CN115149979B - Pseudo code synchronization method applicable to variable sampling rate of any length - Google Patents
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Abstract
The invention discloses a pseudo code synchronization method suitable for variable sampling rate with any length, and relates to the fields of broadband communication and hidden satellite communication. The method adopts the parallel segmentation matching correlation module to realize quick coarse synchronization, the synchronization precision is controlled within half chip time, the method can be simultaneously suitable for sampling rates of 4 times, 8 times and higher times, the capturing length is arbitrarily variable within a certain range, the step is minimum to be 4, the use is flexible, and the method is suitable for most application scenes such as hidden communication and anti-interference communication of broadband satellite communication, unmanned aerial vehicle communication and the like.
Description
Technical Field
The invention relates to the fields of broadband communication and hidden satellite communication, in particular to a pseudo code synchronization method applicable to variable sampling rate of any length, which can be used in the fields of hidden communication and anti-interference communication such as broadband satellite signaling beam communication, unmanned aerial vehicle communication and the like.
Background
The spread spectrum communication is widely applied to satellite communication systems due to the characteristics of strong anti-interference, anti-interception and anti-detection capabilities and the like, and the pseudo code capturing of a direct sequence spread spectrum system is an essential link in pseudo code synchronization, so that the follow-up tasks such as tracking, despreading, demodulation and the like can be successfully completed in sequence only by solving the problem of pseudo code capturing synchronization.
Among the pseudo code capturing algorithms of spread spectrum signals, a matched filter is one of the most widely used algorithms due to its characteristic of parallel search and short synchronization time. In the existing communication system, the pseudo code capturing module is fixed in sampling rate and one or several capturing lengths are fixed for a specific application, if the capturing length is changed or the sampling rate is changed, the pseudo code capturing module needs to be customized, so that the version of the pseudo code capturing module is various and chaotic, and therefore, a general pseudo code capturing module capable of changing the sampling rate and the capturing length is needed.
Disclosure of Invention
In view of this, the present invention provides a pseudo code synchronization method suitable for variable sampling rate of any length, which adopts a capture method based on matched filtering, is suitable for sampling rates of 4 times, 8 times and higher, and can meet most application requirements.
The purpose of the invention is realized in the following way:
a pseudo code synchronization method suitable for variable sampling rate of any length is used for carrying out phase search on demodulation data by utilizing a local spread spectrum code at a receiving end until the phases are consistent, thereby realizing pseudo code synchronization; the method specifically comprises the following steps:
(1) Setting the capturing length as L, setting the size of a code word buffer area as L/N, and setting the size of a data buffer area as L x 2/N; wherein N is related to the sampling rate of the demodulated data, N is 4 when the 8-time chip sampling clock is adopted, and N is 2 when the 4-time chip sampling clock is adopted;
(2) Collecting spreading codes, wherein the period length of the spreading codes is less than or equal to L, equally dividing the spreading codes of one period into N sections, respectively storing the N sections into N code word buffer areas, and supplementing 0 if the high-order part of the code word buffer area has a spare space;
(3) Sequentially sliding the externally input demodulation data stream into a data buffer area according to the count value of a sampling clock, wherein the data length stored into the data buffer area each time is 2 times of the length of a spread spectrum code stored into a code word buffer area, and if the high-order part of the data buffer area has a spare space, 0 is supplemented;
(4) Determining half spread spectrum code chip time according to the count value of the sampling clock, performing correlation operation on data in N code word buffer areas and data in the data buffer areas respectively at intervals of half spread spectrum code chip time to obtain N correlation values, sequentially storing the N correlation values in the correlation value buffer areas, extracting the correlation value buffer areas at intervals of L/N at each half spread spectrum code chip time, and accumulating the extracted N correlation values to obtain a full correlation value C;
(5) Modulo the full correlation value obtained in step (4)C | 2 And modulo the full correlation value at intervals of the capture lengthC | 2 Extracting M|pieces of the extractedC | 2 Accumulating and summing to obtain a non-coherent accumulation value; m has a value range of 32-128;
(6) And (3) comparing and judging the incoherent accumulated value with the capture threshold in sequence within the whole capture length time, outputting a synchronous state mark if the incoherent accumulated value is larger than the capture threshold, otherwise, repeating the steps (4) - (6) until the pseudo codes are synchronous.
Further, the capturing length L in the step (1) is arbitrarily variable in steps of 4 within the range of 16-4096.
Further, the steps (4) - (6) are performed in a manner of sliding chip by chip, namely, each half chip slides once in time to obtain a full correlation value and an incoherent accumulation value, and the full correlation value and the incoherent accumulation value are compared with a capture threshold once.
Further, the setting mode of the capturing threshold in the step (6) is as follows:
according to the power of the demodulation data and the threshold signal-to-noise ratio, the incoherent accumulation values of the signal and the spread spectrum code are obtained through simulation, and the incoherent accumulation values of the spread spectrum code and the noise are obtained; through multiple simulations, a value is defined as the acquisition threshold that can distinguish between the two incoherent accumulated values.
Compared with the background technology, the invention has the following advantages:
(1) The pseudo code capturing method can be suitable for sampling rates of 4 times, 8 times and higher, and can meet most application requirements.
(2) The capturing length of the invention can be configured to be variable in tiny steps within a certain range, so that the universality is improved, the capturing length is expandable, and the capturing length has universal universality.
(3) Compared with the conventional capturing method, the method does not increase the required resources, and the capturing probability is equivalent. In addition, the invention adopts sliding matching capture, and the symbol-by-symbol searching mode can save more time than the traditional window capture.
Detailed Description
The present invention will be described in further detail below.
A pseudo code synchronization method applicable to variable sampling rate with arbitrary length is used for searching the phase of demodulation data by a local spread spectrum code of a receiving end until the phases are consistent so as to realize pseudo code synchronization, and comprises the following steps:
(1) The capturing length is set to be L, the size of the code word buffer area is set to be L/N, the length of the data buffer area is set to be L x 2/N, wherein N is related to the sampling rate of data, N is 4 when an 8-time sampling rate clock is adopted, and N is 2 when a 4-time chip sampling clock is adopted.
(2) The method comprises the steps of collecting spreading codes, wherein the period length of the spreading codes is less than or equal to L, dividing the spreading codes of one period into N sections averagely, storing the N sections into N code word buffer areas respectively, and supplementing 0 if the high-order part of the code word buffer area has a spare space.
For the spread spectrum code with length less than L, the code word is averagely divided into four sections which are sequentially stored in the buffer area, and the rest part less than L/4 is complemented with 0 according to the bit from low to high; the code word is stored in two code word buffer areas with the length of L/2 when the data sampling rate is 4 times, for the spread spectrum code with the length smaller than L/2, the code word is averagely divided into two sections and sequentially stored in the buffer areas, and the code word is stored from low to high according to the bits, and the code word is filled with 0 when the code word is left; the capturing length is configurable, and comprehensively considers resource consumption and application requirements, the capturing length Lmax is 4096, and the expanding length is supported, so that only the length of the memory is required to be changed and the capturing length is required to be reconfigured.
(3) Sequentially sliding the externally input demodulation data stream into a data buffer area according to the count value of a sampling clock, wherein the data length stored into the data buffer area each time is 2 times of the length of a spread spectrum code stored into a code word buffer area, and if the high-order part of the data buffer area has a spare space, 0 is supplemented;
in view of the problem that the sampling interval of data is related to the accuracy of capturing, the capturing error is too large to easily influence the subsequent code tracking and despreading demodulation, thereby influencing the demodulation performance. In the method, when the code tracking capability and the influence on demodulation performance are considered to be less than 0.5dB, the acquisition error needs to be controlled within half chip symbols, and in the method, data is acquired under the counting of a sampling clock according to the principle that each half chip acquires one data, and then the data is acquired into a data buffer area to carry out subsequent related calculation.
(4) And determining half spread spectrum code chip time according to the count value of the sampling clock, performing correlation operation on data in N code word buffer areas and data in the data buffer areas respectively every half spread spectrum code chip time to obtain N correlation values, sequentially storing the N correlation values in the correlation value buffer areas, extracting the correlation value buffer areas every L/N for every half chip time, and accumulating the extracted N correlation values once to obtain a full correlation value C.
The method comprises the steps of performing correlation calculation on cache data and stored segment code words, storing the cache data and the stored segment code words into the cache, performing sliding accumulation on a correlation value of a capturing length of one period to obtain a complete full correlation value, performing sliding accumulation on the full correlation value by using 4 segments of correlation values when the sampling rate of 8 data is adopted, and clearing a cache area and starting accumulation of the next period at the end; and when the sampling rate of the data of 4 times is adopted, 2 sections of related values are used for sliding accumulation, and when the sliding accumulation is finished, the buffer area is cleared and the accumulation of the next period is started. According to simulation research analysis, the data sampling rate for pseudo code capture is higher than 8 times without additionally bringing more capture gain, and only excessive increase of resources is caused, so that the input high-power data in the invention needs to be extracted firstly to reduce the data sampling rate to 8 times or 4 times for capturing.
(5) The full correlation value obtained in the step (4) is subjected to modulo and square obtaining|C | 2 And pairs according to the interval of the capturing lengthC | 2 Extracting M|pieces of the extracted dataC | 2 The non-coherent accumulation value is obtained by accumulation and summation, and each half of the chip time slides to the sub-value in sequenceC | 2 Accumulating and summing to obtain incoherent accumulation values of all phases in the whole capturing length time, comparing and searching the results to obtain the maximum incoherent accumulation value, and simulating the M value according to the requirement of the threshold signal-to-noise ratio.
The full correlation value can be cut and bit adjusted to a value with proper amplitude according to the actual value, and incoherent accumulation is to perform corresponding addition after modulo and squaring on the full correlation value, and the incoherent accumulation value adopts a cyclic shift storage and reading mode, so that symbol-by-symbol searchability can be realized. The incoherent accumulation length is adjustable, supports 1 to 128 to be optional, can be set according to an actual demodulation threshold, and needs to adopt multi-symbol accumulation to reduce noise interference with burst high amplitude through averaging when the required demodulation threshold is lower.
(6) Comparing and judging the maximum incoherent accumulated value with a set capture threshold, outputting a synchronous state mark if the maximum incoherent accumulated value is larger than the set threshold, otherwise, repeating the steps (4) - (6) until pseudo codes are synchronous.
The type of the supporting acquisition threshold is configurable for a relative threshold and an absolute threshold, the absolute threshold is adopted without processing, and the maximum incoherent accumulated value is required to be normalized to the average power of the signal when the relative threshold is adopted. The absolute threshold selection in the application needs to be obtained by simulation according to the power value of the actual received data, and mainly refers to the AGC value and the data bit number of the acquisition module in the demodulation processing. The absolute threshold is set only depending on the signal-to-noise ratio of the data, not the data amplitude, and the code synchronization effect on burst spread spectrum is better.
In a word, the invention adopts the parallel segmentation matching correlation module to realize quick coarse synchronization, the synchronization precision is controlled within half chip time, the invention can be simultaneously suitable for sampling rates of 4 times, 8 times and higher times, the capturing length is arbitrarily changeable within a certain range, the step minimum is 4, the use is flexible, and the invention is suitable for most application scenes such as hidden communication and anti-interference communication of broadband satellite communication, unmanned aerial vehicle communication and the like.
Claims (4)
1. The pseudo code synchronization method is characterized by being used for carrying out phase search on demodulation data by utilizing a local spread spectrum code at a receiving end until phases of the two are consistent, thereby realizing pseudo code synchronization; the method specifically comprises the following steps:
(1) Setting the capturing length as L, setting the size of a code word buffer area as L/N, and setting the size of a data buffer area as L x 2/N; wherein N is related to the sampling rate of the demodulated data, N is 4 when the 8-time chip sampling clock is adopted, and N is 2 when the 4-time chip sampling clock is adopted;
(2) Collecting spreading codes, wherein the period length of the spreading codes is less than or equal to L, equally dividing the spreading codes of one period into N sections, respectively storing the N sections into N code word buffer areas, and supplementing 0 if the high-order part of the code word buffer area has a spare space;
(3) Sequentially sliding the externally input demodulation data stream into a data buffer area according to the count value of a sampling clock, wherein the data length stored into the data buffer area each time is 2 times of the length of a spread spectrum code stored into a code word buffer area, and if the high-order part of the data buffer area has a spare space, 0 is supplemented;
(4) Determining half spread spectrum code chip time according to the count value of the sampling clock, performing correlation operation on data in N code word buffer areas and data in the data buffer areas respectively at intervals of half spread spectrum code chip time to obtain N correlation values, sequentially storing the N correlation values in the correlation value buffer areas, extracting the correlation value buffer areas at intervals of L/N at each half spread spectrum code chip time, and accumulating the extracted N correlation values to obtain a full correlation value C;
(5) Modulo the full correlation value obtained in step (4)C | 2 And modulo the full correlation value at intervals of the capture lengthC | 2 Extracting M|pieces of the extractedC | 2 Accumulating and summing to obtain a non-coherent accumulation value; m has a value range of 32-128;
(6) And (3) comparing and judging the incoherent accumulated value with the capture threshold in sequence within the whole capture length time, outputting a synchronous state mark if the incoherent accumulated value is larger than the capture threshold, otherwise, repeating the steps (4) - (6) until the pseudo codes are synchronous.
2. The pseudo code synchronization method of claim 1, wherein the capturing length L in the step (1) is arbitrarily variable in steps of 4 in a range of 16 to 4096.
3. The pseudo code synchronization method of the variable sampling rate according to claim 1, wherein the steps (4) - (6) are performed in a chip-by-chip sliding manner, that is, each half chip slides once in time, so as to obtain a full correlation value and an incoherent accumulation value, and the full correlation value and the incoherent accumulation value are compared with a capture threshold once.
4. The method for synchronizing pseudo code of variable sampling rate applicable to arbitrary length according to claim 1, wherein the setting mode of the acquisition threshold in step (6) is as follows:
according to the power of the demodulation data and the threshold signal-to-noise ratio, the incoherent accumulation values of the signal and the spread spectrum code are obtained through simulation, and the incoherent accumulation values of the spread spectrum code and the noise are obtained; through multiple simulations, a value is defined as the acquisition threshold that can distinguish between the two incoherent accumulated values.
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| CN115499036B (en) * | 2022-11-14 | 2023-02-24 | 北京航空航天大学合肥创新研究院(北京航空航天大学合肥研究生院) | Parallel capturing method and storage medium for broadband spread spectrum signal |
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