An ASM signal delay measurement system based on software radio peripherals

Abstract

The present invention discloses an ASM signal delay measurement system based on a software radio peripheral (SRP). The system includes a transmitter and a receiver. The transmitter includes a signal generator, a first time-frequency synchronization device, and a VHF transmission antenna. The first time-frequency synchronization device externally triggers the signal generator to transmit a pre-generated ASM signal via the VHF transmission antenna. The receiver includes a SRP, a second time-frequency synchronization device, a computing host, and a VHF reception antenna. The second time-frequency synchronization device externally triggers the SRP to receive the ASM signal via the VHF reception antenna. The SRP transmits the processed received signal sequence to the computing host, and an accurate time delay is obtained using a sliding correlation algorithm. The present invention receives ASM signals based on a universal software radio peripheral (USRP) and simultaneously calculates signal delay using the good autocorrelation of the ASM signal, thereby improving the accuracy of signal transmission delay measurement and ensuring ship navigation safety.

Description

Technical Field

[0001] The present invention relates to the field of marine radio navigation technology, and in particular to a system which utilizes a general software radio device and a signal generator as a hardware platform to realize ASM signal transmission and reception and signal delay measurement. Background Art

[0002] The Global Navigation Satellite System (GNSS) is widely used in fields such as transportation, meteorology, mapping, agriculture, and rescue, providing users with round-the-clock positioning, navigation, velocity measurement, and timing services. However, GNSS is inherently vulnerable to unintentional or intentional interference, resulting in the loss or inaccuracy of positioning, navigation, and timing (PNT) information essential for safe navigation. The VHF Data Exchange System (VDES) integrates existing AIS functionality and adds Application Specific Messages (ASM) and wideband VHF Data Exchange (VDE) to alleviate the data communication burden on existing AIS and ensure navigation safety. ASM signals typically use π / 4 QPSK modulation, which offers high bandwidth efficiency and non-coherent detection capabilities. Furthermore, the ASM signal training sequence typically uses a dual Barker13 code, which has ideal autocorrelation characteristics and strong anti-interference capabilities. Furthermore, in VDES R-Mode, a backup system for the GNSS (Global Navigation Satellite System), ASM signals are often used for ranging and positioning, improving the reliability and safety of ship positioning and navigation at sea. VDES R-Mode operates by measuring the transmission time of wireless signals between the ship and various base stations to calculate the ship-to-shore distance and ultimately determine positioning. Therefore, accurate measurement of the transmission time between ship and shore is essential for land-based positioning and navigation systems to achieve high-precision positioning. Currently, the main methods for measuring time delay are direct time-stamping (DTS) and the EL algorithm. The direct time-stamping (EL) algorithm requires the addition of an additional time stamp at the transmitter, increasing packet overhead and impacting data transmission efficiency. Furthermore, time-stamp accuracy relies on a precise clock; clock deviation directly impacts delay measurement accuracy. The EL algorithm requires two correlators to process early and late signals, respectively, increasing hardware resource consumption and system complexity. This additional hardware overhead can become a development bottleneck, particularly in resource-constrained embedded systems or FPGAs. Therefore, the present invention utilizes the advantages of high performance and low cost of the Universal Software Radio Peripheral (USRP) to design an ASM delay measurement system based on USRP. The system can still perform correlation calculations under interference or low signal-to-noise ratio, and is used to accurately measure signal delay and further calculate signal transmission time. Summary of the Invention

[0003] In view of the shortcomings of the existing technology, the present invention provides an ASM signal delay measurement system based on a universal software radio peripheral (USRP). The present invention receives ASM signals based on a universal software radio peripheral (USRP) and uses the good autocorrelation of ASM signals to calculate signal delay, thereby improving the accuracy of signal delay measurement and ensuring the safety of ship navigation.

[0004] The technical means adopted in the present invention are as follows:

[0005] An ASM signal delay measurement system based on software radio peripherals, the system comprising a transmitting end and a receiving end;

[0006] The transmitting end includes a signal generator, a first time-frequency synchronization device, and a VHF transmitting antenna; the first time-frequency synchronization device externally triggers the signal generator to transmit a pre-generated ASM signal through the VHF transmitting antenna, wherein the data frame of the ASM signal includes a training sequence, and the training sequence is a double Barker 13 code with ideal autocorrelation;

[0007] The receiving end includes a software radio device, a second time-frequency synchronization device, a computing host, and a VHF receiving antenna; the second time-frequency synchronization device externally triggers the software radio device to receive the ASM signal through the VHF receiving antenna, and the software radio device is used to process the received ASM signal to generate a baseband signal, and send the processed baseband signal sequence to the computing host;

[0008] The computing host performs correlation calculations on the local signal and the received signal with the same structure as the expected received signal at different time offsets. By continuously sliding the local signal on the time axis, the correlation values of the local signal and the received signal at different time positions are calculated, and the corresponding point where the correlation value reaches the maximum value is obtained. The time interval of the sampling points is multiplied to obtain the accurate time delay.

[0009] The first time-frequency synchronization device and the second time-frequency synchronization device synchronously output two PPSs respectively.

[0010] Furthermore, the first time-frequency synchronization device and the second time-frequency synchronization device both use FPGA-based rubidium clock training equipment, which receives the second pulse signal from the GPS satellite, compares it with the second pulse signal generated by the rubidium clock, and calculates the clock difference of the rubidium clock using the time interval measurement principle. When the GPS receiver receives the second pulse signal, a timing gate is started, and when the rubidium clock generates the second pulse signal, the timing gate is closed;

[0011] During the period when the timing gate is open, the reference clock pulses within the preset frequency range are counted cumulatively, and the rubidium clock difference is calculated based on the number of recorded clock pulses;

[0012] The Vondrak filter is used to process the clock error of the rubidium clock, and then the PID control algorithm is used to control the rubidium clock voltage and adjust the rubidium clock frequency.

[0013] Furthermore, the computing host performs correlation calculations on the local signal and the received signal with the same structure as the expected received signal at different time offsets. By continuously sliding the local signal on the time axis, the correlation values of the two at different time positions are calculated. The corresponding point where the correlation value reaches the maximum value is multiplied by the time interval to obtain the accurate time delay, including:

[0014] A training sequence of the ASM-TER is modulated using π / 4 QPSK. The training sequence uses the last 26 code elements in the modulation sequence. The code elements are Barker 13 codes and inverse Barker 13 codes with ideal autocorrelation characteristics.

[0015] Calculate the correlation value of the in-phase branch I and the orthogonal branch Q for each symbol:

[0016]

[0017]

[0018] in, represents the correlation value of the I branch (in-phase branch) of the kth symbol under the delay τ, represents the correlation value of the Q branch (orthogonal branch) of the kth symbol under the delay τ, is the phase of the kth symbol, is the phase difference between the received signal and the local signal, represents the symbol period, Represents the carrier angular frequency. The correlation values of the I and Q branches are squared and added to obtain the incoherent correlation values at different time offsets. :

[0019]

[0020] in, N is the sign of the integral;

[0021] By continuously sliding the local signal on the time axis, the correlation values between the two at different time positions are calculated, and the point corresponding to the maximum correlation value is found:

[0022]

[0023] Multiply by the sampling time interval , get the accurate delay :

[0024]

[0025] Furthermore, the process of the signal generator sending a signal includes:

[0026] The ASM signal is modulated on a carrier of a preset frequency, and when a rising edge of the PPS sent by the first time-frequency synchronization device is detected, the trigger signal generator sends the ASM signal.

[0027] Furthermore, the software radio device adopts USRP2954R, and the process of the USRP2954R receiving a signal includes:

[0028] After detecting the rising edge of the PPS, the USRP2954R device receives the signal through the RX1 channel and performs preliminary amplification through the low-noise amplifier;

[0029] The amplified signal is passed through a 10 MHz to 500 MHz frequency synthesizer and a voltage-controlled oscillator for frequency adjustment to ensure that the signal is within the frequency range that the equipment can handle;

[0030] The processed signal is passed through a bandpass filter with a center frequency of 2.44 GHz and a bandwidth of 84 MHz to ensure that only signals within this frequency band are received, and then passed through an 80 MHz low-pass filter to further filter out high-frequency noise;

[0031] The low-pass filtered signal is digitized at a rate of 200 MS / s by an analog-to-digital converter, and the digital signal is processed by a digital down-converter to convert the RF signal into a baseband signal;

[0032] The FPGA filters and adjusts the gain of the baseband signal. The processed signal is routed via a data packet and sent out via the Ethernet port.

[0033] Compared with the prior art, the present invention has the following advantages:

[0034] The present invention realizes the synchronization of the transmitting and receiving ends through two time-frequency synchronization devices. The two time-frequency synchronization devices output two PPSs respectively, and the output PPSs are connected to the signal generator and the USRP device respectively, thereby realizing the trigger time synchronization of the transmitting and receiving ends. At the same time, VHF antennas are used at both ends to better simulate the actual application situation.

[0035] The present invention relies on the USRP device to receive and collect ASM signals. According to the characteristics of the USRP receiving signal, the collected signals are subjected to low-noise amplification, frequency adjustment, filtering, analog-to-digital conversion, down-conversion and other processing. Finally, the signals are received at the center frequency required by the user. Baseband sampling or undersampling is used according to the characteristics of the signals, and the processed signals are transmitted to the host via a 10 Gigabit Ethernet cable.

[0036] The present invention is developed based on the LabVIEW platform and can realize automatic continuous signal acquisition. Through the write waveform file VI and the create incremental suffix VI in the signal storage module, a text file with an incremental suffix is generated in the target folder each time data is collected.

[0037] The present invention imports the collected data into MATLAB, processes it through a sliding correlation delay algorithm, obtains the position of the maximum correlation value, and then measures the accurate signal delay. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0039] Figure 1 The figure is a schematic diagram of the structure of an ASM signal delay measurement system based on software radio peripherals in an embodiment of the present invention.

[0040] Figure 2 The figure is a functional module block diagram of an ASM signal delay measurement system based on software radio peripherals in an embodiment of the present invention.

[0041] Figure 3 2 is a flowchart of the signal transmission workflow in an embodiment of the present invention.

[0042] Figure 4 2 is a flowchart of the signal receiving workflow in an embodiment of the present invention.

[0043] Figure 5 2 is a transmission signal waveform diagram in an embodiment of the present invention.

[0044] Figure 6 FIG. 4 is a spectrum diagram of a transmission signal in an embodiment of the present invention.

[0045] Figure 7 This is a signal acquisition flow chart in an embodiment of the present invention.

[0046] Figure 8 This is a delay estimation flow chart in an embodiment of the present invention.

[0047] Figure 9 Schematic diagram of delay processing results in an embodiment of the present invention. DETAILED DESCRIPTION

[0048] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0049] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0050] The present invention discloses an ASM signal delay measurement system based on software radio peripherals, such as Figure 1 As shown, it includes a transmitter and a receiver. The transmitter includes a signal generator, a first time-frequency synchronization device, and a VHF transmission antenna. The first time-frequency synchronization device externally triggers the signal generator to transmit a pre-generated ASM signal via the VHF transmission antenna. The data frame of the ASM signal includes a training sequence, which is a dual Barker 13 code with ideal autocorrelation. The receiver includes a software radio device, a second time-frequency synchronization device, a computing host, and a VHF reception antenna. The second time-frequency synchronization device externally triggers the software radio device to receive the ASM signal via the VHF reception antenna. The software radio device processes the received ASM signal to generate a baseband signal and transmits the processed baseband signal sequence to the computing host. The computing host performs a cross-correlation operation on the differential function of the original modulation sequence corresponding to the known training sequence and the differential function of the received signal sequence to obtain a correlation function for differential detection. The first time-frequency synchronization device and the second time-frequency synchronization device each synchronously output two PPS channels.

[0051] The delay measurement system realizes the trigger time synchronization between the transmitting and receiving ends. Two PPS are outputted through two time-frequency synchronization devices, which are connected to the signal generator and software radio equipment respectively. The rising edge of PPS is used as the trigger reference to synchronize the transmission and reception of signals.

[0052] The design of the system is as follows:

[0053] The signal generator can send ASM signals and modulate them on a 162MHz carrier. It can also detect the rising edge of the PPS to trigger the sending of ASM signals every second.

[0054] Specifically, the ASM signal uses alternating π / 4 QPSK modulation, which limits the signal phase jumps between adjacent symbols to ±3π / 4 and ±π / 4, rather than ±π phase jumps. The ASM signal's data frame includes a training sequence, a 27-bit dual Barker 13 code with perfect autocorrelation.

[0055] The software radio device uses the NI USRP2954R, which is connected to the computing host via a 10 Gigabit Ethernet cable. The driver of the NI USRP2954R includes twelve functions, which are:

[0056] 1. niUSRP Open Rx Session VI;

[0057] 2. niUSRP Configure Trigger VI;

[0058] 3. niUSRP Configure VI;

[0059] 4. niUSRP property node, i.e. Property Node;

[0060] 5. NIUSRP parameter configuration VI, namely NIUSRP Commit;

[0061] 6. niUSRP and PPS synchronization VI, namely niUSRP EX Synchronize Clocks Mult-Device (PPS);

[0062] 7. niUSRP initialization VI, niUSRP InitiateVI;

[0063] 8. niUSRP Fetch Rx Data VI;

[0064] 9. Abort VI, i.e. niUSRP Abort VI;

[0065] 10. Close VI, i.e. niUSRP Close Session VI;

[0066] 11. Export Waveforms To Spreadsheet File (1D) VI;

[0067] 12. Create the Create File with Incrementing Suffix VI.

[0068] The above functions 1-7 are used to implement the device configuration function, function 8 is used to implement the data reading function, functions 9-10 are used to implement the end function, and functions 11-12 are used to implement the waveform data writing function.

[0069] The signal reception process on the NI USRP2954R is as follows: After detecting the rising edge of the PPS, the USRP2954R receives the signal through channel RX1. The signal is initially amplified by a low-noise amplifier (LNA). The signal then passes through a 10 MHz to 500 MHz frequency synthesizer (PLL) and a voltage-controlled oscillator (VCO) for frequency adjustment to ensure it is within the device's frequency range. The signal then passes through a 2.44 GHz bandpass filter with an 84 MHz bandwidth, ensuring that only signals within this frequency band are received. An 80 MHz low-pass filter further filters out high-frequency noise. An analog-to-digital converter (ADC) converts the analog signal to digital at a rate of 200 MS / s. The digital signal passes through a digital downconverter (DDC) to convert the RF signal to baseband. The FPGA performs further processing on the baseband signal, including filtering and gain adjustment. Finally, the processed signal is routed through a packet router and transmitted over the 1G / 10G Ethernet port, completing the entire signal reception and transmission process.

[0070] The computing host is a host computer PC equipped with a 10 Gigabit network card, equipped with the LabVIEW software platform and the NIUSRP software suite. The NI USRP software suite adds the NI USRP driver to LabVIEW to enable data interaction between the LabVIEW software platform and the USRP. Furthermore, the LabVIEW software platform includes a signal acquisition program, which includes a trigger receiving module and a signal storage module.

[0071] Furthermore, the LabVIEW software platform also adds a waveform diagram and a spectrum diagram to the front panel, which is used to visually check whether the received waveform is an ideal waveform.

[0072] Furthermore, an association function is added to the LabVIEW program to associate the Create Incremental Suffix File Name function with the Write Waveform File function. Each time the program is run, a new file is created, and the file name has an incremental suffix of (1), (2), (3)...

[0073] Furthermore, the computing host processes the collected signals based on the sliding correlation algorithm and measures the specific signal delay:

[0074] The computing host performs correlation calculations on the local signal and the received signal, which have the same structure as the expected received signal, at different time offsets. By continuously sliding the local signal along the time axis, the correlation values between the two are calculated at different time positions. The corresponding point where the correlation value reaches its maximum value is multiplied by the time interval to obtain the precise signal delay, including:

[0075] The training sequence used in the present invention is the training sequence of ASM-TER. It is a 27-bit training sequence that uses π / 4 QPSK modulation. The last 26 code elements are the Barker 13 code (1 1 1 1 1 0 0 1 1 01 0 1) and the inverse Barker 13 code (0 0 0 0 0 1 1 0 0 1 0 1 0) with ideal autocorrelation characteristics, which can be used to detect weak target signals submerged in noise. The present invention uses the ideal autocorrelation characteristics of the double Barker 13 code for ranging. In the training sequence, the symbol "1" is mapped to the π / 4 QPSK symbol "3" (11), and the symbol "0" is mapped to the π / 4 QPSK symbol "0" (00). When the symbol changes, there are four possible phase changes, namely ±π / 4 and ±3π / 4. Since there are only two symbols "11" and "00" in the training sequence, and no "01" and "10", there are only four phase changes.

[0076] Calculate the correlation value of the in-phase branch I and the orthogonal branch Q for each symbol:

[0077]

[0078]

[0079] in, represents the correlation value of the I branch (in-phase branch) of the kth symbol under the delay τ, represents the correlation value of the Q branch (orthogonal branch) of the kth symbol under the delay τ, is the phase of the kth symbol, is the phase difference between the received signal and the local signal, represents the symbol period, Represents the carrier angular frequency. The correlation values of the I and Q branches are squared and added to obtain the incoherent correlation values at different time offsets. :

[0080]

[0081] in, N is the sign of the integral;

[0082] By continuously sliding the local signal on the time axis, the correlation values between the two at different time positions are calculated, and the point corresponding to the maximum correlation value is found:

[0083]

[0084] Multiply by the sampling time interval , get the accurate delay :

[0085]

[0086] Both the first and second time-frequency synchronization devices are FPGA-based rubidium clock training devices. They receive pulse-second signals from GPS satellites, compare them with the pulse-second signals generated by the rubidium clock, and calculate the clock error of the rubidium clock using the principle of time interval measurement. When the GPS receiver receives the pulse-second signal, a timing gate is activated. When the rubidium clock generates the pulse-second signal, the timing gate is closed. While the timing gate is open, reference clock pulses within a preset frequency range are counted. In this embodiment, the preset frequency range is 50 MHz to 150 MHz. The time difference between the two pulse-second signals, i.e., the clock error of the rubidium clock, can be calculated by counting the number of recorded clock pulses. The clock error is processed using a Vondrak filter, and the voltage of the rubidium clock is then controlled using a PID control algorithm to adjust the rubidium clock frequency.

[0087] The scheme and effects of the present invention are further illustrated below through specific application examples.

[0088] This embodiment provides an ASM signal delay measurement system based on software radio device USRP2954R. Figure 1As shown, two time-frequency synchronization devices achieve trigger time synchronization between the transmitter and receiver. Each device outputs two PPS signals, which are connected to a signal generator and a USRP device, respectively. The USRP also needs to be connected to a 10 MHz frequency, achieving time synchronization between the transmitter and receiver. The signal generator and USRP detect the rising edge of the PPS signal, triggering the transmission and reception of the signal. The signal is collected once per second. The signal generator transmits the signal via a VHF antenna, which is also used by the receiver. The collected signal is transmitted to the host computer via a 10 Gigabit Ethernet cable and imported into MATLAB as a text file for sliding-correlation algorithm processing. This allows the precise time delay from signal transmission to acquisition to be calculated.

[0089] like Figure 2 As shown, the functional modules of the system can be divided into a signal transmitting module, a signal receiving module, a signal storage module and a delay processing module.

[0090] Figure 3 As shown in the figure, the specific working process of the signal transmission module is as follows:

[0091] Step 1-1: Generate an ASM signal using MATLAB, set the number of data points to 78,500, the sampling rate to 56 MHz, the center frequency to 0 Hz, and the bandwidth to 25 kHz, and import it into the signal generator using the Waveform Editor software.

[0092] Step 1-2: Enable arbitrary waveform mode on the signal generator, select this waveform sequence, set the carrier frequency to 162 MHz, the sampling rate to 50 MHz, select external trigger as the trigger source, receive the PPS signal through the PPS TRIG IN interface, and select one-at-a-time trigger mode, which means triggering once on each rising edge of the PPS.

[0093] Step 1-3: Connect the RF output port of the signal generator to the VHF antenna to send the signal through the VHF antenna.

[0094] Combine Figure 4 , the process of USRP receiving signals is as follows:

[0095] Step 2-1: After connecting the receiving antenna to the TX / RX1 port of the USRP2954R, connect the PPS output of the receiving frequency synchronization device to the PPS TRIG IN port of the USRP2954R as the trigger signal for reception. Connect the 10 MHz frequency signal to the REF port of the USRP2954R as the frequency reference of the USRP2954R.

[0096] Step 2-2: After waiting for the rising edge of the PPS, signal reception begins. Once triggered by the rising edge of the PPS, the USRP2954R receives the signal through the RX1 channel. The signal is amplified by a low-noise amplifier (LNA), then frequency-adjusted by a frequency synthesizer (PLL) and voltage-controlled oscillator (VCO). A bandpass filter filters the signal to a specific frequency band, and a low-pass filter removes high-frequency noise. The analog-to-digital converter (ADC) converts the analog signal to a digital signal, which is then processed by a digital downconverter (DDC). Finally, the FPGA processes the signal and sends it to the computing host via the USRP's 1G / 10G port.

[0097] Step 2-3: The computing host can detect the IP address of the software radio device through NI's hardware detection software. In the LabVIEW program, set the device IP for signal transmission. The whole process starts with opening the receiving session and matching the connected device, and then specifying the channel list used by the session. Subsequently, set the property node to allow each VI (Virtual Instrument) object to access the private data of the LabVIEW class. After configuring the relevant properties of the received signal, start receiving the mixed signal transmitted to the host. Once the signal is received successfully, the system will obtain the data from the specified channel list. If an error occurs during the reception process, the system will output an error message; if the reception is successful, signal processing will continue, including performing FFT (Fast Fourier Transform) to obtain the frequency domain spectrum of the signal and performing IQ demodulation to obtain the time domain waveform of the signal. The waveform diagram and spectrum diagram can intuitively observe the received signal waveform, such as Figure 5 and Figure 6 shown.

[0098] Combine Figure 7 , the storage process of the signal storage module is as follows:

[0099] Step 3-1: Data is stored every time the program is run. First, the increment suffix VI is created. Each time the program is executed, it checks whether the set file in the target folder exists. If it exists, a new file name is generated based on the original file name, with a suffix starting with (1) and incremented in sequence. The new file name is then transferred to the write waveform file VI.

[0100] Step 3-2: The Write Waveform File VI receives the data stream information transmitted by the program and writes it to a text file in the form of data points. The file is named using the same method as the Create Increment Suffix VI.

[0101] Combine Figure 8 , the process of the signal processing module is as follows:

[0102] Step 4-1: Before starting signal processing, clear all content on the screen and close all open graph windows to ensure that previous data or graphs do not pop up while the algorithm is running. Then load the locally stored baseband signal data, which serves as the input data for the sliding correlation algorithm.

[0103] Step 4-2: Read the file list containing signal data and sort the files in chronological order to facilitate subsequent sequential reading.

[0104] Step 4-3: Read the I and Q data from each file. The I and Q data represent the real and imaginary parts of the signal. Also read the sampling rate of the signal, which determines the time resolution of the signal.

[0105] Step 4-4: If insufficient data is available, the sliding correlation algorithm will skip the current file and not process it. The algorithm then checks to see if all files have been processed. If any files remain, the algorithm continues processing; if all files have been processed, the algorithm proceeds to the next step.

[0106] Step 4-5: Use the sliding correlation algorithm to find the location of the training sequence in the signal, calculate the correlation value to obtain the correlation curve for easy observation and analysis, and record the location of the maximum correlation value.

[0107] Step 4-6: The output processing results of this group of data, including the position of the maximum correlation value recorded, the file name of this group of data and other information are added to an array. Then determine whether the data file has been read. If it has been completed, end the program. If it has not been completed, continue to read the data file and repeat the above process. When all data files have been processed, the array now already has the processing results of all data files. Then calculate the average value and standard deviation of the data in this array, and eliminate the outliers in the array according to the average value and standard deviation. After elimination, calculate the average value and standard deviation again, and perform iterative operations in this way. Set different numbers of iterations according to different accuracy requirements. Since the sampling frequency set for the USRP device is 50MHz, that is, the sampling time interval is 20ns, the final average value after eliminating the outliers is multiplied by 20ns to obtain the transmission delay value of the ASM signal, such as Figure 9 shown.

[0108] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An ASM signal delay measurement system based on software radio peripherals, characterized in that: The system includes a transmitting end and a receiving end; The transmitting end includes a signal generator, a first time-frequency synchronization device, and a VHF transmitting antenna; the first time-frequency synchronization device externally triggers the signal generator to transmit a pre-generated ASM signal through the VHF transmitting antenna, wherein the data frame of the ASM signal includes a training sequence, and the training sequence is a double Barker 13 code with ideal autocorrelation; The receiving end includes a software radio device, a second time-frequency synchronization device, a computing host and a VHF receiving antenna; The second time-frequency synchronization device externally triggers the software radio device to receive the ASM signal through the VHF receiving antenna, and the software radio device is used to process the received ASM signal to generate a baseband signal and send the baseband signal sequence to the computing host; The computing host performs correlation calculations on the local signal and the received signal with the same structure as the expected received signal at different time offsets. By continuously sliding the local signal on the time axis, the correlation values of the local signal and the received signal at different time positions are calculated, and the corresponding point where the correlation value reaches the maximum value is obtained. The time interval of the sampling points is multiplied to obtain the accurate time delay. The first time-frequency synchronization device and the second time-frequency synchronization device synchronously output two PPSs respectively.

2. The ASM signal delay measurement system based on software radio peripherals according to claim 1, characterized in that: The first time-frequency synchronization device and the second time-frequency synchronization device both use FPGA-based rubidium clock training equipment, which receives the second pulse signal from the GPS satellite, compares it with the second pulse signal generated by the rubidium clock, and calculates the clock difference of the rubidium clock using the time interval measurement principle. When the GPS receiver receives the second pulse signal, a timing gate is started, and when the rubidium clock generates the second pulse signal, the timing gate is closed; During the period when the timing gate is open, the reference clock pulses within the preset frequency range are counted cumulatively, and the clock error value of the rubidium clock is calculated based on the number of recorded clock pulses; The Vondrak filter is used to process the clock error of the rubidium clock, and then the PID control algorithm is used to control the rubidium clock voltage and adjust the rubidium clock frequency.

3. The ASM signal delay measurement system based on software radio peripherals according to claim 1, characterized in that: The computing host performs correlation calculations on a local signal and a received signal having the same structure as the expected received signal at different time offsets. By continuously sliding the local signal on the time axis, the correlation values of the local signal and the received signal at different time positions are calculated, and the corresponding point where the correlation value reaches the maximum value is obtained. The corresponding point is multiplied by the sampling point time interval to obtain the accurate time delay, including: A training sequence of the ASM-TER is modulated using π / 4 QPSK. The training sequence uses the last 26 code elements in the modulation sequence. The code elements are Barker 13 codes and inverse Barker 13 codes with ideal autocorrelation characteristics. Calculate the correlation value of the in-phase branch I and the orthogonal branch Q for each symbol: in, represents the correlation value of the same branch I branch of the kth symbol under the delay τ, represents the correlation value of the orthogonal branch Q branch of the kth symbol under the delay τ, is the phase of the kth symbol, is the phase difference between the received signal and the local signal, represents the symbol period, Represents the carrier angular frequency. The correlation values of the I and Q branches are squared and added to obtain the incoherent correlation values at different time offsets. : in, N is the sign of the integral; By continuously sliding the local signal on the time axis, the correlation values between the local signal and the received signal at different time positions are calculated, and the point corresponding to the maximum correlation value is found: Multiply by the sampling time interval , get the accurate delay : 。 4. The ASM signal delay measurement system based on software radio peripherals according to claim 1, characterized in that: The process of the signal generator sending a signal includes: The ASM signal is modulated on a carrier of a preset frequency, and when a rising edge of the PPS sent by the first time-frequency synchronization device is detected, the trigger signal generator sends the ASM signal.

5. The ASM signal delay measurement system based on software radio peripherals according to claim 1, characterized in that: The software radio device adopts USRP2954R, and the process of receiving the signal by the USRP2954R includes: After detecting the rising edge of the PPS, the USRP2954R device receives the signal through the RX1 channel and performs preliminary amplification through the low-noise amplifier; The amplified signal is passed through a 10 MHz to 500 MHz frequency synthesizer and a voltage-controlled oscillator for frequency adjustment to ensure that the signal is within the frequency range that the equipment can handle; The processed signal is passed through a bandpass filter with a center frequency of 2.44 GHz and a bandwidth of 84 MHz to ensure that only signals within this frequency band are received, and then passed through an 80 MHz low-pass filter to further filter out high-frequency noise; The low-pass filtered signal is digitized at a rate of 200 MS / s by an analog-to-digital converter, and the digital signal is processed by a digital down-converter to convert the RF signal into a baseband signal; The FPGA filters and adjusts the gain of the baseband signal. The processed signal is routed via a data packet and sent out via the Ethernet port.

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