Time-frequency pre-compensation access method and system for satellite-to-ground frequency hopping TDMA networking communication

Abstract

The invention provides a time-frequency pre-compensation access method and system for satellite-to-ground frequency hopping TDMA networking communication, and belongs to the technical field of satellite communication. According to the method, time-frequency offset dynamic estimation is carried out on a time slot access module of a satellite-ground frequency hopping TDMA networking communication load, the azimuth elevation and distance of satellite-ground high-speed relative movement are estimated in real time according to broadcast ephemeris TLE and satellite-ground frequency hopping TDMA networking communication system time, and the time-frequency offset of a satellite-ground link for receiving and transmitting a time slot is dynamically estimated according to the azimuth elevation and distance. Slot-by-slot uplink and downlink propagation time delay pre-compensation is performed on a physical layer processing module of a satellite-ground frequency hopping TDMA networking communication load, and satellite-ground alignment of a time-varying frequency hopping pattern is achieved by compensating downlink propagation time delay through advanced emission of a satellite-borne transmitter and compensating uplink propagation time delay through lagging reception of a satellite-borne receiver; through real-time resolving of satellite-ground relative motion, Doppler frequency offset estimation and frequency offset pre-compensation are carried out frequency point by frequency point, and the purpose that satellite-ground receiving and transmitting frequencies are consistent is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of satellite communications, and in particular relates to a time-frequency pre-compensation access method and system for satellite-to-ground frequency hopping TDMA networking communications. Background Art

[0002] In recent years, low-orbit satellite communication-related businesses are gradually growing, and ground users have increasing demands for network access flexibility. Ground mobile communication systems can no longer meet the transmission needs of many businesses in terms of network coverage, communication bandwidth, etc. Low-orbit satellite communication systems are high up and rely on the sky to build networks, which can effectively overcome geographical constraints and provide wireless access and relay transmission services comparable to ground mobile communication systems in the air, offshore, high mountains, wastelands, and remote areas.

[0003] A typical satellite-to-ground frequency-hopping TDMA networking communication system consists of a low-orbit satellite constellation equipped with satellite-to-ground frequency-hopping TDMA networking communication payloads, user terminals of ground frequency-hopping TDMA networking communication terminals, and network elements such as gateway stations and network management stations in the ground segment. Low-orbit satellite constellations are mainly deployed in low-Earth orbits 200 to 2000 kilometers from the ground. They have the advantages of lower communication latency, more available bandwidth, lower power consumption of satellites in orbit, and higher network capacity available for the entire network. The satellite-to-ground frequency-hopping TDMA networking communication payload provides satellite relay transmission services to user terminals through satellite-to-ground links and inter-satellite links, and the network management station provides wireless resource management and user access services to user terminals through feeder links. Optionally, the gateway station, as a gateway node, can achieve interconnection and service expansion with other ground communication systems through wired connections.

[0004] The satellite-ground frequency-hopping TDMA networking communication system requires the use of a satellite-ground integrated transmission system to ensure backward compatibility with the existing ground frequency-hopping TDMA networking communication transmission system and avoid changes or new designs to ground user equipment. The satellite-ground integrated transmission system enables existing user terminals to directly access the satellite-ground frequency-hopping TDMA networking communication system without relying on the relay backhaul of the ground signal gateway, which is conducive to the satellite-ground link optimization and flexible access of user terminals.

[0005] The satellite-to-ground frequency-hopping TDMA networking communication system based on the satellite-to-ground integrated transmission system can form a multi-access communication system that is interconnected and backed up with the ground frequency-hopping TDMA networking communication system, thereby improving the network coverage, flexible access and long-range relay transmission capabilities of the original ground frequency-hopping TDMA networking communication system.

[0006] However, the satellite-to-ground transmission channel characteristics of the satellite-to-ground frequency-hopping TDMA networking communication system are different from those of the ground transmission link. This is mainly reflected in the fact that the dynamics of the propagation delay and carrier frequency offset of the low-orbit satellite-to-ground link are significantly increased compared to the ground-based frequency-hopping TDMA networking communication system. Taking a satellite altitude of 1000km and a minimum receiving elevation angle of 10° as an example, the dynamic range of the satellite-to-ground transmission distance is 1000-2750km, and the dynamic range of the satellite-to-ground transmission delay is about 3.3-9.2ms, which exceeds the time slot width of the ground-based frequency-hopping TDMA networking communication system; the satellite-to-ground Doppler frequency shift varies from 0 to 25.5kHz, which exceeds the maximum anti-Doppler capability (5.55kHz) of the ground-based frequency-hopping TDMA networking communication system.

[0007] Compared with the ground transmission link, the propagation delay of low-orbit satellite to the ground is significantly increased, which has an adverse impact on the time-varying frequency hopping communication system. This is mainly manifested in that when the transmission signal of the current time slot reaches the receiving end, the initial synchronization of the receiving end may have switched to the frequency hopping pattern of the next time slot. The inconsistency of the time-varying frequency hopping patterns of the transmitting and receiving ends will lead to synchronization capture failure, signal loss and link interruption.

[0008] Compared with the ground transmission link, the Doppler frequency deviation of low-orbit satellites to the ground is significantly increased, which has an adverse effect on time-frequency synchronization and signal demodulation, mainly in two aspects: first, the large Doppler frequency deviation formed by the high-speed movement of the satellite and the ground causes the correlation peak to decrease, reducing the sensitivity of the satellite-to-ground link synchronization capture. When the satellite-to-ground link margin is small, the probability of link interruption is high; second, when there is a large Doppler frequency deviation, the inconsistency of the Doppler frequency deviation of each frequency point of the broadband frequency hopping communication system cannot be ignored. The method that simply relies on the Doppler frequency deviation estimation will bring large estimation errors, resulting in a decrease in the quality of the demodulated signal and an increase in the demodulation sensitivity. Summary of the invention

[0009] Under the constraints of the satellite-to-ground integrated transmission system, the transmission processing mechanism of the user terminal cannot be changed. The above problems require the use of a time-frequency pre-compensation access method for satellite-to-ground frequency hopping TDMA networking communication payload to pre-correct delay and frequency offset, thereby improving the synchronization capture probability, frequency accuracy and demodulation signal quality of the satellite-to-ground link. Therefore, the present invention proposes a time-frequency pre-compensation access scheme for satellite-to-ground frequency hopping TDMA networking communication.

[0010] The first aspect of the present invention proposes a time-frequency pre-compensation access system for satellite-to-ground frequency hopping TDMA networking communications, which corrects the delay deviation and Doppler frequency deviation of satellite-to-ground frequency hopping TDMA networking communications, so that the transmission waveform of the satellite-to-ground frequency hopping TDMA networking communications payload adapts to the time-varying high-dynamic channel propagation characteristics; the time-frequency pre-compensation access system includes an ephemeris solution module, an azimuth pointing estimation module, a delay estimation and compensation module, and a frequency deviation estimation and compensation module.

[0011] According to the system of the first aspect of the present invention, the ephemeris solution module is configured to: calculate the satellite position and speed, calculate the satellite-ground orientation according to the satellite position and the ground station position, and output the satellite's azimuth, elevation angle and relative distance to the ground.

[0012] According to the system of the first aspect of the present invention, the beam pointing estimation module is configured to: execute beam pointing control, perform coordinate transformation of the beam direction angle according to the satellite attitude, and transform the beam pointing angle into an antenna direction angle with the satellite local coordinate system as the reference coordinate.

[0013] According to the system of the first aspect of the present invention, the delay estimation and compensation module is configured to: pre-compensate the propagation delay of the satellite-borne transmitting and receiving time slots, send the satellite-borne transmitting time slots in advance according to the minimum propagation delay compensation principle within the beam, and delay the reception of the satellite-borne receiving time slots, so that the maximum propagation delay difference within the beam is less than the synchronization capture window, and the satellite-ground time slots are aligned and the frequency hopping patterns are aligned.

[0014] According to the system of the first aspect of the present invention, the frequency deviation estimation and compensation module is configured to: estimate the Doppler frequency deviation of satellite motion, and perform Doppler frequency shift estimation and frequency deviation pre-compensation of the satellite relative to the center point of the ground mission area according to the principle of independent compensation of satellite-to-ground motion and ground-to-ground motion.

[0015] According to the system of the first aspect of the present invention, the ephemeris solution module is specifically configured as follows: in each transmit and receive time slot, satellite orbit extrapolation is performed in advance according to the time slot table, and six satellite orbit numbers are obtained according to the current satellite broadcast ephemeris TLE, including: orbit semi-major axis a, orbit eccentricity e, orbit inclination i, ascending node right ascension Ω, perigee argument ω and mean anomaly M; orbit recursion is performed according to the six satellite orbit numbers and the system time of the satellite-to-ground frequency hopping TDMA communication system, the satellite position and speed of the transmit and receive time slot are predicted, the coordinates are converted to the Earth-centered Earth-fixed ECEF coordinate system, the satellite-to-ground position pointing calculation is performed according to the position of the ground station, and the satellite-to-ground azimuth, pitch angle and satellite-to-ground relative distance of the satellite pointing to the ground are output.

[0016] According to the system of the first aspect of the present invention, the beam pointing estimation module is specifically configured to: calculate the beam pointing parameters according to the current attitude of the satellite, convert the beam pointing angle into the antenna direction angle, allocate the beam steering vector according to the antenna direction angle and the carrier wavelength, and use the phase shifter unit of the phased array antenna to perform the beam control function.

[0017] According to the system of the first aspect of the present invention, the delay estimation and compensation module is specifically configured to estimate the propagation distance and propagation delay of the lower edge of the beam according to the beam pointing angle, thereby determining the parameters of the delay compensation, and use this to calculate the time slot offset of the transmitting and receiving time slots.

[0018] According to the system of the first aspect of the present invention, the frequency offset estimation and compensation module is specifically configured to: perform Doppler frequency shift estimation based on the beam pointing angle and the carrier frequency point, generate a Doppler frequency shift estimation result for frequency value correction of the frequency hopping pulse sequence.

[0019] The second aspect of the present invention proposes a time-frequency pre-compensation access method for satellite-to-ground frequency hopping TDMA networking communications. The method utilizes the time-frequency pre-compensation access system described in the first aspect of the present invention to implement time-frequency pre-compensation access for satellite-to-ground frequency hopping TDMA networking communications; the method performs satellite position extrapolation and delay compensation under the triggering of a timeslot access control signal, and estimates Doppler frequency offset compensation, thereby adapting to satellite-to-ground link delays and dynamic transmission channel characteristics.

[0020] The method comprises:

[0021] Initialization parameter analysis: When the processor of the satellite-to-ground frequency-hopping TDMA networking communication payload is powered on, parameters are injected, or the task is taken over, the system parameter initialization operation is performed. By reading the broadcast ephemeris, mission area parameters, and time slot allocation table, the initialization parameters of the satellite orbit recursion and time-frequency pre-compensation estimation are updated;

[0022] Ephemeris recursive estimation: perform ephemeris calculation under the trigger signal of the transmit and receive time slot to estimate the satellite position, speed and satellite beam pointing angle;

[0023] Satellite-ground position estimation: Based on the satellite position and the virtual ground station position, the relative position vector of the user terminal and the satellite is calculated, and the relative distance between the satellite and the ground, the satellite-to-ground azimuth angle, and the satellite-to-ground elevation angle are further calculated for delay compensation estimation and Doppler frequency offset compensation estimation;

[0024] Minimum delay compensation estimation within the beam: Using the minimum propagation delay compensation within the beam, the downlink signal is transmitted in advance, and the closest point starts to capture the signal at time zero of the receiving time slot. Other nodes capture the frequency hopping signal of this time slot within the synchronization capture window of no more than 1 time slot. In the uplink, the synchronization capture window is delayed, and the closest point starts to capture at the starting point of the synchronization capture window.

[0025] Doppler frequency offset compensation estimation: Calculate the linear velocity of the satellite movement, and calculate the angle between the satellite movement direction and the satellite-ground line based on the three cosine theorem of the space triangle, and further calculate the Doppler frequency offset caused by the high-speed movement of the satellite relative to the ground;

[0026] Time-frequency pre-compensation parameter transfer: The time-frequency pre-compensation parameter transfer is carried out by adopting the associated control method. The three groups of estimation results including beam pointing control, delay compensation estimation and Doppler compensation estimation are encapsulated into the access control field of the data packet and distributed through the associated control signal at the time of time slot access.

[0027] According to the method of the second aspect of the present invention, the initialized parameter data structure includes:

[0028] (1) Broadcast ephemeris TLE

[0029] TLE ephemeris; character encoding, consisting of two lines of numbers, a total of 21 fields, including: NORAD satellite number, orbit inclination i, ascending node right ascension Ω, orbit eccentricity e, perigee argument ω, mean anomaly M, mean angular velocity n;

[0030] Orbital elements; the only parameters required to determine the trajectory of a space object, including: orbital semi-major axis a, orbital eccentricity e, orbital inclination i, ascending node right ascension Ω, perigee argument ω and mean anomaly M, that is, the six orbital elements;

[0031] Convert from TLE ephemeris to six numbers, read TLE ephemeris, and convert the number of circles around the earth n into the orbital semi-major axis a; according to Kepler's third law, the relationship between the orbital semi-major axis a and n is:

[0032]

[0033] GM = 3.986005e14, which is the standard gravitational constant of the earth. The six orbital elements are used for satellite orbit recursion. According to the satellite motion period and differential elapsed time, the mean anomaly and true anomaly are updated, and the longitude and latitude coordinates are transformed according to the rotation of the earth.

[0034] (2) Task area parameters

[0035] The mission area parameters come from the mission coverage parameters noted on the ground, including: the coordinates of the mission area center point Gs (x, y, z) and the moving trajectory; the mission area center point is a virtual ground station, and the mission area center point coordinates are used to identify the geographic coordinates of the virtual ground station;

[0036] (3) Time Slot Allocation Table

[0037] According to the satellite-to-ground frequency hopping TDMA networking communication system message standard, time slots are allocated to different service types in the form of network participation groups (NPGs); the locally stored time slot allocation table identifies the occupancy status of each time slot within a time frame in units of time frames, including transmission, reception, and idle; the transmission and reception time slots are actually occupied time slots, which perform signal transmission and reception processing and corresponding time-frequency pre-compensation.

[0038] According to the method of the second aspect of the present invention, the recursive estimation of ephemeris specifically includes:

[0039] (1) Calculation of prediction delay

[0040] Prediction delay T k Refers to the satellite starting time T oe To the prediction time T pred The delay, Tk =T pred –T oe ;

[0041] (2) Calculation of mean anomaly angle

[0042] The satellite moves in the low earth orbit. At the time T predicted by the ephemeris k The mean anomaly angle is:

[0043] M k =M0+n·T k

[0044] M k M0 and M1 are the mean anomaly angles at the time of broadcast ephemeris and the time of ephemeris prediction respectively; n is the average angular velocity, T k To predict the time for the ephemeris;

[0045] (3) Solving the partial anomaly angle and true anomaly angle

[0046] The calculation formula of the eccentric anomaly angle E is:

[0047] E n =M k +e·sin(E n-1 )

[0048] E n is the true anomaly, and e is the eccentricity. For satellites in elliptical orbits, the eccentric anomaly is solved by an iterative method. For satellites in near-circular orbits, E≈M k ;

[0049] The calculation formula of the true anomaly angle f is:

[0050]

[0051] For satellites in near circular orbit, f≈E≈M k ;

[0052] (4) Satellite position calculation

[0053] The unit vector of the perigee orientation is P, and the vector Q is the unit vector perpendicular to P on the orbital plane. Then the vector of the satellite in the geocentric inertial coordinate system ECI is:

[0054]

[0055] r is the distance between the satellite and the center of the earth; vectors P and Q are expressed as:

[0056]

[0057] The velocity vector of the satellite in the ECI coordinate system is obtained by taking the derivative of the position vector with respect to t:

[0058]

[0059] In the process of calculating the satellite motion parameters, the satellite coordinates in the ECI coordinate system are converted to the Earth-centered Earth-fixed coordinate system ECEF. The satellite coordinates in the ECI coordinate system rotate around its Z axis by the Greenwich time angle θ g , and obtain its coordinates in the ECEF coordinate system:

[0060]

[0061] θ g =θ g0 +W e (t-t0), θ g0 is the Greenwich hour angle at time t0, W e is the angular velocity of the Earth's rotation.

[0062] According to the method of the second aspect of the present invention, the star location estimation specifically includes:

[0063] According to the satellite position sat =r ECEF =[r sx ,r sy ,r sz ] and the virtual ground station position r gs =[r gx ,r gy ,r gz ], and obtain the relative position vector of the user terminal and the satellite:

[0064] r r =r gs -r sat =[r rx ,r ry ,r rz ]

[0065] Relative distance between satellite and ground R r for:

[0066]

[0067] Star-to-ground azimuth angle A z for:

[0068]

[0069] Satellite-to-ground elevation angle E l for:

[0070]

[0071] Relative distance between satellite and ground R r 、Star-to-ground azimuth A z , satellite-to-ground elevation angle El The satellite position is calculated to obtain the beam pointing of the satellite to the virtual ground station for delay compensation estimation and Doppler frequency offset compensation estimation.

[0072] According to the method of the second aspect of the present invention, the minimum delay compensation estimation within the beam specifically includes:

[0073] (1) Delay compensation calculation

[0074] In each transmit and receive time slot, the minimum propagation delay in the beam corresponds to the lower edge angle of the beam in the section diagram of the satellite-ground elevation angle. In the section diagram of the elevation angle, according to the sine theorem of plane trigonometry, the ground station elevation angle α corresponding to the lower edge of the beam is:

[0075]

[0076] r is the distance between the star and the earth, r e is the radius of the Earth, E l is the elevation angle of the satellite to the center of the mission area, γ is the half beam width; the geocentric angle θ between the virtual ground station corresponding to the lower edge of the beam and the satellite is:

[0077] θ=90-(E l -γ)-α

[0078] The minimum propagation delay Tp corresponding to the lower edge of the beam min for:

[0079]

[0080] c is the speed of light propagation;

[0081] (2) Delay Compensation Strategy

[0082] Different delay compensation strategies are implemented for the receiving and transmitting time slots. The usage status of the time slot is read according to the time slot allocation table. Uts∈{1,-1,0} corresponds to the three time slot usage states of receiving, sending, and idle respectively. The delay pre-compensation of the receiving and transmitting time slots is dynamically assigned as {Tp min ,-Tp min ,0}.

[0083] According to the method of the second aspect of the present invention, the Doppler frequency offset compensation estimation specifically includes:

[0084] For a satellite in a near circular orbit, according to Kepler's third law, the linear velocity of the satellite is:

[0085]

[0086] GM is the standard gravitational constant of the earth, r is the distance between the satellite and the earth; the satellite moves relative to the earth, so that the angle between the satellite's motion direction and the direction of the virtual ground station changes over time. According to the three cosine theorem of the space triangle, the angle between the satellite's motion direction and the line connecting the satellite and the earth is:

[0087] dir sat =arccos[cos(A z )cos(E l )]

[0088] dir sat The Doppler frequency deviation f caused by the high-speed movement of the satellite relative to the ground is d0 The calculation method is:

[0089]

[0090] f0=1GHz is the nominal frequency.

[0091] The third aspect of the present invention proposes a method for physical layer processing of satellite-borne time-frequency precompensation. Based on the time-frequency precompensation access method described in the second aspect of the present invention, the method constrains the physical layer processing of satellite-borne time-frequency precompensation; the physical layer processing of satellite-borne time-frequency precompensation includes beam pointing control, delay precompensation processing, and Doppler frequency offset precompensation processing.

[0092] According to the method of the third aspect of the present invention, the beam pointing control includes: performing coordinate transformation of the beam direction angle according to the satellite attitude, converting the beam pointing angle into the antenna direction angle in the satellite local coordinate system; calculating the beam pointing parameters according to the current attitude of the satellite, and converting the beam pointing angle into the antenna direction angle; allocating the beam steering vector according to the antenna direction angle and the carrier wavelength, and outputting it to the phase shifter unit of the phased array antenna to perform the wave control function of this time slot.

[0093] According to the method of the third aspect of the present invention, the delay pre-compensation processing includes:

[0094] Read the control word of the transmit and receive time slots, and perform three types of time slot control: reception delay, transmission advance, and idle time slot non-processing according to the delay pre-compensation control word. The frequency hopping pattern of each time slot matches the delay characteristics of the corresponding star link.

[0095] For downlink signal transmission, the transmitter timing advance -Tp is used min , the satellite signal is transmitted downlink to the ground user equipment, and the starting time when the user equipment receives the same beam signal varies in the range of {0, Tp max -Tp min}, the synchronization acquisition window length of the user equipment is set to the maximum delay difference within the beam;

[0096] For uplink signal reception, the receiver timing lag Tp is used. min , the user equipment signal is transmitted uplink to the satellite payload receiver, and the starting time of the satellite payload receiving the signal in the same beam varies within the range of {Tp min , Tp max}, the end of the received signal frame is at Tp at the latest max +Ts-T prot Time to reach the receiving end;

[0097] According to the method of the third aspect of the present invention, the Doppler frequency offset pre-compensation processing includes:

[0098] In each time slot, the angle between the satellite's motion direction and the satellite-to-ground line changes constantly; the Doppler frequency deviation of each frequency point in the frequency hopping frequency point set is only linearly related to the frequency point value; in the Doppler frequency deviation estimation, f0=1GHz is used as the nominal frequency point, and the Doppler frequency deviation of other frequency points is multiplied by the corresponding linear amplification factor β i =f i / f0, then each frequency point f i The Doppler frequency deviation is:

[0099] f di =β i ·f d0

[0100] f di is the Doppler frequency deviation estimation of each frequency point in the frequency point set, f d0 It is a Doppler frequency offset estimation for a nominal frequency point of 1 GHz. During the frequency hopping pattern and frequency synthesis of the satellite-borne transmitter and receiver, each frequency point compensates for the corresponding Doppler frequency offset estimation value according to the frequency hopping sequence, thereby compensating against high dynamic Doppler frequency offset.

[0101] Through the delay and Doppler pre-compensation mechanism based on online real-time estimation, the satellite-borne transmitter and receiver can achieve unified setting of frequency hopping synchronization parameters and multi-user time slot alignment without users noticing. Without changing the ground user equipment, the uplink and downlink transmission of the satellite-to-ground link can adapt to the ground frequency hopping TDMA networking communication system.

[0102] In summary, the present invention performs dynamic estimation of time-frequency deviation in the time slot access module of the satellite-to-ground frequency hopping TDMA networking communication payload, estimates the azimuth-elevation-range (AER) and the azimuth-elevation-range (AER) of the satellite-to-ground high-speed relative motion in real time according to the broadcast ephemeris (TLE: two-line orbital element) and the satellite-to-ground frequency hopping TDMA networking communication system (Time Cycle: Epoch / Frame / Slot), and dynamically estimates the satellite-to-ground link time-frequency deviation of the transceiver time slot. Pre-compensation of uplink and downlink propagation delays is performed time slot by time slot in the physical layer processing module of the satellite-to-ground frequency hopping TDMA networking communication payload, and the satellite-to-ground alignment of the time-varying frequency hopping pattern is achieved by compensating the downlink propagation delay by early transmission of the satellite-borne transmitter and compensating the uplink propagation delay by delayed reception of the satellite-borne receiver; Doppler frequency deviation estimation and frequency deviation pre-compensation are performed for each frequency point by real-time solution of the satellite-to-ground relative motion, so as to achieve the purpose of consistent satellite-to-ground transceiver frequency. BRIEF DESCRIPTION OF THE DRAWINGS

[0103] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0104] Figure 1 This is a structural diagram of the time-frequency pre-compensation access system;

[0105] Figure 2 The present invention is a flow chart of a time-frequency pre-compensation access method.

[0106] Figure 3 Elevation slice view of beam coverage.

[0107] Figure 4 This is a flow chart of the Doppler frequency shift pre-compensation method for onboard payloads. DETAILED DESCRIPTION

[0108] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0109] Compared with the ground transmission link, the propagation delay and Doppler frequency deviation of low-orbit satellites to the ground are significantly increased, which will lead to problems such as frequency hopping pattern loss, synchronization capture failure, sensitivity reduction and link interruption in the synchronous frequency hopping communication system. At the same time, under the backward compatibility constraints of satellite-to-ground transmission, the transmission encryption, capture window, coherent demodulation, channel estimation and other transmission mechanisms and system parameters of existing user equipment are not allowed to change.

[0110] In view of this, the present invention provides a time-frequency pre-compensation access scheme for satellite-ground coordinated TDMA networking. The basic idea is to dynamically estimate the time-frequency deviation in the time slot access module of the satellite-ground frequency hopping TDMA networking communication payload, and estimate the azimuth-elevation-range (AER) and the azimuth-elevation-range (AER) of the high-speed relative motion between the satellite and the ground in real time according to the broadcast ephemeris (TLE: two-line orbital element) and the satellite-ground frequency hopping TDMA networking communication system time (Time Cycle: Epoch / Frame / Slot), and dynamically estimate the satellite-ground link time-frequency deviation of the receiving and transmitting time slot. Pre-compensation of uplink and downlink propagation delays is performed slot by slot in the physical layer processing module of the satellite-ground frequency hopping TDMA networking communication payload, and the satellite-ground alignment of the time-varying frequency hopping pattern is achieved by compensating the downlink propagation delay by early transmission of the satellite transmitter and compensating the uplink propagation delay by delayed reception of the satellite receiver; Doppler frequency deviation estimation and frequency deviation pre-compensation are performed on a frequency-point by frequency-point basis through real-time solution of the satellite-ground relative motion, so as to achieve the purpose of consistent satellite-ground receiving and transmitting frequencies.

[0111] The technical solution described in the present invention includes: a time-frequency pre-compensation access system for satellite-to-ground frequency hopping TDMA networking communication, a time-frequency pre-compensation access method for satellite-to-ground frequency hopping TDMA networking communication, and a satellite-borne time-frequency pre-compensation physical layer processing method, which are described as follows.

[0112] 1. A time-frequency pre-compensation access system for satellite-to-ground frequency hopping TDMA networking communication (satellite-borne time-frequency pre-compensation access system, such as Figure 1 (shown)

[0113] During the high-speed movement of low-orbit satellites, the satellite's azimuth pointing direction, propagation delay and Doppler frequency shift are changing with time, which affects the transmission performance of the satellite-to-ground frequency-hopping TDMA networking communication system. The corresponding time-frequency delay deviation and Doppler frequency shift need to be corrected so that the transmission waveform of the satellite-to-ground frequency-hopping TDMA networking communication payload can adapt to the time-varying high-dynamic channel propagation characteristics.

[0114] Since the satellite azimuth pointing, delay compensation and Doppler frequency shift compensation are all based on ephemeris solution for parameter estimation, the real-time estimation of satellite-borne time-frequency offset compensation adopts an integrated design, integrating the three functional components into the satellite-borne time-frequency pre-compensation access system. The functional composition of the satellite-borne time-frequency pre-compensation access system includes the ephemeris solution module, the azimuth pointing estimation module, the delay estimation and compensation module, and the frequency offset estimation and compensation module, as described below.

[0115] (1) Ephemeris calculation module

[0116] The main function of the ephemeris solution module is to calculate the satellite position and speed, and calculate the satellite's position and direction according to the satellite position and the ground station position, and output the satellite's azimuth, elevation and relative distance to the ground.

[0117] In each transmit and receive time slot, the ephemeris solution module performs satellite orbit extrapolation in advance according to the time slot table, and obtains six satellite orbit numbers according to the current satellite broadcast ephemeris (TLE), including six parameters: orbit semi-major axis a, orbit eccentricity e, orbit inclination i, ascending node right ascension Ω, perigee argument ω and mean anomaly M. According to the six satellite orbit numbers and the system time of the satellite-to-ground frequency hopping TDMA communication system, the orbit is recursively calculated to calculate the current satellite position and speed. After the coordinates are converted to the Earth-centered Earth-fixed (ECEF) coordinate system, the satellite-to-ground position pointing calculation is performed according to the position of the ground station or user terminal, and the azimuth, pitch angle and satellite-to-ground relative distance of the satellite pointing to the ground are output.

[0118] (2) Beam pointing estimation module

[0119] The main function of the beam pointing module is beam pointing control. It performs coordinate transformation of the beam direction angle according to the satellite attitude and converts the beam pointing angle into the antenna direction angle in the satellite local coordinate system.

[0120] The beam pointing parameter calculation converts the beam pointing angle into the antenna direction angle according to the current attitude of the satellite and outputs it to the beam control algorithm module. The latter allocates the beam steering vector according to the antenna direction angle and carrier wavelength and outputs it to the phase shifter unit of the phased array antenna to perform the beam control function.

[0121] (3) Delay estimation and compensation module

[0122] The main function of the delay estimation and compensation module is to pre-compensate the propagation delay of the satellite-borne transmit and receive time slots. According to the principle of minimum propagation delay compensation within the beam, the satellite-borne transmit time slot is sent in advance and the satellite-borne receive time slot is received late, so that the maximum propagation delay difference within the beam is less than the synchronization capture window, ensuring the alignment of the satellite-ground time slots and the frequency hopping pattern.

[0123] The parameters for delay compensation are calculated by estimating the propagation distance and propagation delay of the lower edge of the beam according to the beam pointing angle, and the time slot offset of the transmit and receive time slots is calculated based on this.

[0124] (4) Frequency offset estimation and compensation module

[0125] The main function of the frequency deviation estimation and compensation module is to estimate the Doppler frequency deviation of satellite motion. According to the principle of independent compensation of satellite-to-ground motion and ground-to-ground motion, the Doppler frequency shift of the satellite relative to the center of the ground mission area is estimated and the frequency deviation is pre-compensated.

[0126] The frequency offset estimation and compensation module calculates the parameters, estimates the Doppler frequency shift based on the beam pointing angle and carrier frequency, generates a set of Doppler frequency shift estimation results, and outputs them to the signal processing module for frequency value correction of the frequency hopping pulse sequence.

[0127] 2. A time-frequency pre-compensation access method for satellite-to-ground frequency hopping TDMA networking communication (a satellite-borne time-frequency pre-compensation access method, such as Figure 2-4 (shown)

[0128] The ephemeris solution and time-frequency precompensation module performs satellite position extrapolation, delay compensation, and Doppler frequency offset compensation estimation under the triggering of the time slot access control signal, which is used to adapt to the large delay and high dynamic transmission channel characteristics of the satellite-to-ground link. Specifically, the processing steps of the time-frequency offset precompensation access method include:

[0129] (1) Initialization parameter analysis

[0130] When the processor of the satellite-to-ground frequency-hopping TDMA networking communication payload is powered on, parameters are injected, or tasks are taken over, parameter initialization operations are performed. The time slot access module reads the broadcast ephemeris, mission area parameters, and time slot allocation table, and performs satellite orbit recursion and time-frequency pre-compensation estimation initialization parameter updates. The main data structures include:

[0131] a) Broadcast ephemeris

[0132] TLE ephemeris (TLE: two-line orbital element) is a broadcast ephemeris that complies with the North American Aerospace Defense Command (NORAD) international satellite orbit standard. It can describe information such as satellite number, orbit, position and speed, and is used for satellite trajectory tracking.

[0133] The TLE ephemeris is character-coded and consists of two lines of numbers with a total of 21 fields, mainly including: NORAD satellite number, orbital inclination i, ascending node right ascension Ω, orbital eccentricity e, perigee argument ω, mean anomaly M, and mean angular velocity n.

[0134] Orbital Elements are the only parameters required to determine the trajectory of a space object, mainly including six parameters: orbital semi-major axis a, orbital eccentricity e, orbital inclination i, ascending node right ascension Ω, perigee argument ω and mean anomaly M, also known as the six orbital elements.

[0135] To convert the TLE ephemeris to the six numbers, you need to read the TLE ephemeris and convert the number of orbits around the earth n into the orbital semi-major axis a. According to Kepler's third law, the relationship between the orbital semi-major axis a and n is

[0136]

[0137] In the formula, GM=3.986005e14 is the standard gravitational constant of the earth.

[0138] The six orbital numbers are used for satellite orbit recursion. According to the satellite motion period and differential elapsed time, the mean anomaly and true anomaly are updated, and the longitude and latitude coordinates are transformed according to the rotation of the earth.

[0139] b) Mission area parameters

[0140] The mission area parameters come from the mission coverage parameters recorded on the ground, mainly including: the coordinates of the center point of the mission area Gs (x, y, z), the moving trajectory, etc. The center point of the mission area can be regarded as a virtual ground station, and the coordinates of the center point of the mission area are used to identify the geographic coordinates of the virtual ground station.

[0141] c) Time slot allocation table

[0142] According to the satellite-to-ground frequency hopping TDMA networking communication system message standard, time slots are allocated to different service types in the form of network participation groups (NPG). The locally stored time slot allocation table identifies the occupancy status of each time slot in units of time frames, including transmission, reception, and idle. Among them, the transmission and reception time slots are actually occupied time slots, which require signal transmission and reception processing and corresponding time-frequency pre-compensation.

[0143] (2) Ephemeris Recursive Estimation

[0144] Under the trigger signal of the receiving and transmitting time slot, the ephemeris solution is performed to estimate the satellite position, speed and satellite beam pointing angle, including the following calculation steps:

[0145] a) Calculate the prediction delay

[0146] Prediction delay T k Refers to the satellite from the start time T oe To the prediction time T pred The delay, T k =T pred –T oe .

[0147] b) Calculate the mean anomaly angle

[0148] The satellite moves in the low-Earth orbit, and the mean anomaly angle at the ephemeris prediction time Tk is

[0149] M k =M0+n·T k (2)

[0150] Where M k M0 and M1 are the mean anomaly angles at the time of broadcast ephemeris and the time of ephemeris prediction respectively; n is the average angular velocity, T k For the ephemeris predicted time.

[0151] c) Solve for the eccentric anomaly and true anomaly

[0152] The calculation formula of the eccentric anomaly angle E is:

[0153] E n =M k +e·sin(E n-1 ) (3)

[0154] In the formula, E n is the true anomaly, and e is the eccentricity. For elliptical orbit satellites, the eccentric anomaly can be solved by an iterative method.

[0155] For near-circular orbit satellites, since the eccentricity is infinitely close to 0, the eccentric anomaly angle is approximately equal to the mean anomaly angle, that is, E≈M k .

[0156] The calculation formula of true anomaly angle f is:

[0157]

[0158] For near-circular orbit satellites, since the eccentricity is infinitely close to 0, the true anomaly angle and the eccentric anomaly angle are approximately equal, that is, f≈E≈M k .

[0159] d) Satellite position calculation

[0160] Assume that the unit vector of the perigee is P, and vector Q is the unit vector perpendicular to P on the orbital plane. Then the vector of the satellite in the geocentric inertial coordinate system (ECI) is:

[0161]

[0162] In the formula, r is the distance between the satellite and the center of the earth. Vectors P and Q can be obtained as follows.

[0163]

[0164] The velocity vector of the satellite in the ECI coordinate system can be obtained by taking the derivative of the position vector with respect to t.

[0165]

[0166] In the process of calculating satellite motion parameters, it is usually necessary to convert the satellite's coordinates in the ECI coordinate system to the coordinates in the earth-centered earth-fixed (ECEF) coordinate system. The satellite's coordinates in the ECI coordinate system rotate around its Z axis by the Greenwich time angle θ g , we can get its coordinates in the ECEF coordinate system:

[0167]

[0168] where θ g =θ g0 +W e (t-t0), θ g0 is the Greenwich hour angle at time t0, W e is the angular velocity of the Earth's rotation, which is approximately 7.2692e-5rad / s.

[0169] (3) Star location estimation

[0170] According to the satellite position sat =r ECEF =[r sx ,r sy ,r sz ] and the virtual ground station position r gs =[r gx ,r gy ,r gz ], the relative position vector between the user terminal and the satellite can be obtained

[0171] r r =r gs -r sat =[r rx ,r ry ,r rz ] (9)

[0172] At this time, the relative distance between the star and the ground is R r for

[0173]

[0174] Star-to-ground azimuth angle A z for

[0175]

[0176] Satellite-to-ground elevation angle E l for

[0177]

[0178] The above includes the relative distance between the satellite and the ground R r 、Star-to-ground azimuth A z , satellite-to-ground elevation angle E l The satellite position estimate, including the beam pointing value of the satellite to the virtual ground station, is given, which can be used for delay compensation estimation and Doppler frequency offset compensation estimation.

[0179] (4) Estimation of minimum delay compensation within the beam

[0180] The satellite moves at high speed relative to the ground, causing the beam pointing to change over time, and the propagation delay difference from different geographical areas within the beam coverage will also change. In order to reduce the impact of propagation delay on synchronization search and frequency hopping pattern alignment, the present invention adopts the minimum propagation delay compensation method within the beam, transmits the downlink signal in advance, so that the nearest point can start capturing the signal at zero time of the receiving time slot, and other nodes can capture the frequency hopping signal of this time slot within the synchronization capture window of no more than 1 time slot; conversely, the synchronization capture window is delayed in the uplink, so that the nearest point can start capturing at the starting point of the synchronization capture window, reducing power consumption.

[0181] a) Delay compensation calculation

[0182] In each transmit and receive time slot, the minimum propagation delay in the beam corresponds to the lower edge angle of the beam in the elevation angle section diagram. In the elevation angle section, according to the sine theorem of plane trigonometry, the ground station elevation angle α corresponding to the lower edge of the beam is

[0183]

[0184] Where r is the distance between the satellite and the earth, r e is the radius of the Earth, E l is the elevation angle of the satellite to the center of the mission area, and γ is the half beam width.

[0185] At this time, the geocentric angle θ between the virtual ground station corresponding to the lower edge of the beam and the satellite is

[0186] θ=90-(E l -γ)-α (14)

[0187] The minimum propagation delay Tp corresponding to the lower edge of the beam min for

[0188]

[0189] Where c is the speed of light propagation.

[0190] b) Delay compensation strategy

[0191] In order to implement different delay compensation strategies for the transmitting and receiving time slots, the present invention reads the use status of the time slot according to the time slot allocation table and stipulates that Uts∈{1,-1,0} corresponds to the three time slot use states of receiving, sending and idle respectively.

[0192] Correspondingly, the delay precompensation of the transmit and receive time slots is dynamically assigned to {Tp min ,-Tp min ,0}.

[0193] (5) Doppler frequency offset compensation estimation

[0194] For a satellite in a near circular orbit, according to Kepler's third law, the linear velocity of the satellite is

[0195]

[0196] Where GM is the standard gravitational constant of the Earth, and r is the distance between the star and the Earth.

[0197] The satellite moves at high speed, causing the angle between the satellite's direction of motion and the virtual ground station to change over time. According to the three cosine theorem of a space triangle, the angle between the satellite's direction of motion and the line connecting the satellite and the ground is:

[0198] dir sat =arccos[cos(A z )cos(E l )] (17)

[0199] In the formula, dir sat Indicates the angle between the satellite's motion direction and the line connecting the satellite and the ground.

[0200] At this time, the Doppler frequency deviation f caused by the high-speed movement of the satellite relative to the ground d0 The calculation is as follows

[0201]

[0202] In the formula, f0=1GHz is the nominal frequency.

[0203] (6) Time-frequency precompensation parameter transfer

[0204] The time-frequency pre-compensation parameter transmission adopts the in-path control method to encapsulate the three groups of estimation results including beam pointing control, delay compensation estimation, and Doppler compensation estimation into the access control field of the data packet and pass them to the time slot access control module, which distributes the in-path control signal to the execution modules such as beam algorithm and signal processing.

[0205] 3. A physical layer processing method for onboard time-frequency pre-compensation

[0206] The physical layer processing of onboard time-frequency pre-compensation includes three parts: beam pointing control, delay pre-compensation processing, and Doppler frequency offset pre-compensation processing, which are described as follows.

[0207] (1) Beam pointing control

[0208] Beam pointing control, performs coordinate transformation of beam direction angle according to satellite attitude, and converts the beam pointing angle into antenna direction angle with satellite local coordinate system as reference coordinate.

[0209] The beam pointing parameter calculation converts the beam pointing angle into the antenna direction angle according to the current attitude of the satellite and outputs it to the beam control algorithm module. The latter allocates the beam steering vector according to the antenna direction angle and carrier wavelength and outputs it to the phase shifter unit of the phased array antenna to perform the beam control function of this time slot.

[0210] (2) Delay pre-compensation processing

[0211] Delay pre-compensation processing reads the control word of the transmit and receive time slots, and according to the delay pre-compensation control word, performs three types of time slot control strategies: reception delay, transmission advance, and idle time slot non-processing, so that the frequency hopping pattern of each time slot matches the delay characteristics of the corresponding satellite-to-ground link.

[0212] For downlink signal transmission, the transmitter timing advance -Tp is used min , the satellite signal is transmitted downlink to the ground user equipment, and the starting time when the user equipment receives the same beam signal varies in the range of {0, Tp max -Tp min}, then the synchronization capture window length of the user equipment can be set to the maximum delay difference within the beam.

[0213] Taking a satellite altitude of 1000km and a minimum receiving elevation angle of 10° as an example, the satellite-to-ground transmission distance within the beam varies from 1630 to 2750km, the satellite-to-ground transmission delay dynamic range is approximately 5.4 to 9.2ms, and the maximum propagation delay difference within the beam is 3.8ms. The synchronization capture window of the user equipment is set to 4ms to meet the synchronization capture requirements of satellite-to-ground transmission.

[0214] For uplink signal reception, the receiver timing lag Tp is used. min , the user equipment signal is transmitted uplink to the satellite payload receiver, and the starting time of the satellite payload receiving the signal in the same beam varies within the range of {Tp min ,Tp max}, the end of the received signal frame is at Tp at the latest max +Ts-T prot Time to reach the receiving end.

[0215] Taking a satellite altitude of 1000km and a minimum receiving elevation angle of 10° as an example, the satellite-to-ground transmission distance within the beam varies from 1630 to 2750km, and the satellite-to-ground transmission delay dynamic range is approximately 5.4 to 9.2ms. The tail of the received signal frame arrives at the receiving end at the latest within 15ms, and the receiving time slot occupancy is less than 2 time slot widths, which can meet the idle time slot occupancy requirements.

[0216] (3) Doppler frequency offset pre-compensation processing

[0217] In each time slot, the angle between the satellite's motion direction and the satellite-to-ground line changes very little and can be considered a constant. According to equation (18), the Doppler frequency deviation of each frequency point in the frequency hopping frequency point set is only linearly related to the frequency point value. Therefore, in the Doppler frequency deviation estimation step, f0 = 1 GHz is used as the nominal frequency point, and the Doppler frequency deviations of other frequency points are multiplied by the corresponding linear amplification factor β i =f i / f0, then each frequency point f i The Doppler frequency deviation is

[0218] f di =β i ·f d0 (19)

[0219] In the formula, f di is the Doppler frequency deviation estimation of each frequency point in the frequency point set, f d0 is the Doppler frequency deviation estimate for the nominal frequency point of 1 GHz.

[0220] When the frequency hopping patterns and frequencies of the satellite-borne transmitter and receiver are synthesized, each frequency point compensates the corresponding Doppler frequency offset estimation value according to the frequency hopping sequence, so as to achieve the purpose of resisting high dynamic Doppler frequency offset.

[0221] Through the above-mentioned delay and Doppler pre-compensation mechanism based on online real-time estimation, the satellite-borne transmitter and receiver can realize the unified setting of frequency hopping synchronization parameters and multi-user time slot alignment without users noticing. Without changing the ground user equipment, the uplink and downlink transmission of the satellite-to-ground link can be adapted to the ground frequency hopping TDMA networking communication system, thus ensuring the effectiveness and reliability of satellite-to-ground integrated transmission.

[0222] The time-frequency pre-compensation access method for satellite-to-ground frequency-hopping TDMA networking communication of the present invention performs time-frequency offset estimation and pre-correction processing on the satellite-to-ground frequency-hopping TDMA networking communication payload according to the broadcast ephemeris, can adapt to the large delay and large frequency offset characteristics of the satellite-to-ground transmission channel, and does not change the transmission waveform, system parameters and processing method of the user equipment. It has the backward compatibility characteristics of the satellite-to-ground integrated transmission system and can be seamlessly compatible with the ground frequency-hopping TDMA networking communication system.

[0223] The satellite-borne time-frequency pre-compensation access method adopts a frame-by-frame pre-compensation method to estimate the satellite-to-ground propagation delay, supports real-time estimation and pre-correction processing of the minimum delay within the beam, and the propagation delay difference within the beam is less than the width of one time slot. On the one hand, it can reduce the number of protection time slots, and on the other hand, it can reduce the synchronization capture window width, thereby improving the synchronization capture efficiency of the receiver.

[0224] The on-board time-frequency pre-compensation access method adopts the reference point frequency shift estimation method to estimate the satellite-to-ground Doppler frequency shift, supports batch multi-frequency point frequency shift estimation and pre-correction processing of the frequency hopping frequency point set, and can improve the frequency correction synthesis efficiency of the frequency hopping pattern within the time slot.

[0225] The satellite-borne time-frequency pre-compensation access method uses a satellite position elevation angle estimation method based on spherical geometry to estimate the propagation delay and Doppler frequency shift. Compared with the traditional method based on analytic geometry, it has high computational efficiency and is more suitable for real-time calculation of on-board payloads.

[0226] The beneficial effects of the time-frequency pre-compensation access method for satellite-to-ground frequency hopping TDMA networking communication of the present invention include:

[0227] 1) The satellite-borne time-frequency pre-compensation access method performs time-frequency offset estimation and pre-correction processing on the satellite-to-ground frequency-hopping TDMA networking communication payload based on the broadcast ephemeris. It can adapt to the large delay and large frequency offset characteristics of the satellite-to-ground transmission channel without changing the transmission waveform, system parameters and processing methods of the user equipment. It has the backward compatibility characteristics of the satellite-to-ground integrated transmission system and can be seamlessly compatible with the ground frequency-hopping TDMA networking communication system.

[0228] 2) The satellite-borne time-frequency pre-compensation access method adopts the frame-by-frame pre-compensation method to estimate the satellite-to-ground propagation delay, supports the real-time estimation and pre-correction processing of the minimum delay within the beam, and the propagation delay difference within the beam is less than the width of 1 time slot. On the one hand, it can reduce the number of protection time slots, and on the other hand, it can reduce the synchronization capture window width, thereby improving the synchronization capture efficiency of the receiver.

[0229] 3) The onboard time-frequency pre-compensation access method uses the reference point frequency shift estimation method to estimate the satellite-to-ground Doppler frequency shift, supports batch multi-frequency point frequency shift estimation and pre-correction processing of the frequency hopping frequency point set, and can improve the frequency correction synthesis efficiency of the frequency hopping pattern within the time slot.

[0230] 4) The satellite-borne time-frequency pre-compensation access method uses a satellite position elevation angle estimation method based on spherical geometry to estimate the propagation delay and Doppler frequency shift. Compared with the traditional method based on analytic geometry, it has high computational efficiency and is more suitable for real-time calculation of onboard payloads.

[0231] 4. First embodiment: Time-frequency pre-compensation access method for satellite-to-ground frequency hopping TDMA networking communication

[0232] The ephemeris solution and time-frequency precompensation module performs satellite position extrapolation, delay compensation, and Doppler frequency offset compensation estimation under the triggering of the time slot access control signal, which is used to adapt to the large delay and high dynamic transmission channel characteristics of the satellite-to-ground link. Specifically, the processing steps of the time-frequency offset precompensation access method include:

[0233] (1) Initialization parameter analysis

[0234] When the processor of the satellite-to-ground frequency-hopping TDMA networking communication payload is powered on, parameters are injected, or tasks are taken over, the system parameters are initialized. The time slot access module reads the broadcast ephemeris, mission area parameters, and time slot allocation table, and performs satellite orbit recursion and time-frequency pre-compensation estimation initialization parameter updates. The main data structures include:

[0235] a) Broadcast ephemeris

[0236] TLE ephemeris (TLE: two-line orbital element) is a broadcast ephemeris that complies with the North American Aerospace Defense Command (NORAD) international satellite orbit standard. It can describe information such as satellite number, orbit, position and speed, and is used for satellite trajectory tracking.

[0237] The TLE ephemeris is character-coded and consists of two lines of numbers with a total of 21 fields, mainly including: NORAD satellite number, orbital inclination i, ascending node right ascension Ω, orbital eccentricity e, perigee argument ω, mean anomaly M, and mean angular velocity n.

[0238] Orbital Elements are the only parameters required to determine the trajectory of a space object, mainly including six parameters: orbital semi-major axis a, orbital eccentricity e, orbital inclination i, ascending node right ascension Ω, perigee argument ω and mean anomaly M, also known as the six orbital elements.

[0239] To convert the TLE ephemeris to the six numbers, you need to read the TLE ephemeris and convert the number of orbits around the earth n into the orbital semi-major axis a. According to Kepler's third law, the relationship between the orbital semi-major axis a and n is

[0240]

[0241] In the formula, GM=3.986005e14 is the standard gravitational constant of the earth.

[0242] The six orbital numbers are used for satellite orbit recursion. According to the satellite motion period and differential elapsed time, the mean anomaly and true anomaly are updated, and the longitude and latitude coordinates are transformed according to the rotation of the earth.

[0243] b) Mission area parameters

[0244] The mission area parameters come from the mission coverage parameters recorded on the ground, mainly including: the coordinates of the center point of the mission area Gs (x, y, z), the moving trajectory, etc. The center point of the mission area can be regarded as a virtual ground station, and the coordinates of the center point of the mission area are used to identify the geographic coordinates of the virtual ground station.

[0245] c) Time slot allocation table

[0246] According to the satellite-to-ground frequency hopping TDMA networking communication message standard, time slots are allocated to different service types in the form of network participation groups (NPG). The locally stored time slot allocation table identifies the occupancy status of each time slot in the time frame in units of time frames, including transmission, reception, and idle. Among them, the transmission and reception time slots are actually occupied time slots, which require signal transmission and reception processing and corresponding time-frequency pre-compensation.

[0247] (2) Ephemeris Recursive Estimation

[0248] Under the trigger signal of the receiving and transmitting time slot, the ephemeris solution is performed to estimate the satellite position, speed and satellite beam pointing angle, including the following calculation steps:

[0249] a) Calculate the prediction delay

[0250] Prediction delay T k Refers to the satellite from the start time T oe To the prediction time T pred The delay, T k =T pred –T oe .

[0251] b) Calculate the mean anomaly angle

[0252] The satellite moves in the low earth orbit. At the time T predicted by the ephemeris k The mean anomaly angle is

[0253] M k =M0+n·T k (2)

[0254] Where M k M0 and M1 are the mean anomaly angles at the time of broadcast ephemeris and the time of ephemeris prediction respectively; n is the average angular velocity, T k For the ephemeris predicted time.

[0255] c) Solve for the eccentric anomaly and true anomaly

[0256] The calculation formula of the eccentric anomaly angle E is:

[0257] E n =M k +e·sin(E n-1 ) (3)

[0258] In the formula, E n is the true anomaly, and e is the eccentricity. For elliptical orbit satellites, the eccentric anomaly can be solved by an iterative method.

[0259] For near-circular orbit satellites, since the eccentricity is infinitely close to 0, the eccentric anomaly angle is approximately equal to the mean anomaly angle, that is, E≈M k .

[0260] The calculation formula of true anomaly angle f is:

[0261]

[0262] For near-circular orbit satellites, since the eccentricity is infinitely close to 0, the true anomaly angle and the eccentric anomaly angle are approximately equal, that is, f≈E≈M k .

[0263] d) Satellite position calculation

[0264] Assume that the unit vector of the perigee is P, and vector Q is the unit vector perpendicular to P on the orbital plane. Then the vector of the satellite in the geocentric inertial coordinate system (ECI) is:

[0265]

[0266] In the formula, r is the distance between the satellite and the center of the earth. Vectors P and Q can be obtained as follows.

[0267]

[0268] The velocity vector of the satellite in the ECI coordinate system can be obtained by taking the derivative of the position vector with respect to t.

[0269]

[0270] In the process of calculating satellite motion parameters, it is usually necessary to convert the satellite's coordinates in the ECI coordinate system to the coordinates in the earth-centered earth-fixed (ECEF) coordinate system. The satellite's coordinates in the ECI coordinate system rotate around its Z axis by the Greenwich time angle θ g , we can get its coordinates in the ECEF coordinate system:

[0271]

[0272] where θ g =θ g0 +W e (t-t0), θ g0 is the Greenwich hour angle at time t0, W e is the angular velocity of the Earth's rotation, which is approximately 7.2692e-5rad / s.

[0273] (3) Star location estimation

[0274] According to the satellite position sat =r ECEF =[r sx ,r sy ,r sz ] and the virtual ground station position r gs =[r gx ,r gy ,r gz ], the relative position vector between the user terminal and the satellite can be obtained

[0275] r r =r gs -r sat =[r rx ,r ry ,r rz ] (9)

[0276] At this time, the relative distance between the star and the ground is R r for

[0277]

[0278] Star-to-ground azimuth angle A z for

[0279]

[0280] Satellite-to-ground elevation angle E l for

[0281]

[0282] The above includes the relative distance between the satellite and the ground R r 、Star-to-ground azimuth A z , satellite-to-ground elevation angle E l The satellite position estimate, including the beam pointing value of the satellite to the virtual ground station, is given, which can be used for delay compensation estimation and Doppler frequency offset compensation estimation.

[0283] (4) Estimation of minimum delay compensation within the beam

[0284] The satellite moves at high speed relative to the ground, causing the beam pointing to change over time, and the propagation delay difference from different geographical areas within the beam coverage will also change. In order to reduce the impact of propagation delay on synchronization search and frequency hopping pattern alignment, the present invention adopts the minimum propagation delay compensation method within the beam, transmits the downlink signal in advance, so that the nearest point can start capturing the signal at zero time of the receiving time slot, and other nodes can capture the frequency hopping signal of this time slot within the synchronization capture window of no more than 1 time slot; conversely, the synchronization capture window is delayed in the uplink, so that the nearest point can start capturing at the starting point of the synchronization capture window, reducing power consumption.

[0285] a) Delay compensation calculation

[0286] In each transmit and receive time slot, the minimum propagation delay in the beam corresponds to the lower edge angle of the beam in the elevation angle section diagram. In the elevation angle section, according to the sine theorem of plane trigonometry, the ground station elevation angle α corresponding to the lower edge of the beam is

[0287]

[0288] Where r is the distance between the satellite and the earth, r e is the radius of the Earth, E l is the elevation angle of the satellite to the center of the mission area, and γ is the half beam width.

[0289] At this time, the geocentric angle θ between the virtual ground station corresponding to the lower edge of the beam and the satellite is

[0290] θ=90-(E l -γ)-α (14)

[0291] The minimum propagation delay Tp corresponding to the lower edge of the beam min for

[0292]

[0293] Where c is the speed of light propagation.

[0294] b) Delay compensation strategy

[0295] In order to implement different delay compensation strategies for the transmitting and receiving time slots, the present invention reads the use status of the time slot according to the time slot allocation table and stipulates that Uts∈{1,-1,0} corresponds to the three time slot use states of receiving, sending and idle respectively.

[0296] Correspondingly, the delay precompensation of the transmit and receive time slots is dynamically assigned to {Tp min ,-Tp min ,0}.

[0297] (5) Doppler frequency offset compensation estimation

[0298] For a satellite in a near circular orbit, according to Kepler's third law, the linear velocity of the satellite is

[0299]

[0300] Where GM is the standard gravitational constant of the Earth, and r is the distance between the star and the Earth.

[0301] The satellite moves at high speed, causing the angle between the satellite's direction of motion and the virtual ground station to change over time. According to the three cosine theorem of a space triangle, the angle between the satellite's direction of motion and the line connecting the satellite and the ground is:

[0302] dir sat =arccos[cos(A z )cos(E l )] (17)

[0303] In the formula, dir sat Indicates the angle between the satellite's motion direction and the line connecting the satellite and the ground.

[0304] At this time, the Doppler frequency deviation caused by the high-speed movement of the satellite relative to the ground is

[0305]

[0306] (6) Time-frequency precompensation parameter transfer

[0307] The time-frequency pre-compensation parameter transmission adopts the in-path control method to encapsulate the three groups of estimation results including beam pointing control, delay compensation estimation, and Doppler compensation estimation into the access control field of the data packet and pass them to the time slot access control module, which distributes the in-path control signal to the execution modules such as beam algorithm and signal processing.

[0308] 5. Second embodiment: Physical layer processing method for onboard time-frequency pre-compensation

[0309] The physical layer processing of onboard time-frequency pre-compensation includes three parts: beam pointing control, delay pre-compensation processing, and Doppler frequency offset pre-compensation processing, which are described as follows.

[0310] (1) Beam pointing control

[0311] Beam pointing control, performs coordinate transformation of beam direction angle according to satellite attitude, and converts the beam pointing angle into antenna direction angle in the satellite local coordinate system.

[0312] The beam pointing parameter calculation converts the beam pointing angle into the antenna direction angle according to the current attitude of the satellite and outputs it to the beam control algorithm module. The latter allocates the beam steering vector according to the antenna direction angle and carrier wavelength and outputs it to the phase shifter unit of the phased array antenna to perform the beam control function of this time slot.

[0313] (2) Delay pre-compensation processing

[0314] Delay pre-compensation processing reads the control word of the transmit and receive time slots, and according to the delay pre-compensation control word, performs three types of time slot control strategies: reception delay, transmission advance, and no processing of idle time slots, so that the frequency hopping pattern of each time slot matches the delay characteristics of the corresponding Starlink.

[0315] For downlink signal transmission, the transmitter timing advance -Tp is used min , the satellite signal is transmitted downlink to the ground user equipment, and the starting time when the user equipment receives the same beam signal varies in the range of {0, Tp max -Tp min}, then the synchronization capture window length of the user equipment can be set to the maximum delay difference within the beam.

[0316] Taking a satellite altitude of 1000km and a minimum receiving elevation angle of 10° as an example, the satellite-to-ground transmission distance within the beam varies from 1630 to 2750km, the satellite-to-ground transmission delay dynamic range is approximately 5.4 to 9.2ms, and the maximum propagation delay difference within the beam is 3.8ms. The synchronization capture window of the user equipment is set to 4ms to meet the synchronization capture requirements of satellite-to-ground transmission.

[0317] For uplink signal reception, the receiver timing lag Tp is used. min , the user equipment signal is transmitted uplink to the satellite payload receiver, and the starting time of the satellite payload receiving the signal in the same beam varies within the range of {Tp min ,Tp max}, the end of the received signal frame is at Tp at the latest max +Ts-T prot Time to reach the receiving end.

[0318] Taking a satellite altitude of 1000km and a minimum receiving elevation angle of 10° as an example, the satellite-to-ground transmission distance within the beam varies from 1630 to 2750km, and the satellite-to-ground transmission delay dynamic range is approximately 5.4 to 9.2ms. The tail of the received signal frame arrives at the receiving end at the latest within 15ms, and the receiving time slot occupancy is less than 2 time slot widths, which can meet the idle time slot occupancy requirements.

[0319] (3) Doppler frequency offset pre-compensation processing

[0320] In each time slot, the angle between the satellite's motion direction and the satellite-to-ground line changes very little and can be considered a constant. According to equation (18), the Doppler frequency deviation of each frequency point in the frequency hopping frequency point set is only linearly related to the frequency point value. Therefore, in the Doppler frequency deviation estimation step, f0 = 1 GHz is used as the nominal frequency point, and the Doppler frequency deviations of other frequency points are multiplied by the corresponding linear amplification factor β i =f i / f0, then each frequency point fi The Doppler frequency deviation is

[0321] f di =β i ·f d0 (19)

[0322] In the formula, f di is the Doppler frequency deviation estimation of each frequency point in the frequency point set, f d0 is the Doppler frequency deviation estimate for the nominal frequency point of 1 GHz.

[0323] When the frequency hopping patterns and frequencies of the satellite-borne transmitter and receiver are synthesized, each frequency point compensates the corresponding Doppler frequency offset estimation value according to the frequency hopping sequence, so as to achieve the purpose of resisting high dynamic Doppler frequency offset.

[0324] Through the above-mentioned delay and Doppler pre-compensation mechanism based on online real-time estimation, the satellite-borne transmitter and receiver can realize the unified setting of frequency hopping synchronization parameters and multi-user time slot alignment without users noticing. Without changing the ground user equipment, the uplink and downlink transmission of the satellite-to-ground link can be adapted to the ground frequency hopping TDMA networking communication system, thus ensuring the effectiveness and reliability of satellite-to-ground integrated transmission.

[0325] Please note that the technical features of the above embodiments can be combined arbitrarily. In order to make the description concise, all possible combinations of the technical features in the above embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification. The above-mentioned embodiments only express several implementation methods of the present application, and their descriptions are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present application, several variations and improvements can be made, which all belong to the scope of protection of the present application. Therefore, the scope of protection of the patent in this application shall be based on the attached claims.

Claims

1. A time-frequency precompensation access system for satellite-to-ground frequency hopping TDMA networking communication, characterized in that: The time-frequency pre-compensation access system corrects the delay deviation and Doppler frequency deviation of the satellite-to-ground frequency hopping TDMA networking communication, so that the transmission waveform of the satellite-to-ground frequency hopping TDMA networking communication load adapts to the time-varying high dynamic channel propagation characteristics; The time-frequency pre-compensation access system includes an ephemeris solution module, an azimuth pointing estimation module, a delay estimation and compensation module, and a frequency offset estimation and compensation module; wherein: The ephemeris solution module is configured to: calculate the satellite position and speed, calculate the satellite position and direction according to the satellite position and the ground station position, and output the azimuth, elevation angle and relative distance of the satellite to the ground; The beam pointing estimation module is configured to: perform beam pointing control, perform coordinate conversion of the beam direction angle according to the satellite attitude, and convert the beam pointing angle into an antenna direction angle with the satellite local coordinate system as the reference coordinate; The delay estimation and compensation module is configured to: pre-compensate the propagation delay of the satellite-borne transmit and receive time slots, advance the satellite-borne transmit time slots according to the minimum propagation delay compensation principle within the beam, and lag the satellite-borne receive time slots, so that the maximum propagation delay difference within the beam is less than the synchronization capture window, and the satellite-ground time slots are aligned and the frequency hopping patterns are aligned; The frequency deviation estimation and compensation module is configured to estimate the Doppler frequency deviation of satellite motion, and perform Doppler frequency shift estimation and frequency deviation pre-compensation of the satellite relative to the center point of the ground mission area according to the principle of independent compensation of satellite-to-ground motion and ground-to-ground motion.

2. A time-frequency pre-compensation access system for satellite-to-ground frequency hopping TDMA networking communication according to claim 1, characterized in that: The ephemeris solution module is specifically configured to: in each transceiver time slot, perform satellite orbit extrapolation in advance according to the time slot table, and obtain six satellite orbit numbers according to the current satellite broadcast ephemeris TLE, including: orbit semi-major axis a, orbit eccentricity e, orbit inclination i, ascending node right ascension Ω, perigee argument ω and mean anomaly M; perform orbit recursion according to the six satellite orbit numbers and the system time of the satellite-to-ground frequency hopping TDMA communication system, predict the satellite position and speed of the transceiver time slot, convert the coordinates to the earth-centered earth-fixed ECEF coordinate system, perform satellite-to-ground position pointing calculation according to the ground station position, and output the satellite-to-ground azimuth, pitch angle and satellite-to-ground relative distance; The beam pointing estimation module is specifically configured to: calculate beam pointing parameters according to the current attitude of the satellite, convert the beam pointing angle into an antenna direction angle, allocate a beam steering vector according to the antenna direction angle and the carrier wavelength, and perform a beam steering function using a phase shifter unit of a phased array antenna; The delay estimation and compensation module is specifically configured to: estimate the propagation distance and propagation delay of the lower edge of the beam according to the beam pointing angle, thereby determining the parameters of the delay compensation, and calculate the time slot offset of the transmitting and receiving time slots based on this; The frequency offset estimation and compensation module is specifically configured to: perform Doppler frequency shift estimation according to the beam pointing angle and the carrier frequency point, and generate a Doppler frequency shift estimation result for frequency value correction of the frequency hopping pulse sequence.

3. A time-frequency precompensation access method for satellite-to-ground frequency hopping TDMA networking communication, characterized in that: The method uses the time-frequency pre-compensation access system as described in any one of claims 1-2 to realize the time-frequency pre-compensation access of satellite-to-ground frequency hopping TDMA networking communication; The method performs satellite position extrapolation and delay compensation under the triggering of a time slot access control signal, and estimates Doppler frequency offset compensation, thereby adapting to satellite-to-ground link delay and dynamic transmission channel characteristics; The method comprises: Initialization parameter analysis: When the processor of the satellite-to-ground frequency-hopping TDMA networking communication payload is powered on, parameters are injected, or the task is taken over, the system parameter initialization operation is performed. By reading the broadcast ephemeris, mission area parameters, and time slot allocation table, the initialization parameters of the satellite orbit recursion and time-frequency pre-compensation estimation are updated; Ephemeris recursive estimation: perform ephemeris calculation under the trigger signal of the transmit and receive time slot to estimate the satellite position, speed and satellite beam pointing angle; Satellite-ground position estimation: Based on the satellite position and the virtual ground station position, the relative position vector of the user terminal and the satellite is calculated, and the relative distance between the satellite and the ground, the satellite-to-ground azimuth angle, and the satellite-to-ground elevation angle are further calculated for delay compensation estimation and Doppler frequency offset compensation estimation; Minimum delay compensation estimation within the beam: Using the minimum propagation delay compensation within the beam, the downlink signal is transmitted in advance, and the closest point starts to capture the signal at time zero of the receiving time slot. Other nodes capture the frequency hopping signal of this time slot within the synchronization capture window of no more than 1 time slot. In the uplink, the synchronization capture window is delayed, and the closest point starts to capture at the starting point of the synchronization capture window. Doppler frequency offset compensation estimation: Calculate the linear velocity of the satellite movement, and calculate the angle between the satellite movement direction and the satellite-ground line based on the three cosine theorem of the space triangle, and further calculate the Doppler frequency offset caused by the high-speed movement of the satellite relative to the ground; Time-frequency pre-compensation parameter transfer: The time-frequency pre-compensation parameter transfer is carried out by adopting the associated control method. The three groups of estimation results including beam pointing control, delay compensation estimation and Doppler compensation estimation are encapsulated into the access control field of the data packet and distributed through the associated control signal at the time of time slot access.

4. The time-frequency pre-compensation access method for satellite-to-ground frequency hopping TDMA networking communication according to claim 3, characterized in that: The initialized parameter data structure includes: (1) Broadcast ephemeris TLE TLE ephemeris; character encoding, consisting of two lines of numbers, a total of 21 fields, including: NORAD satellite number, orbit inclination i, ascending node right ascension Ω, orbit eccentricity e, perigee argument ω, mean anomaly M, mean angular velocity n; Orbital elements; the only parameters required to determine the trajectory of a space object, including: orbital semi-major axis a, orbital eccentricity e, orbital inclination i, ascending node right ascension Ω, perigee argument ω and mean anomaly M, that is, the six orbital elements; Convert from TLE ephemeris to six numbers, read TLE ephemeris, and convert the number of circles around the earth n into the orbital semi-major axis a; according to Kepler's third law, the relationship between the orbital semi-major axis a and n is: GM = 3.986005e14, which is the standard gravitational constant of the earth. The six orbital elements are used for satellite orbit recursion. According to the satellite motion period and differential elapsed time, the mean anomaly and true anomaly are updated, and the longitude and latitude coordinates are transformed according to the rotation of the earth. (2) Task area parameters The mission area parameters come from the mission coverage parameters noted on the ground, including: the coordinates of the mission area center point Gs (x, y, z) and the moving trajectory; the mission area center point is a virtual ground station, and the mission area center point coordinates are used to identify the geographic coordinates of the virtual ground station; (3) Time Slot Allocation Table According to the satellite-to-ground frequency hopping TDMA networking communication system message standard, time slots are allocated to different service types in the form of network participation groups (NPGs); the locally stored time slot allocation table identifies the occupancy status of each time slot in units of time frames, including transmission, reception, and idle; the transmission and reception time slots are actually occupied time slots, which perform signal transmission and reception processing and corresponding time-frequency pre-compensation.

5. The time-frequency pre-compensation access method for satellite-to-ground frequency hopping TDMA networking communication according to claim 4, characterized in that: The ephemeris recursive estimation specifically includes: (1) Calculation of prediction delay Prediction delay T k Refers to the satellite starting time T oe To the prediction time T pred The delay, T k =T pred –T oe ; (2) Calculation of mean anomaly The satellite moves in the low earth orbit. At the time T predicted by the ephemeris k The mean anomaly angle is: M k =M0+n·T k M k M0 and M1 are the mean anomaly angles at the time of broadcast ephemeris and the time of ephemeris prediction respectively; n is the average angular velocity, T k To predict the time for the ephemeris; (3) Solving the partial anomaly angle and true anomaly angle The calculation formula of the eccentric anomaly angle E is: It is n =M k +e·sin(E n-1 ) E n is the true anomaly, and e is the eccentricity. For satellites in elliptical orbits, the eccentric anomaly is solved by an iterative method. For satellites in near-circular orbits, E≈M k ; The calculation formula of the true anomaly angle f is: For satellites in near circular orbit, f≈E≈M k ; (4) Satellite position calculation The unit vector of the perigee orientation is P, and the vector Q is the unit vector perpendicular to P on the orbital plane. Then the vector of the satellite in the geocentric inertial coordinate system ECI is: r is the distance between the satellite and the center of the earth; vectors P and Q are expressed as: The velocity vector of the satellite in the ECI coordinate system is obtained by taking the derivative of the position vector with respect to t: In the process of calculating the satellite motion parameters, the satellite coordinates in the ECI coordinate system are converted to the Earth-centered Earth-fixed coordinate system ECEF. The satellite coordinates in the ECI coordinate system rotate around its Z axis by the Greenwich time angle θ g , and obtain its coordinates in the ECEF coordinate system: θ g =θ g0 +W e (t-t0), θ g0 is the Greenwich hour angle at time t0, W e is the angular velocity of the Earth's rotation.

6. A time-frequency pre-compensation access method for satellite-to-ground frequency hopping TDMA networking communication according to claim 5, characterized in that: The star location estimation specifically includes: According to the satellite position sat =r ECEF =[r sx , r sy , r sz ] and the virtual ground station position r gs =[r gx , r gy , r gz ], and obtain the relative position vector of the user terminal and the satellite: r r ＝r gs -r sat ＝[r rx ,r ry ,r rz ] Relative distance between satellite and ground R r for: Star-to-ground azimuth angle A z for: Satellite-to-ground elevation angle E l for: Relative distance between satellite and ground R r 、Star-to-ground azimuth A z 、Elevation angle of satellite to ground l The satellite position is calculated to obtain the beam pointing of the satellite to the virtual ground station for delay compensation estimation and Doppler frequency offset compensation estimation.

7. A time-frequency pre-compensation access method for satellite-to-ground frequency hopping TDMA networking communication according to claim 6, characterized in that: The minimum delay compensation estimation within the beam specifically includes: (1) Delay compensation calculation In each transmit and receive time slot, the minimum propagation delay in the beam corresponds to the lower edge angle of the beam in the section diagram of the satellite-ground elevation angle. In the section diagram of the elevation angle, according to the sine theorem of plane trigonometry, the ground station elevation angle α corresponding to the lower edge of the beam is: r is the distance between the star and the earth, r e is the radius of the Earth, E l is the elevation angle of the satellite to the center of the mission area, γ is the half beam width; the geocentric angle θ between the virtual ground station corresponding to the lower edge of the beam and the satellite is: θ=90-(E l -c)-a The minimum propagation delay Tp corresponding to the lower edge of the beam min for: c is the speed of light propagation; (2) Delay Compensation Strategy Different delay compensation strategies are implemented for the receiving and transmitting time slots. The usage status of the time slot is read according to the time slot allocation table. Uts∈{1,-1,0} corresponds to the three time slot usage states of receiving, sending, and idle respectively. The delay pre-compensation of the receiving and transmitting time slots is dynamically assigned as {Tp min ,-Tp min ,0}.

8. The time-frequency pre-compensation access method for satellite-to-ground frequency hopping TDMA networking communication according to claim 7, characterized in that: Doppler frequency offset compensation estimation specifically includes: For a satellite in a near circular orbit, according to Kepler's third law, the linear velocity of the satellite is: GM is the standard gravitational constant of the earth, r is the distance between the satellite and the earth; the satellite moves relative to the earth, so that the angle between the satellite's motion direction and the direction of the virtual ground station changes over time. According to the three cosine theorem of the space triangle, the angle between the satellite's motion direction and the line connecting the satellite and the earth is: say sat =arccos[cos(A z )cos(E l )] dir sat The Doppler frequency deviation f caused by the high-speed movement of the satellite relative to the ground is d0 The calculation method is: f0=1GHz is the nominal frequency.

9. A method for processing physical layer of onboard time-frequency precompensation, characterized in that: The method constrains the physical layer processing of onboard time-frequency precompensation on the basis of the time-frequency precompensation access method as described in any one of claims 3 to 8; The physical layer processing of onboard time-frequency precompensation includes beam pointing control, delay precompensation processing, and Doppler frequency offset precompensation processing; among which: Beam pointing control includes: The coordinate transformation of the beam direction angle is performed according to the satellite attitude, and the beam pointing angle is converted into the antenna direction angle with the satellite local coordinate system as the reference coordinate; the beam pointing parameters are calculated according to the current satellite attitude, and the beam pointing angle is converted into the antenna direction angle; the beam steering vector is allocated according to the antenna direction angle and the carrier wavelength, and output to the phase shifter unit of the phased array antenna to perform the wave control function of this time slot; Delay pre-compensation processing includes: Read the control word of the transmit and receive time slots, and perform three types of time slot control, namely, reception delay, transmission advance, and idle time slot non-processing, according to the delay pre-compensation control word. The frequency hopping pattern of each time slot matches the delay characteristics of the corresponding satellite-to-ground link. For downlink signal transmission, the transmitter timing advance -Tp is used min , the satellite signal is transmitted downlink to the ground user equipment, and the starting time when the user equipment receives the same beam signal varies in the range of {0,Tp max -Tp min }, the synchronization acquisition window length of the user equipment is set to the maximum delay difference within the beam; For uplink signal reception, the receiver timing lag Tp is used. min , the user equipment signal is transmitted uplink to the satellite payload receiver, and the starting time of the satellite payload receiving the signal in the same beam varies within the range of {Tp min ,Tp max }, the end of the received signal frame is at Tp at the latest max +Ts-T prot Time to reach the receiving end; Doppler frequency offset pre-compensation processing includes: In each time slot, the angle between the satellite's motion direction and the satellite-to-ground line changes constantly; the Doppler frequency deviation of each frequency point in the frequency hopping frequency point set is only linearly related to the frequency point value; in the Doppler frequency deviation estimation, f0=1GHz is used as the nominal frequency point, and the Doppler frequency deviation of other frequency points is multiplied by the corresponding linear amplification factor β i =f i / f0, then each frequency point f i The Doppler frequency deviation is: f di =b i ·f d0 f di is the Doppler frequency deviation estimation of each frequency point in the frequency point set, f d0 It is a Doppler frequency offset estimation for a nominal frequency point of 1 GHz; when the frequency hopping pattern and frequency synthesis of the satellite transmitter and receiver are performed, each frequency point is compensated for the corresponding Doppler frequency offset estimation value according to the frequency hopping sequence, thereby compensating for the high dynamic Doppler frequency offset; Through the delay and Doppler pre-compensation mechanism based on online real-time estimation, the satellite-borne transmitter and receiver can achieve unified setting of frequency hopping synchronization parameters and multi-user time slot alignment without users noticing. Without changing the ground user equipment, the uplink and downlink transmission of the satellite-to-ground link can adapt to the ground frequency hopping TDMA networking communication system.

Images