CN101136884B - Channel estimation method for TDS-OFDM system - Google Patents

Abstract

The method includes steps: using channel estimation (CE) result obtained from iteration at last time of previous frame or iteration at previous time of current frame as initial channel impulse response (CIR) for iteration at this time of current frame; based on CIR to remove interference on data block from pseudo random sequence (PRS), and carrying out circulating reconstruction for data block; equalizing the circulating reconstructed result, and carrying out partial judgment for equalized result; based on result of partial judgment and initial CIR to remove interference on PRS from data block, and carrying out circulating reconstruction for PRS; based on the circulating reconstructed result to re-estimate CIR, and considering the CIR as CE of iteration at this time of current frame. Carrying out partial judgment on data block of TDS-OFDM system to assist CE, the invention raises precision of CE, and reduces complexity of calculation.

Description

The channel estimation methods that is used for the TDS-OFDM system

Technical field

The present invention relates to digital information transmission technical field, particularly a kind of channel estimation methods that is used for the TDS-OFDM system.

Background technology

The problem that present wireless communication technology mainly solves is how to improve transmission rate in limited bandwidth reliably.OFDM (Orthogonal Frequency Division Multiplexing, OFDM) can in frequency selective fading channels, realize high rate data transmission reliably, be widely used in as in the wireless communication systems such as WLAN (wireless local area network), fixed wireless access, digital audio and video broadcasting.Current have two kinds of ofdm systems, and a kind of CP-OFDM system that is based on CP (Cyclic Prefix, Cyclic Prefix) adopts CP to fill protection at interval, and protection is located at interval between two OFDM symbols, is used for resisting the time delay expansion of channel.In transmission course, the linear convolution of OFDM symbol and channel impulse response relation is converted into the circular convolution relation, thereby can adopt simple frequency-domain equalization technology to carry out equilibrium to received signal in receiver based on the ofdm system of CP; Another kind is based on ZP (Zero Padding, zero padding) ZP-OFDM system, nil symbol has replaced the CP in the CP-OFDM system, thereby causing under the situation of channel response spectral null owing to the channel deep fade, still can guarantee that the ZP-OFDM system realizes that symbol recovers, referring to (Muquet B, Wang Z, Giannakis G.B, Courville M.de, and Duhamel P, Cyclic Prefixing or Zero Padding for Wireless Multicarrier Transmissions, IEEETrans.on Communications, 2002,50 (12): 2136-2148).In the CP-OFDM and ZP-OFDM system of coherent demodulation, channel impulse response is generally estimated by means of frequency pilot sign (corresponding to the Continuous Flow transmission mode) or targeting sequencing (corresponding to the burst transfer pattern).

In above-mentioned CP-OFDM and ZP-OFDM system, CP and ZP symbol are added the reduction that pilot tone and targeting sequencing have caused spectrum efficiency.For better utilization protection interval; proposed a kind of among the Chinese invention patent ZL01124144.6 " protection of ofdm system is fill method at interval " based on TDS (Time-Domain Synchronous; Domain Synchronous) ofdm system; in this TDS-OFDM system; with known pseudo random sequence filled between the OFDM symbol protection at interval; the pseudo random sequence of this filling can also be used for the synchronous and channel estimating of receiver except as the protection at interval.Referring to Fig. 1, be the frame assumption diagram of TDS-OFDM system, the TDS-OFDM signal frame comprises the pseudo random sequence of OFDM data block and filling, the time domain OFDM data piece { x that i the length of transmitting among the figure is N _n ⁽ⁱ⁾} _N=0 ^N-1It is the pseudo random sequence filled section { c of v that length is followed in the back _n ⁽ⁱ⁾} _N=0 ^V-1Thereby constituting i length is N ₂The TDS-OFDM of=N+v frame { the s that transmits _n ⁽ⁱ⁾} _N=0 ^N-1, suppose that the pseudo random sequence of filling adopts BPSK (Binary Phase Shift Keying, binary phase shift keying) modulation, and have following autocorrelation performance:

$R_c\left(m\right)=\underset{n=0}{\overset{v-1}{\mathrm{\Σ}}}{c}_n{c}_{n-m}^{*}\≈\mathrm{v\δ}\left(m\right)$

Wherein, δ (n) is discrete Dirac function.Suppose that the channel model that adopts is quasistatic L rank FIR (Finite ImpulseResponse, a finite impulse response) filter, and be subjected to the interference of additive white Gaussian noise.TDS-OFDM received signal frame { r then _n ⁽ⁱ⁾} _N=0 ^N-1With the TDS-OFDM frame { s that transmits _n ⁽ⁱ⁾} _N=0 ^N-1Between satisfy linear convolution relation:

$r_n^{\left(i\right)}=\underset{l=0}{\overset{L-1}{\mathrm{\&Sigma;}}}{h}_l^{\left(i\right)}{s}_{n-l}^{\left(i\right)}+w_n^{\left(i\right)},0\&le;n<{\mathrm{<figure-callout\; id="2"\; label="N"\; filenames="H2007101753018E00032.png,H2007101753018E00033.png"\; state="\{\{state\}\}">N</figure-callout>}}_2$

Wherein, w _n ⁽ⁱ⁾Be additive white Gaussian noise.If can in receiver, obtain the pseudo random sequence { c that fills _n ⁽ⁱ⁾} _N=0 ^V-1With channel impulse response { h _l ⁽ⁱ⁾} _L=0 ^L-1Linear convolution p as a result _n ⁽ⁱ⁾, promptly

$p_n^{\left(i\right)}=\underset{l=0}{\overset{L-1}{\mathrm{\&Sigma;}}}{h}_l^{\left(i\right)}{c}_{n-l}^{\left(i\right)}+w_n^{\left(i\right)},$

Channel impulse response can be estimated with the method for the direct linear correlation of time domain so.P to received signal _n ⁽ⁱ⁾With local known array { c _n ⁽ⁱ⁾} _N=0 ^V-1Doing cross-correlation can obtain

$R_{\mathrm{pc}}\left(m\right)=\underset{n=0}{\overset{v-1}{\mathrm{\&Sigma;}}}{p}_n^{\left(i\right)}{\left[c_{n-m}^{\left(i\right)}\right]}^{*}=v\underset{l=0}{\overset{L-1}{\mathrm{\&Sigma;}}}{h}_l\mathrm{\&delta;}(m-l)+\underset{n=0}{\overset{v-1}{\mathrm{\&Sigma;}}}{w}_n^{\left(i\right)}{\left[c_{n-m}^{\left(i\right)}\right]}^{*}.$

Thereby channel impulse response can be estimated with following formula

${\hat{h}}_l^{\left(i\right)}=\frac{1}{v}{R}_{\mathrm{pc}}\left(l\right).$

Perhaps, if can in receiver, obtain the pseudo random sequence { c that fills _n ⁽ⁱ⁾} _N=0 ^V-1With channel impulse response { h _l ⁽ⁱ⁾} _L=0 ^L-1Circular convolution q as a result _n ⁽ⁱ⁾, promptly

$q_n^{\left(i\right)}=\underset{l=0}{\overset{L-1}{\mathrm{\&Sigma;}}}{h}_l^{\left(i\right)}{c}_{{(n-l)}_{N_2}}^{\left(i\right)}+w_n^{\left(i\right)},$ 0≤n＜v，

Channel impulse response can be estimated with the calculating of circular convolution so.The computational methods of circular convolution have two kinds, and a kind of is the method for the direct circular correlation of time domain, and another kind is the auxiliary method of frequency domain FFT.Being calculated as follows shown in the formula of the circular convolution that FFT (Fast Fourier Transform, fast fourier transform) is auxiliary:

${\hat{h}}_n^{\left(i\right)}={\mathrm{IFFT}}^v\left[\frac{{\mathrm{FFT}}^v\left[q_n^{\left(i\right)}\right]}{{\mathrm{FFT}}^v\left[c_n^{\left(i\right)}\right]}\right]$

Wherein, FFT ^M[] and IFFT ^M[] represents that respectively length is FFT and IFFT (Inverse Fast Fourier Transform, inverse fast fourier transform), the M=v here of M.

In the TDS-OFDM system, the protection that pseudo random sequence is filled has replaced the protection interval that traditional CP fills or ZP fills at interval.When the TDS-OFDM signal passes through frequency selective fading channels, at TDS-OFDM frame { s _n ⁽ⁱ⁾} _N=0 ^N-1In, OFDM data block { x _n ⁽ⁱ⁾} _N=0 ^N-1Can disturb the pseudo random sequence { c that fills _n ⁽ⁱ⁾} _N=0 ^N-1, vice versa, also has the interference between padding sequence and the OFDM data block simultaneously in the TDS-OFDM frame.The ideal linearity convolution results of definition pseudo random sequence is for removing the linear convolution result of OFDM data block influence fully.The Ideal Cycle convolution results of definition pseudo random sequence is for removing the circular convolution result of OFDM data block influence fully.Because the pseudo random sequence of filling is known to receiver, therefore under the situation of known channel impulse response, eliminate the interference of pseudo random sequence easily to the OFDM data block; On the contrary, because the OFDM data block of emission is at random, and may be subjected to noise jamming, even under the situation of known channel impulse response, eliminating the OFDM data block also is difficult to the interference of the pseudo random sequence of filling, thereby the ideal linearity convolution results of pseudo random sequence that can not obtain launching in receiver and channel impulse response or Ideal Cycle convolution results promptly can not obtain more precise channels estimation.

In the Chinese invention patent 200510012127.6 " the iteration elimination method that pseudo random sequence is filled in a kind of OFDM modulating system " a kind of method that adopts the iteration elimination method to remove the pseudo random sequence of filling is proposed, this method is at first calculated the linear convolution of pseudo random sequence and channel impulse response, then remove the influence of pseudo random sequence to data block, then data block is carried out frequency domain equalization, remove the influence of data block at last, thereby obtain more precise channels estimation pseudo random sequence.But need know the channel estimating of continuous two the OFDM symbols in front when adopting this method to carry out channel estimating, and all need repeatedly iteration just can obtain channel estimating more accurately, the computing complexity each OFDM symbol.

Summary of the invention

In order to reduce the computational complexity of channel estimating in the TDS-OFDM system, the invention provides the channel estimation methods of a kind of TDS-OFDM of being used for system.Described technical scheme is as follows:

The invention provides the channel estimation methods of a kind of TDS-OFDM of being used for system, described method comprises:

Steps A: previous frame is last or channel estimating that the last iteration of present frame obtains is as the initial channel impulse response of this iteration of present frame, remove in the described present frame pseudo random sequence to the interference of data block according to described initial channel impulse response, and carry out the cyclic reconstruction of described data block;

Step B: described cyclic reconstruction result is carried out equilibrium, and the result of described equilibrium is carried out the part judgement;

Step C: result and described initial channel impulse response according to described part judgement are removed the interference of described data block to described pseudo random sequence, and carry out the cyclic reconstruction of described pseudo random sequence;

Step D: the cyclic reconstruction result of the pseudo random sequence of disturbing according to described removal data block reappraises channel impulse response, and with the channel estimating of described channel impulse response as described this iteration of present frame.

Remove the interference of pseudo random sequence according to described initial channel impulse response in the described steps A, and it is as follows to carry out the concrete steps of cyclic reconstruction of described data block to data block:

Calculate the circular convolution of pseudo random sequence and described initial channel impulse response, the result of described circular convolution is the interference of described pseudo random sequence to data block;

Make up the circular convolution of the channel impulse response of described data block and described this iteration according to the next frame of described present frame and described present frame;

In the circular convolution result of described data block and described initial channel impulse response, remove of the interference of described pseudo random sequence, obtain the cyclic reconstruction result of described data block described data block.

Among the described step B described cyclic reconstruction result being carried out balanced step specifically comprises:

Described cyclic reconstruction result is carried out the FFT conversion;

Described initial channel impulse response is carried out the FFT conversion, carry out conjugate operation by element then;

The result of described conjugate operation and the described result that described cyclic reconstruction result is carried out the FFT conversion are carried out dot product, obtain balanced result.

The step of among the described step B result of described equilibrium being carried out the part judgement specifically comprises:

Described initial channel impulse response is carried out the FFT conversion, and ask for described transformation results absolute value square;

The result of described equilibrium is carried out the part judgement of in-phase component and quadrature component respectively according to the optimal judgement interval parameter in described square of result, constellation symbol and planisphere space.

Described step C specifically comprises:

Calculate the circular convolution of described data block and described initial channel impulse response, the result of described circular convolution is the interference of described data block to described pseudo random sequence;

Make up the circular convolution of the channel impulse response of described pseudo random sequence and this iteration according to the next frame of described present frame and described present frame;

In the circular convolution result of the channel impulse response of described pseudo random sequence and described this iteration, remove of the interference of described data block, obtain the cyclic reconstruction result of described pseudo random sequence described pseudo random sequence.

Described step D specifically comprises:

The cyclic reconstruction result of the pseudo random sequence that described removal data block is disturbed carries out the FFT conversion;

Described pseudo random sequence is carried out the FFT conversion;

Described cyclic reconstruction result's the FFT transformation results and the FFT transformation results of described pseudo random sequence are divided by, described phase division result is carried out the IFFT conversion obtain new channel impulse response, and with the channel estimating of described new channel impulse response as described this iteration of present frame.

The beneficial effect of technical scheme provided by the invention is:

The present invention disturbs removal and channel estimating by making up circular convolution, has reduced the computing length of FFT/IFFT; Adjudicate assisted channel estimation by part, accelerated the convergence rate of iteration; And by in channel estimating, adopting the part judgement, reduced the complexity of algorithm, made channel estimation results more accurate.

Description of drawings

Fig. 1 is the frame assumption diagram of TDS-OFDM system in the prior art;

Fig. 2 is the baseband model figure of the TDS-OFDM system that provides of the embodiment of the invention;

Fig. 3 is the iterative process schematic diagram of the channel estimation methods that is used for the TDS-OFDM system that provides of the embodiment of the invention;

Fig. 4 is the flow chart of the channel estimation methods that is used for the TDS-OFDM system that provides of the embodiment of the invention;

Fig. 5 is a schematic diagram between the part decision area of the QPSK signal that provides of the embodiment of the invention;

Fig. 6 is a schematic diagram between the part decision area of the 16-QAM signal that provides of the embodiment of the invention;

Fig. 7 is the situation of change schematic diagram of the channel estimation errors of the emulation under channel I that provides of the embodiment of the invention with iterations;

Fig. 8 is the situation of change schematic diagram of the channel estimation errors of the emulation under channel II that provides of the embodiment of the invention with iterations;

Fig. 9 is the BER simulation curve figure of TDS-OFDM system under multipath channel of the employing QPSK planisphere that provides of the embodiment of the invention;

Figure 10 is the BER simulation curve figure of TDS-OFDM system under multipath channel of the employing 16-QAM planisphere that provides of the embodiment of the invention.

Embodiment

For making the purpose, technical solutions and advantages of the present invention clearer, embodiment of the present invention is described further in detail below in conjunction with accompanying drawing.

When the embodiment of the invention is carried out channel estimating,, and the data block of TDS-OFDM frame is carried out part adjudicate, improved the convergence rate of iteration, reduced the complexity of computing with assisted channel estimation by the structure circular convolution.

TDS-OFDM frame general reference TDS-OFDM received signal frame in the embodiment of the invention, and the pseudo random sequence of filling in each frame that transmits in the TDS-OFDM signal is identical.Referring to Fig. 2, be the baseband model figure of TDS-OFDM system, S/P and P/S represent serial/parallel conversion and parallel/serial conversion respectively among the figure, AWGN (Additive White Gaussian Noise) represents additive white Gaussian noise.I OFDM frequency domain transmission data block { X among the figure _k ⁽ⁱ⁾} _K=0 ^N-1At first through obtaining i OFDM data block { x after the IFFT conversion _n ⁽ⁱ⁾} _N=0 ^N-1, as the formula (1), wherein N represents the length of IFFT.

$x_n^{\left(i\right)}=\frac{1}{\sqrt{N}}\underset{k=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{X}_k^{\left(i\right)}{e}^{\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="H2007101753018E00032.png,H2007101753018E00033.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;nk}/N},$ 0≤n＜N； (1)

Secondly, at each OFDM data block { x waiting for transmission _n ⁽ⁱ⁾} _N=0 ^N-1Insert a fixing pseudo random sequence { c afterwards _n} _N=0 ^V-1, constitute i the TDS-OFDM frame that transmits

As the formula (2), N wherein ₂=N+v.

$s_n^{\left(i\right)}=\left\{\begin{array}{cc}{x}_n^{\left(i\right)},& 0\&le;n<N\\ c_{n-N},& N\&le;n<N_2\end{array}\right.---\left(2\right)$

Suppose that the channel model that adopts is quasistatic L rank FIR filters, and be subjected to AWGN noise w _n ⁽ⁱ⁾Interference.If the length of the pseudo random sequence of filling is not less than channel length, i.e. v 〉=L-1 is so corresponding to i the TDS-OFDM frame that transmits TDS-OFDM received signal frame be r _n ⁽ⁱ⁾, as the formula (3), wherein, h _l ⁽ⁱ⁾Be channel impulse response,

L is to N in expression ₂Delivery.

$r_n^{\left(i\right)}=\underset{l=0}{\overset{L-1}{\mathrm{\&Sigma;}}}{h}_l^{\left(i\right)}{s}_{{(n-l)}_{N_2}}^{\left(i\right)}+w_n^{\left(i\right)},$ 0≤n＜N ₂ (3)

What fill in the frame because each TDS-OFDM transmits is the pseudo random sequence of fixing, in frequency selective fading channels, pseudo random sequence in i-1 TDS-OFDM frame is for i TDS-OFDM frame, the CP that just is equivalent to the CP-OFDM system, thus can with transmit and channel impulse response between linear convolution relation be converted to the circular convolution relation that formula (3) is described.

Referring to Fig. 3, the channel estimation methods that is used for the TDS-OFDM system that the embodiment of the invention provides is to carry out with the form of iteration, and adopt the part of data block is adjudicated with assisted channel estimation, on the basis of the TDS-OFDM of foregoing description system, referring to Fig. 4, the embodiment of the invention provides the channel estimation methods of a kind of TDS-OFDM of being used for system, specifically may further comprise the steps:

Step 101: the Initial Channel Assignment impulse response is provided with iteration label I and iterations J.

Wherein, Initial Channel Assignment impulse response detailed process is as follows:

Channel impulse response at i TDS-OFDM frame of initialization

The time, if channel estimator just starts working, promptly when i=1, channel impulse response Be initialized as complete zero; Otherwise previous frame is last or channel estimation results that the last iteration of present frame obtains is as the initial channel impulse response of this iteration, promptly

Or

Iteration label I is set to 0 during initialization, i.e. I=0; Iterations J 〉=1.

Step 102: remove in the present frame pseudo random sequence to the interference of data block, the cyclic reconstruction of the line data piece of going forward side by side according to the initial channel impulse response.

Detailed process is as follows:

1) calculates pseudo random sequence c _nWith the initial channel impulse response

Circular convolution

Be pseudo random sequence c _nInterference to data block.Circular convolution

The frequency-domain calculations method as the formula (4), wherein ⊙ represents dot product (multiplying each other by element).

2) according to present frame r _n ⁽ⁱ⁾Next frame r with present frame _N+N ⁽ⁱ⁾Make up data block x _n ⁽ⁱ⁾And channel impulse response h _n ⁽ⁱ⁾Circular convolution y as a result _n ⁽ⁱ⁾, as the formula (5), channel impulse response h _n ⁽ⁱ⁾The channel impulse response of representing this iteration, the circulation result has comprised pseudo random sequence c _nTo data block x _n ⁽ⁱ⁾Interference.

$y_n^{\left(i\right)}=\left\{\begin{array}{cc}{r}_n^{\left(i\right)}+r_{n+N}^{\left(i\right)},& 0\&le;n<L\\ r_n^{\left(i\right)},& L\&le;n<N\end{array}\right.---\left(5\right)$

3) at above-mentioned circular convolution y as a result _n ⁽ⁱ⁾The middle pseudo random sequence c that removes _nTo data block x _n ⁽ⁱ⁾Interference As the formula (6), obtain data block x _n ⁽ⁱ⁾The cyclic reconstruction result

Or

${\hat{y}}_n^{\left(i\right)}={\tilde{r}}_n^{\left(i\right)}=\left\{\begin{array}{cc}{y}_n^{\left(i\right)}-{\hat{q}}_n^{\left(i\right)},& 0\&le;n<L\\ y_n^{\left(i\right)},& L\&le;n<N\end{array}\right.---\left(6\right)$

With respect to linear convolution, the FFT/IFFT computing length of circular convolution is little, therefore in the above-mentioned steps, by making up pseudo random sequence and the circular convolution of initial channel impulse response and the circular convolution of reconstructed data block and channel impulse response, reduced the computing length of FFT/IFFT, improve the convergence rate of iteration, reduced computational complexity.

Step 103: to data block x _n ⁽ⁱ⁾The cyclic reconstruction result

Carry out equilibrium, the result to equilibrium carries out the part judgement then.

Equilibrium comprises phase equalization and amplitude equalization, and it is right that the equilibrium in the present embodiment refers to

Carry out phase equalization.Right

The process of carrying out phase equalization is specific as follows:

1) respectively to the cyclic reconstruction result

With the initial channel impulse response Carry out the FFT conversion, obtain

With

That is, ${\hat{Y}}_k^{\left(i\right)}={\mathrm{FFT}}^N\left[{\hat{y}}_n^{\left(i\right)}\right],$ ${\hat{H}}_k^{\left(i\right)}={\mathrm{FFT}}^N\left[{\hat{h}}_n^{\left(i\right)}\right].$

2) right

Carry out conjugate operation by element, will

By element carry out conjugate operation the result and

Carry out dot product, obtain

Balanced result

As the formula (7), wherein () ^*Expression is carried out conjugate operation by element.

Result to above-mentioned equilibrium

The detailed process of carrying out the part judgement is as follows:

According to the result of formula (8) to equilibrium

Carry out the part judgement, wherein

Expression

The result of part judgement,

X represents constellation symbol, Θ ₁And Θ ₂Expression planisphere space dividing; As can be seen, at interval Θ ₁Right

Carry out hard decision, at interval Θ ₂Right

Carry out zero judgement.

${\hat{X}}_k^{\left(i\right)}=\left\{\begin{array}{cc}{\min }_X|{\hat{Z}}_k^{\left(i\right)}-{\mathrm{\&eta;}}_k^{\left(i\right)}X|,& {\hat{Z}}_k^{\left(i\right)}\&Element;{\mathrm{\&Theta;}}_1\\ 0,& {\hat{Z}}_k^{\left(i\right)}\&Element;{\mathrm{\&Theta;}}_2\end{array}\right.---\left(8\right)$

Further, for QPSK (Quadrature Phase Shift Keying, orthogonal PSK) planisphere, right

Carrying out the part judgement is by right In-phase component and quadrature component adjudicate respectively and obtain, detailed process is as follows: suppose the in-phase component of constellation symbol X and the equal value of quadrature component in assemble of symbol [1 ,+1], right

In-phase component Carry out the part judgement according to formula (9).

Wherein, α represents the optimal judgement interval parameter in QPSK planisphere space, 0＜α＜1, Expression

The result of part judgement, and

Be

In-phase component.Referring to Fig. 5, between part decision area for the QPSK signal.Right

Quadrature component to carry out the method for part judgement identical with in-phase component.

Further, for 16-QAM (QuadratureAmplitude Modulation, quadrature amplitude modulation) planisphere, right

Carrying out the part judgement also is by right

In-phase component and quadrature component adjudicate respectively and obtain, detailed process is as follows: suppose the in-phase component of constellation symbol X and the equal value of quadrature component in assemble of symbol [3 ,-1 ,+1 ,+3], right In-phase component

Carry out the part judgement according to formula (10).

Wherein, β represents the optimal judgement interval parameter in 16-QAM planisphere space, 0＜β＜1,

Expression

The result of part judgement, and

Be

In-phase component.Referring to Fig. 6, between part decision area for the 16-QAM signal.Right

Quadrature component to carry out the method for part judgement identical with in-phase component.

Step 104: remove data block x _n ⁽ⁱ⁾To pseudo random sequence c _nInterference, and carry out pseudo random sequence c _nCyclic reconstruction.

Detailed process is as follows:

1) according to the data block x that obtains in the step 103 _n ⁽ⁱ⁾The part court verdict

Calculated data piece x _n ⁽ⁱ⁾With the initial channel impulse response

Circular convolution

It is data block x _n ⁽ⁱ⁾To pseudo random sequence c _nInterference.Circular convolution

The frequency-domain calculations method as the formula (11):

2) according to present frame r _n ⁽ⁱ⁾Next frame r with present frame _N+N ⁽ⁱ⁾Make up pseudo random sequence c _nAnd channel impulse response h _n ⁽ⁱ⁾Circular convolution y as a result _n ⁽ⁱ⁾, as the formula (12), this result has comprised data block x _n ⁽ⁱ⁾To pseudo random sequence c _nInterference.

$y_n^{\left(i\right)}=r_n^{\left(i\right)}+r_{n+N}^{\left(i\right)},0\&le;n<L---\left(12\right)$

3) at circular convolution y as a result _n ⁽ⁱ⁾The middle data block x of removing _n ⁽ⁱ⁾To pseudo random sequence c _nInterference

As the formula (13), obtain the cyclic reconstruction result of pseudo random sequence

${\tilde{q}}_n^{\left(i\right)}=\left\{\begin{array}{cc}{y}_n^{\left(i\right)}-{\hat{r}}_n^{\left(i\right)},& 0\&le;n<L\\ y_n^{\left(i\right)},& L\&le;n<v\end{array}\right.---\left(13\right)$

Step 105: upgrade channel estimating.

According to pseudo random sequence c _nThe cyclic reconstruction result

Reappraise channel impulse response, and the channel impulse response that will obtain after will reappraising

Channel estimation results as this iteration of present frame.Channel impulse response

The frequency-domain calculations method of zero forcing algorithm as the formula (14).

${\tilde{h}}_n^{\left(i\right)}={\mathrm{IFFT}}^v\left[{\mathrm{FFT}}^v\right[{\tilde{q}}_n^{\left(i\right)}]/{\mathrm{FFT}}^v[c_n\left]\right],0\&le;n<v---\left(14\right)$

Step 106: make I=I+1, judge the iterations J whether iteration label I equals to set in advance, if then finish channel estimating; Otherwise, return step 101.

Based on foregoing description, the channel estimation methods that is used for the TDS-OFDM system that the embodiment of the invention is provided has carried out Computer Simulation.Referring to table 1, be the system parameters that adopts in the emulation.Adopted two multipath channel models in the emulation: channel I and channel II referring to table 2, are the multipath channel parameter that adopts in the emulation.Suppose that two multipath channels all obey independently Rayleigh fading, and channel impulse response is normalized, so that the power after allowing signal by multipath channel remains unchanged, the judgement interval parameter of QPSK planisphere is got α=0.1875, and the judgement interval parameter of 16-QAM planisphere is got β=0.0938.

Table 1

Title	Value
		Subcarrier number (FFT length) N	3780
The subcarrier planisphere	4-QAM，16-QAM
		Baseband signalling speed	7.56MHz
Pseudo random sequence length v	420

Table 2

Referring to Fig. 7, be the channel estimation errors of emulation under channel I situation of change figure with iterations; Referring to Fig. 8, be the channel estimation errors of emulation under channel II situation of change figure with iterations.It is static that channel I and channel II are assumed to be.Channel estimation errors ξ is defined as:

$\mathrm{\&xi;}=\sqrt{\underset{l=0}{\overset{L-1`}{\mathrm{\&Sigma;}}}{|{\hat{h}}_l-h_k|}^2}$

Wherein,

And h _lRepresent estimated channel impulse response and real channel impulse response respectively.As can be seen from Figures 7 and 8, through 3 to 4 times interative computation, channel estimation errors has not almost just reduced.In quasistatic or the channel that slowly changes, if, can need not to obtain channel impulse response estimation performance more accurately under the situation of iteration with the channel impulse response of previous symbol initial channel impulse response as next symbol.

Fig. 9 is for adopting BER (Bit Error Rate, the error rate) the simulation curve figure of TDS-OFDM system under multipath channel of QPSK planisphere, and transverse axis is the signal to noise ratio E of each bit among the figure _b/ N ₀, maximum doppler frequency is made as 18Hz, so that channel is approximate constant in a TDS-OFDM symbol, but channel changes to next symbol from a TDS-OFDM symbol; 900 continuous TDS-OFDM symbols are carried out emulation calculate the error rate, but the error code of two TDS-OFDM symbols that begin is not most added up; Minimum lower bound among the figure is represented the error rate under the ideal communication channel estimation condition.As can be seen from the figure, under channel I and channel II, adopt the method for the channel estimating that present embodiment provides, (J=0) can approach minimum lower bound to the error rate of the TDS-OFDM system that obtains under the situation of iteration need not.

Figure 10 is for adopting the BER simulation curve figure of TDS-OFDM system under multipath channel of 16-QAM planisphere, by the conclusion that can obtain being similar to the QPSK system among the figure.

The embodiment of the invention is carried out channel estimating by the circular convolution that makes up data block and channel impulse response, makes FFT/IFFT computing length minimum; By the very little part judgement assisted channel estimation of time-delay, be convenient to accelerate the convergence rate of iteration; And adopt the part judgement in channel estimating, make estimated result more accurate, this method need not iteration under the channel circumstance of slowly conversion just can make error rate of system reach minimum lower bound.

Above specific embodiments of the invention are had been described in detail, but the present invention is not restricted to the foregoing description.Within the spirit and principle of claim of the present invention, any modification of being done, be equal to and replace and improvement etc., all should be included within protection scope of the present invention.

Claims (6)

1. a channel estimation methods that is used for the TDS-OFDM system is characterized in that, at the TDS-OFDM system receiving terminal, described channel estimation methods comprises:

Steps A: previous frame is last or channel estimating that the last iteration of present frame obtains is as the initial channel impulse response of this iteration of present frame, remove in the described present frame pseudo random sequence to the interference of data block according to described initial channel impulse response, and carry out the cyclic reconstruction of described data block;

Step B: described cyclic reconstruction result is carried out equilibrium, and the result of described equilibrium is carried out the part judgement;

Step C: result and described initial channel impulse response according to described part judgement are removed the interference of described data block to described pseudo random sequence, and carry out the cyclic reconstruction of described pseudo random sequence;

Step D: the cyclic reconstruction result of the pseudo random sequence of disturbing according to described removal data block reappraises channel impulse response, and with the channel estimating of described channel impulse response as described this iteration of present frame.

2. the channel estimation methods that is used for the TDS-OFDM system according to claim 1, it is characterized in that, remove in the described present frame pseudo random sequence to the interference of data block according to described initial channel impulse response in the described steps A, and the step of carrying out the cyclic reconstruction of described data block comprises specifically:

Calculate the circular convolution of pseudo random sequence and described initial channel impulse response, the result of described circular convolution is the interference of described pseudo random sequence to data block;

Make up the circular convolution of the channel impulse response of described data block and described this iteration according to the next frame of described present frame and described present frame;

In the circular convolution result of described data block and described initial channel impulse response, remove of the interference of described pseudo random sequence, obtain the cyclic reconstruction result of described data block described data block.

3. the channel estimation methods that is used for the TDS-OFDM system according to claim 1 is characterized in that, among the described step B described cyclic reconstruction result is carried out balanced step and specifically comprises:

Described cyclic reconstruction result is carried out the FFT conversion;

Described initial channel impulse response is carried out the FFT conversion, carry out conjugate operation by element then;

The result of described conjugate operation and the described result that described cyclic reconstruction result is carried out the FFT conversion are carried out dot product, obtain balanced result.

4. the channel estimation methods that is used for the TDS-OFDM system according to claim 1 is characterized in that, the step of among the described step B result of described equilibrium being carried out the part judgement specifically comprises:

Described initial channel impulse response is carried out the FFT conversion, and ask for described transformation results absolute value square;

The result of described equilibrium is carried out the part judgement of in-phase component and quadrature component respectively according to the optimal judgement interval parameter in described square of result, constellation symbol and planisphere space.

5. the channel estimation methods that is used for the TDS-OFDM system according to claim 1 is characterized in that, described step C specifically comprises:

Calculate the circular convolution of described data block and described initial channel impulse response, the result of described circular convolution is the interference of described data block to described pseudo random sequence;

Make up the circular convolution of the channel impulse response of described pseudo random sequence and this iteration according to the next frame of described present frame and described present frame;

In the circular convolution result of the channel impulse response of described pseudo random sequence and described this iteration, remove of the interference of described data block, obtain the cyclic reconstruction result of described pseudo random sequence described pseudo random sequence.

6. the channel estimation methods that is used for the TDS-OFDM system according to claim 1 is characterized in that, described step D specifically comprises:

The cyclic reconstruction result of the pseudo random sequence that described removal data block is disturbed carries out the FFT conversion;

Described pseudo random sequence is carried out the FFT conversion;

Described cyclic reconstruction result's the FFT transformation results and the FFT transformation results of described pseudo random sequence are divided by, described phase division result is carried out the IFFT conversion obtain new channel impulse response, and with the channel estimating of described new channel impulse response as described this iteration of present frame.

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