CN103414492A - Method for multi-user parallel capture of time delay multi-address spread spectrum system - Google Patents
Method for multi-user parallel capture of time delay multi-address spread spectrum system Download PDFInfo
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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
Technical field
The invention belongs to the communications field, relate to a kind of method of in time delay multi-address extension frequency system, the multi-user being carried out parallel capture.
Background technology
The characteristics such as antijamming capability is strong, the multiple access ability strong, the intercepting and capturing rate is low owing to having in spread spectrum communication, good confidentiality and random access discrete address, be subject in the world common concern fast development, at numerous areas such as communication, range finding, location, controls, be widely used at present.In the early stage, spread spectrum technique is mainly used in military field, it is civilian that spread spectrum communication is in the last thirty years progressively moved towards, and obtained development fast, is the 3-G (Generation Three mobile communication system) of main flow as IS-95 cdma system and in the last few years W-CDMA, CDMA200 and TD-SCDMA.
In spread spectrum communication, the method that comparative maturity has been arranged for the acquisition and tracking of unique user, for example the document " based on the pseudo-code fast Acquisition of FFT " on Harbin Engineering University's journal in 2003 is to " based on the pseudo-code fast Acquisition of FFT ", and the acquisition and tracking of unique user is described in detail.A literary composition is to " based on the frequency deviation fast Acquisition of FFT " for " the pseudo-code fast Acquisition algorithm that short-term correlation and FFT combine " shown by Chen Pei, Wang Yun, Chen Jie on Journal of UEST of China in 2009, 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-purpose access channel is not set, the all users' of this system the processing protocol that transmits is unified, and receiving-transmitting sides communication is without any need in advance interchanges of shaking hands, the low time delay communication that just can realize wanting to send out.In this spread spectrum system, relate to the problem of the multi-user being carried out to parallel capture.If adopt the method for capturing and tracing of above mentioned unique user, the situation that is K for the system user number so just need to realize the acquisition and tracking of unique user K time, can take very large system resource like this.Although the 3-G (Generation Three mobile communication system) that IS-95 cdma system and in the last few years W-CDMA, CDMA200 and TD-SCDMA are main flow can be carried out multi-user's parallel capture, in these systems, all needs the extra special-purpose access channel that arranges.
Summary of the invention
Technology of the present invention is dealt with problems and is: overcome the deficiencies in the prior art, a kind of method of carrying out multi-user's parallel capture in spread spectrum system additional dedicated access channel is not set is provided.The PN code phase that the method is worked as a plurality of users' the same receiving terminal of transmitted signal arrival differs 10 more than code phase, 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 that inputs to spread spectrum system, described base-band input signal is used to the parallel code searching method based on FFT, calculate N
fftThe correlation 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) calculate N
fftThe energy of the correlation of individual code phase;
(3) repeating step (1) and step (2) amount to M time, and the result of M time is carried out to 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 the correlation energy that the correlation energy comes front K, and record this K code phase corresponding to correlation energy, wherein K is the resource number of demodulator;
(5) judge whether the maximum related value energy in K the correlation energy of picking out surpasses detection threshold, if surpass detection threshold proceed to step (6), surpass detection threshold and exit; Described detection threshold passes through
Determine, wherein C is the detection threshold invariant, for being greater than 1 constant;
(6) again ask in step (4) the correlation energy of the code phase location that K correlation energy picking out is corresponding, thereby obtain the correlation energy of this K position, then the up-to-date K obtained a correlation energy is compared with detection threshold successively, be greater than the code phase location of thresholding and enter step (7) from K correlation energy, determining the correlation energy;
(7) for the correlation energy of determining, be greater than the available trace demodulation device of code phase location distribution of thresholding, and by code phase information, give the trace demodulation device and carry out trace demodulation.
The method that in described step (4), definite correlation energy comes the correlation energy of front K is: suppose that first value is maximum, since second value and maximum, compare, if this value is greater than maximum, 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; By after first maximum code phase and the zero clearing of left and right n some code phase thereof, find again second maximum, after finding second maximum, to after second maximum code phase and the zero clearing of left and right n some code phase thereof, find again the 3rd maximum again, carry out successively until find the code phase at K maximum and place thereof, wherein n is positive integer.
The present invention's advantage compared with prior art is: the present invention by rational search, controls on FFT parallel capturing method basis and the distribution of trace demodulation resource is controlled, not only search for simultaneously the multi-user but also distribute in real time the trace demodulation resource, can be in the situation that the certain trace demodulation to greatest extent of trace demodulation device resource user profile.The present invention not only takes full advantage of short advantage of FFT code parallel capture time but also can catch simultaneously a plurality of users, to catch on the other hand and separate with following the tracks of, only need a pair of FFT and anti-FFT, tracking phase can change into traditional relevant accumulator, save the tracking phase resource, can be applied to well in military, civilian similar communication.
The accompanying drawing explanation
Fig. 1 is the FB(flow block) of the inventive method;
Fig. 2 is based on the parallel code searching Method And Principle figure of FFT.
Embodiment
As shown in Figure 1, be the FB(flow block) of the inventive method, concrete steps are as follows:
(1) obtain the base-band input signal x (n) that inputs to spread spectrum system, for this base-band input signal x (n), use the parallel code searching method based on FFT, calculate N
fftThe correlation R (m) of individual code phase;
Based on the parallel code searching method handling process of FFT as shown in Figure 2, the baseband signal x of input (n) is N
fftThe FFT computing of counting obtains Y (k), is N with local PN code PN (n)
fftThe C as a result (k) (this result can be deposited in memory while realizing, save the FFT calculation resources) that the FFT counted gets conjugation multiplies each other.Be afterwards N
fftThe anti-FFT counted obtains N
fftThe correlation 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 anti-FFT computing
fftMeet following formula:
N is the Cycle Length of local PN code, and P is for the chip precision of search, as 1/2 chip precision.
(2) calculate N
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）
R wherein
Re(m) and R
Im(m) be 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 when system Eb/No >=8dB, M gets 4 and gets final product usually; When 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 and come the energy value of front K, and record K the code phase that energy value is corresponding, wherein K is the resource number of demodulator;
For avoiding the same user of repeat track, need to will be in tracking phase user's code phase point and left and right n(6 >=n >=3 thereof) the correlation energy zero clearing of individual code phase point.
In the search energy sequence, the method for K maximum value is as follows: suppose that first value is maximum, compare since second value and a upper value, if this value is greater than maximum, maximum is upgraded, 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.By after first maximum code phase and the zero clearing of left and right n some code phase thereof, find again second maximum, after finding second maximum, by after second maximum code phase and the zero clearing of left and right n some code phase thereof, finding again the 3rd maximum, carry out successively until find the code phase at K maximum and place thereof again.
(5) judge whether the maximum energy value in K the correlation energy of picking out surpasses thresholding, if surpass thresholding proceed to step (6), this search of thinking that surpasses thresholding does not have user profile, exits and wait for search next time.
Detection threshold is determined by following formula:
Wherein C is the detection threshold invariant, for being greater than 1 constant;
(6) carry out 2 resident judgements.The method of resident judgement is, asks for again in step (4) the correlation energy of the code phase location that K correlation energy picking out is corresponding, obtains again the correlation energy of this K position.Then the up-to-date K obtained a correlation energy is compared with threshold value successively, from what K correlation energy, pick out again that the correlation energy is greater than threshold value, enter step (7), and will ignore for code phase location corresponding to the correlation energy that is less than threshold value, 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 in the K of the maximum found correlation energy value, that of correlation energy value maximum surpasses thresholding need to be once resident on this position, when resident, do not need again to search maximum K correlation energy value, only need the correlation of preserving K the location point searched last time to get final product.Correlation and positional value when resident are given the trace demodulation resource allocator, continue on the other hand search.If in K maximum correlation energy value, that of correlation energy value maximum surpasses thresholding continues and search for.
(7) after resident, think that its correlation energy is greater than on the time delay that each code phase of threshold value is corresponding to have user profile, be that it distributes available trace demodulation device.
If the tracking assets free time is now arranged, will carry out next step processing to potential user assignment tracking assets (tracking assets only has K).If there is no the tracking assets free time, do not distribute tracking assets, proceed to next search.
(8) resource information that will distribute to the user is written in the trace demodulation resource allocation table, and by code phase information, gives the trace demodulation device and carry out trace demodulation.
Now, determine the trace demodulation resource for respectively each maximum according to K the different priority of maximum, for example can determine according to the size of correlation energy value, correlation energy value more priority is the highest.At first from the situation that takies of trace demodulation resource 1 is looked into, if trace demodulation resource 1 is not taken, trace demodulation resource 1 is distributed to that of correlation energy value maximum.If trace demodulation resource 1 is occupied, check the situation that takies of trace demodulation resource 2.If still occupied the situation of checking 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 the trace demodulation device just to distribute.By code phase information, give the trace demodulation device and carry out trace demodulation, when demodulation finishes, discharge this trace demodulation device.
Embodiment
A. parameter setting
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. according to formula (2), calculate the correlation of 8192 code phases;
C. according to formula (3), calculate the correlation energy of 8192 code phases, and the result of 4 calculating is added up;
D. according to formula (4), calculate detection threshold;
E. for avoiding the same user of repeat track will to be in the correlation zero clearing (if be not in tracking phase just do not need zero clearing) of 4 location points of location point and left and right thereof of tracking phase user by looking into the trace demodulation resource allocator.
F. in step (4), the peaked method of search is searched 8 maximums successively in the correlation energy of 8192 code phases;
G. whether the maximum energy value in 8 correlation energy picking out of judgement surpasses thresholding, in this search, there is no user profile if do not surpass thresholding think, waits for searching and detecting next time; If surpass thresholding once resident, the resident K obtained a correlation energy compares with threshold value successively, be greater than threshold value for the available trace demodulation device of its distribution, when demodulation completes, discharge this trace demodulation device.
The content be not described in detail in specification of the present invention belongs to those skilled in the art's known technology.
Claims (2)
1. multi-user's parallel capturing method of a time delay multi-address extension frequency system, is characterized in that comprising the steps:
(1) obtain the base-band input signal that inputs to spread spectrum system, described base-band input signal is used to the parallel code searching method based on FFT, calculate N
fftThe correlation 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) calculate N
fftThe energy of the correlation of individual code phase;
(3) repeating step (1) and step (2) amount to M time, and the result of M time is carried out to 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 the correlation energy that the correlation energy comes front K, and record this K code phase corresponding to correlation energy, wherein K is the resource number of demodulator;
(5) judge whether the maximum related value energy in K the correlation energy of picking out surpasses detection threshold, if surpass detection threshold proceed to step (6), surpass detection threshold and exit; Described detection threshold passes through
Determine, wherein C is the detection threshold invariant, for being greater than 1 constant;
(6) again ask in step (4) the correlation energy of the code phase location that K correlation energy picking out is corresponding, thereby obtain the correlation energy of this K position, then the up-to-date K obtained a correlation energy is compared with detection threshold successively, be greater than the code phase location of thresholding and enter step (7) from K correlation energy, determining the correlation energy;
(7) for the correlation energy of determining, be greater than the available trace demodulation device of code phase location distribution of thresholding, and by code phase information, give the trace demodulation device and carry out trace demodulation.
2. multi-user's parallel capturing method of a kind of time delay multi-address extension frequency system according to claim 1, it is characterized in that: the method that in described step (4), definite correlation energy comes the correlation energy of front K is: suppose that first value is maximum, since second value and maximum, compare, if this value is greater than maximum, 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; By after first maximum code phase and the zero clearing of left and right n some code phase thereof, find again second maximum, after finding second maximum, to after second maximum code phase and the zero clearing of left and right n some code phase thereof, find again the 3rd maximum again, carry out successively until find the code phase at K maximum and place thereof, wherein n is positive integer.
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| CN109039511A (en) * | 2018-06-19 | 2018-12-18 | 湖南斯北图科技有限公司 | A kind of receiver is anti-interference and the signal processing method of error lock prevention |
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