A GNSS signal simulation method based on phase resetting and doppler interpolation

Abstract

The application discloses a GNSS signal simulation method based on phase resetting and Doppler interpolation, which comprises: resetting the NCO accumulator phase every interval of a code period, and carrying out three times spline interpolation on the Doppler frequency within the phase resetting interval. The application has the advantages that: the cumulative error is effectively controlled, the NCO accumulator length of each level of the signal does not need special design, and only a first-order NCO is used to realize the simulation of the navigation signal in multiple scenes with small implementation resources and operation amount. The pseudo-range simulation precision is higher, the cumulative error is eliminated, and the simulation precision of the signal Doppler frequency in a high dynamic scene is ensured.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of receiver positioning technology, and particularly relates to a GNSS signal simulation method based on phase resetting and Doppler interpolation. BACKGROUND

[0002] GNSS (global navigation satellite system) signal simulation source generates customized navigation signals to provide a practical and effective means for functional testing and research and development of navigation receivers. The Doppler frequency in the GNSS signal reflects the relative motion between the satellite and the receiver, and the pseudo-range, as the most critical observation parameter in GNSS receiver positioning, directly affects the positioning accuracy of the receiver [2] . Therefore, the calculation and expression of signal Doppler and pseudo-range in the GNSS navigation signal simulation source have become important standards for evaluating the simulation performance of the simulation source signal. For how to accurately calculate the pseudo-range, the literature [3] provides a convenient method for calculating the pseudo-range, which sets a small enough threshold under the premise of knowing the position and receiving time of the receiver user, and iterates the error of the pseudo-range and the true distance of the satellite to obtain the convergent solution of the pseudo-range. The literature [4] proposes to adjust the calculation order of the error delay amount when calculating the pseudo-range, which can reduce the calculation time while increasing the pseudo-range simulation accuracy. The existing technology has made considerable achievements in the pseudo-range calculation method.

[0003] The simulation accuracy of the Doppler frequency and the pseudo-range is related to the dynamic stress of the signal. To adapt to high dynamic scenarios such as missile-borne and rocket-borne, a third-order DDS (direct digital synthesis) model is usually used to simulate the Doppler frequency and the pseudo-range information of the navigation signal, and the essence is the third-order Taylor series expansion of the pseudo-range[4-5]. The literature [1] provides a design method for a DDS model of any order. The simulation method based on the DDS model needs to use multiple accumulators with different lengths when simulating the Doppler frequency, and needs to establish a DDS model for different levels of signals when simulating the pseudo-range. Moreover, due to the limited quantization precision of the control word of the Doppler frequency and its high-order components, it is inevitable to truncate the data in FPGA implementation [6-7] , so the pseudo-range simulation result of the model will have a cumulative error, and therefore the method needs to be updated at a certain time interval, usually 20 ms[8-9]. The literature [2] proposes an online correction and linear interpolation method to explore the simulation accuracy of the Doppler frequency of the signal, and uses the linear interpolation method to simulate the scene with a first-order change rate of the Doppler frequency. However, the method in the literature [2] only studies the simulation accuracy of the Doppler frequency, and does not evaluate the simulation accuracy of the Doppler frequency with high-order components and the pseudo-range.

[0004] Generally, the GNSS signal simulation method based on the third-order DDS model method aims to use a three-level NCO (numerically controlled oscillator) to simulate the Doppler frequency, the first-order and second-order components of the Doppler frequency in the navigation signal respectively. In order to express the pseudorange information in the signal, it is necessary to simulate each level of the signal using the third-order DDS model method, including the text layer, the code layer and the carrier layer. However, the effects of the Doppler effect on the signals at each level are different, so it is necessary to determine the accumulator length of the multi-order NCO of each level of the signal to minimize the cumulative error caused by the inconsistent expression of the Doppler effect [11-12] . And when the update period comes, the initial phase of the three-order NCO accumulator of each level of the signal needs to be updated with the frequency control word, which is a large amount of calculation. And the three-order NCO implementation of each level of the signal consumes a large amount of hardware logic resources. In view of the above problems.

[0005] References

[0006] [1] Zhou C, Wang Y, Qiao C, et al. Design of arbitrary-order direct digital synthesizer for high dynamic GNSS signal Doppler simulation [J]. Journal of National University of Defense Technology, 2016, 38(03): 7-11.

[0007] [2] Sheng DW, Gao Y, Wen H. Phase simulation technology research of high dynamic spread spectrum signal simulator [J]. Modern Defense Technology, 2018, 46(01): 1-6+34.

[0008] [3] Liu M, Wu S. Real-time high dynamic GNSS signal simulator high-precision pseudorange generation method [J]. Journal of Beijing Polytechnic University, 2011, 31(09): 1053-1057.

[0009] [4] Sha H, Chen H, Lv Z, et al. A new real-time high-precision pseudorange calculation method under high dynamic conditions [J]. Journal of Wuhan University (Information Science Edition), 2016, 41(04): 523-528.

[0010] [5] Wang Z, Ji H, Wu Q. Satellite navigation signal simulation method based on 3-DDS and fractional delay [J]. Telemetry and Telecontrol, 2020, 41(01): 34-39.

[0011] [6] Xu Q, Duan Z. Design and FPGA implementation of Taylor series DDS [J]. Computer Engineering and Applications, 2014, 50(05): 208-211.

[0012] [7] Song Y Y, Zhou H, Zeng T, et al. Algorithm and Realization of High Dynamic Satellite Signal Doppler Simulation Based on FPGA[C]. International Technical Meeting of the Satellite Division of the Institute of Navigation, San Diego, CA, 2010;

[0013] [8] Zhu Z, Xiong Y, Zhu X, et al. Design and hardware implementation of a GNSS intermediate frequency signal simulator[J]. Spacecraft Environment Engineering, 2020, 38(04): 74-80;

[0014] [9] Song Y Y, Zhou H, Zeng T, et al. Algorithm and Realization of High Dynamic Satellite Signal Doppler Simulation Based on FPGA[C]. International Technical Meeting of the Satellite Division of the Institute of Navigation, San Diego, CA, 2010;

[0015]

[10] Xie G. GPS Principles and Receiver Design[M]. Beijing: Electronic Industry Press, 2017: 74-76;

[0016]

[11] Cai M Y, Song M Z. FPGA algorithm design and implementation of Galileo / GPS satellite navigation simulation source[J]. Electronic Measurement Technology, 2019, 42(05): 23-28;

[0017]

[12] Wang W T, Li J J, Zhang W X. Research on phase code compensation method to realize DDS without phase truncation spur[J]. Computer Engineering and Applications, 2017, 53(04): 244-250;

[0018]

[13] Van, Manh, Phung, et al. Hermite interpolation on algebraic curves in 2-ScienceDirect[J]. Indagationes Mathematicae, 2019, 30(5): 874-890;

[0019]

[14] Hussain M Z, Irshad M, Sarfraz M, et al. Interpolation of Discrete Time Signals Using Cubic Spline Function[C] / / International Conference on Information Visualisation. IEEE, 2015;

[0020]

[15] Zhao Y X, Chen L J. Exploration of Cubic Spline Interpolation for Solving Navigation Stochastic Differential Model[J]. Control Theory and Applications, 2011, 28(07): 987-993;

[0021]

[16] Liu K, Wu W Q, Tang K H, et al. INS / GNSS Integrated Navigation Simulation Trajectory Generator Based on Actual Flight Data Interpolation[J]. Journal of National University of Defense Technology, 2018, 40(01): 132-137;

[0022]

[17] Zhou K, Chen W J, Chen W H, et al. Speech Enhancement Algorithm Based on Cubic Spline Interpolation of Extended Spectrum[J]. Journal of Beijing University of Aeronautics and Astronautics: 1-12. SUMMARY

[0023] The present application provides a GNSS signal simulation method based on phase resetting and Doppler interpolation to solve the problem of low accuracy of existing Doppler frequency and pseudo-range simulation. Compared with the third-order DDS model method, the pseudo-range simulation accuracy is higher, which to some extent eliminates the cumulative error, and at the same time guarantees the simulation accuracy of signal Doppler frequency in high dynamic scene.

[0024] To achieve the above invention purposes, the technical solutions adopted by the present application are as follows:

[0025] A GNSS signal simulation method based on phase resetting and Doppler interpolation, comprising: resetting the NCO accumulator phase every interval of a pseudo-code period, and performing cubic spline interpolation on the Doppler frequency within the phase resetting interval.

[0026] Further, the GNSS signal simulation method realizes the board card with ZYNQ or DSP+FPGA architecture as the carrier.

[0027] Further, the NCO accumulator phase resetting is as follows:

[0028] Using update interval, each interval a pseudo code integral period in ARM to calculate the real-time Doppler frequency of each level signal corresponding frequency control word and satellite real distance corresponding signal delay time, using the bus to send the results to FPGA, FPGA update signal each level of frequency control word, and reset the phase of each level signal NCO according to the signal delay time.

[0029] Further, the signal delay time according to the calculation of reset each level signal NCO phase, the initial phase calculation as follows:

[0030]

[0031] Wherein is the initial phase of the NCO accumulator of the level to be solved, T delay is the signal delay time, FCW R is the nominal frequency control word of the signal of the level, FCW doppler is the Doppler frequency control word of the signal of the level, L NCO is the NCO accumulator length of the signal of the level.

[0032] FCW R and FCW doppler derived from the formula below

[0033]

[0034] Wherein, f R is the nominal frequency of the signal of the level, f d is the Doppler frequency of the signal of the level.

[0035] Further, the three times spline interpolation is used in the phase reset node interval as follows:

[0036] Three times spline interpolation requires that the interpolation function S(x) is continuous in the second derivative in the interpolation interval, and satisfies the continuity condition below at each interpolation node x i (i=1,2,………n-1).

[0037]

[0038] At the same time, the interpolation function satisfies S(x i )=y i , that is, the node value of the interpolation function is equal to the given value. The boundary condition of the second derivative known and equal at both ends of the interpolation interval is given. Thus, the interpolation function S(x) is obtained on the n small intervals 4 n interpolation conditions, thereby determining 4 undetermined coefficients, and establishing the three times spline interpolation function.

[0039] Further, three times spline interpolation requires 4 nodes.

[0040] Compared with the prior art, the application has the advantages that:

[0041] The cumulative error is effectively controlled, the NCO accumulators of each level of the signal do not need to be specially designed, and only a first-order NCO is used to realize simulation of the navigation signal in multiple scenes with small implementation resources and operation amount.

[0042] The pseudo-range simulation precision is higher, the cumulative error is eliminated, and the simulation precision of the signal Doppler frequency in a high dynamic scene is ensured.

[0043] Compared with using a linear interpolation method, the precision can be improved by 70 dB or more, and the maximum pseudo-range error of the method is reduced by 13 dB compared with a third-order DDS model method in each motion scene. When the relative speed is 15 km / s, the maximum pseudo-range error is 0.014 mm, the Doppler frequency mean square error is -118.5 dB, the maximum pseudo-range error in a high dynamic scene is 0.106 m, and the Doppler frequency mean square error is -115 dB. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 is a schematic diagram of a phase reset method of an embodiment of the application;

[0045] Figure 2 is a diagram of maximum pseudo-range simulation error at different speeds of an embodiment of the application;

[0046] Figure 3 is a diagram of Doppler frequency average error at different speeds of an embodiment of the application;

[0047] Figure 4 is a diagram of Doppler frequency mean square error at different speeds of an embodiment of the application;

[0048] Figure 5 is a diagram of maximum pseudo-range simulation error at different accelerations of an embodiment of the application when the initial speed is fixed;

[0049] Figure 6 is a diagram of Doppler frequency average error at different accelerations of an embodiment of the application when the initial speed is fixed;

[0050] Figure 7 is a diagram of Doppler frequency mean square error at different accelerations of an embodiment of the application when the initial speed is fixed;

[0051] Figure 8 is a diagram of maximum pseudo-range simulation error at different jerk speeds of an embodiment of the application when the initial speed and acceleration are fixed;

[0052] Figure 9 is a diagram of Doppler frequency average error at different jerk speeds of an embodiment of the application when the initial speed and acceleration are fixed;

[0053] Figure 10 is the Doppler frequency mean square error figure of different jerk under the initial velocity and acceleration fixed of the embodiment of the present application. DETAILED DESCRIPTION

[0054] In order to make the object, technical solutions and advantages of the present application more clear and obvious, the present application is further described in detail below according to the drawings and examples.

[0055] 1 Navigation signal simulation model

[0056] 1.1 Doppler frequency simulation model

[0057] When there is relative motion between the navigation receiver and the satellite, the signal frequency received by the receiver antenna will be offset from the nominal frequency of the satellite transmitted signal, which is called Doppler effect

[10] . The additional frequency offset due to the Doppler effect is called Doppler frequency, and the size and rate of change of the Doppler frequency are related to the motion state between the receiver and the satellite. When considering the speed, acceleration and jerk of the relative motion between the satellite and the machine, the Doppler frequency can be expressed by formula (1)

[0058]

[0059] Where, f d (t) is the carrier Doppler frequency; f R is the signal radio frequency, c is the speed of light, v(0), a(0), j(0) are the initial speed, acceleration and jerk of the receiver respectively; t s is the motion time.

[0060] 1.2 Pseudo-range simulation model

[0061] As the most basic parameter in the navigation receiver, the accuracy of the pseudo-range observation directly relates to the positioning effect of the receiver. Therefore, the pseudo-range information in the signal broadcast by the navigation simulation source should be expressed as accurately as possible, and the pseudo-range calculation is shown in formula (2).

[0062] ρ=c(t R -t sv ) (2)

[0063] Where, ρ is the pseudo-range, t R is the receiver local time, and its accuracy is uncontrollable. t sv is the time stamp of the satellite transmission time.

[0064] At time t n , the Taylor series expansion of the pseudo-range ρ(t) is carried out and the high order terms are ignored, and the radial speed, acceleration and jerk of the satellite and the machine at time t n are used to represent the pseudo-range, as shown in formula (3):

[0065]

[0066] where v(t n ), a(t n ) and j(t n ) are the radial velocity, acceleration and jerk between satellite and receiver at time t n , respectively, and p(t n ) is the pseudo-range at time t n .

[0067] GNSS emulators adopt the idea of receiving-oriented, t R is the time when the user receives the signal, then the accurate true range needs to be calculated by backstepping the signal transmission time t sv . In the receiver, t sv can be calculated by formula (4)

[0068]

[0069] where SOW is the second count in a week, N bit is the number of bits in the navigation message, N C is the number of whole cycles of the pseudo-code, Φ C is the current number of chips, and f code is the pseudo-code rate. Therefore, GNSS emulators need to accurately express the above parameters to improve the simulation accuracy of the pseudo-range in the broadcast navigation signal.

[0070] 2 Navigation signal simulation technology based on phase reset and Doppler interpolation

[0071] Generally speaking, the GNSS signal simulation method based on the third-order DDS model method aims to use three levels of NCOs (numerically controlled oscillators) to simulate the Doppler frequency, the first-order and second-order components of the Doppler frequency in the navigation signal, respectively. In order to express the pseudo-range information in the signal, it is necessary to simulate each level of the signal using the third-order DDS model method, including the navigation message layer, the pseudo-code layer and the carrier layer. However, the effects of the Doppler effect on the signals at each level are different, so it is necessary to determine the accumulator length of the multi-order NCOs of each level of signal to minimize the cumulative error caused by the inconsistent expression of the Doppler effect [11-12], and the initial phase of the third-order NCO accumulator of each level signal needs to be updated to the frequency control word when the update period comes, and the calculation amount is large. And the hardware logic resource consumption is large when implementing the third-order NCO of each level signal. In view of the above problems, the application provides a GNSS signal simulation method based on phase resetting and Doppler interpolation, which can effectively control the cumulative error, and the NCO accumulator length of each level signal does not need special design, and only a first-order NCO is used to realize the simulation of navigation signals in multiple scenes with small implementation resource and operation amount.

[0072] 2.1 NCO phase resetting technology

[0073] The implementation carrier of the algorithm is a ZYNQ or DSP+FPGA architecture board, compared with the third-order DDS model method, the method uses a shorter but appropriate update interval, calculates the frequency control word corresponding to the instantaneous Doppler frequency of each level signal and the signal delay time corresponding to the real satellite-machine distance in ARM every interval of a complete code period, sends the results to FPGA using a bus, FPGA updates the frequency control word of each level signal, and resets the phase of each level signal NCO according to the signal delay time, and the basic principle of the phase resetting method is as shown in Figure 1 .

[0074] The step of calculating the reset initial phase according to the signal delay time is completed in FPGA, wherein the modulo operation adopts the truncation implementation, and the initial phase calculation is as shown in formula (5);

[0075]

[0076] Wherein is the initial phase of the NCO accumulator of the level signal, T delay is the signal delay time, FCW R is the nominal frequency control word of the level signal, FCW doppler is the Doppler frequency control word of the level signal, L NCO is the NCO accumulator length of the level signal.

[0077] FCW R and FCW doppler can be obtained by formula (6)

[0078]

[0079] Wherein, f R is the nominal frequency of the level signal, f d is the Doppler frequency of the level signal.

[0080] 2.2 Doppler frequency interpolation technology

[0081] The method can effectively eliminate accumulated errors at the phase reset nodes, but in the update interval, since the algorithm only uses a first-order NCO, high-order components of the Doppler frequency cannot be fully expressed, especially in high dynamic scenarios when the jerk is large, there are step and slope incentives in the Doppler frequency at two adjacent phase reset nodes, this phenomenon has little effect on the simulation accuracy of the pseudo-range, but more spurs and DC will appear in the signal, which will affect the simulation accuracy of the Doppler frequency, and is not conducive to the performance of the receiver test.

[0082] If only the phase reset technique is used, it is equivalent to performing adjacent interpolation on the Doppler frequency in the interval between two adjacent phase reset nodes, which is not applicable to the algorithm. Among other commonly used interpolation methods, linear interpolation cannot represent the interpolation points with a first-order derivative of the change, Hermite interpolation has improved effect compared with linear interpolation, but it needs to give the derivative value at the node, and can only guarantee the first-order derivative continuity of the interpolation point, and the smoothness is not high

[13] . While cubic spline interpolation has good convergence and stability

[14] , and has a second-order smoothness [15-16] . Considering that the navigation signal will produce a large Doppler frequency and high-order components in a high dynamic scenario, and considering the second-order component generated by the jerk, the algorithm selects to use cubic spline interpolation in the interval between the phase reset nodes.

[0083] The cubic spline interpolation method requires that the interpolation function S(x) be continuous in the second derivative in the interpolation interval, and satisfy the continuity condition at each interpolation node x i (i=1, 2, …n-1);

[0084]

[0085] At the same time, the interpolation function satisfies S(x i )=y i , that is, the node value of the interpolation function is equal to the given value. And the second-order component of the Doppler frequency is determined by the acceleration, so the boundary condition that the second-order derivative at both ends of the interpolation interval is known and equal can be given. At this point, the interpolation function S(x) can obtain 4n interpolation conditions on n small intervals, thereby determining 4 undetermined coefficients and establishing a cubic spline interpolation function.

[0086] In implementation, cubic spline interpolation requires more information of nodes than Hermite interpolation, and cubic spline interpolation requires at least 4 nodes

[17] , Hermite interpolation only needs 2. The method of the application calculates a node information every interval of a code period when simulating a navigation signal, so that phase resetting is performed, and therefore each node information is useful information. Cubic spline interpolation of the Doppler frequency using the four node information will not increase the amount of additional operation and algorithm complexity.

[0087] 3 Performance simulation

[0088] A computer with a configuration of Xeon(R) CPU E5-2643 v4 @ 3.40GHz, 64G RAM, and 1TB hard disk is used to perform performance simulation of the algorithm of the application under Win 10 system using Matlab 2018, the signal simulated by the GNSS simulation source is a Beidou B1I signal, the phase resetting interval of the algorithm of the application is 1ms, the NCO accumulator length is selected as 64 bits, and the navigation signal in different scenarios is simulated using the method of the application and the third-order DDS model method respectively. Because the third-order DDS model updates the parameters once every 20ms, the total simulation time is selected as 20ms during performance simulation. Because the third-order DDS model method will produce cumulative error, and the method of the application resets the phase of each level of signal every interval of a code period, the cumulative error is eliminated in real time, so the variance of the pseudo-range simulation of the method of the application and the third-order DDS model method is not compared, and the maximum error of the pseudo-range is used to evaluate the simulation accuracy of the pseudo-range.

[0089] When simulating the simulation effect of the Doppler frequency, not only is the method of the application compared with the third-order DDS model method, but also the simulation effect when the phase resetting technology is combined with different interpolation methods is added, wherein the phase resetting and the cubic spline interpolation method of the frequency are the method of the application, the phase resetting and the linear interpolation method of the frequency are similar to the frequency interpolation principle of the "online correction + linear interpolation" method in document [2] , and only the interval length of interpolation is different.

[0090] 3.1 Uniform motion scenario

[0091] In the scenario where only radial uniform relative motion exists between the satellite and the receiver, the signal simulation accuracy of the method of the application and the third-order DDS model method is as shown in Figures 2-4 .

[0092] From Figure 2It can be seen that, when the total simulation time is 20 ms, i.e. one bit length of the B1I signal, the maximum pseudo-range error of the method of the application is smaller than that of the third-order DDS method, the maximum pseudo-range error is 0.014 mm, and the simulation accuracy is improved by about 13 dB. When simulating any level signal, the method of the application only uses a first-order NCO, resets the accumulator initial phase through a short update interval, and constructs a cubic spline interpolation polynomial by deducing the Doppler frequency at the time points of the next several updates, so that the instantaneous Doppler frequency of each level signal is dynamically updated, thereby reducing the error of pseudo-range simulation.

[0093] If the phase reset interval is further shortened, the accuracy can be further improved, but considering the operation pressure of the board card when the algorithm is implemented and the number of pseudo-code integral periods as one of the parameters when the receiver obtains the pseudo-range observation, it is appropriate to select one pseudo-code integral period as the update interval.

[0094] From Figure 3 , it can be obtained that, in the uniform motion scenario, the effects of different interpolation methods on the interpolation of the Doppler frequency within the phase reset interval are almost the same, because the Doppler frequency value is a fixed value at this time, and any interpolation method can achieve the same simulation accuracy as the third-order DDS model method.

[0095] 3.2 Uniformly accelerated motion scenario

[0096] In the motion scenario where the initial radial velocity of the satellite and the receiver is 15 km / s but the acceleration is different, the signal simulation accuracy of the method of the application and the third-order DDS model method is as shown in Figures 5-7 .

[0097] From Figure 5 , it can be seen that in the uniformly accelerated motion scenario, the pseudo-range simulation accuracy of the method of the application and the third-order DDS model method is lower than that in the uniform motion scenario, but the simulation accuracy of the method of the application is still about 13 dB higher than that of the third-order DDS model method, when the initial velocity is 15 km / s and the acceleration is 70 g, the maximum error of the pseudo-range simulation of the third-order DDS model method is greater than 0 dB, i.e. the maximum error has exceeded 1 m, while the error of the algorithm of the application is still less than 0.1 m.

[0098] According to Figure 6 , 7, in the uniformly accelerated scenario, the effects of different interpolation methods are still not obvious, and the accuracy of the linear interpolation method is slightly lower because the Doppler frequency at this time contains a first-order derivative related component with respect to time, and the interpolation polynomial of the linear interpolation method is not sufficient to express it, if the phase reset interval is extended, the interpolation points are increased, and the linear interpolation accuracy will continue to deteriorate. Therefore, in the uniformly accelerated motion scenario, the linear interpolation is not suitable for the interpolation requirements of the algorithm of the application.

[0099] 3.3 Variable acceleration motion scenario (high dynamic scenario)

[0100] In the case of the initial radial velocity of the satellite and receiver being 15 km / s, the initial acceleration being 150g, and different jerk motion scenarios, the signal simulation accuracy of the method of the application and the third-order DDS model method is as shown in Figures 8-10

[0101] As can be seen from Figure 8 , in the variable acceleration scenario, the change of the jerk has little effect on the method of the application and the third-order DDS model method, and the accuracy of both is stable at the same level. The pseudo-range simulation accuracy of the method of the application is still 13 dB higher than that of the third-order DDS method, and the pseudo-range simulation error of the third-order DDS model is greater than 1 m at any jerk, while the maximum error of the method of the application is about 0.1 m.

[0102] As can be seen from Figure 9 , 10, in the variable acceleration motion scenario, the navigation signal Doppler frequency carries a component related to the second derivative of time, so the accuracy of the linear interpolation method is much lower than that of the remaining interpolation methods, and the Doppler frequency simulation accuracy of the method of the application is improved by 70 dB or more compared with the linear interpolation method. And since the Hermite interpolation only requires the first derivative of the data to be continuous, it cannot effectively fit the Doppler frequency of the high dynamic signal between the phase reset intervals. Therefore, in the high dynamic scenario, only the cubic spline interpolation considers the second derivative continuity of the data, which ensures the simulation accuracy of the Doppler frequency of the navigation signal.

[0103] In combination with the above comparison of the method of the application and the third-order DDS method in different scenarios, it can be explained that the method of the application using timing phase reset and cubic spline interpolation of the Doppler frequency within the phase reset interval is suitable for a wider range of scenarios, and can achieve a frequency simulation accuracy comparable to the third-order DDS model method and a pseudo-range simulation accuracy 13 dB higher than the third-order DDS model in the high dynamic scenario, with a maximum pseudo-range error of 0.1 m.

[0104] 4 Conclusion

[0105] ​The present invention proposes a GNSS signal simulation method of phase reset and Doppler interpolation, which resets the NCO phase of each level of the signal at every pseudo code cycle, effectively controls the cumulative error by using only the first-order NCO, and performs cubic spline interpolation on the Doppler frequency within the phase reset interval, thereby ensuring the accuracy of the signal Doppler frequency simulation in high dynamic scenarios. The simulation results show that in uniform motion, uniform acceleration motion and variable acceleration motion scenarios, the Doppler frequency simulation accuracy of the method of the present invention is comparable to that of the third-order DDS model method, but the pseudorange simulation accuracy is improved by 13dB. Compared with the use of linear interpolation method in high dynamic scenarios, the Doppler frequency simulation accuracy can be improved by more than 70dB. At a speed of 15km / s, an acceleration of 150g, and an acceleration of 1000m / s -2 In a motion scenario, the proposed method achieves a maximum pseudorange simulation error of approximately 0.1m, and a mean square error of -115dB for Doppler frequency simulation. This method is suitable for navigation simulation sources based on ZYNQ or DSP+FPGA architectures. Its low logic resource consumption and minimal computational burden facilitate GNSS signal simulation on boards with fewer logic resources and lower costs.

[0106] The method according to the present invention described above can be implemented in hardware, firmware, or as software or computer code that can be stored on a recording medium (such as a CD ROM, RAM, floppy disk, hard disk, or magneto-optical disk), or as computer code originally stored on a remote recording medium or non-transitory machine-readable medium downloaded over a network and then stored on a local recording medium. Thus, the method described herein can be stored on such a recording medium using a general-purpose computer, a dedicated processor, or programmable or dedicated hardware (such as an ASIC or FPGA). It will be understood that a computer, processor, microprocessor controller, or programmable hardware includes a storage component (e.g., RAM, ROM, flash memory, etc.) that can store or receive software or computer code. When the software or computer code is accessed and executed by the computer, processor, or hardware, the GNSS signal simulation method based on phase resetting and Doppler interpolation described herein is implemented. Furthermore, when a general-purpose computer accesses the code for implementing the process described herein, the execution of the code transforms the general-purpose computer into a dedicated computer for performing the process described herein.

[0107] Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the implementation methods of the present invention, and it should be understood that the scope of protection of the present invention is not limited to such specific descriptions and embodiments. Those skilled in the art can make various other specific variations and combinations based on the technical teachings disclosed in the present invention without departing from the essence of the present invention, and such variations and combinations are still within the scope of protection of the present invention.

Claims

1. A GNSS signal simulation method based on phase reset and Doppler interpolation, characterized in that, Comprise: NCO accumulator phase reset every interval one pseudo code period, and three times spline interpolation for Doppler frequency in phase reset interval; NCO accumulator phase reset is as follows: Using update interval, every interval one pseudo code whole period, calculate the frequency control word corresponding to the real-time Doppler frequency of each level signal and the signal delay time corresponding to the real distance between the satellite and the machine in the ARM, and send the results to the FPGA using the bus, FPGA updates the frequency control word of each level signal of the FPGA, and resets the phase of each level signal NCO according to the signal delay time; According to the signal delay time, the phase of each level signal NCO is reset, and the initial phase is calculated as follows: wherein is the initial phase of the NCO accumulator of the sought level N, T delay is the signal delay time, FCW R is the nominal frequency control word of the level signal, FCW doppler is the Doppler frequency control word of the level signal, L NCO is the NCO accumulator length of the level signal; FCW R and FCW doppler derived from the formula where f R is the nominal frequency of the hierarchical signal, f d is the Doppler frequency of the hierarchical signal.

2. The GNSS signal simulation method based on phase reset and Doppler interpolation according to claim 1, characterized in that: The GNSS signal simulation method realizes the board card with ZYNQ or DSP+FPGA architecture.

3. The GNSS signal simulation method based on phase reset and Doppler interpolation according to claim 1, characterized in that: The three times spline interpolation is used in the phase reset node interval as follows: Cubic spline interpolation requires that the interpolating function S(x) be twice continuously differentiable in the interpolation interval, and that the following continuity conditions be satisfied at each interpolation node x i ; Wherein, i=1, 2, … n-1; At the same time, the interpolation function satisfies S(x i ) = y i , that is, the interpolation function node value is equal to the given value; the boundary conditions are given that the second derivatives of the two ends of the interpolation interval are known and equal; at this point, the interpolation function S(x) has 4n interpolation conditions on n small intervals, thereby determining 4 undetermined coefficients and establishing a cubic spline interpolation function.

4. The GNSS signal simulation method based on phase reset and Doppler interpolation according to claim 3, characterized in that: Three times spline interpolation needs 4 nodes.

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