CN101800729A - Downlink timing synchronization method and system based on timing deviation compensation - Google Patents

Abstract

The invention discloses a downlink timing synchronization method and system based on timing deviation compensation. The method comprises the following steps of: detecting conjugate peak values to acquire relevant results; finding the highest peak value M0 and a sampling point moment d0 corresponding to the highest peak value in the relevant results; and forwards translating the sampling point moment d0 corresponding to the peak value, giving the sampling point number delta d of the timing deviation compensation, and then determining the symbol timing synchronization positions according to the sampling point moment d0 and the sampling point number delta d. The invention can effectively reduce or avoid the interference among symbols, caused by multi-path time delays, and solve the problem of the symbol timing synchronization of multi-path channels.

Description

Down link time synchronization method and system based on the timing offset compensation

Technical field

The present invention relates to IEEE802.16e system down link simultaneous techniques field, relate in particular to down link time synchronization method and system based on the timing offset compensation.

Background technology

IEEE802.16e is as the air interface specification of mobile wide-band wire-less accessing system, by industry be considered as present unique can with the NGBW technology of 3G competition.OFDM (OFDM, Orthogonal frequency division multiplexing) technology converts data flow at a high speed to a plurality of parallel low rate data streams by serial to parallel conversion, convert frequency selective fading channels to a plurality of parallel flat fading channels, has stronger anti-intersymbol interference (ISI, inter symbol interference) ability becomes one of physical layer core technology of 802.16e system.Compare with single-carrier system, multicarrier system requires to keep between the subcarrier strict orthogonality, and is therefore responsive more to carrier wave frequency deviation and timing synchronization.

At present based on the real system of OFDM stationary problem regularly, main method is to utilize training sequence cross-correlation and autocorrelation performance carry out timing synchronously preferably.At the ofdm system down link based on the IEEE802.16e standard, prior art utilizes the conjugate symmetry of training sequence to realize timing synchronization.Half carries out relevantly this method with received signal the first half in a symbolic range and back, correlated results is carried out peak value detects, with the peak value corresponding sampling points as regularly synchronous symbol original position.But this method only has preferable performance under white Gaussian noise (AWGN) channel.Correlated results has only a sharp-pointed peak value under awgn channel, and peak value detects just can find regularly sync bit.Yet a plurality of obvious peak value can appear in correlated results under multipath channel, and the strongest footpath of energy is the effective diameter that arrives of article one not necessarily, so there is timing offset in peak-value detection method.

As shown in Figure 1, under the awgn channel, the correlated results that receiving terminal adopts the conjugation symmetry algorithm to obtain to received signal has and only has a sharp-pointed peak value, and the peak value corresponding sampling points promptly is the position of OFDM sign-on, detects by peak value and then can obtain accurate timing synchronously.Yet under multidiameter fading channel, what receiving terminal received is the stack of different amplitude different delayed time signals, and the correlated results that utilizes the conjugation symmetry algorithm to obtain no longer has only a sharp-pointed peak value, but the different obvious peak value of a plurality of amplitudes occurs.Each obvious peak value is corresponding to a multipath component of signal, just corresponding to a multipath of channel.And the most powerful path of peak-peak correspondence not necessarily appears at first footpath.

For example, Fig. 2-Fig. 5 has carried out emulation to the symmetry of the conjugation under walking B 3km/h and speed of a motor vehicle A 60km/h channel peak-value detection method respectively, obtains two kinds of correlated results.Channel produces a frame at random in the emulation, and signal to noise ratio is 10dB.

Fig. 2 and Fig. 3 are first kind of correlated results under walking B 3km/h and the speed of a motor vehicle A 60km/h channel.As can be seen, the footpath that energy is the strongest in this case is the effective diameter that article one arrives just.If adopt conjugation symmetry peak detection algorithm, peak value corresponding sampling points, the just in time position that begins of is-symbol.

Fig. 4 and Fig. 5 are respectively second kind of correlated results under walking B 3km/h and the speed of a motor vehicle A 60km/h channel.At this moment, the footpath that energy is the strongest is not the effective diameter that article one arrives, and there are several sampled point time-delays in the footpath that energy is the strongest with respect to first footpath.If adopt conjugation symmetry peak value to detect the calculation method, as the symbol original position, regularly sync bit has postponed several sampled points than real symbol original position with the corresponding sampled point of the peak-peak in the correlated results, produces regularly synchronous error.

Hence one can see that, the correlated results of conjugation symmetry has two kinds of situations under multipath channel, if be first kind of situation, conjugation symmetry peak-value detection method can not be affected, if be second kind of situation, conjugation symmetry peak-value detection method carries out timing and will occur synchronously than large deviation, and the performance of method is had a strong impact on.

Summary of the invention

The object of the present invention is to provide a kind of down link time synchronization method and system based on the timing offset compensation.Based on the present invention, the intersymbol interference that can effectively reduce or avoid multidiameter delay to cause has solved the timing synchronization problem of multipath channel.

The invention provides a kind of down link time synchronization method, comprise the steps: peak detection step, the receiving sequence of obtaining is carried out the detection of conjugate peak values, obtain correlated results based on the timing offset compensation; Sampled point is determining step constantly, finds peak-peak M in described correlated results ₀, described peak-peak corresponding sampling points d constantly ₀Timing synchronization position determining step is with described peak value corresponding sampling points moment d ₀Translation forward, the sampled point number Δ d of timing offset compensation given in advance is according to described sampled point moment d ₀Determine the timing synchronization position with described sampled point number Δ d

Above-mentioned down link time synchronization method, in the preferred described peak detection step, the described correlated results that obtains is determined according to following formula:

$M\left[n\right]=\underset{i=1}{\overset{N/2-1}{\mathrm{\Σ}}}r[n+N/2-i]\×r[n+N/2+i]$

Wherein, M[n] be described correlated results, n is the sampled point label, 0＜n≤N, N are the sampled point number that the OFDM symbol lengths is comprised.

Above-mentioned down link time synchronization method, in the preferred sampled point moment determining step, the correlated results peak-peak M that obtains ₀With described peak-peak corresponding sampling points moment d ₀Determine according to following formula:

M ₀＝max(M[n])，d ₀＝argmax(M[n])

Above-mentioned down link time synchronization method, preferred described timing synchronization position

In the determining step, described timing synchronization position

Determine according to following formula:

$\hat{d}=d_0-\mathrm{\Δd}.$

On the other hand, the present invention also provides a kind of down link timing synchronization sytem based on the timing offset compensation, comprising: peak detection block, be used for the receiving sequence of obtaining is carried out the detection of conjugate peak values, and obtain correlated results; Sampled point is d constantly ₀Determination module is used for finding peak-peak M at described correlated results ₀, described peak-peak corresponding sampling points d constantly ₀The timing synchronization position

Determination module is used for described peak value corresponding sampling points moment d ₀Translation forward, the sampled point number Δ d of given timing offset compensation is according to described sampled point moment d ₀Determine the timing synchronization position with described sampled point number Δ d

Above-mentioned down link timing synchronization sytem, in the preferred described peak detection block, the described correlated results that obtains is determined according to following formula:

$M\left[n\right]=\underset{i=1}{\overset{N/2-1}{\mathrm{\Σ}}}r[n+N/2-i]\×r[n+N/2+i]$

Wherein, M[n] be described correlated results, n is the sampled point label, N is the sampled point number that the OFDM symbol lengths is comprised.

Above-mentioned down link timing synchronization sytem, preferred described sampled point is d constantly ₀In the determination module, the correlated results peak-peak M that obtains ₀With described peak-peak corresponding sampling points moment d ₀Determine according to following formula:

M ₀＝max(M[n])，d ₀＝arg?max(M[n])。

Above-mentioned down link timing synchronization sytem, preferred described timing synchronization position

In the determination module, described timing synchronization position

Determine according to following formula:

$\hat{d}=d_0-\mathrm{\Δd}.$

In terms of existing technologies, the present invention has following beneficial effect:

The first, the correlated results of conjugation symmetry has two kinds of situations under multipath channel, first kind of the strongest footpath of correlated results energy is the effective diameter that article one arrives just, second kind of the strongest footpath of correlated results energy is not the effective diameter that article one arrives, and there are several sampled point time-delays in the footpath that energy is the strongest with respect to first footpath.If the received signal auto-correlation obtains first kind of correlated results, most powerful path is first footpath just, compensation Δ d makes that regularly sync bit drops in the undisturbed CP zone, comprises last several sampled points of current OFDM symbol and itself CP in the FFT window, can not influence regularly net synchronization capability; If the received signal auto-correlation obtains second kind of correlated results, most powerful path postpones several sampled points than first footpath, and compensation Δ d makes the position of FFT window shift to an earlier date, and has reduced the possibility that comprises next symbol data in the FFT window, has avoided intersymbol interference.

The second, the inventive method fully takes into account under the multidiameter fading channel the not necessarily situation of most powerful path of first footpath, finds the original position of OFDM symbol by the timing offset compensation.Simulation result under Pedestrian B 3km/hIMT-2000 and Vehicular A 60km/h channel shows that along with the increase of signal to noise ratio, the bit error rate performance of using the inventive method system is significantly improved.

Three, the inventive method at first adopts and carries out auto-correlation to received signal.Then, the peak-peak corresponding sampling points of correlated results is carried out the timing offset compensation constantly; Make the FFT window as far as possible in advance, the initial moment of symbol is positioned not to be subjected in the CP scope that multipath disturbs, thereby the intersymbol interference that reduces or avoid multidiameter delay to cause has solved the timing synchronization problem of multipath channel.

Description of drawings

The correlated results that Fig. 1 adopts the conjugation symmetry approach to obtain for receiving terminal under the awgn channel to received signal;

Fig. 2 is the following first kind of correlated results of walking B 3km/h channel;

Fig. 3 is the following first kind of correlated results of speed of a motor vehicle A 60km/h channel;

Fig. 4 is the following second kind of correlated results of walking B 3km/h channel;

Fig. 5 is the following second kind of correlated results of speed of a motor vehicle A 60km/h channel;

Fig. 6 receives the schematic diagram of the time-domain signal of two different delayed time for receiving terminal under the multipath channel;

Fig. 7 A is the flow chart of steps that the present invention is based on the down link time synchronization method embodiment of timing offset compensation;

Fig. 7 B is the step data flow graph that the present invention is based on the down link time synchronization method embodiment of timing offset compensation;

Fig. 8 is the curve that the timing offset average changes with signal to noise ratio;

Fig. 9 be conjugation symmetry approach and the down link time synchronization method based on timing offset compensation of the present invention under the speed of a motor vehicle A 60km/h channel bit error rate performance relatively;

Figure 10 is the bit error rate performance comparison of conjugation symmetry approach under the walking B 3km/h channel with the down link time synchronization method based on the timing offset compensation of the present invention;

Figure 11 is the structural representation that the present invention is based on the down link timing synchronization sytem of timing offset compensation.

Embodiment

For above-mentioned purpose of the present invention, feature and advantage can be become apparent more, the present invention is further detailed explanation below in conjunction with the drawings and specific embodiments.

The inventive method at first adopts carries out auto-correlation to received signal.Then, the peak-peak corresponding sampling points of correlated results is carried out the timing offset compensation constantly; Make the FFT window as far as possible in advance, the initial moment of symbol is positioned not to be subjected in the CP scope that multipath disturbs, thereby the intersymbol interference that reduces or avoid multidiameter delay to cause has solved the timing synchronization problem of multipath channel.The technical solution adopted for the present invention to solve the technical problems is:

At first adopt conjugation symmetry peak-value detection method to find the position of most powerful path, then timing position is moved several sampled points forward, guarantee that as far as possible final timing position drops in the CP zone of no ISI, thereby guarantee only to comprise in the FFT window data of current OFDM symbol, avoid intersymbol interference.

At ofdm system N subcarrier arranged, the binary bit stream of transmitting terminal input is by chnnel coding and sign map, and the modulation symbol on k subcarrier is X (k), carries out IFFT then and transform to time domain behind serial to parallel conversion, obtain time-domain signal x (n), expression formula is:

$x\left[n\right]=\mathrm{IFFT}\left\{X\left(k\right)\right\}=\frac{1}{\sqrt{N}}\underset{k=0}{\overset{N-1}{\mathrm{\&Sigma;}}}X\left(k\right){\mathrm{<figure-callout\; id="2"\; label="e\; j"\; filenames="HSA00000059478000051.png"\; state="\{\{state\}\}">e</figure-callout>}}^j,n=\mathrm{0,1},...,N-1---\left(1\right)$

Suppose the maximum multipath time delay of protection length at interval greater than channel, the time become multidiameter fading channel the time domain impulse response be expressed as:

$h\left[n\right]=\underset{l=0}{\overset{L-1}{\mathrm{\&Sigma;}}}{\mathrm{\&alpha;}}_l\mathrm{\&delta;}[n-{\mathrm{\&tau;}}_l]---\left(2\right)$

Wherein L is the multipath number of channel, α _lBe the fading coefficients in l footpath, τ _lThe delay sampling that is the l footpath is counted.Under desirable synchronous situation, received signal is

$y\left[n\right]=\underset{l=0}{\overset{L-1}{\mathrm{\&Sigma;}}}{\mathrm{\&alpha;}}_{l}x[n-{\mathrm{\&tau;}}_l]---\left(3\right)$

Have time delay and frequency departure if signal arrives receiving terminal, the received signal that is superimposed with white Gaussian noise is expressed as

$r\left[n\right]=y[n-d]{\mathrm{<figure-callout\; id="2"\; label="e\; j"\; filenames="HSA00000059478000051.png"\; state="\{\{state\}\}">e</figure-callout>}}^j+z\left[n\right]---\left(4\right)$

Wherein d and Δ f are respectively time delay and frequency deviation, and z (n) is a white Gaussian noise.

Ofdm system has been introduced Cyclic Prefix (CP) as protection at interval, thereby has reduced the influence of intersymbol interference (ISI).During the parameter setting of ofdm system, the length of CP is generally greater than the maximum multipath time delay of channel, and therefore, still some CP zone is not subjected to the influence of intersymbol interference under multi-path environment, keeps good correlation with former data.

As shown in Figure 6, first signal is the effective diameter of first arrival, and second signal is a strongest footpath of energy, and the time difference of the two arrival is the channel multi-path time delay.As can be seen, if it is synchronous to utilize conjugation symmetry peak detection algorithm to carry out timing to received signal, receiving terminal is separated the position of timing FFT window from the energy most powerful path, because most powerful path has some time-delays with respect to first footpath, to comprise the data of next OFDM symbol in the FFT window, cause intersymbol interference.For ofdm system, because the existence of CP, and the back part of CP is not subjected to the influence of intersymbol interference, therefore and do not require that the FFT window just drops on the position in first footpath, just it is also bigger to be positioned the first footpath difficulty in the reality, and only require and drop in the undisturbed CP zone, position than first footpath shifts to an earlier date some sampled points, that comprise in the FFT window like this is the interior data of current OFDM symbol and the CP of itself, the influence that causes is the phase place rotation of whole signal, can after channel estimating, compensate, can not impact systematic function.

In order to make the data that do not comprise next OFDM symbol in the FFT window, the timing synchronization position should shift to an earlier date as far as possible, rather than only finds out the most powerful path corresponding sampling points constantly.

With reference to Fig. 7 A, Fig. 7 A is the flow chart of steps that the present invention is based on the down link time synchronization method embodiment of timing offset compensation, comprises the steps: peak detection step 710, carries out the detection of conjugate peak values, obtains correlated results; Sampled point is d constantly ₀Determining step 720 finds peak-peak M in described correlated results ₀, described peak-peak corresponding sampling points d constantly ₀The timing synchronization position

Determining step 730 is with described peak value corresponding sampling points moment d ₀Translation forward, the sampled point number Δ d of given timing offset compensation is according to described sampled point moment d ₀Determine the timing synchronization position with described sampled point number Δ d

When step was carried out, the data that pilot process produces specifically can be referring to shown in Fig. 7 B.

The present invention is described further below in conjunction with an example.

This method embodiment comprises the steps:

Step 1 is carried out conjugation symmetry peak value and is detected, and obtains correlated results M[n], promptly establishing the OFDM symbol lengths is N sampled point, from a certain sampled point of time domain received signal, about N/2 sampled point of search, with the first half and after half carries out auto-correlation.

$M\left[n\right]=\underset{i=1}{\overset{N/2-1}{\mathrm{\&Sigma;}}}r[n+N/2-i]\&times;r[n+N/2+i]$

Step 2 finds peak-peak M in correlated results ₀With its corresponding sampling points moment d ₀

M ₀＝max(M[n])，d ₀＝arg?max(M[n])

Step 3 moves some sampled points forward constantly with the peak value corresponding sampling points, and the sampled point number of definition timing offset compensation is Δ d, and correct symbol original position is

$\hat{d}=d_0-\mathrm{\&Delta;d}$

So just obtain final timing synchronization position, i.e. the position of FFT window.

If the received signal auto-correlation obtains first kind of correlated results, most powerful path is first footpath just, compensation Δ d makes that regularly sync bit drops in the undisturbed CP zone, comprises last several sampled points of current OFDM symbol and itself CP in the FFT window, can not influence regularly net synchronization capability; If the received signal auto-correlation obtains second kind of correlated results, most powerful path postpones several sampled points than first footpath, and compensation Δ d makes the position of FFT window shift to an earlier date, and has reduced the possibility that comprises next symbol data in the FFT window, has avoided intersymbol interference.

Among this method embodiment, the sampled point number Δ d of timing offset compensation is a parameter relevant with multipath channel, and Δ d value is too little, still have the data of next symbol in the FFT window, Δ d value is excessive, has exceeded undisturbed CP zone, and performance all will be affected.

Simulation result

Walking B 3km/h and speed of a motor vehicle A 60km/h channel have been adopted in emulation, the timing position that conjugation symmetry peak detection algorithm under two kinds of channels is estimated with first directly the deviation of ideal position add up.

With reference to Fig. 8, Fig. 8 curve that to be the timing offset average change with signal to noise ratio, expression be under two kinds of multipath channels timing offset sampled point number with the variation of signal to noise ratio.Wherein, curve 8a is the curve of walking B 3km/h channel correspondence, and curve 8b is the curve of speed of a motor vehicle A 60km/h channel correspondence.As can be seen from the figure, under the walking B 3km/h channel, the timing synchronization value of conjugation symmetry peak detection algorithm and the error between the ideal value are greatly between 3-4 sampled point, under the speed of a motor vehicle A 60km/h channel, the timing synchronization value of conjugation symmetry peak detection algorithm and the error between the ideal value are greatly between 2-3 sampled point.In general, undisturbed CP zone is bigger, and timing offset compensates so long as not too shifting to an earlier date, and can not exceed its scope.Therefore, statistics is rounded up deviation compensation Δ d=4 and Δ d=3 when setting respectively in the emulation.

Fig. 9, Figure 10 have provided respectively, and the 802.16e system down link under speed of a motor vehicle A 60km/h and two kinds of multipath channels of walking B 3km/h adopts conjugation symmetry peak value detection time synchronization method and the down link time synchronization method that compensates based on timing offset of the present invention to carry out emulation.In emulation, system bandwidth adopts 10MHz, and sample frequency 11.2MHz, sub-carrier number are 1024, Cyclic Prefix is 128, subcarrier spacing 10.94kHz, OFDM symbol time 102.86us, useful symbol time 91.43us, CP time 11.43us, modulation coding mode QPSK-CTC-1/2.In the down link time synchronization method of timing offset compensation, establish Δ d=3 and Δ d=4 respectively.Wherein, curve 9a, curve 10a are the curve of conjugation symmetry algorithm correspondence; Curve 9b, curve 10b are the curve of the inventive method correspondence.

As can be seen from Figure 9, under the speed of a motor vehicle A 60km/h channel, the down link time synchronization method based on the timing offset compensation of the present invention is better than the performance of conjugation symmetry peak value detection method.Under identical state of signal-to-noise, the error rate of timing offset compensation method obviously descends than the error rate of conjugation symmetry approach.Reaching BER=2 * 10 ^-3The time, about timing offset compensation method required signal-to-noise ratio decline 1.5dB.

As can be seen from Figure 10, under walking B 3km/h multidiameter fading channel, along with the increase of signal to noise ratio, the poor-performing of the time synchronization method that conjugation symmetry peak value detects, its bit error rate performance can only be reduced to 10 ^-2, ber curve begins to occur floor effect subsequently.This timing offset that this algorithm is described is bigger, and timing offset has destroyed the orthogonality between the subcarrier, has caused inter-carrier interference.Therefore, the performance of conjugation symmetry peak detection algorithm is had a strong impact under multidiameter fading channel.Down link time synchronization method performance based on the timing offset compensation of the present invention has clear improvement.At BER=10 ^-2The time, the signal to noise ratio of timing offset compensation method for synchronous has descended about 5dB, and along with the increase of signal to noise ratio, the error rate descends thereupon, levels off to 10 at last ^-3Under identical state of signal-to-noise, timing offset is compensated systematic function afterwards improved an order of magnitude.The timing offset compensation makes the position of FFT window shift to an earlier date as far as possible, drops in the undisturbed CP scope, therefore makes systematic function improve greatly.

On the other hand, the present invention also provides a kind of down link timing synchronization sytem based on the timing offset compensation.With reference to Figure 11, this system comprises:

Peak detection block 1102 is used to carry out the detection of conjugate peak values, obtains correlated results; Sampled point is determination module 1104 constantly, is used for finding peak-peak M at described correlated results ₀, described peak-peak corresponding sampling points d constantly ₀Timing synchronization position determination module 1106 is used for described peak value corresponding sampling points moment d ₀Translation forward, the sampled point number Δ d of given timing offset compensation is according to described sampled point moment d ₀Determine the timing synchronization position with described sampled point number Δ d

The principle of said system embodiment is identical with method embodiment, and relevant part does not repeat them here mutually with reference to getting final product.

More than a kind of down link time synchronization method and system based on timing offset compensation provided by the present invention described in detail, used specific embodiment herein principle of the present invention and execution mode are set forth, the explanation of above embodiment just is used for helping to understand method of the present invention and core concept thereof; Simultaneously, for one of ordinary skill in the art, according to thought of the present invention, part in specific embodiments and applications all can change.In sum, this description should not be construed as limitation of the present invention.

Claims (8)

1. the down link time synchronization method based on the timing offset compensation is characterized in that, comprises the steps:

Peak detection step is carried out the detection of conjugate peak values to the receiving sequence of obtaining, and obtains correlated results;

Sampled point is determining step constantly, finds peak-peak M in described correlated results ₀, described peak-peak corresponding sampling points d constantly ₀

Timing synchronization position determining step is with described peak value corresponding sampling points moment d ₀Translation forward, the sampled point number Δ d of timing offset compensation given in advance is according to described sampled point moment d ₀Determine the timing synchronization position with described sampled point number Δ d

2. down link time synchronization method according to claim 1 is characterized in that, in the described peak detection step, the described correlated results that obtains is determined according to following formula:

Wherein, Be described correlated results, n is the sampled point label, and 0＜n≤N, N are the sampled point number that the OFDM symbol lengths is comprised.

3. down link time synchronization method according to claim 1 is characterized in that, in the sampled point moment determining step, and the correlated results peak-peak M that obtains ₀With described peak-peak corresponding sampling points moment d ₀Determine according to following formula:

M ₀＝max(M[n])，d ₀＝arg?max(M[n])

4. down link time synchronization method according to claim 3 is characterized in that, described timing synchronization position

In the determining step, described timing synchronization position

Determine according to following formula:

5. the down link timing synchronization sytem based on the timing offset compensation is characterized in that, comprising:

Peak detection block is used for the receiving sequence of obtaining is carried out the detection of conjugate peak values, obtains correlated results;

Sampled point is d constantly ₀Determination module is used for finding peak-peak M at described correlated results ₀, described peak-peak corresponding sampling points d constantly ₀

The timing synchronization position

Determination module is used for described peak value corresponding sampling points moment d ₀Translation forward, the sampled point number Δ d of given timing offset compensation is according to described sampled point moment d ₀Determine the timing synchronization position with described sampled point number Δ d

6. down link timing synchronization sytem according to claim 5 is characterized in that, in the described peak detection block, the described correlated results that obtains is determined according to following formula:

Wherein, M[n] be described correlated results, n is the sampled point label, N is the sampled point number that the OFDM symbol lengths is comprised.

7. according to claim 5 or 6 described down link timing synchronization sytems, it is characterized in that described sampled point is d constantly ₀In the determination module, the correlated results peak-peak M that obtains ₀With described peak-peak corresponding sampling points moment d ₀Determine according to following formula:

M ₀＝max(M[n])，d ₀＝arg?max(M[n])。

8. line link timing synchronization sytem according to claim 7 is characterized in that, described timing synchronization position

In the determination module, described timing synchronization position Determine according to following formula:

。

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