A time synchronization-based beidou b1i signal pseudo-range simulation method

Abstract

The application discloses a Beidou B1I signal pseudo-range simulation method based on time synchronization, and relates to the technical field of satellite navigation, wherein initialization effective signal triggering is adopted to load initial parameters, and the rising edge of a time reference source is detected to start delay counting; when a delay threshold is reached, a signal enable is automatically activated to realize time synchronization initialization; two timing controls are adopted to guarantee C / A code timing accuracy and dynamic adaptability; convergent pseudo-range is calculated to guarantee the accuracy of pseudo-range calculated based on C / A code, and dynamic pseudo-range generation is realized; finally, after the simulated C / A code is XORed with navigation text and modulated to a carrier, analog satellite signals are generated through digital-to-analog conversion, and signal modulation and output are realized. The application can provide navigation signals consistent with real signals in an environment without real satellite signals, fills the gap in the prior art, and improves the reliability and applicability of a positioning system.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of satellite navigation technology, and in particular to a Beidou B1I signal pseudo-range simulation method based on time synchronization. BACKGROUND

[0002] In a satellite navigation system, a receiver relies on satellite-transmitted navigation signals (such as Beidou B1I signals) for positioning. However, in environments such as indoors, tunnels, and underground areas where there is no satellite signal coverage, traditional receivers cannot normally complete positioning, resulting in navigation failure. Common solutions currently include:

[0003] Inertial navigation (INS) assisted positioning: relies on sensors such as accelerometers and gyroscopes, but has cumulative errors and the accuracy decreases over time. Pseudolite technology: ground-based deployment of base stations simulating satellite signals, but the cost is high and it is difficult to achieve seamless switching with real satellite signals. Wireless communication network assisted positioning (such as 5G, WiFi): relies on external infrastructure and cannot be used in remote or network-uncovered areas.

[0004] However, the existing technologies all have the following common disadvantages: they cannot completely simulate real satellite signals, resulting in the receiver being unable to correctly parse the pseudo-range information, leading to low positioning accuracy; the time synchronization accuracy is insufficient, causing deviations between the simulated signal and the real satellite, affecting the receiver's timing and positioning functions; and poor compatibility, with some solutions only applicable to specific receivers, making it difficult to adapt to general GNSS devices on the market. SUMMARY

[0005] Therefore, the present application provides a Beidou B1I signal pseudo-range simulation method based on time synchronization to solve the deficiencies of the prior art.

[0006] The first aspect of the present application provides a Beidou B1I signal pseudo-range simulation method based on time synchronization, comprising:

[0007] When the valid signal is initialized trigger, the hardware loads the code NCO initial frequency and G1 / G2 shift register initial phase issued by the SDK;

[0008] The hardware detects the rising edge of the external time reference source, starts a delay counter, and when the delay counter counts reaches the alignment delay threshold issued by the SDK, the hardware automatically activates the signal generation enable;

[0009] Trigger the hardware to reset the G1 / G2 shift register every 1ms, and trigger the hardware to receive the code NCO frequency control word and carrier NCO frequency control word issued by the SDK every 1s, which together constitute a timing control algorithm;

[0010] The real-time pseudo-range is calculated by the following formula and the difference between the real-time pseudo-range and the theoretical pseudo-range is fed back to the SDK, and based on the difference, a damping factor parameter is dynamically adjusted to ensure convergence of the real-time pseudo-range calculation, and a converged pseudo-range is obtained;

[0011]

[0012] a pseudo-range distance deviation correction quantity, an accumulated residual value of the code NCO;

[0013] An initial C / A code is obtained by performing XOR operation between the G1 shift register and the G2 shift register, and the initial C / A code is verified and adjusted by using the timing control algorithm and the converged pseudo-range, and an analog C / A code is obtained.

[0014] After the analog C / A code and the navigation message are subjected to XOR operation, the analog C / A code is modulated to a carrier wave, 8-bit IQ data is output to a digital-to-analog converter for digital-to-analog conversion, and a Beidou B1I radio frequency signal is generated, which is an analog satellite signal.

[0015] In a possible implementation manner of the first aspect, the pseudo-range distance deviation correction quantity is obtained by comprising:

[0016] The remaining code chip number and the current millisecond number are obtained in real time by using a hardware internal counter and are fed back to the SDK;

[0017] Based on the remaining code chip number and the current millisecond number, the pseudo-range distance deviation correction quantity is obtained by combining the SDK algorithm and an accuracy adaptation parameter , the accuracy adaptation parameter is used for processing accuracy deviation of the pseudo-range distance deviation correction quantity .

[0018] In a possible implementation manner of the first aspect, the SDK issues a code NCO frequency control word and a carrier wave NCO frequency control word, which comprises:

[0019] Based on the pseudo-range distance deviation correction quantity , a code chip transmission time deviation quantity and a Doppler frequency shift quantity are obtained by back calculation;

[0020] The code chip transmission time deviation quantity is converted into an identifiable NCO frequency control word, and the Doppler frequency shift quantity is converted into an identifiable carrier wave NCO frequency control word.

[0021] In a possible implementation manner of the first aspect, the hardware reset G1 / G2 shift register is triggered every 1 ms, which comprises:

[0022] The C / A code of Beidou B1I has a complete chip period of 1ms, and the hardware reset G1 / G2 shift register is triggered every 1ms, so that the corresponding shift register starts to generate chips from the initial phase.

[0023] In a possible implementation of the first aspect, the hardware receives the code NCO frequency control word and the carrier NCO frequency control word issued by the SDK every 1s, which includes:

[0024] The code NCO frequency is adjusted by the code NCO frequency control word, so as to compensate for the change in the chip transmission time, and make the analog C / A code consistent with the actual satellite signal arrival time;

[0025] If the satellite is far away from the receiver, the chip transmission time becomes longer, the code NCO frequency control word is increased, and the code NCO frequency is adjusted to be higher;

[0026] If the satellite is close to the receiver, the chip transmission time becomes shorter, the code NCO frequency control word is decreased, and the code NCO frequency is adjusted to be lower.

[0027] In a possible implementation of the first aspect, the hardware receives the code NCO frequency control word and the carrier NCO frequency control word issued by the SDK every 1s, which further includes:

[0028] The carrier NCO frequency is adjusted by the carrier NCO frequency control word, so as to compensate for the Doppler shift, and make the frequency shift characteristics of the analog carrier consistent with the actual satellite signal;

[0029] If the satellite is close to the receiver, the carrier NCO frequency control word is increased, and the carrier NCO frequency is adjusted to be higher;

[0030] If the satellite is far away from the receiver, the carrier NCO frequency control word is decreased, and the carrier NCO frequency is adjusted to be lower.

[0031] In a possible implementation of the first aspect, the navigation message is cached by a FIFO, and satellite ephemeris and clock parameters are dynamically injected.

[0032] In a possible implementation of the first aspect, The module performs calculation of real-time pseudo-range and convergence.

[0033] In a possible implementation of the first aspect, the external time reference source adopts a 1PPS second pulse.

[0034] In a possible implementation of the first aspect, the hardware is an FPGA module.

[0035] The beneficial effect is that the application discloses a Beidou B1I signal pseudo-range simulation method based on time synchronization, aims to solve the problem of positioning failure of a traditional GNSS receiver in a satellite signal-free environment such as an indoor environment or a tunnel, and through initialization of an effective signal trigger, loading initial parameters, detecting a rising edge of a time reference source, starting delay counting, and automatically activating signal enablement when a delay threshold is reached, time synchronization initialization is realized; through two timing controls, C / A code timing accuracy and dynamic adaptability are ensured, through calculation of convergent pseudo-range, the accuracy of pseudo-range calculated based on C / A code is ensured, and pseudo-range dynamic generation is realized; finally, after the simulated C / A code is XORed with navigation text and modulated onto a carrier, and through digital-to-analog conversion, a simulated satellite signal is generated, signal modulation and output are realized. BRIEF DESCRIPTION OF DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only part of the embodiments of the present application, and for those skilled in the art, other drawings can be obtained without creative labor on the basis of the provided drawings.

[0037] Figure 1 It is a kind of based on time synchronization's Beidou B1I signal pseudo-range simulation method flow chart provided in the embodiment of the present application. DETAILED DESCRIPTION

[0038] The technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0039] In this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0040] Example

[0041] In existing technologies, traditional receivers cannot perform positioning correctly in environments without satellite signal coverage, such as indoors, tunnels, and underground, leading to navigation failure. Common solutions include inertial navigation (INS)-assisted positioning, pseudosatellite technology, and wireless communication network-assisted positioning (such as 5G and WiFi). However, these solutions all share the following drawbacks: they cannot fully simulate real satellite signals, causing the receiver to fail to correctly interpret pseudorange information, resulting in low positioning accuracy; time synchronization accuracy is insufficient, with deviations between simulated signals and real satellite signals affecting the receiver's timing and positioning functions; and compatibility is poor, with some solutions only applicable to specific receivers and difficult to adapt to general-purpose GNSS equipment on the market.

[0042] Therefore, this application provides a pseudorange simulation method for BeiDou B1I signals based on time synchronization, such as... Figure 1 As shown, it includes:

[0043] When initialization valid signal Upon triggering, the hardware loads the code issued by the SDK, including the initial frequency of the NCO and the initial phase of the G1 / G2 shift registers.

[0044] The hardware detects the rising edge of the external time reference source and starts a delay counter. When the delay counter counts to reach the alignment delay threshold issued by the SDK, the hardware automatically activates signal generation enable.

[0045] The hardware reset of the G1 / G2 shift register is triggered every 1ms, and the hardware receives the NCO frequency control word and carrier NCO frequency control word sent by the SDK every 1s, which together constitute the timing control algorithm.

[0046] The real-time pseudorange is calculated using the following formula. The difference between the real-time pseudorange and the theoretical pseudorange is fed back to the SDK. Based on the difference, the damping factor parameter is dynamically adjusted to ensure that the real-time pseudorange calculation converges, and the converged pseudorange is obtained.

[0047]

[0048] This is the pseudorange distance deviation correction amount. The cumulative residual value of the code NCO;

[0049] An initial C / A code is obtained by performing an XOR operation between the G1 shift register and the G2 shift register. The initial C / A code is then verified and adjusted using the timing control algorithm and the convergence pseudorange to obtain an analog C / A code.

[0050] After performing an XOR operation between the analog C / A code and the navigation message, the signal is modulated onto the carrier wave and output as 8-bit IQ data to a digital-to-analog converter for digital-to-analog conversion, generating a BeiDou B1I radio frequency signal, which is an analog satellite signal.

[0051] This embodiment provides a pseudorange simulation method for BeiDou B1I signals based on time synchronization, which mainly includes three steps: time synchronization initialization, pseudorange dynamic generation, and signal modulation and output. Specifically:

[0052] Step 1: Time synchronization initialization

[0053] Initialization trigger, when the initialization is valid signal When valid, load the initial parameter code, NCO initial frequency, and G1 / G2 shift register initial phase to complete startup preparation;

[0054] Synchronous control detects the rising edge of an external 1PPS second pulse, starts a delay counter, and when the counter value reaches the alignment delay threshold, the excitation signal generation enable (work=1) is activated, completing the time base alignment.

[0055] Step 2: Dynamic generation of pseudorange

[0056] Timing control: The G1 / G2 shift register is reset every 1ms to update the C / A code phase, ensuring millisecond-level timing matching between the generated chip and the real satellite signal; every 1s, the pseudorange change caused by satellite motion is simulated according to the code NCO frequency control word and carrier NCO frequency control word issued by the SDK.

[0057] Pseudorange calculation, through Module execution core formula Furthermore, based on the residual calculated from the pseudorange, the damping factor is dynamically adjusted to ensure the convergence speed and accuracy of the pseudorange calculation.

[0058] Step 3: Signal Modulation and Output

[0059] The final generated analog C / A code is XORed with the navigation message and then modulated onto the carrier wave to generate 8-bit IQ data. The signal is sent to the DAC (digital-to-analog converter) and finally generates the BeiDou B1I radio frequency signal, which is an analog satellite signal.

[0060] In this embodiment, high-speed chip generation and carrier modulation are mainly achieved through hardware FPGA, and pseudorange distance deviation correction and accuracy adaptation parameters are dynamically calculated using SDK. Specifically:

[0061] FPGA implementation of high-speed chip generation:

[0062] C / A codes are generated by performing an XOR operation using the G1 / G2 shift registers to ensure that the chip structure is completely consistent with the actual satellite signal;

[0063] Precise chip generation rhythm is achieved through built-in timing control. Key control logic includes: resetting the G1 / G2 shift register every 1ms to avoid cumulative chip phase offset and ensure that the chip sequence every millisecond is completely synchronized with the timing of the real satellite signal, further ensuring the accuracy of pseudorange resolution; setting a chip counter to count chips, with a counting range of 0~2045, corresponding to the standard rate of "2046 chips / millisecond" of BeiDou B1I signal, generating 1 chip for each count, and hardware-level counting ensures high speed and zero delay.

[0064] FPGA implementation of carrier modulation:

[0065] The carrier signal is generated through a numerically controlled oscillator (NCO) hardware architecture and supports dynamic frequency adjustment to simulate the carrier characteristics of real satellite signals. The dynamic frequency adjustment involves receiving and updating the carrier frequency correction value (code NCO frequency control word and carrier NCO frequency control word) issued by the SDK every 1 second, thereby changing the frequency of the carrier signal so that the frequency offset of the simulated carrier and the real satellite signal caused by relative motion is completely consistent, ensuring that the receiver can correctly resolve the Doppler component in the pseudorange.

[0066] SDK dynamically calculates pseudorange distance deviation correction and accuracy adaptation parameters:

[0067] The pseudorange distance deviation correction is calculated based on the number of remaining pseudo chips and the current number of milliseconds, derived using the SDK algorithm. Essentially, it reflects the dynamic changes in pseudorange through two real-time variables: the number of remaining chips reflects the chip deviation within the current millisecond, and the current number of milliseconds reflects the timing deviation across milliseconds. The SDK algorithm transforms the "remaining chip deviation" and "timing deviation" into a unified pseudorange distance deviation correction, which is directly applied in the FPGA. The module's pseudorange calculation ensures that the pseudorange calculation takes into account real-time signal propagation deviations;

[0068] The accuracy adaptation parameter is the accuracy deviation calculated after processing the pseudorange distance deviation correction, ensuring that the parameter is compatible with the hardware operation accuracy of the FPGA. (Module bit-width operation requirements).

[0069] In this example, the dynamic generation of pseudorange needs to simulate pseudorange changes caused by satellite motion (such as Doppler shift and pseudorange transmission time changes). These two changes directly correspond to the adjustment requirements of the C / A code frequency and the carrier frequency. Therefore, the core basis for the SDK to calculate the NCO frequency control word and the carrier NCO frequency control word is:

[0070] The calculation of the code NCO frequency control word is based on the changes in C / A code transmission time caused by satellite motion. The relative motion between the satellite and the receiver will cause a slight deviation in the chip transmission time of the C / A code to the receiver. This deviation needs to be simulated by adjusting the generation frequency of the C / A code. The code NCO frequency control word is the code NCO frequency adjustment value calculated by the SDK based on the chip transmission time deviation.

[0071] The basis for the carrier NCO frequency control word: Doppler frequency shift caused by satellite motion. The relative motion between the satellite and the receiver will cause a frequency shift in the carrier signal (Doppler effect). This frequency shift directly affects pseudorange resolution. Therefore, the SDK needs to calculate the carrier NCO frequency control word based on the Doppler frequency shift to adjust the output frequency of the carrier NCO and compensate for the frequency shift deviation.

[0072] The calculation of the NCO frequency control word and the carrier NCO frequency control word is as follows: First, the pseudorange distance deviation correction is calculated using the remaining number of chips and the current number of milliseconds. Then, the chip transmission time deviation and Doppler offset are derived from the pseudorange distance deviation correction. These two physical quantities are then converted into a frequency control word that the NCO can recognize. Finally, the SDK sends the calculated frequency control word to the FPGA to complete the NCO frequency update.

[0073] The real-time pseudorange calculation formula in this embodiment Its construction logic is as follows: the pseudorange distance deviation correction amount is calculated using the remaining chip count and milliseconds (which is also a parameter for dynamically adjusting the damping factor based on the residual). Its function is to compensate for the pseudorange deviation caused by satellite motion and signal propagation, and to adjust the accuracy extension coefficient. The bit width range is increased to be compatible with FPGA hardware operations to avoid loss of operational precision due to excessively small values, and to ensure that the hardware implementation accuracy of pseudorange calculation meets the requirements of nanosecond-level time synchronization. The accumulated residual value of the NCO code is used to compensate for the small precision errors generated by the NCO during frequency adjustment, thereby further improving the accuracy of the final real-time pseudorange value.

[0074] The purpose of setting up a dual-timing control core in this embodiment is to match the characteristics of the C / A code and the satellite motion characteristics respectively, so as to ensure the authenticity of the pseudorange simulation. The specific basis is as follows: the C / A code phase is updated every 1ms. The C / A code rate of the Beidou B1I signal is 1.023MHz, and 2046 chips are generated every millisecond. The G1 / G2 shift register is reset every 1ms, which can accurately match the generation rhythm of the real C / A code and avoid pseudorange errors caused by code phase offset. The NCO frequency is updated every 1s. The satellite motion period is about 11 hours and 58 minutes. Its motion speed relative to the receiver changes slowly. The 1s time interval is sufficient to capture the pseudorange dynamic changes such as Doppler frequency shift and ionospheric delay caused by satellite motion. At the same time, it avoids the waste of system resources due to excessively frequent parameter updates and achieves a balance between accuracy and efficiency.

[0075] The navigation message contains key information such as satellite ephemeris and clock parameters, which are necessary data for the receiver to identify the satellite and calculate its position. In this embodiment, the message is made realistic through caching and dynamic injection. Specifically, during the signal generation process, the cached satellite ephemeris and clock parameters are dynamically injected into the analog signal, so that the analog signal is not only consistent with the real satellite signal in terms of time and pseudorange, but also has complete navigation data characteristics, further ensuring that the general GNSS receiver can be interpreted normally.

[0076] This embodiment addresses the problem that existing positioning schemes cannot fully simulate real satellite signals, leading to receivers' inability to correctly interpret pseudorange information and low positioning accuracy. It proposes a time-synchronized pseudorange simulation method for BeiDou B1I signals to generate navigation signals consistent with real satellite signals in environments without satellite signals, thus inducing a general-purpose GNSS receiver to complete positioning. Specifically, time alignment is triggered by an external 1PPS pulse signal, combined with pseudorange transmission time and alignment delay calculated by the SDK, achieving nanosecond-level synchronization between the simulated signal and the real satellite signal. Based on the C / A code generation logic of the BeiDou B1I signal (G1 / G2 shift register XOR operation), pseudorange changes are simulated in real time. Finally, navigation potentials are buffered via FIFO, and satellite ephemeris and clock parameters are dynamically injected to enhance signal realism.

[0077] The technical solution provided in this embodiment can be widely applied to:

[0078] Indoor positioning provides continuous navigation services in areas without satellite signals, such as shopping malls and underground parking lots.

[0079] Autonomous driving tests generate virtual satellite signals in a closed environment to verify the robustness of the vehicle positioning system.

[0080] In some embodiments, the pseudorange distance deviation correction amount is obtained. include:

[0081] The remaining chip count and current milliseconds are obtained in real time through an internal hardware counter and fed back to the SDK.

[0082] Based on the remaining number of chips and the current number of milliseconds, and using the SDK algorithm, the pseudorange distance deviation correction amount is obtained. and accuracy adaptation parameters The accuracy adaptation parameters Used to process the pseudorange distance deviation correction amount The accuracy deviation.

[0083] In some embodiments, the SDK-issued NCO frequency control word and carrier NCO frequency control word include:

[0084] Based on the pseudorange distance deviation correction amount By reverse calculation, the chip transmission time deviation and Doppler frequency shift can be obtained;

[0085] The chip transmission time deviation is converted into a recognizable NCO frequency control word, and the Doppler frequency shift is converted into a recognizable carrier NCO frequency control word.

[0086] In some embodiments, triggering a hardware reset of the G1 / G2 shift register every 1ms includes:

[0087] The C / A code of Beidou B1I has a complete chip cycle of 1ms. Every 1ms, the hardware reset of the G1 / G2 shift register is triggered, so that the corresponding shift register starts generating chips again from the initial phase.

[0088] In some embodiments, the hardware receives the NCO frequency control word and carrier NCO frequency control word sent by the SDK every 1 second, including:

[0089] The NCO frequency is adjusted by the NCO frequency control word to compensate for changes in chip transmission time, so that the simulated C / A code is consistent with the arrival time of the real satellite signal.

[0090] If the satellite is far from the receiver, the chip transmission time becomes longer, the NCO frequency control word of the code increases, and the NCO frequency of the code is adjusted to increase.

[0091] If the satellite is close to the receiver, the chip transmission time becomes shorter, the NCO frequency control word of the code decreases, and the NCO frequency of the code is adjusted to decrease.

[0092] In some embodiments, the hardware receiving SDK-issued NCO frequency control word and carrier NCO frequency control word triggered every 1 second further include:

[0093] The carrier NCO frequency is adjusted by the carrier NCO frequency control word to compensate for the Doppler frequency shift, so that the frequency shift characteristics of the analog carrier are consistent with the real satellite signal.

[0094] If the satellite is close to the receiver, the carrier NCO frequency control word is increased, and the carrier NCO frequency is adjusted to rise.

[0095] If the satellite moves away from the receiver, the carrier NCO frequency control word decreases, and the carrier NCO frequency is adjusted to decrease.

[0096] In some embodiments, the navigation message is cached via FIFO and satellite ephemeris and clock parameters are dynamically injected.

[0097] In some embodiments, by The module performs calculations of real-time pseudorange and convergence.

[0098] In some embodiments, the external time reference source uses 1PPS second pulses.

[0099] In some embodiments, the hardware is an FPGA module.

[0100] Those skilled in the art will further recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computing software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0101] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0102] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A pseudorange simulation method for BeiDou B1I signals based on time synchronization, characterized in that, include: When initialization valid signal Upon triggering, the hardware loads the code issued by the SDK, including the initial frequency of the NCO and the initial phase of the G1 / G2 shift registers. The hardware detects the rising edge of the external time reference source and starts a delay counter. When the delay counter counts to reach the alignment delay threshold issued by the SDK, the hardware automatically activates signal generation enable. The hardware reset of the G1 / G2 shift register is triggered every 1ms, and the hardware receives the NCO frequency control word and carrier NCO frequency control word sent by the SDK every 1s, which together constitute the timing control algorithm. The real-time pseudorange is calculated using the following formula. The difference between the real-time pseudorange and the theoretical pseudorange is fed back to the SDK. Based on the difference, the damping factor parameter is dynamically adjusted to ensure that the real-time pseudorange calculation converges, and the converged pseudorange is obtained. This is the pseudorange distance deviation correction amount. The cumulative residual value of the code NCO; An initial C / A code is obtained by performing an XOR operation between the G1 shift register and the G2 shift register. The initial C / A code is then verified and adjusted using the timing control algorithm and the convergence pseudorange to obtain an analog C / A code. After performing an XOR operation between the analog C / A code and the navigation message, the signal is modulated onto the carrier wave and output as 8-bit IQ data to a digital-to-analog converter for digital-to-analog conversion, generating a BeiDou B1I radio frequency signal, which is an analog satellite signal.

2. The pseudorange simulation method for BeiDou B1I signals based on time synchronization according to claim 1, characterized in that, The pseudorange distance deviation correction amount is obtained. include: The remaining chip count and current milliseconds are obtained in real time through an internal hardware counter and fed back to the SDK. Based on the remaining number of chips and the current number of milliseconds, and using the SDK algorithm, the pseudorange distance deviation correction amount is obtained. and accuracy adaptation parameters The accuracy adaptation parameters Used to process the pseudorange distance deviation correction amount The accuracy deviation.

3. The pseudorange simulation method for BeiDou B1I signals based on time synchronization according to claim 2, characterized in that, The SDK-issued NCO frequency control word and carrier NCO frequency control word include: Based on the pseudorange distance deviation correction amount By reverse calculation, the chip transmission time deviation and Doppler frequency shift can be obtained; The chip transmission time deviation is converted into a recognizable NCO frequency control word, and the Doppler frequency shift is converted into a recognizable carrier NCO frequency control word.

4. The pseudorange simulation method for BeiDou B1I signals based on time synchronization according to claim 1, characterized in that, The hardware reset of the G1 / G2 shift registers, triggered every 1ms, includes: The C / A code of Beidou B1I has a complete chip cycle of 1ms. Every 1ms, the hardware reset of the G1 / G2 shift register is triggered, so that the corresponding shift register starts generating chips again from the initial phase.

5. The pseudorange simulation method for BeiDou B1I signals based on time synchronization according to claim 1, characterized in that, Every 1 second, the hardware receives the NCO frequency control word and carrier NCO frequency control word sent by the SDK. The NCO frequency is adjusted by the NCO frequency control word to compensate for changes in chip transmission time, so that the simulated C / A code is consistent with the arrival time of the real satellite signal. If the satellite is far from the receiver, the chip transmission time becomes longer, the NCO frequency control word of the code increases, and the NCO frequency of the code is adjusted to increase. If the satellite is close to the receiver, the chip transmission time becomes shorter, the NCO frequency control word of the code decreases, and the NCO frequency of the code is adjusted to decrease.

6. The pseudorange simulation method for BeiDou B1I signals based on time synchronization according to claim 5, characterized in that, Every 1 second, the hardware receives the NCO frequency control word and carrier NCO frequency control word sent by the SDK. The carrier NCO frequency is adjusted by the carrier NCO frequency control word to compensate for the Doppler frequency shift, so that the frequency shift characteristics of the analog carrier are consistent with the real satellite signal. If the satellite is close to the receiver, the carrier NCO frequency control word is increased, and the carrier NCO frequency is adjusted to rise. If the satellite moves away from the receiver, the carrier NCO frequency control word decreases, and the carrier NCO frequency is adjusted to decrease.

7. The pseudorange simulation method for BeiDou B1I signals based on time synchronization according to claim 1, characterized in that, The navigation message is cached in a FIFO and satellite ephemeris and clock parameters are dynamically injected.

8. The pseudorange simulation method for BeiDou B1I signals based on time synchronization according to claim 1, characterized in that, pass The module performs calculations of real-time pseudorange and convergence.

9. The pseudorange simulation method for BeiDou B1I signals based on time synchronization according to claim 1, characterized in that, The external time reference source uses 1PPS second pulses.

10. The pseudorange simulation method for BeiDou B1I signals based on time synchronization according to claim 1, characterized in that, The hardware is an FPGA module.

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