Low-orbit satellite communication Doppler nonlinearity effect simulation device

Abstract

This invention discloses a device for simulating the Doppler nonlinear effect in low-Earth orbit (LEO) satellite communication, comprising: a user interaction unit for reconstructing the three-dimensional propagation environment between the LEO satellite and the ground terminal based on set communication scenario parameters and calculating the Doppler nonlinear factor; a baseband Doppler nonlinear simulation unit for performing non-uniform resampling of the digital baseband signal based on the Doppler nonlinear factor to obtain a time-domain scaled signal; a carrier Doppler compensation unit for compensating the time-domain scaled signal based on the Doppler nonlinear factor and the carrier frequency to obtain a compensation signal with applied Doppler nonlinear effect; a digital-to-analog converter unit for converting the compensation signal with applied Doppler nonlinear effect into a baseband analog signal with applied Doppler nonlinear effect; and an up-conversion converter unit for up-converting the baseband analog signal with applied Doppler nonlinear effect to a radio frequency (RF) frequency to obtain an LEO satellite RF signal with applied Doppler nonlinear effect.

Description

Technical Field

[0001] This invention belongs to the field of wireless communication technology, specifically, it relates to a device for simulating the Doppler nonlinear effect in low-orbit satellite communication. Background Technology

[0002] With the continuous growth of global communication demands, low-Earth orbit (LEO) satellite networks, as a key component of integrated air-space-ground-sea communication systems, are receiving increasing attention for link reliability. However, the high-speed motion of LEO satellites causes significant Doppler nonlinear effects in signal propagation, which traditional anti-Doppler algorithms struggle to fully correct, severely impacting communication quality and system performance. Channel simulators, as effective tools capable of reproducing real channel characteristics under controllable, observable, and repeatable conditions, provide crucial support for the development and verification of system algorithms. Therefore, researching simulation methods capable of accurately reproducing Doppler nonlinear effects under high-speed motion has become a core technical challenge that urgently needs to be addressed.

[0003] The Doppler effect manifests as signal waveform scaling in the time domain and spectral shifting in the frequency domain. Current simulations of Doppler often employ linear frequency shifting methods from terrestrial mobile communications, but these are essentially carrier frequency shifts based on the narrowband assumption, failing to reflect the differentiated shifts of different frequency components in broadband signals and thus completely ignoring the Doppler nonlinear effects caused by high-speed motion. To improve this, some studies have adopted subband division and segmented frequency shifting strategies, but these are only approximations of the spectrum, disrupting spectral continuity at subband edges and introducing phase jumps and additional distortion. Furthermore, some studies have used time-domain scaling methods to simulate the Doppler nonlinear effect in underwater acoustic communications, but due to the fundamental differences in physical mechanisms between underwater acoustic and wireless communications, they are difficult to directly apply to satellite communication systems. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a simulation device for the Doppler nonlinear effect in low-Earth orbit satellite communication, which can effectively reproduce the Doppler nonlinear characteristics experienced by signals in high-speed motion environments, and provide a reliable test and verification platform for low-Earth orbit satellite communication systems.

[0005] To achieve the above technical objectives, the present invention adopts the following technical solution:

[0006] A low-Earth orbit satellite communication Doppler nonlinear effect simulation device includes: a user interaction unit, a down-conversion unit, an analog-to-digital conversion unit, a digital-to-analog conversion unit, an up-conversion unit, and a baseband Doppler nonlinear simulation unit and a carrier Doppler compensation unit disposed in an FPGA; The user interaction unit is used to reconstruct the three-dimensional propagation environment between the low-orbit satellite and the ground end according to the set communication scenario parameters, calculate the Doppler nonlinear factor, perform fixed-point processing, and obtain the Doppler nonlinear factor in the discrete domain. The downconversion unit is used to downconvert low-orbit satellite radio frequency signals into baseband analog signals. The analog-to-digital conversion unit is used to convert baseband analog signals into digital baseband signals; The baseband Doppler nonlinear simulation unit is used to perform non-uniform resampling of the digital baseband signal based on the Doppler nonlinear factor in the discrete domain to obtain a baseband time-domain scaled signal. The carrier Doppler compensation unit is used to compensate the baseband time-domain scaled signal for carrier Doppler effect based on the Doppler nonlinear factor in the discrete domain and the carrier frequency, so as to obtain a baseband signal with the full Doppler nonlinear effect applied. The digital-to-analog converter is used to convert a baseband signal subjected to the full Doppler nonlinear effect into a baseband analog signal subjected to the Doppler nonlinear effect. The upconversion unit is used to upconvert the baseband analog signal with applied Doppler nonlinear effect to the radio frequency to obtain the low-orbit satellite radio frequency signal with applied Doppler nonlinear effect.

[0007] Furthermore, the communication scenario parameters include: the number of satellite orbital elements, the ground-end motion trajectory, the transceiver speed, and the carrier frequency.

[0008] Furthermore, the calculation process for the Doppler nonlinear factor is as follows:

[0009] in, express The Doppler nonlinear factor at time t, Indicates the relative speed of the transmitting and receiving ends. It represents the speed of light.

[0010] Furthermore, the baseband Doppler nonlinear simulation unit 1-4 includes: a sampling point calculation module and a resampling module; The sampling point calculation module is used to calculate the resampling control parameters required for time-domain scaling of the digital baseband signal in real time based on the Doppler nonlinearity factor in the discrete domain. The resampling module is used to perform non-uniform resampling of the digital baseband signal based on the resampling control parameters and a variable fractional delay filter with a polynomial interpolation structure to obtain a baseband time-domain scaled signal.

[0011] Furthermore, the calculation process for the resampling control parameters required for time-domain scaling is as follows: i: Add time-domain position indices sequentially to the digital baseband signal and set the resampling index for the baseband time-domain scaled signal; ii: For the first Each resampling point index, accumulated in the discrete domain. The _th Doppler nonlinear factor is obtained The time-domain location of the resampling point will be the first The temporal location of the resampling point minus the first The time-domain location index is obtained to get the first... The original time offset of each resampling point; iii: Determine the first Whether the original time offset of each resampling point exceeds the delay interval of the variable fractional delay filter, generates the first... Overflow and underflow flags for each resampling point; iv: According to the The overflow and underflow flags of each resampled point update the time offset of that resampled point:

[0012] in, Indicates the updated number Time offset of each resampling point Indicates the first The original time offset of each resampling point This indicates an overflow flag signal. , This indicates the underflow flag signal. ; v: If the first If the original time offset of each resampling point does not exceed the delay interval of the variable fractional delay filter, the time-domain position index is incremented by 1 to update the time-domain position index; otherwise, if the first resampling point... If an overflow occurs at a resampling point, increment the time-domain location index by 2 to update the time-domain location index; otherwise, keep the time-domain location index unchanged. Increment the resampling point index by 1 to update the resampling point index. vi: Repeat steps ii-v, and use the time offset, overflow flag, and underflow flag corresponding to each resampled point index as the resampled control parameters required for time-domain scaling.

[0013] Furthermore, the resampling module includes: a sub-filter bank, an underflow processing unit, a polynomial interpolation unit, and an overflow processing unit; The sub-filter groups are used to filter the digital baseband signal to generate a filtered signal with the same number of sub-filter groups. The RAM of the underflow processing unit is used to sequentially buffer the filtered signals generated by the sub-filter banks. If the first... The underflow flag signal of each resampling point If the current filtered signal is passed to the polynomial interpolation unit, then the filtered signal from the previous time step is passed to the polynomial interpolation unit. The polynomial interpolation unit is used to combine the filtered signal passed to the polynomial interpolation unit with the first... The time offset of each resampling point is used to calculate the non-uniform resampling value of the digital baseband signal; The overflow processing unit is used to process according to the first Overflow flag signal for each resampling point The non-uniform resampled values ​​of the digital baseband signal are stored in the RAM of the overflow processing unit, and the baseband time-domain scaling signal is output from the RAM of the overflow processing unit.

[0014] Furthermore, the carrier Doppler compensation unit 1-5 includes: an angle calculation module, a complex harmonic generation module, and a Doppler compensation module; The angle calculation module is used to calculate the carrier Doppler phase offset based on the Doppler nonlinearity factor and the carrier frequency. The complex harmonic generation module is used to generate a corresponding complex rotation vector based on the carrier Doppler phase shift. The Doppler compensation module is used to compensate the time-domain scaled signal using a complex rotation vector to obtain a baseband signal with the full Doppler nonlinear effect applied.

[0015] Furthermore, the complex harmonic generation module includes: an angle folding unit, an angle rotation unit, and an angle de-folding unit; The angle folding unit is used to fold the carrier Doppler phase offset by an angle to obtain the folded phase, record the flag of the corresponding angle folding mode, and construct the angle defolding matrix according to the flag of the angle folding mode. The angle rotation unit is used to decompose the folded phase into a combination of basic rotation angles, and obtain the complex rotation vector of the folded phase through rotation iteration; The angle defolding unit is used to obtain the corresponding angle defolding matrix according to the flag of the angle folding mode, and multiply the complex rotation vector of the folded phase with the corresponding angle defolding matrix to obtain the complex rotation vector of the carrier phase offset.

[0016] Furthermore, the process of obtaining the folded phase is as follows: The angular interval is divided into 8 smaller angular intervals. The carrier Doppler phase shift is mapped to its corresponding smaller angular interval, and the folded phase is calculated. :

[0017] in, Indicates carrier Doppler phase shift, This indicates that the carrier Doppler phase shift is mapped to its corresponding small-angle interval. The maximum angle value in the previous angle interval, when hour, .

[0018] Furthermore, the process of obtaining the complex rotation vector of the folded phase is as follows:

[0019] in, Indicates folded phase The real part of the complex rotation vector, Indicates folded phase The imaginary part of the complex rotation vector, This represents the cumulative gain coefficient of the rotation iteration. This represents the total number of rotation iterations. express index, Indicates the first The base rotation angle under each rotation iteration Indicates the first Rotation decision under rotation iterations .

[0020] Compared with the prior art, the present invention has the following beneficial effects: (1) The Doppler nonlinear effect simulation device for low-orbit satellite communication of the present invention performs time-domain scaling on digital baseband signals through a baseband Doppler nonlinear simulation unit and performs carrier phase compensation on the time-domain scaled signals through a carrier Doppler compensation unit. By scaling the time-domain signal in the baseband, nonlinear Doppler frequency shift is simulated. Combined with carrier phase compensation, the Doppler nonlinear effect under high-speed motion is completely reproduced, breaking through the limitations of the traditional linear frequency shift model. (2) The baseband Doppler nonlinear simulation unit in this invention utilizes a baseband Doppler nonlinear simulation architecture based on polynomial interpolation. By converting continuous time-domain scaling into non-uniform resampling and using variable fractional delay filtering to achieve real-time continuous scaling, the continuity of the signal waveform and spectrum is ensured, and the distortion caused by subband segmentation is avoided. (3) The carrier Doppler compensation unit in this invention utilizes a carrier phase compensation scheme based on the CORDIC algorithm. It calculates and applies Doppler phase offset in real time through low-complexity hardware iteration, effectively simulating the carrier Doppler effect. It complements and coordinates with the baseband time-domain scaling processing, and completely reproduces the end-to-end nonlinear Doppler phenomenon. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the Doppler nonlinear effect simulation device for low-orbit satellite communication according to the present invention; Figure 2 This is a schematic diagram of the baseband Doppler nonlinear simulation unit in this invention; Figure 3 This is a schematic diagram of the carrier Doppler compensation unit in this invention; Figure 4 A schematic diagram of the spectrum output by the frequency domain linear frequency shift method; Figure 5 A schematic diagram of the frequency spectrum output by the segmented frequency shifting method; Figure 6 This is a schematic diagram of the spectrum output of the low-orbit satellite communication Doppler nonlinear effect simulation device of the present invention. Detailed Implementation

[0022] The technical solution of the present invention will be further explained and described below with reference to the accompanying drawings.

[0023] like Figure 1 This is a schematic diagram of the low-Earth orbit (LEO) satellite communication Doppler nonlinear effect simulation device of the present invention. The device includes: a user interaction unit 1-1, a down-conversion unit 1-2, an analog-to-digital converter 1-3, a digital-to-analog converter 1-6, an up-conversion unit 1-7, and a baseband Doppler nonlinear simulation unit 1-4 and a carrier Doppler compensation unit 1-5, both housed in an FPGA. The present invention uses the baseband Doppler nonlinear simulation unit 1-4 to perform time-domain scaling on the digital baseband signal, and the carrier Doppler compensation unit 1-5 to perform carrier phase compensation on the time-domain scaled signal. By scaling the time-domain signal in the baseband, the nonlinear Doppler frequency shift is simulated. Combined with carrier phase compensation, the Doppler nonlinear effect under high-speed motion is fully reproduced, overcoming the limitations of traditional linear frequency shift models.

[0024] User interaction unit 1-1 is used to reconstruct the three-dimensional propagation environment between the low-Earth orbit satellite and the ground terminal based on the set communication scenario parameters, calculate the Doppler nonlinear factor, and perform fixed-point processing to obtain the discrete-domain Doppler nonlinear factor. The communication scenario parameters in this invention include: the six roots of the satellite orbit, the ground terminal's motion trajectory, the transceiver speed, and the carrier frequency.

[0025] The calculation process of the Doppler nonlinear factor in this invention is as follows:

[0026] in, express The Doppler nonlinear factor at time t, The relative velocity between the transmitting and receiving ends is determined by the six elements of the satellite orbit, the trajectory of the ground terminal, and the velocity of the transmitting and receiving ends. It represents the speed of light.

[0027] Downconversion unit 1-2 is used to downconvert low-orbit satellite radio frequency signals into baseband analog signals. Analog-to-digital conversion unit 1-3 is used to convert baseband analog signals into digital baseband signals. The digital baseband signal output value is then converted into baseband Doppler nonlinear analog unit 1-4.

[0028] Baseband Doppler nonlinear simulation units 1-4 are used to perform non-uniform resampling of digital baseband signals based on the discrete-domain Doppler nonlinear factor to obtain baseband time-domain scaled signals, such as... Figure 2 The baseband Doppler nonlinear simulation unit 1-4 includes: a sampling point calculation module and a resampling module.

[0029] The sampling point calculation module is used to calculate in real time the resampling control parameters required for time-domain scaling of the digital baseband signal based on the Doppler nonlinearity factor in the discrete domain. This module transforms the baseband time-domain scaling process into a hardware-executable non-uniform resampling operation, which is a necessary prerequisite for hardware implementation of nonlinear Doppler simulation. Specifically: i: Add time-domain position indices sequentially to the digital baseband signal and set the resampling index for the baseband time-domain scaled signal; ii: For the first Each resampling point index, accumulated in the discrete domain. The _th Doppler nonlinear factor is obtained The time-domain location of the resampling point will be the first The temporal location of the resampling point minus the first The time-domain position index of the first digital baseband signal is obtained. Original time offset of each resampling point ,in, Indicates the first One Doppler nonlinear factor; iii: Determine the first Whether the original time offset of each resampling point exceeds the delay interval of the variable fractional delay filter, generates the first... Overflow and underflow flags for each resampling point; iv: According to the The overflow and underflow flags of each resampled point are used to update the time offset of that resampled point, resulting in the final time offset that can be used for the fractional delay filter.

[0030] in, Indicates the updated number Time offset of each resampling point Indicates the first The original time offset of each resampling point This indicates an overflow flag signal. , This indicates the underflow flag signal. ; v: If the first If the original time offset of each resampling point does not exceed the delay interval of the variable fractional delay filter, the time-domain position index is incremented by 1 to update the time-domain position index; otherwise, if the first resampling point... If an overflow occurs at a resampling point, the resampling point will skip one digital baseband signal and the time-domain position index will be incremented by 2 to update the time-domain position index. Otherwise, the resampling point will fall between the current two digital baseband signals, so the time-domain position index will remain unchanged; the resampling point index will be incremented by 1 to update the resampling point index. vi: Repeat steps ii-v, and use the time offset, overflow flag, and underflow flag corresponding to each resampled point index as the resampled control parameters required for time-domain scaling.

[0031] The resampling module is used to perform non-uniform resampling of the digital baseband signal based on resampling control parameters and a variable fractional delay filter with a polynomial interpolation structure, obtaining a baseband time-domain scaled signal. This achieves non-linear scaling of the time axis, thereby simulating the Doppler non-linear effect of the baseband signal. This invention utilizes a baseband Doppler non-linear simulation architecture based on polynomial interpolation. By transforming continuous time-domain scaling into non-uniform resampling and using variable fractional delay filtering to achieve real-time continuous scaling, it ensures the continuity of the signal waveform and spectrum, avoiding distortion caused by sub-band segmentation. Specifically, the resampling module includes: a sub-filter bank, an underflow processing unit, a polynomial interpolation unit, and an overflow processing unit. The underflow and overflow processing units are used to handle the "hold" and "skip" operations of the digital baseband signal during resampling, respectively. By introducing a RAM group to decouple the direct data flow between the sub-filter bank and the polynomial interpolation unit, the sequential processing limitations of the traditional variable fractional delay filter architecture are overcome, ensuring the implementation of non-uniform resampling operations.

[0032] Sub-filter banks are used to filter digital baseband signals, generating filtered signals with the same number of sub-filter banks. The first sub-filter bank... The filtered signal output by each sub-filter for:

[0033] In the formula For the first The coefficients of each sub-filter For the first The order of each sub-filter It is a digital baseband signal. This is the discrete-time index for digital baseband signals.

[0034] The RAM of the underflow processing unit is used to sequentially buffer the filtered signals generated by the sub-filter banks. The underflow flag signal of each resampling point If the current value is 0, it indicates that no underflow has occurred, and the current filtered signal is passed to the polynomial interpolation unit; otherwise, it indicates that underflow has occurred, and the filtered signal from the previous time step is passed to the polynomial interpolation unit.

[0035] The polynomial interpolation unit is used to combine the filtered signal passed to the polynomial interpolation unit with the first... The time offset of each resampling point is used to calculate the non-uniform resampling value of the digital baseband signal. :

[0036] In the formula, Let be the order of the polynomial.

[0037] The overflow processing unit is used to handle overflow according to the first The overflow flag signal of each resampling point stores the non-uniform resampling value of the digital baseband signal into the RAM of the overflow processing unit. Specifically: when This indicates that no overflow has occurred, and the current non-uniform resampled value is... If valid, it is stored in the RAM of the overflow processing unit; when This indicates an overflow has occurred, and the current non-uniform resampled value... Invalid, discard. The baseband time-domain scaling signal is output from the RAM of the overflow processing unit. .

[0038] Carrier Doppler compensation units 1-5 are used to apply corresponding carrier phase compensation to the baseband time-domain scaled signal based on the discrete-domain Doppler nonlinearity factor and carrier frequency to simulate the carrier Doppler effect and generate a complete Doppler nonlinear signal. Carrier Doppler compensation units 1-5, through a hardware-efficient CORDIC architecture, generate complex exponential compensation signals in real time with low complexity and low resource consumption, thereby achieving continuous simulation of the carrier Doppler effect. Complementing and cooperating with baseband time-domain scaling processing, they completely reproduce the end-to-end nonlinear Doppler phenomenon. Figure 3 The carrier Doppler compensation unit 1-5 includes: an angle calculation module, a complex harmonic generation module, and a Doppler compensation module.

[0039] The angle calculation module is used to calculate the angle based on the Doppler nonlinearity factor in the discrete domain. With carrier frequency Calculate carrier Doppler phase shift .

[0040] The complex harmonic generation module is used to generate a corresponding complex rotation vector based on the carrier Doppler phase shift. Specifically, the complex harmonic generation module includes: an angle folding unit, an angle rotation unit, and an angle defolding unit.

[0041] The angle folding unit is used to fold the carrier Doppler phase offset at an angle to obtain a folded phase, which directly reduces the number of iterations and hardware complexity required by CORDIC; it also records a flag for the corresponding angle folding method. sign And construct an angle defolding matrix based on the indicator of the angle folding method. Specifically, the process of obtaining the folding phase is as follows: The angular interval is divided into 8 smaller angular intervals. The carrier Doppler phase shift is mapped to its corresponding smaller angular interval, and the folded phase is calculated. ,in, Indicates carrier Doppler phase shift, This indicates that the carrier Doppler phase shift is mapped to its corresponding small-angle interval. The maximum angle value of the previous small angle interval, when hour, The specific mapping relationship is shown in Table 1.

[0042] Table 1: Folded Phase Mapping Relationship

[0043] Angle rotation units are used to decompose the folded phase into a combination of basic rotation angles. The complex rotation vector of the folded phase is obtained through rotation iteration. Specifically: Decompose the folded phase into a combination of basic rotation angles. ,in, This represents the total number of rotation iterations. express index, Indicates the first The base rotation angle under each rotation iteration Indicates the first Rotation decision under rotation iterations In FPGA hardware implementation, because data is stored using binary fixed-point encoding, the binary bit string of the folded phase... It can be directly used as an iterative rotation decision sequence without the need for additional iterative comparison operations, which greatly reduces hardware complexity and logic resource consumption.

[0044] Through multi-level rotation iterations, the complex rotation vector of the folded phase can be calculated:

[0045] in, Indicates folded phase The real part of the complex rotation vector, Indicates folded phase The imaginary part of the complex rotation vector, The cumulative gain coefficient representing the rotation iteration is determined by the basic rotation angles at each stage, and is represented by the binary decision bits in the rotation matrix. Directly control whether this level of rotation takes effect: when When the rotation matrix degenerates into an identity matrix, there is no rotation transformation; when At that time, execute the corresponding angle. Rotational transformation.

[0046] Angle-folding units are used to indicate the folding angle. sign Obtain the corresponding angle defolding matrix As shown in Table 2, the complex rotation vector of the folded phase is multiplied by the corresponding angle defolding matrix to obtain the complex rotation vector of the carrier phase offset.

[0047] Table 2: Indicators for Angled Folding Methods sign With angle defolding matrix mapping relationship

[0048] The Doppler compensation module is used to compensate for time-domain scaled signals using complex rotation vectors, resulting in a baseband signal with applied Doppler nonlinear effects.

[0049] in, A complex rotation vector representing the carrier phase offset. This represents the compensation signal applied due to the Doppler nonlinear effect.

[0050] The digital-to-analog conversion units 1-6 are used to convert the compensation signal with applied Doppler nonlinear effect into a baseband analog signal with applied Doppler nonlinear effect. The upconversion conversion units 1-7 are used to upconvert the baseband analog signal with applied Doppler nonlinear effect to the radio frequency to obtain the low-orbit satellite radio frequency signal with applied Doppler nonlinear effect, thus completing the full-link simulation of the Doppler nonlinear effect.

[0051] To verify the simulation performance of the low-Earth orbit satellite communication Doppler nonlinear effect simulation device of this invention, it was compared and analyzed with two traditional methods: frequency domain linear frequency shift and piecewise frequency shift. The test scenario was set as the satellite passing overhead. When the low-Earth orbit satellite approaches the observation point, a positive Doppler nonlinear effect is generated, and the signal spectrum is broadened; when the satellite passes overhead and gradually moves away from the observation point, a negative Doppler nonlinear effect is generated, and the signal spectrum is compressed. The results of the frequency domain linear frequency shift method are as follows: Figure 4As shown, the spectrum only exhibits an overall translation, failing to reflect the nonlinear characteristics of Doppler over time, and the spectral shape does not show any broadening or compression matching the scene; the results of the segmented frequency shifting method are as follows. Figure 5 As shown, although the Doppler nonlinear effect was approximately reproduced through piecewise fitting, local distortions and discontinuities still exist in the spectrum; the spectrum output by the device of this invention is as follows. Figure 6 As shown, the spectral variation characteristics are highly consistent with the theoretical laws of the Doppler nonlinear effect, accurately presenting the continuous evolution of the Doppler effect from positive broadening to negative compression during satellite overhead, which is consistent with the spectral characteristics in actual scenarios. Through comparison, it can be seen that this device can accurately simulate the Doppler nonlinear effect in low-Earth orbit satellite communication scenarios. The effectiveness and superiority of the simulation results are significantly better than traditional methods such as frequency domain linear frequency shifting and piecewise frequency shifting, providing reliable technical support for the performance evaluation and testing of low-Earth orbit satellite communication systems.

[0052] The Doppler nonlinear effect simulation device for low-Earth orbit satellite communication of this invention, through the collaborative architecture of baseband Doppler nonlinear simulation based on polynomial interpolation method and radio frequency Doppler compensation based on coordinate rotation digital computer (CORDIC) algorithm, can effectively reproduce the Doppler nonlinear characteristics experienced by the signal in high-speed motion environment in baseband signal processing, and provide a reliable test and verification platform for low-Earth orbit satellite communication systems.

[0053] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A device for simulating the Doppler nonlinear effect in low-Earth orbit satellite communication, characterized in that, include: The system includes a user interaction unit, a down-conversion unit, an analog-to-digital conversion unit, a digital-to-analog conversion unit, an up-conversion unit, and a baseband Doppler nonlinearity simulation unit and a carrier Doppler compensation unit, all housed within the FPGA. The user interaction unit is used to reconstruct the three-dimensional propagation environment between the low-orbit satellite and the ground end according to the set communication scenario parameters, calculate the Doppler nonlinear factor, perform fixed-point processing, and obtain the Doppler nonlinear factor in the discrete domain. The downconversion unit is used to downconvert low-orbit satellite radio frequency signals into baseband analog signals. The analog-to-digital conversion unit is used to convert baseband analog signals into digital baseband signals; The baseband Doppler nonlinear simulation unit is used to perform non-uniform resampling of the digital baseband signal based on the Doppler nonlinear factor in the discrete domain to obtain a baseband time-domain scaled signal. The carrier Doppler compensation unit is used to compensate the baseband time-domain scaled signal for carrier Doppler effect based on the Doppler nonlinear factor in the discrete domain and the carrier frequency, so as to obtain a baseband signal with the full Doppler nonlinear effect applied. The digital-to-analog converter is used to convert a baseband signal subjected to the full Doppler nonlinear effect into a baseband analog signal subjected to the Doppler nonlinear effect. The upconversion unit is used to upconvert the baseband analog signal with applied Doppler nonlinear effect to the radio frequency to obtain the low-orbit satellite radio frequency signal with applied Doppler nonlinear effect.

2. The Doppler nonlinear effect simulation device for low-Earth orbit satellite communication according to claim 1, characterized in that, The communication scenario parameters include: the number of satellite orbital elements, the ground-end motion trajectory, the transceiver speed, and the carrier frequency.

3. The Doppler nonlinear effect simulation device for low-Earth orbit satellite communication according to claim 1, characterized in that, The calculation process for the Doppler nonlinear factor is as follows: in, express The Doppler nonlinear factor at time t, Indicates the relative speed of the transmitting and receiving ends. It represents the speed of light.

4. The Doppler nonlinear effect simulation device for low-Earth orbit satellite communication according to claim 1, characterized in that, The baseband Doppler nonlinear simulation unit 1-4 includes: a sampling point calculation module and a resampling module; The sampling point calculation module is used to calculate the resampling control parameters required for time-domain scaling of the digital baseband signal in real time based on the Doppler nonlinearity factor in the discrete domain. The resampling module is used to perform non-uniform resampling of the digital baseband signal based on the resampling control parameters and a variable fractional delay filter with a polynomial interpolation structure to obtain a baseband time-domain scaled signal.

5. The Doppler nonlinear effect simulation device for low-Earth orbit satellite communication according to claim 4, characterized in that, The calculation process for the resampling control parameters required for time-domain scaling is as follows: i: Add time-domain position indices sequentially to the digital baseband signal and set the resampling index for the baseband time-domain scaled signal; ii: For the first Each resampling point index, accumulated in the discrete domain. The _th Doppler nonlinear factor is obtained The time-domain location of the resampling point will be the first The temporal location of the resampling point minus the first The time-domain location index is obtained to get the first... The original time offset of each resampling point; iii: Determine the first Whether the original time offset of each resampling point exceeds the delay interval of the variable fractional delay filter, generates the first... Overflow and underflow flags for each resampling point; iv: According to the The overflow and underflow flags of each resampled point update the time offset of that resampled point: in, Indicates the updated number Time offset of each resampling point Indicates the first The original time offset of each resampling point This indicates an overflow flag signal. , This indicates the underflow flag signal. ; v: If the first If the original time offset of each resampling point does not exceed the delay interval of the variable fractional delay filter, the time-domain position index is incremented by 1 to update the time-domain position index; otherwise, if the first resampling point... If an overflow occurs at a resampling point, increment the time-domain location index by 2 to update the time-domain location index; otherwise, keep the time-domain location index unchanged. Increment the resampling point index by 1 to update the resampling point index. vi: Repeat steps ii-v, and use the time offset, overflow flag, and underflow flag corresponding to each resampled point index as the resampled control parameters required for time-domain scaling.

6. The Doppler nonlinear effect simulation device for low-Earth orbit satellite communication according to claim 5, characterized in that, The resampling module includes: a sub-filter bank, an underflow processing unit, a polynomial interpolation unit, and an overflow processing unit; The sub-filter groups are used to filter the digital baseband signal to generate a filtered signal with the same number of sub-filter groups. The RAM of the underflow processing unit is used to sequentially buffer the filtered signals generated by the sub-filter banks. If the first... The underflow flag signal of each resampling point If the current filtered signal is passed to the polynomial interpolation unit, then the filtered signal from the previous time step is passed to the polynomial interpolation unit. The polynomial interpolation unit is used to combine the filtered signal passed to the polynomial interpolation unit with the first... The time offset of each resampling point is used to calculate the non-uniform resampling value of the digital baseband signal; The overflow processing unit is used to process according to the first Overflow flag signal for each resampling point The non-uniform resampled values ​​of the digital baseband signal are stored in the RAM of the overflow processing unit, and the baseband time-domain scaling signal is output from the RAM of the overflow processing unit.

7. The Doppler nonlinear effect simulation device for low-Earth orbit satellite communication according to claim 1, characterized in that, The carrier Doppler compensation unit 1-5 includes: an angle calculation module, a complex harmonic generation module, and a Doppler compensation module; The angle calculation module is used to calculate the carrier Doppler phase offset based on the Doppler nonlinearity factor and the carrier frequency. The complex harmonic generation module is used to generate a corresponding complex rotation vector based on the carrier Doppler phase shift. The Doppler compensation module is used to compensate the time-domain scaled signal using a complex rotation vector to obtain a baseband signal with the full Doppler nonlinear effect applied.

8. A low-Earth orbit satellite communication Doppler nonlinear effect simulation device according to claim 7, characterized in that, The complex harmonic generation module includes: an angle folding unit, an angle rotation unit, and an angle de-folding unit; The angle folding unit is used to fold the carrier Doppler phase offset by an angle to obtain the folded phase, record the flag of the corresponding angle folding mode, and construct the angle defolding matrix according to the flag of the angle folding mode. The angle rotation unit is used to decompose the folded phase into a combination of basic rotation angles, and obtain the complex rotation vector of the folded phase through rotation iteration; The angle defolding unit is used to obtain the corresponding angle defolding matrix according to the flag of the angle folding mode, and multiply the complex rotation vector of the folded phase with the corresponding angle defolding matrix to obtain the complex rotation vector of the carrier phase offset.

9. A low-Earth orbit satellite communication Doppler nonlinear effect simulation device according to claim 8, characterized in that, The process of obtaining the folded phase is as follows: The angular interval is divided into 8 smaller angular intervals. The carrier Doppler phase shift is mapped to its corresponding smaller angular interval, and the folded phase is calculated. : in, Indicates carrier Doppler phase shift, This indicates that the carrier Doppler phase shift is mapped to its corresponding small-angle interval. The maximum angle value in the previous angle interval, when hour, .

10. A low-Earth orbit satellite communication Doppler nonlinear effect simulation device according to claim 8, characterized in that, The process of obtaining the complex rotation vector of the folded phase is as follows: in, Indicates folded phase The real part of the complex rotation vector, Indicates folded phase The imaginary part of the complex rotation vector, This represents the cumulative gain coefficient of the rotation iteration. This represents the total number of rotation iterations. express index, Indicates the first The base rotation angle under each rotation iteration Indicates the first Rotation decision under rotation iterations .

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