IRNSS navigation signal simulation generation method and system based on parameter compensation

Abstract

The invention relates to an IRNSS navigation signal simulation generation method and system based on parameter compensation, and the method comprises the steps: receiving original signal data outputted by an IRNSS navigation receiver, and receiving a target machine position coordinate and a velocity vector; analyzing the navigation message to extract ephemeris parameters, and calculating the real-time position and velocity vector of the satellite; calculating a Doppler frequency compensation value and a pseudo code time delay compensation value; according to the pseudo code time delay compensation value and a preset target simulation coordinate, modifying a signal emission time field in the navigation message, generating a simulation navigation message frame, carrying out forward error correction coding processing, generating a coding symbol sequence, and carrying out modulo-two addition operation on the coding symbol sequence and a pre-generated PRN pseudo code sequence to obtain a baseband spread spectrum signal; generating an intermediate frequency carrier signal according to the Doppler frequency compensation value and the carrier phase; and modulating the baseband spread spectrum signal to the intermediate frequency carrier signal, and outputting an intermediate frequency analog signal. According to the invention, the concealment of signal simulation and the success rate of capturing the analog signal by the target receiver can be improved.

Description

Technical Field

[0001] This application relates to the field of satellite navigation signal generation, and in particular to a method and system for simulating and generating IRNSS navigation signals based on parameter compensation. Background Technology

[0002] With the widespread application of satellite navigation technology in civil aviation, intelligent transportation, precision agriculture, and autonomous navigation of unmanned platforms, the reliance on GNSS signals is deepening, while also exposing its vulnerabilities in terms of security. Especially in complex electromagnetic environments, how to achieve controllable guidance of specific receiving devices or reconstruct the signal environment within a local space has become a key technological focus in current navigation applications. Against this backdrop, generating analog signals that are highly consistent with real GNSS signals in terms of time-frequency characteristics, modulation structure, and propagation behavior is not only of great significance for the testing and verification of navigation receivers, but also shows potential value in specific application scenarios such as security, airspace management, and intervention against non-cooperative targets.

[0003] Currently, the Indian Regional Navigation Satellite System (IRNSS) is a regional satellite navigation system led by the Indian Space Research Organisation (ISRO), designed to provide independent and reliable positioning, navigation and timing services to users in India and its surrounding area within a radius of approximately 1,500 kilometers.

[0004] However, under current technological conditions, the signal simulation capabilities for the IRNSS regional navigation system remain relatively weak. Compared to systems like GPS or BeiDou, which have established complete simulation ecosystems, IRNSS, due to its limited service range, limited publicly available technical information, and unique signal system, makes it difficult for general-purpose GNSS simulators to directly support accurate reproduction of its signal format. Especially in application scenarios requiring dynamic responses to changes in the external target's state, traditional static signal playback or pre-recorded signal playback methods cannot meet the requirements for real-time performance and consistency. More importantly, when the target receiver is in motion, the navigation signal it receives will experience a significant Doppler shift due to relative motion, accompanied by continuous changes in the pseudocode phase. If the generated simulated signal fails to accurately reflect the temporal evolution of these physical layer parameters, it can lead to problems such as correlation peak splitting and tracking loop loss during the acquisition phase, thereby reducing signal acceptability and fusion capabilities. Summary of the Invention

[0005] To address the aforementioned technical problems, this application provides a method for simulating and generating IRNSS navigation signals based on parameter compensation.

[0006] Firstly, this application provides a method for simulating and generating IRNSS navigation signals based on parameter compensation, employing the following technical solution: A method for simulating and generating IRNSS navigation signals based on parameter compensation, the method comprising: The system receives raw signal data output from the IRNSS navigation receiver, and simultaneously receives the target aircraft's position coordinates and velocity vector provided by external detection equipment; wherein, the raw signal data includes carrier phase, pseudocode phase, and navigation message; The navigation message is parsed to extract ephemeris parameters, and the satellite's real-time position and velocity vector are calculated based on the ephemeris parameters; Based on the target aircraft's position coordinates and velocity vector, as well as the satellite's real-time position and velocity vector, calculate the Doppler frequency compensation value and the pseudocode delay compensation value. Based on the pseudocode delay compensation value and the preset target simulated coordinates, the signal transmission time field in the navigation message is modified to generate a simulated navigation message frame. The simulated navigation message frame is subjected to forward error correction coding to generate a coded symbol sequence, and then modulo-2 addition is performed with the pre-generated PRN pseudocode sequence to obtain the baseband spread spectrum signal. Based on the Doppler frequency compensation value and carrier phase, a frequency-controllable intermediate frequency carrier signal is generated; The baseband spread spectrum signal is modulated onto the intermediate frequency carrier signal to output an intermediate frequency analog signal.

[0007] By adopting the above technical solution, the external sensing information and GNSS internal parameters are deeply integrated. By dynamically compensating for Doppler frequency offset and pseudo-code delay, the generated analog signal is synchronized with the real IRNSS signal in terms of carrier frequency and code phase. This reduces the target receiver's recognition threshold for the analog signal, thereby improving the concealment of the signal simulation and the target receiver's success rate in capturing the analog signal. This provides reliable technical support for applications such as dynamic deception control of UAVs and protection of sensitive areas in specific scenarios.

[0008] Secondly, this application provides an IRNSS navigation signal simulation generation system based on parameter compensation, which adopts the following technical solution: A parameter-compensated IRNSS navigation signal simulation generation system, the system comprising: The data receiving module is used to receive the raw signal data output by the IRNSS navigation receiver, and simultaneously receive the target machine's position coordinates and velocity vector provided by external detection equipment; wherein, the raw signal data includes carrier phase, pseudocode phase and navigation message; The data parsing module is used to parse the navigation message to extract ephemeris parameters and calculate the satellite's real-time position and velocity vector based on the ephemeris parameters; The compensation calculation module is used to calculate the Doppler frequency compensation value and the pseudocode delay compensation value based on the target machine's position coordinates and velocity vector, as well as the satellite's real-time position and velocity vector. The simulation generation module is used to modify the signal transmission time field in the navigation message according to the pseudocode delay compensation value and the preset target simulation coordinates, and generate a simulated navigation message frame. The signal processing module is used to perform forward error correction coding on the analog navigation message frame, generate a coded symbol sequence, and perform a modulo-2 addition operation with the pre-generated PRN pseudocode sequence to obtain the baseband spread spectrum signal. The carrier signal generation module is used to generate a frequency-controllable intermediate frequency carrier signal based on the Doppler frequency compensation value and the carrier phase. The signal modulation module is used to modulate the baseband spread spectrum signal onto the intermediate frequency carrier signal and output an intermediate frequency analog signal.

[0009] Thirdly, this application provides a computer device, which adopts the following technical solution: A computer device includes a memory, a processor, and a computer program stored in the memory, the processor executing the computer program to perform the steps of the method as described in the first aspect.

[0010] Fourthly, this application provides a computer-readable storage medium, which adopts the following technical solution: A computer-readable storage medium storing a computer program that can be loaded by a processor and executed as in any of the methods in the first aspect.

[0011] In summary, this application offers at least one of the following beneficial technical effects: It achieves high-precision simulation and controllable reconstruction of real navigation signals. By comprehensively utilizing key technologies such as ephemeris analysis, Doppler frequency compensation, pseudo-code delay correction, and signal transmission time manipulation, it generates a simulated signal highly consistent with the real IRNSS signal in frequency, code phase, and message structure. This simulated signal possesses strong concealment and protocol compatibility, effectively inducing the target receiver to misjudge its position and gradually lock onto the simulated signal. Its practical significance lies in filling the gap in navigation simulation technology for IRNSS systems, providing crucial technical support for the development of satellite navigation safety testing, anti-UAV jamming systems, and regional electronic warfare equipment, and possessing promising application prospects and engineering deployment value. Attached Figure Description

[0012] Figure 1 This is a first flowchart illustrating a parameter-compensated IRNSS navigation signal simulation generation method according to one embodiment of this application.

[0013] Figure 2This is a second flowchart illustrating a parameter-compensated IRNSS navigation signal simulation generation method according to one embodiment of this application.

[0014] Figure 3 This is a third flowchart illustrating a parameter-compensated IRNSS navigation signal simulation generation method according to one embodiment of this application.

[0015] Figure 4 This is a schematic diagram of the fourth process of the parameter-compensated IRNSS navigation signal simulation generation method according to one embodiment of this application.

[0016] Figure 5 This is a fifth flowchart of a parameter-compensated IRNSS navigation signal simulation generation method according to one embodiment of this application.

[0017] Figure 6 This is a schematic diagram of the sixth step of the parameter-compensated IRNSS navigation signal simulation generation method according to one embodiment of this application.

[0018] Figure 7 This is a schematic diagram of the seventh process of a parameter-compensated IRNSS navigation signal simulation generation method according to one embodiment of this application.

[0019] Figure 8 This is a schematic diagram of the IRNSS main frame structure of one embodiment of this application.

[0020] Figure 9 This is a schematic diagram of the specific field layout of subframe 1 and subframe 2 in one embodiment of this application.

[0021] Figure 10 This is a schematic diagram of the bit layout of the DATA field in subframe 1 and subframe 2, which is one embodiment of this application.

[0022] Figure 11 This is a schematic diagram of the intermediate frequency signal output process according to one embodiment of this application.

[0023] Figure 12 This is a schematic diagram of the execution flow of the forward error correction coding module according to one embodiment of this application.

[0024] Figure 13 This is a schematic diagram of the shift operation of the feedback shift register according to one embodiment of this application. Detailed Implementation

[0025] To make the purpose, technical solution, and advantages of this application clearer, the following description is provided in conjunction with the appendix. Figure 1-13 The present application will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the application.

[0026] This application discloses a method for simulating and generating IRNSS navigation signals based on parameter compensation.

[0027] Reference Figure 1 A method for simulating and generating IRNSS navigation signals based on parameter compensation, the method comprising, Step S101: Receive the raw signal data output by the IRNSS navigation receiver, and simultaneously receive the target aircraft's position coordinates and velocity vector provided by the external detection equipment; The raw signal data includes carrier phase, pseudocode phase, and navigation message; Specifically, the carrier phase reflects the instantaneous frequency change of the signal during transmission caused by the Doppler effect and can be used as a reference for subsequent frequency compensation; the pseudo-code phase records the time offset of the spreading code sequence relative to the local reference code, directly determining the pseudorange measurement result; and the navigation message, as a data stream containing key information such as ephemeris, almanac, and clock correction parameters, provides the necessary basis for reconstructing the satellite's orbital state. Meanwhile, the target aircraft's three-dimensional coordinates and its velocity vector provided by external detection equipment such as radar, electro-optical tracking systems, or cooperative communication links provide the necessary prior conditions for constructing spatial geometric relationships. Although this type of information does not depend on GNSS itself, as an auxiliary sensing means, it can significantly improve the spatial consistency and temporal continuity of analog signals, making the generated signals more consistent with the requirements of the real physical propagation environment.

[0028] Understandably, the dual-source data fusion, namely the "GNSS receiver + external sensing" architecture, constitutes the prerequisite for this solution to achieve accurate parameter prediction.

[0029] Step S102: Analyze the navigation message to extract ephemeris parameters, and calculate the satellite's real-time position and velocity vector based on the ephemeris parameters; The ephemeris parameters are a set of precise parameters describing the satellite's orbital state, typically distributed across subframes 1 and 2. These include the six Keplerian parameters (mean anomaly, eccentricity, square root of semi-major axis, ascending node longitude, perigee argument, and orbital inclination), orbital perturbation corrections, and a time reference. Using a standard orbital mechanics model, combined with the Earth's gravitational constant μ and the time of week (TOW) at the time of signal transmission, the satellite's precise position and velocity vectors in the geocentric-ground-fixed (ECEF) coordinate system can be iteratively solved.

[0030] Specifically, the mean anomaly angle E is first solved using Newton's iteration method with the mean anomaly angle M and the eccentricity e. Then, the true anomaly angle ν is calculated from E. Finally, the satellite's position in the orbital coordinate system is obtained by combining the geometric relationships within the orbital plane. Finally, the position is transformed to the ECEF coordinate system using a coordinate rotation matrix. This process ensures a high-fidelity reproduction of the satellite's dynamic behavior, laying an accurate spatiotemporal foundation for subsequent Doppler effect analysis and pseudorange calculations.

[0031] It should be noted that since the IRNSS system uses dual-frequency broadcasting in L5 (1176.45 MHz) and S-band (2492.028 MHz), the propagation characteristics at different frequencies are slightly different. However, in this application embodiment, the modeling is mainly based on the L5 band, because it has stronger atmospheric penetration capability and is widely used in civilian standard positioning services.

[0032] Step S103: Based on the target aircraft's position coordinates and velocity vector, as well as the satellite's real-time position and velocity vector, calculate the Doppler frequency compensation value and the pseudocode delay compensation value. The Doppler frequency variation originates from the relative motion between the signal source and the receiver, manifesting as a shift in the received frequency relative to the transmitted frequency during radio signal propagation. For this system, two Doppler effects need to be considered: first, the Doppler frequency shift caused by the relative motion between the satellite and the target aircraft; and second, the additional frequency shift caused by the relative displacement between the jammer (i.e., the platform where the signal simulation device is located) and the target aircraft.

[0033] Specifically, the former can be obtained by projecting the satellite's velocity vector onto the line connecting it to the target receiver to obtain the radial velocity component. Dividing this by the speed of light *c* and multiplying by the carrier frequency *f0* yields the corresponding Doppler frequency shift. The latter depends on the rate of change of distance between the jammer and the target receiver; if there is relative motion between them, additional frequency deviation will also occur. To ensure seamless access and stable tracking of the generated analog signal at the target receiver, both of these effects must be considered comprehensively, and corresponding frequency compensation must be applied in the local signal generator through negative feedback. Therefore, the final Doppler frequency compensation value should be the sum of the two factors mentioned above, ensuring that the carrier frequency of the generated signal is strictly consistent with the desired receiving frequency, thus avoiding correlation peak broadening or even loss of lock due to excessive frequency difference.

[0034] Meanwhile, the determination of the pseudocode delay compensation value aims to achieve precise alignment of the spreading code sequence on the time axis. Since the real navigation signal requires a certain time delay to propagate from the satellite to the target device, corresponding to the geometric distance between the satellite and the ground divided by the speed of light, and the signal generated in this embodiment is transmitted from the local device and arrives at the same target via a shorter path, the starting phase of the local PRN code must be adjusted to start it "advanced" in time so that it presents the same arrival time as the original signal at the target end.

[0035] Specifically, first calculate the true pseudorange ρ from the satellite to the target aircraft. st And the actual pseudorange ρ from the satellite to the jammer sj The difference between the two is Δρ = ρ st -ρ sj This represents the required distance increment for simulation. Furthermore, the actual transmission distance L between the jammer and the target must also be considered. Therefore, the total code phase compensation delay τ can be expressed as (Δρ-L) / c, where c is the speed of light in a vacuum. This formula embodies the core idea of ​​signal propagation path reconstruction: it not only compensates for the difference in distance between the satellite and the ground but also covers the influence of the local transmission path, thereby ensuring that the total effective propagation time is consistent with expectations. This compensation mechanism is not only applicable to static scenarios but can also be extended to dynamic trajectory simulation, supporting continuous position guidance functions.

[0036] Step S104: Based on the pseudocode delay compensation value and the preset target simulated coordinates, modify the signal transmission time field in the navigation message to generate a simulated navigation message frame. Specifically, based on the calculated pseudocode delay compensation value and the preset target simulated coordinates, the signal transmission time field (i.e., Time of Week Count, TOWC) in the original navigation message is modified to generate a new navigation message frame structure. The TOWC field records the number of seconds within the GPS week to which the navigation message was sent, and is a key timestamp for the receiver to calculate the pseudorange.

[0037] Specifically, by substituting the target's simulated coordinates into the geometric model, the theoretical pseudorange at that position is recalculated and compared with the original pseudorange to obtain the time correction. This time correction is then superimposed on the original TOWC value to form the updated transmission time stamp. This timestamp reconstruction strategy is essentially a non-intrusive data repackaging operation that preserves the validity of the original ephemeris parameters while introducing controllable positional deviation information, enabling the receiver to calculate a position result conforming to a predetermined trajectory based on the updated message content.

[0038] The entire process strictly follows the frame structure specifications defined in the IRNSS ICD document, ensuring that the bit layout, parity check, Hamming coding, and other formats in subframe 1 and subframe 2 are correct and error-free, thus guaranteeing the protocol compatibility and receiver recognition of the signal.

[0039] Step S105: Perform forward error correction coding on the analog navigation message frame to generate a coded symbol sequence, and perform modulo-2 addition with the pre-generated PRN pseudocode sequence to obtain the baseband spread spectrum signal. The modified analog navigation message frame undergoes forward error correction (FEC) coding to enhance its anti-interference capability and transmission reliability. The IRNSS system employs convolutional coding or a similar linear block code mechanism, applying specific generator polynomials G1(x) and G2(x) to each bit of raw data for recursive operations to generate coded outputs from two branches, which are ultimately combined into a symbol sequence with doubled rate.

[0040] Specifically, the encoding process is implemented internally within the FPGA by a high-speed clock: the original message data is loaded bit by bit into the input register on the rising edge of the 25Hz master clock; logical operations are performed within each cycle, and the results are sent to the shift register chain; simultaneously, a 50Hz clock controls the output selector switching mechanism, ensuring that each original bit corresponds to two encoded symbols, achieving a 1:2 symbol spread ratio. This approach not only effectively combats bit errors caused by channel noise but also improves the spreading gain, which is beneficial for enhancing subsequent related detection performance.

[0041] Next, the FEC-encoded symbol sequence is modulo-2 added (i.e., XOR operation) with the pre-generated PRN pseudo-random noise code sequence to complete the spread spectrum modulation. The PRN code is a binary sequence with excellent autocorrelation properties. The IRNSS system uses the Gold code as the unique identifier for each satellite, with a length of 1023 chips and a code rate of 1.023 Mcps.

[0042] In this embodiment, the PRN code consists of two 10-level linear feedback shift registers, which generate basic sequences according to G1 and G2 polynomials respectively, and then synthesize the final satellite-specific code pattern through modulo-2 addition. The essence of the spread spectrum process is to expand low-speed information data into a high-speed broadband signal, greatly improving the signal's concealment and anti-interception capability. The output baseband spread spectrum signal has a rate as high as 1.023 Mbps and possesses good noise-class characteristics, making it easy to combine with the carrier in subsequent mixing processes.

[0043] Step S106: Generate a frequency-controllable intermediate frequency carrier signal based on the Doppler frequency compensation value and carrier phase; Specifically, after baseband processing is completed, a frequency-controllable intermediate frequency (IF) carrier signal needs to be constructed to carry the spread spectrum information. Considering the significant hardware challenges in directly generating L5 or S-band RF signals, especially given the extremely high requirements for frequency resolution and phase continuity, this embodiment employs Direct Digital Synthesis (DDS) to generate stable IF sine / cosine waveforms. The core of the DDS module is a phase accumulator, whose step value is determined by the frequency control word (FCW), which is dynamically configured by the ARM processor based on the aforementioned calculated Doppler frequency compensation value.

[0044] For example, if the nominal intermediate frequency is 4.092 MHz (i.e., 4 times 1.023 Mcps), when a Doppler shift of +5 kHz is detected, the FCW increases accordingly, making the output carrier frequency 4.097 MHz, thus achieving fine frequency adjustment. The advantages of DDS are fast frequency switching speed, good phase continuity, and high resolution, making it very suitable for real-time variable parameter navigation signal simulation scenarios.

[0045] Step S107: Modulate the baseband spread spectrum signal onto the intermediate frequency carrier signal and output the intermediate frequency analog signal.

[0046] This modulation typically employs double-sideband suppressed carrier (DSB-SC) or BPSK modulation, where the spread-spectrum ±1 level signal is multiplied by the carrier to form an analog intermediate frequency (IF) signal output. This signal is then converted to analog voltage form by a DAC and shifted to the L5 or S operating frequency band via an up-conversion circuit, ultimately being radiated to the target receiving area through an antenna. In the entire signal generation chain, the ARM processor handles high-level algorithm processing, including message parsing, ephemeris calculation, parameter compensation calculation, and frame assembly; while the FPGA undertakes the low-level high-speed real-time tasks, covering FEC encoding, PRN code generation, spread-spectrum modulation, and DDS carrier synthesis. The two interact efficiently through the AXI4-Lite or AXI-Stream bus, achieving hardware-software co-optimization.

[0047] In addition, the system also has an intelligent simplification mechanism: when the target is stationary, its velocity vector is zero and the Doppler change between the satellite and the target tends to be stable. At this time, the dynamic frequency compensation module can be turned off to reduce power consumption. Similarly, when the jammer is very close to the target (e.g., less than 10 meters), the L term can be ignored and the pseudo-code delay compensation can also be omitted, further improving operating efficiency without affecting overall performance.

[0048] In the above implementation, external sensing information and GNSS internal parameters are deeply integrated. By dynamically compensating for Doppler frequency offset and pseudo-code delay, the generated analog signal is synchronized with the real IRNSS signal in terms of carrier frequency and code phase. This reduces the target receiver's recognition threshold for the analog signal, thereby improving the concealment of the signal simulation and the target receiver's success rate in capturing the analog signal. This provides reliable technical support for applications such as dynamic deception control of UAVs and protection of sensitive areas in specific scenarios.

[0049] Reference Figure 2 As one implementation of step S103, the step of calculating the Doppler frequency compensation value based on the target machine's position coordinates and velocity vector, and the satellite's real-time position and velocity vector, includes: Step S201: Obtain the target aircraft velocity vector, jammer position coordinates, target aircraft position coordinates, and satellite real-time velocity vector; These data come from ephemeris information provided by external detection equipment (such as radar or electro-optical tracking systems) and GNSS receiving modules, forming the basic input for subsequent vector calculations.

[0050] Step S202: Calculate the line-of-sight vector from the jammer to the target machine based on the difference between the jammer's position coordinates and the target machine's position coordinates; Among them, the line-of-sight vector reflects the spatial direction of the signal propagation from the jammer to the target machine, and is a key geometric reference for judging the relative motion state between the two. Step S203: Based on the projection component of the target machine's velocity vector onto the line-of-sight vector, generate the first relative velocity scalar between the jammer and the target machine; The first relative velocity scalar represents the rate at which the target aircraft approaches or moves away from the local signal transmission point along the propagation path. For example, this value is negative (indicating a shortening distance) when the target UAV is flying towards the jammer, and positive otherwise. The existence of this component means that even if the satellite is stationary, the locally generated signal still needs to account for the additional frequency shift caused by the target's movement; otherwise, phase mismatch will occur.

[0051] Step S204: Calculate the relative motion velocity vector of the satellite relative to the target aircraft based on the satellite velocity vector and the target aircraft velocity vector; The relative velocity vector describes the overall motion trend of the satellite relative to the target receiver and is the core basis for Doppler estimation in traditional GNSS receivers. However, directly using this vector is insufficient to obtain the frequency control quantity that can be used for modulation; its effective components along the actual signal propagation path must be further determined.

[0052] Step S205: Determine the satellite signal propagation direction vector based on the direction of the line connecting the real-time satellite position and the target aircraft position coordinates; The satellite signal propagation direction vector represents the propagation path of the real navigation signal from the satellite to the target aircraft, and is also the main axis of action for the Doppler effect.

[0053] Step S206: Extract the projection component of the relative motion velocity vector onto the satellite signal propagation direction vector to generate a second relative velocity scalar between the satellite and the target aircraft; The second relative velocity scalar represents the relative approach speed between the satellite and the target aircraft in the line-of-sight direction, which directly affects the magnitude of the carrier frequency change.

[0054] Step S207: Divide the first relative velocity scalar by the IRNSS signal carrier wavelength to obtain the first Doppler frequency component; Step S208: Divide the second relative velocity scalar by the IRNSS signal carrier wavelength to obtain the second Doppler frequency component; Step S209: Superimpose the first Doppler frequency component and the second Doppler frequency component to output the Doppler frequency compensation value.

[0055] Specifically, the first relative velocity scalar v proj1 Second relative velocity scalar v proj2 Dividing by the same carrier wavelength λ yields two independent Doppler frequency components: The first Doppler frequency component is f d1 =v proj1 / λ, the second Doppler frequency component is f d2 =v proj2 / λ; The former reflects the additional frequency shift introduced by target motion in the local forwarding path, while the latter corresponds to the classical Doppler frequency shift in the original satellite-to-ground link. These two components essentially represent frequency deviations on different physical paths, but they must be uniformly processed during the final signal synthesis. Therefore, an algebraic superposition method is used to merge them: f d =f d1 +f d2 .

[0056] The final output total Doppler frequency compensation value f d The frequency control word is written into the DDS (Direct Digital Frequency Synthesis) module in the FPGA to dynamically adjust the intermediate frequency carrier frequency, ensuring that the carrier frequency of the generated signal is always consistent with the signal that should be received in the target environment.

[0057] In the above embodiments, a dual-path relative motion analysis model is established, comprehensively considering the dynamic frequency shift factors in the two propagation links from the satellite to the target and from the jammer to the target, thus achieving refined modeling of Doppler frequency compensation. This technical solution combines spatial vector projection and physical law mapping, enabling accurate reconstruction of signal carrier characteristics in complex dynamic environments, ensuring high consistency and continuity of the generated signal in the frequency dimension, thereby supporting stable acquisition and tracking by the receiver.

[0058] Reference Figure 3 As another implementation of step S103, the step of calculating the pseudocode delay compensation value based on the target machine's position coordinates and velocity vector, and the satellite's real-time position and velocity vector, includes: Step S301: Calculate the straight-line transmission distance between the jammer and the target machine based on their position coordinates; Among them, based on the known jammer location (x) i ,y i ,z i ) and target machine position (x t ,y t ,z t The straight-line transmission distance L between the two is calculated using the Euclidean distance formula, which is expressed as follows: ; This distance represents the actual airborne propagation path length of the simulated signal from the transmitter to the receiver, and is one of the key parameters for constructing the equivalent propagation delay. Since this path segment is independent of the satellite-to-ground link, it needs to be considered separately in the entire signal time reconstruction model. This calculation method is based on a three-dimensional Cartesian coordinate system, is applicable to relative positioning scenarios under arbitrary terrain conditions, and does not rely on the geoid or projected coordinate transformations, exhibiting high versatility and computational efficiency.

[0059] Step S302: Calculate the first pseudorange from the satellite to the target aircraft based on the real-time position of the satellite and the position coordinates of the target aircraft; The first pseudorange is not a purely geometric distance, but a comprehensive ranging quantity that includes multiple error terms such as satellite clock error, receiver clock error, ionospheric delay, tropospheric delay, and hardware delay. However, in this scheme, to simplify modeling and focus on relative time delay relationships, it can be approximated as a purely geometric distance and calculated using the Euclidean distance formula.

[0060] Step S303: Calculate the second pseudorange from the satellite to the jammer based on the real-time position of the satellite and the position coordinates of the jammer. The same method was used to calculate the second pseudorange between the satellite and the jammer. The first and second pseudoranges reflect the spatial distance difference between the same satellite and two different observation points, forming the basis for subsequent bias analysis.

[0061] Step S304: Based on the difference between the first pseudorange and the second pseudorange, obtain the pseudorange deviation. Specifically, the difference between the first pseudorange and the second pseudorange is used to obtain the pseudorange deviation Δρ = ρ st -ρ sj This difference essentially reflects the range variation caused by the target aircraft's positional shift relative to the jammer in the satellite-to-ground line-of-sight direction. If the target aircraft is in front of the jammer, then ρ st >ρ sj A deviation is positive; otherwise, it is negative.

[0062] However, using only this difference as the basis for compensation still has significant errors because the total path of the real signal from the satellite to the target is "satellite → target," while the path of the locally generated signal is "satellite → jammer → target," with an additional local relay path L between the two. If this is not corrected, the generated signal will be too advanced or too late in time, causing the receiver correlator to fail to lock or to exhibit periodic jitter.

[0063] Step S305: The net pseudorange difference is generated by subtracting the straight-line transmission distance from the pseudorange deviation. Net pseudo-distance difference represents the net distance increment of the target machine relative to the jammer on the overall propagation path after eliminating the influence of the local forwarding path.

[0064] It should be noted that only when this net pseudorange difference is zero can the locally generated signal completely reproduce the state of the original signal arriving at the target aircraft in time. If the net pseudorange difference is positive, it means that the target aircraft is farther away from the satellite than the jammer, so the code phase of the local signal needs to be appropriately delayed; if it is negative, the opposite is true.

[0065] Step S306: Divide the net pseudo-range difference by the speed of light and output the pseudo-code delay compensation value.

[0066] This delay value, output in seconds, is used to adjust the starting phase of the local PRN code generator. For example, if τ = 50 ns is calculated, it means the local spreading code should start 50 nanoseconds later than the original signal to match the actual reception timing at the target device. This compensation mechanism is not only applicable to static scenarios but can also achieve continuous tracking in dynamic environments by updating coordinate points in real time, supporting trajectory-guided applications.

[0067] It should be noted that when the straight-line transmission distance L between the jammer and the target is extremely small (e.g., less than 10 meters), its impact on the overall propagation path is negligible. Under this condition, the system can automatically enter simplified mode, directly setting the net pseudorange difference as the pseudorange deviation, i.e., net pseudorange difference = Δρ, thus omitting the subtraction operation, reducing computational overhead without affecting accuracy. This adaptive optimization strategy improves the system's operating efficiency, and is particularly suitable for close-range collaborative operations or integrated deployment scenarios.

[0068] The above implementation fully considers the integrity of the signal propagation path, introduces the concept of net pseudorange difference to effectively eliminate path redundancy introduced by local forwarding, and achieves spatiotemporal consistency matching between the generated signal and the target receiving environment. Simultaneously, combined with a threshold judgment mechanism, it possesses good computational flexibility and resource adaptability, making it suitable for real-time navigation signal simulation systems on embedded platforms.

[0069] Reference Figure 4 As one implementation of step S104, the step of modifying the signal transmission time field in the navigation message and generating a simulated navigation message frame based on the pseudocode delay compensation value and the preset target simulated coordinates includes: Step S401: Obtain the pseudocode delay compensation value and the preset target simulated geographic coordinates; The pseudocode delay compensation value reflects the actual propagation delay from the jammer to the target and the time offset introduced by the local forwarding path; the target simulated geographic coordinates represent the desired location point calculated by the receiver, which can be a static coordinate or a position at a certain moment on a dynamic trajectory. These two parameters together form the basis for the subsequent generation of time correction values.

[0070] In this embodiment, the pseudocode delay compensation value is derived from the accurate modeling of the difference between the real satellite signal propagation path and the locally generated path, ensuring the physical consistency of the generated signal with the target environment on the time axis; while the target simulation coordinates reflect the functional requirements at the application level, such as for testing, simulation or regional guidance scenarios.

[0071] Step S402: Calculate the pseudorange deviation between the simulated geographic coordinates of the target and the position coordinates of the target aircraft. Here, the pseudorange deviation is not the actual ranging error, but rather refers to the distance ρ from the satellite to the target position from the same satellite's perspective. d Distance ρ to the actual target location t The difference Δρ between them. This difference represents the additional distance change perceived by the receiver if it uses the modified signal timestamp for positioning.

[0072] For example, when the simulated target position is in front of the satellite's line of sight, Δρ>0, meaning that the signal propagation time needs to be extended to match a greater distance. This calculation process relies on high-precision ephemeris data and vector operations in a geocentric-geocentric coordinate system, ensuring the accuracy of spatial geometric relationships.

[0073] Based on this, the system further converts the pseudorange deviation value into an equivalent time deviation component Δt. range Since electromagnetic waves propagate at the speed of light c≈3×10⁸ m / s, unit conversion can be achieved using the following formula: Δt range =Δρ / c; This time deviation component represents the additional or reduced signal flight time required for the receiver to perceive the signal as originating from the simulated direction of the target.

[0074] Step S403: Based on the pseudocode delay compensation value and pseudorange deviation value, generate the signal transmission time correction amount; It should be noted that considering only this component is insufficient to achieve complete time alignment, because the local signal generation system itself has inherent delays caused by the forwarding path, i.e., the pseudocode delay compensation value τ calculated earlier. delay Therefore, the two need to be algebraically added together to generate the final signal transmission time correction ΔT, as shown in the formula: ΔT=Δt range +τ delay ; This correction factor combines two aspects: first, the active time offset required for positioning guidance (provided by Δtrange); and second, the passive latency introduced by the local hardware link (by τ). delay (Compensation). This dual compensation mechanism ensures that the timing adjustment satisfies the functional objectives while maintaining the physical rationality of the signal timing, avoiding problems such as phase jumps or correlation peak lock-out.

[0075] Step S404: Read the signal transmission time field value from the navigation message; The system reads the signal transmission time field, or Time of Week Count (TOWC), carried in the original IRNSS navigation message. This field records the precise time (in seconds, relative to the start of the current GPS week) when the navigation signal was transmitted from the satellite, and is one of the key bases for the receiver to calculate pseudorange. According to the IRNSS interface control document ISRO-IRNSS-ICD-SPS-1.1, TOWC is usually encoded with a one-position width (e.g., 17 bits), representing an integer value in the range of 0 to 2n−12n−1 seconds. Therefore, the issue of numerical overflow must be considered before performing the superposition operation on the original TOWC value.

[0076] Step S405: The signal transmission time field value is added together with the signal transmission time correction amount to update the signal transmission time field in the navigation message; The system performs a superposition operation on the original TOWC value and the aforementioned correction amount ΔT, and then uses a modulo operation to truncate the value: TOWC new =(TOWC old +ΔT)mod 2 n ; Here, n is the bit width of the TOWC field. This operation ensures that the updated value strictly conforms to the encoding format specified in the protocol, preventing frame parsing failure or receiver malfunction due to out-of-bounds errors. For example, if the original TOWC is 604799 seconds (close to the end of a week), and the correction is +10 seconds, the new value should be 9 seconds instead of 604809 seconds, reflecting the cyclical nature of time. This compliance processing ensures the recognizability and compatibility of the generated message, enabling it to be received and decoded normally by a standard IRNSS receiver.

[0077] Step S406: Based on the predefined frame structure, the updated signal transmission time field and other navigation parameters are recombined into an analog navigation message frame.

[0078] Specifically, based on the frame structure defined by the IRNSS standard (such as the arrangement of subframes 1 to 4, bit order, and check mechanism), the updated TOWC field and other unchanged navigation parameters (such as ephemeris, clock bias, and health status) are re-encapsulated into a complete analog navigation message frame. This frame data is transmitted to the FPGA via the AXI bus or other high-speed interface for subsequent spread spectrum modulation and intermediate frequency signal generation.

[0079] It should be noted that during the entire reorganization process, fields other than TOWC can be updated synchronously depending on the application scenario, such as maintaining the validity of the original ephemeris or injecting virtual orbital parameters to support long-term simulation.

[0080] Furthermore, for dynamic application scenarios, such as when the simulated coordinates of the target change continuously over time (e.g., simulating a movement trajectory), the system can incorporate a kinematic model for iterative optimization. Specifically, by combining the target's velocity vector and acceleration information, the system predicts its position at the next moment in real time and dynamically updates the pseudorange deviation value Δρ and the corresponding time correction ΔT, thereby achieving smooth and continuous message updates. This approach is not only applicable to static deviation induction but can also be extended to simulate navigation response behavior under complex motion paths, enhancing the system's flexibility and practicality.

[0081] In the above embodiments, a closed-loop mapping mechanism from target spatial coordinates to signal time parameters is established, and a high-precision, protocol-compatible analog navigation message generation method is proposed. This method fully integrates spatial geometric analysis, time delay compensation, and communication protocol constraints, realizing the controllable reconstruction of key fields of the navigation message. While ensuring the legality of the signal, it also supports the receiver output of predetermined spatial location information.

[0082] Reference Figure 5 As one implementation of step S105, the steps of performing forward error correction coding on the analog navigation message frame to generate a coded symbol sequence, and performing modulo-2 addition with the pre-generated PRN pseudocode sequence to obtain the baseband spread spectrum signal include: Step S501: Receive the analog navigation message frame and the pre-generated PRN pseudocode sequence; Among them, the pre-configured or dynamically generated PRN pseudocode sequence is used to uniquely identify a virtual satellite signal source and serves as a spreading factor to achieve bandwidth expansion.

[0083] Step S502: Input the analog navigation message frame into the forward error correction encoder and perform a linear feedback shift operation under the control of the first clock domain; The forward error correction encoder employs a linear feedback shift register (LFSR) architecture, performing bit-by-bit shift operations driven by the first clock domain—the 25Hz master clock. With each rising edge of the previous clock cycle, a new data bit is shifted into the head of the register chain. Simultaneously, a feedback value is calculated based on a preset generator polynomial and injected into the first and second inputs, forming a closed-loop recursive structure. This design essentially implements convolutional coding or Gold code-like coding mechanisms, significantly improving the error tolerance of transmitted data.

[0084] Specifically, the system employs two sets of specific generator polynomials: ; In this embodiment, the forward error correction coding module includes two six-level linear feedback shift registers, which operate according to the following feedback logic: the feedback input of the first register G1 is the modulo-2 addition result of the outputs Q1, Q2, Q3, and Q6 at each level; the feedback input of the second register G2 is the modulo-2 addition result of Q2, Q3, Q5, and Q6. The encoder sequentially outputs the least significant bit of G1 and G2 at the current time within each information bit period, forming a double-symbol coding sequence.

[0085] Step S503: Drive the symbol output selector through the second clock domain to extract the encoded symbol from the shift register state; Specifically, a second clock domain—a high-speed clock signal with a frequency of 50Hz—is introduced to drive the symbol output selector, enabling the conversion from low-speed data to a double-rate symbol stream. Each time the rising edge of the 50Hz clock arrives, the selector triggers a sampling operation, reading one bit of status value from the outputs of the G1 and G2 shift registers at the current moment, and alternately selecting one of them as the current output symbol according to a preset rule. Specifically, within each pair of consecutive 50Hz cycles: the output of G1 is selected in the first cycle, and the output of G2 is selected in the second cycle, forming a symbol pair structure such as G1_out, G2_out. This alternating switching mechanism essentially achieves time interleaving of the two pseudocode sequences, thereby constructing a composite coded symbol stream.

[0086] Step S504: Merge two consecutive coded symbols to form a symbol group, generating a double-rate coded symbol sequence; Since the original message rate is 25bps, and the IRNSS standard requires each information bit to be expanded into two symbols (i.e. BPSK(2) modulation), two independent coded symbols need to be output within a 25Hz cycle.

[0087] Therefore, a symbol selection operation is triggered on each rising edge of the 50Hz clock: the first half-cycle selects the output bits from the G1 polynomial, and the second half-cycle selects the output bits from the G2 polynomial, forming an alternating switching mechanism. This process essentially time-multiplexes the outputs of the two LFSRs to form a composite symbol sequence. For example, when the input data is "1", after processing by the two polynomials, it may result in "1" and "0", so the symbols "1" and "0" are output sequentially within one cycle to form a symbol group. Thus, the continuously extracted coded symbols are arranged in chronological order to form a double-rate coded symbol sequence with a rate of 50 symbols / s.

[0088] It should be noted that the dual-rate symbol stream is not a simple repetition or zero-insertion operation, but rather an asynchronous interleaved output based on two independent pseudocode generation paths. This results in stronger randomness and spectral flatness, which is beneficial for improving the correlation detection performance of the signal at the receiver. Furthermore, since the two polynomial outputs maintain orthogonality in time and logic, the generated symbol sequence has good statistical uniformity, avoiding the carrier recovery difficulties caused by prolonged consecutive "0"s or "1"s.

[0089] Step S505: Perform a modulo-2 addition operation on the encoded symbol sequence and the PRN pseudocode sequence to output the baseband spread spectrum signal.

[0090] Specifically, the generated 50symbols / s encoded symbol sequence is subjected to modulo-2 addition (i.e., XOR operation) with the PRN pseudocode sequence.

[0091] The PRN code is generated by two 10-stage linear feedback shift registers operating in parallel at a high-speed clock of 1.023MHz. Its output, after modulo-2 addition, forms a long-period pseudo-random sequence with a rate of 1.023Mcps, conforming to the spreading code rate standard of the IRNSS SPS signal. Since each information symbol lasts for 20ms (corresponding to 50 symbols / s), and each PRN chip width is approximately 977.5ns (1 / 1.023M), each symbol is spread into approximately 2046 chips, achieving a speed of up to 10log... 10 The processing gain is approximately 46 dB (1.023M / 25). The essence of the modulo-2 addition operation is to embed low-speed information into high-speed pseudo-code, so that the output signal exhibits broadband characteristics similar to white noise in the frequency domain, and has strong anti-narrowband interference capability.

[0092] The final output baseband spread spectrum signal is a binary sequence with a rate of 1.023 Mbps, where each bit is determined by the original navigation information after double encoding and spread spectrum processing. This signal can be directly fed into a subsequent digital upconverter (DUC) or DAC for intermediate frequency modulation, or it can be buffered for multi-channel synchronous transmission. The entire spread spectrum process is completed at the FPGA hardware level, leveraging its parallel computing advantages to ensure real-time performance and deterministic latency.

[0093] In the above embodiments, a forward error correction coding architecture driven by dual clock domains is constructed. Combined with multi-state polynomial feedback and symbol interleaving mechanisms, efficient mapping from the 25bps raw message to the 1.023Mcps spread spectrum signal is achieved. This technical solution not only strictly adheres to the technical specifications of the IRNSS interface control document but also enhances the robustness and concealment of the signal through optimized coding structure, making it suitable for high-fidelity navigation signal simulation systems.

[0094] Reference Figure 6 As one implementation of step S502, the first clock domain is a 25Hz clock signal, and the second clock domain is a 50Hz clock signal; the step of performing the linear feedback shift operation includes: Step S601: Calculate the feedback value according to the preset generator polynomial; Based on two independently defined generator polynomials G1 and G2, two sets of parallel-running six-stage feedback shift registers are constructed. The feedback logic of G1 is expressed as: Input⊕Q1⊕Q2⊕Q3⊕Q6, indicating that the bit value newly input to the register's head is determined by the XOR operation result of a specific position in the current outputs Q1 to Q6. Similarly, the feedback logic of G2 is Input⊕Q2⊕Q3⊕Q5⊕Q6, reflecting a different set of connection relationships. Here, "Input" does not refer to direct external data injection, but rather to the recursive value rewritten to the head after calculation by the feedback network, forming a closed-loop recursive structure.

[0095] In step S602, the data sequence bits are shifted into the first stage of the shift register at the rising edge of the clock, and the feedback value is injected into the first stage input at the same time.

[0096] When the system receives the original analog navigation message frame data sequence, the bit stream enters the encoder module bit by bit at a rate of 25 bps, and triggers each shift operation under the drive of the first clock domain (i.e., the 25 Hz master clock). At the arrival of each clock rising edge, the current data bit is shifted into the first stage of the shift register chain (usually denoted as Q6 or the Input end), and at the same time, the state of all stages inside the register is shifted one bit to the right (e.g., Q6→Q5, Q5→Q4…Q2→Q1).

[0097] Meanwhile, based on the current output states of each register level (Q1 to Q6), the feedback value is calculated in real time according to the Boolean expressions of the G1 and G2 polynomials, and this value is re-injected into the head level as the input for the next cycle. For example, if at a certain moment Q1=1, Q2=0, Q3=1, and Q6=0 in the G1 path, the feedback value is 1⊕0⊕1⊕=0, and this value will become the new input at the next clock edge. This process realizes a typical non-homogeneous linear recursive relationship, causing the entire register state to evolve continuously over time, and the output sequence exhibits pseudo-random behavior.

[0098] It should be noted that this feedback mechanism not only determines the period length and autocorrelation performance of the sequence, but also directly affects the spectral distribution and anti-reconnaissance capability of the subsequent modulated signal. Since the IRNSS standard requires navigation messages to possess certain diffusion characteristics and error tolerance during transmission, the dual polynomial parallel structure can introduce additional information dimensions without increasing bandwidth. More importantly, the output sequence generated by each path (G1 / G2) can be regarded as an independent Gold code branch. The combination of these two can form a composite symbol stream through time alternation, laying the foundation for subsequent double-rate symbol generation. Furthermore, since the calculation of the feedback value depends entirely on the current register state and fixed logic gate combinations, the entire process does not require table lookups or complex algorithms, making it highly suitable for efficient implementation on hardware platforms such as FPGAs, with deterministic latency and low resource consumption.

[0099] In the above embodiments, a linear feedback shift mechanism based on a preset polynomial is constructed to complete the dynamic encoding processing of the original navigation information under precise timing control. This technical solution integrates encoding theory, timing logic design, and hardware feasibility considerations in digital communication. It not only meets the technical specifications of the IRNSS interface control document for signal format, but also provides a high-quality encoding source stream for subsequent spread spectrum modulation, significantly improving the usability and consistency of the signal in complex electromagnetic environments.

[0100] Reference Figure 7 As one implementation of step S106, the step of generating a frequency-controllable intermediate frequency carrier signal based on the Doppler frequency compensation value and carrier phase includes: Step S701: Load the Doppler frequency compensation value and the initial carrier phase value; The Doppler frequency compensation value originates from the front-end ARM processor's calculation of spatial geometry, reflecting the frequency offset caused by relative motion between the target receiver and the satellite. This value is not fixed but dynamically updated over time to adapt to potential speed changes or turning behaviors of the target receiver. The initial carrier phase value ensures phase continuity at the start of each signal generation, avoiding spectral spread or transient interference introduced by phase jumps. This is crucial for maintaining signal coherence during correlation detection. These two parameters together form the basis of the DDS module's initial configuration, determining the initial state and evolution trajectory of the output carrier.

[0101] Step S702: Convert the Doppler frequency compensation value into a frequency control word; This conversion process needs to consider the mathematical mapping relationship between the system master clock frequency fclk and the desired output frequency resolution.

[0102] Specifically, if the phase accumulator bit width of the DDS system is N, then its maximum addressable phase step number is 2N, corresponding to a frequency resolution of Δf = f clk / 2 N Therefore, in practical applications, a scaling factor K=2 needs to be introduced. N / f clk The control word that quantizes physical frequency quantities (in Hz) into dimensionless integer form is: FTW=f comp ×K, where f comp This is the Doppler frequency compensation value. Essentially, this operation is the digital encoding of analog frequency commands, allowing any decimal multiple of frequency deviation to be approximated using high-precision fixed-point numbers, significantly improving the flexibility and accuracy of frequency adjustment.

[0103] Step S703: Driven by the system master clock, the frequency control word is periodically accumulated using a phase accumulator to obtain the accumulation result; At each rising edge of the clock, the phase accumulator modulo-2 its currently stored phase value with the frequency control word. N The addition operation is ϕ[n] = (ϕ[n−1] + FTW) mod 2 N, thus forming a linearly increasing digital phase sequence. Since the FTW represents the magnitude of the phase increment within each clock cycle, this accumulation process is equivalent to constructing a uniformly rotating phase vector in the digital domain, whose angular velocity is proportional to the set frequency value. When the target exhibits accelerated motion, the Doppler frequency shows a non-linear change trend. At this time, by dynamically inserting additional phase offset compensation values between adjacent accumulation periods, the correction of the second-order frequency drift caused by acceleration can be achieved, further enhancing the time consistency of the signal.

[0104] Step S704: Superimpose the accumulation result with the initial carrier phase value to generate an instantaneous phase value; Specifically, the obtained accumulation result is the digital phase value at the current moment. However, to achieve seamless connection with the initial phase, it is necessary to superimpose it with the pre-loaded initial carrier phase value. Since the initial phase is usually represented with a relatively low bit width (such as 16 bits), while the output of the phase accumulator is a high-bit width value (such as 32 bits or 48 bits), the binary bit width of this initial value must first be extended, and it is aligned with the accumulator output by padding with zeros or sign extension. Subsequently, an addition operation is performed in the sense of modulo 2 N to ensure that the instantaneous angular position can be correctly reflected even in the case of phase wrapping. This design effectively supports the phase continuity control between multiple frames of signals, especially suitable for application scenarios that require long-term coherent accumulation.

[0105] Step S705: Periodically query the waveform memory according to the instantaneous phase value and output the corresponding sine wave sample sequence; Among them, the system uses this instantaneous phase value as an address pointer to periodically access the waveform look-up table (Waveform Look-Up Table, LUT) that stores the sampling values of the standard sine function. This table usually pre-stores the normalized sine samples of a complete cycle, and its length is determined by the phase resolution. Considering hardware resource limitations, not all N-bit phase values are used as indexes, but only the high M bits (M < N, M < N) are taken to form the look-up table address, and the remaining low bits are used for interpolation or discarded. For example, if N = 32 and M = 10, the look-up table contains 2 10 = 1024 sample points, which is sufficient to cover the uniform distribution within the interval [0, 2π). Whenever a new phase value is generated, the system reads the corresponding amplitude code word from the LUT to form a discrete digital sine wave sequence. This process realizes the non-linear mapping from "phase" to "amplitude", which is one of the core steps for the DDS technology to achieve arbitrary waveform synthesis.

[0106] Step S706: Convert the sine wave sample sequence into an analog voltage signal to generate an intermediate frequency carrier with controllable frequency.

[0107] The digital sine wave sample sequence is fed into a digital-to-analog converter (DAC), where it undergoes zero-order hold and low-pass filtering to convert into a continuous analog voltage signal. The DAC operates at a rate synchronized with the system's master clock, ensuring a constant time interval between sampling points and thus reproducing an intermediate frequency (IF) sine wave with stable frequency characteristics. The center frequency of this IF carrier is typically set in the range of several MHz to tens of MHz, facilitating subsequent upsampling via analog mixer circuitry to the L5 (1176.45 MHz) or S (2492.028 MHz) operating frequency band specified by the IRNSS.

[0108] More importantly, because its frequency is precisely controlled by the Doppler compensation value calculated in real time, the generated carrier can dynamically track the changes in the target's motion state, ensuring that the modulated navigation signal has good coherence and time alignment characteristics when it enters the receiver front end.

[0109] In the above embodiments, the intermediate frequency carrier generation method integrates Doppler compensation mechanism and all-digital frequency synthesis technology to construct a carrier control system with high precision, high stability, and strong adaptability. This technical solution not only achieves effective correction of frequency offset under complex motion conditions, but also ensures high-quality performance of the output signal in both the frequency and time domains through phase continuity control and efficient waveform reconstruction.

[0110] This application also discloses an IRNSS navigation signal simulation generation system based on parameter compensation.

[0111] A parameter-compensated IRNSS navigation signal simulation generation system, the system comprising: The data receiving module is used to receive the raw signal data output by the IRNSS navigation receiver, and at the same time receive the target aircraft's position coordinates and velocity vector provided by external detection equipment; the raw signal data includes carrier phase, pseudocode phase and navigation message; The data parsing module is used to parse navigation messages to extract ephemeris parameters and calculate the satellite's real-time position and velocity vectors based on the ephemeris parameters; The compensation calculation module is used to calculate the Doppler frequency compensation value and the pseudocode delay compensation value based on the target aircraft's position coordinates and velocity vector, as well as the satellite's real-time position and velocity vector. The simulation generation module is used to modify the signal transmission time field in the navigation message based on the pseudocode delay compensation value and the preset target simulation coordinates to generate a simulated navigation message frame. The signal processing module is used to perform forward error correction coding on the analog navigation message frame, generate a coded symbol sequence, and perform modulo-2 addition with the pre-generated PRN pseudocode sequence to obtain the baseband spread spectrum signal. The carrier signal generation module is used to generate a frequency-controllable intermediate frequency carrier signal based on the Doppler frequency compensation value and the carrier phase. The signal modulation module is used to modulate the baseband spread spectrum signal onto the intermediate frequency carrier signal and output an intermediate frequency analog signal.

[0112] An IRNSS navigation signal simulation generation system based on parameter compensation according to an embodiment of this application can implement any of the above-mentioned navigation signal simulation methods, and the specific working process of each module in the navigation signal simulation system can refer to the corresponding process in the above-mentioned method embodiments.

[0113] In this embodiment, the ARM processor serves as the core control and data processing unit of the system, undertaking core functions such as navigation message parsing, key parameter calculation, and simulation strategy implementation.

[0114] Reference Figure 8 , Figure 9 , Figure 10 As shown, firstly, the navigation signal broadcast by the IRNSS satellite uses a specific frame structure to organize navigation information. The main frame consists of four subframes, each containing 600 symbols, with a transmission period of 30 seconds. Subframes 1 and 2 transmit primary navigation parameters, including ephemeris data, clock correction parameters, and critical information such as satellite health status; subframes 3 and 4 transmit secondary navigation parameters, such as the ionospheric delay model and UTC time synchronization parameters. This frame structure strictly adheres to the standard format defined in the Indian Space Research Organisation (ISRO)'s "IRNSS Interface Control Document" (ISRO-IRNSS-ICD-SPS-1.1), such as... Figure 8 The diagram shown is a schematic of the IRNSS main frame structure. Figure 9 The specific field layout of subframe 1 and subframe 2 is shown. Figure 10 Tables 1 and 2 in the table list the navigation parameters carried by the DATA field in subframe 1 and subframe 2, as well as their bit width, unit, and scaling factor (LSB).

[0115] The ARM processor acquires the raw navigation message, carrier phase, and pseudo-code phase information by connecting to the IRNSS navigation receiver, and decodes the navigation signal according to the ICD document, extracting and updating ephemeris parameters in real time. Simultaneously, external detection equipment transmits the target receiver's position information (x... t ,y t ,z t ) and velocity vector V t The data is transmitted to the ARM processor for subsequent simulation parameter calculations.

[0116] To ensure that the generated analog signal closely matches the real IRNSS signal in frequency characteristics, thereby effectively inducing the target receiver to acquire and track the analog signal, precise compensation must be performed on the spreading code Doppler frequency and the carrier Doppler frequency. Since there may be relative motion between the jammer and the target, their relative velocity will introduce an additional Doppler frequency shift. Therefore, the ARM processor first calculates the Doppler frequency based on the known jammer position... Position of the target machine Calculate the distance L between the two, and then the Doppler frequency between the jammer and the target machine. It can be calculated using the following formula: ; Where λ is the carrier wavelength of the signal. In addition, the Doppler frequency between the satellite and the target receiver also needs to be calculated. This calculation relies on the satellite orbital state determined by the ephemeris parameters demodulated from the navigation message. Specifically, using the Kepler orbital dynamics model, the anomalous angle E is first solved iteratively. k : ; Where μ is the Earth's gravitational constant, a s Let $\mathbf{x}$ be the orbital major radius and $\mathbf{x}$ be the ephemeris reference time. Then, calculate the ascending node angular distance $Φ$. k : ; Next, based on the perturbation correction coefficients Cuc, Cus, Crc, Crs, Cic, Cis provided in the ICD document, the perturbation corrections for the ascending node angular distance, orbital radius, and orbital inclination are calculated: ; Based on this, the orbital parameters at the time of signal transmission are obtained: ascending node angular distance uk = Φk + δuk, orbital radius. Track inclination angle i k =i0+δi k The right ascension of the ascending node is Ωk = Ω - Ωe. Further, calculate the satellite's position derivative (i.e., the instantaneous velocity component) in the orbital plane rectangular coordinate system: ; Then, the coordinates are transformed to the Earth-centered Earth-fixed (ECEF) coordinate system to obtain the satellite's velocity vector (v) relative to the Earth's center. sx ,v sy ,v sz By combining the target receiver's velocity vector, the projection of the relative velocity between the satellite and the target receiver onto the line-of-sight direction can be calculated, and the corresponding Doppler frequency can then be obtained. Finally, combining the two Doppler effects mentioned above, the total frequency compensation that the jammer needs to apply to the analog signal is calculated as follows: ; This frequency compensation value will be passed to the FPGA as a key input parameter for carrier modulation, and used by the DDS module to generate an intermediate frequency carrier with correct Doppler characteristics.

[0117] To further ensure that the analog signal is aligned with the real signal in code phase and to avoid the inability to establish a lock due to code phase deviation, secondary compensation of the pseudo-code phase is required. The ARM processor calculates the true pseudorange from the satellite to the jammer and from the satellite to the target, respectively, according to the pseudorange calculation method specified in the interface control document, and obtains the difference Δρ between the two. Considering the physical distance L between the jammer and the target, a compensation delay needs to be introduced to ensure that the analog signal exhibits the correct propagation delay characteristics at the target. ; Where c is the speed of light. This compensation delay is used to adjust the phase of the locally generated PRN code, ensuring that the spreading code of the analog signal is precisely aligned with the real signal on the time axis.

[0118] Among all the simulation parameters, the most critical is the manipulation of the signal transmission time field towc (Time of Week Count). This is because the IRNSS receiver calculates the pseudorange and completes the positioning solution by comparing the difference between the signal transmission time and the local reception time. Therefore, this embodiment sets a desired simulation coordinate (x... f ,y f ,z f And based on this coordinate, calculate its corresponding ideal pseudorange ρ in reverse. f Further calculate the difference Δρ between the ideal pseudorange and the current actual pseudorange. f Therefore, the required time offset is derived as: Δt = Δρ f / c; The time offset is used to modify the towc field in the original navigation message, causing the receiver to mistakenly believe the signal originates from a simulated position. Subsequently, the ARM processor reassembles the modified navigation parameters into a data frame conforming to the protocol specification according to the IRNSS ICD standard, and transmits it to the FPGA via the AXI bus for subsequent modulation.

[0119] In summary, the ARM processor, through comprehensive analysis and multi-dimensional parameter reconstruction of the received signal, achieves precise control over Doppler frequency, code phase, and timestamp information, laying the foundation for generating high-fidelity, highly concealed IRNSS analog signals. The entire algorithm fully considers satellite orbital dynamics, relative motion effects, and communication protocol consistency, ensuring seamless matching of the analog signal with the real signal at both the physical and protocol layers, significantly improving simulation success rate and anti-detection capability.

[0120] In a parameter-compensated IRNSS navigation signal simulation generation system according to an embodiment of this application, the FPGA (Field-Programmable Gate Array) serves as the core hardware unit for signal modulation and real-time processing, undertaking key tasks such as forward error correction coding, PRN pseudocode generation, spread spectrum modulation, and intermediate frequency carrier synthesis. Its operation relies on key parameters issued by the ARM processor and achieves high-fidelity analog signal reconstruction through precise timing control.

[0121] Reference Figure 11 First, the ARM processor parses and calculates the navigation message data, pseudocode phase initial value, carrier phase information, and frequency control word, and writes these parameters into the FPGA's internal registers via the AXI (Advanced eXtensible Interface) bus, completing the initialization configuration. Then, the FPGA initiates the signal generation process based on this input data.

[0122] For the raw navigation message data with a transmission rate of 25 bps, the FPGA first performs forward error correction (FEC) coding to improve the signal's anti-interference capability during transmission and ensure protocol consistency. The system uses a 100 MHz master clock source, which generates two synchronous clock signals of 25 Hz and 50 Hz via a clock divider: the 25 Hz clock is used to sample and latch each bit of the navigation message, latching the input 1 bit of message data into the input buffer register when its rising edge arrives; subsequently, combinational logic circuits are used to calculate the output results of the G1 and G2 Gold code generator polynomials.

[0123] Reference Figure 12 The diagram illustrates the execution flow of the forward error correction coding module. Data from the buffer register is fed into the first stage of a multi-bit shift register, with the remaining stages shifted right sequentially. The most significant bit is discarded after shifting out, thus achieving dynamic encoding. Furthermore, the rising edge of the 50 Hz clock triggers a symbol output selector switch, resulting in the output of two coded symbols within a 25 Hz fundamental cycle. This ultimately forms a coded sequence with a rate doubled to 50 symbols / second, satisfying the symbol extension requirements specified in the IRNSS standard.

[0124] Meanwhile, the FPGA independently generates the PRN (Pseudo-Random Noise) pseudocode sequence corresponding to the target satellite. The PRN code of the IRNSS system is implemented using two 10-level linear feedback shift register (LFSR) structures, corresponding to branches G1 and G2 respectively, driven by a dedicated clock signal of 1.023 MHz.

[0125] Reference Figure 13At the rising edge of each 1.023 MHz clock cycle, each of the two shift registers performs a shift operation, and the new feedback value is calculated according to its respective characteristic polynomial and then injected into the first stage. The feedback logic for the G1 and G2 polynomials is as follows: ; The output of each clock cycle is G1

[10] ⊕G2

[10] , which is the XOR value of the output of the 10th level of the two registers, thereby generating a pseudo-random sequence with a rate of 1.023 Mcps.

[0126] Next, the FPGA upsamples the aforementioned 50 symbols / second navigation information stream after forward error correction coding to 1.023 Mcps to match the PRN code rate. Then, it performs a modulo-2 addition operation (i.e., bit-by-bit XOR operation) on the two to complete BPSK spread spectrum modulation, outputting a spread spectrum signal with a rate of 1.023 Mcps. This spread spectrum signal contains the tampered analog navigation message and has the same autocorrelation and cross-correlation characteristics as the real signal.

[0127] Because the L5 band (1165.45–1188.45 MHz) and S band (2483.5–2500 MHz) have relatively high frequencies, directly generating RF carriers within the FPGA presents engineering challenges. Therefore, this invention employs an intermediate frequency (IF) modulation strategy. Specifically, a stable IF carrier signal (e.g., 4.092 MHz) is first generated within the FPGA, and its frequency is dynamically controlled using DDS (Direct Digital Synthesis) technology. The DDS module receives the frequency control word from the ARM terminal and, combined with the initial carrier phase value, generates a variable-frequency IF sine wave signal with compensated Doppler frequency characteristics in real time. This design accurately reflects the frequency offset caused by the relative motion between the satellite and the target aircraft, ensuring that the analog signal is highly consistent with the real signal in the frequency domain.

[0128] Finally, the generated 1.023 Mcps spread spectrum signal is combined with the intermediate frequency carrier generated by the DDS and then BPSK modulated. This involves using the spread spectrum signal as the baseband modulation signal to phase-modulate the intermediate frequency carrier, thus completing the fully digital synthesis of the intermediate frequency IRNSS analog signal. The generated intermediate frequency signal can be converted into an analog signal by a DAC, then fed into an upconverter for frequency shifting, and finally transmitted to the L5 or S-band space channel to the target receiver.

[0129] In summary, the FPGA-based system achieves end-to-end analog signal construction from digital baseband to intermediate frequency (IF) signal through refined clock management, protocol-level encoding and restoration, high-precision PRN code generation, and dynamic carrier synthesis. The entire modulation process strictly adheres to the technical specifications of the IRNSS interface control document (ISRO-IRNSS-ICD-SPS-1.1), ensuring that the generated signal maintains a high degree of consistency with the real navigation signal in terms of physical layer characteristics, modulation format, and timing structure, significantly improving success rate and anti-detection capabilities.

[0130] In the several embodiments provided in this application, it should be understood that the provided methods and systems can be implemented in other ways. For example, the system embodiments described above are merely illustrative; for example, the division of a certain module is merely a logical functional division, and in actual implementation there may be other division methods, such as multiple modules can be combined or integrated into another system, or some features can be ignored or not executed.

[0131] This application also discloses a computer device.

[0132] A computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement a parameter-compensated IRNSS navigation signal simulation generation method as described above.

[0133] This application also discloses a computer-readable storage medium.

[0134] A computer-readable storage medium storing a computer program that can be loaded by a processor and executed as described above in any of the methods for simulating and generating IRNSS navigation signals based on parameter compensation.

[0135] The computer-readable storage medium can be any tangible medium that contains or stores a program that can be used by or in connection with an instruction execution system, apparatus, or device; the program code contained on the computer-readable medium can be transmitted using any suitable medium, including but not limited to wireless, wire, optical fiber, RF, etc., or any suitable combination thereof.

[0136] It should be noted that the computer device and storage medium in the embodiments of this application are respectively electronic devices and storage media that apply the above-described method for simulating and generating IRNSS navigation signals based on parameter compensation. Therefore, all embodiments of the above-described signal simulation and generation method are applicable to the computer device and storage medium, and can achieve the same or similar beneficial effects. For the computer device / storage medium embodiments, since they are basically similar to the method embodiments, the description is relatively simple; relevant details can be found in the descriptions of the method embodiments.

[0137] In this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0138] Although this application has been described herein in conjunction with various embodiments, those skilled in the art, by reviewing the accompanying drawings, disclosure, and appended claims, will understand and implement other variations of the disclosed embodiments in carrying out the claimed application. In the claims, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude a plurality. A single processor or other unit can implement several functions listed in the claims. While different dependent claims may recite certain measures, this does not mean that these measures cannot be combined to produce a good effect.

[0139] The above are all preferred embodiments of this application and are not intended to limit the scope of protection of this application. Any feature disclosed in this specification (including the abstract and drawings) may be replaced by other equivalent or similar features unless specifically stated otherwise. That is, unless specifically stated otherwise, each feature is only one example of a series of equivalent or similar features.

Claims

1. A method for generating an IRNSS navigation signal simulation based on parametric compensation, characterized by, The method comprises, receiving original signal data output by an IRNSS navigation receiver, while receiving target machine position coordinates and a velocity vector provided by an external detection device; wherein the original signal data comprises a carrier phase, a pseudo-code phase and a navigation message; parsing the navigation message to extract ephemeris parameters, and calculating real-time positions and velocity vectors of satellites according to the ephemeris parameters; calculating a Doppler frequency compensation value and a pseudo-code time delay compensation value based on the target machine position coordinates and the velocity vector and the real-time positions and velocity vectors of the satellites; modifying a signal transmission time field in the navigation message according to the pseudo-code time delay compensation value and preset target simulation coordinates, to generate a simulation navigation message frame; performing forward error correction coding processing on the simulation navigation message frame to generate a coding symbol sequence, and performing modulo-2 addition operation on the coding symbol sequence and a pre-generated PRN pseudo-code sequence to obtain a baseband spread spectrum signal; generating a frequency-controllable intermediate frequency carrier signal according to the Doppler frequency compensation value and the carrier phase; modulating the baseband spread spectrum signal onto the intermediate frequency carrier signal to output an intermediate frequency analog signal.

2. The method for generating IRNSS navigation signal simulation based on parameter compensation according to claim 1, characterized in that, The step of calculating a Doppler frequency compensation value based on the position coordinates and the velocity vector of the target machine and the real-time positions and velocity vectors of the satellites comprises: obtaining a target machine velocity vector, an interferometer position coordinate, a target machine position coordinate and a satellite real-time velocity vector; calculating a line-of-sight direction vector of the interferometer pointing to the target machine according to the difference between the interferometer position coordinate and the target machine position coordinate; generating a first relative velocity scalar between the interferometer and the target machine based on the projection component of the target machine velocity vector on the line-of-sight direction vector; calculating a relative motion velocity vector of the satellite relative to the target machine according to the satellite velocity vector and the target machine velocity vector; determining a satellite signal propagation direction vector based on the line direction between the satellite real-time position and the target machine position coordinate; extracting the projection component of the relative motion velocity vector on the satellite signal propagation direction vector to generate a second relative velocity scalar between the satellite and the target machine; dividing the first relative velocity scalar by the IRNSS signal carrier wavelength to obtain a first Doppler frequency component; dividing the second relative velocity scalar by the IRNSS signal carrier wavelength to obtain a second Doppler frequency component; superimposing the first Doppler frequency component and the second Doppler frequency component to output the Doppler frequency compensation value.

3. The method for generating IRNSS navigation signal simulation based on parameter compensation according to claim 1, characterized in that, The step of calculating a pseudo-code time delay compensation value based on the position coordinates and the velocity vector of the target machine and the real-time positions and velocity vectors of the satellites comprises: calculating the straight-line transmission distance between the interferometer position coordinate and the target machine position coordinate; calculating a first pseudo-range from the satellite to the target machine according to the satellite real-time position and the target machine position coordinate; calculating a second pseudo-range from the satellite to the interferometer according to the satellite real-time position and the interferometer position coordinate; obtaining a pseudo-range deviation based on the difference between the first pseudo-range and the second pseudo-range; generating a net pseudo-range difference by deducting the straight-line transmission distance from the pseudo-range deviation; dividing the net pseudo-range difference by the speed of light to output the pseudo-code time delay compensation value.

4. The method for generating IRNSS navigation signal simulation based on parameter compensation according to claim 3, characterized in that, The step of modifying the signal transmission time field in the navigation message according to the pseudo-code time delay compensation value and the preset target simulation coordinate includes: Obtaining a pseudo-code time delay compensation value and a preset target simulation geographic coordinate; According to the target simulation geographic coordinate and the target machine position coordinate, calculating the pseudo-range deviation value between the two; Based on the pseudo-code time delay compensation value and the pseudo-range deviation value, generating a signal transmission time correction amount; Reading the signal transmission time field value in the navigation message; Superimposing the signal transmission time field value and the signal transmission time correction amount to update the signal transmission time field in the navigation message; According to the pre-defined frame structure, recombining the updated signal transmission time field and other navigation parameters into a simulation navigation message frame.

5. The method for generating IRNSS navigation signal simulation based on parameter compensation according to claim 4, characterized in that, The step of performing forward error correction encoding processing on the simulation navigation message frame to generate a code symbol sequence, and performing modulo-2 addition operation on the code symbol sequence and the pre-generated PRN pseudo-code sequence to obtain a baseband spread spectrum signal includes: Receiving a simulation navigation message frame and a pre-generated PRN pseudo-code sequence; Inputting the simulation navigation message frame into a forward error correction encoder to perform a linear feedback shift operation under the control of a first clock domain; Extracting a code symbol from the shift register state through a second clock domain driving symbol output selector; Merging two consecutive code symbols to form a symbol group to generate a double-rate code symbol sequence; Performing modulo-2 addition operation on the code symbol sequence and the PRN pseudo-code sequence to output a baseband spread spectrum signal.

6. The method for generating IRNSS navigation signal simulation based on parameter compensation according to claim 5, characterized in that, The first clock domain is a 25Hz clock signal, and the second clock domain is a 50Hz clock signal; The step of performing a linear feedback shift operation includes: Calculating a feedback value according to a preset generating polynomial; At the clock rising edge, moving the data sequence bits into the first level of the shift register, and injecting the feedback value into the first level input.

7. The method for generating IRNSS navigation signal simulation based on parameter compensation according to any one of claims 1 to 6, characterized in that, The step of generating a frequency-controllable intermediate frequency carrier signal according to the Doppler frequency compensation value and the carrier phase includes: Loading a Doppler frequency compensation value and an initial carrier phase value; Converting the Doppler frequency compensation value into a frequency control word; Under the driving of a system master clock, performing periodic accumulation operation on the frequency control word through a phase accumulator to obtain an accumulation result; Superimposing the accumulation result and the initial carrier phase value to generate an instantaneous phase value; Periodically querying a waveform memory according to the instantaneous phase value to output a corresponding sine wave sample sequence; Converting the sine wave sample sequence into an analog voltage signal to generate a frequency-controllable intermediate frequency carrier.

8. A system for parametric-compensation-based IRNSS navigation signal simulation generation, characterized by, The system includes: A data receiving module for receiving original signal data output by an IRNSS navigation receiver, and receiving target machine position coordinates and velocity vectors provided by an external detection device; wherein the original signal data includes carrier phase, pseudo-code phase and navigation message; A data analysis module for analyzing the navigation message to extract ephemeris parameters, and calculating real-time positions and velocity vectors of satellites according to the ephemeris parameters; A compensation calculation module for calculating Doppler frequency compensation values and pseudo-code time delay compensation values based on the target machine position coordinates and velocity vectors, and the real-time positions and velocity vectors of the satellites; An analog generation module is configured to modify a signal transmission time field in the navigation message according to the pseudo-code time delay compensation value and a preset target analog coordinate, and to generate an analog navigation message frame; A signal processing module is configured to perform forward error correction coding processing on the analog navigation message frame, to generate a coded symbol sequence, and to perform modulo-2 addition on the coded symbol sequence and a pre-generated PRN pseudo-code sequence to obtain a baseband spread spectrum signal; A carrier signal generation module is configured to generate a frequency-controllable intermediate frequency carrier signal according to the Doppler frequency compensation value and a carrier phase; A signal modulation module is configured to modulate the baseband spread spectrum signal onto the intermediate frequency carrier signal to output an intermediate frequency analog signal.

9. A computer device, characterized by: A computer program product comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, the processor implementing the method of any one of claims 1 to 7 when executing the program.

10. A computer-readable storage medium, characterized in that: A computer program product comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, the processor implementing the method of any one of claims 1 to 7 when executing the program.

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