A satellite signal rapid acquisition system and method based on ZYNQ

Abstract

The present invention relates to a satellite signal rapid capture system and method based on ZYNQ, including a clock control module, a first carrier generation module, a second carrier generation module, a pseudo code generation module, a down-conversion module, a matched filter module, an FFT module, a data storage module, and a threshold detection module; the present invention can process the digital signal after down-conversion processing, and the algorithm is a PMF-FFT algorithm combining matched filtering and FFT operations, which searches for the code phase while searching for the Doppler frequency, effectively improving the capture probability and the estimation accuracy of the Doppler frequency. The core content is to divide the pre-processed signal into segments and enter the matched filter for correlation matching, then perform FFT operation on the correlation integral of each segment, select the largest result peak for threshold detection, and judge whether the signal is captured successfully.

Description

Technical Field

[0001] The present invention belongs to the field of satellite navigation and positioning technology, and in particular relates to a signal rapid capture system and method implemented using a ZYNQ hardware platform. Background Art

[0002] The satellite signal capture process is the first step in the signal processing of the navigation receiver. This process obtains the rough estimate of the carrier Doppler frequency and code phase of the visible satellite signal. The satellite navigation receiver initializes the tracking loop according to these key parameters and enters the tracking process. The capture speed and the estimation accuracy of the Doppler frequency directly affect the performance indicators of the satellite navigation receiver. The receiver based on the ZYNQ platform proposed in this invention can fully meet the performance requirements and has more and more application scenarios.

[0003] The ZYNQ hardware platform launched by Xilinx has the advantages of flexibility and fast processing. It consists of two parts: a processing system (PS) composed of dual-core ARM Cortex-A9 as the core, and a programmable logic array (PL). It has rich logic resources and flexible configuration. It can process multi-channel data in parallel with high efficiency. Due to the limited resources and poor portability of PC platform and DSP processor system, the new receiver of ZYNQ platform has obvious advantages over the traditional PC+DPS platform.

[0004] Chinese patent document CN 105866803 A discloses "Baseband signal fast capture algorithm for Beidou-2 satellite navigation receiver based on FPGA". The invention proposes a fast capture algorithm using C / A code multiplication and discrete Fourier transform, and a capture solution using FPGA for parallel processing. The patent solves the problem of long operation time of traditional capture algorithms. However, the discrete Fourier operation of the patent occupies a lot of resources, and there is a large delay and error in signal transmission between multiple RAM storages. There is an error in the peak value of the capture result, and the accuracy cannot be guaranteed.

[0005] Chinese patent document CN 102540217 A discloses "a system for rapidly capturing GLONASS satellite signals in a system", which uses FPGA to realize a system for rapidly capturing GLONASS satellite signals, and realizes receiver units such as a down-conversion module, a local filtering module, and an FFT operation module in the FPGA. However, the data sliding comparison mode of the sampling storage unit and the partial matching filter module of the patent is backward, and it is impossible to realize the segmented correlation operation of the pre-processed I / Q two-way data in multiple filters, the signal code phase is incomplete, and the FFT operation peak has an error and cannot participate in the threshold determination. Summary of the invention

[0006] In view of the shortcomings of the prior art, the present invention provides a satellite signal acquisition system based on the ZYNQ hardware platform, which can not only improve the acquisition probability, but also improve the estimation accuracy of the Doppler frequency, and meet the requirements for capturing satellite signals in a high-dynamic environment. The present invention also provides a satellite signal rapid acquisition method based on ZYNQ.

[0007] The present invention realizes the satellite signal capture process in ZYNQ, and can process the digital signal after down-conversion. The algorithm is a PMF-FFT algorithm that combines matched filtering and FFT operations. It searches for the code phase while searching for the Doppler frequency, effectively improving the capture probability and the estimation accuracy of the Doppler frequency. The core content is to segment the pre-processed signal into a matched filter for correlation matching, then perform FFT operations on the correlation integral of each segment, select the largest result peak for threshold detection, and determine whether the signal is captured successfully.

[0008] Terminology explanation:

[0009] 1. ZYNQ is a new hardware platform launched by Xilinx. Different from traditional FPGA devices, ZYNQ realizes the integration of software programming and hardware programmable resources. ZYNQ mainly consists of two parts: a processing system (PS) composed of dual-core ARM A9 as the core, and a programmable logic array (PL). The ZYNQ device of the present invention makes full use of the advantages of PS and PL, and proposes a fast capture solution for software and hardware collaborative applications based on ZYNQ.

[0010] 2. DSP processor, digital signal processor, is a unique microprocessor that processes large amounts of information using digital signals. Traditional navigation receiver platforms use a combination of DSP+FPGA, which has a complex hardware design, high cost, and processing capabilities limited by bus bandwidth. The Zynq platform used in the present invention replaces the combination structure, simplifies the hardware design of the receiver, and reduces resource costs.

[0011] 3. PMF filter, partial matching filter. The present invention uses M partial matching filters, each with a length of N, and a pseudo code cycle length of L = MN. During the entire capture process, the local pseudo code generated by the receiver is stored in the matching filter, and the pseudo code fragment remains unchanged. The demodulated capture signal will continuously enter the matching filter and perform correlation operations with the local pseudo code. Finally, the output of these M filters is subjected to S-point FFT transformation.

[0012] 4. Incoherent accumulation and incoherent integration. In the accumulation and summation process, the I-channel and Q-channel data are separated instead of mixing the two.

[0013] The technical solution of the present invention is:

[0014] A satellite signal acquisition system based on the ZYNQ hardware platform, including a clock control module, a carrier generation module, a pseudo code generation module, a down-conversion module, a matched filter module, an FFT module, a data storage module, and a threshold detection module;

[0015] The down-conversion module, the matched filter module, the FFT module, the data storage module, and the threshold detection module are connected in sequence; the carrier generation module and the pseudo code generation module are both connected to the down-conversion module;

[0016] The clock control module is used to generate clocks of different frequencies in the capture system to ensure the synchronization of the entire capture system; the carrier generation module is used to generate sine and cosine signals locally through digitally controlled oscillator technology; the pseudo code generation module is used to generate the corresponding code phase of the collected signal and complete the stripping of the ranging code of the signal; the down-conversion module is used to move the frequency of the digital intermediate frequency signal to zero frequency; the matched filter module is used to perform matched filtering on the signal obtained after processing by the down-conversion module, and transfer the operation result to RAM for temporary storage; the FFT module is used to retrieve the operation result from RAM, perform non-coherent operation, and store the obtained result in the data storage module; the threshold detection module is used to search the maximum value of the data storage module for threshold detection and judge the capture state.

[0017] Preferably, according to the present invention, the ZYNQ hardware platform includes a processing system PS part and a programmable logic array PL part;

[0018] The functions of the carrier generation module, pseudo code generation module, down-conversion module, matched filter module, FFT module and data storage module are implemented in the programmable logic array PL part; the function of the threshold detection module is implemented in the processing system PS part.

[0019] Further preferably, the processing system PS part includes a dual-core ARM Cortex-A9;

[0020] Preferably according to the present invention, the FFT module uses the IP core of Xilinx for logic control.

[0021] A satellite signal acquisition method based on the ZYNQ hardware platform includes the following steps:

[0022] Step 1: Down-sampling the digital intermediate frequency signal collected by the receiver;

[0023] Step 2: Mix the signal with the locally generated carrier to obtain a signal close to zero frequency;

[0024] Step 3: Divide the signal into segments and enter the matched filter for sliding comparison, and perform matched filtering with the locally generated code segments;

[0025] Step 4: Fill the correlation value with zeros to perform FFT operation and select the maximum value from the incoherent integral value;

[0026] Step 5: Compare the maximum value with the threshold value to determine the capture status.

[0027] Preferably, according to the present invention, in step 2, a signal close to zero frequency is obtained by mixing a locally generated carrier with a signal, including: a digital intermediate frequency signal received by a receiver is subjected to local carrier mixing processing, demodulated to obtain I / Q two-way signals, and after downsampling and anti-interference and aliasing processing, a digital intermediate frequency signal with high-frequency components removed is obtained.

[0028] Preferably, according to the present invention, in step 3, the signal is segmented and enters the matched filter for sliding comparison, and matched filtering is performed with the local generated code segment, including: the signal close to zero frequency obtained in step 2 is sent to the PMF filter, and correlation operation is performed with the corresponding local pseudo-code phase segment; there are M PMF filters, each segment is N in length, and the data length of each signal code period is L=MN.

[0029] Preferably, according to the present invention, in step 4, the correlation value is padded with zeros for FFT operation, and the maximum value is selected from the incoherent integral value; including: the correlation results output by M filters are subjected to Fourier FFT transformation and then incoherently accumulated to obtain incoherent integral values, and the maximum value, i.e. the maximum value of the peak value, is selected.

[0030] Preferably, according to the present invention, in step 5, the maximum value of the output peak and the threshold value are detected. If it is greater than the threshold value, the capture is successful. If it is less than the threshold value, the local pseudo code is moved by a code phase and returns to step 1 until the satellite signal is successfully captured.

[0031] Preferably, according to the present invention, during the satellite signal capture process, the signal status includes IDLE state, WAIT state, DATA state, FFT state, and OUT state;

[0032] The IDLE state is the initial state of the receiver, the WAIT state is the state of waiting to enter the matched filter sliding comparison, the DATA state is the state before the FFT operation of the matched filter data, the FFT state is the state of waiting for the FFT operation, and the OUT state is the state of obtaining the maximum value by FFT incoherent accumulation.

[0033] The beneficial effects of the present invention are:

[0034] 1. The present invention is based on ZYNQ hardware equipment, and each module of the signal capture process is independent of each other, with high operating efficiency and short capture time.

[0035] 2. The PMF-FFT acquisition algorithm provided by the present invention can improve the estimation accuracy of the detection probability and Doppler frequency shift, and is suitable for high-speed signal acquisition in a high dynamic environment.

[0036] 3. The capture solution provided by the present invention can be directly embedded in the design of Beidou receiver and has strong practical application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a structural schematic diagram of a satellite signal acquisition system based on the ZYNQ hardware platform of the present invention;

[0038] Figure 2 The schematic diagram is a schematic diagram of the principle of generating sine and cosine signals by numerically controlled oscillator technology (NCO);

[0039] Figure 3 A schematic diagram of the principle of generating the corresponding code phase of the collected signal;

[0040] Figure 4 This is a schematic diagram of IQ demodulation;

[0041] Figure 5 It is a schematic diagram of the state transition of the signal;

[0042] Figure 6 It is a schematic diagram of the PMF-FFT algorithm in the satellite signal acquisition method based on the ZYNQ hardware platform;

[0043] Figure 7 It is a schematic diagram of the structure of the ZYNQ hardware platform of the present invention. DETAILED DESCRIPTION

[0044] The present invention is further defined below in conjunction with the accompanying drawings and embodiments of the specification, but the protection scope of the present invention is not limited to the following.

[0045] Example 1

[0046] A satellite signal acquisition system based on the ZYNQ hardware platform, such as Figure 1 As shown, it includes a clock control module, a carrier generation module, a pseudo code generation module, a down-conversion module, a matched filter module, an FFT module, a data storage module, and a threshold detection module;

[0047] The down-conversion module, the matched filter module, the FFT module, the data storage module, and the threshold detection module are connected in sequence; the carrier generation module and the pseudo code generation module are both connected to the down-conversion module;

[0048] The clock control module is used to generate clocks of different frequencies in the capture system to ensure the synchronization of the entire capture system; the carrier generation module is used to generate sine and cosine signals locally through numerically controlled oscillator technology (NCO); Figure 2 As shown. The function is to perform complex mixing processing on the local carrier and the intermediate frequency signal for receiving and processing, and to strip the carrier of the signal. The pseudo code generation module is used to: generate the corresponding code phase of the collected signal, and complete the stripping of the ranging code of the signal; the analysis of the Weil code generation principle shows that the Legendre sequence used is the same, and different pseudo codes are obtained by different interception points p and phase differences w. The present invention first generates the Legendre sequence through MATLAB software, stores the generated Legendre sequence in ROM, and then reads different values ​​through the table lookup method, such as Figure 3 As shown. The down-conversion module is used to: move the frequency of the digital intermediate frequency signal to zero frequency; it is suitable for subsequent signal processing and is the preliminary processing of the entire algorithm. The matched filter module is used to: perform matched filtering on the signal obtained after processing by the down-conversion module, and transfer the operation result to RAM for temporary storage; the FFT module is used to: retrieve the operation result from RAM, perform incoherent operation, and store the result in the data storage module; the threshold detection module is used to: search for the maximum value of the data storage module for threshold detection, and determine the capture status.

[0049] The satellite signal acquisition system based on the ZYNQ hardware platform makes full use of the structural characteristics and operation mode of the ZYNQ device in its acquisition process, such as Figure 7 As shown, the ZYNQ hardware platform includes the processing system PS (Processing System) part and the programmable logic array PL (Programmable Logic) part; the functions of the carrier generation module, pseudo code generation module, down-conversion module, matched filter module, FFT module, and data storage module are implemented in the programmable logic array PL part; the function of the threshold detection module is implemented in the processing system PS part. There is a high-bandwidth, low-latency AXI interface in the processing system PS part and the programmable logic array PL part, which perfectly meets the signal transmission requirements. The ZYNQ hardware platform matches the feasibility and performance requirements of the algorithm, while adapting to factors such as data transmission, computing resource occupancy, rate matching and control, and can perfectly provide the implementation framework of the capture system.

[0050] In the ZYNQ hardware platform, the functions of the carrier generation module, pseudo code generation module, down conversion module, matched filter module, FFT module, and data storage module of the capture process are implemented in the programmable logic array PL part, and a reasonable operation framework is planned. Local oscillators are provided for the carrier and pseudo code generation modules, and clocks are provided to provide a unified source clock for each module; a PMF-FFT capture algorithm is provided, which can search the code phase while searching the carrier frequency, thereby improving the detection probability and reducing the capture time.

[0051] The PS part of the processing system includes a dual-core ARM Cortex-A9; the FFT module uses the Xilinx IP core for logic control. It addresses and fetches data from the storage RAM for FFT operations, and transmits the incoherent integration results to the data storage module.

[0052] Example 2

[0053] A satellite signal acquisition method based on ZYNQ hardware platform, such as Figure 6 As shown, the steps include:

[0054] Step 1: Down-sampling the digital intermediate frequency signal collected by the receiver;

[0055] Step 2: Mix the signal with the locally generated carrier to obtain a signal close to zero frequency;

[0056] Step 3: Divide the signal into segments and enter the matched filter for sliding comparison, and perform matched filtering with the locally generated code segments;

[0057] Step 4: Fill the correlation value with zeros to perform FFT operation and select the maximum value from the incoherent integral value;

[0058] Step 5: Compare the maximum value with the threshold value to determine the capture status.

[0059] In step 2, a signal close to zero frequency is obtained by mixing a locally generated carrier with a signal, including: a digital intermediate frequency signal received by a receiver is mixed with a local carrier, demodulated to obtain an I / Q two-way signal, and then processed by downsampling and anti-interference aliasing to obtain a digital intermediate frequency signal with high-frequency components removed. Figure 4 shown.

[0060] In step 3, the signal is segmented and sent into the matched filter for sliding comparison, and matched filtering is performed with the local generated code segment, including: the signal close to zero frequency obtained in step 2 is sent to the PMF filter, and correlation operation (multiplication and accumulation) is performed with the corresponding local pseudo code phase segment; there are M PMF filters in total, each segment is N in length, and the data length of each signal code period is L=MN.

[0061] In step 4, the correlation value is padded with zeros for FFT operation, and the maximum value is selected from the incoherent integral value; including: the correlation results output by M filters are subjected to Fourier FFT transformation and then incoherently accumulated to obtain incoherent integral values, and the maximum value, i.e. the maximum value of the peak value, is selected.

[0062] In step 5, the maximum value of the output peak and the threshold are detected. If it is greater than the threshold, the capture is successful. If it is less than the threshold, the local pseudo code is moved by a code phase and returns to step 1 until the satellite signal is successfully captured. The threshold is a variable set by oneself and can be modified locally according to different systems and satellites. The algorithm of the present invention can effectively resist the characteristics of the correlation peak attenuation caused by the Doppler frequency shift, and improve the estimation accuracy of the Doppler frequency shift. The above capture algorithm uses the Verilog language in ZYNQ.

[0063] During the satellite signal acquisition process, Figure 5 As shown, the signal states include IDLE state, WAIT state, DATA state, FFT state, and OUT state; the IDLE state is the initial state of the receiver, the WAIT state is the state of waiting to enter the matched filter sliding comparison, the DATA state is the state before the FFT operation of the matched filter data, the FFT state is the state of waiting for the FFT operation, and the OUT is the state of obtaining the maximum value by FFT incoherent accumulation.

[0064] In this embodiment, the pseudo code period of the simulated Beidou B1C signal is 10ms, so the capture system correlation integration time is at least 10ms, and the baseband signal sampling rate f s =4MHz, main clock frequency f clk =100MHz, the number of matched filters is 256, and the capture is successful in 8 out of 10 captures on average, and the single code phase cycle is 320 clocks. The built-in integrated logic analyzer (ILA) of VIVADO software is used to observe the signs of capture success and capture failure, and the total duration of a complete signal capture is counted by a calculator.

[0065] The average capture time is calculated as:

[0066]

[0067] The calculation results show that the average capture time of the satellite is 138ms. The standard capture time for the B1C signal in the market is 300ms. By comparison, the capture speed of the capture algorithm of the present invention is faster in a high dynamic environment, and the rapid capture of high-speed objects such as aircraft and missiles can be achieved.

[0068] Table 1 shows the resource occupancy of the ZYNQ hardware platform:

[0069] Table 1

[0070]

[0071] From Table 1, we can see that the resource occupancy of the configurable logic parts Slice Registers and Slice LUTs of the ZYNQ device is reasonable, and the device has a lot of resource margin during the capture process.

Claims

1. A satellite signal acquisition system based on the ZYNQ hardware platform, characterized in that: It includes a clock control module, a carrier generation module, a pseudo code generation module, a down-conversion module, a matched filter module, an FFT module, a data storage module, and a threshold detection module; The down-conversion module, the matched filter module, the FFT module, the data storage module, and the threshold detection module are connected in sequence; the carrier generation module and the pseudo code generation module are both connected to the down-conversion module; The clock control module is used to generate clocks of different frequencies in the capture system to ensure the synchronization of the entire capture system; the carrier generation module is used to generate sine and cosine signals locally through digitally controlled oscillator technology; the pseudo code generation module is used to generate the corresponding code phase of the collected signal and complete the stripping of the ranging code of the signal; the down-conversion module is used to move the frequency of the digital intermediate frequency signal to zero frequency; the matched filter module is used to perform matched filtering on the signal obtained after processing by the down-conversion module, and transfer the operation result to RAM for temporary storage; the FFT module is used to retrieve the operation result from RAM, perform non-coherent operation, and store the obtained result in the data storage module; the threshold detection module is used to search the maximum value of the data storage module for threshold detection and judge the capture state.

2. According to claim 1, a satellite signal acquisition system based on the ZYNQ hardware platform is characterized in that: The ZYNQ hardware platform includes the processing system PS part and the programmable logic array PL part; The functions of the carrier generation module, pseudo code generation module, down-conversion module, matched filter module, FFT module and data storage module are implemented in the programmable logic array PL part; the function of the threshold detection module is implemented in the processing system PS part.

3. According to claim 2, a satellite signal acquisition system based on the ZYNQ hardware platform is characterized in that: The PS part of the processing system includes a dual-core ARM Cortex-A9.

4. According to claim 1, a satellite signal acquisition system based on the ZYNQ hardware platform is characterized in that: The FFT module uses the IP core of Xilinx for logic control.

5. A satellite signal acquisition method based on the ZYNQ hardware platform, characterized in that: The steps include: Step 1: Down-sampling the digital intermediate frequency signal collected by the receiver; Step 2: Mix the signal with the locally generated carrier to obtain a signal close to zero frequency; Step 3: Divide the signal into segments and enter the matched filter for sliding comparison, and perform matched filtering with the locally generated code segments; Step 4: Fill the correlation value with zeros to perform FFT operation and select the maximum value from the incoherent integral value; Step 5: Compare the maximum value with the threshold value to determine the capture status.

6. The satellite signal acquisition method based on the ZYNQ hardware platform according to claim 5, characterized in that: In step 2, a signal close to zero frequency is obtained by mixing a locally generated carrier with a signal, including: a digital intermediate frequency signal received by a receiver is subjected to local carrier mixing processing, demodulated to obtain an I / Q two-way signal, and after downsampling and anti-interference and aliasing processing, a digital intermediate frequency signal with high-frequency components removed is obtained.

7. The satellite signal acquisition method based on the ZYNQ hardware platform according to claim 5, characterized in that: In step 3, the signal is segmented and sent into the matched filter for sliding comparison, and matched filtering is performed with the local generated code segment, including: the signal close to zero frequency obtained in step 2 is sent to the PMF filter, and correlation operation is performed with the corresponding local pseudo code phase segment; there are M PMF filters, each segment is N in length, and the data length of each signal code period is L=MN.

8. The satellite signal acquisition method based on the ZYNQ hardware platform according to claim 5, characterized in that: In step 4, the correlation value is padded with zeros for FFT operation, and the maximum value is selected from the incoherent integral value; including: the correlation results output by M filters are subjected to Fourier FFT transformation and then incoherently accumulated to obtain incoherent integral values, and the maximum value, i.e. the maximum value of the peak value, is selected.

9. The satellite signal acquisition method based on the ZYNQ hardware platform according to claim 5, characterized in that: In step 5, the maximum value of the output peak and the threshold are detected. If it is greater than the threshold, the capture is successful. If it is less than the threshold, the local pseudo code is moved by a code phase and returns to step 1 until the satellite signal is successfully captured.

10. A satellite signal acquisition method based on the ZYNQ hardware platform according to any one of claims 5 to 9, characterized in that: During the satellite signal acquisition process, the signal status includes IDLE status, WAIT status, DATA status, FFT status, and OUT status; The IDLE state is the initial state of the receiver, the WAIT state is the state of waiting to enter the matched filter sliding comparison, the DATA state is the state before the FFT operation of the matched filter data, the FFT state is the state of waiting for the FFT operation, and the OUT state is the state of obtaining the maximum value by FFT incoherent accumulation.

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