A method for acquisition and tracking suitable for high-speed spread spectrum communication systems

Abstract

This invention relates to the field of spread spectrum communication technology, and particularly to an acquisition and tracking method suitable for high-speed spread spectrum communication systems. The method involves receiving a baseband signal and sampling it to obtain sampling points. These sampling points are then subjected to polyphase filtering. Using polyphase filtering technology, a filter coefficient of a given phase is selected to filter the sampling points to recover a high sampling rate waveform. Subsequently, the recovered waveform is used for code acquisition and code tracking operations. By performing polyphase filtering on the sampling points, the sampling rate is increased to N times the original, thus increasing the accuracy of subsequent acquisition and tracking algorithms. Although only one phase data path needs to be processed, slightly increasing the latency of the acquisition and tracking algorithm, compared to traditional acquisition and tracking algorithms, it does not require increasing the processing clock speed or performing parallel filtering, exhibiting low complexity.

Description

Technical Field

[0001] This invention relates to the field of spread spectrum communication technology, and in particular to a capture and tracking method suitable for high-speed spread spectrum communication systems. Background Technology

[0002] Spread spectrum communication (SSC) is a method of information transmission where the bandwidth occupied by the signal is much larger than the minimum bandwidth required to transmit the information. This bandwidth expansion is achieved through an independent code sequence (usually a pseudo-random code) using encoding and modulation methods, independent of the transmitted data. At the receiving end, the same code is used for correlation synchronization reception, despreading, and recovery of the transmitted data. The accuracy of acquisition and tracking algorithms in traditional spread spectrum communication systems is limited by the ADC sampling rate. In high-speed spread spectrum communication systems, the accuracy of acquisition and tracking algorithms is often limited by the ADC sampling rate and high-speed signal processing capabilities, and cannot be improved further. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a low-complexity acquisition and tracking method that does not require a high ADC sampling rate.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0005] A capture and tracking method suitable for high-speed spread spectrum communication systems includes the following steps:

[0006] S1. Receive the baseband signal and perform a sampling operation on the received baseband signal to obtain sampling points;

[0007] S2. Perform multiphase filtering operation on the sampling points;

[0008] S3. Perform code capture operation on the filtered sampling points and determine whether the filtered sampling points have reached the capture state.

[0009] S4. If so, then perform code tracking operation on the filtered sampling points;

[0010] S5. Adjust the selected filter phase number based on the code tracking operation result.

[0011] The beneficial effects of this invention are as follows:

[0012] This scheme receives baseband signals and samples them to obtain sampling points. Multiphase filtering is then applied to these sampling points, followed by code acquisition. The scheme determines whether the filtered sampling points have reached the acquisition state; if so, code tracking is performed. Based on the code tracking result, the selected filter phase number is adjusted. Using multiphase filtering, one filter coefficient of a given phase is selected to filter the sampling points to recover a high sampling rate waveform. Subsequently, code acquisition and code tracking operations are performed on the recovered waveform. By performing multiphase filtering on the sampling points, the sampling rate is increased to N times the original, thus increasing the accuracy of the subsequent acquisition and tracking algorithms. Although only one phase data path needs to be processed, slightly increasing the latency of the acquisition and tracking algorithm, it is significantly less complex than traditional acquisition and tracking algorithms because it does not require increasing the processing clock speed or performing parallel filtering. Attached Figure Description

[0013] Figure 1 This is a flowchart of the acquisition and tracking method for high-speed spread spectrum communication systems according to the present invention. Detailed Implementation

[0014] To explain in detail the technical content, objectives, and effects of the present invention, the following description is provided in conjunction with the embodiments and accompanying drawings.

[0015] Please refer to Figure 1 The technical solution adopted in this invention is as follows:

[0016] A capture and tracking method suitable for high-speed spread spectrum communication systems includes the following steps:

[0017] S1. Receive the baseband signal and perform a sampling operation on the received baseband signal to obtain sampling points;

[0018] S2. Perform multiphase filtering operation on the sampling points;

[0019] S3. Perform code capture operation on the filtered sampling points and determine whether the filtered sampling points have reached the capture state.

[0020] S4. If so, then perform code tracking operation on the filtered sampling points;

[0021] S5. Adjust the selected filter phase number based on the code tracking operation result.

[0022] As can be seen from the above description, the beneficial effects of the present invention are as follows:

[0023] This scheme receives baseband signals and samples them to obtain sampling points. Multiphase filtering is then applied to these sampling points, followed by code acquisition. The scheme determines whether the filtered sampling points have reached the acquisition state; if so, code tracking is performed. Based on the code tracking result, the selected filter phase number is adjusted. Using multiphase filtering, one filter coefficient of a given phase is selected to filter the sampling points to recover a high sampling rate waveform. Subsequently, code acquisition and code tracking operations are performed on the recovered waveform. By performing multiphase filtering on the sampling points, the sampling rate is increased to N times the original, thus increasing the accuracy of the subsequent acquisition and tracking algorithms. Although only one phase data path needs to be processed, slightly increasing the latency of the acquisition and tracking algorithm, it is significantly less complex than traditional acquisition and tracking algorithms because it does not require increasing the processing clock speed or performing parallel filtering.

[0024] Furthermore, step S3 specifically includes:

[0025] S31. Based on the filtered sampling points, obtain the synchronous sampling sequence;

[0026] S32. Perform the operation of calculating the correlation peak on the synchronous sampling sequence, and determine whether the calculated correlation peak has reached the maximum value and whether the maximum value exceeds the preset capture threshold;

[0027] S33. If so, then determine that the filtered sampling points have reached the capture state.

[0028] Furthermore, step S4 specifically involves:

[0029] S41. If the filtered sampling points reach the capture state, then the lead sampling sequence and the lag sampling sequence are obtained based on the filtered sampling points.

[0030] S42. Perform correlation operations on the ahead sampling sequence and the lag sampling sequence with the local spreading code sequence, and calculate the squared difference of the correlation values.

[0031] Furthermore, step S5 specifically involves:

[0032] S51. Adjust the selected filter phase number based on the squared difference of the calculated correlation values.

[0033] Furthermore, step S51 also includes the following steps:

[0034] If the squared difference of the calculated correlation values ​​is positive, then the selected filter phase number should be reduced.

[0035] If the squared difference of the calculated correlation values ​​is negative, then the selected filter phase number should be increased.

[0036] Furthermore, the following steps are included between step S5 and step S42:

[0037] The squared difference of the calculated correlation values ​​is filtered.

[0038] As can be seen from the above description, in the actual system implementation, due to the noise in the input sampling sequence, the sampling point number adjustment may be frequently triggered. Therefore, it is necessary to perform a first-level filter on the squared difference result to smooth out the spikes. The filter can be a low-pass filter such as a moving average filter.

[0039] Furthermore, after filtering the squared differences of the calculated correlation values, the following steps are also included:

[0040] Take the absolute value of the squared difference of the calculated correlation values ​​and compare the absolute value of the squared difference with a preset threshold. If the absolute value of the squared difference is greater than the preset threshold, then proceed to step S5.

[0041] As can be seen from the above description, by taking the absolute value of the squared difference of the calculated correlation values ​​and comparing the absolute value of the squared difference with a preset threshold, the filter phase number is adjusted when the absolute value of the squared difference is greater than the preset threshold. This can minimize the false triggering of sampling adjustment caused by noise fluctuations, thereby further improving the accuracy of the acquisition and tracking algorithm.

[0042] Furthermore, after filtering the squared differences of the calculated correlation values, the following steps are also included:

[0043] Based on the filtered squared difference, determine whether to perform sampling point index adjustment. The specific steps are as follows:

[0044] If a sampling point index adjustment operation is required, then determine whether there is data output at the current clock.

[0045] If the current clock has data output, determine whether to adjust the sampling point index backward and cross the boundary of N sampling point indices; where N is the maximum phase number of the selected filter;

[0046] If yes, the adjustment amount will be stored and the sampling point index will be adjusted in the next clock cycle; otherwise, the sampling point index will be adjusted directly.

[0047] As can be seen from the above description, since the tracking process continuously adjusts the sampling time, that is, changes the selected filter phase number, when the cumulative adjustment amount is large, it may cross the N sampling point index boundaries, causing the subsequent data output clock to change. Therefore, using the above method to determine whether to perform sampling point index adjustment operation can further improve the accuracy of the acquisition and tracking algorithm.

[0048] Furthermore, after filtering the squared differences of the calculated correlation values, the following steps are also included:

[0049] If there is no data output at the current clock, the adjustment amount will be stored and the sampling point index will be adjusted in the next clock cycle.

[0050] Furthermore, in step S2, an FIR filter is used to perform multiphase filtering on the sampling points.

[0051] Please refer to Figure 1 Embodiment 1 of the present invention is as follows:

[0052] A capture and tracking method suitable for high-speed spread spectrum communication systems includes the following steps:

[0053] S1. Receive baseband signal, the baseband signal has a bandwidth and a chip rate f. c =15.36MHz spread spectrum signal, and the received baseband signal is fed with f s A sampling operation is performed at a sampling rate of 30.72MHz to obtain sampling points; in this embodiment, sampling is performed at a lower sampling rate (i.e., twice the signal bandwidth);

[0054] S2. Perform multiphase filtering on the sampling points, with a total number of phases N = 8. Since sampling is performed at a sampling rate of twice the signal bandwidth, a total of 16 phases are contained in one symbol width, i.e., the phase numbers are 0 to 15.

[0055] In step S2, an FIR filter is used to perform multiphase filtering on the sampling points; a set of filter coefficients corresponding to the phase number is selected from the 16-phase filter coefficients to filter the sampled signal; a 63rd-order low-pass filter is selected as the FIR filter.

[0056] S3. Perform code capture operation on the filtered sampling points and determine whether the filtered sampling points have reached the capture state.

[0057] S4. If so, then perform code tracking operation on the filtered sampling points;

[0058] S5. Adjust the selected filter phase number according to the code tracking operation result;

[0059] Step S3 is as follows:

[0060] S31. Based on the filtered sampling points, a synchronous sampling sequence is obtained; assuming the initial sampling phase number is set to 7, the 7th group of filter coefficients is selected to filter the sampling points to obtain the synchronous sampling sequence.

[0061] S32. Perform the operation of calculating the correlation peak on the synchronous sampling sequence and the local spreading code sequence, calculate the square of the correlation value to obtain the correlation peak, and determine whether the calculated correlation peak reaches the maximum value and the maximum value exceeds the preset capture threshold.

[0062] S33. If so, then determine that the filtered sampling points have reached the capture state;

[0063] Step S4 is as follows:

[0064] S41. If the filtered sampling points reach the capture state, then the lead sampling sequence and the lag sampling sequence are obtained based on the filtered sampling points. The phase number of the lead sampling sequence is the synchronous sampling sequence number plus N-1, and the lag sampling sequence is obtained by delaying the previous lead sampling sequence by one chip length (i.e., delaying by N sampling points).

[0065] S42. Perform correlation operations on the ahead sampling sequence and the lag sampling sequence with the local spreading code sequence, and calculate the squared difference of the correlation values.

[0066] Step S5 is as follows:

[0067] S51. Adjust the selected filter phase number based on the squared difference of the calculated correlation values;

[0068] Step S51 also includes the following steps:

[0069] If the squared difference of the calculated correlation values ​​is positive, the selected filter phase number should be reduced. Two thresholds, Y1 and Y2, can be set, each corresponding to a different adjustment step size. When the absolute value of the squared difference of the correlation values ​​is greater than Y1 and less than Y2, the filter phase number is reduced by 1. When the absolute value of the squared difference of the correlation values ​​is greater than Y2, the filter phase number is reduced by 2. The values ​​of Y1 and Y2 can be set according to the actual noise and interference conditions of the deployment.

[0070] If the squared difference of the calculated correlation values ​​is negative, the selected filter phase number should be increased. Similarly, two thresholds Y3 and Y4 can be set, each corresponding to a different adjustment step size. When the absolute value of the squared difference of the correlation values ​​is greater than Y3 and less than Y4, the filter phase number is incremented by 1. When the absolute value of the squared difference of the correlation values ​​is greater than Y4, the filter phase number is incremented by 2. The values ​​of Y3 and Y4 can be set according to the actual noise and interference conditions of the deployment.

[0071] The following steps are also included between step S5 and step S42:

[0072] The squared difference of the calculated correlation values ​​is filtered; the filter can be a low-pass filter such as a moving average filter, which is mainly used to smooth out glitches.

[0073] After filtering the squared differences of the calculated correlation values, the following steps are also included:

[0074] Take the absolute value of the squared difference of the calculated correlation values ​​and compare the absolute value of the squared difference with a preset threshold. If the absolute value of the squared difference is greater than the preset threshold, then proceed to step S5.

[0075] After filtering the squared differences of the calculated correlation values, the following steps are also included:

[0076] Based on the filtered squared difference, determine whether to perform sampling point index adjustment. The specific steps are as follows:

[0077] If a sampling point index adjustment operation is required, then determine whether there is data output at the current clock.

[0078] If the current clock has data output, determine whether to adjust the sampling point index backward and cross the boundary of N sampling point indices; where N is the maximum phase number of the selected filter;

[0079] If yes, the adjustment amount will be stored and the sampling point index will be adjusted in the next clock cycle; otherwise, the sampling point index will be adjusted directly.

[0080] After filtering the squared differences of the calculated correlation values, the following steps are also included:

[0081] If there is no data output at the current clock, the adjustment amount will be stored and the sampling point index will be adjusted in the next clock cycle.

[0082] Because the tracking process continuously adjusts the sampling time, i.e. changes the selected filter phase number, when the cumulative adjustment is large, it may cross the N sampling point index boundaries, causing changes in the subsequent data output clock. Therefore, when the sampling point index is 0 or N, the change in the data output clock needs to be considered when adjusting the sampling point forward or backward.

[0083] To illustrate the tracking adjustment process, the sampling rate is 2fc, which is twice the chip rate, and the number of signal paths selected by the filter is N=8. Therefore, at each rising edge of the sampling clock, the filter outputs one set of data, either the intermediate sampling point or the lagging sampling point. In the initial state, the index of the synchronous sampling point is 7, and the index of the sampling point remains unchanged at 7 until the tracking adjustment signal arrives.

[0084] As shown in Table 1 (Table 1 is a data sampling and clock diagram), each column of the table represents the data obtained by sampling and filtering in one clock cycle. Since the number of signal paths selected by the filter is N=8, the total number of data indices in each cycle is 8. And because the sampling rate is 2fc, that is, twice the chip rate, it takes two clock cycles to completely output the signal of one chip. The next stage performs data sampling on the rising edge of the high clock, and the sampling result is the sampling point number corresponding to the data index, which can ensure the accuracy of data and data clock. At the same time, when the sampling index moves across 0 and 7 (data needs to be output earlier or later during the tracking process), some additional judgments are required. As shown in the position marked in Table 1 (that is, the position of the last row of the seventh column from the left in Table 1, indicated by *), the sampling point moves one position to the right from 7 to 8.

[0085]

[0086] Table 1

[0087] Therefore, every two rising edges of the clock will output filtered data with index 7; the position is marked in Table 1 (i.e., the position of the last row of the seventh column from the left in Table 1, indicated by *), and the subsequent tracking adjustment signal gives the operation of moving the sampling point backward by 1 sampling point; subsequently, the sampling point index number changes to 8; in this case, an extra clock cycle needs to be waited before the data clock can be output and the sampling point adjusted, otherwise it will result in two points being sampled consecutively within one symbol (sampling indices 7 and 8); while when moving forward (e.g. from 0 to 15), no additional judgment is required; at the same time, it is necessary to ensure that the adjustment timing must arrive when the output data clock is 1, that is, the subsequent tracking feedback index adjustment operation needs to be buffered first, and the adjustment is performed when the data clock is 1.

[0088] This scheme designs an acquisition and tracking method suitable for high-speed spread spectrum communication systems. The received baseband signal is first sampled at a low sampling rate (e.g., 2 to 4 times the signal bandwidth). Then, a set of filter coefficients is selected according to the given phase index to filter the sampled signal, i.e., the sampled signal is reconstructed. The signal reconstruction filter is generally an FIR filter (low-pass filter or multiphase component of raised cosine filter). In this way, the reconstructed signal is equivalent to increasing the sampling rate to N times the original, which increases the accuracy of subsequent acquisition and tracking algorithms. At the same time, since there is no rate change in the processing, the data processing does not require increasing the processing clock rate or performing parallel filtering, thus having low implementation difficulty. After multiphase filtering, the signal filtered by different multiphase components actually represents a signal with a phase difference of π (where π is the chip width), and the signal is then input to the acquisition and tracking module for processing.

[0089] In summary, the acquisition and tracking method provided by this invention for high-speed spread spectrum communication systems involves receiving baseband signals, sampling the received baseband signals to obtain sampling points, performing polyphase filtering on the sampling points, performing code acquisition on the filtered sampling points, and determining whether the filtered sampling points have reached the acquisition state. If so, code tracking is performed on the filtered sampling points. The selected filter phase number is adjusted according to the code tracking result. Using polyphase filtering technology, one filter coefficient of a given phase is selected to filter the sampling points to recover the high sampling rate waveform. Subsequently, the recovered waveform is subjected to subsequent code acquisition and code tracking operations. By performing polyphase filtering on the sampling points, the sampling rate is increased to N times the original, thus increasing the accuracy of the subsequent acquisition and tracking algorithms. Since only one phase data needs to be processed, although the acquisition and tracking algorithm delay is slightly increased, compared with traditional acquisition and tracking algorithms, it does not require increasing the processing clock speed or performing parallel filtering processing, and has the characteristics of low complexity.

[0090] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent modifications made based on the content of the present invention specification and drawings, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for acquisition and tracking suitable for high-speed spread spectrum communication systems, characterized in that, Includes the following steps: S1. Receive the baseband signal and perform a sampling operation on the received baseband signal to obtain sampling points; S2. Perform multiphase filtering operation on the sampling points; S3. Perform code capture operation on the filtered sampling points and determine whether the filtered sampling points have reached the capture state. S4. If so, then perform code tracking operation on the filtered sampling points; step S4 is as follows: S41. If the filtered sampling points reach the capture state, then the lead sampling sequence and the lag sampling sequence are obtained based on the filtered sampling points. S42. Perform correlation operations on the ahead sampling sequence and the lag sampling sequence with the local spreading code sequence, and calculate the squared difference of the correlation values; S5. Adjust the selected filter phase number according to the code tracking operation result; The following steps are also included between step S5 and step S42: Filter the squared difference of the calculated correlation values; After filtering the squared differences of the calculated correlation values, the following steps are also included: Based on the filtered squared difference, determine whether to perform sampling point index adjustment. The specific steps are as follows: If a sampling point index adjustment operation is required, then determine whether there is data output at the current clock. If the current clock has data output, determine whether to adjust the sampling point index backward and cross the boundary of N sampling point indices; where N is the maximum phase number of the selected filter; If yes, the adjustment amount will be stored and the sampling point index will be adjusted in the next clock cycle; otherwise, the sampling point index will be adjusted directly.

2. The acquisition and tracking method for high-speed spread spectrum communication systems according to claim 1, characterized in that, Step S3 is as follows: S31. Based on the filtered sampling points, obtain the synchronous sampling sequence; S32. Perform the operation of calculating the correlation peak on the synchronous sampling sequence, and determine whether the calculated correlation peak has reached the maximum value and whether the maximum value exceeds the preset capture threshold; S33. If so, then determine that the filtered sampling points have reached the capture state.

3. The acquisition and tracking method for high-speed spread spectrum communication systems according to claim 1, characterized in that, Step S5 is as follows: S51. Adjust the selected filter phase number based on the squared difference of the calculated correlation values.

4. The acquisition and tracking method for high-speed spread spectrum communication systems according to claim 3, characterized in that, Step S51 also includes the following steps: If the squared difference of the calculated correlation values ​​is positive, then the selected filter phase number should be reduced. If the squared difference of the calculated correlation values ​​is negative, then the selected filter phase number should be increased.

5. The acquisition and tracking method for high-speed spread spectrum communication systems according to claim 1, characterized in that, After filtering the squared differences of the calculated correlation values, the following steps are also included: Take the absolute value of the squared difference of the calculated correlation values ​​and compare the absolute value of the squared difference with a preset threshold. If the absolute value of the squared difference is greater than the preset threshold, then proceed to step S5.

6. The acquisition and tracking method for high-speed spread spectrum communication systems according to claim 1, characterized in that, After filtering the squared differences of the calculated correlation values, the following steps are also included: If there is no data output at the current clock, the adjustment amount will be stored and the sampling point index will be adjusted in the next clock cycle.

7. The acquisition and tracking method for high-speed spread spectrum communication systems according to claim 1, characterized in that, In step S2, an FIR filter is used to perform polyphase filtering on the sampling points.

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