CN115149979A - Pseudo code synchronization method suitable for variable sampling rate with any length - Google Patents
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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
- H04B1/707—Spread spectrum techniques using direct sequence modulation
- H04B1/7073—Synchronisation aspects
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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
- H04B1/707—Spread spectrum techniques using direct sequence modulation
- H04B1/7073—Synchronisation aspects
- H04B1/7075—Synchronisation aspects with code phase acquisition
Abstract
The invention discloses a pseudo code synchronization method suitable for variable sampling rate with any length, and relates to the field of broadband communication and the field of covert satellite communication. The method adopts a parallel subsection matching correlation module to realize rapid 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 capture length is randomly variable within a certain range, the stepping minimum is 4, the method is flexible to use, 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 field of broadband communication and covert satellite communication, in particular to a pseudo code synchronization method suitable for variable sampling rate with any length, which can be used in covert communication and anti-interference communication fields such as broadband satellite signaling beam communication and unmanned aerial vehicle communication.
Background
Spread spectrum communication is widely applied to a satellite communication system due to the characteristics of strong anti-interference performance, strong anti-interception and anti-detection capabilities and the like, pseudo code capture of a direct sequence spread spectrum system is an essential link in pseudo code synchronization, and subsequent work such as tracking, despreading, demodulation and the like can be successfully completed in sequence only by solving the problem of pseudo code capture synchronization.
In the pseudo code acquisition algorithm of spread spectrum signals, a matched filter becomes one of the most widely applied algorithms due to the characteristics of parallel search and short synchronization time. In the existing communication system, the pseudo code capturing modules are all fixed in sampling rate, one or more capturing lengths are fixed, and specific applications are aimed at, if the capturing length is changed or the sampling rate is changed, the pseudo code capturing modules need to be customized, so that the pseudo code capturing modules have various versions and are disordered, and therefore, a universal pseudo code capturing module which can change the sampling rate and the capturing length is urgently needed.
Disclosure of Invention
In view of this, the present invention provides a pseudo code synchronization method suitable for variable sampling rates of any length, which is suitable for sampling rates of 4 times, 8 times and higher by adopting a capture method based on matched filtering, and can meet most application requirements.
The purpose of the invention is realized by the following steps:
a pseudo code synchronization method suitable for variable sampling rate of any length, is used for utilizing the local spread spectrum code to carry on the phase search to the demodulation data at the receiving end, until the two phases are unanimous, thus realize the pseudo code is synchronous; the method specifically comprises the following steps:
(1) Setting capture length as L, size of code word buffer zone as L/N, and size of data buffer zone as L x 2/N; wherein, N is related to the sampling rate of the demodulation data, N is 4 when 8 times of chip sampling clock is adopted, and N is 2 when 4 times of chip sampling clock is adopted;
(2) Collecting spread spectrum codes, wherein the cycle length of the spread spectrum codes is less than or equal to L, averagely dividing the spread spectrum codes of one cycle into N sections, respectively storing the N sections into N code word cache regions, and supplementing 0 if the high-order part of each code word cache region has a vacancy;
(3) Sequentially sliding and storing externally input demodulation data streams into a data cache region according to the count value of a sampling clock, wherein the length of data stored into the data cache region every time is 2 times of the length of spread spectrum codes stored into a code word cache region, and if the high-order part of the data cache region is vacant, 0 is supplemented;
(4) Determining half spreading code chip time according to the counting value of a sampling clock, performing correlation operation on data in N code word cache regions and data in a data cache region every half spreading code chip time to obtain N correlation values, sequentially storing the N correlation values into a correlation value cache region, performing extraction on the correlation value cache region every L/N every half spreading code chip time, and accumulating the extracted N correlation values to obtain a full correlation value C;
(5) Performing module calculation on the full correlation value obtained in the step (4)C | 2 And comparing the modulo of the full correlation value with the modulo of the capture lengthC | 2 Performing extraction to count M cellsC | 2 Accumulating and summing to obtain an incoherent accumulated value; the value range of M is 32 to 128;
(6) And (4) sequentially comparing the incoherent accumulation value with the capture threshold within the whole capture length time, if the incoherent accumulation value is greater than the capture threshold, outputting a synchronous state mark, otherwise, repeating the steps (4) to (6) until the pseudo codes are synchronous.
Furthermore, the capture length L in the step (1) is arbitrarily variable within the range of 16 to 4096 by 4 steps.
Further, the steps (4) - (6) are performed in a chip-by-chip sliding manner, that is, sliding once every half chip time to obtain a full correlation value and an incoherent accumulation value, and comparing the full correlation value and the incoherent accumulation value with the capture threshold once.
Further, the setting mode of the capture threshold in the step (6) is as follows:
according to the power of the demodulated data and the threshold signal-to-noise ratio, simulating to obtain the incoherent accumulated values of the signal and the spread spectrum code, and obtaining the incoherent accumulated values of the spread spectrum code and the noise; through multiple simulations, a numerical value capable of distinguishing the two incoherent accumulation values is defined as the capture threshold.
Compared with the background technology, the invention has the following advantages:
(1) The pseudo code capturing method can be suitable for sampling rates which are 4 times, 8 times and higher, and can meet the application requirements of most.
(2) The capture length of the invention can be changed in a micro-step configuration within a certain range, thus improving the universality, being expandable and having universal universality.
(3) The resources required by the invention are not increased compared with the conventional acquisition method, the capture probability is also comparable. In addition, the invention adopts sliding matching capture, and the symbol-by-symbol searching mode can save time compared with the traditional window capture.
Detailed Description
The present invention is described in further detail below.
A pseudo code synchronization method suitable for variable sampling rate of any length is used for phase search of local spread spectrum code of a receiving end on demodulated data until the phase of the local spread spectrum code is consistent with that of the demodulated data, so that pseudo code synchronization is realized, and the method comprises the following steps:
(1) Setting capture length as L, code word buffer size as L/N, data buffer length as L2/N, where N is related to data sampling rate, N is 4 when 8 times sampling rate clock, and N is 2 when 4 times chip sampling clock.
(2) Collecting spread spectrum codes, wherein the cycle length of the spread spectrum codes is less than or equal to L, averagely dividing the spread spectrum codes of one cycle into N sections, respectively storing the N sections into N code word cache regions, and supplementing 0 if the high-order part of each code word cache region has a vacancy.
When the data sampling rate is 8 times, four code word cache regions with the length of L/4 are used for storing code words, for spread spectrum codes with the length less than L, the code words are evenly divided into four sections and are sequentially stored in the cache regions, the code words are stored from low to high according to the bits, and the rest parts which are less than L/4 are supplemented with 0; when the data sampling rate is 4 times, the code words are stored by using two code word cache regions with the length of L/2, for the spread spectrum codes with the length of less than L/2, the code words are evenly divided into two sections and are sequentially stored in the cache regions, the code words are stored from low to high according to the bit, and if the code words are empty, 0 is supplemented; the capture length is configurable, the resource consumption and the application requirement are comprehensively considered, the maximum capture length L is selected to be 4096, the extension length is supported, and only the length of a memory needs to be changed and the capture length needs to be reconfigured.
(3) Sequentially sliding and storing externally input demodulation data streams into a data cache region according to the count value of a sampling clock, wherein the length of data stored into the data cache region every time is 2 times of the length of spread spectrum codes stored into a code word cache region, and if the high-order part of the data cache region is vacant, 0 is supplemented;
in view of the problem of acquisition precision related to the sampling interval of data, an excessive acquisition error easily affects the subsequent code tracking and despreading demodulation, thereby affecting the demodulation performance. In the method, when the code tracking capability and the influence on the demodulation performance are considered to be less than 0.5dB, the acquisition error needs to be controlled within a half chip symbol, and the method acquires data under the sampling clock counting according to the principle that each half chip acquires one data and enters a data cache region for subsequent correlation calculation.
(4) Determining half spreading code chip time according to the counting value of a sampling clock, performing correlation operation on data in N code word cache regions and data in a data cache region every half spreading code chip time to obtain N correlation values, sequentially storing the N correlation values into a correlation value cache region, performing extraction on the correlation value cache region every L/N every half chip time, and accumulating the extracted N correlation values once to obtain a full correlation value C.
Performing correlation calculation on the cache data and the stored segmented code words, then storing the calculated data into a cache, performing sliding accumulation on a correlation value of a capture length of one period to obtain a complete full correlation value, performing sliding accumulation by using 4 segments of correlation values when 8 times of data sampling rate is adopted, and resetting a cache region and starting accumulation of the next period at the same time when the data sampling rate is finished; and when the data sampling rate is 4 times, performing sliding accumulation by using 2 sections of correlation values, and resetting the buffer area and starting accumulation of the next period at the same time when the data sampling rate is finished. According to simulation research and analysis, the sampling rate of data for capturing the pseudo code is higher than 8 times, more capturing gain is not additionally brought, and resources are excessively increased, so for input high-power data, extraction processing is required to be firstly carried out to reduce the sampling rate of the data to 8 times or 4 times, and then the data is captured.
(5) Performing modulo and squaring on the full correlation value obtained in the step (4) to obtain the noncashC | 2 And facing the calvities according to the interval of the capture lengthC | 2 Performing extraction to obtain M number of cellsC | 2 Accumulating and summing to obtain non-coherent accumulated value, sequentially aligning each half chip time slideC | 2 Accumulating and summing to obtain the non-coherent accumulated value of all phases in the whole capture length time, and comparing the resultAnd comparing the search result to obtain the maximum incoherent accumulated value, and simulating the M value according to the requirement of the threshold signal-to-noise ratio.
The full correlation value can be truncated according to the actual value and adjusted to a value with a proper amplitude, the incoherent accumulation is that the full correlation value is subjected to modulo and squaring and then correspondingly added, and the incoherent accumulation value adopts a cyclic shift storage and reading mode, so that symbol-by-symbol searching can be realized. The length of the incoherent accumulation is adjustable, the support is 1 to 128 optional, the incoherent accumulation can be set according to an actual demodulation threshold, and when the required demodulation threshold is lower, multi-symbol accumulation is required to be adopted to reduce the burst high-amplitude noise interference through averaging.
(6) And (4) comparing the maximum incoherent accumulation value with a set capture threshold, outputting a synchronous state mark if the maximum incoherent accumulation value is greater than the set threshold, otherwise, repeating the steps (4) to (6) until the pseudo codes are synchronous.
The types of the supported capture threshold are a relative threshold and an absolute threshold which are configurable, the absolute threshold is not processed, and when the relative threshold is adopted, the maximum incoherent accumulation value needs to be normalized to the average power of the signal. The selection of the absolute threshold 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 in the demodulation processing and the data bit number of the acquisition module. The setting of the absolute threshold only depends on the signal-to-noise ratio of the data rather than the data amplitude, and the code synchronization effect of burst spread spectrum is better.
In a word, the invention adopts a parallel segmentation matching correlation module to realize rapid coarse synchronization, the synchronization precision is controlled in half chip time, the invention can be simultaneously suitable for sampling rates of 4 times, 8 times and higher times, the capture length can be randomly changed in a certain range, the stepping minimum is 4, the use is flexible, and the invention is suitable for most application scenes such as broadband satellite communication, unmanned aerial vehicle communication and other covert communication and anti-interference communication.
Claims (4)
1. A pseudo code synchronization method suitable for variable sampling rate of any length is characterized in that the method is used for carrying out phase search on demodulation data by using a local spread spectrum code at a receiving end until the phases of the demodulation data and the local spread spectrum code are consistent, thereby realizing pseudo code synchronization; the method specifically comprises the following steps:
(1) Setting capture length as L, size of code word buffer area as L/N, and size of data buffer area as L x 2/N; wherein, N is related to the sampling rate of the demodulation data, N is 4 when 8 times of chip sampling clock is adopted, and N is 2 when 4 times of chip sampling clock is adopted;
(2) Collecting spread spectrum codes, wherein the cycle length of the spread spectrum codes is less than or equal to L, averagely dividing the spread spectrum codes of one cycle into N sections, respectively storing the N sections into N code word cache regions, and complementing 0 if the high-order part of the code word cache region has spare parts;
(3) Sequentially sliding and storing externally input demodulation data streams into a data cache region according to the count value of a sampling clock, wherein the length of data stored into the data cache region every time is 2 times of the length of spread spectrum codes stored into a code word cache region, and if the high-order part of the data cache region is vacant, 0 is supplemented;
(4) Determining half spreading code chip time according to the counting value of a sampling clock, performing correlation operation on data in N code word cache regions and data in a data cache region every half spreading code chip time to obtain N correlation values, sequentially storing the N correlation values into a correlation value cache region, extracting the correlation value cache region every other L/N in every half spreading code chip time, and accumulating the extracted N correlation values to obtain a full correlation value C;
(5) Calculating a model of the full correlation value obtained in the step (4)C | 2 And comparing the modulo of the full correlation value with the modulo of the capture lengthC | 2 Performing extraction to count M cellsC | 2 Accumulating and summing to obtain an incoherent accumulated value; the value range of M is 32 to 128;
(6) And (4) sequentially comparing the incoherent accumulation value with the capture threshold within the whole capture length time, if the incoherent accumulation value is greater than the capture threshold, outputting a synchronous state mark, otherwise, repeating the steps (4) to (6) until the pseudo codes are synchronous.
2. The pseudo code synchronization method for variable sampling rate of any length as claimed in claim 1, wherein the capture length L in step (1) is arbitrarily variable in 4 steps within a range of 16 to 4096.
3. The pseudo code synchronization method for any length of variable sampling rate according to claim 1, wherein the steps (4) - (6) are performed in a chip-by-chip sliding manner, that is, sliding once every half chip time to obtain a full correlation value and an incoherent accumulation value, and comparing once with the acquisition threshold.
4. The pseudo code synchronization method for any length of variable sampling rate according to claim 1, wherein the capture threshold in step (6) is set by:
according to the power of the demodulated data and the threshold signal-to-noise ratio, simulating to obtain an incoherent accumulated value of the signal and the spread spectrum code, and obtaining an incoherent accumulated value of the spread spectrum code and the noise; through multiple simulations, a numerical value capable of distinguishing the two incoherent accumulation values is defined as the capture threshold.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN115499036A (en) * | 2022-11-14 | 2022-12-20 | 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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