Method and system for rapidly capturing low-orbit high-dynamic signals

Abstract

The invention discloses a method and a system for quickly capturing a low-orbit high-dynamic signal, which relate to satellite communication and signal processing technologies, and comprise a time-sharing parallel correlation step: receiving an intermediate frequency signal, searching a code phase by performing correlation operation on a local pseudo code and the intermediate frequency signal, and after each correlation operation, performing time-sharing parallel correlation on the local pseudo code and the intermediate frequency signal; enabling the local binary phase shift keying (BPSK) modulation pseudo code to slide on a code phase by a stepping amount corresponding to the number of parallel correlators so as to finish coarse capture of the code phase; a frequency secondary search step: applying a plurality of different Doppler frequency compensation values to the intermediate frequency signal in sequence according to the code phase coarsely captured by the code phase, and repeating correlation operation after each compensation; and determining the Doppler frequency compensation value corresponding to the generated maximum correlation peak value as the optimal Doppler frequency estimation value. According to the method, the problem of discontinuous MCSK signal code phases in the capturing process is solved, and the signal capturing speed is greatly increased.

Description

Technical Field

[0001] This application relates to the fields of satellite communication and signal processing technology, and in particular to a method and system for rapid acquisition of low-Earth orbit high dynamic signals. Background Technology

[0002] With the rapid development of low-Earth orbit (LEO) satellite navigation enhancement technology, how to capture high-dynamic satellite navigation signals has become a focus of academic attention. Multiple Code Shift Keying (MCSK) modulation, by dividing time slots and allocating different signals to each slot, can effectively improve message transmission rates and is expected to be widely used in the future field of LEO navigation enhancement. How to capture such discontinuous code period signals is a key issue.

[0003] Currently, traditional signal time-domain acquisition methods include the serial sliding correlation method and the parallel correlator method.

[0004] The serial sliding correlation method aims to estimate the code phase and Doppler frequency shift of the received signal and use these estimates to initialize the tracking loop. A typical BPSK signal acquisition model is as follows: Figure 1 As shown.

[0005] As the acquisition model shows, the I and Q signals will only reach their maximum amplitude when the local pseudo-code rate matches the pseudo-code rate in the received signal, and the local carrier frequency matches the carrier frequency of the received signal with the added Doppler shift. Therefore, the acquisition of the spread spectrum signal involves two steps: estimating the pseudo-code phase shift and estimating the Doppler shift. In the traditional time-domain sliding correlation method, the code phase step is half a chip, and the Doppler shift step is one Doppler shift unit. Thus, one code phase search unit and one Doppler shift unit constitute a two-dimensional search unit, such as... Figure 2 As shown. When the correlation result between the local code and the pseudocode of the received signal is higher than the preset detection threshold, the acquisition is complete.

[0006] Parallel correlator technology refers to the application of multiple correlators during the acquisition process. This allows for parallel searching of multiple code phases, thereby improving the acquisition speed. The acquisition principle diagram is as follows: Figure 3 As shown, the intermediate frequency signal is mixed to obtain a zero intermediate frequency signal, which is then correlated using a parallel correlator. Figure 3 Ten parallel correlators were used, which can search for 10 code phases in parallel at a time, making the code phase search speed 10 times faster than before. This achieves the effect of parallel code phase search within a small range, thereby improving the acquisition speed.

[0007] The MCSK signal, and its modulation model, can be represented as MCSK(U,K,P). This model is mainly determined by three parameters: U represents the number of bits per CSK symbol, K represents the number of time slots, and P represents the number of time slots containing the data. For example, MCSK(6,2,1) means that each CSK symbol represents 6 bits, divided into two time slots, with the data in the odd time slots. The time slot allocation diagram is shown in Table 1 below.

[0008] Table 1 Since the code phase of MCSK signals is not continuous, it poses a great challenge to signal acquisition. Traditional time-domain acquisition algorithms are no longer suitable for this type of signal with discontinuous code phase.

[0009] In traditional signal time-domain acquisition methods, the serial sliding correlation method, while simple, is slow because it can only search for one code phase at a time. This slowness leads to a mismatch between the frequency step size during frequency domain search and the high Doppler shift rate of the low-orbit signal, resulting in acquisition failure. While the parallel correlator method can accelerate acquisition, its inability to be directly applied to low-orbit MCSK signal acquisition is due to the discontinuous code phase characteristics of the signal. Summary of the Invention

[0010] This application provides a method and system for rapid acquisition of low-Earth orbit high-dynamic signals, which solves the problem of discontinuous MCSK signal code phase in the acquisition process, greatly improves the signal acquisition speed, and ensures the success rate of acquiring low-Earth orbit high-dynamic MCSK signals.

[0011] This application provides a method for rapid acquisition of low-orbit high dynamic signals, including: Time-division parallel correlation steps: Receive the intermediate frequency (IF) signal, search for the code phase by performing correlation operations between the local pseudocode and the IF signal. After each correlation operation, slide the local binary phase shift keying (BPSK) pseudocode on the code phase by a step amount corresponding to the number of parallel correlators. If the outputs of the parallel correlators do not exceed a preset threshold, repeat the correlation operation and code phase sliding until at least one correlator output shows a correlation peak, thus completing coarse code phase acquisition and achieving acquisition only for the BPSK period of the IF signal. Frequency secondary search step: Based on the coarsely captured code phase, apply multiple different Doppler frequency compensation values ​​to the intermediate frequency signal in sequence, and repeat the correlation operation after each compensation; compare the correlation peak values ​​obtained under each compensation, and determine the Doppler frequency compensation value corresponding to the maximum correlation peak value as the optimal Doppler frequency estimate.

[0012] This application also proposes a fast acquisition system for low-Earth orbit high dynamic signals, including a processor and a memory. The memory stores a computer program, which, when executed by the processor, implements the steps of the aforementioned fast acquisition method for low-Earth orbit high dynamic signals.

[0013] This application employs a time-domain time-division parallel correlation joint frequency secondary search method to solve the problem of discontinuous code phase in MCSK signal acquisition from the perspectives of code phase and frequency. This greatly improves the signal acquisition speed, ensures the success rate of acquiring low-orbit high-dynamic MCSK signals, and ensures that the signal processing can smoothly transition from the acquisition stage to the tracking stage.

[0014] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0015] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 This is a schematic diagram of a typical BPSK signal acquisition model; Figure 2 This is a schematic diagram of the existing time-domain sliding correlation method; Figure 3 This is a schematic diagram of the existing parallel correlator method; Figure 4 This is a schematic diagram of the overall process of the method for rapid acquisition of low-orbit high dynamic signals according to an embodiment of this application. Detailed Implementation

[0016] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0017] Due to the discontinuous phase characteristic of MCSK codes, the traditional time-domain sliding serial correlation method correlates the code phase for each cycle. However, since the even time slots of this signal use CSK modulation, when U=6, there are a total of =64 pseudo-codes, capturing this time slot is meaningless. Because high dynamic signals have a high Doppler change rate, if a serial sliding scheme is used, a single traversal of the code phase requires 8-9 seconds. During this time, the Doppler change of the signal exceeds the Doppler frequency step value, causing the signal to fail to enter tracking, resulting in the capture of an incorrect frequency. This application's embodiment adopts a time-division acquisition architecture, capturing only the BPSK code period of odd time slots, effectively reducing signal processing complexity. Specifically, this application's embodiment proposes a fast acquisition method for low-orbit high dynamic signals, including the following steps: Time-division parallel correlation steps: Receive the intermediate frequency (IF) signal, and search for the code phase by performing correlation operations between the local pseudocode and the IF signal. After each correlation operation, slide the local binary phase shift keying (BPSK) pseudocode on the code phase by a step amount corresponding to the number of parallel correlators. If the outputs of the parallel correlators do not exceed a preset threshold, repeat the correlation operation and code phase sliding until at least one correlator output shows a correlation peak, thus completing coarse acquisition of the code phase and achieving acquisition only for the BPSK period of the IF signal.

[0018] Frequency secondary search step: Based on the coarsely captured code phase, apply multiple different Doppler frequency compensation values ​​to the intermediate frequency signal in sequence, and repeat the correlation operation after each compensation; compare the correlation peak values ​​obtained under each compensation, and determine the Doppler frequency compensation value corresponding to the maximum correlation peak value as the optimal Doppler frequency estimate.

[0019] The method in this application uses a parallel correlator method combined with a frequency quadratic search method for MCSK signal acquisition. The use of multiple parallel correlators improves the acquisition speed, ensures that the Doppler variation does not exceed the tracking loop pull range, and uses a frequency quadratic search to ensure the frequency accuracy of the acquisition estimate, greatly reducing the probability of re-acquisition after loss of lock, ensuring the acquisition success rate, and improving the performance of the receiver.

[0020] In some embodiments, the correlation operation between the local pseudocode and the intermediate frequency signal to search for the code phase is achieved by using a multi-channel parallel correlator to simultaneously calculate the correlation values ​​of multiple adjacent code phases. For example, in some embodiments, the number of multi-channel parallel correlators is 20-25; the step size is the corresponding 20-25 half-chips.

[0021] In some embodiments, after each relevant operation, the BPSK pseudocode is made to slide a step size over a specified time period.

[0022] In some embodiments, the frequency secondary search step includes sequentially applying 3-5 different unidirectionally varying Doppler frequency compensation values.

[0023] In a specific example of this application, the time-sharing parallel steps include: This application achieves the key objective of reducing the difficulty of acquisition by capturing the BPSK cycle of the signal through a time-division acquisition mechanism. The CSK cycle is not meaningful to capture; only the BPSK cycle needs to be captured and the tracking can be successfully entered.

[0024] Specifically, such as Figure 4 As shown in one example of this application, the intermediate frequency signal and the local code are correlated. The local code uses a 22-channel parallel correlator to identify the code phase. The local code shifts 22 half-codes every 2ms. If no correlation peak appears in any of the 22 correlators in a single correlation, it indicates that the correct code phase was not identified in this correlation operation. The local code continues to shift 22 half-codes until a correlation peak appears in one channel. At this point, the local code shifts by Index +1. At this time, the correlator output should show alternating large and small values ​​because the cross-correlation between the CSK code and the local BPSK code is weak during the CSK code period, and no correlation peak will appear. Next, a secondary frequency search is performed. The specific number of channels and shifting method mentioned above are merely examples and are not intended to limit the method of this application.

[0025] In some embodiments, during the time-division parallel correlation step, when a correlation peak is detected and it is determined that the correlator output exhibits an alternating pattern of large and small values, it is determined that the current period is in the BPSK cycle and the confirmation code phase capture is successful.

[0026] In some embodiments, the following threshold decision step is also included: In the time-division parallel correlation step, a first detection threshold is set for the detection of the correlation peak; In the frequency secondary search step, a second detection threshold is set to confirm successful final capture.

[0027] In one specific embodiment, since the influence of frequency on the correlation peak is much smaller than the influence of code phase on the correlation peak, such as Figure 4 As shown, based on the parallel correlator identified earlier, the correct code phase is obtained, and then the correlation peaks are compared three times under different unidirectional Doppler frequency compensation values. The maximum value is selected to obtain the optimal Doppler frequency estimate.

[0028] The purpose of the secondary search proposed in this application is to effectively improve the acquisition efficiency by comparing the correlation peaks a limited number of times after the 74-fold decision, accurately identify the position of the true frequency, reduce the number of signal loss and re-acquisition, thereby reducing the signal acquisition time, enabling the receiver to smoothly enter tracking and demodulate the signal, and improving the receiver performance.

[0029] This application proposes a time-division acquisition scheme to address the discontinuous phase characteristics of MCSK signals. It acquires only the BPSK period of the odd time slots and skips the CSK period of the even time slots, reducing the complexity of signal processing. In view of the high dynamic characteristics of MCSK signals, this application adopts a time-domain parallel correlator combined with a secondary frequency search method to ensure the acquisition success rate, accurately identify the position of the true frequency, and ensure that the signal processing process can smoothly transition to the tracking stage.

[0030] This application also proposes a rapid acquisition system for low-Earth orbit high dynamic range signals, characterized in that it includes a processor and a memory, wherein the memory stores a computer program, and when the computer program is executed by the processor, it implements the steps of the aforementioned rapid acquisition method for low-Earth orbit high dynamic range signals.

[0031] It should be noted that, in the embodiments of this application, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0032] The sequence numbers of the embodiments in this application are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0033] The embodiments of this application have been described above with reference to the accompanying drawings. However, this application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims. All of these forms are within the protection scope of this application.

Claims

1. A method for rapid acquisition of low-orbit high dynamic range signals, characterized in that, include: Time-division parallel correlation steps: Receive the intermediate frequency (IF) signal, search for the code phase by performing correlation operations between the local pseudocode and the IF signal. After each correlation operation, slide the local binary phase shift keying (BPSK) pseudocode on the code phase by a step amount corresponding to the number of parallel correlators. If the outputs of the parallel correlators do not exceed a preset threshold, repeat the correlation operation and code phase sliding until at least one correlator output shows a correlation peak, thus completing coarse code phase acquisition and achieving acquisition only for the BPSK period of the IF signal. Frequency secondary search step: Based on the coarsely captured code phase, apply multiple different Doppler frequency compensation values ​​to the intermediate frequency signal in sequence, and repeat the correlation operation after each compensation; compare the correlation peak values ​​obtained under each compensation, and determine the Doppler frequency compensation value corresponding to the maximum correlation peak value as the optimal Doppler frequency estimate.

2. The method for rapid acquisition of low-orbit high dynamic signals as described in claim 1, characterized in that, The search for code phase is achieved by performing correlation operations between the local pseudocode and the intermediate frequency signal. This is accomplished by using a multi-parallel correlator to simultaneously calculate the correlation values ​​of multiple adjacent code phases.

3. The method for rapid acquisition of low-orbit high dynamic signals as described in claim 2, characterized in that, The number of parallel correlators is 20-25. The step size corresponds to 20-25 half-chips.

4. The method for rapid acquisition of low-orbit high dynamic signals as described in claim 3, characterized in that, After each relevant operation, the BPSK pseudocode is made to slide a step size within a specified time.

5. The method for rapid acquisition of low-orbit high dynamic signals as described in claim 1, characterized in that, The frequency secondary search step includes sequentially applying 3-5 different unidirectionally varying Doppler frequency compensation values.

6. The method for rapid acquisition of low-orbit high dynamic signals as described in claim 1, characterized in that, In the time-division parallel correlation step, when a correlation peak is detected, if it is determined that the correlator output shows an alternating pattern of large and small values, then it is determined that the current period is BPSK and the confirmation code phase capture is successful.

7. The method for rapid acquisition of low-orbit high dynamic signals as described in claim 1, characterized in that, It also includes the following threshold decision steps: In the time-division parallel correlation step, a first detection threshold is set for the detection of the correlation peak; In the frequency secondary search step, a second detection threshold is set to confirm successful final capture.

8. A rapid acquisition system for low-orbit high dynamic signals, characterized in that, It includes a processor and a memory, the memory storing a computer program that, when executed by the processor, implements the steps of the fast acquisition method for low-orbit high dynamic signals as described in any one of claims 1 to 7.

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