High-sensitivity GPS signal rapid capturing method and system

Abstract

The invention discloses a high-sensitivity GPS signal rapid capturing method and system, and the method comprises the steps: S1, carrying out the down-conversion and sampling of a satellite analog signal transmitted by a navigation satellite, and obtaining a digital baseband signal of residual carrier frequency offset; s2, carrying out time delay processing on the data, putting the data into buffer queues, and capturing the data at the back stage of each buffer queue at the same time to form multi-path parallel capturing; s3, segment interception is carried out, and first data with the starting point being cache output is intercepted; s4, by utilizing the linear property of FFT, integral data is shortened through an integral-clearing process, so that the calculation complexity and the calculation time related to subsequent circulation are reduced; s5, performing FFT (Fast Fourier Transform) operation on the data output in the step S4; s6, performing cyclic shift on an output result of the FFT operation in the step S5 by using the frequency domain cyclic shift property of the FFT so as to search and compensate Doppler frequency offset; s7, carrying out zero padding on locally stored pseudo codes, and carrying out correlation operation on the pseudo codes and the data output in the step S6 by utilizing FFT / IFFT cyclic convolution to complete coherent integral operation of a single-path signal; and S8, arranging and combining the integral results, sending the integral results to a peak detector, and outputting the results according to a threshold. According to the method, weak GPS signal capturing can be efficiently and rapidly carried out, and the calculated amount can be greatly reduced on the premise that the capturing precision is guaranteed.

Description

Technical Field

[0001] The invention belongs to the field of weak navigation satellite signal capture, and in particular relates to a high-sensitivity GPS signal rapid capture method and system. Background Art

[0002] GPS receiver baseband signal processing mainly includes capture, tracking, navigation message extraction, and solution. Signal capture is the first and most critical step, and its performance directly affects the overall performance of the receiver. At present, with the development of satellite navigation systems, users have higher and higher requirements for their use. Tunnels, forests, subways, and indoor places such as large buildings or underground garages have gradually become important places for the application of navigation technology. With the complexity of the application environment of navigation systems, the demand for high-dynamic and high-sensitivity GPS signal capture technology is also increasing.

[0003] In order to capture weak GPS signals, it is necessary to integrate the signals of multiple code periods. As the integration time becomes longer, the Doppler frequency points that need to be searched also increase accordingly, both of which will cause a sharp increase in capture time and calculation amount. Therefore, how to improve the integration efficiency and reduce the capture time under the constraints of a certain time and calculation amount has become the focus of research.

[0004] Traditional parallel frequency search and parallel code phase search based on Fast Fourier Transform (FFT) have improved the operation efficiency to a certain extent, but when the integration time is long, the parallel frequency search needs to increase the number of FFT points to achieve sufficient accuracy, and still needs to perform long-term serial correlation operations to complete code phase synchronization. The number of FFT / IFFT points of parallel code phase search will also increase as the integration time becomes longer. GJRPovey et al. proposed a partial matching filtering (PMF) algorithm to reduce the number of FFT points during parallel frequency search, but its premise is to complete code phase synchronization; Ziedan NI et al. used the double block zero padding (DBZP) technology to reduce the correlation power loss caused by the change of code rate caused by Doppler frequency shift during FFT calculation, but it requires multiple FFT / IFFT operations; the segmented correlation-video accumulation fast capture algorithm proposed by Zhang Pengcheng et al. is similar to the DBZP algorithm and still requires multiple FFT / IFFT operations; the commonly used differential coherent integration technology can eliminate the integral power loss caused by Doppler frequency shift, but it will bring additional square loss to reduce the signal-to-noise ratio, and the signal-to-noise ratio reduction is more serious when the signal is weak. Summary of the invention

[0005] In view of the above technical problems, the present invention provides a high-sensitivity GPS signal rapid capture method and system, which can effectively solve the problems of long capture time, large calculation amount and low capture accuracy in the prior art when capturing high-dynamic and weak GPS signals.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A high-sensitivity GPS signal rapid acquisition method comprises the following steps:

[0008] S1, down-converting and sampling the satellite analog signal transmitted by the navigation satellite to obtain a digital baseband signal of residual carrier frequency deviation;

[0009] S2, delay processing is performed on the data and the data is placed in a buffer queue. Each buffer queue is captured at the same time to form a multi-channel parallel capture;

[0010] S3, segmented interception, the interception starting point is the first data output from the cache;

[0011] S4, using the linear property of FFT, shortening the integrated data through an integrate-clear process to reduce the computational complexity and computational time associated with subsequent cycles;

[0012] S5, performing FFT operation on the data output in step S4;

[0013] S6, utilizing the frequency domain cyclic shift property of FFT to cyclically shift the output result of the FFT operation in step S5, so as to search for and compensate for the Doppler frequency offset;

[0014] S7, padding the locally stored pseudo code with zeros, and performing correlation operation with the data output in step S6 by using FFT / IFFT circular convolution to complete the coherent integration operation of the single-channel signal;

[0015] S8. Arrange and combine the integration results, send them to the peak detector, and output the results according to the threshold.

[0016] As a preferred embodiment of the above scheme, step S2 is specifically as follows: first, by calculation or simulation, it is estimated that the time required to process a set of data with a required coherent integration length of n milliseconds is m milliseconds, and then, at intervals of 1 millisecond per C / A code period, digital signals with a required integration time of n milliseconds are taken out in turn and placed into at least m cache queues.

[0017] As a preferred embodiment of the above scheme, step S3 is specifically as follows: each group of n milliseconds of data output by each cache queue is intercepted in sequence with the C / A code period as the interval, each interception length is 2 milliseconds, and there will be overlapping parts between two adjacent interceptions. The total interception length is the required coherent integration length of n milliseconds, thereby obtaining n groups of 2 milliseconds of data slices.

[0018] As a preferred embodiment of the above scheme, step S4 is specifically as follows: the n groups of 2 millisecond data slices obtained in step S3 are accumulated to obtain one group of 2 millisecond data, which is sent to the FFT module, and then the accumulated result is cleared to zero, waiting for the next n groups of 2 millisecond data to arrive.

[0019] As a preferred embodiment of the above solution, step S5 specifically includes: performing FFT operation on the 2 milliseconds data outputted from step S4.

[0020] As a preferred embodiment of the above scheme, in step S6: when the FFT correlation time is 2 milliseconds, the frequency search resolution is 500 Hz, that is, a cyclic shift of one code bit is performed, and the frequency deviation compensation value is 500 Hz. A reasonable cyclic shift range and shift step can be set according to the frequency deviation variation range and integration time.

[0021] As a preferred embodiment of the above scheme, step S7 is specifically as follows: pad the locally stored 1 millisecond pseudo code with zeros to obtain 2 milliseconds of data, and perform correlation operation on it and the 2 milliseconds of data output by step S6 using FFT / IFFT circular convolution to complete the coherent integration operation of a single-channel n millisecond signal.

[0022] As a preferred embodiment of the above solution, step S8 specifically comprises: arranging and combining the integration results of m channels for n milliseconds in time sequence and sending them to a peak detector. When a peak value exceeding a threshold is detected, it is considered that the GPS signal is captured.

[0023] A high-sensitivity GPS signal rapid acquisition system, comprising:

[0024] Frequency conversion sampling module: down-convert and sample the satellite analog signal transmitted by the navigation satellite;

[0025] Delay processing module: performs delay processing on data and puts it into the buffer queue;

[0026] Segment interceptor module: segment interception, the interception starting point is the first data output by the cache;

[0027] Integrate-Clear module: Utilizes the linear nature of FFT to shorten the integrated data through the integrate-clear process to reduce the computational complexity and computational time associated with subsequent loops;

[0028] FFT calculation module: FFT operation of the signal output by the integrator-cleaner module;

[0029] Frequency domain cyclic shift frequency offset compensator module: Utilizes the frequency domain cyclic shift property of FFT to cyclically shift the output result of FFT operation to search and compensate for Doppler frequency offset;

[0030] Local memory module: fills the locally stored pseudo code with zeros, and performs correlation operation with the data output by the frequency domain cyclic shift frequency offset compensator module using FFT / IFFT circular convolution to complete the coherent integration operation of the single-channel signal;

[0031] Result output module: Arrange and combine the integration results, send them to the peak detector, and output the results according to the threshold.

[0032] Due to the above structure, the beneficial effects of the present invention are:

[0033] 1. Use the cyclic correlation property of FFT / IFFT to replace the coherent integration in the time domain, convert multiple parallel complex multipliers into one complex multiplication, reduce the computational complexity and improve the computational speed;

[0034] 2. Utilize the linear property of FFT to intercept different time slices with the same code sequence and accumulate them, which greatly shortens the number of FFT points, thereby increasing the coherent integration time to capture weak GPS signals;

[0035] 3. The frequency domain cyclic shift property of FFT is used to complete the search and compensation of Doppler frequency deviation, replacing the complex time domain search process, thereby reducing the amount of calculation and the capture time, while avoiding the square loss caused by the use of differential coherent integration technology;

[0036] 4. Considering the processing delay of the cyclic correlation calculation, set the cache queue related to the processing delay for parallel capture, so that the capture accuracy is maintained at one chip time;

[0037] 5. Considering the uncertainty of the starting point of segment cutting, segments of twice the C / A cycle time are cut in sequence to ensure that each segment contains a complete C / A code sequence, ensuring that the circular convolution property of FFT can be implemented;

[0038] 6. The present invention can not only efficiently and quickly capture weak GPS signals, but also significantly reduce the amount of calculation while ensuring capture accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for describing the embodiments are briefly introduced below.

[0040] Figure 1 It is a diagram of the method steps of the present invention;

[0041] Figure 2 A schematic diagram of a processing delay buffer queue of the present invention;

[0042] Figure 3 It is a schematic diagram of the segment interceptor of the present invention. DETAILED DESCRIPTION

[0043] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention.

[0044] like Figure 1 As shown, this embodiment provides a high-sensitivity GPS signal fast acquisition method, which specifically includes the following steps:

[0045] S1, down-converting and sampling the satellite analog signal transmitted by the navigation satellite to obtain a digital baseband signal of residual carrier frequency deviation;

[0046] S2. First, through calculation or simulation, it is estimated that the time required to process a set of data with the required coherent integration length (n milliseconds) is m milliseconds, that is, the processing time of a set of n milliseconds of data from step S3 to step S7 is m milliseconds. With a C / A code period of 1 millisecond as an interval, digital signals with the required integration time (n milliseconds) are taken out in sequence and put into at least m cache queues. The number of cache queues must be greater than or equal to m (m milliseconds / 1 millisecond). Each cache queue is captured at the same time to form a multi-channel parallel capture. The purpose of this step is to improve the capture accuracy. The single-channel capture result will have uncertainty in the length of the capture processing.

[0047] Assuming that the coherent integration time required for the capture process of the following specific embodiment is n=20ms, and the capture code has a period of 1ms, the length of a single FFT / IFFT data after processing by the segment interceptor and the integral cleaner is m=2ms. Assuming that the processing delay from the output of the buffer queue data to the output of the complete correlation result by IFFT is 3ms, at least 3 ping-pong buffers are required for parallel processing to ensure the capture accuracy.

[0048] The received data stream is continuously intercepted based on the time axis. The interception length each time is the required coherent integration time of 20ms, and the interception interval is the capture code period of 1ms. The simulation results show that the time required to process 20ms of data is about 3ms. At this time, at least 3 cache queues should be prepared for 3-way parallel capture, such as Figure 2 As shown, this limits the capture accuracy to within one capture code period;

[0049] S3. Each group of 20ms data output by each cache queue is intercepted in sequence at intervals of 1ms. The interception starting point is the first data output by the cache. The length of each interception is 2ms. There will be overlapping parts between two adjacent interceptions. The total interception length is 20ms. At this time, 20 groups of 2 millisecond data slices are obtained, such as Figure 3As shown. Combined with the cache queue of step S2, such interception can obtain a complete cyclic correlation result corresponding to the input data stream in time in step S8. Each interception of 2 milliseconds of data ensures that there is a complete C / A code cycle, and the C / A code phase in each 2 millisecond data slice is exactly the same, ensuring that the cyclic convolution property is implemented;

[0050] S4, accumulate the corresponding points of the 20 groups of 2ms data slices obtained in step S3 to obtain a group of 2ms data, send it to the FFT module, then clear the accumulated result, and wait for the next 20 groups of 2ms data to arrive. This step uses the linear property of FFT to shorten the 20 milliseconds of integrated data to 2 milliseconds, greatly reducing the computational complexity and computational time associated with subsequent cycles;

[0051] S5, performing FFT operation on the 2ms data outputted in step S4;

[0052] S6. Utilize the frequency domain cyclic shift property of FFT to cyclically shift the output result of the FFT operation in step S5 to search and compensate for the Doppler frequency offset. When the correlation time of FFT is 2 milliseconds, the frequency search resolution obtained by the frequency shift property of FFT is 500 Hz, that is, a cyclic shift of one chip is performed, and the frequency offset compensation value is 500 Hz. A reasonable cyclic shift range and shift step can be set according to the frequency offset variation range and integration time. Assume that the baseband signal has a carrier frequency deviation of ±50KHz, the signal code rate is 1.023Mcps, the code period is 1ms, and the signal-to-noise ratio after despreading is 0dB. When the coherent integration gain makes the signal-to-noise ratio reach 16dB, the capture accuracy can be guaranteed to be 100%. Considering the power loss of the frequency deviation to the coherent integration, the tolerable residual frequency deviation range is about ±825Hz. The output result of the FFT operation in step S5 is cyclically shifted, the shift step is 1 code chip, the shift range is 50 code chips on the left and right, and the frequency search accuracy is 500Hz. The Doppler frequency deviation is searched and compensated in turn.

[0053] S7, pad the locally stored 1 millisecond pseudo code with zeros to obtain 2 milliseconds of data, and use FFT / IFFT circular convolution to perform correlation operation with the 2 milliseconds of data output in step S6 to complete the integration operation of a single 20ms signal. This step is combined with step S4 and utilizes the linear operation property of FFT;

[0054] S8. Arrange and combine the three 20-millisecond integration results in chronological order and send them to a peak detector. When a peak value exceeding a threshold is detected, it is considered that the GPS signal has been captured.

[0055] This embodiment also provides a high-sensitivity GPS signal rapid acquisition system, including:

[0056] Frequency conversion sampling module: down-convert and sample the satellite analog signal transmitted by the navigation satellite;

[0057] Delay processing module: performs delay processing on data and puts it into the buffer queue;

[0058] Segment interceptor module: segment interception, the interception starting point is the first data output by the cache;

[0059] Integrate-Clear module: Utilizes the linear nature of FFT to shorten the integrated data through the integrate-clear process to reduce the computational complexity and computational time associated with subsequent loops;

[0060] FFT calculation module: FFT operation of the signal output by the integrator-cleaner module;

[0061] Frequency domain cyclic shift frequency offset compensator module: Utilizes the frequency domain cyclic shift property of FFT to cyclically shift the output result of FFT operation to search and compensate for Doppler frequency offset;

[0062] Local memory module: fills the locally stored pseudo code with zeros, and performs correlation operation with the data output by the frequency domain cyclic shift frequency offset compensator module using FFT / IFFT circular convolution to complete the coherent integration operation of the single-channel signal;

[0063] Result output module: Arrange and combine the integration results, send them to the peak detector, and output the results according to the threshold.

[0064] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A high-sensitivity GPS signal rapid acquisition method, characterized in that: The following steps are involved: S1, down-converting and sampling the satellite analog signal transmitted by the navigation satellite to obtain a digital baseband signal of residual carrier frequency deviation; S2, delay processing is performed on the data and the data is placed in a buffer queue. Each buffer queue is captured at the same time to form a multi-channel parallel capture; S3, segmented interception, the interception starting point is the first data output from the cache; S4, using the linear property of FFT, shortening the integrated data through an integrate-clear process to reduce the computational complexity and computational time associated with subsequent cycles; S5, performing FFT operation on the data output in step S4; S6, utilizing the frequency domain cyclic shift property of FFT to cyclically shift the output result of the FFT operation in step S5, so as to search for and compensate for the Doppler frequency offset; S7, padding the locally stored pseudo code with zeros, and performing correlation operation with the data output in step S6 by using FFT / IFFT circular convolution to complete the coherent integration operation of the single-channel signal; S8. Arrange and combine the integration results, send them to the peak detector, and output the results according to the threshold.

2. A high-sensitivity GPS signal rapid acquisition method according to claim 1, characterized in that: Step S2 is specifically as follows: first, by calculation or simulation, it is estimated that the time required to process a set of data with a required coherent integration length of n milliseconds is m milliseconds, and then, at intervals of 1 millisecond of the C / A code period, digital signals with the required integration time of n milliseconds are taken out in turn and placed into at least m cache queues.

3. A high-sensitivity GPS signal rapid acquisition method according to claim 1, characterized in that: Step S3 is specifically as follows: each group of n milliseconds of data output by each cache queue is intercepted in sequence at intervals of the C / A code period, each interception length is 2 milliseconds, and there will be overlapping parts between two adjacent interceptions. The total interception length is the required coherent integration length of n milliseconds, thereby obtaining n groups of 2 milliseconds of data slices.

4. A high-sensitivity GPS signal rapid acquisition method according to claim 1, characterized in that: Step S4 is specifically as follows: the n groups of 2 millisecond data slices obtained in step S3 are accumulated to obtain one group of 2 millisecond data, which is sent to the FFT module, and then the accumulated result is cleared to wait for the next n groups of 2 millisecond data to arrive.

5. A high-sensitivity GPS signal rapid acquisition method according to claim 1, characterized in that: Step S5 specifically includes: performing FFT operation on the 2 milliseconds data outputted from step S4.

6. A high-sensitivity GPS signal rapid acquisition method according to claim 1, characterized in that: In step S6: when the FFT correlation time is 2 milliseconds, the frequency search resolution is 500 Hz, that is, a cyclic shift of one chip is performed, and the frequency offset compensation value is 500 Hz. A reasonable cyclic shift range and shift step can be set according to the frequency offset variation range and integration time.

7. A high-sensitivity GPS signal rapid acquisition method according to claim 1, characterized in that: Step S7 specifically includes: padding the locally stored 1 millisecond pseudo code with zeros to obtain 2 milliseconds of data, performing correlation operation on the 2 milliseconds of data output from step S6 using FFT / IFFT circular convolution, and completing the coherent integration operation of a single-channel n millisecond signal.

8. A high-sensitivity GPS signal rapid acquisition method according to claim 1, characterized in that: Step S8 specifically includes: arranging and combining the integration results of m channels for n milliseconds in time sequence, and sending them to a peak detector. When a peak value exceeding a threshold is detected, it is considered that the GPS signal is captured.

9. A high-sensitivity GPS signal rapid acquisition system according to any one of claims 1 to 8, characterized in that: include: Frequency conversion sampling module: down-convert and sample the satellite analog signal transmitted by the navigation satellite; Delay processing module: performs delay processing on data and puts it into the buffer queue; Segment interceptor module: segment interception, the interception starting point is the first data output by the cache; Integrate-Clear module: Utilizes the linear nature of FFT to shorten the integrated data through the integrate-clear process to reduce the computational complexity and computation time associated with subsequent loops; FFT calculation module: FFT operation of the signal output by the integrator-cleaner module; Frequency domain cyclic shift frequency offset compensator module: Utilizes the frequency domain cyclic shift property of FFT to cyclically shift the output result of FFT operation to search and compensate for Doppler frequency offset; Local memory module: fills the locally stored pseudo code with zeros, and performs correlation operation with the data output by the frequency domain cyclic shift frequency offset compensator module using FFT / IFFT circular convolution to complete the coherent integration operation of the single-channel signal; Result output module: Arrange and combine the integration results, send them to the peak detector, and output the results according to the threshold.

Images