Capturing method compatible with multiple modes and multiple sampling rates

Abstract

The invention discloses a capturing method compatible with multiple modes and multiple sampling rates, and relates to the field of spread spectrum and non-spread spectrum communication systems in satellite communication. According to the method, two paths of parallel code words are mainly adopted, matching, accumulation and other processing are carried out, and capturing synchronization of various signals is flexibly adapted by changing parameters such as data bit width, matching mode selection, sampling rate adjustment and the like. A universal capturing method is adopted, the problem of capturing module customization under the condition of different modes or different sampling rates is solved, preliminary estimation of carrier frequency offset can be achieved in an auxiliary mode, and carrier synchronization is accelerated. The method is easy to implement, few in occupied resources, operable and high in transportability. The method is very suitable for FPGA implementation, and is beneficial to rapid synchronization of spread spectrum and non-spread spectrum signals.

Description

Technical Field

[0001] The present invention relates to the field of satellite communication, and in particular to a capture method compatible with multiple modes and multiple sampling rates, which can improve the signal detection and synchronization capabilities in broadband satellite communication. Background Art

[0002] Spread spectrum communication is widely used in satellite communication systems due to its strong anti-interference, anti-interception and anti-detection capabilities. Pseudo-code capture of direct sequence spread spectrum systems is an indispensable link in pseudo-code synchronization. Only when the pseudo-code capture and synchronization problem is solved can subsequent tasks such as tracking, despreading, and demodulation be completed smoothly in sequence.

[0003] In the pseudo code acquisition algorithm of spread spectrum signals, the matched filter has become one of the most widely used algorithms due to its parallel search and short synchronization time. In existing communication systems, pseudo code acquisition modules have fixed sampling rates and fixed one or several capture lengths, which are targeted at a specific application. If the capture length or sampling rate changes, the pseudo code acquisition module needs to be customized, and the conventional capture method for long code capture wastes a lot of register resources. Therefore, there is an urgent need for a universal pseudo code acquisition module that can change the sampling rate and is suitable for multiple modes. Summary of the invention

[0004] The purpose of the present invention is to provide a capture method compatible with multiple modes and multiple sampling rates. The present invention can be applied to multiple modes, multiple sampling rates, multiple matching methods and capture lengths, and can provide a frequency deviation estimation result, solving the problem of using different modules in different modes, and has universality.

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

[0006] A multi-mode and multi-sampling rate compatible capture method comprises the following steps:

[0007] (1) Using the spread spectrum code module to generate two spread spectrum codes pn1 and pn2 respectively, and output them to the spread spectrum code shift registers reg1 and reg2 respectively, and output a work completion signal load_over after the codeword of the spread spectrum code is completely filled into the spread spectrum code shift register;

[0008] (2) After load_over is pulled high, two parallel data paths enter the shift register; each time a data path is shifted, the two data paths of the shift register are respectively XORed with the code words of the spread spectrum code shift registers reg1 and reg2;

[0009] (3) The two XOR operation results are accumulated according to the coherent accumulation length L, and the amplitude of the accumulated value is adjusted according to the truncation setting;

[0010] (4) storing the accumulated values ​​after the two amplitude adjustments;

[0011] (5) Processing the two-channel amplitude-adjusted accumulated values ​​under the configuration of the acquisition mode. If the coherent mode is adopted, the two-channel accumulated values ​​are respectively subjected to the square sum operation of the in-phase branch and the orthogonal branch and then stored, and each channel of data is stored as one channel; if the differential mode is adopted, the accumulated values ​​corresponding to adjacent symbols are respectively differentiated and then stored, and each channel of data is stored as two channels;

[0012] (6) Under the control of the incoherent accumulation length, control the storage data to accumulate and store the interval coherent accumulation length until the storage length reaches the incoherent accumulation length N;

[0013] (7) Processing the incoherent accumulated value under the configuration of the capture mode, when the storage length reaches the incoherent accumulated length N, performing the square sum operation of the accumulated values ​​of the two stored data corresponding to the in-phase branch and the orthogonal branch in the differential mode and then outputting them; directly outputting the accumulated value of the stored data in the coherent mode;

[0014] (8) Compare and judge the capture threshold and the output value. If it is greater than the capture threshold, capture synchronization is performed and a capture synchronization signal is output to complete the capture synchronization of the signal. After the signal is captured and synchronized, the accumulated value after amplitude adjustment is read to estimate the frequency deviation.

[0015] Furthermore, the specific method of step (1) is: the spread spectrum code module generates a spread spectrum code under the drive of the code length, initial phase and generating polynomial. If the input data is two channels of one-time sampling data, pn1 and pn2 use the same spread spectrum code. If the input data is greater than one-time sampling data, only one spread spectrum code is required and one of the two input data is set to 0.

[0016] Furthermore, in step (2), the bit width of the shift register is less than or equal to 5 bits.

[0017] Furthermore, the specific process of step (8) is as follows:

[0018] In the incoherent accumulation, a counting method is adopted. A maximum value search is performed during the incoherent accumulation N-1 period, and the position of the maximum value max_addr is recorded. The position corresponding to max_addr during the incoherent accumulation N period is the accumulated value corresponding to max_addr+sample*L. The accumulated value is compared with the preset capture threshold. If it is greater than the capture threshold, it is considered that the capture is synchronized, and a capture synchronization signal is output. After the signal capture synchronization is completed, the accumulated value of 128 sample points with amplitude adjustment in the storage is read according to the capture synchronization indication interval sample*L for frequency deviation estimation; wherein N is the incoherent accumulation length, L is the coherent accumulation length, and sample represents the number of sampling points per symbol data.

[0019] Compared with the background technology, the present invention has the following advantages:

[0020] 1. The algorithm adopted by the present invention is suitable for the capture and synchronization of spread spectrum signals, and is also suitable for the detection and synchronization of non-spread spectrum signals.

[0021] 2. The present invention adopts multi-level adaptation and can be applied to a variety of capture algorithms. It can realize differential capture as well as coherent capture, and the sampling rate can also be configured.

[0022] 3. The capture algorithm adopted by the present invention is independent of the spread spectrum ratio, and auxiliary estimation of frequency offset can be realized while capturing, so that rapid synchronization of the carrier can be achieved. DETAILED DESCRIPTION

[0023] The present invention is described in further detail below.

[0024] A multi-mode and multi-sampling rate compatible capture method comprises the following steps:

[0025] (1) Using the spread spectrum code module to generate two spread spectrum codes pn1 and pn2 respectively, and output them to the spread spectrum code shift registers reg1 and reg2 respectively, and output a work completion signal load_over after the codeword of the spread spectrum code is completely filled into the spread spectrum code shift register;

[0026] The spread spectrum code module generates a spread spectrum code driven by the code length, initial phase and generating polynomial. If the input data is two channels of one-time sampling data, pn1 and pn2 use the same spread spectrum code. If the input data is greater than one-time sampling data, only one spread spectrum code is needed and one of the two input data is set to 0.

[0027] (2) After load_over is pulled high, two parallel data paths enter the shift register; each time a data path is shifted, the two data paths of the shift register are respectively XORed with the code words of the spread spectrum code shift registers reg1 and reg2.

[0028] The bit width of the shift register is designed to be up to 5 bits, which can achieve data input of less than or equal to 5 bits. For non-spread spectrum signal capture, only 1 bit of input data is required, and for spread spectrum applications, 5 bits can meet the vast majority of existing spread spectrum code capture requirements.

[0029] (3) The two XOR operation results are accumulated according to the coherent accumulation length L, and the amplitude of the accumulated value is adjusted according to the truncation setting.

[0030] (4) The accumulated values ​​after the two amplitude adjustments are stored.

[0031] (5) Processing the two-channel amplitude-adjusted accumulated values ​​under the configuration of the acquisition mode. If the coherent mode is adopted, the two-channel accumulated values ​​are respectively subjected to the square sum operation of the in-phase branch and the orthogonal branch and then stored, and each channel of data is stored as one channel; if the differential mode is adopted, the accumulated values ​​corresponding to adjacent symbols are respectively differentiated and then stored, and each channel of data is stored as two channels;

[0032] The storage still uses two-way storage. In the differential mode, two-way storage is performed. In the coherent mode, only one way is used for storage, and the other way is set to 0.

[0033] (6) Under the control of the incoherent accumulation length, the stored data is controlled to be accumulated and stored at intervals of the coherent accumulation length until the storage length reaches the incoherent accumulation length N.

[0034] (7) In the capture mode, the incoherent accumulated value is processed. When the storage length reaches the incoherent accumulated length N, the accumulated values ​​of the two stored data are output after the square sum operation corresponding to the in-phase branch and the orthogonal branch is performed in the differential mode; the accumulated value of the stored data is directly output in the coherent mode.

[0035] (8) Compare and judge the capture threshold and the output value. If it is greater than the capture threshold, capture synchronization is performed and a capture synchronization signal is output to complete the capture synchronization of the signal. After the signal is captured and synchronized, the accumulated value after amplitude adjustment is read to estimate the frequency deviation.

[0036] In the incoherent accumulation, a counting method is adopted. A maximum value search is performed during the incoherent accumulation N-1 period, and the position of the maximum value max_addr is recorded. The position corresponding to max_addr during the incoherent accumulation N period is the accumulated value corresponding to max_addr+sample*L. The accumulated value is compared with the preset capture threshold. If it is greater than the capture threshold, it is considered that the capture is synchronized, and a capture synchronization signal is output. After the signal capture synchronization is completed, the accumulated value of 128 sample points with amplitude adjustment in the storage is read according to the capture synchronization indication interval sample*L for frequency deviation estimation; wherein N is the incoherent accumulation length, L is the coherent accumulation length, and sample represents the number of sampling points per symbol data.

[0037] In summary, the present invention discloses a capture method compatible with multiple modes and multiple sampling rates, and relates to the field of spread spectrum and non-spread spectrum communication systems in satellite communications. The present invention mainly adopts two-way parallel codewords and matching, accumulation and other processing, and utilizes the changes in parameters such as data bit width, matching method selection, and sampling rate adjustment to flexibly adapt the capture synchronization of various signals. A universal capture method is adopted to solve the problem of customization of capture modules under different modes or different sampling rates, and it can also assist in the preliminary estimation of carrier frequency deviation and accelerate carrier synchronization. The present invention is simple to implement, occupies few resources, and is operable and highly portable. It is very suitable for FPGA implementation and is conducive to the rapid synchronization of spread spectrum and non-spread spectrum signals.

[0038] The above is only a specific implementation of the present invention, but the protection scope of the present invention is not limited thereto. Any equivalent replacement or change made by a person skilled in the art based on the technical solution and inventive concept of the present invention shall be included in the protection scope of the present invention.

Claims

1. A capture method compatible with multiple modes and multiple sampling rates, characterized in that: The following steps are involved: (1) Using the spread spectrum code module to generate two spread spectrum codes pn1 and pn2 respectively, and output them to the spread spectrum code shift registers reg1 and reg2 respectively, and output a work completion signal load_over after the codeword of the spread spectrum code is completely filled into the spread spectrum code shift register; (2) After load_over is pulled high, two parallel data paths enter the shift register; each time a data path is shifted, the two data paths of the shift register are respectively XORed with the code words of the spread spectrum code shift registers reg1 and reg2; (3) The two XOR operation results are accumulated according to the coherent accumulation length L, and the amplitude of the accumulated value is adjusted according to the truncation setting; (4) storing the accumulated values ​​after the two amplitude adjustments; (5) Processing the two-channel amplitude-adjusted accumulated values ​​under the configuration of the capture mode. If the coherent mode is adopted, the two-channel accumulated values ​​are respectively subjected to the square sum operation of the in-phase branch and the orthogonal branch and then stored, and each channel of data is stored as one channel; If the differential mode is used, the accumulated values ​​corresponding to adjacent symbols are differentiated and then stored, and each data path is stored as two paths; (6) Under the control of the incoherent accumulation length, control the storage data to accumulate and store the interval coherent accumulation length until the storage length reaches the incoherent accumulation length N; (7) Processing the incoherent accumulated value under the configuration of the capture mode, when the storage length reaches the incoherent accumulated length N, performing the square sum operation of the accumulated values ​​of the two stored data corresponding to the in-phase branch and the orthogonal branch in the differential mode and then outputting them; directly outputting the accumulated value of the stored data in the coherent mode; (8) Compare and judge the capture threshold and the output value. If it is greater than the capture threshold, capture synchronization is performed and a capture synchronization signal is output to complete the capture synchronization of the signal. After the signal is captured and synchronized, the accumulated value after amplitude adjustment is read to estimate the frequency deviation.

2. A capture method compatible with multiple modes and multiple sampling rates according to claim 1, characterized in that: The specific method of step (1) is as follows: the spread spectrum code module generates a spread spectrum code driven by the code length, initial phase and generating polynomial. If the input data is two channels of one-time sampling data, pn1 and pn2 use the same spread spectrum code. If the input data is greater than one-time sampling data, only one spread spectrum code is required and one of the two input data is set to 0.

3. The capture method compatible with multiple modes and multiple sampling rates according to claim 1, characterized in that: The bit width of the shift register in step (2) is less than or equal to 5 bits.

4. The capture method compatible with multiple modes and multiple sampling rates according to claim 1, characterized in that: The specific process of step (8) is as follows: In the incoherent accumulation, a counting method is adopted. A maximum value search is performed during the incoherent accumulation N-1 period, and the position of the maximum value max_addr is recorded. The position corresponding to max_addr during the incoherent accumulation N period is the accumulated value corresponding to max_addr+sample*L. The accumulated value is compared with the preset capture threshold. If it is greater than the capture threshold, it is considered that the capture is synchronized, and a capture synchronization signal is output. After the signal capture synchronization is completed, the accumulated value of 128 sample points with amplitude adjustment in the storage is read according to the capture synchronization indication interval sample*L for frequency deviation estimation; wherein N is the incoherent accumulation length, L is the coherent accumulation length, and sample represents the number of sampling points per symbol data.