Ionized layer scintillation signal simulation monitoring system and method in Beidou / GPS

Abstract

The invention relates to the technical field of satellite navigation, in particular to an ionospheric scintillation signal simulation monitoring system and method in Beidou / GPS, after initial information is issued by an upper computer, a baseband signal board processes the initial information to generate a GPS / BDS simulation intermediate frequency signal; a Cornell model is built in a DSP algorithm of a baseband signal board, an ionosphere delay model and a troposphere delay model are built at the same time, and finally ionosphere scintillation signal simulation is carried out. A GPS / BDS intermediate frequency signal is received through a signal processing module; and the upper computer software module performs man-machine interaction, defines the working environment of the user receiver and displays and controls data of the GPS / BDS simulator. The upper computer software module provides a good man-machine interaction interface, so that a user can conveniently define the working environment of a user receiver and display and control data of a GPS / BDS simulator. Therefore, the problem that the measurement precision is affected by signal propagation delay caused by ionospheric flicker is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of satellite navigation, and particularly to a Beidou / GPS ionospheric scintillation signal simulation and monitoring system and method. Background Art

[0002] Ionospheric scintillation is a natural phenomenon that occurs in the Earth's ionosphere. Due to the irregular fluctuations of the electron density in the ionosphere, the radio wave signals propagating through the ionosphere are interfered. Such fluctuations are usually caused by plasma instabilities in the ionosphere, especially during periods of enhanced geomagnetic activity, such as during solar storms or magnetic storms, when ionospheric scintillation is more common.

[0003] In satellite navigation systems, ionospheric scintillation can cause signal propagation delays, which are converted into positioning errors, making the position calculation of the receiver inaccurate. At the same time, due to the irregular changes in signal amplitude and phase, the measurement accuracy of the navigation system will decrease, affecting the accurate determination of the user's position, speed, and time. Summary of the Invention

[0004] The purpose of the present invention is to provide a Beidou / GPS ionospheric scintillation signal simulation and monitoring system and method, aiming to solve the problem that ionospheric scintillation can cause signal propagation delays and affect the measurement accuracy.

[0005] To achieve the above purpose, in the first aspect, the present invention provides a Beidou / GPS ionospheric scintillation signal simulation and monitoring method, including the following steps:

[0006] After the initial information is sent by the upper computer, it is processed by the baseband signal board to generate GPS / BDS analog intermediate frequency signals;

[0007] By building the Cornell model in the DSP algorithm of the baseband signal board, and at the same time building the ionospheric delay model and the tropospheric delay model, and finally simulating the ionospheric scintillation signal;

[0008] Receiving the GPS / BDS intermediate frequency signals through the signal processing module;

[0009] The upper computer software module conducts human-computer interaction, defines the working environment of the user receiver, and the data display and control of the GPS / BDS simulator.

[0010] Among them, in "After the initial information is sent by the upper computer, it is processed by the baseband signal board to generate GPS / BDS analog intermediate frequency signals", it includes:

[0011] Receiving the scenario file and ephemeris file sent by the upper computer software module, and extracting relevant information;

[0012] Generate a carrier motion trajectory according to the carrier motion mode set by the user;

[0013] Calculate the spatial coordinates of all satellites based on ephemeris parameters and determine the satellite visibility status;

[0014] For the first 12 visible satellites of BDS and GPS, the pseudorange and pseudorange change rate between the carrier and each satellite are calculated in real time to obtain the initial state of the signal at the start time of system simulation, and generate the code initial phase, carrier initial phase, integer code chip number, code frequency control word and carrier frequency control word;

[0015] Encode the BDS and GPS messages respectively and pre-store the navigation messages;

[0016] After calculating the initialization data, the DSP sends the channel status word to the FPGA. Each channel of the FPGA starts to generate GPS / BDS intermediate frequency signals. The DSP updates the signal generation parameters in real time and exchanges data with the FPGA through the EMIF.

[0017] Among them, in "After DSP calculates the initialization data, it sends the channel status word to FPGA, and each channel of FPGA starts to generate GPS / BDS intermediate frequency signal. DSP updates the signal generation parameters in real time and exchanges data with FPGA through EMIF", the generation of GPS / BDS intermediate frequency signal includes:

[0018] The satellite number is extracted from the channel status word and the corresponding signal channel is selected. The navigation message NH modulation, pseudo code modulation, and carrier modulation are performed to synthesize the pseudo code and carrier of the frequency band signal corresponding to the satellite number. Finally, multiple multi-channel signals in the same frequency band are synthesized to generate multi-frequency satellite digital intermediate frequency signals for BDS and GPS systems.

[0019] Among them, "After DSP calculates the initialization data, it sends the channel status word to FPGA, and each channel of FPGA starts to generate GPS / BDS intermediate frequency signal. DSP updates the signal generation parameters in real time and exchanges data with FPGA through EMIF". The data interaction between DSP and FPGA includes:

[0020] DSP first initializes its own system configuration, and then resets FPGA through McBSP; DSP receives host computer data through FPGA's FIFO, and exchanges data with FPGA through EMIF, including carrier and code frequency control words, etc.; data transmission is carried out in two times, FPGA pieces together 32-bit and 4-bit data into 36 bits, DSP triggers DSP interrupt 4 every 16ms, updates FPGA's frequency control word, and corrects the frequency; FPGA triggers interrupt 5 every 20ms, DSP counts navigation messages, and sends new navigation message subframes to FPGA every 300 counts.

[0021] Among them, in "By building the Cornell model in the DSP algorithm of the baseband signal board, simultaneously building the ionospheric delay model and the tropospheric delay model, and finally simulating the ionospheric scintillation signal", the intensity change of the signal simulated by the Cornell model follows the Rice distribution, the carrier phase change follows the Gaussian distribution with a mean of zero, and both the signal intensity spectral density and the phase spectral density follow a certain power-law distribution.

[0022] The digital intermediate frequency satellite signal under ionospheric scintillation conditions can be expressed as:

[0023]

[0024] In the formula, N is the number of visible satellites, j is the visible satellite number, D(t) is the navigation message, C(t) is the spread spectrum code signal, is the ionospheric delay, is the signal propagation delay excluding the ionospheric delay, n(t) is the additive white Gaussian noise, f IF is the intermediate frequency, f L is the radio frequency. A j (t) and are respectively the amplitude and the carrier phase of the received signal, and

[0025]

[0026] In the formula, the signal amplitude fluctuation sequence δA(t) and the carrier phase fluctuation sequence can be obtained through operations on a series of scintillation amplitude values and phase values generated by the ionospheric scintillation simulation program, thereby realizing the ionospheric scintillation simulation. The data obtained from the ionospheric scintillation simulation is controlled by the FPGA clock count, and the fluctuation data with corresponding exponents is added to the signal amplitude and phase every 100 ms, thereby further realizing the satellite signal with the ionospheric scintillation effect.

[0027] In the second aspect, the ionospheric scintillation signal simulation and monitoring system in Beidou / GPS adopts the ionospheric scintillation signal simulation and monitoring method described in the first aspect, and includes a baseband signal board, a signal processing module, and a host computer software module. The baseband signal board, the signal processing module, and the host computer software module are connected in sequence.

[0028] The Beidou / GPS ionospheric scintillation signal simulation and monitoring method of the present invention includes the following steps: After receiving the initial information sent by the host computer, it is processed by the baseband signal board to generate GPS / BDS analog intermediate frequency signals; By building the Cornell model into the DSP algorithm of the baseband signal board, and simultaneously building the ionospheric delay model and the tropospheric delay model, and finally simulating the ionospheric scintillation signal; Receiving the GPS / BDS intermediate frequency signals through the signal processing module; The host computer software module conducts human-computer interaction to define the working environment of the user receiver and the data display and control of the GPS / BDS simulator. The initial data is processed by the algorithm on the DSP+FPGA hardware platform to generate digital intermediate frequency signals, and then the digital-to-analog conversion is completed by the DA chip to generate GPS / BDS analog intermediate frequency signals. The signal processing module realizes the receiving function of GPS / BDS dual-mode multi-frequency point scintillation monitoring. The host computer software module provides a good human-computer interaction interface, which enables users to conveniently define the working environment of the user receiver and the data display and control of the GPS / BDS simulator. Thus, the problem that ionospheric scintillation can cause signal propagation delay and affect measurement accuracy is solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0030] Figure 1 It is the structural block diagram of the baseband signal processing module.

[0031] Figure 2 It is the architecture diagram of the ionospheric scintillation monitoring host computer software module.

[0032] Figure 3 It is the structural diagram of the DSP processing module.

[0033] Figure 4 It is the schematic diagram of data interaction between the FPGA and the DSP.

[0034] Figure 5 It is the block diagram of the digital intermediate frequency satellite signal simulator for ionospheric scintillation simulation.

[0035] Figure 6 It is the overall technical solution principle block diagram of the Beidou / GPS ionospheric scintillation signal simulation and monitoring system provided by the present invention.

[0036] Figure 7 It is the flowchart of the Beidou / GPS ionospheric scintillation signal simulation and monitoring method provided by the present invention.

[0037] Figure 8 It is a flowchart for processing the initial information sent by the host computer to generate GPS / BDS simulated intermediate frequency signals.

[0038] In the figure: 1 - baseband signal board, 2 - signal processing module, 3 - host computer software module. Specific implementation mode

[0039] Please refer to Figures 7 to 8 , in the first aspect, the present invention provides a method for simulating and monitoring ionospheric scintillation signals in Beidou / GPS, including the following steps:

[0040] S1: After the initial information sent by the host computer is processed by the baseband signal board, GPS / BDS simulated intermediate frequency signals are generated;

[0041] S11: Receive the scenario file and ephemeris file sent by the host computer software module 3, and extract relevant information;

[0042] Specifically, first receive the scenario file and ephemeris file sent by the host computer software module 3, and extract relevant information.

[0043] S12: Generate the carrier motion trajectory according to the carrier motion mode set by the user;

[0044] Specifically, then generate the carrier motion trajectory according to the carrier motion mode set by the user.

[0045] S13: Calculate the spatial coordinates of all satellites according to the ephemeris parameters, and judge the visibility of the satellites;

[0046] Specifically, calculate the spatial coordinates of all satellites according to the ephemeris parameters, and judge the visibility of the satellites.

[0047] S14: For the first 12 visible satellites of BDS and GPS respectively, calculate the pseudorange and pseudorange rate of change between the carrier and each satellite in real time, obtain the signal initial state at the starting time of system simulation, and generate the code initial phase, carrier initial phase, integer chip number, code frequency control word and carrier frequency control word;

[0048] Specifically, for the first 12 visible satellites of BDS and GPS respectively, calculate the pseudorange and pseudorange rate of change between the carrier and each satellite in real time, and then obtain the signal initial state at the starting time of system simulation, and generate the code initial phase, carrier initial phase, integer chip number, code frequency control word and carrier frequency control word.

[0049] S15: Encode the navigation messages for BDS and GPS respectively, and pre-store the navigation messages;

[0050] Specifically, perform message encoding on BDS and GPS respectively, and pre-store navigation messages.

[0051] During the generation process of BDS / GPS satellite signals, the RTC timing module in the FPGA performs timing control and triggers DSP interrupt 4 every 16 ms. The main function of the interrupt 4 service program is to send the newly calculated carrier frequency control word and code frequency control word to the FPGA through the EMIF. The FPGA synthesizes signals according to the new frequency control word. In the interrupt 4 service program, read the values of the carrier NCO and code NCO phase accumulators in the FPGA to correct the carrier frequency control word and code frequency control word. The FPGA triggers interrupt 5 every 20 ms. The main function of the interrupt 5 service program is to count the navigation messages. When the navigation message count reaches 300 times, the DSP sends the navigation message of the next sub-frame to the FPGA.

[0052] The DSP interrupt 5 service program counts the navigation message counter NavCount. NavCount incrementing by 1 indicates that the message propagation duration increases by 20 ms, and the GEO satellite and MEO satellite count separately. When NavCount accumulates to the message length of a sub-frame, NavCount is set to 0. At this time, the DSP sends the navigation message of the next sub-frame to the FPGA.

[0053] When the system is initialized, the DSP pre-sends navigation messages with a duration of 12 s. When NavCount counts to 9 s, the navigation message of the third sub-frame is sent. After that, every time NavCount increases by 300, the DSP sends the next frame of the message. For the GPS L1 band signal, the same transmission timing as that of BDS IGSO / MEO can be adopted. For the BDS GEO satellite, since the duration of each bit of the navigation message is 2 ms, the NavCount count value needs to be adjusted accordingly.

[0054] S16: After the DSP calculates the initialization data, it sends the channel status word to the FPGA. Each channel of the FPGA starts to generate GPS / BDS intermediate frequency signals. The DSP updates the signal generation parameters in real time and conducts data interaction with the FPGA through the EMIF.

[0055] After receiving the carrier NCO parameters, pseudo-code NCO parameters, navigation messages, and channel status word sent by the DSP, the FPGA in the baseband signal board extracts the satellite number from the channel status word, selects the corresponding signal channel, and performs navigation message NH modulation, pseudo-code modulation, and carrier modulation, synthesizing the pseudo-code and carrier of the signal corresponding to the satellite number frequency band. Finally, multiple multi-channel signals in the same frequency band are synthesized to generate the multi-frequency point satellite digital intermediate frequency signals of the BDS and GPS systems.

[0056] The DSP first initializes its own system configuration and then resets the FPGA through the McBSP. The DSP receives the data from the host computer through the FIFO of the FPGA and exchanges data with the FPGA through the EMIF, including carrier and code frequency control words, etc. The data transmission is carried out in two times. The FPGA combines 32-bit and 4-bit data into 36-bit data. The DSP triggers DSP interrupt 4 every 16 ms to update the frequency control word of the FPGA and correct the frequency. The FPGA triggers interrupt 5 every 20 ms. The DSP performs navigation message counting. Every 300 counts, a new navigation message sub-frame is sent to the FPGA.

[0057] Specifically, after the DSP calculates the initialization data, it sends the channel status word to the FPGA, and each channel of the FPGA starts to generate signals. After the system starts, the DSP updates the signal generation parameters in real time and exchanges data with the FPGA through the EMIF. The DSP information processing module mainly completes functions such as system initialization information extraction, signal generation parameter calculation, and system control parameter calculation. First, it receives the scenario file and ephemeris file sent by the host computer software module 3 and extracts relevant information. Then, according to the carrier motion mode set by the user, it generates the carrier motion trajectory; calculates the spatial coordinates of all satellites according to the ephemeris parameters and judges the visibility of the satellites; for the first 12 visible satellites of BDS and GPS respectively, it calculates the pseudorange and pseudorange rate of change between the carrier and each satellite in real time, and then obtains the signal initial state at the start time of system simulation, and generates the code initial phase, carrier initial phase, integer chip number, code frequency control word, and carrier frequency control word. It encodes the navigation messages for BDS and GPS respectively and pre-stores the navigation messages. After the DSP calculates the initialization data, it sends the channel status word to the FPGA, and each channel of the FPGA starts to generate signals. After the system starts, the DSP updates the signal generation parameters in real time and exchanges data with the FPGA through the EMIF.

[0058] S2: By building the Cornell model into the DSP algorithm of the baseband signal board, building the ionospheric delay model and tropospheric delay model at the same time, and finally simulating the ionospheric scintillation signal;

[0059] Specifically, the intensity change of the signal simulated by the Cornell model follows the Rice distribution, the carrier phase change follows the Gaussian distribution with a mean of zero, and the signal intensity spectral density and phase spectral density both follow a certain power-law distribution.

[0060] Under ionospheric scintillation conditions, the digital intermediate-frequency satellite signal can be expressed as:

[0061]

[0062] In the formula, N is the number of visible satellites, j is the visible satellite number, D(t) is the navigation message, and C(t) is the spread-spectrum code signal. is the ionospheric delay, is the signal propagation delay excluding the ionospheric delay, and n(t) is the additive

[0063] white Gaussian noise, and f IF is the intermediate frequency, and f L is the radio frequency. A j (t) and are respectively the amplitude and carrier phase of the received signal, and

[0064]

[0065] wherein, the signal amplitude fluctuation sequence δA(t) and the carrier phase fluctuation sequence can be obtained through operations on a series of scintillation amplitude values and phase values generated by the ionospheric scintillation simulation program, thereby realizing ionospheric scintillation simulation. The data obtained from ionospheric scintillation simulation is controlled by the FPGA clock count, and the fluctuation data with corresponding exponents is added to the signal amplitude and phase every 100 ms, thereby further realizing the satellite signal of the ionospheric scintillation effect.

[0066] S3: Receive the GPS / BDS intermediate frequency signal through signal processing module 2;

[0067] Specifically, the FPGA in the signal processing module acts as a coprocessor responsible for radio frequency unit configuration, signal acquisition, signal tracking, and caching the acquisition results as well as the correlation values and carrier integrated Doppler of the leading, prompt, and lagging branches of the signal tracking loop. The ARM receives the interrupt signal from the FPGA, reads the data cached in the FPGA, and is responsible for acquisition control, tracking loop control, message demodulation, and positioning solution, encodes the corresponding data according to a certain data protocol, and then sends it to the host computer through the serial port.

[0068] The radio frequency unit configured by the FPGA is responsible for down-converting and analog-to-digital conversion (ADC) of the GPS / BD L1 / L2 and B1 / B2 frequency signals received by the antenna, successively obtaining the digital intermediate frequency signals of these four frequency points, and receiving them by the baseband signal processing module.

[0069] S4: The host computer software module 3 performs human-computer interaction, defines the working environment of the user receiver, and the data display and control of the GPS / BDS simulator.

[0070] Specifically, the implementation of various functions in the entire ionospheric scintillation monitoring host computer software module 3 mainly relies on the functional logic modules in the logic layer, which are mainly divided into 6 modules: data preprocessing logic module, amplitude scintillation solution logic module, phase scintillation solution logic module, TEC solution logic module, ionospheric scintillation monitoring logic module, and data access logic module.

[0071] ① Data preprocessing logic module

[0072] The function of the data preprocessing logic module is to read the raw data from the buffer in the DAL layer, decode it to obtain data of the corresponding type, and store it in the corresponding position in the buffer in the BLL layer according to the data type. At the same time, the read raw data is also cached in the buffer in the BLL layer. The whole process is the exact opposite of the data encoding mentioned in the previous section.

[0073] After completing the reading of the data part, perform CRC check on the data log including the data header. If the CRC check passes, then perform data parsing according to the current data type, number the parsed data with consecutive 64-bit unsigned long integers, and then cache it in the corresponding buffer in the BLL layer for other functional modules in the logic layer to read and process.

[0074] ② Amplitude scintillation calculation logic module

[0075] The basic unit of the amplitude scintillation calculation logic module is the amplitude scintillation index calculator. The amplitude scintillation calculation logic module first reads the raw signal strengths of the L1 / L2 frequency points of all currently visible GPS satellites and the raw signal strengths of the B1 / B2 frequency points of all currently visible Beidou satellites from the buffer in the BLL layer in sequence, and sends them to the corresponding amplitude scintillation index calculator for processing.

[0076] In the amplitude scintillation index calculator, first filter using a Butterworth low-pass filter, then calculate the detrended value of the signal strength, and calculate the amplitude scintillation index S4 according to the ionospheric amplitude scintillation monitoring algorithm.

[0077] ③ Phase scintillation calculation logic module

[0078] The phase scintillation calculation logic is similar to the amplitude scintillation calculation logic. It reads the carrier phase measurement values of the L1 / L2 frequency point signals of all currently visible GPS satellites and the B1 / B2 frequency point signals of Beidou satellites from the buffer in the BLL layer in sequence, then performs detrended high-pass filtering, and performs operations on the detrended values according to the ionospheric phase scintillation monitoring algorithm to obtain the phase scintillation index σ φ .

[0079] ④ TEC calculation logic module

[0080] The TEC calculation logic mainly reads the dual-frequency carrier phase measurement values of GPS and Beidou satellites to calculate TEC, σ TEC , ROT, ROTI, and cache the calculation results of each satellite in the buffer in the BLL layer.

[0081] The TEC calculation process is as follows:

[0082] First, traverse each satellite in the satellite list in sequence. If the current satellite is visible, for GPS satellites, check whether the signals of the L1 frequency band and the L2 frequency band of this satellite are available respectively. For Beidou satellites, detect whether the signals of the B1 frequency band and the B2 frequency band of this satellite are available respectively. When the dual-frequency signals of the satellite are available, calculate the TEC, σ TEC , ROT, and ROTI of this satellite.

[0083] The calculation process of TEC-related parameters is as follows:

[0084] First, use the dual-frequency signals to calculate the instantaneous TEC value, then perform detrending filtering all the way, and use the detrended TEC value to calculate the standard deviation σ TEC , while on the other path, calculate the average TEC value within 1 second, then calculate ROT and ROTI at 1-minute intervals, and finally cache the calculated data into the buffer layer of the BLL layer for other functional modules to read.

[0085] ⑤ Ionospheric Scintillation Monitoring Logic Module

[0086] The main function of the ionospheric scintillation monitoring logic module is to judge, analyze, and record ionospheric scintillation events. Since in actual measurements, various factors such as multipath effects and clock errors will affect the results of ionospheric amplitude scintillation and phase scintillation monitoring, resulting in a relatively large value of a certain frequency point signal of GPS / BD at a certain moment. However, this occasional phenomenon does not indicate the occurrence of ionospheric scintillation. Therefore, it is usually necessary to comprehensively consider the scintillation conditions and the frequency of scintillation occurrence monitored by the L1 / L2 frequency band signals of each GPS satellite and the B1 / B2 frequency band signals of Beidou satellites.

[0087] The logic for ionospheric scintillation monitoring using GPS satellite signals is as follows:

[0088] Traverse the amplitude scintillation index and phase scintillation index of the available L1 / L2 frequency bands and B1 / B2 frequency bands of all visible BDS / GPS satellites in sequence, and respectively obtain the maximum amplitude scintillation index MaxBD-S4 and MaxGPS-S4 of BDS / GPS satellites, the minimum amplitude scintillation index MinBD-S4 and MinGPS-S4, the maximum phase scintillation index MaxBD-SigmaPhi and MaxGPS-SigmaPhi, and the minimum phase scintillation index MinBD-SigmaPhi and MinGPS-SigmaPhi of BDS / GPS satellites, and count the proportion RBD-S4 and RGPS-S4 of the number of satellites with the amplitude scintillation index S4 greater than the amplitude scintillation threshold TAmp in the L1 / L2 frequency bands and B1 / B2 frequency bands of signals to the number of all visible BDS / GPS satellites, and the phase scintillation index σ φThe ratios RBD-SigmaPhi and RGPS-SigmaPhi of the number of satellites greater than the phase scintillation threshold TPhase to the total number of visible BDS / GPS satellites.

[0089] Finally, the current maximum amplitude scintillation index MaxS4 is obtained by synthesizing MaxGPS-S4 and MaxBD-S4, and the maximum phase scintillation index MaxSigmaPhi is obtained by synthesizing MaxGPS-SigmaPhi and MaxBD-SigmaPhi.

[0090] ⑥ Data access logic module

[0091] Under the control of the data access logic, the data access logic module reads the raw data, amplitude scintillation monitoring data, phase scintillation monitoring data, and TEC monitoring data from the BLL layer buffer at a certain time interval, and then writes the latter three types of data into a file or database in a certain format.

[0092] Please refer to Figures 1 to 6 In a second aspect, the present invention provides an ionospheric scintillation signal simulation and monitoring system for Beidou / GPS, which adopts the ionospheric scintillation signal simulation and monitoring method described in the first aspect, and includes a baseband signal board 1, a signal processing module 2, and a host computer software module 3. The baseband signal board 1, the signal processing module 2, and the host computer software module 3 are connected in sequence.

[0093] In this embodiment, the baseband signal board 1 receives the initial information sent by the host computer through a serial port, generates a digital intermediate frequency signal through the algorithm processing of the DSP+FPGA hardware platform, and then completes the digital-to-analog conversion by a DA chip to generate a GPS / BDS analog intermediate frequency signal. The signal processing module 2 takes FPGA and ARM as the core, uses DDR3 as the external memory, and NOR Flash as the memory to store the programs of ARM and FPGA. It is responsible for implementing the receiving function of GPS / BDS dual-mode multi-frequency point scintillation monitoring. The host computer software module 3 provides a good human-computer interaction interface, which enables users to conveniently define the working environment of the user receiver and the data display and control of the GPS / BDS simulator.

[0094] The baseband signal board 1 adopts a DSP+FPGA+DA architecture based on the idea of software radio;

[0095] The DSP information processing module calculates the initial code phase, integer chip number, code frequency control word, and carrier frequency control word for each channel of the BDS and GPS systems based on the BDS / GPS system ephemeris parameters, the receiver's motion trajectory, and the system simulation start time. At the same time, it generates corresponding amplitude and phase fluctuation data by receiving parameters from the host computer, encodes the navigation messages of the satellites in each channel of the BDS and GPS systems, and sends them to the FPGA via the EMIF bus of the DSP. Due to the existence of Doppler frequency shift, the DSP updates the code frequency control word and carrier frequency control word in real time and sends them to the FPGA in real time via the EMIF bus of the DSP.

[0096] The FPGA signal generation module receives the initial code phase, integer chip number, code frequency control word, carrier frequency control word, and navigation message sent by the DSP and stores them in registers. After receiving the channel start flag bit sent by the DSP information processing module, Baseband Signal Board 1 synchronously starts the BDS signal channel and GPS signal channel in Baseband Signal Board 1. The signal channels respectively complete the generation of carrier signals at corresponding frequencies, the generation of pseudo-random code signals, the simulation and modulation of navigation messages, and carrier modulation.

[0097] The up-conversion module performs frequency conversion on the analog intermediate frequency signal generated by the D / A module and up-converts it to the radio frequency signal at the corresponding frequency point.

[0098] The signal processing module 2 uses the FPGA chip 5CEFA7U19 and the ARM chip AM3352 as the core, uses DDR3 as the external memory, and NOR Flash as the memory to store the programs of the ARM and FPGA. In addition, since the data output from the serial port of the ARM is at TTL level, while the serial port connector of the computer is at RS232 level, a level conversion chip MAX232 is required for level conversion. The structure of the entire signal processing module 2 is shown in Figure 1 。

[0099] The FPGA uses a crystal oscillator as the clock source, and the crystal oscillator frequency is 25 MHz. The input clock of the crystal oscillator is frequency-multiplied inside the FPGA to obtain a 100 MHz clock, which is used as the main clock frequency for FPGA baseband signal processing. 60 signal tracking channels are implemented inside the FPGA, which can simultaneously track the signals of the L1 / L2 frequency points of GPS and the B1 / B2 frequency points of Beidou, and output the correlation peaks every 1 ms to the ARM chip. The ARM chip, as the main control chip of the signal processing module 2, uses an external crystal oscillator of 24 MHz as the input clock and internally frequency-multiplies it to 504 MHz as the working clock.

[0100] The ARM chip interacts with the FPGA through the General-Purpose Memory Controller (GPMC) module. As a functional module in the ARM series chip AM335x, GPMC is an interface used for data access to external storage devices such as NOR Flash, NAND Flash, and SDRAM. Since in the signal processing module 2, the ARM acts as the main controller and the FPGA acts as the coprocessor, the FPGA is equivalent to being mounted as a peripheral on the GPMC interface of the ARM. For the ARM, the FPGA is equivalent to a memory.

[0101] Since the FPGA can achieve precise timing control, the FPGA provides an interrupt signal to the ARM. The ARM can use the interrupt signal to achieve precise timing, and based on this timing, it periodically conducts data interaction, capture control, tracking control, message demodulation, and positioning calculation with the FPGA.

[0102] The working process of the signal processing module 2 is as follows: The ARM generates a satellite list and searches for the Doppler frequency. The FPGA traverses the list and captures the signals of the specified satellites. After the FPGA successfully captures the signals, it transmits the carrier Doppler frequency and code phase to the ARM. The ARM pre-sets the tracking loop and starts signal tracking. The signal strength is calculated using the method of the difference between the narrowband power and the broadband power. To improve the transmission reliability and save bandwidth, the original data of the receiver is encoded. Referring to the Novatel data protocol, the reserved positions for unused data are set to 0.

[0103] The calculation formula for the signal strength is as follows:

[0104]

[0105] Among them, N in the formula represents the sum of all noise terms, I is the correlation value of the instantaneous I branch, and Q is the correlation value of the instantaneous Q branch.

[0106] The overall architecture of the upper computer software module 3 is a three-layer architecture, namely, the presentation layer (UI), the business logic layer (BLL), and the data access layer (DAL);

[0107] Among them, the presentation layer mainly realizes the human-machine interface and is responsible for interacting with the user.

[0108] The logic layer is responsible for implementing various functions of the entire software, including the implementation of the ionospheric amplitude scintillation monitoring algorithm, the phase scintillation monitoring algorithm, the TEC monitoring algorithm, the scintillation event judgment, and the data storage control. The logic layer plays a connecting role. On the one hand, it receives the operation commands sent by the presentation layer and reads data through the data access layer. On the other hand, after processing the read data, it returns the corresponding results to the presentation layer.

[0109] The data access layer is mainly responsible for accessing the computer serial port, local files or databases, and completing data reading and writing.

[0110] The above-disclosed is only the preferred embodiment of the ionospheric scintillation simulation monitoring system and method in the Beidou GPS navigation system of the present invention. Of course, the scope of the rights of the present invention cannot be limited thereby. Those of ordinary skill in the art can understand all or part of the processes of implementing the above embodiments, and the equivalent changes made according to the claims of the present invention still fall within the scope covered by the invention.

Claims

1. A method for simulating and monitoring ionospheric scintillation signals in Beidou / GPS, characterized in that: The following steps are involved: After the initial information is sent by the host computer, it is processed by the baseband signal board to generate GPS / BDS analog intermediate frequency signal; By building the Cornell model into the DSP algorithm of the baseband signal board, the ionospheric delay model and the tropospheric delay model are built at the same time, and finally the ionospheric scintillation signal is simulated; Receive GPS / BDS intermediate frequency signals through the signal processing module; The host computer software module performs human-computer interaction, defines the working environment of the user receiver, and displays and controls the GPS / BDS simulator data.

2. The method for simulating and monitoring ionospheric scintillation signals in Beidou / GPS as claimed in claim 1, characterized in that: In "After the initial information is sent by the host computer, the baseband signal board processes it and generates the GPS / BDS analog intermediate frequency signal", it includes: Receive the scene file and ephemeris file sent by the host computer software module, and extract relevant information; Generate a carrier motion trajectory according to the carrier motion mode set by the user; Calculate the spatial coordinates of all satellites based on ephemeris parameters and determine the satellite visibility status; For the first 12 visible satellites of BDS and GPS, the pseudorange and pseudorange change rate between the carrier and each satellite are calculated in real time to obtain the initial state of the signal at the start time of system simulation, and generate the code initial phase, carrier initial phase, integer code chip number, code frequency control word and carrier frequency control word; Encode the BDS and GPS messages respectively and pre-store the navigation messages; After DSP calculates the initialization data, it sends the channel status word to FPGA. Each channel of FPGA starts to generate GPS / BDS intermediate frequency signal. DSP updates the signal generation parameters in real time and exchanges data with FPGA through EMIF.

3. The method for simulating and monitoring ionospheric scintillation signals in Beidou / GPS as claimed in claim 2, characterized in that: In "After DSP calculates the initialization data, it sends the channel status word to FPGA, and each channel of FPGA starts to generate GPS / BDS intermediate frequency signal. DSP updates the signal generation parameters in real time and exchanges data with FPGA through EMIF", the generation of GPS / BDS intermediate frequency signal includes: The satellite number is extracted from the channel status word and the corresponding signal channel is selected. The navigation message NH modulation, pseudo code modulation, and carrier modulation are performed to synthesize the pseudo code and carrier of the frequency band signal corresponding to the satellite number. Finally, multiple multi-channel signals in the same frequency band are synthesized to generate multi-frequency satellite digital intermediate frequency signals for BDS and GPS systems.

4. The method for simulating and monitoring ionospheric scintillation signals in Beidou / GPS as claimed in claim 2, characterized in that: In "After DSP calculates the initialization data, it sends the channel status word to FPGA, and each channel of FPGA starts to generate GPS / BDS intermediate frequency signal. DSP updates the signal generation parameters in real time and exchanges data with FPGA through EMIF", the data interaction between DSP and FPGA includes: DSP first initializes its own system configuration, and then resets FPGA through McBSP; DSP receives host computer data through FPGA's FIFO, and exchanges data with FPGA through EMIF, including carrier and code frequency control words, etc.; data transmission is carried out in two times, FPGA pieces together 32-bit and 4-bit data into 36 bits, DSP triggers DSP interrupt 4 every 16ms, updates FPGA's frequency control word, and corrects the frequency; FPGA triggers interrupt 5 every 20ms, DSP counts navigation messages, and sends new navigation message subframes to FPGA every 300 counts.

5. The method for simulating and monitoring ionospheric scintillation signals in Beidou / GPS as claimed in claim 1, characterized in that: In "Ionospheric scintillation simulation by implementing the Cornell model in the DSP of the baseband signal board", we include: The intensity variation of the signal simulated by the Cornell model obeys the Rice distribution, the carrier phase variation obeys the Gaussian distribution with a mean of zero, and the signal intensity spectral density and phase spectral density both obey a certain power-law distribution. The digital intermediate frequency satellite signal under ionospheric scintillation conditions can be expressed as: Where N is the number of visible satellites, j is the visible satellite number, D(t) is the navigation message, C(t) is the spread spectrum code signal, is the ionospheric delay, is the signal propagation delay excluding the ionospheric delay, n(t) is the additive white Gaussian noise, and f IF is the intermediate frequency, f L is the RF frequency. j (t) and are the amplitude and carrier phase of the received signal, respectively.

6. The method for simulating and monitoring ionospheric scintillation signals in Beidou / GPS as claimed in claim 5, characterized in that: The "A j (t) and are the amplitude and carrier phase of the received signal, respectively. "Calculated by the following formula: In the formula, the signal amplitude fluctuation sequence δA(t) and the carrier phase fluctuation sequence A series of scintillation amplitude values ​​and phase values ​​generated by the ionospheric scintillation simulation program can be calculated to achieve ionospheric scintillation simulation. The data obtained by ionospheric scintillation simulation is controlled by FPGA clock counting, and the fluctuation data of the corresponding index is added to the signal amplitude and phase every 100ms, thereby further realizing the satellite signal of ionospheric scintillation effect.

7. A BeiDou / GPS ionospheric scintillation signal simulation monitoring system, using the BeiDou / GPS ionospheric scintillation signal simulation monitoring method according to any one of claims 1 to 6, characterized in that: It comprises a baseband signal board, a signal processing module and a host computer software module, wherein the baseband signal board, the signal processing module and the host computer software module are connected in sequence.

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