A space-air-ground integrated network communication method based on satellite communication

Abstract

This invention relates to the field of satellite communication technology, specifically disclosing a space-air-ground integrated network communication method based on satellite communication. This method utilizes the spatial distribution of user coordinates in the orbital coordinate system during historical handover events to fit a separating boundary line, and statistically analyzes the offset phase window of the handover time within the satellite's transit arc. During handover, the target satellite corresponding to the event with the closest distance to the historical boundary at the current coordinates is used as the pre-handover target. Handover is triggered when the real-time phase falls within the phase window and the coordinates approach the boundary, thus replacing signal strength measurement. This ensures that the handover target matches the user's movement direction, and the handover timing avoids signal fluctuation edges, reducing continuous handovers and service interruptions.

Description

Technical Field

[0001] This invention relates to the field of satellite communication technology, and more specifically to an integrated air-space-ground network communication method based on satellite communication. Background Technology

[0002] In low-Earth orbit (LEO) satellite communication systems, the coverage window of a single satellite over a fixed ground location typically lasts from several minutes to over ten minutes. A user terminal may need to undergo multiple satellite handovers during a single communication session. Existing LEO satellite handover methods employ a handover triggering mechanism based on signal strength measurement. The user terminal continuously measures the downlink reference signal received power of the currently serving satellite and neighboring satellites. When the downlink reference signal received power falls below a handover threshold configured by the network side, a measurement report is submitted. The network side then selects the target satellite based on the signal strength ranking of neighboring satellites in the measurement report and executes the handover signaling procedure.

[0003] The aforementioned handover mechanism suffers from a coordination error between the selection of the handover target and the timing of the handover trigger in low-Earth orbit satellite scenarios. The single signal strength measurement reflects the signal attenuation state of the instantaneous relative position between the user terminal and the satellite, and cannot characterize the repetitive pattern of the user terminal's movement trajectory within the satellite coverage area. This causes the target satellite selected by the network side to trigger the handover process again shortly after the user terminal completes the handover access, increasing the handover signaling overhead and prolonging the service data interruption time. Summary of the Invention

[0004] The purpose of this invention is to provide an integrated air-space-ground network communication method based on satellite communication, and to solve the following technical problems.

[0005] The objective of this invention can be achieved through the following technical solutions: A satellite-based integrated air-space-ground network communication method includes the following steps: Receive communication requests from user terminals, extract user terminal identification codes and current coordinates of user terminals, retrieve historical handover events based on user terminal identification codes, and obtain handover information for each historical handover event; The coordinate sequences before and after the handover information are transformed to the service satellite orbit coordinate system before the handover to form the first point cluster and the second point cluster, and the dividing boundary line between the first point cluster and the second point cluster is solved. Transform the current coordinates to the orbital coordinate system of the service satellite before the handover to obtain the transformed coordinates. Obtain the distance between the transformed coordinates and the separation boundary line as the handover distance. Select the historical handover event A corresponding to the smallest handover distance. Use the handover target satellite number in the handover information corresponding to historical handover event A as the pre-handover target satellite. For a single handover information, the zero Doppler time is calculated based on the ephemeris of the serving satellite before the handover and the coordinates of the user terminal at the time of the handover. The stable handover phase window is then determined based on the zero Doppler time. When the real-time offset phase falls within the stable switching phase window and the distance between the real-time coordinates of the user terminal and the separation boundary line corresponding to the target satellite to be switched is less than the preset approximation threshold, a switching command carrying the access parameters of the target satellite to be switched is sent to the user terminal.

[0006] As a further aspect of the present invention: the process of obtaining switching information is as follows: The historical handover record database is queried based on the user terminal identification code. Each record in the historical handover record database corresponds to a historical handover event. The handover information includes the serving satellite number before the handover, the target satellite number after the handover, the coordinates of the user terminal at the time of the handover, the ephemeris of the serving satellite before the handover, the user terminal coordinate sampling sequence within a preset time period before the handover, and the user terminal coordinate sampling sequence within a preset time period after the handover.

[0007] As a further aspect of the present invention, the process of solving the separating boundary line is as follows: The user terminal coordinate sampling sequence within a preset time period before the handover occurs and the user terminal coordinate sampling sequence within a preset time period after the handover occurs are respectively used as the coordinate sequence before handover and the coordinate sequence after handover. The orbital coordinate system of the pre-switching service satellite is established based on the orbital six-root parameters in the ephemeris of the pre-switching service satellite. The pre-switching service satellite orbital coordinate system has the centroid of the pre-switching service satellite as the origin, the direction pointing to the perigee in the orbital plane of the pre-switching service satellite as the first coordinate axis, and the normal to the orbital plane of the pre-switching service satellite as the second coordinate axis. Each coordinate point in the coordinate sequence before and after the switch is transformed from the geocentric and earth-fixed coordinate system to the orbital coordinate system of the service satellite before the switch, resulting in the first point cluster and the second point cluster. The support vector data description algorithm is used to obtain the first hyperspherical boundary surrounding the first point cluster and the second hyperspherical boundary surrounding the second point cluster. The set of intermediate points that are equidistant between the first hyperspherical boundary and the second hyperspherical boundary is extracted, and the separating boundary line is obtained by fitting the master curve to the set of intermediate points.

[0008] As a further aspect of the present invention: the process of determining the stable switching phase window is as follows: The position and velocity vector sequence of the serving satellite in the inertial coordinate system is extrapolated based on the orbital root parameters in the ephemeris of the serving satellite before the switchover. Calculate the projection value of the position velocity vector in the position velocity vector sequence onto the direction of the line connecting the coordinates of the serving satellite before the handover and the user terminal at the time of the handover, and take the moment when the projection value is zero as the zero Doppler moment; Calculate the time difference between the handover time and the zero Doppler time in historical handover event A, obtain the total duration of the transit arc corresponding to the ephemeris of the serving satellite before the handover, and divide the time difference by the total duration of the transit arc to obtain the offset phase value at the handover time. Kernel density estimation is performed on the offset phase values ​​corresponding to all historical switching events, and the continuous phase intervals exceeding the preset density threshold in the kernel density estimation curve are extracted as the stable switching phase window.

[0009] As a further aspect of the present invention: the process of sending the switching command is as follows: Send a resource reservation request to the target satellite to be switched over. The resource reservation request carries the user terminal identifier and the real-time coordinates of the user terminal. The pre-switched target satellite adjusts the beam pointing of the onboard phased array antenna according to the real-time coordinates of the user terminal, allocates a random access preamble and the corresponding time and frequency resource block number, and returns the random access preamble and the time and frequency resource block number. Receive the random access preamble and time-frequency resource block number returned by the target satellite to be switched, and generate access parameters. The access parameters include the downlink beam center frequency number, uplink beam center frequency number, random access preamble and time-frequency resource block number of the target satellite to be switched. The access parameters are encapsulated into a handover command, which is then sent to the user terminal via the downlink control channel of the currently serving satellite.

[0010] As a further aspect of the present invention: before the user terminal performs data communication by switching target satellites, a protocol conversion process is also included: Extract the source address field, destination address field, payload field, and check field from the pre-switched target satellite communication protocol data frame; The source address field and destination address field are re-encoded according to the address encoding rules of the ground communication protocol. The payload field is segmented according to the maximum transmission unit of the ground communication protocol and a segment sequence number is added to each segment. The check field is replaced with the cyclic redundancy check code specified by the ground communication protocol. The re-encoded source address field, the re-encoded destination address field, the segmented payload field, and the replaced check field are combined into a data frame in the terrestrial communication protocol format.

[0011] As a further aspect of the present invention: after the user terminal establishes a communication link with the pre-switched target satellite, a channel compensation process is also included. The downlink reference signal of the target satellite to be switched is acquired, and the amplitude attenuation and phase rotation are extracted from the downlink reference signal. The amplitude attenuation is compared with the predicted amplitude attenuation in the pre-stored non-stationary channel model to obtain the amplitude compensation coefficient. The phase rotation is compared with the predicted phase rotation in the pre-stored non-stationary channel model to obtain the phase compensation coefficient. The amplitude compensation coefficient and the phase compensation coefficient are multiplied by the amplitude component and phase component of the received data symbol, respectively, to obtain the channel-compensated data symbol.

[0012] As a further aspect of the present invention: the switching command and access parameters are transmitted using quantum key distribution encryption during transmission. The quantum key distribution device requests a quantum key, and sends the quantum key sequence to the core control layer through the quantum channel. The switching command and access parameters are XORed with the quantum key sequence bit by bit to obtain encrypted data. The encrypted data is then sent to the user terminal through the downlink control channel of the current serving satellite. The user terminal uses the same quantum key sequence obtained in advance from the quantum key distribution device to XOR the encrypted data to obtain the switching command and access parameters.

[0013] The beneficial effects of this invention compared to the prior art are as follows: In this invention, the selection of the target satellite for handover is based on the geometric distance between the handover boundary, which is derived from the historical movement trajectory of the user terminal in the orbital coordinate system of the serving satellite before handover, and the current coordinates of the user terminal, rather than the comparison result of the instantaneous signal strength measurement. The matching degree between the selection result of the target satellite for handover and the actual movement direction of the user terminal within the satellite coverage area is improved, the probability of triggering the handover process again in a short period of time after handover is completed is reduced, and the total number of handover signaling interactions is reduced.

[0014] The handover trigger timing is determined based on whether the real-time offset phase falls within the stable handover phase window and whether the distance between the user terminal's real-time coordinates and the corresponding separation boundary line of the pre-handover target satellite is less than the approximation threshold, rather than the result of a single comparison of signal strength with a fixed threshold value. This enhances the synchronization between the handover trigger timing and the Doppler variation pattern during satellite transit, avoids periods of severe signal fluctuations in the satellite coverage edge area, and shortens the duration of service data interruption during handover. The time-frequency resources and random access preamble corresponding to the pre-handover target satellite are pre-allocated before handover triggering. After receiving the handover command, the user terminal directly uses the pre-allocated access parameters to execute the random access procedure, reducing the random access response waiting time. Attached Figure Description

[0015] The invention will now be further described with reference to the accompanying drawings.

[0016] Figure 1This is a flowchart illustrating an integrated air-space-ground network communication method based on satellite communication according to the present invention. Figure 2 This is a schematic diagram of the process for solving the boundary line of the present invention. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] Please see Figures 1-2 As shown, this invention is an integrated air-space-ground network communication method based on satellite communication, comprising the following steps: Receive communication requests from user terminals, extract user terminal identification codes and current coordinates of user terminals, retrieve historical handover events based on user terminal identification codes, and obtain handover information for each historical handover event; In a preferred embodiment of the present invention, the process of obtaining switching information is as follows: A retrieval operation is performed in the historical handover record database based on the user terminal identification code. This database stores all historical handover event records associated with the user terminal identification code. Each record uniquely corresponds to a completed historical handover event. The record fields include the serving satellite number before handover, the target satellite number after handover, the geographic coordinates of the user terminal at the time of handover, the orbital ephemeris parameters of the serving satellite at the time of handover, the location sampling sequence reported by the user terminal within a preset time period preceding the time of handover, and the location sampling sequence reported by the user terminal within a preset time period following the time of handover. For example, the preset time period for preceding and following handover is 30 seconds, and the sampling interval is 1 second. Thus, the coordinate sequence before handover contains 30 user terminal coordinate points arranged in chronological order, and the coordinate sequence after handover also contains 30 user terminal coordinate points arranged in chronological order. The user terminal coordinates can be obtained from the positioning data output by the user terminal's built-in satellite positioning module, or from the positioning estimate calculated by the network side based on the time difference of arrival or angle of arrival measurements. The orbital ephemeris parameters are expressed in Keplerian orbital six-element form, including at least the semi-major axis, eccentricity, orbital inclination, right ascension of the ascending node, argument of perigee, and mean perigee. The set of switching information obtained above forms the raw data basis for subsequent coordinate transformations, boundary line solutions, and phase window statistics.

[0019] It should be noted that the historical handover event set obtained by retrieving the user terminal identifier in the above steps may contain multiple handover records of the user terminal occurring in different geographical areas and under the coverage of different pre-handover service satellites. Since each satellite has a different number of orbital root numbers, the orientation of its corresponding orbital coordinate system in inertial space is also different. To ensure geometric consistency in coordinate transformation and boundary line solution, in the actual implementation of this method, the retrieved historical handover events are first grouped according to the pre-handover service satellite number in the historical handover information. For the same specific pre-handover service satellite, all historical handover events under its coverage are extracted, and only this group of data is used to construct the separating boundary line and stable handover phase window in the unique orbital plane coordinate system corresponding to that specific satellite. Once the current service satellite number corresponding to the current communication request is determined, the system only calls the historical data group corresponding to that satellite number for decision-making, thereby completely avoiding the boundary line confusion caused by inconsistent spatial references in different orbital planes. This grouping mechanism ensures that each group of boundary lines and phase windows is strongly correlated with a specific satellite orbital configuration, possessing a rigorous physical correspondence.

[0020] The coordinate sequences before and after the handover information are transformed to the service satellite orbit coordinate system before the handover to form the first point cluster and the second point cluster, and the dividing boundary line between the first point cluster and the second point cluster is solved. In another preferred embodiment of the present invention, the process of solving the separating boundary line is as follows: The user terminal coordinate sampling sequence extracted from the historical handover records within a preset time period before the handover occurred is marked as the pre-handover coordinate sequence, and the user terminal coordinate sampling sequence within a preset time period after the handover occurred is marked as the post-handover coordinate sequence.

[0021] An orbital coordinate system corresponding to the satellite is constructed based on the orbital root parameters in the ephemeris of the serving satellite before the switchover. The origin of the coordinate system is located at the centroid of the serving satellite before the switchover. The first coordinate axis points in the direction of perigee in the orbital plane, the second coordinate axis is along the normal to the orbital plane, and the third coordinate axis is determined by the right-hand rule.

[0022] Each coordinate point in the coordinate sequence before and after the switch is transformed sequentially through a coordinate transformation chain from the geocentric-fixed coordinate system to the geocentric-inertial coordinate system and then to the orbital coordinate system. The transformed point sets constitute the first point cluster and the second point cluster, respectively. Then, a support vector data description algorithm is used to process the first and second point clusters respectively. This algorithm searches for the smallest hypersphere containing each point cluster in a high-dimensional feature space. The hypersphere parameters are obtained by solving an optimization problem containing a kernel function, such as a Gaussian kernel function. The first point cluster corresponds to the boundary of the first hypersphere, and the second point cluster corresponds to the boundary of the second hypersphere.

[0023] After obtaining the two hyperspherical boundaries, the set of points in space equidistant from the first hyperspherical boundary and the second hyperspherical boundary is calculated as the intermediate point set. A master curve fitting process is then performed on this intermediate point set. The master curve fitting uses an iterative algorithm to find a smooth curve passing through the intermediate positions of the data points. The fitting result is the dividing boundary line corresponding to this historical switching event. This dividing boundary line characterizes the spatial boundary between the pre-switching and post-switching position distributions in the orbital coordinate system.

[0024] Understandingly, mapping the user terminal coordinate sampling points for periods before and after the handover to the serving satellite's orbital coordinate system before the handover essentially establishes a spatial reference frame relatively fixed to the satellite's orbital motion. Within this reference frame, the satellite's own positional changes are abstracted away, and the user terminal's trajectory relative to the satellite's orbital plane is visually presented. The point clusters formed by the pre-handover coordinate sequence record the spatial distribution characteristics of the user terminal relative to the satellite's orbital plane before the handover is completed, while the point clusters formed by the post-handover coordinate sequence record the changes in the user terminal's spatial distribution within the same reference frame after the handover is completed. These two clusters of points naturally form a spatial separation in the orbital coordinate system. The fundamental reason for this is that in low-Earth orbit satellite communication, handover typically occurs during the transition phase where the user terminal gradually leaves the current serving satellite and moves towards the coverage area of ​​another satellite. This transition is represented in the orbital coordinate system as a trend of the user's coordinates migrating from one side of the orbital plane to the other.

[0025] The support vector data description algorithm is used to wrap the two clusters of points to generate hyperspherical boundaries. This takes advantage of the algorithm's ability to compactly characterize the distribution contour of high-dimensional point sets. The hyperspherical boundary is essentially the geometric envelope of the pre-switching and post-switching position dispersion ranges in historical handover events.

[0026] Extracting the set of midpoints of two equidistant hyperspheres and fitting a separating boundary line essentially involves finding a spatial boundary line within the orbital coordinate system that maximizes the distinction between the pre-switching and post-switching states. This boundary line encapsulates the critical characteristics of the user terminal's spatial location at the time of the historical handover event; that is, the user terminal underwent a handover from the current serving satellite to the target satellite before and after crossing this boundary line in the orbital coordinate system.

[0027] Applying the above processing to each historical handover event yields the separation boundary line corresponding to each handover. When processing the current communication request, the user terminal's current coordinates are transformed to the orbital coordinate system of the corresponding historical handover event, and its distance from the separation boundary line is calculated. This distance reflects the proximity of the current user's location to the spatial critical position that actually triggered the handover in history. The smaller the distance, the closer the current user terminal's position in orbital space is to the critical state at the time of the historical handover event, meaning that the target satellite selected at that time has higher reference value in the current context. This series of operations bypasses the dependence on instantaneous radio signal strength, instead predicting the handover direction by analyzing the user terminal's historical movement patterns in satellite orbital space. This ensures that the selection of the target satellite for handover matches the actual spatial evolution trend of the user terminal within the coverage area, reducing unnecessary handovers caused by instantaneous fluctuations in signal measurements or misjudgments of direction.

[0028] Transform the current coordinates to the orbital coordinate system of the service satellite before the handover to obtain the transformed coordinates. Obtain the distance between the transformed coordinates and the separation boundary line as the handover distance. Select the historical handover event A corresponding to the smallest handover distance. Use the handover target satellite number in the handover information corresponding to historical handover event A as the pre-handover target satellite. For a single handover information, the zero Doppler time is calculated based on the ephemeris of the serving satellite before the handover and the coordinates of the user terminal at the time of the handover. The stable handover phase window is then determined based on the zero Doppler time. In a preferred embodiment of the present invention, the process of determining a stable switching phase window is as follows: Based on the orbital root parameters recorded in the ephemeris of the serving satellite before the switchover, these six root parameters include the semi-major axis, eccentricity, orbital inclination, right ascension of the ascending node, argument of perigee, and mean anomaly at the reference time. Using the Kepler orbit prediction algorithm, starting from the reference time, the Kepler equations are solved for each subsequent discrete time to obtain the mean anomaly angle value. The solution process employs methods such as Newton's iteration to control convergence accuracy. The true anomaly angle can be further derived from the mean anomaly angle combined with the orbital eccentricity. The true anomaly angle describes the satellite's true angular position on the orbital ellipse. The true anomaly angle, combined with the orbital semi-major axis and eccentricity, calculates the satellite's polar coordinate position and velocity components in the orbital plane. Then, through a coordinate rotation sequence composed of the orbital inclination, right ascension of the ascending node, and argument of perigee, the position and velocity vectors in the orbital plane are transformed to the geocentric inertial coordinate system. The extrapolation and transformation operations described above are repeated within a fixed step size, for example, 0.1 seconds, covering a complete transit period. This means that every 0.1 seconds, a set of three-dimensional position and velocity vectors in the inertial coordinate system is calculated and arranged chronologically to form a position and velocity vector sequence. The start and end times of this sequence are defined by the predicted satellite entry and exit times from the user terminal's field of view, ensuring that the sequence completely covers the entire transit arc.

[0029] For each set of position velocity vectors in the sequence, the projection scalar value of the velocity vector in the direction of the line connecting the satellite position to the user terminal coordinates at the time of handover is calculated, and the precise moment when the projection value is zero is recorded; this moment is the zero Doppler moment. Subsequently, the absolute time difference between the handover occurrence time recorded in historical handover event A and this zero Doppler moment is calculated, and the difference is expressed in seconds.

[0030] Obtain the total duration of the transit arc of the serving satellite relative to the user terminal at the time of the handover. The total duration of the transit arc is pre-calculated using orbit prediction tools combined with ephemeris parameters and the user terminal coordinates; for example, the total duration of a transit is 480 seconds. Divide the aforementioned time difference by the total duration of the transit arc; the resulting dimensionless ratio is the offset phase value corresponding to the historical handover event, ranging from 0 to 1. Perform the above offset phase value calculation operation on all retrieved historical handover events to obtain a set of offset phase values.

[0031] A kernel density estimation method is applied to the set of offset phase values. The kernel density estimation uses a Gaussian kernel function, and the bandwidth parameter is adaptively selected based on the sample size, for example, using the Scott rule. The kernel density estimation outputs a continuous probability density curve reflecting the density of the offset phase value distribution. A preset density threshold is set on this curve, for example, 40% of the maximum density peak value. Phase intervals in the curve where the density values ​​continuously exceed this threshold are extracted. The phase range defined by the upper and lower boundaries of this interval is the stable switching phase window. For example, when the density of offset phase values ​​is consistently higher than the threshold in the range of 0.2 to 0.4, this interval constitutes a stable switching phase window, indicating that historically, the vast majority of switching events occur at relative time positions between 20% and 40% of the transit arc. This phase window is used for subsequent real-time offset phase decision comparison.

[0032] It is worth noting that extrapolating satellite position and velocity based on orbital ephemeris and calculating the zero Doppler moment essentially involves finding the instant when the satellite's radial velocity relative to the user is zero. This instant corresponds to the moment in the satellite's transit arc when it is closest to the user and the signal's Doppler shift is most gradual. Dividing the time difference between the handover occurrence and the zero Doppler moment by the entire transit arc length yields a normalized offset phase value. This approach transforms an absolute time measure into a relative position indicator independent of the transit period length, providing a unified benchmark for comparing handover timing in transit events of different durations.

[0033] Kernel density estimation of all historical offset phase values ​​and extraction of high-density intervals utilize statistical methods to automatically identify concentrated periods of handover activity during transit from a large amount of historical data. These periods reflect the recurring handover inertia patterns exhibited by user terminals during actual movement. The resulting stable handover phase window provides a data-driven timing reference interval for subsequent real-time decisions. When the real-time offset phase falls within this interval, it indicates that the relative motion between the satellite and the user has entered a historically frequent handover-triggered phase. At this point, combining the spatial boundary distance condition with the handover command can constrain the handover execution time to the relatively smooth Doppler changes and low signal fluctuations in the middle of the transit period, avoiding unstable periods of drastic signal fluctuations at the coverage edge, thereby improving the handover success rate and shortening service interruption duration.

[0034] Considering that user terminals are not always fixed at a specific geographical coordinate, their large-scale movement during communication (such as being carried by high-speed aircraft) can significantly alter the characteristics of the transit arc relative to the same serving satellite (such as transit duration and zero Doppler point position), thereby diminishing the statistical validity of stable switching phase windows derived from early historical data. To maintain the robustness of the decision conditions, a dynamic correction mechanism for the phase window based on real-time ephemeris and the current position can be introduced. When calculating the real-time offset phase, the difference between the current actual total transit arc duration and the historical average total transit arc duration is calculated simultaneously. If the difference exceeds a preset threshold (e.g., changes in the user terminal's latitude and longitude cause geometrically visible window compression exceeding 20%), a recalculation or sliding update of the stable switching phase window is triggered. This involves using recent switching event samples (or simulated samples generated based on the current orbit forecast) to replace the full historical samples for kernel density estimation, thereby generating a dynamically stable switching phase window adapted to the current flight trajectory. If the sample size is insufficient recently, it can also be degraded to a conservative switching window with a fixed bias preset based on the current zero Doppler moment, so as to ensure that the timeliness and reliability of the switching command are not affected by the long-distance movement of the user terminal.

[0035] When the real-time offset phase falls within the stable switching phase window and the distance between the real-time coordinates of the user terminal and the separation boundary line corresponding to the target satellite to be switched is less than the preset approximation threshold, a switching command carrying the access parameters of the target satellite to be switched is sent to the user terminal.

[0036] In another preferred embodiment of the present invention, the process of sending the switching command is as follows: Once the target satellite for pre-switching is identified, the network-side equipment sends a resource reservation request message to the target satellite. This message carries the user terminal identifier and the user terminal's real-time geographic coordinates. Upon receiving the resource reservation request message, the target satellite calculates the required azimuth and elevation angles of the onboard phased array antenna beam based on the user terminal's real-time coordinates. It then adjusts the phase weighting values ​​of each element of the phased array antenna to align the downlink beam main lobe with the user terminal's location.

[0037] Meanwhile, the pre-switching target satellite selects a random access preamble that is not occupied by other terminals from its random access resource pool and specifies the time-frequency resource block number corresponding to the preamble. For example, it selects the preamble with the sequence number 15 from 64 available preambles, and the corresponding time-frequency resource block number is the 3rd time-frequency position of the physical random access channel.

[0038] The target satellite to be handed over will send the allocated random access preamble value and time-frequency resource block number back to the network-side equipment via the satellite-to-ground link. Upon receiving these parameters, the network-side equipment will assemble an access parameter set. This set specifically includes the downlink beam center frequency number of the target satellite (e.g., 12345), the uplink beam center frequency number (e.g., 67890), the random access preamble value, and the corresponding time-frequency resource block number. The network-side equipment will encapsulate this access parameter set into a handover command message body, which will be encoded according to the radio resource control message format specified in the current serving satellite's air interface protocol. After encoding, the network-side equipment will send the handover command message to the user terminal via the downlink control channel of the current serving satellite. Upon receiving the message, the user terminal can directly initiate a random access procedure to the target satellite based on the access parameters.

[0039] In a preferred embodiment, a quantum key distribution encryption mechanism is introduced during the transmission of switching instructions and access parameters to enhance the security of air interface signaling. The network-side quantum key distribution device initiates a key request to the quantum key management device. The quantum key management device sends a quantum key sequence to the network-side quantum key distribution device through a quantum channel. This quantum key sequence is a stream of truly random binary bits, and its length is the same as the total bit length of the switching instructions and access parameters to be encrypted, for example, 2048 bits.

[0040] The network-side quantum key distribution device temporarily stores the received quantum key sequence in a secure buffer. Simultaneously, the quantum key receiving module configured on the user terminal side has obtained a completely identical quantum key sequence from the same quantum key management device via another quantum channel, and similarly stores it temporarily in the user terminal's secure storage unit.

[0041] The network-side equipment jointly encodes the set of access parameters, including the downlink beam center frequency number, uplink beam center frequency number, random access preamble value, and time-frequency resource block number of the target satellite to be switched, with the switching command message body to form the original binary data stream to be encrypted. Subsequently, the network-side equipment performs an XOR operation on the original binary data stream and the quantum key sequence bit by bit, with the XOR operation rule being that the same bits are 0 and different bits are 1. The result of the operation generates an encrypted data stream.

[0042] The network-side equipment uses this encrypted data stream as the payload of the downlink control channel message, radiating it wirelessly to the user terminal via the downlink control channel of the currently serving satellite. Upon receiving the encrypted data stream, the user terminal reads the pre-acquired identical quantum key sequence from its secure storage unit and performs an XOR operation on the encrypted data stream again, bit-by-bit. Due to the reversible nature of the XOR operation, the result of the second XOR operation precisely restores the original binary data stream, containing the original information of the handover command and access parameter set. The user terminal decodes the restored data stream, extracts the handover command and access parameters, and then initiates a random access procedure to the target satellite based on the access parameters. The entire encryption and decryption process relies on the absolute security provided by quantum key distribution technology. Any eavesdropping in the quantum channel will be detected by both communicating parties due to quantum state collapse, thus ensuring the unbreakable nature of the handover signaling during the air interface transmission phase.

[0043] In a preferred embodiment of the present invention, the user terminal performs a protocol conversion operation before conducting data communication via a pre-switched target satellite.

[0044] First, the source address field, destination address field, payload field, and check field are extracted from the pre-switched target satellite communication protocol data frame. For example, the source address field uses a 48-bit satellite terminal identifier encoding, and the destination address field uses a 24-bit beam coverage area identifier encoding.

[0045] The source address field and destination address field are then re-encoded according to the address encoding rules of the terrestrial communication protocol. For example, the satellite terminal identifier is mapped to the 32-bit Internet Protocol version 4 address format, and the beam area identifier is mapped to the corresponding gateway address format.

[0046] The payload field is segmented according to the maximum transmission unit specified in the terrestrial communication protocol. For example, the maximum transmission unit is 1500 bytes. When the original payload length exceeds this value, it is split into multiple data segments, and a segment number is added to each segment, such as sequence number 1, sequence number 2, and sequence number 3, so that the receiving end can reassemble them in order. The check field is completely removed and replaced with a cyclic redundancy check (CRC) code specified in the terrestrial communication protocol. The CRC code is generated, for example, using a 32-bit polynomial.

[0047] Finally, the re-encoded source address field, the re-encoded destination address field, the segmented payload field, and the replaced cyclic redundancy check code field are concatenated and combined according to the order of the ground communication protocol frame structure to form a protocol data frame that meets the transmission requirements of the ground core network.

[0048] In a preferred embodiment of the present invention, after the user terminal establishes a communication link with the pre-switched target satellite, a channel compensation process is further included: The downlink reference signal of the target satellite to be switched is acquired, and the amplitude attenuation and phase rotation are extracted from the downlink reference signal. The amplitude attenuation is compared with the predicted amplitude attenuation in the pre-stored non-stationary channel model to obtain the amplitude compensation coefficient. The phase rotation is compared with the predicted phase rotation in the pre-stored non-stationary channel model to obtain the phase compensation coefficient. The amplitude compensation coefficient and the phase compensation coefficient are multiplied by the amplitude component and phase component of the received data symbol, respectively, to obtain the channel-compensated data symbol.

[0049] It is important to note that after the user terminal successfully establishes a communication link with the target satellite for the pre-switching, a channel compensation process is initiated to offset the time-varying fading effect suffered by the signal during propagation. The user terminal continuously acquires the downlink reference signal transmitted by the target satellite for the pre-switching, which is, for example, a demodulation reference signal symbol inserted every 1 millisecond time slot.

[0050] Channel estimation is performed on the acquired reference signal symbols to extract the amplitude attenuation and phase rotation of the signal at the current moment. The amplitude attenuation is expressed in decibels or a linear ratio, and the phase rotation is expressed in radians.

[0051] The user terminal has non-stationary channel model parameters pre-stored locally. This model is generated offline by the ground network equipment based on the orbital altitude of the target satellite to be switched, the moving speed of the user terminal, the current communication frequency band and atmospheric environment parameters, and is pre-distributed to the user terminal. The model output is a predicted amplitude attenuation sequence and a predicted phase rotation sequence that vary with the satellite's transit time.

[0052] The real-time extracted amplitude attenuation is numerically compared with the predicted amplitude attenuation corresponding to the current satellite transit time, and the ratio of the two is calculated as the amplitude compensation coefficient. For example, when the actual attenuation is 10% more than the predicted attenuation, the amplitude compensation coefficient is set to 1.1. Similarly, the real-time extracted phase rotation is compared with the predicted phase rotation, and the inverse value of the phase difference is calculated as the phase compensation coefficient. For example, when the actual phase rotation is 0.2 radians more than the predicted phase rotation, the phase compensation coefficient is set to a phase rotation of -0.2 radians.

[0053] The user terminal then decomposes the received service data symbols into amplitude and phase components in complex signal form. The amplitude component is multiplied by the amplitude compensation coefficient to obtain the compensated amplitude component, and the phase component is added by the phase compensation coefficient to obtain the compensated phase component. The compensated amplitude component and the compensated phase component are then combined to form a channel-compensated data symbol. The subsequent demodulation decision process is based on this compensated data symbol, thereby improving the demodulation accuracy.

[0054] This invention addresses the mismatch between the handover target and the user's movement direction, as well as the asynchrony between the handover triggering timing and the satellite's transit dynamics, in low-Earth orbit satellite communication by mining the spatiotemporal patterns inherent in the historical handover behavior of user terminals, instead of relying on instantaneous wireless signal strength. The core idea is to transform the user coordinate sampling sequence before and after each historical handover event into an orbital coordinate system established with the orbital plane of the serving satellite before the handover as the reference. Under this reference system, the coordinate point clusters before and after the handover naturally exhibit a spatial separation trend. Using a support vector data description algorithm, the hypersphere envelopes of the two point clusters are obtained, and equidistant intermediate point sets are extracted to fit a separating boundary line. This boundary line characterizes the spatial critical position of the user terminal transitioning from the current serving satellite to the target satellite. Meanwhile, the zero-Doppler time is extrapolated based on the ephemeris of the serving satellite before the handover. The time difference between the handover occurrence time and the zero-Doppler time is divided by the total duration of the entire transit arc to obtain the normalized offset phase value. Kernel density estimation is performed on the offset phase values ​​of all historical events, and a high-density continuous interval is selected as the stable handover phase window. This phase window reflects the statistically concentrated period of the handover behavior during the satellite transit process. When a real-time communication request arrives, the user terminal's current coordinates are transformed to the corresponding historical orbit coordinate system, and its distance to each separation boundary line is calculated. The target satellite corresponding to the historical handover event with the smallest distance is selected as the pre-handover target satellite. This selection is based on the principle of spatial proximity, ensuring that the target satellite matches the user's actual direction of travel. When the real-time offset phase falls into the stable handover phase window and the distance between the current coordinates and the pre-handover target satellite boundary line is less than the approximation threshold, the network sends the user terminal access parameters, such as the random access preamble and time-frequency resource block number, which were obtained in advance from the pre-handover target satellite. The user terminal then directly executes random access to complete the handover. The entire process transforms the selection of handover targets and the determination of handover timing from signal strength ranking and fixed threshold comparison to matching and determining the historical spatial boundary and transit time phase, so that the handover execution period avoids the area of ​​severe signal fluctuation at the coverage edge. The pre-allocation resource mechanism further compresses the signaling interaction latency, ultimately achieving the dual effect of reducing handover frequency and shortening service interruption time.

[0055] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the present invention should still fall within the scope of the present invention.

Claims

1. A space-air-ground integrated network communication method based on satellite communication, characterized in that, Includes the following steps: Receive communication requests from user terminals, extract user terminal identification codes and current coordinates of user terminals, retrieve historical handover events based on user terminal identification codes, and obtain handover information for each historical handover event; The coordinate sequences before and after the handover information are transformed to the service satellite orbit coordinate system before the handover to form the first point cluster and the second point cluster, and the dividing boundary line between the first point cluster and the second point cluster is solved. Transform the current coordinates to the orbital coordinate system of the service satellite before the handover to obtain the transformed coordinates. Obtain the distance between the transformed coordinates and the separation boundary line as the handover distance. Select the historical handover event A corresponding to the smallest handover distance. Use the handover target satellite number in the handover information corresponding to historical handover event A as the pre-handover target satellite. For a single handover information, the zero Doppler time is calculated based on the ephemeris of the serving satellite before the handover and the coordinates of the user terminal at the time of the handover. The stable handover phase window is then determined based on the zero Doppler time. When the real-time offset phase falls within the stable switching phase window and the distance between the real-time coordinates of the user terminal and the separation boundary line corresponding to the target satellite to be switched is less than the preset approximation threshold, a switching command carrying the access parameters of the target satellite to be switched is sent to the user terminal.

2. The space-ground-integrated network communication method based on satellite communication according to claim 1, characterized in that, The process of obtaining switching information is as follows: The historical handover record database is queried based on the user terminal identification code. Each record in the historical handover record database corresponds to a historical handover event. The handover information includes the serving satellite number before the handover, the target satellite number after the handover, the coordinates of the user terminal at the time of the handover, the ephemeris of the serving satellite before the handover, the user terminal coordinate sampling sequence within a preset time period before the handover, and the user terminal coordinate sampling sequence within a preset time period after the handover.

3. The space-ground-integrated network communication method based on satellite communication according to claim 1, characterized in that, The process of solving for the dividing boundary line is as follows: The user terminal coordinate sampling sequence within a preset time period before the handover occurs and the user terminal coordinate sampling sequence within a preset time period after the handover occurs are respectively used as the coordinate sequence before handover and the coordinate sequence after handover. The orbital coordinate system of the pre-switching service satellite is established based on the orbital six-root parameters in the ephemeris of the pre-switching service satellite. The pre-switching service satellite orbital coordinate system has the centroid of the pre-switching service satellite as the origin, the direction pointing to the perigee in the orbital plane of the pre-switching service satellite as the first coordinate axis, and the normal to the orbital plane of the pre-switching service satellite as the second coordinate axis. Each coordinate point in the coordinate sequence before and after the switch is transformed from the geocentric and earth-fixed coordinate system to the orbital coordinate system of the service satellite before the switch, resulting in the first point cluster and the second point cluster. The support vector data description algorithm is used to obtain the first hyperspherical boundary surrounding the first point cluster and the second hyperspherical boundary surrounding the second point cluster. The set of intermediate points that are equidistant between the first hyperspherical boundary and the second hyperspherical boundary is extracted, and the separating boundary line is obtained by fitting the master curve to the set of intermediate points.

4. The integrated air-space-ground network communication method based on satellite communication according to claim 1, characterized in that, The process of determining a stable switching phase window is as follows: The position and velocity vector sequence of the serving satellite in the inertial coordinate system is extrapolated based on the orbital root parameters in the ephemeris of the serving satellite before the switchover. Calculate the projection value of the position velocity vector in the position velocity vector sequence onto the direction of the line connecting the coordinates of the serving satellite before the handover and the user terminal at the time of the handover, and take the moment when the projection value is zero as the zero Doppler moment; Calculate the time difference between the handover time and the zero Doppler time in historical handover event A, obtain the total duration of the transit arc corresponding to the ephemeris of the serving satellite before the handover, and divide the time difference by the total duration of the transit arc to obtain the offset phase value at the handover time. Kernel density estimation is performed on the offset phase values ​​corresponding to all historical switching events, and the continuous phase intervals exceeding the preset density threshold in the kernel density estimation curve are extracted as the stable switching phase window.

5. The space-ground-integrated network communication method based on satellite communication according to claim 1, characterized in that, The process of sending a switching command is as follows: Send a resource reservation request to the target satellite to be switched over. The resource reservation request carries the user terminal identifier and the real-time coordinates of the user terminal. The pre-switched target satellite adjusts the beam pointing of the onboard phased array antenna according to the real-time coordinates of the user terminal, allocates a random access preamble and the corresponding time and frequency resource block number, and returns the random access preamble and the time and frequency resource block number. Receive the random access preamble and time-frequency resource block number returned by the target satellite to be switched, and generate access parameters. The access parameters include the downlink beam center frequency number, uplink beam center frequency number, random access preamble and time-frequency resource block number of the target satellite to be switched. The access parameters are encapsulated into a handover command, which is then sent to the user terminal via the downlink control channel of the currently serving satellite.

6. The space-ground-integrated network communication method based on satellite communication according to claim 1, wherein, Before a user terminal can communicate via a target satellite, a protocol conversion process is also required: Extract the source address field, destination address field, payload field, and check field from the pre-switched target satellite communication protocol data frame; The source address field and destination address field are re-encoded according to the address encoding rules of the ground communication protocol. The payload field is segmented according to the maximum transmission unit of the ground communication protocol and a segment sequence number is added to each segment. The check field is replaced with the cyclic redundancy check code specified by the ground communication protocol. The re-encoded source address field, the re-encoded destination address field, the segmented payload field, and the replaced check field are combined into a data frame in the terrestrial communication protocol format.

7. The space-ground-integrated network communication method based on satellite communication according to claim 1, characterized in that, After the user terminal establishes a communication link with the target satellite to be switched, a channel compensation process is also included: The downlink reference signal of the target satellite to be switched is acquired, and the amplitude attenuation and phase rotation are extracted from the downlink reference signal. The amplitude attenuation is compared with the predicted amplitude attenuation in the pre-stored non-stationary channel model to obtain the amplitude compensation coefficient. The phase rotation is compared with the predicted phase rotation in the pre-stored non-stationary channel model to obtain the phase compensation coefficient. The amplitude compensation coefficient and the phase compensation coefficient are multiplied by the amplitude component and phase component of the received data symbol, respectively, to obtain the channel-compensated data symbol. 8.The space-ground-integrated network communication method based on satellite communication according to claim 5, wherein, Switching commands and access parameters are transmitted using quantum key distribution encryption during the transmission process. The quantum key distribution device requests a quantum key, and sends the quantum key sequence to the core control layer through the quantum channel. The switching instruction and the access parameter are subjected to XOR operation with the quantum key sequence to obtain encrypted data, and the encrypted data is sent to the user terminal through the downlink control channel of the current service satellite, and the user terminal uses the same quantum key sequence obtained from the quantum key distribution device in advance to perform XOR operation on the encrypted data to obtain the switching instruction and the access parameter.

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