A satellite narrowband communication terminal

Abstract

The present invention belongs to the field of communication technologies. Specifically, it relates to a satellite narrowband communication terminal, which includes a radio frequency receiving module, a frequency tracking module, and a radio frequency transmitting module. The radio frequency receiving module is used to receive radio frequency signals transmitted from a satellite link. The frequency tracking module is used to selectively switch the frequency tracking mode by setting a reasonable threshold according to the Doppler frequency shift change rate of the baseband signal under different motion states of the satellite relative to the ground communication terminal. By setting an appropriate threshold based on the Doppler frequency shift change rate, the dynamic switching between the fast frequency tracking mode and the fine frequency tracking mode is achieved, enabling the ground communication terminal to adaptively process different motion scenarios and frequency shift changes of the satellite, ensuring the stability and reliability of the communication link. It has high practicality in application scenarios under the condition of relatively high-speed motion of the satellite and narrowband communication environments.

Description

Technical Field

[0001] The present invention belongs to the field of communication technologies, and specifically, relates to a satellite narrowband communication terminal. Background Art

[0002] Narrowband communication technologies are usually applied in the field of low-earth orbit satellite communications. Since low-earth orbit satellites and ground terminals have relatively high-speed motion phases and relatively stable motion phases, existing satellite communication terminals usually adopt a fixed compensation strategy when dealing with Doppler frequency shift. However, due to the relatively low spectral bandwidth of narrowband communication signals, they are often greatly affected by the Doppler effect, and the motion state of low-earth orbit satellites changes greatly, making it difficult to effectively cope with the dynamic changes of frequency shift under different motion states.

[0003] This fixed-mode frequency compensation method can often only effectively target scenarios where the frequency offset amplitude is relatively large during single high-speed satellite orbit motion or relatively small during stable motion, and it is difficult to ensure the stability of the entire communication link stage, thereby resulting in data transmission interruption or unstable communication signals. Summary of the Invention

[0004] To solve the technical problem in the above background art that the existing fixed-mode frequency compensation method can often only effectively target a single high-speed satellite orbit motion scenario and it is difficult to ensure the stability of the entire communication link stage, the present invention provides a satellite narrowband communication terminal; innovatively introduces a frequency tracking mode switching mechanism based on the Doppler frequency shift change rate; by setting reasonable thresholds, the terminal can dynamically switch between a fast frequency tracking mode and a fine frequency tracking mode to ensure adaptation to different satellite motion states and frequency shift change situations.

[0005] The object of the present invention can be achieved through the following technical solutions:

[0006] A satellite narrowband communication terminal includes a radio frequency receiving module, a frequency tracking module, and a radio frequency transmitting module

[0007] The radio frequency receiving module is used to receive radio frequency signals transmitted from a satellite link, and perform down-conversion, filtering, and demodulation processing to convert them into baseband signals;

[0008] The frequency tracking module is used to selectively switch the frequency tracking mode according to the Doppler frequency shift change rate of the baseband signal by setting reasonable thresholds under different motion states of the satellite relative to the ground communication terminal, including a fast frequency tracking mode or a fine frequency tracking mode;

[0009] The fast frequency tracking mode or the fine frequency tracking mode adopts different frequency shift compensation algorithms to dynamically compensate the transmission frequency and reception frequency of the ground communication terminal to ensure the stability of the communication link;

[0010] The radio frequency transmitting module is used to dynamically correct the transmitting frequency of the ground communication terminal according to the real-time calculation result of the frequency tracking mode;

[0011] The radio frequency receiving module is also used to dynamically correct the receiving frequency of the ground communication terminal according to the real-time calculation result of the frequency tracking mode;

[0012] The implementation process of the frequency tracking module includes:

[0013] Extract the features of the received baseband signal, and calculate the change rate of the Doppler frequency shift in the baseband signal in real time by analyzing its frequency change characteristics;

[0014] Set a threshold for the change rate of the Doppler frequency shift to be used for switching different frequency tracking modes;

[0015] When the change rate of the Doppler frequency shift is greater than the set threshold, switch to the fast frequency tracking mode. The fast frequency tracking mode uses the Doppler frequency shift formula to calculate the compensation amount to adapt to the change of large-scale frequency offset;

[0016] When the change rate of the Doppler frequency shift is less than the set threshold, switch to the fine frequency tracking mode. The fine frequency tracking mode uses the phase difference method to calculate the compensation amount to achieve higher-precision Doppler frequency shift compensation.

[0017] Preferably, the calculation method of the change rate of the Doppler frequency shift is:

[0018] Calculate the change rate of the Doppler frequency shift by calculating the change of the Doppler frequency shift over time. Its calculation formula is:

[0019] ;

[0020] In the formula, is the change rate of the Doppler frequency shift within a specific time interval; is the specific time interval; is the Doppler frequency shift amount of the downlink signal.

[0021] Preferably, the set threshold of the change rate of the Doppler frequency shift is a value between 600 - 800 Hz / s.

[0022] Preferably, the process of calculating the compensation amount using the Doppler frequency shift formula in the fast frequency tracking mode is as follows:

[0023] Calculate the frequency offset caused by the Doppler effect according to the relative velocity between the satellite and the ground terminal. Its calculation formula is:

[0024] ;

[0025] ;

[0026] In the formula, is the Doppler frequency shift of the uplink signal, is the standard frequency of the uplink signal; is the Doppler frequency shift of the downlink signal, is the standard frequency of the downlink signal; is the relative velocity between the satellite and the ground communication terminal, is the speed of light;

[0027] Perform corresponding compensation according to the Doppler frequency shift. Among them, the compensation calculation formula for the transmission frequency in the fast frequency tracking mode is:

[0028] ;

[0029] In the formula, is the transmission frequency after compensating the frequency shift;

[0030] Similarly, the compensation calculation formula for the reception frequency in the fast frequency tracking mode is:

[0031] ;

[0032] In the formula, is the reception frequency after compensating the frequency shift.

[0033] Preferably, the process of calculating the compensation amount in the fine frequency tracking mode using the phase difference method is as follows:

[0034] S1) Sample the received baseband signal, set an appropriate sampling rate, and convert the continuous sampled data analog signal into a discrete digital signal, which is represented by the functional relationship:

[0035] , , ;

[0036] In the formula, is the discrete digital signal after sampling; is the sampling period, is the sampling point serial number;

[0037] S2) Perform low-pass filtering on the discrete digital signal after sampling to extract the baseband frequency component; the filtering formula for the baseband frequency component is:

[0038] ;

[0039] In the formula, represents the baseband frequency component; is the standard frequency of the downlink signal, represents the mixing operation;

[0040] S3) Calculate the signal phase information in the baseband frequency component, and then extract the signal phase sequence for analyzing the change of the signal frequency. The signal phase sequence can be expressed as:

[0041] ;

[0042] where, is the phase sequence of the signal; is the imaginary part of the signal, is the real part of the signal;

[0043] S4) Frequency offset will cause the phase to change with time. Calculate the instantaneous frequency offset through the phase difference between adjacent sampling points. The calculation formula is:

[0044] ;

[0045] ;

[0046] where, is the phase difference, representing the phase change between adjacent sampling points; is the instantaneous frequency offset; is the sampling period, and n is the sampling point number;

[0047] S5) Perform corresponding compensation according to the instantaneous frequency offset. Among them, the compensation calculation formula for the transmit frequency in the fine frequency tracking mode is:

[0048] ;

[0049] where, is the transmit frequency after compensating the frequency shift; is the standard frequency of the uplink signal;

[0050] The compensation calculation formula for the receive frequency in the fine frequency tracking mode is:

[0051] ;

[0052] where, is the receive frequency after compensating the frequency shift; is the standard frequency of the downlink signal;

[0053] Preferably, between step S4) and step S5), it further includes: performing Kalman filtering or moving average filtering on the calculated instantaneous frequency offset, and then performing subsequent corresponding compensation calculations.

[0054] Preferably, the relative velocity between the satellite and the ground communication terminal, the standard frequencies of the uplink signal and the downlink signal of the communication terminal can all be obtained from the known satellite orbit information.

[0055] Preferably, the radio frequency receiving module includes a down-converter, a local oscillator, a filter, and a demodulator;

[0056] The down-converter is used to convert the high-frequency satellite signal into a baseband signal;

[0057] The local oscillator is used to dynamically adjust the local oscillator frequency according to the received frequency after compensating for the frequency shift, ensuring correct mixing of the received radio frequency signal in cooperation with the down-converter;

[0058] The filter is used to filter out interference signals and retain signals in the target frequency band;

[0059] The demodulator is used to modulate the baseband signal and convert it into a baseband digital signal or an analog signal.

[0060] Preferably, the radio frequency transmitting module includes a local oscillator and a power amplifier; the local oscillator is used to dynamically adjust the local oscillator frequency according to the transmitted frequency after compensating for the frequency shift;

[0061] The power amplifier is used to amplify the radio frequency signal after modulation and frequency adjustment.

[0062] Preferably, the frequency tracking module includes a phase calculator, a pilot timer, and a phase-locked loop controller;

[0063] The phase calculator is used to calculate the phase, i.e., the argument, according to the real part and the imaginary part of the baseband signal;

[0064] The pilot timer is used to convert and output the pilot signal in the baseband signal into a time signal, providing the time count in the phase difference calculation process;

[0065] The phase-locked loop controller is used to calculate the change rate of the Doppler frequency shift in real time, compare and determine the change rate of the Doppler frequency shift with a set threshold, and then selectively switch different frequency tracking modes; the phase-locked loop controller is also used to calculate the Doppler frequency shift compensation amount in real time and output the transmitted frequency or the received frequency after compensating for the frequency shift.

[0066] Advantages of the present invention:

[0067] 1. The communication terminal of the present invention is composed of a radio frequency receiving module, a frequency tracking module, and a radio frequency transmitting module, which are respectively responsible for functions such as radio frequency signal reception and processing, frequency tracking and compensation, and transmitted frequency adjustment. This modular design facilitates independent optimization of each function and improves the overall performance of the system.

[0068] 2. By setting an appropriate threshold according to the change rate of the Doppler frequency shift, dynamic switching between a fast frequency tracking mode and a fine frequency tracking mode is achieved, enabling the ground communication terminal to adaptively process different motion scenarios and frequency shift changes of the satellite, ensuring the stability and reliability of the communication link.

[0069] 3. The fast frequency tracking mode calculates the compensation amount using the Doppler frequency shift formula to adapt to large-scale frequency offset changes. The fine frequency tracking mode calculates the compensation amount using the phase difference method to achieve higher-precision Doppler frequency shift compensation. The communication terminal can correct the transmission frequency and reception frequency of the communication terminal through accurate frequency tracking and real-time compensation according to the relative motion state of the satellite and the ground terminal. It has high practicability in application scenarios under the condition of high-speed relative motion of the satellite and narrowband communication environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0071] Figure 1 It is a schematic diagram of the frame structure of a satellite narrowband communication terminal of the present invention.

[0072] Figure 2 It is a flowchart of the frequency tracking module of the present invention.

[0073] Figure 3 It is a flowchart of the calculation method of the fine tracking mode of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0074] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0075] Please refer to Figure 1 As shown, a satellite narrowband communication terminal includes a radio frequency receiving module, a frequency tracking module, and a radio frequency transmitting module

[0076] The radio frequency receiving module is used to receive the radio frequency signal transmitted from the satellite link, and perform down-conversion, filtering, and demodulation processing to convert it into a baseband signal;

[0077] The frequency tracking module is used to selectively switch the frequency tracking mode, including the fast frequency tracking mode or the fine frequency tracking mode, according to the Doppler frequency shift change rate of the baseband signal under different motion states of the satellite relative to the ground communication terminal by setting a reasonable threshold;

[0078] The fast frequency tracking mode or the fine frequency tracking mode adopts different frequency shift compensation algorithms to dynamically compensate the transmission frequency and reception frequency of the ground communication terminal, ensuring the stability of the communication link;

[0079] The radio frequency transmission module is used to dynamically correct the transmission frequency of the ground communication terminal according to the real-time calculation result of the frequency tracking mode;

[0080] The radio frequency reception module is also used to dynamically correct the reception frequency of the ground communication terminal according to the real-time calculation result of the frequency tracking mode.

[0081] Furthermore, the radio frequency reception module includes a downconverter, a local oscillator, a filter, and a demodulator;

[0082] The downconverter is used to convert the high-frequency satellite signal into a baseband signal;

[0083] The local oscillator is used to dynamically adjust the local oscillator frequency according to the reception frequency after compensating for the frequency shift, ensuring correct mixing of the received radio frequency signal in cooperation with the downconverter;

[0084] The filter is used to filter out interference signals and retain the signals in the target frequency band;

[0085] The demodulator is used to modulate the baseband signal and convert it into a baseband digital signal or an analog signal.

[0086] Furthermore, the radio frequency transmission module includes a local oscillator and a power amplifier; the local oscillator is used to dynamically adjust the local oscillator frequency according to the transmission frequency after compensating for the frequency shift;

[0087] The power amplifier is used to amplify the radio frequency signal after modulation and frequency adjustment to meet the transmission power requirement. After adjusting the transmission frequency, the power amplifier is responsible for transmitting the signal to the satellite at an appropriate power level.

[0088] Furthermore, the frequency tracking module includes a phase calculator, a pilot timer, and a phase-locked loop controller;

[0089] The phase calculator is used to calculate the phase, i.e., the argument, according to the real part and the imaginary part of the baseband signal;

[0090] The pilot timer is used to convert and output the pilot signal in the baseband signal into a time signal to provide the time count in the phase difference calculation process;

[0091] The phase-locked loop controller is used to calculate the change rate of the Doppler frequency shift in real time, compare the change rate of the Doppler frequency shift with a set threshold for determination, and then selectively switch different frequency tracking modes; the phase-locked loop controller is also used to calculate the Doppler frequency shift compensation amount in real time and output the transmission frequency or reception frequency after compensating for the frequency shift.

[0092] Please refer to Figure 2 and Figure 3 As shown, the implementation process of the frequency tracking module includes:

[0093] Extract the features of the received baseband signal, and by analyzing its frequency change characteristics, calculate the Doppler frequency shift change rate in the baseband signal in real time;

[0094] Set a threshold for the Doppler frequency shift change rate to be used for switching different frequency tracking modes;

[0095] When the Doppler frequency shift change rate is greater than the set threshold, switch to the fast frequency tracking mode. The fast frequency tracking mode uses the Doppler frequency shift formula to calculate the compensation amount to adapt to the change of large-amplitude frequency offset;

[0096] When the Doppler frequency shift change rate is less than the set threshold, switch to the fine frequency tracking mode. The fine frequency tracking mode uses the phase difference method to calculate the compensation amount to achieve higher-precision Doppler frequency shift compensation.

[0097] Specifically, the orbital altitude of a low Earth orbit (LEO) satellite is usually between 500 - 2000 km, and the operating speed is about 7 - 8 km / s. For common narrowband satellite communication frequency bands (L band, 1 - 2 GHz), the magnitude of the Doppler frequency shift can reach several kHz or even higher. Therefore, at different frequency bands, the change rate of the frequency offset will also be different.

[0098] Furthermore, the calculation method of the Doppler frequency shift change rate is:

[0099] Calculate the change rate of the Doppler frequency shift by calculating the change of the Doppler frequency shift over time. The calculation formula is:

[0100] ;

[0101] In the formula, is the Doppler frequency shift change rate within a specific time interval; is the specific time interval; is the Doppler frequency shift amount of the downlink signal.

[0102] Specifically, assume that the relative speed of the satellite increases from 7.5 km / s to 7.7 km / s within a short time, and the change time is 1 second. At this time, the frequency offset change rate can be calculated as:

[0103] ;

[0104] Substitute = 1 GHz, = 1 second; it can be calculated that the change rate of the frequency offset can reach 667 Hz; if the change rate exceeds this value, the communication system can switch to the fast frequency tracking mode.

[0105] Based on the above analysis, the threshold of the reasonable Doppler frequency shift change rate can be set between 600 Hz / s and 800 Hz / s, specifically depending on factors such as the design of the ground communication terminal, the operating frequency band, the satellite orbital altitude and speed, etc. This range can cover the change situations in the fast moving stage and the relatively stable stage of most LEO satellites.

[0106] Furthermore, the set threshold of the Doppler frequency shift change rate is a value between 600 - 800 Hz / s.

[0107] Through the collaborative work of the RF receiving module, the frequency tracking module and the RF transmitting module, the present invention can effectively solve the frequency offset problem caused by the Doppler effect during satellite communication. The frequency tracking module selects a suitable tracking mode according to the set threshold; the two tracking modes can be switched according to the actual relative motion state of the satellite and the ground terminal, and different frequency shift compensation algorithms are respectively used to compensate the transmitting and receiving frequencies to ensure the continuity and stability of the satellite communication link.

[0108] The specific working mechanism is as follows: Fast frequency tracking mode: applicable to scenarios where the satellite moves fast or the frequency changes drastically, and quickly calculates the frequency compensation amount through a relatively simple Doppler frequency shift formula to adapt to the large - amplitude frequency offset change.

[0109] Fine frequency tracking mode: applicable to scenarios where the satellite moves relatively slowly or the frequency changes smoothly, and calculates the compensation amount through a high - precision phase difference method to achieve higher - precision Doppler frequency shift compensation.

[0110] Furthermore, the process of calculating the compensation amount using the Doppler frequency shift formula in the fast frequency tracking mode is as follows:

[0111] According to the relative velocity between the satellite and the ground terminal, calculate the frequency offset caused by the Doppler effect; its calculation formula is:

[0112] ;

[0113] ;

[0114] In the formula, is the Doppler frequency shift amount of the uplink signal, is the standard frequency of the uplink signal; is the Doppler frequency shift amount of the downlink signal, is the standard frequency of the downlink signal; is the relative velocity between the satellite and the ground communication terminal, is the speed of light;

[0115] Perform corresponding compensation according to the Doppler frequency shift amount. Among them, the compensation calculation formula for the transmission frequency in the fast frequency tracking mode is:

[0116] ;

[0117] In the formula, is the transmission frequency after compensating the frequency shift;

[0118] Similarly, the compensation calculation formula for the reception frequency in the fast frequency tracking mode is:

[0119] ;

[0120] In the formula, is the reception frequency after compensating the frequency shift.

[0121] Specifically, its factual logic can be intuitively understood as:

[0122] When the ground terminal approaches the satellite, the Doppler frequency shift amount is positive. Therefore, the transmission frequency of the ground terminal needs to be appropriately reduced so that the frequency can return to the standard uplink frequency when received by the satellite. At the same time, the reception frequency will be higher than the standard frequency of the downlink signal; through compensation, the reception frequency can be corrected back to the standard frequency.

[0123] When the ground terminal moves away from the satellite, the Doppler frequency shift amount is negative. The transmission frequency of the ground terminal needs to be increased so that the frequency received by the satellite matches the standard uplink frequency. At the same time, the reception frequency will be lower than the standard frequency of the downlink signal. Through compensation, the reception frequency can also be corrected back to the standard frequency.

[0124] Furthermore, the process of calculating the compensation amount using the phase difference method in the fine frequency tracking mode is as follows:

[0125] S1) Sample the received baseband signal, set an appropriate sampling rate, and convert the continuous sampled data analog signal into a discrete digital signal, which is represented by the functional relationship:

[0126] , , ;

[0127] In the formula, is the discrete digital signal after sampling; is the sampling period, and n is the sampling point serial number;

[0128] S2) Perform low-pass filtering on the sampled discrete digital signal to extract the baseband frequency component; the filtering formula for the baseband frequency component is:

[0129] ;

[0130] In the formula, represents the baseband frequency component; is the standard frequency of the downlink signal, represents the mixing operation;

[0131] S3) Calculate the signal phase information in the baseband frequency component, and then extract the signal phase sequence for analyzing the change of the signal frequency. The signal phase sequence can be expressed as:

[0132] ;

[0133] In the formula, is the phase sequence of the signal; is the imaginary part of the signal, is the real part of the signal;

[0134] S4) Frequency offset will cause the phase to change with time. Calculate the instantaneous frequency offset through the phase difference between adjacent sampling points. The calculation formula is:

[0135] ;

[0136] ;

[0137] In the formula, is the phase difference, representing the phase change between adjacent sampling points; is the instantaneous frequency offset; is the sampling period; n is the sampling point number;

[0138] S5) Perform corresponding compensation according to the instantaneous frequency offset. Among them, the compensation calculation formula for the transmission frequency in the fine frequency tracking mode is:

[0139] ;

[0140] In the formula, is the transmission frequency after compensating the frequency shift; is the standard frequency of the uplink signal;

[0141] The compensation calculation formula for the reception frequency in the fine frequency tracking mode is:

[0142] ;

[0143] In the formula, is the reception frequency after compensating the frequency shift; is the standard frequency of the downlink signal;

[0144] Furthermore, after step S4), the calculated instantaneous frequency offset is subjected to Kalman filtering or moving average filtering, and then the corresponding subsequent compensation calculation is performed, thereby reducing the influence of noise in the phase difference calculation and further improving the accuracy of frequency compensation.

[0145] Furthermore, the relative speed between the satellite and the ground communication terminal, the standard frequency of the uplink signal of the communication terminal, and the standard frequency of the downlink signal can all be obtained from the known satellite orbit information.

[0146] It should be noted that the orbital information of the satellite mentioned in the present invention, including orbital altitude, relative speed, etc., can be accurately calculated by a satellite orbital mechanics model (such as the Kepler orbital model).

[0147] The standard frequencies of the uplink and downlink signals of the satellite communication system are pre-planned according to standard organizations such as the International Telecommunication Union (ITU), and are usually fixed frequency bands. Therefore, the standard frequencies of the uplink signal and the downlink signal are known. Therefore, the present invention does not perform specific calculations.

[0148] The present invention is based on the frequency tracking mode switching mechanism of the Doppler frequency shift change rate. By setting a reasonable threshold, the terminal can dynamically switch between the fast frequency tracking mode and the fine frequency tracking mode to ensure adaptation to different satellite motion states and frequency shift changes. The fast frequency tracking mode uses the Doppler frequency shift formula to deal with large frequency offsets, while the fine frequency tracking mode achieves high-precision compensation through the phase difference method to ensure frequency correction accuracy in different frequency shift scenarios.

[0149] This dynamic switching mechanism can not only significantly improve the stability and reliability of the communication link, but also accurately correct the transmission and reception frequencies of the ground terminal according to the real-time motion status. It is particularly suitable for scenarios where satellites move at high speeds, and has wide practicality and advancement. Compared with existing technologies, this solution can deal with frequency shift problems more flexibly and efficiently, ensuring smooth narrowband communication.

[0150] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the terminals, modules and electronic devices described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0151] In several embodiments provided in this application, it should be understood that the disclosed terminals, modules, and methods can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For example, the division of the units is only a logical function division. In actual implementation, there can be other division methods. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the displayed or discussed coupling, direct coupling, or communication connection between each other can be through some interfaces. The indirect coupling or communication connection of the device or unit can be in electrical, mechanical, or other forms.

[0152] In addition, each functional unit in various embodiments of this application can be integrated in a processing unit, or each unit can exist physically alone, or two or more units can be integrated in one unit. The above-mentioned integrated unit can be implemented in the form of hardware or in the form of a software functional unit.

[0153] If the above-mentioned integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or all or part of this technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to enable a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in various embodiments of this application. The foregoing storage medium includes: various media such as USB flash drives, mobile hard disks, read-only memories (ROM, read-only memory), random access memories (RAM, random access memory), magnetic disks, or optical discs that can store program codes.

[0154] In the description of the specification, the description with reference to terms such as "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials, or characteristics described in combination with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0155] The above content is only an example and explanation of the structure of the present invention. Those skilled in the art of this technology can make various modifications or supplements to the described specific embodiments or use similar methods to replace them, as long as they do not deviate from the structure of the invention or exceed the scope defined by this claim book, they should all belong to the protection scope of the present invention.

Claims

1. A satellite narrowband communication terminal, characterized in that: It includes a radio frequency receiving module, a frequency tracking module, and a radio frequency transmitting module; The radio frequency receiving module is used to receive radio frequency signals transmitted from the satellite link, and perform down-conversion, filtering, and demodulation processing to convert them into baseband signals; The frequency tracking module is used to selectively switch the frequency tracking mode according to the Doppler frequency shift change rate of the baseband signal by setting reasonable thresholds under different motion states of the satellite relative to the ground communication terminal, including the fast frequency tracking mode or the fine frequency tracking mode; The fast frequency tracking mode or the fine frequency tracking mode adopts different frequency shift compensation algorithms to dynamically compensate the transmission frequency and reception frequency of the ground communication terminal to ensure the stability of the communication link; The radio frequency transmitting module is used to dynamically correct the transmission frequency of the ground communication terminal according to the real-time calculation results of the frequency tracking mode; The radio frequency receiving module is also used to dynamically correct the reception frequency of the ground communication terminal according to the real-time calculation results of the frequency tracking mode; The implementation process of the frequency tracking module includes: Performing feature extraction on the received baseband signal, and by analyzing its frequency change characteristics, calculating the Doppler frequency shift change rate in the baseband signal in real time; Setting a threshold for the Doppler frequency shift change rate for switching different frequency tracking modes; When the Doppler frequency shift change rate is greater than the set threshold, switch to the fast frequency tracking mode, and the fast frequency tracking mode uses the Doppler frequency shift formula to calculate the compensation amount; When the Doppler frequency shift change rate is less than the set threshold, switch to the fine frequency tracking mode, and the fine frequency tracking mode uses the phase difference method to calculate the compensation amount.

2. A satellite narrowband communication terminal according to claim 1, wherein: The calculation method of the Doppler frequency shift change rate is: Calculating the change rate of the Doppler frequency shift by calculating the change of the Doppler frequency shift over time, and its calculation formula is: ； Wherein, is the rate of change of the Doppler frequency shift within a specific time interval; is the specific time interval; is the amount of the Doppler frequency shift of the downlink signal; The process of the fast frequency tracking mode using the Doppler frequency shift formula to calculate the compensation amount includes: Calculating the frequency offset caused by the Doppler effect according to the relative velocity between the satellite and the ground terminal; its calculation formula is: ； ； In the formula, is the Doppler frequency shift of the uplink signal, is the standard frequency of the uplink signal; is the Doppler frequency shift of the downlink signal, is the standard frequency of the downlink signal; is the relative velocity between the satellite and the ground communication terminal, is the speed of light; Performing corresponding compensation according to the Doppler frequency shift amount, wherein the compensation calculation formula for the transmission frequency in the fast frequency tracking mode is: ； In the formula, is the transmitted frequency after compensating for the frequency shift; The compensation calculation formula for the reception frequency in the fast frequency tracking mode is: ； In the formula, is the received frequency after compensating for the frequency shift.

3. The satellite narrowband communication terminal according to claim 1, characterized in that: The process of the fine frequency tracking mode using the phase difference method to calculate the compensation amount includes: S1) Sampling the received baseband signal, setting an appropriate sampling rate, and converting the continuous sampled data analog signal into a discrete digital signal, which is represented by a functional relationship as: ， ， ； In the formula, is the discrete digital signal after sampling; is the sampling period, and n is the sampling point serial number; S2) Performing low-pass filtering on the sampled discrete digital signal to extract the baseband frequency component; the filtering formula for the baseband frequency component is: ； In the formula, represents the baseband frequency component; is the standard frequency of the downlink signal, represents the mixing operation; S3) Calculating the signal phase information in the baseband frequency component, and then extracting the signal phase sequence for analyzing the change of the signal frequency. The signal phase sequence can be expressed as: ； wherein, is the phase sequence of the signal; is the imaginary part of the signal, is the real part of the signal; S4) The frequency offset will cause the phase to change over time. Calculate the instantaneous frequency offset through the phase difference between adjacent sampling points, and the calculation formula is: ； ； wherein, is the phase difference, representing the phase change between adjacent sampling points; is the instantaneous frequency offset; is the sampling period, and n is the sampling point serial number; S5) Performing corresponding compensation according to the instantaneous frequency offset amount, wherein the compensation calculation formula for the transmission frequency in the fine frequency tracking mode is: ； Wherein, is the transmission frequency after compensating for the frequency shift; is the standard frequency of the uplink signal; The compensation calculation formula for the received frequency in the fine frequency tracking mode is as follows: ； Wherein, is the received frequency after compensating for the frequency shift; is the standard frequency of the downlink signal.

4. A satellite narrowband communication terminal according to claim 3, characterized in that: Between step S4) and step S5), it further includes: performing Kalman filtering or moving average filtering on the calculated instantaneous frequency offset, and then performing subsequent corresponding compensation calculations.

5. A satellite narrowband communication terminal according to claim 2 or 3, characterized in that: The relative velocity between the satellite and the ground communication terminal, the standard frequency of the uplink signal and the standard frequency of the downlink signal of the communication terminal are all obtained from the known satellite orbit information.

6. A satellite narrowband communication terminal according to any one of claims 1-4, characterized in that: The RF receiving module includes a downconverter, a local oscillator, a filter, and a demodulator; The downconverter is used to convert the high-frequency satellite signal into a baseband signal; The local oscillator is used to dynamically adjust the local oscillator frequency according to the received frequency after compensating for the frequency shift, so as to ensure correct mixing of the received RF signal in cooperation with the downconverter; The filter is used to filter out interference signals and retain the target band signals; The demodulator is used to modulate the baseband signal and convert it into a baseband digital signal or an analog signal.

7. A satellite narrowband communication terminal according to any one of claims 1-4, characterized in that: The RF transmitting module includes a local oscillator and a power amplifier; the local oscillator is used to dynamically adjust the local oscillator frequency according to the transmitted frequency after compensating for the frequency shift; The power amplifier is used to amplify the RF signal after modulation and frequency adjustment.

8. A satellite narrowband communication terminal according to any one of claims 1-4, characterized in that: The frequency tracking module includes a phase calculator, a pilot timer, and a phase-locked loop controller; The phase calculator is used to calculate the phase, that is, the argument, according to the real part and the imaginary part of the baseband signal; The pilot timer is used to convert and output the pilot signal in the baseband signal into a time signal to provide the time count in the phase difference calculation process; The phase-locked loop controller is used to calculate the change rate of the Doppler frequency shift in real time, compare the change rate of the Doppler frequency shift with a set threshold for determination, and then select and switch different frequency tracking modes; the phase-locked loop controller is also used to calculate the Doppler frequency shift compensation amount in real time and output the transmitted frequency or the received frequency after compensating for the frequency shift.

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