CN110830077B - Quick capture method for improving receiving performance of multipath burst signals - Google Patents
Quick capture method for improving receiving performance of multipath burst signals Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/69—Spread spectrum techniques
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
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Abstract
A quick capture method for improving the receiving performance of multi-path burst signals is used for solving the problem that a message communication user uses a special pseudo code to carry out signal modulation capture. The method comprises the steps of firstly, acquiring zero intermediate frequency data and pseudo codes, then, dividing the zero intermediate frequency data and the pseudo codes into blocks, and completing expansion of zero intermediate frequency data blocks and pseudo code blocks by using a double-block expansion method; and according to the arrangement rule of the zero intermediate frequency data and the main spread spectrum pseudo code correlation calculation result, phase parallel search and frequency parallel search are completed, and then the capturing of all pseudo code phases is completed. The acquisition method greatly shortens the acquisition search time, has excellent acquisition performance and enables the special pseudo code structure to be applied to actual engineering.
Description
Technical Field
The invention relates to a rapid capturing method for improving the receiving performance of a multipath burst signal, belonging to the technical field of spread spectrum communication.
Background
The signal format of the message communication receiver is a short burst mode, and the duration of the signal is variable. The signal is composed of a synchronization header, a service segment and a data segment. The synchronous head is composed of periodic short codes, does not carry out data modulation and is used for capturing signals by the message communication receiver. The message communication receiver receives message communication signals sent by each terminal, wherein each user synchronization head part consists of the same periodic short code. When a plurality of message communication users send inbound signals simultaneously, the problem of user collision exists, and the multi-access inhibition capability among the users is limited. Aiming at the problem, a new pseudo code is designed. The pseudo code design is realized based on two spreading codes with shorter period, which are respectively called a main spreading code and a secondary spreading code.
The main spread spectrum code is periodically repeated, and the special pseudo code structure is formed by inserting the auxiliary spread spectrum codes with different lengths after each main spread spectrum code period. Different from a constant period repetition code, a plurality of chips of secondary spread spectrum code sequences are inserted after each period of the primary spread spectrum code, and the periodicity of the synchronization head can be effectively destroyed by reasonably designing the number of the inserted spread spectrum code chips after each period, so that the probability of simultaneous inbound collision of different users is reduced, and a specific insertion mode is shown in fig. 1.
In the design of the special pseudo code structure of the message communication signal, the special pseudo code structure comprises main spread spectrum pseudo codes of X1 periods, the number of the inserted auxiliary spread spectrum codes among the main spread spectrum codes meets the relation of arithmetic progression, and the tolerance number is d. The pseudo code structure design can solve the collision problem of simultaneous inbound of multiple users and improve the interference suppression capability among multiple users. However, for the message communication receiver, the new pseudo code structure destroys the characteristics of the periodic pseudo code, and puts new requirements on the design of an acquisition system. The existing capture method is not suitable for capturing a special pseudo code structure.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the method overcomes the defects of the prior art, provides a rapid capturing method for improving the receiving performance of multi-path burst signals, realizes the rapid capturing of modulation signals with special pseudo code structures, has the capturing probability of inbound signals at any time more than 99 percent, and has short capturing time.
The technical solution of the invention is as follows:
a fast acquisition method for improving the receiving performance of a multipath burst signal comprises the following steps:
(1) zero intermediate frequency data and pseudo code acquisition
Generating an acquisition starting moment according to the acquisition starting identifier, finishing acquisition of zero intermediate frequency data and pseudo codes at a pseudo code rate of 2 times, and generating an acquisition ending identifier after the acquisition is ended; the pseudo code is a main spread spectrum code, the collected zero intermediate frequency data is stored in a data area, the collected pseudo code is stored in a pseudo code area, and the collection starting time corresponds to the S-th main spread spectrum code of the zero intermediate frequency data;
(2) double block expansion
After the acquisition is finished, dividing the zero intermediate frequency data and the pseudo code into blocks according to the position of the zero intermediate frequency data stored in the data area and the position of the pseudo code stored in the pseudo code area, and completing the expansion of the zero intermediate frequency data block and the pseudo code block according to a double-block expansion method; wherein the zero intermediate frequency data is the same as the number of blocks divided by the pseudo code;
(3) phase parallel search
Performing FFT operation on each expanded zero intermediate frequency data and each expanded pseudo code, performing conjugate multiplication operation on the k-th zero intermediate frequency data and the FFT operation result of the k-th pseudo code, performing IFFT operation on the operation result to obtain a related calculation result of the zero intermediate frequency data and the pseudo code, and storing the related calculation result in a search area; k is 1, 2, … …, and K is the number of division blocks of the zero intermediate frequency data or the pseudo code in the step (2);
(4) frequency parallel search
Acquiring related results of the same pseudo code phase calculation according to the arrangement rule of the related calculation results of the zero intermediate frequency data and the pseudo codes in a search area, and performing FFT (fast Fourier transform) operation to complete frequency search corresponding to each pseudo code phase;
(5) acquisition decision
And (4) performing energy calculation according to the result output by the FFT operation in the step (4), simultaneously calculating the power of noise, setting a detection threshold according to the capture detection probability and the false alarm probability, and completing capture judgment of all the pseudo code phases.
In the step (1), if the zero intermediate frequency data acquisition time is set to be T milliseconds, then:
setting that the original zero intermediate frequency data contains X1 main spreading codes, and acquiring X2 main spreading codes in T milliseconds, wherein X2 is less than X1;
the pseudo code acquisition time is determined according to the period of the pseudo code, and if the period length of the pseudo code is greater than T milliseconds, the pseudo code acquisition time is equal to T milliseconds; and if the period length of the pseudo code is less than or equal to T milliseconds, the acquisition time of the pseudo code is equal to the period length of one main spread spectrum code.
In the step (2), the method for partitioning the pseudo code comprises the following steps:
setting a main spread spectrum code to be represented by s, wherein one main spread spectrum code period comprises Q chips, and 2Q half chips are obtained after the acquisition is finished at 2 times of the pseudo code rate to form a pseudo code block;
the values of the pseudo code blocks are the same, and let sk(i) Representing the ith half-chip in the kth pseudo-code block, then:
sk(i)＝s(i)1≤i≤2Q
where s (i) denotes the ith half-chip of any one of the dummy code blocks.
In the step (2), the method for performing block division processing on the zero intermediate frequency data comprises the following steps:
the length of a zero intermediate frequency data block is the same as that of a pseudo code block, the zero intermediate frequency data block comprises 2Q sampling data, the zero intermediate frequency data acquired in the T millisecond acquisition time is represented by r, d represents the tolerance number of the main spreading code inserted into the auxiliary spreading code, and rk(i) Represents the ith data in the kth zero intermediate frequency data block
rk(i)＝r(2Qk-2Q-2d+kd+i)1≤i≤2Q。
In the step (2), the spreading of the pseudo code block is completed according to the following method:
the expanded length of the pseudo code block is 8Q,
denotes sk(i) The expanding method of the expanded pseudo code block is as follows:
sk(i) the ith half chip in the kth pseudo-code block.
In the step (2), the zero intermediate frequency data block is expanded according to the following method:
the zero intermediate frequency data block has a length of 8Q after expansion,
is represented by rk(i) The expanding method of the zero intermediate frequency data block after expansion is as follows:
rk(i) is the ith data in the kth zero intermediate frequency data block.
In the step (4), the implementation method for searching the frequency corresponding to each pseudo code phase is as follows:
the acquired zero intermediate frequency data comprises X2 main spreading codes, and as the acquisition starting time corresponds to the S-th main spreading code of the zero intermediate frequency data, the correlation values obtained by the same pseudo code phase calculation are sequentially moved backwards by 2d S phases according to the arrangement rule of the correlation calculation results of the zero intermediate frequency data and the pseudo codes in the search area;
traversing search is carried out on any main spread spectrum period of the original data corresponding to the acquisition time, correlation values obtained by the same pseudo code phase calculation are selected, FFT calculation is carried out, and frequency search corresponding to each pseudo code phase is completed; the correlation values obtained by the same pseudo code phase calculation are X2 in total, and the number of the correlation values is the same as that of the main spreading codes.
The number of FFT calculation points preferably satisfies the n power of 2, n is an integer satisfying 2n-X2 ≧ 0 and taking the minimum value if X2 is less than 2n Adding 2 after the correlation value calculated by the same pseudo code phasen-X2 zeros are calculated for FFT; if X2 equals 2nAnd directly performing FFT calculation.
The implementation manner of the line energy calculation according to the result output by the FFT operation in the step (5) is as follows:
and calculating a capture detection quantity I according to the homodromous component and the orthogonal component output by the FFT operation:
wherein, IPiFor the ith syntropy component, QP, output by FFT operationiThe ith orthogonal component output for the FFT operation;
under the condition of only noise, the noise variance is calculated according to the captured detection quantity I
Then the center of the detected quantity I meeting the standard is captured only when the noise exists
Distributing; if the signal exists, the captured detection quantity I obeys non-center
Distributed, non-central
The distributed parameter λ is 2X snr, X is 1, and snr is the signal-to-noise ratio after coherent accumulation.
In the step (5), a threshold V is detectedtThe calculation is as follows:
Pfais the false alarm probability.
Compared with the prior art, the invention has the advantages that:
(1) aiming at a special pseudo code structure, accumulating energy by adopting a main spread spectrum signal, and discarding the signal energy of a secondary spread spectrum code; according to the rule that the auxiliary spreading code is inserted into the main spreading code, the zero intermediate frequency data are divided into blocks, the division utilizes the characteristics of the auxiliary spreading code inserted into the main spreading code, the sampling rate is twice of the pseudo code rate, the starting time of the divided zero intermediate frequency data blocks is shifted backwards in sequence, and the division method provides conditions for subsequent fast FFT calculation.
(2) The zero intermediate frequency data block and the pseudo code block are subjected to double-block expanding operation, the expanding operation mode ensures the correctness of fast FFT calculation of the zero intermediate frequency data and the pseudo code, and the parallel search of the pseudo code phase can be completed quickly.
(3) Aiming at the capture method of the special pseudo code structure, the position of the correlation value corresponding to the same code phase calculated each time is changed, and the change meets a certain rule. The initial time of capturing data acquisition is located in the S-th main spread spectrum pseudo code interval, and the phases of zero intermediate frequency data and the correlation values of the same pseudo code phases are calculated and are sequentially moved backwards by 2x d x S. According to the arrangement rule, related results of the same pseudo code phase calculation are read to perform FFT operation, and frequency search corresponding to each pseudo code phase is completed. The parallel search of the frequency saves the acquisition computation time of the serial search a lot.
Drawings
FIG. 1 is a pseudo code structure design of a special structure;
FIG. 2 is a pseudo code structure of a special structure;
FIG. 3 is a flow chart of the present invention;
FIG. 4 is a pseudo code sequence of a message communication signal special structure;
fig. 5 division of zero intermediate frequency data blocks;
fig. 6 shows a zero if block after spreading;
fig. 7 shows an extended pseudo code block.
Detailed Description
When a plurality of message communication users send inbound signals simultaneously, there is a problem of user collision and the multiple access suppression capability among users is limited, and the problem can be solved by using the spreading code shown in fig. 2. The pseudo code design is realized based on two spreading codes with shorter period, which are respectively called a main spreading code and a secondary spreading code. The main spread spectrum code is periodically repeated, and the special pseudo code structure is formed by inserting the auxiliary spread spectrum codes with different lengths after each main spread spectrum code period. Each user of the message communication enters the message communication with this special pseudo-code modulated sync header information, which contains X1 primary spreading codes, a primary spreading code period containing Q chips, and d represents the number of the primary spreading code inserted in the secondary spreading code. The message communication receiver receives the inbound information of the message communication user and captures signals through the synchronous head. Intermediate frequency signals received by the message communication receiver are input to a digital down-conversion module after being subjected to AD sampling, digital down-conversion is carried out, zero intermediate frequency data are obtained and sent to a low-pass filter, and the zero intermediate frequency data only contain Doppler information.
The invention is that the zero intermediate frequency data after low-pass filtering is captured and calculated, the capture calculation core aims to solve the problem that the synchronization head pseudo code is inserted into the auxiliary spread spectrum code to destroy the periodicity of the pseudo code, and a new capture method is designed to capture the message communication signal, thereby improving the performance of the message communication receiver for receiving multi-channel burst signals.
The message communication receiver receives the sampled single-path intermediate frequency signal as follows:
in the above formula, tjFor the jth sampling moment, the sampling rate of the local received signal is twice of the pseudo code rate; tau is the time delay of the signal arriving at the message communication receiver; a is the signal amplitude, fL1Is a radio frequency carrier frequency, fdIs Doppler shift, fIFIs the carrier frequency of the intermediate frequency,
is the initial phase, C (t) is the pseudo code, n (t)j) Is additive white gaussian noise at the jth sampling instant.
And performing digital down-conversion on the intermediate frequency signal to obtain zero intermediate frequency data, sending the zero intermediate frequency data to a low-pass filter, and finally obtaining zero intermediate frequency data which can be used for capturing, wherein the original zero intermediate frequency data totally comprises X1 main spreading codes, the acquired zero intermediate frequency data is represented by r (X), the zero intermediate frequency data only comprises Doppler information, and X represents the X-th acquired data.
For the special pseudo code structure, the designed fast capture method is shown in fig. 3, and the steps are as follows:
(1) acquiring zero intermediate frequency data and pseudo codes: generating a sampling start moment according to the capture start identifier, and completing the acquisition of zero intermediate frequency data and pseudo codes at a pseudo code rate of 2 times, wherein the pseudo codes are main spread spectrum codes and are used for the capture calculation of received signals; and collecting the S-th main spread spectrum code of zero intermediate frequency data corresponding to the initial time.
Generating acquisition starting time according to the capture starting identifier, wherein the acquisition starting time has no time reference, the generated time is random, the zero intermediate frequency data totally comprises X1 main spread spectrum codes, the acquisition results are stored in a data area and a pseudo code area respectively, the storage address of each area corresponds to one acquisition result, the acquisition time of the zero intermediate frequency data is set to be T milliseconds, the zero intermediate frequency data totally comprises X2 main spread spectrum codes, and X2 is less than X1; the pseudo code acquisition time is determined according to the period of the pseudo code, and if the period length of the pseudo code is greater than T milliseconds, the pseudo code acquisition time is equal to T milliseconds; if the period length of the pseudo code is less than or equal to T milliseconds, the acquisition time of the pseudo code is equal to the period length of a main spread spectrum code; and after the acquisition of the zero intermediate frequency data and the pseudo code is finished, generating an acquisition finishing identifier.
(2) Double-block expansion: dividing the zero intermediate frequency data and the pseudo code into blocks according to the position of the zero intermediate frequency data stored in the data area and the position of the pseudo code stored in the pseudo code area, wherein the number of the blocks divided by the zero intermediate frequency data and the pseudo code is the same, and the zero intermediate frequency data block and the pseudo code block form a double block; according to a double-block expansion method, dividing and expanding a zero intermediate frequency data block and a pseudo code block;
the main spread spectrum code is represented by s, the period of one main spread spectrum code is Q chips, the acquisition is completed at 2 times of pseudo code rate, and the total number of the chips is 2Q half chips to form a pseudo code block, s (i) represents the ith half chip of the pseudo code block, k represents the block number of the pseudo code block, s (i) represents the number of the pseudo code blockk(i) The ith half chip in the kth pseudo code block is represented, and all the pseudo code blocks have the same value and are represented by the following formula:
sk(i)＝s(i)1≤i≤2Q
the length of a zero intermediate frequency data block is the same as that of a pseudo code block, the zero intermediate frequency data block comprises 2Q sampling data, the zero intermediate frequency data acquired in T millisecond time is represented by r, and r (x) represents the x-th zero intermediate frequency data; k represents a block number of a zero intermediate frequency data block; d represents the tolerance number of the primary spreading code inserted into the secondary spreading code, rk(i) The ith data in the kth zero intermediate frequency data block is represented, and the position of the zero intermediate frequency data is obtained by calculating 2Qk-2Q-2d + kd + i, and can be represented by the following formula:
rk(i)＝r(2Qk-2Q-2d+kd+i)1≤i≤2Q
k is 1, 2, … …, K is the total number of division blocks of zero intermediate frequency data or pseudo code.
The length of the zero intermediate frequency data block and the pseudo code block after double-block expansion is 8Q,
denotes sk(i) The expanding method of the expanded pseudo code block is shown as a formula:
(3) Phase parallel search: respectively carrying out FFT (fast Fourier transform) operation on each expanded zero intermediate frequency data and each expanded pseudo code, carrying out conjugate multiplication operation on the k-th zero intermediate frequency data and the FFT operation result of the k-th pseudo code, and carrying out IFFT operation on the operation result to obtain the related calculation result of the zero intermediate frequency data and the pseudo code
Is stored in the search area in such a manner that,
the position of each phase of the primary spreading code.
And (3) according to the steps and the method, finishing the calculation and result storage of all the zero intermediate frequency data blocks and the pseudo code blocks in the step (2).
(4) Frequency parallel search: the generation time of the acquisition start identifier is unknown, the zero intermediate frequency data and the pseudo code acquisition start time are located at any position of the main spread spectrum code, and the acquisition start time needs to be considered when being located at any position of the main spread spectrum code. Reading the correlation result of the same pseudo code phase calculation to perform FFT operation according to the arrangement rule of the zero intermediate frequency data and the pseudo code correlation calculation in the region, and completing the frequency search corresponding to each pseudo code phase;
collecting and storingThe stored zero-if data contains X2 periods of the main spreading code, and the sampling start time is random and can be located in any period of the main spreading code. And when the initial sampling time of the zero intermediate frequency data is at the S-th main spread spectrum, the correlation value obtained by calculating the same pseudo code phase is sequentially moved backwards by 2x d S phases. Traversing any main spread spectrum period in which the acquisition time is positioned, selecting a correlation value obtained by calculating the same pseudo code phase, and then performing FFT calculation; the correlation values obtained by the same pseudo code phase calculation are X2 in total, and are the same as the cycle number of the main spreading pseudo code; the number of FFT calculation points preferably satisfies the n-th power of 2 (n is an integer satisfying 2)n-X2 ≧ 0 and minimum), if X2 is less than 2nInputting the correlation value obtained by the same pseudo code phase calculation into 2nFFT calculation of X2 zeros, if X2 equals 2nAnd directly performing FFT calculation.
(5) And (3) capturing and judging: according to the result output by FFT operation, energy calculation is carried out, and meanwhile, the power of noise is calculated; and setting a detection threshold according to the capture detection probability and the false alarm probability to finish the capture judgment of all the pseudo code phases.
And calculating a capture detection quantity I according to the homodromous component and the orthogonal component output by the FFT operation:
wherein, IPiFor the ith syntropy component, QP, output by FFT operationiThe ith orthogonal component output for the FFT operation; with an I-obedience degree of freedom of 2
And (4) distribution.
Under the condition of only noise, the noise variance is calculated according to the captured detection quantity I
Then I meets the center of the standard only with noise
Distribution, I obeys non-centre if signal is present
Distribution, non-central distribution parameter is λ 2X snr (performed
X equals 1, snr is the signal-to-noise ratio after coherent accumulation), the center with 2 degrees of freedom can be obtained
Distributed and non-central
The probability distribution of the distribution captures a threshold V according to the detection valuation theory and the calculation relationtCalculated as follows, the false alarm probability PfaIn known amounts.
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with actual simulation data.
In the message communication project, the performance simulation verification is carried out on the capturing method, and the test conditions are as follows:
signal center frequency point: 85.9MHz
Primary spreading code pseudo code period number N2: 50 are provided with
Number of one-period chips of primary spreading code N1: 1023
Pseudo code rate: 1.023MHz
Secondary spreading code length: 1275 are provided with
Length tolerance d of inserted secondary spreading code: 1
Generating a pseudo code rate X MHz: 1.023MHz
Pseudo code period: 1ms
Doppler frequency of 300Hz
Sampling frequency of data and pseudo code: 2.046MHz
Frequency of signal inbound: 1 s/time
The point number of FFT-IFFT of the double expansion data and the pseudo code is as follows: 8192 point
Frequency search FFT point number: 32 points
The message communication users are in random inbound mode, the time of arriving at the message communication receiver meets Poisson random distribution, and the entrance carrier-to-noise ratio C/N0 of the message communication receiver is 36 dBHz. The synchronous head pseudo code adopts the special pseudo code structure, the main spread spectrum adopts an m sequence with the period length of 1023, the auxiliary spread spectrum code adopts an m sequence with the period length of 2046, the length tolerance d of the inserted auxiliary spread spectrum code is equal to 1, the structure of the inserted pseudo code is shown in figure 4 to form a pseudo code sequence with a special structure of the message communication signal, and 10 ten thousand inbound signals are generated to complete the simulation verification of the capturing method.
The data acquisition time is generated by a random number, and matlab randomly generates an integer smaller than 24 as the data acquisition starting time. The zero intermediate frequency data acquisition time is 26ms and comprises 25 finished main spread spectrum codes; the pseudo code acquisition time is determined according to the period of the pseudo code, and the acquisition time is 1 ms; the acquisition of zero intermediate frequency data and pseudo codes is completed at 2 times of pseudo code rate, and the acquisition rate is 2.046 MHz; the data and the pseudo code are divided into 25 blocks, the divided zero intermediate frequency data block is shown in fig. 5, the expanded zero intermediate frequency data block is shown in fig. 6, the expanded pseudo code data block is shown in fig. 7, and the length of the expanded data block is 8184.
The simulation verification is carried out on 10 ten thousand inbound signals, 99920 inbound signals are successfully accessed by a user, the receiving success rate is 99.92%, the capturing time is about 22ms, and the capturing of multiple random access signals can be rapidly completed. By adopting the pseudo code structure design, the user capacity can be improved, and the multi-access inhibition capability is enhanced, so that the receiving performance of multi-path burst signals is improved, and the special pseudo code structure can be applied to actual engineering. Meanwhile, the method can be subjected to parametric design according to the specific requirements of the project, the data acquisition time and the number of points of FFT calculation can be changed according to the actual requirements, and the method has high expansibility.
The above description is only for the best mode of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.
Those skilled in the art will appreciate that the invention may be practiced without these specific details.
Claims (6)
1. A fast acquisition method for improving the receiving performance of a multipath burst signal is characterized by comprising the following steps:
(1) zero intermediate frequency data and pseudo code acquisition
Generating an acquisition starting moment according to the acquisition starting identifier, finishing acquisition of zero intermediate frequency data and pseudo codes at a pseudo code rate of 2 times, and generating an acquisition ending identifier after the acquisition is ended; the pseudo code is a main spread spectrum code, the collected zero intermediate frequency data is stored in a data area, the collected pseudo code is stored in a pseudo code area, and the collection starting time corresponds to the S-th main spread spectrum code of the zero intermediate frequency data;
(2) double block expansion
After the acquisition is finished, dividing the zero intermediate frequency data and the pseudo code into blocks according to the position of the zero intermediate frequency data stored in the data area and the position of the pseudo code stored in the pseudo code area, and completing the expansion of the zero intermediate frequency data block and the pseudo code block according to a double-block expansion method; wherein the zero intermediate frequency data is the same as the number of blocks divided by the pseudo code;
the method for partitioning the pseudo code comprises the following steps:
setting a main spread spectrum code to be represented by s, wherein one main spread spectrum code period comprises Q chips, and 2Q half chips are obtained after the acquisition is finished at 2 times of the pseudo code rate to form a pseudo code block;
the values of the pseudo code blocks are the same, and let sk(i) Representing the ith half-chip in the kth pseudo-code block, then:
sk(i)＝s(i) 1≤i≤2Q
where s (i) denotes the ith half-chip of any one of the dummy code blocks;
the method for dividing and processing the zero intermediate frequency data comprises the following steps:
the length of a zero intermediate frequency data block is the same as that of a pseudo code block, the zero intermediate frequency data block comprises 2Q sampling data, the zero intermediate frequency data acquired in the T millisecond acquisition time is represented by r, d represents the tolerance number of the main spreading code inserted into the auxiliary spreading code, and rk(i) Represents the ith data in the kth zero intermediate frequency data block
rk(i)＝r(2Qk-2Q-2d+kd+i) 1≤i≤2Q；
The expansion of the pseudo code block is completed according to the following method:
the length of the pseudo code block after expansion is 8Q, s'k(i) Denotes sk(i) The expanding method of the expanded pseudo code block is as follows:
sk(i) is the ith half chip in the kth pseudo code block;
the zero intermediate frequency data block is expanded according to the following method:
the length of the zero intermediate frequency data block after expansion is 8Q, r'k(i) Is represented by rk(i) The expanding method of the zero intermediate frequency data block after expansion is as follows:
rk(i) the ith data in the kth zero intermediate frequency data block;
(3) phase parallel search
Performing FFT operation on each expanded zero intermediate frequency data and each expanded pseudo code, performing conjugate multiplication operation on the k-th zero intermediate frequency data and the FFT operation result of the k-th pseudo code, performing IFFT operation on the operation result to obtain a related calculation result of the zero intermediate frequency data and the pseudo code, and storing the related calculation result in a search area; k is 1, 2, … …, and K is the number of division blocks of the zero intermediate frequency data or the pseudo code in the step (2);
(4) frequency parallel search
Acquiring related results of the same pseudo code phase calculation according to the arrangement rule of the related calculation results of the zero intermediate frequency data and the pseudo codes in a search area, and performing FFT (fast Fourier transform) operation to complete frequency search corresponding to each pseudo code phase;
(5) acquisition decision
And (4) performing energy calculation according to the result output by the FFT operation in the step (4), simultaneously calculating the power of noise, setting a detection threshold according to the capture detection probability and the false alarm probability, and completing capture judgment of all the pseudo code phases.
2. The fast acquisition method for improving the receiving performance of the multi-channel burst signal as claimed in claim 1, wherein in the step (1), if the zero intermediate frequency data acquisition time is T milliseconds, then:
setting that the original zero intermediate frequency data contains X1 main spreading codes, and acquiring X2 main spreading codes in T milliseconds, wherein X2 is less than X1;
the pseudo code acquisition time is determined according to the period of the pseudo code, and if the period length of the pseudo code is greater than T milliseconds, the pseudo code acquisition time is equal to T milliseconds; and if the period length of the pseudo code is less than or equal to T milliseconds, the acquisition time of the pseudo code is equal to the period length of one main spread spectrum code.
3. The method as claimed in claim 1, wherein in the step (4), the frequency corresponding to each pseudo code phase is searched for by the following steps:
the acquired zero intermediate frequency data comprises X2 main spreading codes, and as the acquisition starting time corresponds to the S-th main spreading code of the zero intermediate frequency data, the correlation values obtained by the same pseudo code phase calculation are sequentially moved backwards by 2d S phases according to the arrangement rule of the correlation calculation results of the zero intermediate frequency data and the pseudo codes in the search area;
traversing search is carried out on any main spread spectrum period of the original data corresponding to the acquisition time, correlation values obtained by the same pseudo code phase calculation are selected, FFT calculation is carried out, and frequency search corresponding to each pseudo code phase is completed; the correlation values obtained by the same pseudo code phase calculation are X2 in total, and the number of the correlation values is the same as that of the main spreading codes.
4. The fast acquisition method for improving the receiving performance of multi-channel burst signals as claimed in claim 3, wherein the number of FFT calculation points satisfies the power n of 2, n is an integer satisfying 2n-X2 ≧ 0 and taking the minimum value if X2 is less than 2nAdding 2 after the correlation value calculated by the same pseudo code phasen-X2 zeros are calculated for FFT; if X2 equals 2nAnd directly performing FFT calculation.
5. The fast acquisition method for improving the receiving performance of multi-path burst signals according to claim 1, wherein the line energy calculation according to the result output by the FFT operation in step (5) is implemented as follows:
and calculating a capture detection quantity I according to the homodromous component and the orthogonal component output by the FFT operation:
wherein, IPiFor the ith syntropy component, QP, output by FFT operationiThe ith orthogonal component output for the FFT operation;
under the condition of only noise, the noise variance is calculated according to the captured detection quantity I
Then only noise exists, the center x of the standard which is met by the detection quantity I is captured2Distributing; if the signal exists, the captured detection quantity I obeys non-center x2Distribution, non-central χ2The distributed parameter λ is 2X snr, X is 1, and snr is the signal-to-noise ratio after coherent accumulation.
6. The method as claimed in claim 5, wherein the fast acquisition method for improving the performance of receiving the multi-path burst signalWherein in said step (5), the detection threshold V is settThe calculation is as follows:
Pfais the false alarm probability.
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