Adaptive satellite portable station receiver synchronization system with variable spread spectrum ratio

Abstract

The invention relates to the technical field of satellite portable station communication, and discloses an adaptive variable spread spectrum ratio satellite portable station receiver synchronization system, which is characterized by comprising a data preprocessing module, a spread spectrum code synchronization module, a symbol synchronization module, a spread spectrum ratio / frame synchronization module, a frequency synchronization module, a phase synchronization module and the like. The synchronization of signals with different spread spectrum ratios is realized, so that the communication system of the satellite portable station can obtain reliable communication under the environment of low signal-to-noise ratio and strong interference, and the flexibility of the system is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of satellite portable station communication, more particularly, it relates to a satellite portable station receiver synchronization system with adaptive variable spreading ratio. BACKGROUND

[0002] The communication system of satellite portable station has high use value in remote areas, mountainous areas and ocean areas due to its large coverage, immunity to land environment, and difficulty in being artificially destroyed and interfered, but the signal-to-noise ratio of the received signal is extremely low due to the influence of electromagnetic environment, shadow effect, multipath fading and high Doppler frequency shift, and various measures need to be taken to ensure reliable communication. Spread spectrum communication has been widely used in military and commercial communication systems due to its advantages of anti-interference, code division multiple access and signal concealment, and the satellite spread spectrum communication technology with adaptive variable spreading ratio considers the communication rate and anti-interference ability, and responds to different environments and communication objects by changing the channel spreading ratio in real time, thereby greatly improving the flexibility of the system.

[0003] However, the accurate synchronization of the receiver spreading sequence in the system is a primary problem that must be solved, and the synchronization includes spreading ratio synchronization, chip synchronization, symbol synchronization, carrier synchronization, phase synchronization and frame synchronization, among which frame synchronization and spreading code synchronization are the focus, and the de-spreading and de-framing information of the subsequent information can be obtained by detecting the characteristic code of different spreading ratios, which is an important link of system demodulation.

[0004] Therefore, the present application provides a satellite portable station receiver synchronization system with adaptive variable spreading ratio, which improves the above technical problems. SUMMARY

[0005] The present application aims to solve the problems of the prior art, and provides a satellite portable station receiver synchronization system with adaptive variable spreading ratio, which realizes the synchronization of signals with different spreading ratios through data preprocessing, spreading code synchronization, symbol synchronization, spreading ratio / frame synchronization, frequency synchronization and phase synchronization, so as to ensure reliable communication of the system in a low signal-to-noise ratio and strong interference environment, and improve the flexibility of the system.

[0006] The above technical purpose of the present application is achieved by the following technical scheme: a satellite portable station receiver synchronization system with adaptive variable spreading ratio, comprising: A data preprocessing module is configured to perform pilot de-spreading, differential and integral operations on the received signal with frequency offset, and output a pulse signal with a pilot spreading code length as a period; A spreading code synchronization module is configured to find a stable maximum value in the preprocessed pulse signal, and determine a preliminary spreading code synchronization position pk by comparing the stable maximum value with a capture threshold; A symbol synchronization module is configured to calculate a symbol synchronization position temporary variable mkk according to front, middle and rear sampling points of the spread spectrum code synchronization pulse signal, and adjust the spread spectrum code synchronization position pk and the symbol synchronization position mk according to the value of mkk. A spread spectrum ratio / frame synchronization module is configured to use a multi-spread spectrum ratio parallel detection technology, pre-de-spread the data at the lowest spread spectrum ratio and store the data, perform parallel unique word (UW) detection on the pre-de-spread data at different spread spectrum ratios, mark the data start position according to the detected frame header position, and complete spread spectrum ratio synchronization. A frequency synchronization module is configured to use a multi-phase lock loop technology, use different frequency offset estimation formulas in different stages through a plurality of frequency discriminators with different phases and precisions to estimate the frequency offset, and realize frequency synchronization. A phase synchronization module is configured to correct the phase offset of the signal according to the phase of the de-mapped unique word (UW) after completing the frequency synchronization, and complete phase synchronization.

[0007] As a preferred technical solution of the present application, the pilot de-spreading operation of the data preprocessing module is realized by the following formula:

[0008] Wherein, k represents the sampling time, W represents a pilot spread spectrum code with a length of L, represents the received signal.

[0009] As a preferred technical solution of the present application, the spread spectrum code synchronization module determines the interval of the spread spectrum code synchronization pulse signal as SPSxW, wherein SPS is the number of sampling points per chip, and W is the length of the pilot spread spectrum code.

[0010] As a preferred technical solution of the present application, in the symbol synchronization module, the calculation formula of the symbol synchronization position temporary variable mkk is: mkk=sign[R(0)-R(-1)] / 2+sign[R(1)-R(0)] / 2 Wherein, R(-1), R(0) and R(1) represent the front, middle and rear three sampling points of the spread spectrum code synchronization pulse signal sampling, and sign represents a sign function with a value of ±1. The adjustment rule is: When mkk>0.75, mk=mk+1, pk=pk+1, and mkk=mkk-1. When mkk<-0.75, mk=mk-1, pk=pk-1, and mkk=mkk+1.

[0011] The threshold value of the adjustment is set to 0.75 instead of 0.5, so that a certain margin is left to avoid the influence of noise and make the adjustment around 0.5.

[0012] As a preferred technical scheme of the present application, the frame header in the spread spectrum ratio / frame synchronization module is an inserted frame header, and the start position synchronization of the frame header is completed through multi-path parallel detection.

[0013] As a preferred technical scheme of the present application, in the frequency synchronization module, the initial formula for frequency offset estimation is:

[0014] wherein Arg is the amplitude angle, and S is the differential step; The frequency offset estimation formula in different stages corresponds to different differential steps, including 2S, 4S, etc., when the differential step is 2S, the frequency offset estimation formula is: .

[0015] As a preferred technical scheme of the present application, the phase synchronization module completes the phase offset correction by multiplying the demapped unique code UW after amplitude normalization and conjugation with the signal.

[0016] In summary, the present application has the following advantages: compared with the prior art, through the unique synchronization process design, the present application can realize the accurate synchronization of the spread spectrum ratio, chip, symbol, carrier, phase and frame without pre-spread spectrum ratio synchronization at the transceiving two ends of the satellite portable station, by virtue of the characteristics that the spread spectrum code is unique and the code length is fixed, and the spread spectrum ratio is continuously segmented when the spread spectrum ratio is reduced; the data preprocessing link is improved in signal-to-noise ratio through pilot despreading, differential and integral operations, the symbol synchronization avoids noise interference through threshold adjustment, the spread spectrum ratio / frame synchronization reduces the processing amount through multi-spread spectrum ratio parallel detection and lowest spread spectrum ratio pre-despreading, the frequency synchronization takes into account the capture range and accuracy through multiple phase-locked loops, and the phase synchronization corrects the deviation through the unique code phase. In the overall satellite communication environment of low signal-to-noise ratio, strong interference and high Doppler frequency shift, the present application not only retains the advantages of spread spectrum communication such as anti-interference, but also balances the communication rate and anti-interference ability through adaptive adjustment of the spread spectrum ratio, greatly improving the system flexibility and communication reliability. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 A frame diagram of a satellite portable station receiver synchronization system with adaptive variable spread spectrum ratio provided by the embodiment of the present application; Figure 2 A spread spectrum code / symbol synchronization flowchart provided by the embodiment of the present application; Figure 3 A frame synchronization flowchart provided by the embodiment of the present application; Figure 4 A frequency synchronization flowchart provided by the embodiment of the present application. DETAILED DESCRIPTION

[0018] The application will be described in detail below with specific embodiments. The following examples will help those skilled in the art to further understand the application, but do not limit the application in any form. It should be noted that for those skilled in the art, without departing from the concept of the application, a number of modifications and improvements can be made. These are within the scope of the application.

[0019] In order to make the purpose, technical scheme and advantages of the application more clear, the application will be further described in detail below in combination with the drawings and examples. It should be understood that the specific embodiments described herein are only used to explain the application and not to limit the application.

[0020] Unless otherwise defined, all technical and scientific terms used in the specification are the same as those commonly understood by those skilled in the art of the technology to which the application belongs. The terms used in the specification of the application are only for the purpose of describing the specific embodiments and are not intended to limit the application. The term "and / or" used in the specification includes any and all combinations of one or more related listed items.

[0021] In addition, the technical features involved in each embodiment of the application described below can be combined with each other as long as there is no conflict between them.

[0022] The embodiments of the present disclosure aim to solve the problem of accurate synchronization of the receiver spreading sequence in the adaptive variable spreading ratio satellite portable station communication system. Through the processes of data preprocessing, spreading code synchronization, symbol synchronization, spreading ratio / frame synchronization, frequency synchronization, phase synchronization, synchronization of signals with different spreading ratios is realized to ensure reliable communication of the system in low signal-to-noise ratio and strong interference environment and to improve the flexibility of the system.

[0023] Please refer to Figure 1 , Figure 1 A framework diagram of a satellite portable station receiver synchronization system with adaptive variable spreading ratio according to the embodiments of the present disclosure is shown. It mainly includes the following modules: Data preprocessing module, spreading code synchronization module, symbol synchronization module, spreading ratio / frame synchronization module, frequency synchronization module, phase synchronization module.

[0024] Receiver synchronization can be divided into time domain synchronization and frequency domain synchronization, and the focus is on time domain synchronization. Especially in the spread spectrum system, due to the low signal-to-noise ratio, the traditional synchronization algorithm is invalid, so new algorithms or methods are needed. In the above demodulation process, pk is the spreading code synchronization point, mk is the (integer) sampling symbol synchronization point, rk is the frame synchronization point, fk is the estimated frequency offset, and sk is the estimated phase offset. The starting phases of the time domain signals pk, mk and rk are the same, but the periods are different. After these parameters are determined, subsequent data demapping, decoding and descrambling operations can be performed.

[0025] (1) Data pre-processing module: The original information processed by the matched filter cannot be directly processed and the relevant parameters cannot be directly extracted due to low signal-to-noise ratio and containing frequency offset and phase offset, and needs to be pre-processed against noise and frequency offset and phase offset, so it needs to be processed by pilot despreading, difference (conjugate multiplication), integration (in-phase addition) and the like to obtain a processable signal for frequency synchronization, bit synchronization and spread spectrum code synchronization.

[0026] Let the received wireless communication signal r with frequency offset be simply represented as the sum of a communication signal s and a noise signal n:

[0027] In the formula, k is the sampling time, A is the modulated complex envelope, f is the residual frequency offset, is a random phase, and n is a complex additive white Gaussian noise. After matched filtering, the despread signal of the pilot code is:

[0028] In the formula, W is the pilot spread spectrum code with a length of L. After despread, the signal is anti-frequency offset and phase offset, and needs to be differentiated between adjacent symbols, and then integrated to improve the signal-to-noise ratio, so the pre-processed output signal is:

[0029] In the formula, K is the integration length, S is the difference step, and N is the sum of the noise cross-phase and noise square terms. After the above operation, the pilot signal forms a pulse signal with only phase offset and high signal-to-noise ratio with the pilot minimum spread spectrum code length as the period.

[0030] (2) Spread spectrum code synchronization module: As shown in Figure 2 , a stable maximum value is searched for in the above pre-processed pilot signal, i.e. the pulse signal with the pilot minimum spread spectrum code length as the period. In the initial state, a capture threshold is set, and when the signal amplitude is greater than the threshold, it is considered that this is the preliminary spread spectrum code synchronization position pk and the best sampling point of spread spectrum code synchronization, i.e. symbol synchronization mk. At this time, the best integer sampling point may not be accurate, so it needs to be continuously adjusted through subsequent symbol synchronization.

[0031] The initial synchronization process is: according to the positions of pk and mk, a spread spectrum code synchronization pulse signal with an interval of SPS×W is generated, where SPS is the number of sampling points per chip, and W is the pilot spread spectrum code length. At this time, the spread spectrum code synchronization pulse signal and the spread spectrum signal complete the initial synchronization.

[0032] (3) Symbol synchronization module: Let the three sampling points of the spread spectrum code synchronization pulse signal sample before, in the middle and after be R(-1), R(0) and R(1), then define the symbol synchronization position temporary variable: mkk=sign[R(0)-R(-1)] / 2+sign[R(1)-R(0)] / 2 In the formula, sign is the sign, and the value is ±1.

[0033] Through long time calculation and average of mkk, the value of mkk is judged to adjust the spread spectrum code synchronization position pk and the symbol synchronization position mk. The specific adjustment rules are as follows: When mkk>0.75, then mk=mk+1, pk=pk+1, mkk=mkk-1; When mkk<-0.75, then mk=mk-1, pk=pk-1, mkk=mkk+1.

[0034] The threshold of adjustment is 0.75 instead of 0.5, because in this way a certain margin is left, which can avoid the influence of noise and make it not stop adjusting back and forth around 0.5.

[0035] (4) Spread spectrum ratio / frame synchronization module: As shown in Figure 3 , frame synchronization mainly uses correlation algorithm, and since the received frame has multiple spread spectrum ratio types, multiple spread spectrum ratio parallel detection technology is used to detect the frame header data, and the despread data is copied into multiple, each detection module has its own spread spectrum code, and only one module will detect the correlation peak, and then output. Before being sent into the frame detection module, in order to reduce the processing rate, pre-despread processing of the minimum spread spectrum ratio is carried out, which significantly reduces the subsequent processing data amount.

[0036] Frame synchronization design mainly includes three parts. First, pre-despread the data according to different spread spectrum ratios, and store the despread data respectively. Second, detect the pre-despread data under different spread spectrum ratios in parallel with different unique codes UW. Since it is an inserted frame header, the frame header starting position needs to be synchronized when detecting the frame header, and the frame header synchronization work is completed through multiple parallel detection. Finally, after detecting the frame header, the starting data position in the memory is located according to the position rk of the last data, and the data is despread and output, completing the spread spectrum ratio synchronization.

[0037] (5) Frequency synchronization module: As shown in Figure 4The frequency synchronization sampling multiphase frequency-locked loop technology is shown. The multiphase frequency-locked loop is based on the traditional frequency-locked loop single frequency discriminator, adopts multiple discriminators of different phases and precision, and uses the parallel frequency-locked loop of different discriminators through the criterion. The phase tracking part is added to make up for the deficiency of the frequency-locked loop that cannot track the phase. Through the linkage of multiple hierarchical discriminators, the multiphase frequency-locked loop has the characteristics of simple implementation, wide capture range, fast convergence speed, high tracking precision and low signal-to-noise ratio requirement.

[0038] The preprocessed pilot signal can be directly used for frequency offset estimation, and the frequency synchronization frequency offset estimation value is:

[0039] In the formula, Arg is the amplitude angle, and S is the differential step.

[0040] The multiphase frequency discriminator adopts multiple discriminator groups with different phase differences on the basis of the traditional frequency discriminator, and completes frequency discrimination together. The multiple hierarchical phase differences are S, 2S, 4S, etc. When 2S, the output of the above preprocessing module becomes:

[0041] At this time, the estimation value of the frequency offset becomes:

[0042] In the application of the multiphase frequency-locked loop, the above different hierarchical frequency estimation formulas have different estimation ranges and precision. The differential step from small to large is the estimation range that is smaller and smaller and the estimation precision that is higher and higher. Therefore, the multiphase frequency-locked loop cannot use the above estimation formulas at the same time, but uses different estimation formulas in different estimation stages. The specific estimation strategy is as follows: in the early estimation stage, the estimation formula with large estimation range and low estimation precision is used, when the estimation formula reaches its estimation precision, the next formula with small estimation range and high estimation precision is replaced, and so on.

[0043] The switching strategy of different estimation range and estimation precision formulas is as follows: when the formula reaches its estimation precision, switch to the next formula with higher estimation precision and narrower estimation range. The estimation precision of each formula is related to the signal-to-noise ratio, the differential step S and the integral time length K. When switching, the estimation range of the next formula is required to be slightly larger than the estimation precision of the previous formula.

[0044] (6) Phase synchronization module: Since the frequency synchronization uses the frequency lock loop technology, no phase synchronization is implemented, and after the frequency synchronization is completed, the correction of the phase deviation needs to be considered. The unique code UW in the received signal is subjected to symbol synchronization and frequency synchronization, and then the UW is demapped to obtain the UW signal with all 1s. At this time, the phase deviation of the UW is the phase deviation of the system. At this time, the phase deviation sk can be corrected according to the phase of the demapped unique code UW, that is, the demapped UW is subjected to amplitude normalization and conjugation, and then multiplied by the signal, so that the phase synchronization is completed.

[0045] The above only describes the preferred embodiments of the present application, and the protection scope of the present application is not limited to the above-described embodiments. Any technical solution falling within the concept of the present application belongs to the protection scope of the present application. It should be noted that, for ordinary skilled persons in the art, some improvements and refinements without departing from the principles of the present application are also considered to be within the protection scope of the present application.

Claims

1. A self-adapting variable spreading ratio satellite portable station receiver synchronization system, characterized by, The application relates to a method for receiving a signal with frequency offset, comprising the following steps: A data preprocessing module is used for pilot despreading, differential and integral operations on the received signal with frequency offset, and an impulse signal with a pilot spreading code length as a period is outputted; A spreading code synchronization module is used for searching for a stable maximum value in the preprocessed impulse signal, and a preliminary spreading code synchronization position pk is determined by comparing with a capture threshold value; A symbol synchronization module is used for calculating a symbol synchronization position temporary variable mkk according to the front, middle and rear sampling points of the spreading code synchronization impulse signal, and adjusting the spreading code synchronization position pk and the symbol synchronization position mk according to the value of mkk; A spreading ratio / frame synchronization module adopts a multi-spreading ratio parallel detection technology, pre-despreads the data with the lowest spreading ratio and stores the data, carries out parallel unique word (UW) detection on the pre-despreaded data under different spreading ratios, marks the data starting position according to the detected frame header position, and completes the spreading ratio synchronization; A frequency synchronization module adopts a multi-phase frequency-locked loop technology, uses different frequency offset estimation formulas in different stages through a plurality of frequency discriminators with different phases and precisions, and realizes frequency synchronization; A phase synchronization module is used for correcting the phase offset of the signal according to the phase of the demapped unique word (UW) after completing the frequency synchronization, and completing the phase synchronization.

2. A self-adapting variable spreading factor ratio satellite portable station receiver synchronization system according to claim 1, characterized in that, The pilot despreading operation of the data preprocessing module is realized by the following formula: ； where k denotes a sampling time, W denotes a pilot spreading code of length L, denotes a received signal.

3. The adaptive variable spreading factor satellite portable station receiver synchronization system of claim 1 wherein, The interval of the spreading code synchronization impulse signal determined by the spreading code synchronization module is SPS x W, wherein SPS is the number of sampling points per chip, and W is the pilot spreading code length.

4. The adaptive variable spreading factor satellite portable station receiver synchronization system of claim 1 wherein, In the symbol synchronization module, the calculation formula of the symbol synchronization position temporary variable mkk is as follows: mkk=sign[R(0)-R(-1)] / 2+sign[R(1)-R(0)] / 2 Wherein, R(-1), R(0) and R(1) represent the front, middle and rear three sampling points of the spreading code synchronization impulse signal sampling, and sign represents a sign function and the value is +1 or -1; The adjustment rule is as follows: When mkk>0.75, mk=mk+1, pk=pk+1, and mkk=mkk-1; When mkk<-0.75, mk=mk-1, pk=pk-1, and mkk=mkk+1. The threshold value of the adjustment is set as 0.75 instead of 0.5, so that a certain margin is left, noise influence is avoided, and the adjustment is prevented from being repeatedly carried out near 0.

5.

6. An adaptive variable spreading factor satellite portable station receiver synchronization system according to claim 1 wherein, The frame header in the spreading ratio / frame synchronization module is an inserted frame header, and the frame header starting position synchronization is completed through multi-path parallel detection.

7. The adaptive variable spreading factor satellite portable station receiver synchronization system of claim 1 wherein, In the frequency synchronization module, the initial formula of the frequency offset estimation is as follows: ； Wherein, Arg is an amplitude angle, and S is a differential step length; The frequency offset estimation formulas in different stages correspond to different differential step lengths, including 2S, 4S and the like, and when the differential step length is 2S, the frequency offset estimation formula is as follows: 。 8. The adaptive variable spreading factor satellite portable station receiver synchronization system of claim 1 wherein, The phase synchronization module corrects the phase offset by multiplying the demapped unique word (UW) after amplitude normalization and conjugation with the signal.

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