\right)$

Convolution matrix H ' _{K, cir}=H _k+ H ' _kBe the corresponding channel matrix of k sub-block,

C. eliminate sub-interblock crosstalk with reconstruction cycle prefix basis on each is received sub-piece; Carry out FFT earlier; The length of its FFT is consistent with sub-block length, and each receives sub-piece to utilize the equilibrium of single-order frequency domain equalization device again, and the balanced valuation of the every sub-block after the equilibrium is through contrary FFT; Obtain the time domain equalization estimated value of every sub-block, the time domain equalization estimated value table of k sub-block is shown

${\hat{\tilde{s}}}_k\left(i\right)=F^H({\mathrm{\Λ}}_k^i{\mathrm{\Λ}}_k^{\mathrm{iH}}+{\mathrm{\σ}}_w^2{I}_T){\mathrm{\Λ}}_k^{\mathrm{iH}}F{\tilde{r}}_k^{\′\′}\left(i\right)$

Diagonal matrix

wherein

D. last balanced estimated value to every sub-block merges; The time domain equalization estimated value of every sub-block is that N symbol

obtains the piecemeal frequency-domain equilibrium method after FFT output

promptly is the estimated value of the frequency domain orthogonal frequency-division multiplex singal that sends according to the synthetic length of the der group of piecemeal.

Advantage of the present invention:

(1) the present invention proposes blocking equalizing algorithm in a kind of OFDM system under Quick-Change channel condition, become the influence of disturbing between carrying of causing when having reduced owing to channel, method is simple, and highly versatile, can be used for any ofdm system;

The increase of range degree when (2) blocking equalizing algorithm of the present invention is along with channel, advantage is more obvious.

(3) blocking equalizing algorithm of the present invention need not known all channel parameters constantly in the whole OFDM symbol transmission time, has reduced the complexity of system channel estimator, and is practical.

(4) the present invention will utilize the sub-piece of reconstruction signal; Eliminating the sub-interblock that is caused by previous signal subspace piece in each reception signal subspace piece crosstalks; And constitute the Cyclic Prefix of current reception signal subspace piece, and then guarantee the cycle characteristics of its channel matrix and suppress to disturb between remaining carrying, equalization performance improved.

Description of drawings

Fig. 1 ofdm system transmitting terminal block diagram

Fig. 2 is based on the ofdm system receiving terminal block diagram of blocking equalizing

Fig. 3 is that the receiving terminal piecemeal is handled sketch map

Fig. 4 is that the normalization Doppler frequency shift is f _NThe bit error rate comparison diagram of=0.0124 o'clock 3 kind of equalization methods

Fig. 5 is that the normalization Doppler frequency shift is f _NThe bit error rate comparison diagram of=0.05 o'clock 3 kind of equalization methods

Fig. 6 is that the normalization Doppler frequency shift is f _NThe bit error rate comparison diagram of=0.1 o'clock 3 kind of equalization methods

Embodiment

1, blocking equalizing method in the ofdm system under a kind of Quick-Change channel condition is characterized in that:

At transmitting terminal, through the bit signal behind cyclic redundancy code stream b (n) channel encode, interweave, formation frequency domain orthogonal frequency-division multiplex singal behind sign map and the serial to parallel conversion, i frequency domain orthogonal frequency division multiplex ransmitting feed signals is expressed as s (i)=[s (i; 0), s (i, 1);, s (i, N-1)] ^T, N is a sub-carrier number, s (i) becomes time domain orthogonal frequency division multiplex ransmitting feed signals through contrary FFT

After, inserting length is the Cyclic Prefix of G, and behind parallel serial conversion, sends to wireless channel;

At receiving terminal, the first step: after removing Cyclic Prefix, serial to parallel conversion, i time domain orthogonal frequency division multiplexing receiving symbol $\tilde{r}\left(i\right)={[\tilde{r}(i,0),\tilde{r}(i,1),...,\tilde{r}(i,N-1)]}^T$ Can be expressed as:

$\tilde{r}\left(i\right)=H_t^i\tilde{s}\left(i\right)+\tilde{w}\left(i\right)=H_t^i{F}^{H}s\left(i\right)+\tilde{w}\left(i\right)$

Here

Be channel matrix,

Expression power is σ ²White Gaussian noise vector, F representes fourier transform matrix, () ^HThe operation of expression conjugate transpose; Balanced in order to carry out the single-order frequency domain equalization device, it is static earlier the channel hypothesis to be as the criterion, and promptly the variation of channel can be ignored in 1 OFDM symbol transmission time; Multipath channel is modeled as the FIR filter of constant finite impulse response when having the L-1 rank, uses h _l(i) expression l rank impulse response,

is a convolution matrix at this moment, can be expressed as

$H_t^i=F^H{\mathrm{\Λ}}^{i}F$

Here Λ ⁱBe diagonal matrix,

becomes frequency domain OFDM receiving symbol

to utilize the balanced frequency domain OFDM receiving symbol r (i) of single-order frequency domain equalization device through FFT, and the frequency domain orthogonal frequency-division multiplex singal estimated value

of equalizer output can be expressed as:

$\hat{s}\left(i\right)={\mathrm{\Λ}}^{\mathrm{iH}}{({\mathrm{\Λ}}^i{\mathrm{\Λ}}^{\mathrm{iH}}+{\mathrm{\σ}}^{2}I)}^{-1}r\left(i\right)$

Wherein I is the unit matrix of N * N,

is through parallel serial conversion; Separate mapping; Interweave, decoding obtains the estimated value of transmitting terminal bit signal stream

Second step: the transmitting terminal bit signal estimated value

to obtaining is carried out CRC; If CRC is correct, then output; If CRC is incorrect, then carry out blocking equalizing, with the output of blocking equalizing input as parallel serial conversion in the first step,

Above-mentioned blocking equalizing method can be represented as follows:

A. the estimated value that the transmitting terminal bit signal that obtains in the first step is flowed

Carry out the chnnel coding identical, interweave, after the sign map, serial to parallel conversion, contrary FFT, obtain time domain orthogonal frequency division multiplexing reconstruction signal with transmitting terminal ${\tilde{s}}^{\′}\left(i\right)={[{\tilde{s}}^{\′}(i,0),{\tilde{s}}^{\′}(i,1),...,{\tilde{s}}^{\′}(i,N-1)]}^T,$

B. with each time domain orthogonal frequency division multiplexing symbol that receives

Be divided into M isometric reception signal subspace piece, sub-piece is counted M and is satisfied:

And be 2 integral number power, here Expression rounds operation downwards, and the length of every sub-block is T=N/M, T＞L, and the k sub-block can be expressed as ${\tilde{r}}_k\left(i\right)={[{\tilde{r}}_k(i,0),{\tilde{r}}_k(i,1),...,{\tilde{r}}_k(i,T-1)]}^T={[\tilde{r}(i,\mathrm{KT}),\tilde{r}(i,\mathrm{KT}+1),...,\tilde{r}(i,(k+1)T-1)]}^T,$ { 0, M-1} in the time of every sub-block transmission, thinks that the time change of wireless channel can be ignored, promptly to k ∈

N=kT ..., (k+1) T-1, l ∈ 0, L-1},

Be the channel l rank impulse response of the time of k sub-block transmission, at this moment

Can be expressed as

${\tilde{r}}_k\left(i\right)=H_k^{\′}{\tilde{s}}_{k-1}\left(i\right)+H_k{\tilde{s}}_k\left(i\right)+{\tilde{w}}_k\left(i\right)$

Here ${\tilde{s}}_k\left(i\right)={[{\tilde{s}}_k(i,0),{\tilde{s}}_k(i,1),...,{\tilde{s}}_k(i,T-1)]}^T={[\tilde{s}(i,\mathrm{KT}),\tilde{s}(i,\mathrm{KT}+1),...,\tilde{s}(i,(k+1)T-1)]}^T,$

Characterized k-1 signal subspace piece the interblock that current k sub-block causes crosstalked,

The time domain of reconstruct is sent signal

Being divided into length is the sub-piece of T ${\tilde{s}}_k^{\′}\left(i\right)={[{\tilde{s}}_k^{\′}(i,0),{\tilde{s}}_k^{\′}(i,1),...,{\tilde{s}}_k^{\′}(i,T-1)]}^T={[{\tilde{s}}^{\′}(i,\mathrm{KT}),{\tilde{s}}^{\′}(i,\mathrm{KT}+1),...,{\tilde{s}}^{\′}(i,(k+1)T-1)]}^T,$ Utilize

Eliminate k-1 signal subspace piece the interblock that current k sub-block causes crosstalked,

${\tilde{r}}_k^{\′}\left(i\right)={\tilde{r}}_k\left(i\right)-H_k^{\′}{\tilde{s}}_{k-1}^{\′}\left(i\right)=H_k^{\′}({\tilde{s}}_{k-1}\left(i\right)-{\tilde{s}}_{k-1}^{\′}\left(i\right))+H_k{\tilde{s}}_k\left(i\right)+{\tilde{w}}_k\left(i\right)$

And carry out loop restructuring, and guaranteed the cycle characteristics of channel matrix, disturb between suppressing to carry,

${\tilde{r}}_k^{\′\′}\left(i\right)={\tilde{r}}_k^{\′}\left(i\right)+H_k^{\′}{\tilde{s}}_k^{\′}\left(i\right)=H_k^{\′}({\tilde{s}}_{k-1}\left(i\right)-{\tilde{s}}_{k-1}^{\′}\left(i\right))+H_k{\tilde{s}}_k\left(i\right)+H_k^{\′}{\tilde{s}}_k^{\′}\left(i\right)+{\tilde{w}}_k\left(i\right)$

If do not consider the error that reconstruct causes, promptly

then

${\tilde{r}}_k^{\′\′}\left(i\right)=H_{k,\mathrm{cir}}^{\′}{\tilde{s}}_k\left(i\right)+{\tilde{w}}_k\left(i\right)$

Convolution matrix H ' _{K, cir}=H _k+ H ' _kBe the corresponding channel matrix of k sub-block,

C. eliminate sub-interblock crosstalk with reconstruction cycle prefix basis on each is received sub-piece; Carry out FFT earlier; The length of its FFT is consistent with sub-block length, and each receives sub-piece to utilize the equilibrium of single-order frequency domain equalization device again, and the balanced valuation of the every sub-block after the equilibrium is through contrary FFT; Obtain the time domain equalization estimated value of every sub-block, the time domain equalization estimated value of k sub-block can be expressed as

${\hat{\tilde{s}}}_k\left(i\right)=F^H({\mathrm{\Λ}}_k^i{\mathrm{\Λ}}_k^{\mathrm{iH}}+{\mathrm{\σ}}_w^2{I}_T){\mathrm{\Λ}}_k^{\mathrm{iH}}F{\tilde{r}}_k^{\′\′}\left(i\right)$

Diagonal matrix wherein

D. last balanced estimated value to every sub-block merges; The time domain equalization estimated value of every sub-block is that N symbol

obtains the piecemeal frequency-domain equilibrium method after FFT output

promptly is the estimated value of the frequency domain orthogonal frequency-division multiplex singal that sends according to the synthetic length of the der group of piecemeal.

Below in conjunction with accompanying drawing the present invention is done to further describe, so that the object of the invention, feature and advantage are clearer.

The consideration sub-carrier number is N, and cyclic prefix CP (cyclic prefix) is the CP-OFDM system of G.As shown in Figure 1, at transmitting terminal, bit stream b (n) channel behind cyclic redundancy code coding interweaves, sign map, forming size behind the serial to parallel conversion is the grouping of N, i grouping sheet be shown s (i)=[s (i, 0), s (i, 1) ..., s (i, N-1)] ^TVector s (i) modulates through N point IFFT; After being transformed into time domain vector

; Insert the cyclic prefix CP that length is G again, behind parallel serial conversion, send into wireless channel.

As shown in Figure 2; At receiving terminal; The time-domain signal that receives is at first removed CP; Through serial to parallel conversion, i the OFDM symbol that receives

can be expressed as:

$\tilde{r}\left(i\right)=H_t^i\tilde{s}\left(i\right)+\tilde{w}\left(i\right)=H_t^i{F}^{H}s\left(i\right)+\tilde{w}\left(i\right)---\left(1\right)$

Here

Expression power is σ ²White Gaussian noise vector, F representes FFT matrix, () ^HThe operation of expression conjugate transpose.

If it is static that the channel hypothesis is as the criterion, promptly the variation of channel can be ignored in 1 OFDM symbol transmission time, and multipath channel is modeled as the FIR filter of constant finite impulse response when having the L-1 rank, uses h _l(i) expression l rank impulse response.

Then is exactly a convolution matrix, can be expressed as

$H_t^i=F^H{\mathrm{\Λ}}^{i}F$

Here Λ ⁱIt is diagonal matrix.Therefore at receiving terminal, send signal and can utilize simple single order equalizer to detect:

$\hat{s}\left(i\right)={\mathrm{\Λ}}^{\mathrm{iH}}{({\mathrm{\Λ}}^i{\mathrm{\Λ}}^{\mathrm{iH}}+{\mathrm{\σ}}^{2}I)}^{-1}\mathrm{Fr}\left(i\right)---\left(2\right)$

Wherein I is the unit matrix of N * N.

Yet under Quick-Change channel condition, the variation of channel can not ignore in 1 OFDM symbol transmission time, disturbs between having caused year (ICI).Be modeled as the L-1 rank limited FIR filter that when having become impulse response with multipath channel this moment, uses h _{N, l}(i) the expression l rank impulse response of n constantly, therefore

At this moment,

$H_t^i={\mathrm{FH}}_f^i{F}^H$

Here

is not diagonal matrix; Between having caused year, element in

on off-diagonal disturbs (inter-carrier interference; ICI), the equalization performance of at this moment traditional single order equalizer must be affected.Some equalization algorithms that propose can alleviate or eliminate the influence of channel ICI, but inevitably bring the change of signal format, the increase of computational complexity, the unfavorable factors such as reduction of efficiency of transmission.

In real system, the significance degree that becomes when channel is is relevant with the length of observing time.Though; For the high-speed mobile ofdm system, in 1 OFDM mark space, become during channel and can not ignore, but carry out equilibrium respectively if 1 OFDM symbol is divided into the experimental process piece; Then for every sub-block experience the time at interval in channel the time to become possibly be very little, even can ignore.Based on this thought, the present invention proposes blocking equalizing method in the ofdm system under a kind of Quick-Change channel condition

As shown in Figure 2, carry out the process identical earlier at receiving terminal and carry out initial estimation with traditional ofdm system demodulation.

transforms to frequency domain through FFT, and the frequency-domain OFDM symbolic representation is r (i).After carrying out the equilibrium of frequency domain single order by formula (2); The estimation

that obtains generation signals s (i) is through parallel serial conversion; Separate mapping; Interweave; After decoding obtains transmitting terminal bit signal estimated value

, carry out CRC.If CRC is correct, then output; Otherwise, then carry out blocking equalizing.

Before blocking equalizing, utilize decoding to obtain earlier

Carry out the chnnel coding identical, interweave, after the sign map, serial to parallel conversion, contrary FFT, obtain time domain orthogonal frequency division multiplexing reconstruction signal with transmitting terminal ${\tilde{s}}^{\′}\left(i\right)={[{\tilde{s}}^{\′}(i,0),{\tilde{s}}^{\′}(i,1),...,{\tilde{s}}^{\′}(i,N-1)]}^T.$

As shown in Figure 3, with each time domain orthogonal frequency division multiplexing symbol that receives

Be divided into M isometric reception signal subspace piece, sub-piece is counted M and is satisfied:

And be 2 integral number power, here

Expression rounds operation downwards, and the length of every sub-block is T=N/M, T＞L, the k sub-block of i OFDM symbol ${\tilde{r}}_k\left(i\right)={[{\tilde{r}}_k(i,0),{\tilde{r}}_k(i,1),...,{\tilde{r}}_k(i,T-1)]}^T={[\tilde{r}(i,\mathrm{KT}),\tilde{r}(i,\mathrm{KT}+1),...,\tilde{r}(i,(k+1)T-1)]}^T,$ K ∈ 0, M-1}.In the time of every sub-block transmission; Think wireless channel the time become and can ignore; I.e.

n=kT; (k+1) T-1; { 0, L-1},

are the channel l rank impulse responses of the time of k sub-block transmission to l ∈;

can be expressed as

${\tilde{r}}_k\left(i\right)=H_k^{\′}{\tilde{s}}_{k-1}\left(i\right)+H_k{\tilde{s}}_k\left(i\right)+{\tilde{w}}_k\left(i\right)---\left(3\right)$

Here s _k(i)=[s _k(i, 1), s _k(i, 2) ..., s _k(i, T)] ^T,

${\tilde{w}}_k\left(i\right)={[{\tilde{w}}_k(i,1),{\tilde{w}}_k(i,2),...,{\tilde{w}}_k(i,T)]}^T.$

characterized previous signal subspace piece the interblock that current sub-block causes crosstalked in the formula (3).The piecemeal frequency-domain equilibrium method that people such as LiWei propose is not only considered

Influence, and simply with H _kDeng being all convolution matrix, its equalization methods causes at frequency domain and disturbs between bigger carrying, and causes equalization performance to descend.The present invention utilizes

carries out loop restructuring to

; Both solved sub-interblock cross-interference issue; Guaranteed the cycle characteristics of channel matrix again; Disturb between suppressing to carry, obviously improved equalization performance.

The time domain of reconstruct is sent signal

Being divided into length is the sub-piece of T ${\tilde{s}}_k^{\′}\left(i\right)={[{\tilde{s}}_k^{\′}(i,0),{\tilde{s}}_k^{\′}(i,1),...,{\tilde{s}}_k^{\′}(i,T-1)]}^T={[{\tilde{s}}^{\′}(i,\mathrm{KT}),{\tilde{s}}^{\′}(i,\mathrm{KT}+1),...,{\tilde{s}}^{\′}(i,(k+1)T-1)]}^T,$ Utilize

Eliminate k-1 signal subspace piece the interblock that current k sub-block causes crosstalked,

${\tilde{r}}_k^{\′}\left(i\right)={\tilde{r}}_k\left(i\right)-H_k^{\′}{\tilde{s}}_{k-1}^{\′}\left(i\right)=H_k^{\′}({\tilde{s}}_{k-1}\left(i\right)-{\tilde{s}}_{k-1}^{\′}\left(i\right))+H_k{\tilde{s}}_k\left(i\right)+{\tilde{w}}_k\left(i\right)---\left(4\right)$

And carry out loop restructuring, and guaranteed the cycle characteristics of channel matrix, disturb between suppressing to carry,

${\tilde{r}}_k^{\′\′}\left(i\right)={\tilde{r}}_k^{\′}\left(i\right)+H_k^{\′}{\tilde{s}}_k^{\′}\left(i\right)=H_k^{\′}({\tilde{s}}_{k-1}\left(i\right)-{\tilde{s}}_{k-1}^{\′}\left(i\right))+H_k{\tilde{s}}_k\left(i\right)+H_k^{\′}{\tilde{s}}_k^{\′}\left(i\right)+{\tilde{w}}_k\left(i\right)---\left(5\right)$

If do not consider the error that reconstruct causes, promptly then

${\tilde{r}}_k^{\′\′}\left(i\right)=H_{k,\mathrm{cir}}^{\′}{\tilde{s}}_k\left(i\right)+{\tilde{w}}_k\left(i\right)---\left(6\right)$

Here convolution matrix H ' _{K, cir}=H _k+ H ' _kIt is the corresponding channel matrix of k sub-block.Eliminate sub-interblock crosstalk with reconstruction cycle prefix basis on each is received sub-piece; Carry out FFT earlier; The length of its FFT is consistent with sub-block length, and each receives sub-piece to utilize the equilibrium of single-order frequency domain equalization device again, and the balanced valuation of the every sub-block after the equilibrium is through contrary FFT; Obtain the time domain equalization estimated value of every sub-block, the time domain equalization estimated value of k sub-block can be expressed as

${\hat{\tilde{s}}}_k\left(i\right)=F^H({\mathrm{\Λ}}_k^i{\mathrm{\Λ}}_k^{\mathrm{iH}}+{\mathrm{\σ}}_w^2{I}_T){\mathrm{\Λ}}_k^{\mathrm{iH}}F{\tilde{r}}_k^{\′\′}\left(i\right)$

Diagonal matrix

wherein

The then estimation

of i OFDM time domain transmission symbol transforms to frequency domain through FFT to merge that every sub-block is estimated ; The output

that obtains the piecemeal frequency-domain equilibrium method of i OFDM symbol is through separating mapping; After deinterleaving and the decoding, carry out CRC.If cyclic redundancy is correct, then output; Otherwise, carry out the blocking equalizing process once more.

It is can not ignore that starting point of the present invention becomes during channel in 1 OFDM mark space; But, 1 OFDM symbol carries out equilibrium respectively if being divided into the experimental process piece; Then for every sub-block experience the time at interval in channel the time to become possibly be very little, even can ignore.Therefore to guarantee every sub-block experience the time at interval in channel the time become and can ignore, size that must suitable choice block count M.M is bigger, and then every sub-block is more little, therefore every sub-block experience the time at interval in the Shi Bianyue of channel little.Yet, to crosstalk in order to eliminate sub-interblock, the selection of M must guarantee sub-block length T＞L.And because every sub-block all need be carried out loop restructuring before equilibrium, so the selection of block count M size also will consider because the error propagation that loop restructuring causes and the influence of system's computational complexity.Simultaneously, in order to lower complexity, the time-frequency domain conversation of every sub-block realizes with fast Fourier transform (FFT) that normally therefore sub-block length T should be 2 integral number power when realizing.Therefore sub-piece is counted M and need be satisfied:

and be 2 integral number power; Here expression rounds operation downwards; The length of every sub-block is T=N/M; T＞L; Select M=8 for the N=1024 system, it is more satisfactory that M=4 selects in the N=256 system.

Be example with WiMAX (IEEE802.16) system below, further specify the blocking equalizing algorithm of proposition.Its sub-carrier number is M=256.The operating frequency of system is f _c=3.5GHz, sample frequency is f _s=2MHz, CP length is 8; Channel model adopts Stanford University's the third model of intermediate channels model (SUI3) of the modification of IEEE802.16 working group suggestion, and maximum delay expands to 1 μ s, has 3 footpaths; Time delay is respectively 0 μ s, 0.5 μ s, 1 μ s; The average power in 3 footpaths is respectively 0dB ,-5dB ,-10dB.Definition normalization Doppler frequency shift for

here v be the translational speed of communication terminal, c is the light velocity.Consider that because the error propagation that causes of loop restructuring and the influence of system's computational complexity, selection piecemeal number is M=4.

Fig. 4,5 and 6 has shown portable terminal under different translational speeds, traditional single order is balanced, the piecemeal frequency-domain equilibrium method of Li Wei and the performance of BER that the present invention proposes the blocking equalizing algorithm relatively.

As shown in Figure 4, the portable terminal translational speed is 30km/h, and this moment, corresponding normalization Doppler frequency shift was 0.0124.As can be seen from the figure, under the low speed mobile environment, Doppler frequency shift is less; The time range degree of channel is not obvious; The piecemeal frequency-domain equilibrium method of Li Wei has influenced equalization performance, its performance of BER even poorer slightly than traditional single order equalizer owing to do not consider sub-inter-block-interference.And the blocking equalizing algorithm that the present invention proposes solves sub-interblock cross-interference issue, has guaranteed the cycle characteristics of channel matrix again, disturbs between suppressing to carry, and has obviously improved equalization performance, is 10 in bit error rate ^-2The time, compare with traditional single order equalizer, obtained the gain of about 2dB.

Under the low speed mobile environment, Doppler frequency shift is smaller, and the time range degree of channel is not obvious, and the blocking equalizing algorithm advantage that therefore proposes is not obvious.

As shown in Figure 5, the portable terminal translational speed is 120km/h, and this moment, corresponding normalization Doppler frequency shift was about 0.05.As can be seen from the figure, because translational speed increases, the time range degree of channel is apparent in view, and therefore traditional single order equalizer performance reduces, and the error code flat bed after signal to noise ratio is higher than 20dB, occurred.The equalization performance of the blocking equalizing algorithm that the present invention proposes obviously is superior to traditional single order equalizer performance, and is 10 in bit error rate ^-2The time, compare the gain that 5dB is also arranged with the piecemeal frequency-domain equilibrium method of Li Wei.

As shown in Figure 6, the portable terminal translational speed is 250km/h, and this moment, corresponding normalization Doppler frequency shift was about 0.1.As can be seen from the figure, because translational speed further increases, the time range degree aggravation of channel, therefore traditional single order equalizer performance further reduces, and after signal to noise ratio is higher than 15dB, the error code flat bed just occurred.This moment, the piecemeal frequency-domain equilibrium method equalization performance of Li Wei also decreased, and the equalization performance of the blocking equalizing algorithm that the present invention proposes still can bit error rate reach 10 when signal to noise ratio is 21dB ^-2, obviously be superior to the piecemeal frequency-domain equilibrium method of Li Wei.

Claims (1)

1. blocking equalizing method in the ofdm system under the Quick-Change channel condition is characterized in that:

At transmitting terminal, through the bit signal behind cyclic redundancy code stream b (n) channel encode, interweave, formation frequency domain orthogonal frequency-division multiplex singal behind sign map and the serial to parallel conversion, i frequency domain orthogonal frequency division multiplex ransmitting feed signals is expressed as s (i)=[s (i; 0), s (i, 1);, s (i, N-1)] ^T, N is a sub-carrier number, s (i) becomes time domain orthogonal frequency division multiplex ransmitting feed signals through contrary FFT

After, inserting length is the Cyclic Prefix of G, and behind parallel serial conversion, sends to wireless channel;

At receiving terminal, the first step: after removing Cyclic Prefix, serial to parallel conversion, i time domain orthogonal frequency division multiplexing receiving symbol $\tilde{r}\left(i\right)={[\tilde{r}(i,0),\tilde{r}(i,1),...,\tilde{r}(i,N-1)]}^T$ Can be expressed as:

$\tilde{r}\left(i\right)=H_t^i\tilde{s}\left(i\right)+\tilde{w}\left(i\right)=H_t^i{F}^{H}s\left(i\right)+\tilde{w}\left(i\right)$

Here

Be channel matrix,

Expression power is σ ²White Gaussian noise vector, F representes fourier transform matrix, () ^HThe operation of expression conjugate transpose; Balanced in order to carry out the single-order frequency domain equalization device, it is static earlier the channel hypothesis to be as the criterion, and promptly the variation of channel can be ignored in 1 OFDM symbol transmission time; Multipath channel is modeled as the FIR filter of constant finite impulse response when having the L-1 rank, uses h _l(i) expression l rank impulse response;

is a convolution matrix at this moment, can be expressed as

$H_t^i=F^H{\mathrm{\Λ}}^{i}F$

Here Λ ⁱBe diagonal matrix,

becomes frequency domain OFDM receiving symbol

to utilize the balanced frequency domain OFDM receiving symbol r (i) of single-order frequency domain equalization device through FFT, and the frequency domain orthogonal frequency-division multiplex singal estimated value

of equalizer output can be expressed as:

$\hat{s}\left(i\right)={\mathrm{\Λ}}^{\mathrm{iH}}{({\mathrm{\Λ}}^i{\mathrm{\Λ}}^{\mathrm{iH}}+{\mathrm{\σ}}^{2}I)}^{-1}r\left(i\right)$

Wherein I is the unit matrix of N * N,

is through parallel serial conversion; Separate mapping; Interweave, decoding obtains the estimated value

of transmitting terminal bit signal stream

Second step: the transmitting terminal bit signal estimated value

to obtaining is carried out CRC; If CRC is correct, then output; If CRC is incorrect, then carry out blocking equalizing, with the output of blocking equalizing input as parallel serial conversion in the first step,

Above-mentioned blocking equalizing method can be represented as follows:

A. the estimated value

of the transmitting terminal bit signal that obtains in first step stream is carried out the chnnel coding identical with transmitting terminal, interweaved, after the sign map, serial to parallel conversion, contrary FFT, obtains time domain orthogonal frequency division multiplexing reconstruction signal

B. with each time domain orthogonal frequency division multiplexing symbol that receives

Be divided into M isometric reception signal subspace piece, sub-piece is counted M and is satisfied:

And be 2 integral number power, here

Expression rounds operation downwards, and the length of every sub-block is T=N/M, T＞L, and the k sub-block can be expressed as ${\tilde{r}}_k\left(i\right)={[{\tilde{r}}_k(i,0),{\tilde{r}}_k(i,1),...,{\tilde{r}}_k(i,T-1)]}^T={[\tilde{r}(i,\mathrm{KT}),\tilde{r}(i,\mathrm{KT}+1),...,\tilde{r}(i,(k+1)T-1)]}^T,$ { 0, M-1} in the time of every sub-block transmission, thinks that the time change of wireless channel can be ignored, promptly to k ∈

N=kT ..., (k+1) T-1, l ∈ 0, L-1},

It is channel l rank impulse response this moment of the time of k sub-block transmission

Can be expressed as

${\tilde{r}}_k\left(i\right)=H_k^{\′}{\tilde{s}}_{k-1}\left(i\right)+H_k{\tilde{s}}_k\left(i\right)+{\tilde{w}}_k\left(i\right)$

Here ${\tilde{s}}_k\left(i\right)={[{\tilde{s}}_k(i,0),{\tilde{s}}_k(i,1),...,{\tilde{s}}_k(i,T-1)]}^T={[\tilde{s}(i,\mathrm{KT}),\tilde{s}(i,\mathrm{KT}+1),...,\tilde{s}(i,(k+1)T-1)]}^T,$

Having characterized k-1 signal subspace piece crosstalks to the sub-interblock that current k sub-block causes;

The time domain of reconstruct is sent signal

Being divided into length is the sub-piece of T ${\tilde{s}}_k^{\′}\left(i\right)={[{\tilde{s}}_k^{\′}(i,0),{\tilde{s}}_k^{\′}(i,1),...,{\tilde{s}}_k^{\′}(i,T-1)]}^T={[{\tilde{s}}^{\′}(i,\mathrm{KT}),{\tilde{s}}^{\′}(i,\mathrm{KT}+1),...,{\tilde{s}}^{\′}(i,(k+1)T-1)]}^T,$ Utilize Eliminate k-1 signal subspace piece the interblock that current k sub-block causes crosstalked,

${\tilde{r}}_k^{\′}\left(i\right)={\tilde{r}}_k\left(i\right)-H_k^{\′}{\tilde{s}}_{k-1}^{\′}\left(i\right)=H_k^{\′}({\tilde{s}}_{k-1}\left(i\right)-{\tilde{s}}_{k-1}^{\′}\left(i\right))+H_k{\tilde{s}}_k\left(i\right)+{\tilde{w}}_k\left(i\right)$

And carry out loop restructuring, and guaranteed the cycle characteristics of channel matrix, disturb between suppressing to carry,

${\tilde{r}}_k^{\′\′}\left(i\right)={\tilde{r}}_k^{\′}\left(i\right)+H_k^{\′}{\tilde{s}}_k^{\′}\left(i\right)=H_k^{\′}({\tilde{s}}_{k-1}\left(i\right)-{\tilde{s}}_{k-1}^{\′}\left(i\right))+H_k{\tilde{s}}_k\left(i\right)+H_k^{\′}{\tilde{s}}_k^{\′}\left(i\right)+{\tilde{w}}_k\left(i\right)$

If do not consider the error that reconstruct causes, promptly

then

${\tilde{r}}_k^{\′\′}\left(i\right)=H_{k,\mathrm{cir}}^{\′}{\tilde{s}}_k\left(i\right)+{\tilde{w}}_k\left(i\right)$

Convolution matrix H ' _{K, cir}=H _k+ H ' _kBe the corresponding channel matrix of k sub-block,

C. eliminate sub-interblock crosstalk with reconstruction cycle prefix basis on each is received sub-piece; Carry out FFT earlier; The length of its FFT is consistent with sub-block length, and each receives sub-piece to utilize the equilibrium of single-order frequency domain equalization device again, and the balanced valuation of the every sub-block after the equilibrium is through contrary FFT; Obtain the time domain equalization estimated value of every sub-block, the time domain equalization estimated value table of k sub-block is shown

${\hat{\tilde{s}}}_k\left(i\right)=F^H({\mathrm{\Λ}}_k^i{\mathrm{\Λ}}_k^{\mathrm{iH}}+{\mathrm{\σ}}_w^2{I}_T){\mathrm{\Λ}}_k^{\mathrm{iH}}F{\tilde{r}}_k^{\′\′}\left(i\right)$

Diagonal matrix

wherein

D. last balanced estimated value to every sub-block merges; The time domain equalization estimated value of every sub-block is that N symbol

obtains the piecemeal frequency-domain equilibrium method after FFT output promptly is the estimated value of the frequency domain orthogonal frequency-division multiplex singal that sends according to the synthetic length of the der group of piecemeal.

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