An adaptive variable spreading ratio satellite portable station receiver synchronization system

Abstract

The application relates to the technical field of satellite portable station communication, and discloses a satellite portable station receiver synchronization system with adaptive variable spreading ratio, which has the technical scheme as follows: through a data preprocessing module, a spreading code synchronization module, a symbol synchronization module, a spreading ratio / frame synchronization module, a frequency synchronization module, a phase synchronization module and other processes, the synchronization of signals with different spreading ratios is realized, so that reliable communication of the communication system of the satellite portable station can be obtained under a low signal-to-noise ratio and a strong interference environment, and the flexibility of the system is improved.

Description

Technical Field

[0001] This invention relates to the field of satellite portable station communication technology, and more specifically, to an adaptive variable spread spectrum ratio satellite portable station receiver synchronization system. Background Technology

[0002] Satellite portable station communication systems are highly valuable in remote areas, mountainous regions, and oceans due to their wide coverage, immunity to terrestrial environments, and resistance to human interference. However, they suffer from extremely low signal-to-noise ratios due to electromagnetic interference, shadowing effects, multipath fading, and high Doppler shift, necessitating various measures to ensure reliable communication. Spread spectrum communication, with its advantages of anti-interference, code division multiple access, and signal concealment, is widely used in military and commercial communication systems. Adaptive variable spreading ratio satellite spread spectrum communication technology, building upon this foundation, comprehensively considers communication speed and anti-interference capabilities, adapting to different environments and communication targets by real-time adjustment of the channel spreading ratio, thus greatly enhancing system flexibility.

[0003] However, accurate synchronization of the receiver spreading sequence in this system is the primary problem that must be solved. Synchronization includes spreading ratio synchronization, chip synchronization, symbol synchronization, carrier synchronization, phase synchronization, and frame synchronization. Among these, frame synchronization and spreading code synchronization are the key points. By detecting the feature codes of different spreading ratios, the despreading and deframe information of subsequent information can be obtained, which is an important part of the system demodulation.

[0004] Therefore, the present invention provides an adaptive variable spread ratio satellite portable station receiver synchronization system, which improves the above-mentioned technical problems. Summary of the Invention

[0005] This disclosure aims to address the shortcomings of existing technologies by providing an adaptive variable spread spectrum ratio satellite portable station receiver synchronization system. The present invention achieves synchronization of signals with different spread spectrum ratios through processes such as data preprocessing, spread spectrum code synchronization, symbol synchronization, spread spectrum ratio / frame synchronization, frequency synchronization, and phase synchronization, so as to ensure that the system can obtain reliable communication in low signal-to-noise ratio and strong interference environments and improve system flexibility.

[0006] The above-mentioned technical objective of the present invention is achieved through the following technical solution: an adaptive variable spread ratio satellite portable station receiver synchronization system, comprising:

[0007] The data preprocessing module is used to perform pilot despreading, differential and integral operations on the received frequency offset signal, and output a pulse signal with a period of the pilot spreading code length.

[0008] The spreading code synchronization module is used to find a stable maximum value in the preprocessed pulse signal and determine the initial spreading code synchronization position pk by comparing it with the capture threshold.

[0009] The symbol synchronization module is used to calculate the temporary variable mkk of the symbol synchronization position based on the front, middle and back sampling points of the spreading code synchronization pulse signal, and to adjust the spreading code synchronization position pk and the symbol synchronization position mk according to the value of mkk.

[0010] The spreading ratio / frame synchronization module adopts a multi-spreading ratio parallel detection technology. First, the data is pre-despread and stored at the lowest spreading ratio. Then, the pre-despread data under different spreading ratios is detected in parallel using unique code (UW). The data start position is marked according to the detected frame header position to complete the spreading ratio synchronization.

[0011] The frequency synchronization module adopts multi-phase frequency-locked loop technology. It uses multiple frequency discriminators with different phases and precisions to estimate the frequency offset in stages using different frequency offset estimation formulas, thereby achieving frequency synchronization.

[0012] The phase synchronization module is used to correct the phase offset of the signal based on the phase of the demapped unique code UW after frequency synchronization is completed, thus completing phase synchronization.

[0013] As a preferred embodiment of the present invention, the pilot despreading operation performed by the data preprocessing module is achieved by the following formula:

[0014]

[0015] Where k represents the sampling time, and W represents the pilot spreading code of length L. This indicates that a signal has been received.

[0016] As a preferred embodiment of the present invention, the interval of the spreading code synchronization pulse signal determined by the spreading code synchronization module is SPS×W, where SPS is the number of sampling points per chip and W is the length of the pilot spreading code.

[0017] As a preferred embodiment of the present invention, the formula for calculating the temporary variable mkk of the symbol synchronization position in the symbol synchronization module is as follows:

[0018] mkk=sign[R(0)-R(-1)] / 2+sign[R(1)-R(0)] / 2

[0019] Where R(-1), R(0) and R(1) represent the first, middle and last sampling points of the spread spectrum code synchronization pulse signal, and sign represents the sign function, which takes a value of ±1;

[0020] The adjustment rules are as follows:

[0021] When mkk > 0.75, then mk = mk + 1, pk = pk + 1, mkk = mkk - 1;

[0022] When mkk < -0.75, then mk = mk-1, pk = pk-1, and mkk = mkk+1.

[0023] The threshold was set at 0.75 instead of 0.5 because this leaves a margin to avoid noise interference and allows it to be adjusted back and forth around 0.5.

[0024] As a preferred embodiment of the present invention, the frame header in the spread spectrum ratio / frame synchronization module is an inserted frame header, and the frame header start position synchronization is completed through multi-channel parallel detection.

[0025] As a preferred embodiment of the present invention, the initial formula for frequency offset estimation in the frequency synchronization module is:

[0026]

[0027] Where Arg is the argument angle and S is the difference step size;

[0028] The frequency offset estimation formula corresponds to different difference step sizes for different stages, including 2S, 4S, etc. When the difference step size is 2S, the frequency offset estimation formula is:

[0029] .

[0030] As a preferred embodiment of the present invention, the phase synchronization module performs phase offset correction by multiplying the demapped unique code UW with the signal after amplitude normalization and conjugation.

[0031] In summary, the present invention has the following beneficial effects: Compared with the prior art, the present invention, through a unique synchronization process design, can achieve precise synchronization of spreading ratio, chips, symbols, carrier, phase, and frames without pre-synchronization of the spreading ratio at the transmitting and receiving ends of the satellite portable station. This is due to the unique and fixed code length of the spreading code and its continuous segmented use when reducing the spreading ratio. The data preprocessing stage improves the signal-to-noise ratio through pilot despreading, differential and integral operations. Symbol synchronization avoids noise interference through threshold adjustment. Spreading ratio / frame synchronization adopts parallel detection of multiple spreading ratios and pre-despreading of the lowest spreading ratio to reduce the processing load. Frequency synchronization uses a multi-phase frequency-locked loop to balance the acquisition range and accuracy. Phase synchronization uses a unique code phase to correct deviations. Overall, in satellite communication environments with low signal-to-noise ratio, strong interference, and high Doppler shift, the present invention retains the advantages of spread spectrum communication such as anti-interference, and balances communication rate and anti-interference capability by adaptively adjusting the spreading ratio, thus greatly improving system flexibility and communication reliability. Attached Figure Description

[0032] Figure 1 A framework diagram of an adaptive variable spread ratio satellite portable station receiver synchronization system provided in an embodiment of the present invention;

[0033] Figure 2 This is a flowchart of the spreading code / symbol synchronization process provided in an embodiment of the present invention;

[0034] Figure 3 A flowchart of frame synchronization provided for embodiments of the present invention;

[0035] Figure 4 A frequency synchronization flowchart provided for an embodiment of the present invention. Detailed Implementation

[0036] The present application will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present application, but do not limit the present application in any way. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present application. These all fall within the protection scope of the present application.

[0037] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0038] Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. The term "and / or" as used in this specification includes any and all combinations of one or more of the associated listed items.

[0039] Furthermore, the technical features involved in the various embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0040] The embodiments disclosed herein aim to solve the problem of accurate synchronization of receiver spreading sequences in an adaptive variable spreading ratio satellite portable station communication system. Through processes such as data preprocessing, spreading code synchronization, symbol synchronization, spreading ratio / frame synchronization, frequency synchronization, and phase synchronization, synchronization of signals with different spreading ratios is achieved, so as to ensure that the system can obtain reliable communication in low signal-to-noise ratio and strong interference environments and improve system flexibility.

[0041] Please refer to Figure 1 , Figure 1 A framework diagram of an adaptive variable spread ratio satellite portable station receiver synchronization system according to an embodiment of this disclosure is shown. It mainly includes the following modules:

[0042] Data preprocessing module, spreading code synchronization module, symbol synchronization module, spreading ratio / frame synchronization module, frequency synchronization module, and phase synchronization module.

[0043] Receiver synchronization can be divided into time-domain synchronization and frequency-domain synchronization, with time-domain synchronization being the most important, especially in spread spectrum systems where the low signal-to-noise ratio renders traditional synchronization algorithms ineffective, necessitating the use of new algorithms or methods. In the demodulation process described above, pk is the spreading code synchronization point, mk is the (integer) sampled symbol synchronization point, rk is the frame synchronization point, fk is the estimated frequency offset, and sk is the estimated phase offset. The time-domain signals pk, mk, and rk have the same initial phase but different periods. Once these parameters are determined, subsequent data demapping, decoding, and descrambling operations can be performed.

[0044] (1) Data preprocessing module:

[0045] The raw information processed by the matched filter has a low signal-to-noise ratio and contains frequency and phase offsets, so it cannot be processed directly or the relevant parameters can be extracted directly. It needs to be preprocessed to resist noise and resist frequency and phase offsets. Therefore, it needs to go through pilot despreading, differential (conjugate multiplication), integration (in-phase addition) and other operations to obtain a processable signal so as to perform frequency synchronization, bit synchronization and spreading code synchronization.

[0046] Suppose that the received wireless communication signal r with frequency offset can be simply expressed as the sum of the communication signal s and the noise signal n:

[0047]

[0048] In the formula, k is the sampling time, A is the modulated complex envelope, and f is the residual frequency offset. The phase is random, and n is additive white Gaussian noise. After matched filtering, the pilot code is despread, and the despread signal is:

[0049]

[0050] In the formula, W is the pilot spreading code of length L. After despreading, to resist frequency and phase offset, differential analysis between adjacent symbols is required, followed by integration to improve the signal-to-noise ratio. Therefore, the preprocessed output signal is:

[0051]

[0052] In the formula, K is the integration length, S is the differential step size, and N is the sum of the noise crossover phase and the noise squared terms. After the above operation, the pilot signal is formed into a pulse signal with a period of the pilot spreading code length, which has only phase offset and no frequency offset and a high signal-to-noise ratio.

[0053] (2) Spreading code synchronization module:

[0054] like Figure 2 As shown, a stable maximum value is sought in the preprocessed pilot signal, i.e., a pulse signal with a period equal to the minimum spreading code length of the pilot. Initially, a capture threshold is set. When the signal amplitude is greater than the threshold, this is considered the initial spreading code synchronization position pk and the optimal sampling point for spreading code synchronization, i.e., symbol synchronization mk. The optimal integer sampling point at this time may not be accurate, so it needs to be continuously adjusted through subsequent symbol synchronization.

[0055] The initial synchronization process is as follows: Based on the positions of pk and mk, a spreading 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 length of the pilot spreading code. At this time, the spreading code synchronization pulse signal and the spreading signal complete the initial synchronization.

[0056] (3) Symbol synchronization module:

[0057] Let the three sampling points before, during, and after the sampling of the spreading code synchronization pulse signal be R(-1), R(0), and R(1), then define a temporary variable for the symbol synchronization position:

[0058] mkk=sign[R(0)-R(-1)] / 2+sign[R(1)-R(0)] / 2

[0059] In the formula, sign is the sign parameter, and its value is ±1.

[0060] By calculating and averaging mkk over a long period, the value of mkk is used to adjust the spreading code synchronization position pk and the symbol synchronization position mk. The specific adjustment rules are as follows:

[0061] When mkk > 0.75, then mk = mk + 1, pk = pk + 1, mkk = mkk - 1;

[0062] When mkk < -0.75, then mk = mk-1, pk = pk-1, and mkk = mkk+1.

[0063] The threshold was set at 0.75 instead of 0.5 because this leaves a margin to avoid noise interference and allows it to be adjusted back and forth around 0.5.

[0064] (4) Spreading ratio / frame synchronization module:

[0065] like Figure 3As shown, frame synchronization mainly employs a correlation algorithm. Given that the received frame has multiple spreading ratio types, a multi-spreading-ratio parallel detection technique is used to detect the frame header data. The despread data is copied into multiple copies, each with its own spreading code. Only one module detects the correlation peak before outputting the result. Before being sent to the frame detection module, pre-despreading processing with the lowest spreading ratio is performed to reduce the processing rate, thus significantly reducing the amount of data processed subsequently.

[0066] The frame synchronization design mainly consists of three parts. First, data pre-despreading is performed according to different spreading ratios, and the despread data is stored separately. Second, parallel detection of different unique codes (UWs) is performed on the pre-despread data under different spreading ratios. Since it is an inserted frame header, the start position of the frame header needs to be synchronized during frame header detection, which is accomplished through multi-channel parallel detection. Finally, after the frame header is detected, the start data position in the memory is located according to the position rk of the last data, and the data is deframed and output, completing the spreading ratio synchronization.

[0067] (5) Frequency synchronization module:

[0068] like Figure 4 As shown, the frequency synchronous sampling multiphase frequency-locked loop (MLL) technology is based on the traditional single-frequency discriminator MLL. It employs multiple discriminators with different phases and accuracies, and uses parallel MLLs with different discriminators based on criteria. A phase tracking component is added to compensate for the inability of MLLs to track phase. Through the linkage of multiple levels of discriminators, the MLL features simple implementation, wide acquisition range, fast convergence speed, high tracking accuracy, and low signal-to-noise ratio requirements.

[0069] The preprocessed pilot signal can be directly used for frequency offset estimation. The estimated frequency offset value for frequency synchronization is:

[0070]

[0071] In the formula, Arg is the argument angle and S is the difference step size.

[0072] The multiphase frequency discriminator, based on the traditional frequency discriminator, employs multiple groups of discriminators with different phase differences to jointly complete frequency discrimination. These discriminators utilize multiple levels of phase differences, such as S, 2S, and 4S. For example, at 2S, the output of the aforementioned preprocessing module becomes:

[0073]

[0074] At this point, the estimated value of the frequency offset becomes:

[0075]

[0076] In multiphase frequency-locked loop (MPL) applications, the frequency estimation formulas at different levels have different estimation ranges and accuracies. The differential step size, from smallest to largest, corresponds to a decreasing estimation range and increasing estimation accuracy. Therefore, MPLs cannot use these estimation formulas simultaneously; instead, they sample different formulas at different estimation stages. Specifically, the estimation strategy is to initially use an estimation formula with a large estimation range and low accuracy. Once the estimation formula reaches its required accuracy, it is replaced with the next level formula, which has a smaller estimation range and higher accuracy, and so on.

[0077] The switching strategy for different estimation ranges and accuracies is as follows: once an equation reaches its estimation accuracy, switch to the next equation with higher accuracy and a narrower estimation range. The estimation accuracy of each equation is related to the signal-to-noise ratio, the difference step size S, and the integration time length K. During switching, the estimation range of the next equation should be slightly larger than the estimation accuracy of the previous one.

[0078] (6) Phase synchronization module:

[0079] Since frequency synchronization uses frequency-locked loop technology and phase synchronization is not implemented, phase deviation correction needs to be considered after frequency synchronization is completed. The unique code UW in the received signal undergoes symbol synchronization and frequency synchronization, followed by demapping to obtain a UW signal consisting entirely of 1s. The phase deviation of this UW signal is the system's phase deviation. The phase deviation sk can then be corrected based on the phase of the demapped unique code UW. This is achieved by normalizing and conjugating the amplitude of the demapped UW signal, then multiplying it by the signal, thus completing phase synchronization.

[0080] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. An adaptive variable spread ratio satellite portable station receiver synchronization system, characterized in that, include: The data preprocessing module is used to perform pilot despreading, differential and integral operations on the received frequency offset signal, and output a pulse signal with a period of the pilot spreading code length. The spreading code synchronization module is used to find a stable maximum value in the preprocessed pulse signal and determine the initial spreading code synchronization position pk by comparing it with the capture threshold. The symbol synchronization module is used to calculate the temporary variable mkk of the symbol synchronization position based on the front, middle and back sampling points of the spreading code synchronization pulse signal, and to adjust the spreading code synchronization position pk and the symbol synchronization position mk according to the value of mkk. The spreading ratio / frame synchronization module adopts a multi-spreading ratio parallel detection technology. First, the data is pre-despread and stored at the lowest spreading ratio. Then, the pre-despread data under different spreading ratios is detected in parallel using unique code (UW). The data start position is marked according to the detected frame header position to complete the spreading ratio synchronization. The frequency synchronization module adopts multi-phase frequency-locked loop technology. It uses multiple frequency discriminators with different phases and precisions to estimate the frequency offset in stages using different frequency offset estimation formulas, thereby achieving frequency synchronization. The phase synchronization module is used to correct the phase offset of the signal based on the phase of the demapped unique code UW after frequency synchronization is completed, thus completing phase synchronization.

2. The adaptive variable spread ratio satellite portable station receiver synchronization system according to claim 1, characterized in that, The pilot despreading operation performed by the data preprocessing module is achieved by the following formula: ； Where k represents the sampling time, and W represents the pilot spreading code of length L. This indicates that a signal has been received.

3. The adaptive variable spread ratio satellite portable station receiver synchronization system according to claim 1, characterized in that, The interval of the spreading code synchronization pulse signal determined by the spreading code synchronization module is SPS×W, where SPS is the number of sampling points per chip and W is the length of the pilot spreading code.

4. The adaptive variable spread ratio satellite portable station receiver synchronization system according to claim 1, characterized in that, In the symbol synchronization module, the formula for calculating the temporary variable mkk of the symbol synchronization position is: mkk=sign[R(0)-R(-1)] / 2+sign[R(1)-R(0)] / 2 Where R(-1), R(0) and R(1) represent the first, middle and last sampling points of the spread spectrum code synchronization pulse signal, and sign represents the sign function, which takes a value of ±1; The 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, and mkk = mkk+1.

5. The threshold was set at 0.75 instead of 0.5 because this leaves a margin to avoid noise interference and allows it to be adjusted back and forth around 0.

5.

6. The adaptive variable spread ratio satellite portable station receiver synchronization system according to claim 1, characterized in that, The frame header in the spread spectrum ratio / frame synchronization module is an inserted frame header, and the frame header start position synchronization is completed through multi-channel parallel detection.

7. The adaptive variable spread ratio satellite portable station receiver synchronization system according to claim 1, characterized in that, In the frequency synchronization module, the initial formula for frequency offset estimation is: ； Where Arg is the argument angle and S is the difference step size; The frequency offset estimation formula corresponds to different difference step sizes for different stages, including 2S, 4S, etc. When the difference step size is 2S, the frequency offset estimation formula is: 。 8. The adaptive variable spread ratio satellite portable station receiver synchronization system according to claim 1, characterized in that, The phase synchronization module performs phase offset correction by multiplying the demapped unique code UW with the signal after amplitude normalization and conjugation.

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