A demodulation and synchronization method for large spreading ratio signals in broadband satellite anti-interference communication

Abstract

The present invention discloses a demodulation and synchronization method for a large spread spectrum ratio signal of broadband satellite anti-interference communication, and relates to the field of broadband satellite communication and covert communication. The method uses a short code periodically cycled long code to spread the spectrum, uses a PMF-FFT method to achieve two-dimensional search and capture of code phase and frequency deviation, uses a method of adjusting data sampling points to achieve code tracking synchronization, and uses a matched filter capture method to achieve symbol synchronization, while solving the problem that the initial phase of short code capture symbol data cannot be determined. A unified clock and parallel multi-channel data demodulation processing method is used to reduce the processing clock frequency, which can adapt to data demodulation with a large spread spectrum ratio under a certain range of Doppler frequency deviation, and is suitable for most application scenarios such as drone communication in broadband satellite communication, covert communication behind special platforms such as submarines, and anti-interference communication.

Description

Technical Field

[0001] The present invention relates to the fields of broadband communication and concealed satellite communication, and in particular to a demodulation and synchronization method for a large spread spectrum ratio signal of broadband satellite anti-interference communication, which can be used in the fields of concealed communication and anti-interference communication behind special weapon platforms such as broadband satellites, unmanned aerial vehicle communications, and submarine communications. Background Art

[0002] Spread spectrum communication is widely used in satellite communication systems due to its strong anti-interference, anti-interception and concealment capabilities. With the growing demand for communication bandwidth, the requirement for anti-interference capability to achieve normal communication in complex electromagnetic environments is also increasing, and modulation and demodulation of large spread spectrum ratio signals has also been born.

[0003] In the future, the spread spectrum ratio supported in broadband covert waveforms will be as high as tens of thousands, or even hundreds of thousands. If long code spread spectrum is used, it will be difficult to continue to use traditional pseudo-code capture due to resource occupation. Therefore, the receiving end needs to ensure strict timing assistance. Even with the strict timing assistance of Beidou and high-precision clock sources, long code capture synchronization cannot be achieved due to the inability to accurately estimate the transmission delay. Summary of the invention

[0004] In view of this, the present invention provides a demodulation and synchronization method for a large spreading ratio signal of broadband satellite anti-interference communication. The method comprehensively considers the complexity and resource occupancy of pseudo code capture implementation, and the large spreading ratio spread spectrum considers the use of short codes periodically cyclically converted into long codes for spread spectrum, so that the receiving end can greatly save capture resources, while improving feasibility and reducing implementation complexity.

[0005] The technical solution adopted by the present invention is:

[0006] A demodulation synchronization method for a large spreading ratio signal of a broadband satellite anti-interference communication is used for demodulation synchronization of a broadband large spreading ratio signal at a receiving end, comprising the following steps:

[0007] (1) A short pseudo-random sequence of length L with good autocorrelation is selected, and the short pseudo-random sequence of L is repeated periodically M times to form a spread spectrum code of length ML; at the transmitting end, the coded modulated signal is spread with the spread spectrum code and data mapping is performed, and then sent to the shaping filter module for data shaping, and then sent to the D / A module, and sent out after intermediate frequency modulation;

[0008] (2) The demodulator uses PMF-FFT to capture pseudo code of the data to be demodulated after demodulation preprocessing and matched filtering, so as to achieve coarse synchronization between the local codeword and the spread spectrum data to be demodulated, and reduce the synchronization error to within half a code chip;

[0009] (3) According to the pseudo code synchronization indication, the start code generator generates a local pseudo code sequence and sends it to the full correlator module. The spread spectrum data to be demodulated and the local spread spectrum sequence are directly correlated and accumulated and delayed correlated in the full correlator. Then, the leading branch data and the lagging branch data are output to the tracking and detection module. The tracking and detection module performs power statistics on the data of the leading and lagging branches and compares the power values. If the leading branch is greater than the lagging branch, the number of samples of the currently received spread spectrum chip data is increased. Otherwise, the number of samples of the currently received spread spectrum chip data is reduced, thereby achieving pseudo code tracking synchronization;

[0010] (4) After the pseudo code is captured and synchronized, the L spreading code periods are sequentially slid, and the sliding matched filter capture method is repeatedly used for each spreading code period to obtain the non-correlated accumulation result, and the non-correlated accumulation result is compared with the set threshold. If it exceeds the threshold, it is considered that the search is correct, thereby determining the starting phase of the symbol and achieving symbol synchronization;

[0011] Complete the demodulation and synchronization of large spread spectrum ratio signals for broadband satellite anti-interference communications.

[0012] Furthermore, in step (1), the length of the short pseudo-random sequence does not exceed 1024, and the short code whose length is less than an integral period uses a truncated sequence of the pseudo-random sequence, and ensures that the length of the long code is an integer multiple of the length of the short code.

[0013] Furthermore, the PMF-FFT capture in step (2) is implemented by parallel multi-channel processing, and a periodic cumulative statistical value is obtained by multi-cycle calculation and accumulation to improve the noise resistance and capture performance. n The FFT data with times the length is padded with 0.

[0014] Furthermore, the specific method of sliding matched filter capture in step (4) is:

[0015] The local spread spectrum sequence is stored, and every time the data to be demodulated slides half a code chip, the local spread spectrum sequence and the spread spectrum data to be demodulated are first correlated and accumulated with a length of L, and then the correlation accumulation result is correlated and accumulated with a length of M to obtain full correlation accumulation data, and finally the full correlation accumulation data is non-correlatedly accumulated to obtain a non-correlated accumulation result.

[0016] Compared with the background technology, the present invention has the following advantages:

[0017] 1. The spread spectrum code of the present invention adopts a long code with a short code periodically circulating, so as to solve the problem that the long code capture consumes a lot of resources and is difficult to implement.

[0018] 2. The present invention can be applied to both continuous spread spectrum communication and demodulation synchronization of burst spread spectrum communication.

[0019] 3. The demodulation performance of the present invention is comparable to that of conventional short code demodulation, and the capture probability is also comparable. Implementation

[0020] The present invention is described in further detail below.

[0021] A demodulation and synchronization method for a large spreading ratio signal of broadband satellite anti-interference communication comprises the steps of:

[0022] (1) A short pseudo-random sequence of length L with good autocorrelation and good balance is selected, and the short pseudo-random sequence of L is periodically repeated M times to form a spread spectrum code of length ML. At the transmitting end, the coded modulated signal is spread with the spread spectrum code and then data mapping is performed. The signal is then sent to the shaping filter module for data shaping and then sent to the D / A module for intermediate frequency modulation and then sent out;

[0023] (2) The demodulator uses PMF-FFT to capture the spread spectrum code of the data to be demodulated after demodulation preprocessing and matched filtering, so as to achieve coarse synchronization between the local codeword and the spread spectrum data to be demodulated, and reduce the synchronization error to within half a code chip;

[0024] (3) The pseudo-code synchronization indication is used to start the code generator to generate a local spread spectrum sequence and send it to the full correlator module. The spread spectrum data to be demodulated and the local spread spectrum sequence are directly correlated and accumulated and delayed correlated in the full correlator, and then the leading branch data and the lagging branch data are output and sent to the tracking and detection module. The tracking and detection module performs power statistics of a certain length on the data of the leading and lagging branches and compares the power values. If the leading branch is greater than the lagging branch, the number of samples of the current local spread spectrum code chip data is increased, otherwise the number of samples of the current local spread spectrum code chip is reduced, thereby achieving pseudo-code tracking synchronization;

[0025] (4) After pseudo-code capture synchronization, the idea of ​​sliding matched filter capture is adopted to first perform correlation accumulation of length L on the local spread spectrum sequence and the spread spectrum data to be demodulated, and then perform correlation accumulation of length M on the correlation accumulation result to obtain the full correlation accumulation data. Finally, a certain length of non-correlation accumulation is performed on the full correlation accumulation data, and the above process is repeated by sliding L spread spectrum code periods in turn. The non-correlation accumulation result is compared with the set threshold. If it exceeds the threshold, it is considered that the search is correct, thereby determining the starting phase of the symbol, solving the phase ambiguity problem after short code demodulation, and achieving symbol synchronization.

[0026] Complete the demodulation and synchronization of large spread spectrum ratio signals for broadband satellite anti-interference communications.

[0027] This method uses short codes to periodically cycle into long codes for spectrum spread, uses PMF-FFT to achieve two-dimensional search and capture of code phase and frequency deviation, and uses codeword sampling rate conversion to achieve code tracking synchronization. For the problem that the initial phase of short code capture symbol data cannot be determined, the matched filter capture method is used to achieve symbol synchronization. This method can adapt to burst data demodulation with large spread ratio under a certain range of Doppler frequency deviation, and is flexible and extensible to use.

[0028] The following is a more specific embodiment:

[0029] A demodulation synchronization method for a large spreading ratio signal of broadband satellite anti-interference communication is used for despreading and demodulating a burst broadband spread spectrum signal at a receiving end, comprising the following steps:

[0030] (1) A short pseudo-random sequence of length L with good autocorrelation and good balance is selected, and the short pseudo-random sequence of L is periodically repeated M times to form a spread spectrum code of length ML. At the transmitting end, the coded modulated signal is spread with the spread spectrum code and then data mapping is performed. The signal is then sent to the shaping filter module for data shaping and then sent to the D / A module for intermediate frequency modulation and then sent out;

[0031] The spread spectrum of the large spreading ratio signal adopts the method of periodically circulating a short pseudo-random sequence into a long code. Taking into account the implementation complexity and resource occupancy rate, the maximum length L of the short pseudo-random sequence is selected to be 1024. For the short code whose length L is less than an integer period, a truncated sequence of the periodic pseudo-random sequence is used, and the long code length is an integer multiple M of the short code length, which can reduce the processing complexity and save storage resources.

[0032] (2) The demodulator uses the PMF-FFT method to capture the spread spectrum code of the data to be demodulated after demodulation preprocessing and matched filtering, so as to achieve coarse synchronization between the local codeword and the spread spectrum data to be demodulated, and reduce the synchronization error to within half a code chip.

[0033] The PMF-FFT capture method requires the use of chip clocks to process parallel multi-channel data, and the use of multi-cycle calculation and accumulation to improve noise resistance, and the accumulated statistical value is used for judgment. The cycle accumulation number is generally greater than 16. In the pseudo code capture method based on PMF-FFT, for less than 2 n The FFT data with a length of multiples needs to be padded with zeros before FFT, which can reduce spectrum leakage and improve performance. The selection of partial correlation accumulation length and FFT length needs to consider the signal-to-noise ratio requirements, and ensure that FFT can clearly guarantee frequency discrimination when the signal-to-noise ratio requirements are met.

[0034] (3) The pseudo-code synchronization indication is used to start the code generator to generate a local spread spectrum sequence and send it to the full correlator module. The spread spectrum data to be demodulated and the local spread spectrum sequence are directly correlated and accumulated and delayed correlated in the full correlator, and then the leading branch data and the lagging branch data are output and sent to the tracking and detection module. The tracking and detection module performs power statistics of a certain length on the data of the leading and lagging branches and compares the power values. If the leading branch is greater than the lagging branch, the number of samples of the current local spread spectrum code chip data is increased, otherwise the number of samples of the current local spread spectrum code chip is reduced, thereby achieving pseudo-code tracking synchronization;

[0035] For broadband spread spectrum signals, due to the high chip rate, parallel multi-channel processing is required to complete tracking, demodulation and other processing. In order to improve the tracking adjustment accuracy and tracking performance, the chip clock and 8-channel parallel data processing are adopted. The error between the local chip and the spread spectrum data to be demodulated is controlled within 1 / 8 chip, and the impact on the demodulation performance is no more than 0.5dB.

[0036] (4) After pseudo-code capture synchronization, the idea of ​​sliding matched filter capture is adopted to first perform correlation accumulation of length L on the local spread spectrum sequence and the spread spectrum data to be demodulated, and then perform correlation accumulation of length M on the correlation accumulation result to obtain the full correlation accumulation data. Finally, a certain length of non-correlation accumulation is performed on the full correlation accumulation data, and the correlation and non-correlation processing is repeated by sliding L spread spectrum code periods in turn. The non-correlation accumulation result is compared with the set threshold. If it exceeds the threshold, it is considered that the search is correct, thereby determining the starting phase of the symbol, solving the phase ambiguity problem after short code demodulation, and achieving symbol synchronization.

[0037] The use of short code cyclic long code to spread spectrum needs to solve the symbol ambiguity problem after pseudo code capture, that is, after the short code capture is completed, the starting position of the symbol data cannot be accurately determined. The method of matching the initial phase of the symbol using the sliding matching filter algorithm is not sensitive to data with long continuous 0 or long continuous 1. In order to achieve fast and accurate data synchronization, the data after the pseudo code capture is required to be scrambled symbol data or known auxiliary data.

[0038] In summary, the present invention uses short codes to periodically cycle into long codes for spectrum spread, uses PMF-FFT to achieve two-dimensional search and capture of code phase and frequency deviation, uses the method of adjusting data sampling points to achieve code tracking synchronization, and uses the method of matched filter capture to achieve symbol synchronization, while solving the problem that the initial phase of short code capture symbol data cannot be determined. The processing method of unified clock and parallel multi-channel data demodulation reduces the processing clock frequency, can adapt to data demodulation with large spread ratio under a certain range of Doppler frequency deviation, and is suitable for most application scenarios such as drone communication in broadband satellite communication, covert communication behind special platforms such as submarines, and anti-interference communication.

Claims

1. A demodulation and synchronization method for a large spreading ratio signal of broadband satellite anti-interference communication, characterized in that: The demodulation synchronization of a broadband and large spreading ratio signal at a receiving end includes the following steps: (1) A short pseudo-random sequence of length L with good autocorrelation is selected, and the short pseudo-random sequence of L is repeated periodically M times to form a spread spectrum code of length ML; at the transmitting end, the coded modulated signal is spread with the spread spectrum code and data mapping is performed, and then sent to the shaping filter module for data shaping, and then sent to the D / A module, and sent out after intermediate frequency modulation; (2) The demodulator uses PMF-FFT to capture pseudo code of the data to be demodulated after demodulation preprocessing and matched filtering, so as to achieve coarse synchronization between the local codeword and the spread spectrum data to be demodulated, and reduce the synchronization error to within half a code chip; (3) According to the pseudo code synchronization indication, the start code generator generates a local pseudo code sequence and sends it to the full correlator module. The spread spectrum data to be demodulated and the local spread spectrum sequence are directly correlated and accumulated and delayed correlated in the full correlator. Then, the leading branch data and the lagging branch data are output to the tracking and detection module. The tracking and detection module performs power statistics on the data of the leading and lagging branches and compares the power values. If the leading branch is greater than the lagging branch, the number of samples of the currently received spread spectrum code chip data is increased. Otherwise, the number of samples of the currently received spread spectrum code chip data is reduced, thereby achieving pseudo code tracking synchronization; (4) After the pseudo code is captured and synchronized, the L spreading code periods are sequentially slid, and the sliding matched filter capture method is repeatedly used for each spreading code period to obtain the non-correlated accumulation result, and the non-correlated accumulation result is compared with the set threshold. If it exceeds the threshold, it is considered that the search is correct, thereby determining the starting phase of the symbol and achieving symbol synchronization; Complete the demodulation and synchronization of large spread spectrum ratio signals for broadband satellite anti-interference communications.

2. The demodulation and synchronization method of a large spreading ratio signal for broadband satellite anti-interference communication according to claim 1, characterized in that: In step (1), the length of the short pseudo-random sequence does not exceed 1024. The short code whose length is less than an integral period uses a truncated sequence of the pseudo-random sequence, and ensures that the length of the long code is an integer multiple of the length of the short code.

3. The demodulation and synchronization method of a large spreading ratio signal for broadband satellite anti-interference communication according to claim 1, characterized in that: The PMF-FFT capture in step (2) is implemented by parallel multi-channel processing, and the periodic cumulative statistical value is obtained by multi-cycle calculation and accumulation to improve the noise resistance and capture performance. n The FFT data with times the length are padded with 0.

4. The demodulation and synchronization method of a large spreading ratio signal for broadband satellite anti-interference communication according to claim 1, characterized in that: The specific method of sliding matched filtering capture in step (4) is: The local spread spectrum sequence is stored, and every time the data to be demodulated slides half a code chip, the local spread spectrum sequence and the spread spectrum data to be demodulated are first correlated and accumulated with a length of L, and then the correlation accumulation result is correlated and accumulated with a length of M to obtain full correlation accumulation data, and finally the full correlation accumulation data is non-correlatedly accumulated to obtain a non-correlated accumulation result.