Signal Capture Method for High Dynamic Satellite Communication System

Abstract

The present invention discloses a method for capturing signals of a high-dynamic satellite communication system, and relates to the technical field of signal detection in satellite communication systems. The present invention includes the steps of parallel branching, partial correlation, zero-filled FFT, searching for the maximum amplitude, accumulating several adjacent amplitudes, judging, calculating Doppler frequency deviation and code deviation, etc., which can realize the capture of high-dynamic satellite signals, and simultaneously calculate the Doppler frequency deviation and code deviation of the satellite, thus solving the problem of difficulty in capturing high-dynamic signals. Compared with traditional capture methods, the present invention is adaptable to a large frequency deviation range, high capture performance, and lower signal-to-noise ratio conditions; and by using a parallel method, the length of the shift register is reduced, the complexity of the operation is reduced, and the problem of more resource occupation caused by FFT is alleviated. The method is applicable to most high-dynamic platforms, such as low-orbit satellites, airborne platforms, missile-borne platforms, etc., and can well realize the capture function, and is particularly suitable for signal detection in communication systems.

Description

Technical Field

[0001] The invention relates to the field of communications, and in particular to a signal capture method for a high-dynamic satellite communication system. Background Art

[0002] With the rapid development of low-orbit satellite applications and the communication needs of airborne and missile-borne platforms, the capture of high-dynamic signals is an important issue that needs to be solved in satellite communications. If traditional methods such as matched filter search, linear search, code phase search, and parallel frequency search are used to capture high-dynamic signals, then in order to adapt to large Doppler frequency shifts, these methods need to be repeatedly called, time-sharing or captured multiple times at the same time, which will consume more hardware resources and computing time, and will prolong the overall synchronization time of the system, affecting the communication performance of the receiving terminal.

[0003] Therefore, it is necessary to propose a fast acquisition method for high dynamic satellite communication systems. Summary of the invention

[0004] In view of this, the present invention provides a high-dynamic satellite communication system signal capture method. This method can not only realize the capture of high-dynamic satellite signals, but also calculate the Doppler frequency deviation and code deviation of the satellite, solving the problem of difficulty in capturing high-dynamic signals. Compared with traditional capture methods, this method has a large frequency deviation range and high capture performance; and by using a parallel method, the length of the shift register is reduced, and the problem of occupying more resources caused by FFT is alleviated. For most high-dynamic platforms, such as low-orbit satellites, airborne platforms, and missile-borne platforms, the capture function can be well realized.

[0005] The object of the present invention is achieved in that:

[0006] A high-dynamic satellite communication system signal acquisition method comprises the following steps:

[0007] (1) Receive a 4-times oversampled signal r(k);

[0008] (2) splitting r(k) into four parallel signals;

[0009] (3) Sliding storage is performed on the four parallel signals respectively, and the storage length is the frame header length;

[0010] (4) The signals stored in the four channels are respectively divided into a plurality of segments of equal length; accordingly, the local codewords are also divided into the same number of segments of equal length; the local codewords are the known frame header contents;

[0011] (5) performing correlation operation on the received signal and the local codeword in each segment, obtaining the correlation operation result y(k) of each segment, and storing the correlation operation result of each segment;

[0012] (6) Pad the tail of y(k) with zeros, then perform an N-point FFT operation and output Y(k); the four parallel signals will generate four Y(k), which are recorded as Y1(k), Y2(k), Y3(k), and Y4(k);

[0013] (7) Calculate the amplitudes of Y1(k), Y2(k), Y3(k), and Y4(k) respectively, and add up the adjacent amplitudes of each path;

[0014] (8) Search for the maximum amplitude of each channel after accumulation, then compare the maximum amplitudes of the four channels and take the maximum amplitude P among the four channels max As the final relevant result;

[0015] (9) The maximum amplitude P max Compared with the threshold, if it is greater than the threshold, it is considered that the capture is successful; if it is not greater than the threshold, it is considered that the frame header is not captured, and steps (3) to (8) are repeated to continue sliding storage and FFT calculation until the capture is successful;

[0016] (10) After successful capture, the Doppler frequency deviation and code deviation of the tracked high-dynamic satellite signal are determined according to the position k of the maximum value.

[0017] Furthermore, in step (3), a shift register is used for storage, and the length of the shift register is the frame header length; the content of the memory slides once for each symbol clock, that is, the oldest data is removed for each symbol clock, and the latest data is entered at the same time.

[0018] Furthermore, in step (4), the length of each segment is greater than 1 and less than or equal to M m鐀x ;in:

[0019]

[0020] In the formula, R s is the symbol rate, f d is the Doppler frequency deviation that needs to be adapted.

[0021] Furthermore, in step (10), the Doppler frequency deviation f of the high dynamic satellite signal d The calculation method is as follows:

[0022]

[0023] Where N is the number of points in the FFT, M is the length of each segment in step (4), k is the position of the maximum amplitude in the N-point FFT, and R s is the symbol rate.

[0024] Furthermore, in step (10), the code offset δ is calculated according to the Doppler frequency offset f dThe calculation results are:

[0025]

[0026] Where f0 is the carrier frequency.

[0027] Compared with the background technology, the present invention has the following advantages:

[0028] 1. Compared with the traditional capture method, the present invention has a wider frequency deviation range and higher capture performance.

[0029] 2. The present invention adopts a parallel method, reduces the length of the shift register, reduces the complexity of the operation, and alleviates the problem of occupying more resources caused by FFT.

[0030] 3. The present invention accumulates the amplitudes by sliding and then takes the maximum value, thereby reducing the influence of spectrum leakage on the capture performance and improving the adaptability to low signal-to-noise ratio conditions.

[0031] 4. The present invention is applicable to most high-dynamic platforms, such as low-orbit satellites, airborne platforms, missile-borne platforms, etc., and can well realize the capture function. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a block diagram of the composition of the method of the present invention.

[0033] Figure 2 This is a schematic diagram of the segmentation method of step (4).

[0034] Figure 3 It is a capture performance diagram of the method of the present invention. DETAILED DESCRIPTION

[0035] The present invention is further described below.

[0036] like Figure 1 As shown, a high dynamic satellite communication system signal acquisition method comprises the following steps:

[0037] (1) Receive a 4-times oversampled signal r(k), which is generally a signal after matched filtering. s Taking 2Msps as an example, we can know that the sampling rate of r(k) is 8MHz;

[0038] (2) Split r(k). Split r(k) into 4 parallel signals; each signal is equivalent to 1 times the sampling data, that is, the rate is 2 MHz;

[0039] (3) The four signals are respectively stored in a sliding manner according to a certain length, where the storage length is the frame header length; the calculation is performed using a frame header length of 128 as an example.

[0040] A shift register can be used for storage, and the length of the shift register is the frame header length 128. The content of the memory slides once for each symbol clock, that is, the oldest data is removed for each symbol clock, and the latest data is entered at the same time.

[0041] (4) Figure 2 As shown, the signals stored in the four channels are respectively divided into a number of segments of equal length; correspondingly, the local codewords are also divided into the same number of segments of equal length;

[0042] In practical applications, according to the symbol rate R s and Doppler frequency shift f d Determine the size of the length M.

[0043]

[0044] If the Doppler frequency deviation to be adapted is f d , then the length of each segment must be less than or equal to M m鐀x .

[0045] With Doppler frequency deviation as f d Calculated for -220kHz, we get:

[0046]

[0047] That is, the length of each segment is at most 4 symbols. In order to facilitate implementation on hardware FPGA, the length of each segment can be selected to be 4 symbols, so there are a total of 128 / 4=32 segments.

[0048] (5) Perform correlation operation on the received signal and the local codeword in each segment to obtain the correlation operation result y(k) of each segment, and store the correlation operation result of each segment; in this example, 32 correlation results can be obtained.

[0049] (6) Padded a certain length of zeros at the end of y(k), and then sent it to the FFT processing unit for N-point FFT operation, outputting Y(k); the length of the data after zero padding is generally 2 N , N is an integer. The more zero padding is, the higher the estimation accuracy of Doppler frequency offset will be, but it will not increase infinitely. The problem is that the amount of calculation will increase and more resources will be occupied.

[0050] In engineering applications, it is sufficient to add fewer zeros so that the total data length meets 2^N. The number of zeros to be added can also be determined based on requirements and conditions such as estimation accuracy and signal-to-noise ratio.

[0051] To improve the accuracy, a 512-point FFT can be performed and 480 zeros can be added. The estimated accuracy is 2000 / 4 / 512=0.98kHz.

[0052] (7) The four parallel signals will generate four Y(k), which are recorded as Y1(k), Y2(k), Y3(k), and Y4(k);

[0053] (8) Calculate the amplitudes of Y1(k), Y2(k), Y3(k), and Y4(k) respectively, and perform sliding accumulation of three or more adjacent amplitudes of each path;

[0054] Generally, the number of accumulated amplitudes does not exceed 5. In this embodiment, 3 are selected.

[0055] (9) Search for the maximum amplitude of each channel after accumulation, then compare the maximum amplitudes of the four channels and take the maximum amplitude P among the four channels max As the final relevant result;

[0056] (10) The maximum amplitude P max Compared with the threshold, if it is greater than the threshold, it is considered that the capture is successful; if it is not greater than the threshold, it is considered that the frame header is not captured, and the above steps 3 to 9 are repeated, and sliding storage and FFT operations are continued until the capture is successful.

[0057] When the capture is successful, the amplitude of the simulation output is as shown in the attached figure. Figure 3 As shown in the figure, it can be seen that the maximum value is located at the 287th point, that is, the position k of the maximum value is 287.

[0058] (11) After successful capture, the Doppler frequency deviation and code deviation of the tracked high-dynamic satellite signal are determined according to the position k of the maximum value.

[0059] Doppler frequency deviation f of high dynamic satellite signal d The calculation method is as follows:

[0060]

[0061] Where N is the number of points in the FFT, M is the length of each segment in step (4), k is the kth position of the maximum amplitude in the N-point FFT, and R s is the symbol rate.

[0062] Convert k=287 to a signed number and substitute have to:

[0063]

[0064] and Doppler frequency shift f d The true value is very close, with a difference of only 0.3kHz, so the frequency offset estimation can be considered correct.

[0065] Code deviation δ and Doppler frequency deviation f d is a positive proportional relationship, the estimated f d Substitution That is, the Doppler code deviation. Where f0 is the carrier frequency.

[0066] In summary, the present invention includes the steps of parallel branching, partial correlation, zero-filled FFT, searching for maximum amplitude, accumulating several adjacent amplitudes, judging, calculating Doppler frequency deviation and code deviation, etc., which can realize the capture of high-dynamic satellite signals, and simultaneously calculate the Doppler frequency deviation and code deviation of the satellite, thus solving the problem of difficulty in capturing high-dynamic signals. Compared with the traditional capture method, the present invention is adaptable to a large frequency deviation range, high capture performance, and lower signal-to-noise ratio conditions; and by using a parallel method, the length of the shift register is reduced, the complexity of the operation is reduced, and the problem of more resource occupation caused by FFT is alleviated. This method is applicable to most high-dynamic platforms, such as low-orbit satellites, airborne platforms, missile-borne platforms, etc., and can well realize the capture function, and is particularly suitable for signal detection in communication systems.

[0067] 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 high dynamic satellite communication system signal acquisition method, characterized in that: The following steps are involved: (1) Receive a 4-times oversampled signal r(k); (2) splitting r(k) into four parallel signals; (3) Sliding storage is performed on the four parallel signals respectively, and the storage length is the frame header length; (4) The signals stored in the four channels are divided into a plurality of segments of equal length respectively; accordingly, the local codewords are also divided into the same number of segments of equal length; the local codewords are the known frame header contents; (5) performing correlation operation on the received signal and the local codeword in each segment, obtaining the correlation operation result y(k) of each segment, and storing the correlation operation result of each segment; (6) Pad the tail of y(k) with zeros, then perform an N-point FFT operation and output Y(k); the four parallel signals will generate four Y(k), which are recorded as Y1(k), Y2(k), Y3(k), and Y4(k); (7) Calculate the amplitudes of Y1(k), Y2(k), Y3(k), and Y4(k) respectively, and add up the adjacent amplitudes of each path; (8) Search for the maximum amplitude of each channel after accumulation, then compare the maximum amplitudes of the four channels and take the maximum amplitude P among the four channels max As the final relevant result; (9) The maximum amplitude P max Compared with the threshold, if it is greater than the threshold, it is considered that the capture is successful; If it is not greater than the threshold, it is considered that the frame header has not been captured, and steps (3) to (8) are repeated, and sliding storage and FFT calculations are continued until the capture is successful; (10) After successful capture, the Doppler frequency deviation and code deviation of the tracked high-dynamic satellite signal are determined according to the position k of the maximum value.

2. A high dynamic satellite communication system signal acquisition method according to claim 1, characterized in that: In step (3), a shift register is used for storage, and the length of the shift register is the length of the frame header; the content of the memory slides once for each symbol clock, that is, the oldest data is removed for each symbol clock, and the latest data is entered at the same time.

3. A high dynamic satellite communication system signal acquisition method according to claim 1, characterized in that: In step (4), the length of each segment is greater than 1 and less than or equal to M max ; in: In the formula, R s is the symbol rate, f d is the Doppler frequency deviation that needs to be adapted.

4. A high dynamic satellite communication system signal acquisition method according to claim 1, characterized in that: In step (10), the Doppler frequency deviation f of the high dynamic satellite signal d The calculation method is as follows: Where N is the number of points in the FFT, M is the length of each segment in step (4), k is the position of the maximum amplitude in the N-point FFT, and R s is the symbol rate.

5. The high dynamic satellite communication system signal acquisition method according to claim 1, characterized in that: In step (10), the code offset δ is calculated based on the Doppler frequency offset f d The calculation results are: Where f0 is the carrier frequency.

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