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CN115296698B - Signal Capture Method for High Dynamic Satellite Communication System - Google Patents

Signal Capture Method for High Dynamic Satellite Communication System Download PDF

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CN115296698B
CN115296698B CN202210916480.0A CN202210916480A CN115296698B CN 115296698 B CN115296698 B CN 115296698B CN 202210916480 A CN202210916480 A CN 202210916480A CN 115296698 B CN115296698 B CN 115296698B
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dynamic satellite
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CN115296698A (en
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陈敬乔
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CETC 54 Research Institute
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/14—Relay systems
    • H04B7/15—Active relay systems
    • H04B7/185—Space-based or airborne stations; Stations for satellite systems
    • H04B7/1851—Systems using a satellite or space-based relay
    • 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

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Physics & Mathematics (AREA)
  • Astronomy & Astrophysics (AREA)
  • Aviation & Aerospace Engineering (AREA)
  • General Physics & Mathematics (AREA)
  • Radio Relay Systems (AREA)

Abstract

本发明公开了一种高动态卫星通信系统信号捕获方法，涉及卫星通信系统中的信号检测技术领域。本发明包括并行分路、部分相关、补零FFT、搜索最大幅值、邻近若干个幅值累加、判决、计算多普勒频偏和码偏等步骤，可实现高动态卫星信号的捕获，同时计算出卫星的多普勒频偏和码偏，解决了高动态信号捕获困难的问题。本发明相对于传统的捕获方法，适应频偏范围大、捕获性能高，适应更低的信噪比情况；而且利用并行方式，减小了移位寄存器的长度，降低了运算的复杂度，减轻了FFT带来的占用资源较多的问题。该方法适用于绝大多数的高动态平台，如低轨卫星、机载平台、弹载平台等，都可以很好实现捕获功能，特别适用于通信系统的信号检测。

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

Signal capturing method for high dynamic satellite communication system
Technical Field
The invention relates to the field of communication, in particular to a signal capturing method of a high-dynamic satellite communication system.
Background
With the rapid development of low-orbit satellite applications and the communication demands of airborne and missile-borne platforms, the capturing of high-dynamic signals is an important problem to be solved in satellite communication. If the conventional methods of matched filtering search, linear search, code phase search, parallel frequency search and the like are continuously used for capturing the high dynamic signals, in order to adapt to large doppler shift, the methods need to repeatedly call, time-sharing or capture for multiple times at the same time, which consumes more hardware resources and calculation time, prolongs the whole synchronization time of the system and affects the communication performance of the receiving terminal.
Therefore, there is a need for a fast acquisition method for a high dynamic satellite communication system.
Disclosure of Invention
In view of this, the present invention provides a signal acquisition method for a high dynamic satellite communication system. The method not only can realize the capturing of the high dynamic satellite signals, but also can calculate the Doppler frequency offset and the code offset of the satellite, and solves the problem of difficult capturing of the high dynamic signals. Compared with the traditional capturing method, the method has the advantages of wide frequency offset range and high capturing performance, reduces the length of the shift register by using a parallel mode, reduces the problem of more occupied resources caused by FFT, and can well realize the capturing function for most of high-dynamic platforms, such as low-orbit satellites, airborne platforms and missile-borne platforms.
The purpose of the invention is realized in the following way:
a method for signal acquisition in a high dynamic satellite communication system, comprising the steps of:
(1) Receiving a 4-times oversampled signal r (k);
(2) The shunt is performed on r (k), dividing r (k) into 4 parallel paths of parallel signals;
(3) Respectively carrying out sliding storage on 4 paths of parallel signals, wherein the storage length is the frame head length;
(4) Dividing the 4 paths of stored signals into a plurality of equal-length segments, and correspondingly, dividing the local code word into the same number of equal-length segments;
(5) Performing correlation operation on the received signal and the local code word in each segment to obtain a correlation operation result y (k) of each segment, and storing the correlation operation result of each segment;
(6) Zero padding is carried out at the tail part of Y (k), then N-point FFT operation is carried out, Y (k) is output, 4 paths of parallel signals can generate 4 paths of Y (k), and the Y (k) is respectively marked as Y 1(k)、Y2(k)、Y3(k)、Y4 (k);
(7) Respectively calculating the amplitude values of Y 1(k)、Y2(k)、Y3(k)、Y4 (k), and sliding and accumulating a plurality of adjacent amplitude values of each path;
(8) Searching the accumulated maximum amplitude value of each path, comparing the maximum amplitude values of the 4 paths, and taking the maximum amplitude value P max in the 4 paths as a final correlation result;
(9) Comparing the maximum amplitude P max with a threshold, if the maximum amplitude P max is larger than the threshold, the capturing is considered to be successful, if the maximum amplitude P max is not larger than the threshold, the frame head is considered not captured, and the steps (3) - (8) are repeated, and sliding storage and FFT operation are continued until the capturing is successful;
(10) After successful acquisition, the Doppler frequency offset and the code offset of the tracked high-dynamic satellite signals are determined according to the position k of the maximum value.
Further, in the step (3), a shift register is used for storing, the length of the shift register is the length of the frame header, and the content of the memory slides once for each symbol clock, namely, each symbol clock removes the oldest data and enters the latest data.
Further, in the step (4), the length of each segment is greater than 1 and less than or equal to M m Is (1) x, wherein:
where R s is the symbol rate and f d is the Doppler frequency offset to be adapted.
Further, in the step (10), the method for calculating the doppler frequency offset f d of the high dynamic satellite signal is as follows:
wherein N is the number of FFT points, 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.
Further, in step (10), the code offset δ is calculated according to the doppler frequency offset f d:
Wherein f 0 is the carrier frequency.
Compared with the background technology, the invention has the following advantages:
1. compared with the traditional capturing method, the method has the advantages of wide adaptive frequency offset range and high capturing performance.
2. The invention adopts a parallel mode, reduces the length of the shift register, reduces the complexity of operation and reduces the problem of more occupied resources caused by FFT.
3. The method and the device take the maximum value after the amplitude sliding accumulation, reduce the influence of spectrum leakage on the capturing performance, and improve the adaptability to the condition of low signal to noise ratio.
4. The invention is suitable for most high dynamic platforms, such as low-orbit satellites, airborne platforms, missile-borne platforms and the like, and can well realize the capturing function.
Drawings
FIG. 1 is a block diagram of the components of the method of the present invention.
Fig. 2 is a schematic diagram of the segmentation method of step (4).
FIG. 3 is a graph of capture performance of the method of the present invention.
Detailed Description
The present invention will be further described below.
As shown in fig. 1, a signal capturing method of a high dynamic satellite communication system includes the following steps:
(1) A 4 times oversampled signal r (k) is received, r (k) typically being a matched filtered signal. Taking symbol rate R s as 2Msps as an example, it can be seen that the sampling rate of R (k) is 8MHz;
(2) And (3) branching r (k). Dividing r (k) into 4 parallel signals, wherein each signal is equivalent to 1 time of sampling data, namely the speed is 2M Hz;
(3) The 4 paths of signals are respectively stored in a sliding way according to a certain length, wherein the storage length is the frame head length, and the frame head length is calculated by taking the frame head length as 128 as an example.
A shift register may be used for storage, the shift register length being the frame header length 128. The memory content is slid once per symbol clock, i.e. each symbol clock removes one oldest data while entering one newest.
(4) As shown in fig. 2, the 4 paths of stored signals are respectively divided into a plurality of equal-length segments, and the local code word is correspondingly divided into the same number of equal-length segments;
In practical applications, the length M is determined according to the symbol rate R s and the doppler frequency offset f d.
If the doppler frequency offset to be adapted is f d, the length of each segment must be less than or equal to M m Is (1) x.
Calculated by using Doppler frequency offset f d as-220 kHz, the method can be obtained:
I.e. at most 4 symbols per segment length, for convenience of implementation on a hardware FPGA, 4 symbols per segment length may be selected, and there are 128/4=32 segments in total.
(5) And performing correlation operation on the received signal and the local code word in each segment to obtain a correlation operation result y (k) of each segment, and storing the correlation operation result of each segment, wherein 32 correlation results can be obtained in the example.
(6) And (3) supplementing zeros with a certain length at the tail part of Y (k), then sending the zeros into an FFT processing unit for N-point FFT operation, and outputting Y (k), wherein the length of data after zero supplementation is generally 2 N, and N is an integer. The more the zero padding number is, the estimation accuracy of Doppler frequency offset is generally improved, but the estimation accuracy is not increased infinitely. The problem is that the operand is increased and the occupied resources are increased.
In engineering application, less zeros are added so that the total data length can meet 2≡n, and the zero added number can be determined according to the requirements and conditions of estimation precision, signal-to-noise ratio and the like.
To improve accuracy, a 512-point FFT may be performed, with 480 zeros being padded. The estimation accuracy is 2000/4/512=0.98 kHz.
(7) The 4-path parallel signal generates 4 paths Y (k), which are respectively marked as Y 1(k)、Y2(k)、Y3(k)、Y4 (k);
(8) Calculating the amplitude values of Y 1(k)、Y2(k)、Y3(k)、Y4 (k) respectively, and sliding and accumulating 3 or more adjacent amplitude values of each path;
Typically, the number of accumulated magnitudes is no more than 5. In this example, 3 were taken.
(9) Searching the accumulated maximum amplitude value of each path, comparing the maximum amplitude values of the 4 paths, and taking the maximum amplitude value P max in the 4 paths as a final correlation result;
(10) And if the maximum amplitude P max is not greater than the threshold, no frame header is captured, continuing to repeat the steps 3-9, and continuing to perform sliding storage and FFT operation until the capturing is successful.
The magnitude of the simulated output is shown in figure 3 when the capture is successful. It can be seen from the figure that the position of the maximum is 287 th point, i.e. the position k of the maximum is 287.
(11) After successful acquisition, the Doppler frequency offset and the code offset of the tracked high-dynamic satellite signals are determined according to the position k of the maximum value.
The Doppler frequency offset f d of the high dynamic satellite signal is calculated as follows:
Wherein N is the number of FFT points, M is the length of each segment in step (4), k is the kth position where the maximum amplitude is in the N-point FFT, and R s is the symbol rate.
Converting k=287 to signed number, substitutingObtaining:
Is very close to the true value of the doppler frequency offset f d, only 0.3kHz difference, the frequency offset estimate may be considered correct.
The code bias delta and the Doppler bias f d are in a direct proportion relation, and the estimated f d is substituted intoObtaining Doppler code bias. Wherein f 0 is the carrier frequency.
In a word, the method comprises the steps of parallel branching, partial correlation, zero padding FFT, searching for the maximum amplitude, accumulating a plurality of adjacent amplitude values, judging, calculating Doppler frequency offset and code offset and the like, so that the method can realize the capturing of the high dynamic satellite signals, calculate the Doppler frequency offset and the code offset of the satellites at the same time, and solve the problem of difficult capturing of the high dynamic signals. Compared with the traditional capturing method, the method has the advantages of wide frequency offset range, high capturing performance and lower signal to noise ratio, and reduces the length of the shift register, the operation complexity and the occupation of more resources caused by FFT by using a parallel mode. The method is suitable for most of high-dynamic platforms, such as low-orbit satellites, airborne platforms, missile-borne platforms and the like, can well realize the capturing function, and is particularly suitable for signal detection of a communication system.
The above description is only one embodiment of the present invention, but the scope of the present invention is not limited thereto. Any equivalent substitutions or changes made by those skilled in the art according to the technical scheme and the inventive concept of the present invention should be included in the scope of the present invention.

Claims (5)

1.一种高动态卫星通信系统信号捕获方法，其特征在于，包括以下步骤：1. A high dynamic satellite communication system signal acquisition method, characterized in that it comprises the following steps: (1)接收4倍过采样信号r(k)；(1) Receive a 4-times oversampled signal r(k); (2)对r(k)进行分路，将r(k)分为并行4路并行信号；(2) splitting r(k) into four parallel signals; (3)分别对4路并行信号进行滑动存储，存储长度为帧头长度；(3) Sliding storage is performed on the four parallel signals respectively, and the storage length is the frame header length; (4)分别将4路存储的信号划分为多个等长度的段；相应地，将本地码字也划分为相同数量的等长度的段；本地码字即为已知的帧头内容；(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; (5)在各段内对接收信号和本地码字做相关运算，得到各段的相关运算结果y(k)，并将各段的相关运算结果进行存储；(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)在y(k)的尾部补零，然后进行N点FFT运算，输出Y(k)；4路并行信号会产生4路Y(k)，分别记为Y1(k)、Y2(k)、Y3(k)、Y4(k)；(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 Y 1 (k), Y 2 (k), Y 3 (k), and Y 4 (k); (7)分别计算Y1(k)、Y2(k)、Y3(k)、Y4(k)的幅值，并将每路的相邻多个幅值滑动累加；(7) Calculate the amplitudes of Y 1 (k), Y 2 (k), Y 3 (k), and Y 4 (k) respectively, and perform sliding accumulation of multiple adjacent amplitudes of each path; (8)搜索累加后的每路的最大幅值，然后对比4路的最大幅值，取4路中的最大幅值Pmax作为最终相关结果；(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 max among the four channels as the final correlation result; (9)将最大幅值Pmax与门限比较，如果大于门限，则认为捕获成功；如果不大于门限，则认为没有捕获到帧头，重复步骤(3)～步骤(8)，继续进行滑动存储和FFT运算，直到捕获成功；(9) Compare the maximum amplitude P max 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 operation until the capture is successful. (10)捕获成功后，根据最大值的位置k确定所跟踪的高动态卫星信号的多普勒频偏和码偏。(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.根据权利要求1所述的一种高动态卫星通信系统信号捕获方法，其特征在于，步骤(3)中，采用移位寄存器进行存储，移位寄存器长度为帧头长度；每个符号时钟，存储器的内容滑动一次，即每个符号时钟去掉一个最旧的数据，同时进入一个最新数据。2. A high-dynamic satellite communication system signal capture 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 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. 3.根据权利要求1所述的一种高动态卫星通信系统信号捕获方法，其特征在于，步骤(4)中，每段的长度大于1，小于或等于Mmax；其中：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 ; wherein: 式中，Rs为符号速率，fd为需适应的多普勒频偏。Where Rs is the symbol rate and fd is the Doppler frequency deviation that needs to be adapted. 4.根据权利要求1所述的一种高动态卫星通信系统信号捕获方法，其特征在于，步骤(10)中，高动态卫星信号的多普勒频偏fd计算方法如下：4. The method for capturing signals of a high-dynamic satellite communication system according to claim 1, wherein in step (10), the Doppler frequency deviation fd of the high-dynamic satellite signal is calculated as follows: 其中，N为FFT的点数，M为步骤(4)中每段的长度，k为最大幅值在N点FFT中所在的位置，Rs为符号速率。Where N is the number of FFT points, M is the length of each segment in step (4), k is the position of the maximum amplitude in the N-point FFT, and Rs is the symbol rate. 5.根据权利要求1所述的一种高动态卫星通信系统信号捕获方法，其特征在于，步骤(10)中，码偏δ根据多普勒频偏fd计算得到：5. The high dynamic satellite communication system signal acquisition method according to claim 1, characterized in that in step (10), the code deviation δ is calculated according to the Doppler frequency deviation f d : 其中，f0为载波频率。Where f0 is the carrier frequency.
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CN107135013A (en) * 2017-05-04 2017-09-05 中国电子科技集团公司第五十四研究所 A kind of Rapid Acquisition for Direct Sequence Spread-Spectrum Signals method
CN112600588A (en) * 2020-12-08 2021-04-02 西安思丹德信息技术有限公司 Non-integer period spread spectrum communication capturing method

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN107135013A (en) * 2017-05-04 2017-09-05 中国电子科技集团公司第五十四研究所 A kind of Rapid Acquisition for Direct Sequence Spread-Spectrum Signals method
CN112600588A (en) * 2020-12-08 2021-04-02 西安思丹德信息技术有限公司 Non-integer period spread spectrum communication capturing method

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