CN103873421A - Symbol synchronizing method of multi-path channel - Google Patents
Symbol synchronizing method of multi-path channel Download PDFInfo
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Abstract
The invention discloses a symbol synchronizing method of a multi-path channel. The symbol synchronizing method of the multi-path channel comprises the steps that a self-correlation operation of received signals and a cross-correlation operation of the received signals and a local known training sequence are simultaneously carried out, and the strongest path is locked; forward searching is carried out on the locked strongest path to obtain an FFT window initial position, and symbol synchronization is finished.
Description
Technical field
The present invention relates to communication technical field, be specifically related to the symbol timing synchronization method under a kind of multipath channel.
Background technology
Multipath effect is the overriding challenge that high-speed radiocommunication system faces.Multipath effect can cause intersymbol crosstalking and the serious distortion of signal, must compensate the signal constellation point of disperse by equilibrium at receiving terminal.The OFDM (OFDM) and the single carrier frequency domain equalization (SC-FDE) that are transmitted as feature with piece are to two of anti-multipath mainstream technologys, they are transformed into frequency domain equalization by fast Fourier transform (FFT) by time domain equalization, greatly reduce hard-wired complexity, promoted the development of high-speed radiocommunication technology.In OFDM and SC-FDE system, accurately and reliably determine that FFT window original position is very crucial.In multipath channel, sign synchronization is for the primary sign position (determining the original position of FFT window) of specified data frame, most important for catching with error performance of burst packets.
In current communication system (as WIFI and WIMAX), conventionally can add training sequence to carry out synchronous the completing of auxiliary symbol.For example, in WIFI system, sign synchronization is divided into thick synchronous and fine synchronization two steps, to guarantee synchronous reliability and accuracy: slightly synchronously complete based on short leader sequence, and fine synchronization completes based on long preambles sequence, autocorrelation value and the dynamic threshold based on energy are compared, judge the original position of sign synchronization.Another common symbol timing synchronization method carries out based on cross-correlation, select the good sequence of correlation properties as training sequence, and reception signal and local training sequence are carried out to related operation, and obtain correlation peak, complete Symbol Timing thereby search for first correlation peak.
The problem existing based on autocorrelative symbol timing synchronization method is: autocorrelation peak is comparatively smooth, has flat site near symbol synchronization point, and peak value decrease speed is comparatively slow, and therefore synchronization accuracy is lower; The problem that symbol timing synchronization method based on cross-correlation exists is: in the time that multipath exists, the amplitude of cross-correlation peak value will decline, and occurs multiple peak values, is difficult for determining the first footpath, causes synchronization dependability to decline.
Summary of the invention
Technical problem to be solved by this invention is that the synchronization accuracy of existing symbol timing synchronization method under multipath conditions is low, the problem of poor reliability.
For this purpose, the present invention proposes the symbol timing synchronization method under a kind of multipath channel, and the method comprises:
S1. receive the auto-correlation computation of signal and the computing cross-correlation of reception signal and local known training sequence, locking most powerful path simultaneously;
S2. the most powerful path of described locking is carried out to sweep forward, obtain FFT window original position, complete sign synchronization.
Wherein, described step S1 comprises:
S11. receive the auto-correlation computation of signal, obtain most powerful path region, receive signal and local known training sequence computing cross-correlation simultaneously;
S12. in described most powerful path region, utilize the result of described computing cross-correlation, locking most powerful path.
Wherein, described step S11 comprises:
S111. according to the intensity that receives signal, obtain threshold value Th, the size of described threshold value Th is determined by the intensity size that receives signal;
S112. receive the auto-correlation computation of signal, the result of described auto-correlation computation is P
a(d), obtain most powerful path region, described most powerful path region is | P
a(d) |
2the region of >Th receives signal and local known training sequence computing cross-correlation simultaneously, and the result of described computing cross-correlation is P
c(d).
Wherein, described step S12 comprises:
S121. in described most powerful path region, record | P
c(d) |
2the cross-correlation peak value that >Th1 is corresponding, wherein, Th1 is default threshold value;
S122. in multipath maximum protection interval, store the peak value larger than the peak value of described record;
S123. selecting peak value maximum in the peak value of described storage is most powerful path.
Wherein, described step S2 comprises:
The most powerful path of described locking is carried out to sweep forward, judge whether to exist forward multi-path, if there is forward multi-path, locate the first footpath, if there is not forward multi-path, most powerful path is the first footpath, and described the first footpath is FFT window original position.
Wherein, described sweep forward comprises: from described most powerful path, successively the mould value of peak value corresponding with most powerful path the mould value of the cross-correlation peak value recording before most powerful path is compared, the scope of search is no more than multipath maximum protection interval forward.
Wherein, described judging whether exists forward multi-path to comprise: judge whether the α that cross-correlation peak value that sweep forward obtains is greater than the corresponding peak value of most powerful path doubly sets up, wherein, 0< α <1, if set up, judge that the position of the computing cross-correlation that sweep forward obtains exists forward multi-path.
Wherein, the first footpath, described location comprises: pass through sweep forward; all cross-correlation peak value in the maximum protection interval of traversal most powerful path; orientate the position corresponding cross-correlation peak value satisfying condition as first footpath; wherein, described condition comprises: the α that cross-correlation peak value is greater than the corresponding peak value of most powerful path doubly and footpath corresponding to cross-correlation peak value be the Article 1 footpath in multipath maximum protection interval.
Than prior art, be precision and the reliability that improves sign synchronization under multipath conditions by the beneficial effect of method provided by the invention.
Accompanying drawing explanation
In order to be illustrated more clearly in the embodiment of the present invention or technical scheme of the prior art, to the accompanying drawing of required use in embodiment or description of the Prior Art be briefly described below, apparently, accompanying drawing in the following describes is some embodiments of the present invention, for those of ordinary skills, do not paying under the prerequisite of creative work, can also obtain according to these accompanying drawings other accompanying drawing.
Fig. 1 shows the frame assumption diagram of burst packet;
Fig. 2 shows the symbol timing synchronization method flow chart under a kind of multipath channel.
Embodiment
For making object, technical scheme and the advantage of the embodiment of the present invention clearer, below in conjunction with the accompanying drawing in the embodiment of the present invention, the technical scheme in the embodiment of the present invention is clearly described, obviously, described embodiment is the present invention's part embodiment, rather than whole embodiment.Based on the embodiment in the present invention, those of ordinary skills, not making the every other embodiment obtaining under creative work prerequisite, belong to the scope of protection of the invention.
Embodiment 1:
The present embodiment discloses the symbol timing synchronization method under a kind of multipath channel, the burst communication while being applicable to have multipath effect, and can in the time of low signal-to-noise ratio, complete reliable synchronization location.As shown in Figure 1, add the frame of training sequence formation burst packet before burst packet Burst-Data, training sequence is made up of two sections of on all four sequences, i.e. TS1 and TS2.The sign synchronization of burst packets is completed by training sequence.Receiver, by receiving signal and local known training sequence carries out computing cross-correlation and auto-correlation computation, is combined and is estimated the first footpath time delay, thereby completes the sign synchronization of burst packet, and as shown in Figure 2, the method comprises:
S1. receive the auto-correlation computation of signal and the computing cross-correlation of reception signal and local known training sequence simultaneously, locking most powerful path, most powerful path is exactly the multipath that energy is the strongest, shows as the mould value maximum of cross-correlation;
S2. the most powerful path of described locking is carried out to sweep forward, obtain FFT window original position, complete sign synchronization.
Wherein, described step S1 comprises:
S11. receive the auto-correlation computation of signal, obtain most powerful path region, receive signal and local known training sequence computing cross-correlation simultaneously;
S12. in described most powerful path region, utilize the result of described computing cross-correlation, locking most powerful path.
In the present embodiment, wireless channel brings the linear distortion of signal transmission on frequency domain and can be equivalent to the multipath effect of time domain.Multipath effect is equivalent to the convolution of signal transmission and discrete channel impulse response.Consider the impact of noise and symbol timing error, the discrete reception signal at receiver place is:
Wherein h
lrepresent discrete channel impulse response, w (n) represents white noise, and d represents the first footpath time delay.L represents the maximum protection length (maximum delay in the first footpath and last footpath is poor) of multipath.
The smooth peak value producing by means of the related operation that receives signal self is limited to most powerful path compared with in zonule, meanwhile, within the scope of localized area, utilize reception signal to carry out computing cross-correlation with local known training sequence and obtain precipitous correlation peak, and then accurately lock most powerful path.
In the present embodiment, suppose that training sequence length is M, the length of TS1 and TS2 is M/2.From the sampled signal receiving, choose respectively the sequence that two continuous segment lengths are ordered for MN/2, carry out, to a conjugate multiplication summation, being auto-correlation result P
a(d):
Wherein, the number that m is multipath,
for the conjugation of the sampled point in the first half TS1 of training sequence, r
m+d+MN/2for the sampled point in the latter half TS2 of training sequence.
Wherein N represents over-sampling factor, N=4 in the present embodiment.Owing to receiving the irrelevance of signal and the stochastic behaviour of noise, when auto-correlation computation is not in the timesharing of training training department, the actual expectation of auto-correlation computation value is tending towards 0, in the time being just in time TS1 and TS2 for continuous two sections of sequences of auto-correlation computation, gained correlated results value is larger, there will be a significant peak region.Rely on the absolute size of correlated results amplitude to be difficult to lock peak value, larger because the result of correlation peak is subject to the impact of signal strength signal intensity.
Wherein, described step S11 comprises:
S111. according to the intensity that receives signal, obtain threshold value Th, the size of described threshold value Th is determined by the intensity size that receives signal;
Th=k|R(d)|
2
Wherein k is an adjustable coefficient, scope from 0 to 1.R (d) is the long gross energy for MN/2 signal sampling point, and described R (d) is:
S112. receive the auto-correlation computation of signal, the result of described auto-correlation computation is P
a(d), obtain most powerful path region, described most powerful path region is | P
a(d) |
2the region of >Th wherein, receives signal and local known training sequence computing cross-correlation simultaneously, and the result of described computing cross-correlation is P
c(d), wherein.
In the time that following condition is set up, it is multiple points that autocorrelation peak, described autocorrelation peak have been found in preliminary identification, has formed one section of continuous high plateau value, determine a region, thereby most powerful path has been locked in a finite region,
|P
a(d)|
2>Th
And Th>Th0
Th0 is for preventing that noise from causing the definite thresholding that false-alarm arranges, and only has when energy threshold Th just thinks during higher than Th0 and signal detected but not noise.Generally speaking, Th0 and Th should arrange lowlyer, to guarantee high detection probability.
Wherein, described step S12 comprises:
S121. in described most powerful path region, record | P
c(d) |
2the cross-correlation peak value that >Th1 is corresponding, wherein, Th1 is default threshold value;
S122. in multipath maximum protection interval, store the peak value larger than the peak value of described record; Described multipath maximum protection interval is set according to actual conditions.
S123. selecting peak value maximum in the peak value of described storage is most powerful path.
Concrete, computing cross-correlation is to carry out convolution algorithm by receiving signal and known local training sequence.Implementation is a training sequence design matched filter known according to this locality, will receive signal and pass through matched filter.Local known training sequence is c
m, length is M/2, filter output P
c(d) be
|P
c(d)|
2>Th1
Filter output is computing cross-correlation result, and operation result comprises I/Q two-way, and it is carried out to the processing of mould side.Determine after peak region in auto-correlation result, started most powerful path (top) search.A basic thresholding Th1 is set, for detection of cross-correlation peak.
In the time that following formula is set up, think that cross-correlation peak value occurs, and corresponding cross-correlation peak value is deposited in register Reg1,
|P
c(d)|
2>Th1
Th1>Th2
Wherein, Th2 is the threshold value arranging in order to prevent too low relevant peaks from entering register Reg1, and the value in the corresponding Reg1 of Th1, needs to constantly update.
In the time that institute's poke value appears and be greater than in Reg1 in peak value next time, use the content of new peak value alternative registers.So the numerical value in register can become large along with the appearance of new peak value (these peak values are mostly to produce because multipath exists) constantly refreshes, until peak-peak (corresponding most powerful path) occurs.If the content in register continues the maximum protection interval of the corresponding multipath of LN() the individual sampling period do not upgrade, and thinks that peak-peak finds.
Multipath disperse is more serious, and relevant peaks number is more, and top amplitude can be less, and therefore arranging of thresholding Th1 need to take into full account the situation that multipath exists, and thresholding is too high, may occur undetected phenomenon, and thresholding is too low, may occur flase drop phenomenon.
Wherein, described step S2 comprises:
The most powerful path of described locking is carried out to sweep forward, judge whether to exist forward multi-path, if there is forward multi-path, locate the first footpath, if there is not forward multi-path, most powerful path is the first footpath, and described the first footpath is FFT window original position.
Wherein, described sweep forward comprises from described most powerful path, successively the mould value of peak value corresponding with most powerful path the mould value of the cross-correlation peak value recording before most powerful path is compared, and the scope of search is no more than multipath maximum protection interval forward.
Wherein, described judging whether exists forward multi-path to comprise: judge whether the α that cross-correlation peak value that sweep forward obtains is greater than the corresponding peak value of most powerful path doubly sets up, wherein, 0< α <1, α=3/8 in the present embodiment, α be one flexibly value arrange according to actual needs, generally speaking, suggestion is less than 0.5, is greater than 0.25, if set up, judge that the position of the computing cross-correlation that sweep forward obtains exists forward multi-path.
Wherein, the first footpath, described location comprises: pass through sweep forward; all cross-correlation peak value in the maximum protection interval of traversal most powerful path; orientate the position corresponding cross-correlation peak value satisfying condition as first footpath; wherein, described condition comprises: the α that cross-correlation peak value is greater than the corresponding peak value of most powerful path doubly and footpath corresponding to cross-correlation peak value be the Article 1 footpath in multipath maximum protection interval.
At the aspect of performance of weighing symbol timing synchronization method, false alarm probability and false dismissal probability are two most important indexs, and the threshold value thresholding changing in auto-correlation and computing cross-correlation is adjustable false-alarm and undetected performance.
Embodiment 2:
The present embodiment is in conjunction with SC-FDE system, and in system, the length of FFT is 64, discloses the symbol timing synchronization method under a kind of multipath channel.
Transmitting terminal sends training sequence, and the m sequence that training sequence is repeated by Cyclic Prefix and two ends forms.Circulating prefix-length is that 34, m sequence length is 63, and therefore training sequence comprises 160 symbols.Send afterwards valid data part.
The baseband signal of receiving terminal is discrete digital signal, can be characterized by the convolution that sends sequence and channel impulse response:
D wherein represents the first footpath time delay, h
lrepresent discrete channel impulse response, w (n) represents white Gaussian noise.
Utilize the feature that comprises two sections of consistent m sequences in training sequence, the signal receiving is carried out to auto-correlation computation, can obtain an outstanding high value, can tentatively lock the time delay of most powerful path according to this level.
Meanwhile, by receive signal be sent to one long be 63 filter, its parameter is corresponding one by one with m sequence, the effect of this filter is that reception signal and m sequence are carried out to computing cross-correlation.Because m sequence has good correlation properties, therefore in the output of filter, comprise very precipitous correlation peak.In the high level region of auto-correlation computation locking, the strongest cross-correlation peak value of search, searches after highest peak value, carries out sweep forward, finds first peak value, thereby determines the time delay in the first footpath.
Although described by reference to the accompanying drawings embodiments of the present invention, but those skilled in the art can make various modifications and variations without departing from the spirit and scope of the present invention, such modification and modification all fall into by within claims limited range.
Claims (8)
1. the symbol timing synchronization method under multipath channel, is characterized in that, the method comprises:
S1. receive the auto-correlation computation of signal and the computing cross-correlation of reception signal and local known training sequence, locking most powerful path simultaneously;
S2. the most powerful path of described locking is carried out to sweep forward, obtain FFT window original position, complete sign synchronization.
2. method according to claim 1, is characterized in that, described step S1 comprises:
S11. receive the auto-correlation computation of signal, obtain most powerful path region, receive signal and local known training sequence computing cross-correlation simultaneously;
S12. in described most powerful path region, utilize the result of described computing cross-correlation, locking most powerful path.
3. method according to claim 2, is characterized in that, described step S11 comprises:
S111. according to the intensity that receives signal, obtain threshold value Th, the size of described threshold value Th is determined by the intensity size that receives signal;
S112. receive the auto-correlation computation of signal, the result of described auto-correlation computation is P
a(d), obtain most powerful path region, described most powerful path region is | P
a(d) |
2the region of >Th receives signal and local known training sequence computing cross-correlation simultaneously, and the result of described computing cross-correlation is P
c(d).
4. according to the method in claim 2 or 3, it is characterized in that, described step S12 comprises:
S121. in described most powerful path region, record | P
c(d) |
2the cross-correlation peak value that >Th1 is corresponding, wherein, Th1 is default threshold value;
S122. in multipath maximum protection interval, store the peak value larger than the peak value of described record;
S123. selecting peak value maximum in the peak value of described storage is most powerful path.
5. method according to claim 4, is characterized in that, described step S2 comprises:
The most powerful path of described locking is carried out to sweep forward, judge whether to exist forward multi-path, if there is forward multi-path, locate the first footpath, if there is not forward multi-path, most powerful path is the first footpath, and described the first footpath is FFT window original position.
6. method according to claim 5; it is characterized in that; described sweep forward comprises: from described most powerful path; successively the mould value of peak value corresponding with most powerful path the mould value of the cross-correlation peak value recording before most powerful path is compared, the scope of search is no more than multipath maximum protection interval forward.
7. method according to claim 5, it is characterized in that, described judging whether exists forward multi-path to comprise: judge whether the α that cross-correlation peak value that sweep forward obtains is greater than the corresponding peak value of most powerful path doubly sets up, wherein, 0< α <1, if set up, judge that the position of the computing cross-correlation that sweep forward obtains exists forward multi-path.
8. according to the method described in claim 5 or 6; it is characterized in that; the first footpath, described location comprises: pass through sweep forward; all cross-correlation peak value in the maximum protection interval of traversal most powerful path; orientate the position corresponding cross-correlation peak value satisfying condition as first footpath; wherein, described condition comprises: the α that cross-correlation peak value is greater than the corresponding peak value of most powerful path doubly and footpath corresponding to cross-correlation peak value be the Article 1 footpath in multipath maximum protection interval.
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