CN1529443A - CDMA system multi-path peak value searching method - Google Patents

Abstract

The method scans power time delay function point-by-point, records magnitude of peak value and location, which is larger than threshold of multipath power. Then, the said peak values in searching region are removed from power time delay function. With scanning pointer going back for several sampling points, scanning is continued. If recorded number of peak value in power time delay function is larger than searching limit of multipath number M in searching end, then M pieces of lager values are selected from them. Locations of multipath time delay are corresponding to their locations. Comparing with prior art, the invention takes full advantages of peak value shape attribute of scrambling code autocorrelation, and combines with method for canceling out interference so as to determine location of multipath time delay with accuracy, decrease interference from multipaths with higher energy as well as raise performances for searching multipath peak value of CDMA system.

Description

Code division multiple access system multipath peak value searching method

Technical field

The present invention relates to code division multiple access (CDMA, Code-Division Multiple-Access) communication system, relate in particular to the multipath searching method of code division multiple access system.

Background technology

Code division multiple access is a kind of multiple access method, it is based on spread spectrum, recently become except that frequency division multiple access (FDMA, Frequency-Divisoin Multiple-Access) and be applied to another multiple access method of mobile communication system and satellite communication system outside time division multiple access (TDMA, the Time-Division Multiple-Access) cut-in method.Compare with existing multiple access method, code division multiple access has availability of frequency spectrum height, plans advantages such as simple.Adopt the system of CDMA access method to mainly contain at present: Narrowband CDMA (IS-95, InterimStandard 95) system, Wideband Code Division Multiple Access (WCDMA) (WCDMA, Wideband CDMA) system, the CDMA 2000 system, Time Division-Synchronous Code Division Multiple Access (TD-SCDMA, Time DivisionSynchronous Code Division Multiple Access) system, TD-CDMA Time Division-Code Division Multiple Access (TD-CDMA, Time Division Code Division Multiple Access) system etc., these code division multiple access systems have all adopted many yards spread spectrums (or claiming double-deck spreading code distribution technology), that is to say, in these code division multiple access systems, the spread spectrum of the reverse link from mobile subscriber to the base station was divided into for two steps, the first step is that cross-correlation is zero orthogonal function (Walsh function when aliging with time delay, ovsf code) as channel spread sign indicating number spread spectrum, promptly add expansion, the recovery process of corresponding receiving terminal is called despreading; Second step was to use the auto-correlation and all reasonable pseudo noise code (the PN sequence of cross-correlation performance of the unique distribution of each user, the M sequence, the Gold sequence) further spread spectrum, it is scrambling, the recovery process of corresponding receiving terminal is called descrambling, above-mentioned pseudo noise code is called scrambler, can distinguish different mobile subscribers according to scrambler.Equally, the spread spectrum mode of the forward link in these systems from the base station to mobile subscriber also in two steps, unique difference is that the scrambler in the forward link is used for distinguishing base station or sub-district, the scrambler difference of different base stations or sub-district.

In general mobile communication environment, the signal between base station and the travelling carriage is propagated along the some paths between the Receiver And Transmitter, and this multipath transmisstion phenomenon mainly is to be caused by the reflection of signal in transmitter and receiver ambient surface.Because it is also different that propagation path difference, the different multipath compositions of same signal arrive the propagation delay of receiver, thereby cause multipath to disturb and signal fadeout.The receiver that uses in the code division multiple access system is a kind of receiver of multiple-branching construction, wherein, the essentially identical multipath composition of each branch and propagation delay is synchronous, it is an independent receiving element, its function is the signal component that the demodulation expectation receives, the multipath composition that then the different receivers unit is received merges, and so just the multipath composition of same user's different delay is superimposed by rule, and this receiver is called Rake (Rake) receiver.

Spreading code in local spreading code and the received signal is the prerequisite of code division multiple access system proper communication synchronously.Multipath searching detects the multipath signal propagation delay exactly from received signal, to adjust local spreading code, make it with received signal in the spreading code of each multipath composition keep synchronously, to guarantee the operate as normal of back Rake receiver.

Multipath searching method of the prior art is: the power time delay function (PDP of first calculation expectation subscriber signal, Power Delay Profile), it is the mould value square of scrambler and received signal slip correlation intergal, then, search out the higher value that meets certain condition from the power time delay function, the position of these higher value correspondences is exactly the multidiameter delay position.Determine that according to the power time delay functional value method of the higher value of multidiameter delay position correspondence can be divided into two kinds in these multipath searching methods: first kind is that functional value when both sides in the power time delay function is during all less than the intermediate function value, then Zhong Jian functional value is exactly a peak value, search out higher value then from the whole peak values that search out, the position of these higher value correspondences is exactly the multidiameter delay position; Second kind is to choose bigger functional value from the power time delay function from big to small, and the position of these big functional value correspondences is exactly the multidiameter delay position.In the practice, the Multipath searching precision of Rake receiver is two sampled points of every chip, it is higher more than or equal to the multipath accuracy of a chip period that it differentiates time delay, but differentiate the erroneous judgement that time delay is easy to generate less than the multipath of a chip period, produce erroneous judgement two kinds of situations are arranged usually, the one, a multipath is judged into the multipath that two time delays are not more than a chip period, the 2nd, the multipath of two time delay spacings less than a chip period, judge into a multipath, more than either way can cause reception to descend.The method of first kind of search multidiameter delay of the prior art, under the situation of two sampled points of every chip period, time delay spacing is not less than a chip between each bar footpath that search is come out, this can be avoided two multipaths that two time delays are not more than a chip period are judged in a footpath, but easily two time delay spacings are judged into a multipath less than the multipath of a chip period, especially, if there are several multidiameter delays all to differ about a chip period, their power will aliasing, form the peak value (being called " fat peak ") of a broad, at this moment adopt first kind of multidiameter delay searching method can only search a multi-path location; Adopt second kind of multidiameter delay searching method can not judge into a multipath to two or more time delay spacing less than the multipath of a chip period, but probably a multipath is judged into two multipaths, when fat peak particularly occurring, may be because multipath be judged in the false footpath that aliasing causes.

In a word, code division multiple access system multipath peak value searching method of the prior art is judged inaccurate to the multipath peak, thereby causing the multidiameter delay search inaccurate, trace it to its cause, is the scrambler autocorrelation performance that does not make full use of the power time delay function when searching code division multiple access system multipath peak value.The scrambler of the emission in the communication is subjected to the influence of radio system median filter, its power time delay function, the peak value that is the auto-correlation function of corresponding scrambler has specific shape, as shown in Figure 3, about a peak-peak in chip period scope, correlation is pressed special ratios and is descended, and code division multiple access system multipath peak value searching method of the prior art is also underused this peak value style characteristic of power time delay function.

Summary of the invention

The objective of the invention is to overcome the defective that code division multiple access system multipath peak value searching method of the prior art does not make full use of the scrambler autocorrelation performance of power time delay function and can't accurately judge the multidiameter delay position, to propose a kind of code division multiple access system multipath peak value searching method, by making full use of power time delay function scrambler autocorrelation performance, from the power time delay function, search out multidiameter delay exactly.

Core concept of the present invention is: to the power time delay function in order pointwise scan, if search a peak value greater than the multipath power threshold, then write down the size and the position of this peak value, and from the power time delay function, remove local peaking in this hunting zone, to avoid its interference to search, scan pointer retreats several sampled points then, continue scanning, until the end of scan, if the power time delay peak of function number of sweep record is greater than the multipath number M of limit search, then choose M bigger power time delay functional value from sweep record, its corresponding position is the multidiameter delay position.

For achieving the above object, code division multiple access system multipath peak value searching method of the present invention is characterized in that, may further comprise the steps:

The first step is according to formula $\mathrm{PDP}\left(n\right)={\left|\right|\underset{k=0}{\overset{K}{\mathrm{\Σ}}}R(k+n)*S^{*}\left(k\right)\left|\right|}^2,$ N=0,1,2 ..., Klen-1 rated output time delay function PDP (n), wherein, R (k) is a baseband digital signal, and S (k) is a scrambler sequence, and K is a correlation intergal length, subscript " * " expression complex conjugate, Klen is a search window length;

Second step, initialization search window length K len, multipath energy thresholding Thsd, search pointer kp, search pointer adjusting range BSTP;

In the 3rd step, judge that power time delay function PDP (kp) corresponding to search pointer kp whether less than multipath power threshold Thsd, if then jumped to for the 8th step, otherwise continues;

In the 4th step, judge whether this power time delay function PDP (kp) is peak value, if not peak value, then skips to for the 8th step in hunting zone, otherwise continue;

In the 5th step, write down the numerical value of this power time delay peak of function PDP (kp) and the position kp of correspondence;

The 6th step deducted from the power time delay function and works as previous peaks, and then new power time delay group of functions becomes PDP (kp+i)=PDP (kp+i)-PDP (kp) * P (i), wherein, P (i) is desirable peak value shape, and is proportional with scrambler auto-correlation function peak value shape, i=0, ± 1, ..., ± I, I are positive integer, if in the power time delay function that obtains negative is arranged, then this negative is replaced with 0;

The 7th step, adjust search pointer kp value, make kp=kp-BSTP, if the kp that obtains＜0 then is changed to 0 to kp, went to for the 3rd step.

The 8th step, adjust search pointer kp value, make kp=kp+1;

The 9th step, judge whether search pointer kp equals search window length K len, if, continue, otherwise, three steps of jumping to;

The tenth step, limit the multipath number M that allows search, if the power time delay peak of function number of current sweep record is greater than the multipath number M of limit search, then choose M value by descending order from the multipath power time delay peak of function that searches, the position of this M power time delay functional value correspondence is exactly the multidiameter delay position.

Code division multiple access system multipath peak value searching method of the present invention, overcome the scrambler autocorrelation performance that the code division multiple access system multipath peak value searching method that exists in the prior art does not make full use of the power time delay function, can't accurately judge the defective of multidiameter delay position, made full use of scrambler auto-correlation peak value style characteristic, and adopted the method for similar Interference Cancellation, reduced of the interference of the stronger multipath of energy significantly to other multipath, peak value searching can be searched out at interval less than the multipath of a chip period with easily by the strong weak footpath of directly flooding, can avoid again two or more multipaths are judged in same footpath, obviously improve the multipath peak value searching performance of code division multiple access system.

Description of drawings

Fig. 1 is the position assumption diagram of Multipath searching module in receiving system.

Fig. 2 is Multipath searching modular structure figure.

Fig. 3 is the auto-correlation function peak feature figure of a scrambler in the code division multiple access system.

Fig. 4 is a code division multiple access system multipath peak value searching method flow chart of the present invention.

Fig. 5 is ideal code division multiple access system multipath peak value shape figure.

Fig. 6 uses the exemplary plot that code division multiple access system multipath peak value searching method of the present invention carries out the multipath peak value searching.

Embodiment

Below in conjunction with accompanying drawing the present invention is described in detail.

Fig. 1 is the position assumption diagram of Multipath searching module in receiving system.Reception antenna 101 receives the on-air radio radiofrequency signal, radio-frequency channel 102 is carried out processing such as low noise amplification, automatic gain control, carrier wave demodulation, baseband-converted, A/D sampling, noise filtering to the radio frequency signal of accepting antenna 101 receptions, obtains baseband digital signal.Accepting to have many antenna parallel receives in the system, the every corresponding radio-frequency channel of handling radiofrequency signal of antenna, and Multipath searching module 103 and Rake receiver module 104 are sent to the baseband digital signal that obtains in each radio-frequency channel.Generally speaking, the sampling rate of 104 pairs of baseband digital signals of Rake receiver module is than the sampling rate height of 103 pairs of baseband digital signals of Multipath searching module, the local scrambler of Multipath searching module 103 usefulness carries out the coupling correlation intergal of different delay to the signal of each radio-frequency channel, search out the multidiameter delay information in each circuit-switched data, Rake receiver 104 is according to the multidiameter delay information of each circuit-switched data, the alignment multi-path location carries out descrambling and de-spreading, channel estimating compensation etc., solves sign level data for subsequent module for processing.

Fig. 2 is Multipath searching modular structure figure, comprises relevant matches module 201 and multipath and confirms module 202, and R (k) is the baseband digital signal of input relevant matches module 201, and its sampling period is Ts, and local scrambler sequence is S (k), then power time delay function $\mathrm{PDP}\left(n\right)={\left|\right|\underset{k=0}{\overset{K}{\mathrm{\Σ}}}R(k+n)*S^{*}\left(k\right)\left|\right|}^2,$ Wherein, K is a correlation intergal length, and " * " represents complex conjugate.Multipath confirms that module 202 searches out the functional value PDP (n greater than certain power time delay function threshold in power time delay function PDP (n) _m), then corresponding multidiameter delay is t _m=n _m* Ts.

Fig. 3 is the auto-correlation letter peak of function performance plot of a scrambler in the WCDMA system, and time delay is divided into 1/8 chip period Tc mutually between the wherein adjacent small circle.Because in communication system, scrambler in the received signal is by pulse shaping filtering, and the local scrambler that produces is not pass through pulse shaping, the value of its real part and imaginary part is 1 or-1, so the auto-correlation function here refers to the auto-correlation function of the local scrambler that is shaped by the scrambler in the received signal of pulse shaping filtering with without extra pulse.The correlation function maximum is near 1 among the figure, corresponding local scrambler and the situation that connects the scrambler alignment in the signal, the 1/4Tc if time delay staggers, then coefficient correlation drops to about 0.88, the 1/2Tc if time delay staggers, and then coefficient correlation drops to about 0.58, simultaneously, if two multidiameter delay is at interval less than two chips, both energy are also overlapped probably, and the relation of lap and peak energy as shown in the figure.Code division multiple access system multipath peak value searching method of the present invention has utilized this peak value style characteristic, after searching a peak-peak, deduct this peak value and this peak value from power time delay function kind and overlap energy on the sampled point on every side, to eliminate this peak value there being the influence of multipath on every side.

Fig. 4 is a code division multiple access system multipath peak value searching method flow chart of the present invention, may further comprise the steps:

Step 401 is according to formula $\mathrm{PDP}\left(n\right)={\left|\right|\underset{k=0}{\overset{K}{\mathrm{\Σ}}}R(k+n)*S^{*}\left(k\right)\left|\right|}^2,$ N=0,1,2 ..., Klen-1 rated output time delay function PDP (n), wherein, R (k) is the base digital signal, and S (k) is a scrambler sequence, and K is the sampled point number, subscript " * " expression complex conjugate, Klen is a search window length;

Step 402, initiation parameter, multipath peak value searching process need is configured parameter, some parameter is by system design decision, such as sampling period Ts, and the desirable peak value shape P (i) relevant with sampling period Ts, wherein, i=0, ± 1 ..., ± I, I is a positive integer, but the size of desirable peak value shape P (i) also will establish according to the style characteristic of desirable peak value, and the shape of letter of guarantee number curve P (i) and the shape of desirable peak value are near consistent.Such as, the general value of peak value shape P (i) corresponding to three sampled points of I=1 is P (1)=8/15, P (0)=1, P (1)=8/15, some parameter also can dynamic change in communication process, such as search window length K len, multipath power threshold Thsd etc., in addition, also want initialization search pointer kp to make kp=0, and determine search pointer adjusting range BSTP according to sampling period Ts, the span of search pointer adjusting range BSTP is generally I＜BSTP＜2I;

Step 403 judges that power time delay function PDP (kp) corresponding to search pointer kp whether less than multipath power threshold Thsd, if then jumped to for the 8th step, otherwise continues;

Whether step 404 judges power time delay function PDP (kp) being peak value in the hunting zone, if peak value then continues, otherwise, skip to step 408;

Step 405 writes down the position kp of this multipath power time delay peak of function PDP (kp) and this peak value correspondence;

Step 406 deducts from power time delay function PDP (n) and works as previous peaks, and then new power time delay group of functions becomes PDP (kp+i)=PDP (kp+i)-PDP (kp) * P

(i), if the PDP as a result (kp+i) that obtains is a negative, then this PDP (kp+i) value is changed to 0; Wherein P (i) is proportional with scrambler auto-correlation function peak value shape, be " desirable peak value shape ", and i=0, ± 1 ..., ± I, I are positive integer;

Step 407 is adjusted search pointer kp value, makes kp=kp-BSTP, if kp＜0 then is changed to 0 to kp, jumps to step 403, and in this step search pointer kp back being adjusted is the weak footpath that may be flooded by current multipath in order to search for;

Step 408 is adjusted search pointer kp value, makes kp=kp+1;

Step 409 judges whether search pointer kp equals search window length K len, if, show the end of scan, change step 410 over to, otherwise, show that scanning does not finish, and skips to step 403;

Step 410, the multipath number M that the quantity limit search of the multipath that the energy of getting rid of according to Rake receiver number of branches and needs is less allows, if the multipath power peak number of current sweep record is greater than the multipath number M of limit search, then choose M bigger power time delay functional value by descending order, the position of these power time delay functional value correspondences is exactly the multidiameter delay position, and these multidiameter delay information are exported to subsequent module.

Fig. 5 is desirable multipath peak value shape figure.During 2 sampled points of the corresponding every chip period of this figure, in the auto-correlation function performance plot of local scrambler and received signal scrambler, the relative position between two functional values of peak value and adjacent half chip period.But the size of desirable peak value shape P (i) is set according to this ideal multipath peak value shape, with the shape of the shape of letter of guarantee number curve P (i) and desirable multipath peak value near consistent.

Fig. 6 uses the exemplary plot that code division multiple access system multipath peak value searching method of the present invention carries out the multipath peak value searching.Wherein, Fig. 6 (a) is the part of a concrete power time delay function PDP (n), sampling period Ts is an one half chip period, be 2 sampled points of every chip period, suppose to have 3 multipath P1, P2, P3, its time delay is respectively 4Ts, 5Ts, 7Ts, (7) three positions of corresponding PDP (4), PDP (5) and PDP, and multipath power threshold Thsd is shown in dotted line 601.If, then in Fig. 1 (a), can only be judged as effective peak to PDP (5), so can only find multipath P2 according to first method search multipath peak value of the prior art; If according to second method search multipath peak value of the prior art, then in Fig. 1 (a), can be judged as effective peak to PDP (4), PDP (5), PDP (6), PDP (7) and PDP (8), so except finding (7) three multipaths of PDP (4), PDP (5) and PDP, also these two non-multipaths of PDP (6) and PDP (8) are also judged into effective multipath, increased the interference noise energy after the demodulation greatly.If employing the method for the invention, search pointer kp is since 0, when kp=5, PDP (5) is judged as effective peak, thereby search multipath P2, peak value shape by Fig. 5 cuts multipath P2 then, reduces the interference to the next door multipath, and the power time delay function PDP (n) that obtains is shown in Fig. 6 (b); Make search pointer kp=kp-BSTP, get BSTP=2, continue search from PDP (3), can judge into effective peak to PDP (4) then, thereby search multipath P1, the peak value shape by Fig. 5 cuts multipath P1 again, and the power time delay function PDP (n) that obtains is shown in Fig. 6 (c); Equally, make search pointer kp=kp-2, continue search from PDP (2), can judge into effective peak to PDP (7), search multipath P3, the peak value shape by Fig. 5 cuts multipath P3 again, obtain the result shown in Fig. 6 (d), make search pointer kp=kp-2 again, begin to continue search from PDP (5), up to power time delay function PDP (n) has been searched for.As can be seen, compare with multipath peak value searching method of the prior art, code division multiple access system multipath peak value searching method of the present invention is missed multipath or is searched out false probability directly and reduced greatly, multipath peak value acquisition probability is improved, false alarm probability is descended, and has improved the Multipath searching performance of code division multiple access system.

Claims (3)

1. a code division multiple access system multipath peak value searching method is characterized in that, may further comprise the steps:

The first step is according to formula $\mathrm{PDP}\left(n\right)={\left|\right|\underset{k=0}{\overset{K}{\mathrm{\Σ}}}R(k+n)*S^{*}\left(k\right)\left|\right|}^2,$ N=0,1,2 ..., Klen-1 rated output time delay function PDP (n), wherein, R (k) is a baseband digital signal, and s (k) is a scrambler sequence, and K is a correlation intergal length, subscript " * " expression complex conjugate, Klen is a search window length;

Second step, initialization search window length K len, multipath energy thresholding Thsd, search pointer kp, search pointer adjusting range BSTP;

In the 3rd step, judge that power time delay function PDP (kp) corresponding to search pointer kp whether less than multipath power threshold Thsd, if then jumped to for the 8th step, otherwise continues;

The 4th step, judge whether this power time delay function PDP (kp) is peak value in hunting zone, if not, then jumped to for the 8th step, otherwise continue;

In the 5th step, write down the numerical value of this power time delay peak of function PDP (kp) and the position kp of correspondence;

The 6th step, from former power time delay function PDP (kp), deduct and work as previous peaks, then new power time delay group of functions becomes PDP (kp+i)=PDP (kp+i)-PDP (kp) * P (i), and wherein P (i) is desirable peak value shape, i=0, ± 1, ..., ± I, I are positive integer, if in the new power time delay combination of function that obtains negative is arranged, then this negative is replaced with 0;

The 7th step, adjust search pointer kp value, make kp=kp-BSTP, if the kp that obtains＜0 then is changed to 0 to kp, jumped to for the 3rd step;

The 8th step, adjust search pointer kp value, make kp=kp+1;

The 9th step, judge whether search pointer kp equals search window length K len, if, continue, otherwise, three steps of jumping to;

The tenth step, limit the multipath number M that allows search, if the power time delay peak of function number of current sweep record is greater than the multipath number M of limit search, then choose M value by descending order from multipath power time delay peak of function, the position of these power time delay function higher value correspondences is exactly the multidiameter delay position.

2. code division multiple access system multipath peak value searching method according to claim 1 is characterized in that, the span of the search pointer adjusting range BSTP in described second step is I＜BSTP＜2I, and wherein, I is a positive integer.

3. code division multiple access system multipath peak value searching method according to claim 1, it is characterized in that, the size of desirable peak value shape P (i) in described the 6th step will be established according to the style characteristic of desirable peak value, and the shape of letter of guarantee number curve P (i) and the shape of desirable peak value are near consistent.

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