CN103414492B - Method for multi-user parallel capture of time delay multi-address spread spectrum system - Google Patents

Abstract

A method for multi-user parallel capture of a time delay multi-address spread spectrum system comprises the steps that (1) according to a base band input signal, the correlation energy values of Nfft code phase positions are calculated according to the parallel code searching method based on FFT; (2) the step (1) is repeated for M times and incoherent accumulation is conducted on results; (3) the first K correlation energy values are determined from the correlation energy values of the Nfft code phase positions obtained after incoherent accumulation, wherein K is the number of demodulator resources; (4) whether the maximum value of the K correlation energy values exceeds a capture threshold or not is judged, if the answer is positive, the next step is continued and if the answer is negative, quitting is conducted; (5) the correlation energy values of the code phase positions corresponding to the K correlation energy values are calculated again, then, the latest K correlation energy values are compared with the capture threshold one by one, and therefore the code phase positions with the correlation energy values larger than the capture threshold are determined; (6) tracking demodulation resources are distributed to the determined code phase positions with the correlation energy values larger than the capture threshold and tracking demodulation is conducted according to the code phase position information.

Description

A kind of multi-user's parallel capturing method of time delay multi-address extension frequency system

Technical field

The invention belongs to the communications field, relate to a kind of method of in time delay multi-address extension frequency system, multi-user being carried out to parallel capture.

Background technology

The features such as antijamming capability is strong owing to having in spread spectrum communication, multiple access capability is strong, intercepting and capturing rate is low, good confidentiality and random access discrete address, receive common concern in the world and fast development, widely use at numerous areas such as communication, range finding, location, controls at present.In the early stage, spread spectrum technique is mainly used in military field, spread spectrum communication in the last thirty years progressively moves towards civilian, and obtains and develop fast, if IS-95 cdma system and W-CDMA, CDMA200 and TD-SCDMA are in the last few years the 3-G (Generation Three mobile communication system) of main flow.

In spread spectrum communication, acquisition and tracking for unique user has had the method for comparative maturity, such as, document " Interference excision based on FFT " on Harbin Engineering University's journal in 2003 is to " Interference excision based on FFT ", and the acquisition and tracking of unique user is described in detail." in short-term the relevant Interference excision algorithm combined with FFT " that Journal of UEST of China in 2009 is shown by Chen Pei, Wang Yun, Chen Jie a literary composition is to " the frequency deviation fast Acquisition based on FFT ", and the acquisition and tracking of unique user is described in detail.

In some low time delay cordless communication networks, need a kind of time delay multi-address extension frequency system that special access channel is not set, the processing protocol that transmits of all users of this system is unified, and receiving-transmitting sides communication, without any need for interchange of shaking hands in advance, can realize wanting to send out the low time delay communication just sent out.The problem of multi-user being carried out to parallel capture is related in this spread spectrum system.If adopt the method for capturing and tracing of above mentioned unique user, being so that the acquisition and tracking of unique user realizes K time with regard to needing by the situation of K for system user number, very large system resource can being taken like this.Although the 3-G (Generation Three mobile communication system) that IS-95 cdma system and W-CDMA, CDMA200 and TD-SCDMA are in the last few years main flow can carry out the parallel capture of multi-user, all need in such systems extra to arrange special access channel.

Summary of the invention

Technology of the present invention is dealt with problems and is: overcome the deficiencies in the prior art, provides a kind of method of carrying out multi-user's parallel capture in spread spectrum system not arranging additional dedicated access channel.The method differs more than 10 code phases when the PN code phase reaching same receiving terminal that transmits a signal to of multiple user, just can distinguish the transmission information of different user.

Technical solution of the present invention is: a kind of multi-user's parallel capturing method of time delay multi-address extension frequency system, comprises the steps:

(1) obtain the base-band input signal inputing to spread spectrum system, the parallel code searching method based on FFT is used to described base-band input signal, calculate N _fftcorrelation R (m) of individual code phase; Wherein n is the Cycle Length of local PN code, and P is the chip precision of search;

(2) N is calculated _fftthe energy of the correlation of individual code phase;

(3) repetition step (1) and step (2) amount to M time, and the result of M time is carried out noncoherent accumulation, obtain N _fftthe correlation energy noncoherent accumulation value of individual code phase;

(4) N obtained after noncoherent accumulation _fftin the correlation energy of individual code phase, determine that correlation energy comes the correlation energy of front K, and record this K the code phase that correlation energy is corresponding, wherein K is the resource number of demodulator;

(5) judge whether the maximum related value energy in K correlation energy picking out exceedes detection threshold, if exceed detection threshold, proceeds to step (6), does not exceed detection threshold and then exit; Described detection threshold passes through determine, wherein C is detection threshold invariant, for being greater than the constant of 1;

(6) the correlation energy of code phase location corresponding to K correlation energy picking out in step (4) is again asked for, thus obtain the correlation energy of this K position, then the up-to-date K obtained a correlation energy is compared with detection threshold successively, from K correlation energy, determine that correlation energy is greater than the code phase location of thresholding and enters step (7);

(7) code phase location that the correlation energy for determining is greater than thresholding distributes available trace demodulation device, and code phase information is given trace demodulation device and carry out trace demodulation.

Determine in described step (4) that the method that correlation energy comes the correlation energy of front K is: assuming that first value is maximum, compare with maximum from second value, if this value is greater than maximum, then maximum is upgraded, be updated to currency; Otherwise maximum keeps, keep last maximum, and so forth, until N _fftindividual value is more complete, obtains the code phase at first maximum and place thereof; After first maximum code phase and left and right n some code phase thereof are reset, find second maximum again, after finding second maximum, the 3rd maximum is found again after second maximum code phase and left and right n some code phase thereof being reset again, carry out until find the code phase at K maximum and place thereof successively, wherein n is positive integer.

The present invention's advantage is compared with prior art: the present invention controls and the control of trace demodulation Resourse Distribute by reasonably searching on FFT parallel capturing method basis, not only searched for multi-user simultaneously but also distributed trace demodulation resource in real time, can when trace demodulation device resource is certain trace demodulation user profile to greatest extent.The present invention had not only taken full advantage of FFT code parallel capture time short advantage but also can catch multiple user simultaneously, on the other hand acquisition and tracking is separated, only need a pair FFT and inverse FFT, tracking phase can change into traditional correlator accumulator, save tracking phase resource, can be applied to well in military, civilian similar communication.

Accompanying drawing explanation

Fig. 1 is the FB(flow block) of the inventive method;

Fig. 2 is the code searching Method And Principle figure that walks abreast based on FFT.

Embodiment

As shown in Figure 1, be the FB(flow block) of the inventive method, concrete steps are as follows:

(1) obtain base-band input signal x (n) inputing to spread spectrum system, for this base-band input signal x (n), use the parallel code searching method based on FFT, calculate N _fftcorrelation R (m) of individual code phase;

Based on FFT parallel code searching method handling process as shown in Figure 2, the baseband signal x (n) of input is N _fftthe FFT computing of counting obtains Y (k), is N with local PN code PN (n) _fftthe result C (k) (can be deposited in memory by this result when realizing, save FFT calculation resources) that the FFT counted gets conjugation is multiplied.Be N afterwards _fftthe inverse FFT of counting obtains N _fftcorrelation R (m) of individual code phase.

Mathematical principle is as follows:

R(m)=x(n)*PN(-n)=IFFT[FFT(x(n))·FFT ^*(PN(n))] （1）

In formula, * represents circular convolution, and FFT represents Fourier transform, and IFFT represents inverse fourier transform, FFT ^*represent the conjugation of Fourier transform.

Plural FFT wherein and the points N of inverse FFT computing _fftmeet following formula:

$N_{\mathrm{fft}}=\frac{N}{P}---\left(2\right)$

N is the Cycle Length of local PN code, and P is the chip precision of search, as 1/2 chip precision.

(2) N is calculated _fftthe energy of the correlation of individual code phase;

R(m) ²=|R(m)| ²=R _re(m) _i ²+R _im(m) _i ²（3）

Wherein R _re(m) and R _imm () is respectively real part and the imaginary part of R (m) in formula (2).

(3) step (1), (2) continuous N time are calculated, and by each N of M time _fftindividual code phase correlation energy carries out noncoherent accumulation.

M is accumulative frequency, and usually as system Eb/No >=8dB, M gets 4; As Eb/No<8dB, M gets 8 or 16.Wherein Eb/No is the ratio of energy per bit to noise spectral density.

(4) N obtained after noncoherent accumulation _fftin the energy sequence of individual code phase correlation, determine in energy sequence the energy value coming front K, and record code phase corresponding to K energy value, wherein K is the resource number of demodulator;

For avoiding the same user of repeat track, needing will be in code phase point and n(6 >=n >=3, left and right thereof of tracking phase user) the correlation energy of individual code phase point resets.

The method of K value maximum in search energy sequence is as follows: assuming that first value is maximum, compare with a upper value from second value, if this value is greater than maximum, then maximum upgrades, and is updated to currency; Otherwise maximum keeps, keep last maximum, and so forth, until N _fftindividual value is more complete; Obtain the code phase at first maximum and place thereof.After first maximum code phase and left and right n some code phase thereof are reset, find second maximum again, after finding second maximum, find the 3rd maximum again after second maximum code phase and left and right n some code phase thereof being reset again, carry out successively until find the code phase at K maximum and place thereof.

(5) judge whether the maximum energy value in K correlation energy picking out exceedes thresholding, if exceed thresholding, proceed to step (6), what do not exceed thresholding then thinks that this search does not have user profile, then exit and wait for and search for next time.

Detection threshold is determined by following formula:

$\frac{C}{N_{\mathrm{fft}}}\underset{m=1}{\overset{N_{\mathrm{fft}}}{\mathrm{\&Sigma;}}}R{\left(m\right)}^2---\left(4\right)$

Wherein C is detection threshold invariant, for being greater than the constant of 1;

(6) 2 resident judgements are carried out.The method of resident judgement is, asks for the correlation energy of code phase location corresponding to K correlation energy picking out in step (4) again, obtains the correlation energy of this K position again.Then the up-to-date K obtained a correlation energy is compared with threshold value successively, that from K correlation energy, again picks out that correlation energy is greater than threshold value enters step (7), and will ignore for the code phase location that the correlation energy being less than threshold value is corresponding, no longer give in consideration.

It should be noted that, step (5) and step (6) are mainly in order to reduce false alarm probability, if maximum that of correlation energy value exceedes thresholding in maximum K the correlation energy value found, need on this position once resident, do not need time resident again to search a maximum K correlation energy value, only need preserve the correlation of K the location point searched last time.Give trace demodulation resource allocator by correlation time resident and positional value, continue search on the other hand.If maximum that of correlation energy value does not exceed thresholding in maximum K correlation energy value, continue search.

(7) after resident, think that its correlation energy is greater than in time delay corresponding to each code phase of threshold value and there is user profile, then for it distributes available trace demodulation device.

If now there is tracking assets idle, then the process of will distribute tracking assets (tracking assets only has K) to potential user to carry out next step.If do not have tracking assets idle, then do not distribute tracking assets, proceed to next search.

(8) resource information distributing to user is written in trace demodulation resource allocation table, and code phase information is given trace demodulation device and carry out trace demodulation.

Now, the priority different according to K maximum gives each maximum determination trace demodulation resource respectively, and such as can determine according to the size of correlation energy value, the larger then priority of correlation energy value is the highest.First from the situation that takies of trace demodulation resource 1 is looked into, if trace demodulation resource 1 is not taken, then trace demodulation resource 1 is distributed to maximum that of correlation energy value.If trace demodulation resource 1 is occupied, that checks trace demodulation resource 2 takies situation.If still occupied, check the situation of next trace demodulation device, to the last a trace demodulation resource device.If all occupied, do not distribute trace demodulation resource device, continue search until there is trace demodulation device just to distribute.Code phase information is given trace demodulation device and carry out trace demodulation, at the end of demodulation, discharge this trace demodulation device.

Embodiment

A. optimum configurations

The Eb/No=8dB of system, the PN code cycle is N=4096, chip search precision P=1/2, accumulative frequency M=4, detection threshold invariant C=2, system requirements trace demodulation resource K=8.

Like this according to formula (1) N _fft=8192.

B. the correlation of 8192 code phases is calculated according to formula (2);

C. calculate the correlation energy of 8192 code phases according to formula (3), and the result that 4 times calculate is added up;

D. detection threshold is calculated according to formula (4);

E. for avoid the same user of repeat track by looking into trace demodulation resource allocator, the correlation being in location point and left and right thereof 4 location points of tracking phase user is reset (if be not in tracking phase just do not need reset).

F. in step (4), the method for search maximum searches 8 maximums successively in the correlation energy of 8192 code phases;

G. judge whether the maximum energy value in 8 the correlation energy picked out exceedes thresholding, if do not exceed thresholding, think there is no user profile in this search, wait for searching and detecting next time; If exceed thresholding, once resident, the resident K obtained a correlation energy compares with threshold value successively, and what be greater than threshold value distributes available trace demodulation device for it, discharges this trace demodulation device when demodulation completes.

The content be not described in detail in specification of the present invention belongs to the known technology of those skilled in the art.

Claims (1)

1. multi-user's parallel capturing method of time delay multi-address extension frequency system, is characterized in that comprising the steps:

(1) obtain the base-band input signal inputing to spread spectrum system, the parallel code searching method based on FFT is used to described base-band input signal, calculate N _fftcorrelation R (m) of individual code phase; Wherein n is the Cycle Length of local PN code, and P is the chip precision of search;

(2) N is calculated _fftthe energy of the correlation of individual code phase;

(3) repetition step (1) and step (2) amount to M time, and the result of M time is carried out noncoherent accumulation, obtain N _fftthe correlation energy noncoherent accumulation value of individual code phase;

(4) N obtained after noncoherent accumulation _fftin the correlation energy of individual code phase, determine that correlation energy comes the correlation energy of front K, and record this K the code phase that correlation energy is corresponding, wherein K is the resource number of demodulator;

The described method determining that correlation energy comes the correlation energy of front K is: assuming that first value is maximum, from second value and maximum compare, if this value is greater than maximum, then maximum is upgraded, is updated to currency; Otherwise maximum keeps, keep last maximum, and so forth, until N _fftindividual value is more complete, obtains the code phase at first maximum and place thereof; After first maximum code phase and left and right n some code phase thereof are reset, find second maximum again, after finding second maximum, the 3rd maximum is found again after second maximum code phase and left and right n some code phase thereof being reset again, carry out until find the code phase at K maximum and place thereof successively, wherein n is positive integer, 6>=n>=3;

(5) judge whether the maximum related value energy in K correlation energy picking out exceedes detection threshold, if exceed detection threshold, proceeds to step (6), does not exceed detection threshold and then exit; Described detection threshold passes through determine, wherein C is detection threshold invariant, for being greater than the constant of 1;

(6) the correlation energy of code phase location corresponding to K correlation energy picking out in step (4) is again asked for, thus obtain the correlation energy of this K position, then the up-to-date K obtained a correlation energy is compared with detection threshold successively, from K correlation energy, determine that correlation energy is greater than the code phase location of thresholding and enters step (7); If do not have correlation energy to be greater than the code phase location of thresholding in K correlation energy, then think there is no user profile in this search, wait for searching and detecting next time and return step (4);

(7) code phase location that the correlation energy for determining is greater than thresholding distributes available trace demodulation device, and code phase information is given trace demodulation device and carry out trace demodulation.