CN101404633B - Carrier wave tracing method for single carrier system based on block transmission - Google Patents

Abstract

The invention provides a carrier wave tracking method of a single carrier wave system based on block transmission. The method includes: step A: carrying out equalization treatment of the data block by phase compensation in the current frame and selecting the corresponding soft judgment data of cyclic prefix from soft judgment element data after equalization and compensation; step B: utilizing the phase estimation algorithm to calculate the soft judgment data and obtaining the phase estimation of the present data block; step C: carrying out accumulated smoothing treatment of the estimation phase and using the phase estimation value of next data block by accumulated smooth output to compensate the next data block; carrying out step A to step C repeatly until the transmission of all data blocks in the current frame is finished. The invention solves the shortcomings of the original calculation and achieves the frequency tracking directly by phase estimation. In the tracking process, the invention carries out the phase compensation and reduces the realization complexity; in addition, the algorithm is not only high in accuracy but also low in complexity.

Description

Carrier wave tracing method based on the single-carrier system of piece transmission

Technical field

The present invention designs communication technique field, relates in particular to a kind of carrier wave tracing method of the single-carrier system based on piece transmission.

Background technology

SC-FDE (single carrier frequency domain equalization) is the method that a kind of up-and-coming anti-multipath disturbs in the broadband wireless transmission; The same branch of taking with OFDM transmits soon; And adopt Cyclic Prefix Cyclic Prefix (CP) mode; So just can be converted into circular convolution to signal in the linear convolution of channel impulse response, and eliminate the interference of the data block that multipath causes.Adopt simple frequency-domain equalization technology just can eliminate intersymbol interference at receiving terminal.

A most crucial problem in the digital communication technology field is exactly a stationary problem, is divided into carrier synchronization technically with regularly synchronously.In the baseband sampling signal that obtains through the receiving terminal behind the wireless mobile channel, exist carrier frequency offset; Phase deviation; Timing offset; These deviations generally derive from crystal oscillator between the transmitter and receiver do not match with wireless mobile channel in Doppler effect and these several aspects of frequency selectivity, even if, also can have these deviations in the indoor environment of channel relatively flat.

Use the SC-FDE system of piece transmission technology that these synchronous deviations are had higher requirement.The simultaneous techniques of SC-FDE system be divided into carrier synchronization with regularly synchronously, its receiving terminal mainly contain following task synchronously:

Frame arrive to detect, and is used for judging whether detect signal, and this is the synchronous first step, has only and judges that what receive is that useful signal just can carry out the processing of back;

Carrier wave frequency deviation is caught;

Carrier frequency tracking;

The symbol original position is estimated (piece is synchronous), promptly before equilibrium, accurately knows original position (initial Fourier transform FFT position); For obtaining more accurate position, need timing estimation.

The tracking of sampling clock frequency.

The signal of SC-FDE system arrives along the time shaft order, and each data block of SC-FDE signal of piecemeal transmission is made up of data segment and Cyclic Prefix.Because not matching of crystal oscillator can produce very large frequency departure, the error that frequency deviation causes pure single-carrier system is equivalent to cause signal rotation and decay to the SC-FDE radiofrequency signal in separating the process of being transferred to baseband signal; When this frequency deviation appears at the SC-FDE system; Also can cause intersymbol interference ISI; Inter-carrier interference ICI has influence on the frequency domain equalization algorithm accuracy of SC-FDE system, so the frequency deviation of the baseband sampling signal that after the receiving terminal down-conversion, obtains must catch earlier and compensate; The frequency deviation of local carrier is locked in the small range, makes the system can operate as normal.The remaining frequency deviation in compensation back is referred to as residual frequency departure again.As time goes on, the phase shift difference that residual frequency departure causes is along with the accumulation of time, can make angle of receiving symbol rotation, cause can't be correct the symbol that demodulates; Channel estimating and frequency domain equalization that the cumulative departure of while phase place also can lead to errors.In order to keep good synchronization performance, must carry out carrier track.Carrier track is promptly followed the tracks of the variation of carrier phase deviation, prevents the accumulation of phase effect that frequency deviation causes.

In the general SC-FDE system; Data flow is transmitted by piecemeal; The time domain data vector paragraph

that it is N that every blocks of data stream certain encoding process of process and constellation mapping form a length afterwards adds afterwards that at data segment

length is the Cyclic Prefix of L---UW sequence (unique word sequence; Be generally chu, frank, PN sequence), obtain the vector that length is M=L+N

and be called data block.Data block after transmission through the channel at the receiving end to get their corresponding signal flow

and then after equalizing get soft decision data

finally decoded.

At present; General carrier tracking method utilizes the information of the Cyclic Prefix in the adjacent data blocks among the SC-FDE to obtain the frequency deviation of current block; Or the information after utilizing soft decision information or reconstruct behind the frequency domain equalization to recover is estimated the frequency deviation of current block; Reach the effect of frequency tracking with this, and then carry out phase compensation, realize carrier tracking.These solutions mostly are from the related synchronization algorithm of OFDM, to use for reference and come.

Carry out this type algorithm of frequency offset tracking for the phase difference that directly utilizes the UW in the receiving terminal adjacent data blocks; Because the reception data of algorithm utilization this moment are the information through not passing through isostatic compensation behind the wireless mobile channel; Therefore the carrier wave frequency deviation error that obtains is bigger; Precision is low, can't reach the purpose of tracking.And soft-decision data after the existing another kind of utilization equilibrium or reconstruct recovered data are carried out the algorithm that frequency deviation is followed the trail of, and utilize the current block frequency deviation that obtains to remove to compensate current data block, and complex algorithm implements time-delay greatly.These algorithms all are after accomplishing the frequency deviation tracking simultaneously, carry out phase compensation again, have further strengthened the complexity that realizes.

Summary of the invention

In view of above-mentioned analysis, the object of the invention is to provide a kind of carrier wave tracing method of the single-carrier system based on the piece transmission, in order to solve the problem that carrier tracking methodical error of the prior art is big, precision is low or complexity is big.

The object of the invention is mainly realized through following technical scheme:

The invention provides a kind of carrier wave tracing method of the single-carrier system based on piece transmission, said method comprises:

Steps A: the data block through phase compensation in the present frame is carried out equilibrium treatment, and choose the corresponding soft-decision data of Cyclic Prefix the soft decision symbols data that after isostatic compensation, obtain;

Step B: utilize maximum likelihood phase estimation algorithm that said soft-decision data is calculated, obtain the phase estimation of current data block;

Step C: the estimation phase place that will the obtain smoothing processing that adds up, and the level and smooth output that will add up is used to compensate next data block as the phase estimation value of next data block; Said step C specifically comprises: the estimation phase place that will obtain is through a predefined smoother that the adds up smoothing processing that adds up, and the time domain expression formula of the smoother that adds up is: $S(i+1)=\left(\begin{array}{c}S\left(i\right)+\frac{1}{i-1}\left(\underset{m=2}{\overset{i}{\mathrm{\Σ}}}\mathrm{Est}\left(i\right)\right)....i\≥2\\ \mathrm{Est}\left(i\right)......i=1\end{array}\right),$ S (1)=0 wherein, i representes the i blocks of data, est (i) is the smoother input of i piece, promptly goes up one and goes on foot the phase estimation value of trying to achieve

S (i+1) is the level and smooth output of adding up of i piece, and the level and smooth phase estimation value of exporting as next data block that adds up is used to compensate next data block;

Repeated execution of steps A is to step C, up to all end of transmission blocks of present frame.

Further, said step B specifically comprises:

Obtain the correlation of the known Cyclic Prefix soft-decision data corresponding earlier, then this correlation is asked argument, obtain the estimation phase place of current data block with it;

Perhaps, said step B specifically comprises:

Utilize the decoding judgement output of soft-decision data to carry out relevant estimation phase place of trying to achieve current data block with soft-decision data.

Beneficial effect of the present invention is following:

The invention solves the shortcoming of original algorithm, directly reach frequency tracking, in the process of following the trail of, carrying out phase compensation simultaneously, reduced the complexity that realizes through phase estimation; Not only precision is high for algorithm simultaneously, and complexity is very low, and whole algorithm does not constitute loop structure truly, and it is very little to delay time, and very high practical value is arranged.

Other features and advantages of the present invention will be set forth in specification subsequently, and from specification, becoming apparent of part perhaps understood by embodiment of the present invention.The object of the invention can be realized through the structure that in the specification of being write, claims and accompanying drawing, is particularly pointed out and obtained with other advantages.

Description of drawings

Fig. 1 is for being the structural representation of the data block of single-carrier frequency domain equalization system;

Fig. 2 is the schematic flow sheet of the said method of the embodiment of the invention.

Embodiment

Specifically describe preferential embodiment of the present invention below in conjunction with accompanying drawing, wherein, accompanying drawing constitutes the application's part, and is used to explain principle of the present invention with embodiments of the invention.

Consider and before carrier tracking, carried out capturing carrier; The frequency deviation of this moment has been locked in the small range; It is not responsive especially to carrier synchronization that while SC-FDE compares OFDM; Therefore utilize through Cyclic Prefix in the current data block after the equilibrium, i.e. the corresponding soft-decision data r of UW sequence (the unique word sequence is generally chu sequence, frank-zadaff sequence, the PN sequence of IEEE802.16a standard code); Estimate the phase place of current data block according to ML (maximum likelihood, Maximum Likelihood) phase estimation algorithm; Again with the phase place that estimates through the smoother that adds up; To through the phase value that obtains after the smoothing processing that adding up and go to compensate next data block, go down, to reach the purpose of carrier tracking with this recursion.

The SC-FDE system is that every frame is n data block altogether by the frame transmission, and the every blocks of data of SC-FDE signal of piecemeal transmission is made up of useful data and Cyclic Prefix, and Cyclic Prefix is taken as Chu sequence (L Baud Length), obtains the vector that length is M=L+N

As shown in Figure 1, i data block correspondence

Obtain the signal flow corresponding through after the Channel Transmission at receiving terminal with it

Obtain the soft decision symbols data through isostatic compensation again ${\stackrel{v}{z}}_i=[z\left(1\right),L,z\left(M\right)]$ Decode at last.

Specifically can may further comprise the steps:

Step 200: phase compensation; The expression formula of phase compensation is:

Step 201: first valid data piece of present frame

is chosen the corresponding soft-decision data [z (N+1) of Chu sequence through obtaining soft decision symbols data

after the isostatic compensation; L; Z (M)]; Use to quantity symbol

expression [z (N+1); L, z (M)].Here, the existing in the prior art ripe solution of isostatic compensation repeats no more here.

Step 202: because fixing frequency deviation causes is the linear phase deviation; The accumulated phase that residual carrier wave frequency deviation causes in a data block is very little; Carrier wave frequency deviation is regarded as the fixedly photograph deviation of an accumulation to the phase effect of every blocks of data; Promptly can regard carrier wave frequency deviation as a fixed value to the phase effect of each data in the data block is approximate; Therefore can utilize one section known Cyclic Prefix in each block data structure of SC-FDE, the ML in the binding data aided algorithm (maximum likelihood) phase estimation algorithm obtains the phase estimation of current data block.Specifically can utilize ML phase estimation algorithm to obtain the phase estimation value of first data block; This algorithm is to obtain known Chu sequence U=[U (1) earlier; L; U (L)] correlation

(k is the sequence number in the sequence, i.e. k data in i data block) of the soft-decision data corresponding with it; Again correlation is asked argument; Promptly obtain ML phase estimation algorithm in estimation phase place

embodiment of the invention of current data block and also can select to utilize the decoding judgement output A=(a (1) of soft-decision data; ...; A (N)) with soft-decision data z=[z (1); L; Z (N)] be correlated with try to achieve phase estimation

but like this under the lower situation of signal to noise ratio because the unreliable of judgement can reduce be followed the trail of precision; Equally also can utilize soft-decision data to utilize the auxiliary phase estimation algorithm of free of data; For example V&V (A.J.Vitebi and A.M.Viterbi) algorithm carries out phase estimation; Such precision of estimation result is lower, but it is better under the low situation of signal to noise ratio, to compare a kind of scheme effect.

Step 203: the estimation phase place that will obtain

Obtain φ (1) through a predefined smoother that the adds up smoothing processing that adds up, the time domain expression formula of the smoother that adds up is: $S(i+1)=\left(\begin{array}{c}S\left(i\right)+\frac{1}{i-1}\left(\underset{m=2}{\overset{i}{\mathrm{\Σ}}}\mathrm{Est}\left(i\right)\right)....i\≥2\\ \mathrm{Est}\left(i\right)......i=1\end{array}\right),$ S (1)=0 wherein, i representes the i blocks of data, est (i) is the smoother input of i piece, promptly goes up one and goes on foot the phase estimation value of trying to achieve

S (i+1) is the level and smooth output φ (1) of adding up of i piece.Because what handled this moment is first blocks of data, what therefore try to achieve is S (2).

Original algorithm all is to estimate frequency deviation to carry out phase compensation again; Consider through the residual frequency departure behind the capturing carrier and regard a fixed value as that it is that the linear phase of variable changes that the i.e. phase deviation that forms of residual frequency departure can be regarded as based on data block to the phase effect of each data in the data block is approximate; Therefore the accumulated phase α of i piece in theory _i=α ₁+ k (i-1) (k=2 π fMT is a slope) representes every theoretic accumulation variable.Therefore the accumulation smoother of design designs according to this formula, owing to be to utilize next piece of estimation phase estimation of last, so the phase estimation value of each data block

With regard to a measured value of the slope k on the theory of correspondences, through smoothing filter Existing measured value asked on average reduce the influence that noise brings, the estimated value of the k that obtains more accurately

Utilize sum filter

Can reach the purpose of carrier tracking, therefore the time domain expression formula of the smoothing filter that adds up of design is $S(i+1)=\left(\begin{array}{c}S\left(i\right)+\frac{1}{i-1}\left(\underset{m=2}{\overset{i}{\mathrm{\Σ}}}\mathrm{Est}\left(i\right)\right)....i\≥2\\ \mathrm{Est}\left(i\right)......i=1\end{array}\right).$ The accumulation function of smoother of adding up solves the accumulation of phase between the data block that frequency deviation causes, and has reached the purpose that carrier wave frequency deviation is followed the trail of; Smoothing function has solved the effect of the level and smooth accumulation of influence of the phase estimation result's shake that is caused by noise, has further improved the tracking precision.Certainly, the smoother that adds up also can have other forms, must have accumulation function and smoothing function just can achieve the goal, but the smoother performance that adds up of embodiment of the invention design is relatively good.

Forward step 200 to, with the level and smooth output φ (1) that adds up that obtains, promptly the level and smooth output s (2) that adds up in the step 203 compensates the next data block that receives The expression formula of phase compensation is: ${\stackrel{v}{r}}_i={\stackrel{v}{r}}_i\×e^{-\mathrm{J\φ}\left(i\right)}.$

Data after the compensation obtain the corresponding soft-decision data

of second data block through the equilibrium treatment of step 201 again and try to achieve

φ (2) successively; Utilize φ (2) to go to compensate the 3rd data block again, with this recursion all end of transmission blocks up to present frame.

Here; The embodiment of the invention is that example is illustrated with the Chu sequence in the UW sequence only; But those skilled in the art according to the invention should be understood that two kinds of forms of UW sequence (frank-zadaff sequence and PN sequence) and go for the embodiment of the invention equally that just the size with length L has relation; Be the length of frank-zadaff sequence be necessary for n square, the PN sequence is necessary for 2 n power and subtracts 1.

In sum, the embodiment of the invention provides a kind of carrier wave tracing method of the single-carrier system based on piece transmission, because algorithm use is through the soft-decision data after the isostatic compensation; Utilize equalization algorithm can compensate stationary phase deviation and two characteristics must carrying out the piecemeal processing; The phase estimation result of current block is used for next pending of compensation, and whole algorithm does not form real loop processed like this, but has reached the effect of loop; Reached the purpose of following the trail of; It is big to compare the loop time-delay that original algorithm solved in the common tracing algorithm, poor stability, the problem that precision is low.

And the accumulation of phase between the data block that the frequency deviation that solves smoothing filter that adds up of the embodiment of the invention, the accumulation function of the smoother that adds up causes has reached the purpose that carrier wave frequency deviation is followed the trail of; Smoothing function has solved the effect of the level and smooth accumulation of influence of the phase estimation result's shake that is caused by noise, has further improved the tracking precision.

The above; Be merely the preferable embodiment of the present invention, but protection scope of the present invention is not limited thereto, any technical staff who is familiar with the present technique field is in the technical scope that the present invention discloses; The variation that can expect easily or replacement all should be encompassed within protection scope of the present invention.Therefore, protection scope of the present invention should be as the criterion with the protection range of claims.

Claims (2)

1. carrier wave tracing method based on the single-carrier system of piece transmission is characterized in that said method comprises:

Steps A: the data block through phase compensation in the present frame is carried out equilibrium treatment, and choose the corresponding soft-decision data of Cyclic Prefix the soft decision symbols data that after isostatic compensation, obtain;

Step B: utilize maximum likelihood phase estimation algorithm that said soft-decision data is calculated, obtain the phase estimation of current data block;

Step C: the estimation phase place that will the obtain smoothing processing that adds up, and the level and smooth output that will add up is used to compensate next data block as the phase estimation value of next data block; Said step C specifically comprises: the estimation phase place that will obtain is through a predefined smoother that the adds up smoothing processing that adds up, and the time domain expression formula of the smoother that adds up is: $S(i+1)=\left(\begin{array}{c}S\left(i\right)+\frac{1}{i-1}\left(\underset{m=2}{\overset{i}{\mathrm{\Σ}}}\mathrm{Est}\left(i\right)\right)....i\≥2\\ \mathrm{Est}\left(i\right)......i=1\end{array}\right),$ S (1)=0 wherein, i representes the i blocks of data, est (i) is the smoother input of i piece, promptly goes up one and goes on foot the phase estimation value of trying to achieve

S (i+1) is the level and smooth output of adding up of i piece, and the level and smooth phase estimation value of exporting as next data block that adds up is used to compensate next data block;

Repeated execution of steps A is to step C, up to all end of transmission blocks of present frame.

2. method according to claim 1 is characterized in that, said step B specifically comprises:

Obtain the correlation of the known Cyclic Prefix soft-decision data corresponding earlier, then this correlation is asked argument, obtain the estimation phase place of current data block with it;

Perhaps, said step B specifically comprises:

Utilize the decoding judgement output of soft-decision data to carry out relevant estimation phase place of trying to achieve current data block with soft-decision data.

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