A capture method compatible with multiple modes and multiple sampling rates

Abstract

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 parallel codewords and matching, accumulation and other processing, and utilizes changes in parameters such as data bit width, matching method selection, and sampling rate adjustment to flexibly adapt the capture synchronization of various signals. The use of a universal capture method solves the problem of customizing capture modules under different modes or different sampling rates, and can also assist in achieving preliminary estimation of carrier frequency deviation and accelerate carrier synchronization. The present invention is simple to implement, occupies few resources, and is highly operational and portable. It is very suitable for FPGA implementation and is conducive to the rapid synchronization of spread spectrum and non-spread spectrum signals.

Description

Technical Field

[0001] The present invention relates to the field of satellite communications, and in particular to a multi-mode and multi-sampling rate compatible capture method capable of improving signal detection and synchronization capabilities in broadband satellite communications. 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.

[0003] Among spread spectrum signal pseudo-code acquisition algorithms, the matched filter, with its parallel search and short synchronization time, is one of the most widely used. In existing communication systems, pseudo-code acquisition modules typically operate at a fixed sampling rate and have one or several fixed capture lengths, tailored to specific applications. Changing the capture length or sampling rate requires customizing the module, and capturing long codes using conventional capture methods wastes significant register resources. Therefore, a universal pseudo-code acquisition module with variable sampling rates and adaptability to multiple modes is urgently needed. Summary of the Invention

[0004] The present invention aims to provide a multi-mode and multi-sampling rate capture method. The present invention is applicable to multiple modes, multiple sampling rates, multiple matching methods, and capture lengths, and can provide a single frequency offset estimation result, thus solving the problem of using different modules in different modes and demonstrating its versatility.

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

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

[0007] (1) The spread spectrum code module generates two spread spectrum codes pn1 and pn2 respectively, and outputs them to the spread spectrum code shift registers reg1 and reg2 respectively. After the spread spectrum code codeword is completely filled into the spread spectrum code shift register, the work completion signal load_over is output;

[0008] (2) After load_over is pulled high, two parallel data are input into the shift register. Each time a data is shifted, the two data in the shift register are XORed with the code words of the spread spectrum code shift registers reg1 and reg2 respectively.

[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-way amplitude-adjusted accumulated values ​​in the acquisition mode configuration. If the coherent mode is used, the two-way accumulated values ​​are respectively subjected to the square sum operation of the in-phase branch and the orthogonal branch and then stored, with each data path stored as one path; if the differential mode is used, the accumulated values ​​corresponding to adjacent symbols are respectively differentiated and then stored, with each data path stored as two paths;

[0012] (6) Under the control of the incoherent accumulation length, the stored data is controlled to be accumulated at intervals of the coherent accumulation length and stored until the storage length reaches the incoherent accumulation length N;

[0013] (7) Processing the incoherent accumulated value in the capture mode configuration. 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 the result; directly outputting the accumulated value of the stored data in the coherent mode;

[0014] (8) Compare and judge the output value using the capture threshold. 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 as follows: 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 double sampling data, pn1 and pn2 use the same spread spectrum code. If the input data is greater than double sampling data, only one spread spectrum code is required and one of the two input data is set to 0.

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

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

[0018] In the non-coherent accumulation, a counting method is adopted. A maximum value search is performed during the non-coherent accumulation N-1 period, and the position of the maximum value max_addr is recorded. The position corresponding to max_addr during the non-coherent 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 after amplitude adjustment in the storage is read according to the capture synchronization indication interval sample*L for frequency deviation estimation; where N is the non-coherent 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 used in 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 both differential capture and 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 can realize auxiliary estimation of frequency offset while capturing, thereby achieving rapid synchronization of the carrier. 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) The spread spectrum code module generates two spread spectrum codes pn1 and pn2 respectively, and outputs them to the spread spectrum code shift registers reg1 and reg2 respectively. After the spread spectrum code codeword is completely filled into the spread spectrum code shift register, the work completion signal load_over is output;

[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 double sampling data, pn1 and pn2 use the same spread spectrum code. If the input data is greater than double sampling data, only one spread spectrum code is required and one of the two input data is set to 0.

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

[0028] The bit width of the shift register is designed to be up to 5 bits, which can realize data input of less than or equal to 5 bits. For non-spread spectrum signal capture, only 1 bit of input data is required, while 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-way amplitude-adjusted accumulated values ​​in the acquisition mode configuration. If the coherent mode is used, the two-way accumulated values ​​are respectively subjected to the square sum operation of the in-phase branch and the orthogonal branch and then stored, with each data path stored as one path; if the differential mode is used, the accumulated values ​​corresponding to adjacent symbols are respectively differentiated and then stored, with each data path stored as two paths;

[0032] The storage still uses two-way storage. In differential mode, two-way storage is performed. In 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 at intervals of the coherent accumulation length and stored 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 in the differential mode; the accumulated value of the stored data is directly output in the coherent mode.

[0035] (8) Compare and judge the output value using the capture threshold. 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 non-coherent accumulation, a counting method is adopted. A maximum value search is performed during the non-coherent accumulation N-1 period, and the position of the maximum value max_addr is recorded. The position corresponding to max_addr during the non-coherent 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 after amplitude adjustment in the storage is read according to the capture synchronization indication interval sample*L for frequency deviation estimation; where N is the non-coherent 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, which relates to the field of spread spectrum and non-spread spectrum communication systems in satellite communications. The present invention mainly adopts two parallel codewords and matching, accumulation and other processing, and utilizes changes in parameters such as data bit width, matching method selection, and sampling rate adjustment to flexibly adapt the capture synchronization of various signals. The use of a universal capture method solves the problem of customizing the capture module under different modes or different sampling rates, and 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 highly operational and 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 embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent replacement or modification 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 scope of protection 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) The spread spectrum code module generates two spread spectrum codes pn1 and pn2 respectively, and outputs them to the spread spectrum code shift registers reg1 and reg2 respectively. After the spread spectrum code codeword is completely filled into the spread spectrum code shift register, the work completion signal load_over is output; (2) After load_over is pulled high, two parallel data enter the shift register; each time a data is shifted, the two data in the shift register are respectively XORed with the code words of the spread spectrum code shift register 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) Process the two-channel amplitude-adjusted accumulated values ​​in the capture mode. If the coherent mode is used, the two-channel accumulated values ​​are respectively squared and summed for the in-phase branch and the quadrature branch and then stored. 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, the stored data is controlled to be accumulated at intervals of the coherent accumulation length and stored until the storage length reaches the incoherent accumulation length N; (7) Process the non-coherent accumulated value in the capture mode. When the storage length reaches the non-coherent accumulated length N, the accumulated values ​​of the two stored data are calculated by the square sum of the corresponding in-phase branch and the orthogonal branch in the differential mode and then output; in the coherent mode, the accumulated value of the stored data is directly output; (8) Compare and judge by using the capture threshold and the output value. If it is greater than the capture threshold, the capture synchronization is performed and the 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. The specific method of step (1) is as follows: 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 double sampling data, pn1 and pn2 use the same spread spectrum code. If the input data is greater than double sampling data, only one spread spectrum code is needed and one of the two input data is set to 0.

2. The multi-mode and multi-sampling rate compatible capture method 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.

3. The multi-mode and multi-sampling rate compatible capture method according to claim 1, characterized in that: The specific process of step (8) is as follows: In the non-coherent accumulation, a counting method is adopted. A maximum value search is performed during the non-coherent accumulation N-1 period, and the position of the maximum value max_addr is recorded. The position corresponding to max_addr during the non-coherent 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 after amplitude adjustment in the storage is read according to the capture synchronization indication interval sample*L for frequency deviation estimation; where N is the non-coherent accumulation length, L is the coherent accumulation length, and sample represents the number of sampling points per symbol data.