CN112821941B - Pre-switching method for multi-beam low-orbit satellite communication system - Google Patents
Pre-switching method for multi-beam low-orbit satellite communication system Download PDFInfo
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- CN112821941B CN112821941B CN202110058292.4A CN202110058292A CN112821941B CN 112821941 B CN112821941 B CN 112821941B CN 202110058292 A CN202110058292 A CN 202110058292A CN 112821941 B CN112821941 B CN 112821941B
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/14—Relay systems
- H04B7/15—Active relay systems
- H04B7/185—Space-based or airborne stations; Stations for satellite systems
- H04B7/1851—Systems using a satellite or space-based relay
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/14—Relay systems
- H04B7/15—Active relay systems
- H04B7/185—Space-based or airborne stations; Stations for satellite systems
- H04B7/18521—Systems of inter linked satellites, i.e. inter satellite service
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/14—Relay systems
- H04B7/15—Active relay systems
- H04B7/185—Space-based or airborne stations; Stations for satellite systems
- H04B7/1853—Satellite systems for providing telephony service to a mobile station, i.e. mobile satellite service
- H04B7/18532—Arrangements for managing transmission, i.e. for transporting data or a signalling message
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/14—Relay systems
- H04B7/15—Active relay systems
- H04B7/185—Space-based or airborne stations; Stations for satellite systems
- H04B7/1853—Satellite systems for providing telephony service to a mobile station, i.e. mobile satellite service
- H04B7/18539—Arrangements for managing radio, resources, i.e. for establishing or releasing a connection
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/14—Relay systems
- H04B7/15—Active relay systems
- H04B7/185—Space-based or airborne stations; Stations for satellite systems
- H04B7/1853—Satellite systems for providing telephony service to a mobile station, i.e. mobile satellite service
- H04B7/18545—Arrangements for managing station mobility, i.e. for station registration or localisation
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Abstract
The invention relates to a pre-switching method of a multi-beam low-orbit satellite communication system, which belongs to the field of WeChat satellite communication and comprises the following steps that 1, after a terminal is accessed into a satellite network, reported position information is registered; and 2, judging whether inter-planet beam switching is needed by the satellite, forwarding the inter-planet beam switching to the ground control center if the inter-planet beam switching is needed, and carrying out intra-planet beam switching on the satellite side if the inter-planet beam switching is not needed. The satellite network predicts the switching time and the time of reserving resources to a target beam according to the ephemeris information and the terminal position information; step 3, after reserving channel resources by the target wave beam, forwarding the channel resources to the terminal through the source wave beam; and 4, directly accessing the target wave beam by the terminal after the pre-switching time is reached, and completing the switching. According to the invention, through the predictability of the satellite trajectory, the switching signaling flow can be simplified, the switching success rate and the user communication experience can be improved.
Description
Technical Field
The invention belongs to the field of satellite communication, and relates to a pre-switching method of a multi-beam low-orbit satellite communication system.
Background
The low-earth orbit satellite communication system is regarded as an important component of 5G communication as the complement of the ground communication system, and has irreplaceable advantages of lower propagation delay, higher throughput and the like. Unlike ordinary terrestrial communication networks, satellite networks have a fixed and unchanging network topology whose constellation operation follows orbital information. The periodicity and predictability of satellite operation is often overlooked by researchers studying satellite handoff. How to realize the multi-beam switching optimization by utilizing the prediction information to reduce the call interruption probability is a problem worthy of study.
In the existing prediction switching strategy, a terminal is independent of a satellite network, ephemeris data of a satellite needs to be updated regularly through the internet or other modes, the terminal needs to perform a large amount of calculation so as to predict switching time, the energy consumption and the actual engineering situation of the terminal are not considered, and the influence of a multi-beam coverage model on the predicted switching time is ignored.
Disclosure of Invention
In view of the above, the present invention provides a method for pre-switching a multi-beam low-earth orbit satellite communication system based on terminal position information, which considers a multi-beam-to-terminal coverage model under oblique projection and predicts a switching time, so as to simplify a switching signaling process and improve a switching success rate.
In order to achieve the purpose, the invention provides the following technical scheme:
a pre-switching method for a multi-beam low-orbit satellite communication system comprises the following steps:
s1: the terminal accesses and registers;
s2: pre-switching decision of the satellite network;
s3: preparing for switching;
s4: and executing the switching.
Further, the step S1 of accessing and registering the terminal specifically includes the following steps:
s11: after the terminal accesses the satellite, the terminal adds the position information of the terminal into a registration signaling by using the GPS function, and registers in a satellite network;
s12: when the terminal registers and registers to the satellite network, whether the terminal is switched among the satellites or not is judged at the satellite terminal according to the beam number accessed by the terminal, and if the terminal is switched among the satellites, the terminal is handed to a ground control center to enter a decision of switching among the satellites; otherwise, the satellite makes the inter-beam switching decision.
Further, the pre-switching decision of the satellite network in step S2 includes the following steps:
s21: storing an under-satellite point trajectory equation and ephemeris information of a constellation system in a satellite network, and acquiring a beam central point of each beam in each satellite in real time by the satellite network by utilizing the fixed and static property of the beam relative to the direction of the under-satellite point of the satellite;
s22: establishing a coverage time model of a single beam to a terminal in an oblique projection mode; calculating the switching time in the satellite network according to the known information, namely the terminal coordinate, the current beam central point coordinate and the beam central point coordinate at the switching time;
s23: and considering the average residence time of the terminal when the terminal is uniformly distributed in the beam, and sending a channel resource reservation message to the target beam by taking the average residence time as a reference so as to reduce the time for reserving the channel.
Further, the obtaining of the beam center point in step S21 includes the following steps:
s211: knowing the longitude and latitude of the satellite and the pointing direction of each antenna in the satellite, namely the half-pitch angle; the geocentric angle of each layer of wave beam is obtained from the space geometric relationship of the satellite and the wave beam
The distance between the center point of each layer of beams and the point under the satellite is expressed as
Wherein alpha is i Is the geocentric angle, beta, of the i-th layer beam i Is the half-pitch angle, R, of the ith layer beam e Is the radius of the earth, h is the satellite orbital height, d i The distance between the beam center point of the ith layer of beam and the sub-satellite point is calculated;
s212: three beams uniformly cover the points under the satellite, and three central points are respectively positioned at the original points d which form included angles of 30 degrees, 150 degrees and 270 degrees with the X axis and take C as the original point i Is on the circumference of a radius; making the 3 circle centers respectively along X and Y axes as vertical lines to obtain a beam center point B i,j Distance division of projection to longitude and latitudeIs shown as
Wherein, d i Is the distance between the beam center point of the ith layer beam and the point under the satellite, az i,j Azimuth, CB, of the ith beam of the ith layer x And CB y Respectively representing the beam center points B i,j The distance projected onto the warp and weft;
s213: conversion to earth sphere with longitude and latitude expressed as
Wherein s is lon And s lat Respectively representing the longitude and latitude, CB of the sub-satellite point x And CB y Respectively represent the beam center points B i,j Distance projected onto the warp and weft, B i,jlon And B i,jlat Respectively representing the beam center points B i,j Latitude and longitude in the earth's sphere.
Further, the step S22 specifically includes the step of using the single beam to cover the terminal in the oblique projection mode in the time model:
s221: o is the geocenter, S, C, B and U are the satellite, the subsatellite point of the satellite, the center point of any wave beam and the position of the terminal; taking S as a vertex, taking a straight line SC as an axis, making an included angle between a bus and the BS, namely a half-pitch angle beta of the satellite antenna, as a cone, and taking the intersection of the cone and the earth as the coverage range of the wave beam;
s222: the terminal coordinates are acquired by GPS U (U) lon ,u lat ) The arc distance BU from the center point of each beam is expressed as gamma in geocentric angle 0 ＝arccos(cos(90°-B lat )cos(90°-u lat )+sin(90°-B lat )sin(90°-u lat )cos(B lon -u lon ) Distance of the terminal from the center point of any beam
S223: the synchronization step S222 obtains the distance d between the satellite and the beam center point BS And distance d of satellite to terminal US The deviation angle between the terminal and the beam center point
S224: replacing the terminal U with any point P in the beam to obtain an included angle beta between a bus and an axis SC, and a beam central point B and a point Q k The longitude and latitude of (a) is a function of the independent variable; calculating all points Q under the beam coverage range by setting the step length to meet the point of step S223 k The longitude and latitude coordinates of;
s225: obtaining the distance omega of the terminal relative to the central point of the wave beam according to the coordinates of the switching boundary Q of the terminal and the wave beam b Then the shortest arc distance gamma from the terminal to the central point track of the wave beam b (t)＝min{2arcsin(Ω b )}；
S226: moment of switching
Omega is the angular velocity of the satellite relative to the terminal under the geocentric geostationary coordinate system.
Further, the step S23 of predicting the reservation time of the channel resource reservation message includes:
s231: terminal is at t 0 Time of day directional beam B 0 Initiating a call application if the source beam B 0 If there is a free channel, directly accessing;
s232: the average call duration of the user is greater than the coverage duration of one beam, at t 0 +T 0 -t pre At the moment, the next service beam B is applied for the user 1 Of the channel, i.e. advanced by t pre Applying for switching the used channel resources at all times;
s233: terminals are uniformly distributed in the wave beam, and newly arrived calls occur at any point in the wave beam at equal probability; the terminal call duration T follows the exponential distribution with the mean value T; the terminals are randomly distributed on the ground, and the distances from the terminals to the central point of the wave beam are uniformly distributed; thus, gamma 0 Obey U (0-gamma) bmax ) To obtain gamma 0 A probability density function of;
s234: the coverage time t is obtained from S233 cm Is derived to cover timet cm A probability density function of;
s235: for the coverage time t cm The average coverage time is calculated by the probability density function, and the predicted channel resource reservation time is set as t pre ＝E(t cm ) In advance of t, depending on the network state pre And occupying channel resources for the switching terminal from the target wave beam at the moment.
Further, step S3 specifically includes the following steps:
s31: the ground control center sends a pre-switching request message to a target satellite beam to request switching;
s32: the target satellite receives the terminal information contained in the pre-switching request message and forwards the message to the target wave beam so as to execute channel resource reservation;
s33: the target wave beam adds the prepared wireless resource into the pre-switching request response message, and forwards the pre-switching request response message to the ground control center through the target satellite to confirm that the switching preparation is completed;
s34: the ground control center adds the satellite, the wave beam, the channel resource, the frequency resource and the like in the received pre-switching request response message into the pre-switching notification message, adds the switching time in the pre-switching decision into the information, and forwards the information to the terminal through the source wave beam of the source satellite.
Further, step S4 specifically includes:
s41: when the switching time is reached, the terminal initiates switching to a target satellite or a target beam; after the terminal is successfully switched to a target satellite, updating and registering to a satellite network;
s42: and after the switching is successful, the satellite network releases the resource of the source wave beam after receiving the updating message.
The invention has the beneficial effects that: the invention designs a pre-switching method between wave beams based on terminal position information aiming at the characteristics of high-speed movement, predictability and the like of a satellite network. And predicting the switching time and predicting the resource reservation time by establishing a multi-beam terminal coverage model in an oblique projection mode. Meanwhile, a set of complete pre-switching scheme and signaling flow are designed, so that the signaling switching flow is simplified, and the switching success rate is improved.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims thereof.
Drawings
For the purposes of promoting a better understanding of the objects, aspects and advantages of the invention, reference will now be made to the following detailed description taken in conjunction with the accompanying drawings in which:
FIG. 1 is a schematic diagram of the relationship between the sub-satellite point and the center point of a first layer beam;
FIG. 2 is a schematic diagram of a single-beam terminal coverage duration model in an oblique projection mode;
FIG. 3 is a schematic diagram of an inter-satellite beam pre-handover signaling flow;
fig. 4 is a schematic diagram of an intra-satellite inter-beam pre-handover signaling flow.
Detailed Description
The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention. It should be noted that the drawings provided in the following embodiments are only for illustrating the basic idea of the present invention in a schematic way, and the features in the following embodiments and examples may be combined with each other without conflict.
Wherein the showings are for the purpose of illustrating the invention only and not for the purpose of limiting the same, and in which there is shown by way of illustration only and not in the drawings in which there is no intention to limit the invention thereto; to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of an actual product; it will be understood by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted.
The same or similar reference numerals in the drawings of the embodiments of the present invention correspond to the same or similar components; in the description of the present invention, it should be understood that if there is an orientation or positional relationship indicated by terms such as "upper", "lower", "left", "right", "front", "rear", etc., based on the orientation or positional relationship shown in the drawings, it is only for convenience of description and simplification of description, but it is not an indication or suggestion that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes, and are not to be construed as limiting the present invention, and the specific meaning of the terms may be understood by those skilled in the art according to specific situations.
The invention provides a pre-switching method between beams of a low earth orbit satellite communication system, which comprises the following steps:
11 After the terminal accesses the satellite, the terminal adds the position information of the terminal into a registration signaling by using the GPS function and registers in a satellite network;
12 When the terminal registers to the satellite network, the satellite terminal can judge whether the terminal will generate inter-satellite switching according to the beam number accessed by the terminal. Judging whether inter-planet switching is needed or not by the satellite terminal, and if the inter-planet switching is about to happen, handing over the satellite terminal to the ground control center to make an inter-planet beam switching decision; otherwise, the satellite makes the inter-beam switching decision.
Step 2, pre-switching decision of the satellite network specifically comprises the following steps:
21 The satellite network stores an under-satellite point trajectory equation and ephemeris information of a constellation system, and can acquire the beam center point of each beam in each satellite in real time by utilizing the fixed and static property of the beam relative to the direction of the under-satellite point of the satellite; the beam center point acquisition process comprises the following steps:
211 Known satellite latitude and longitude, and each antenna in the satellite is pointed, i.e., at half-pitch. According to the space geometrical relationship between the satellite and the beams, the geocentric angle of each layer of beams is
The distance between the center point of each layer beam and the sub-satellite point is expressed as
Wherein, beta i Is the half-pitch angle, R, of the ith layer beam e Is the earth radius, and h is the satellite orbit height;
212 In fig. 1, three beams uniformly cover the intersatellite point, and three central points are respectively positioned at the C-based origin d with the included angles of 30 degrees, 150 degrees and 270 degrees with the X axis i On the circumference of a radius. Making the 3 circle centers respectively along X and Y axes as vertical lines to obtain a beam center point B i,j The distances projected to the warp and weft are respectively expressed as
Wherein, az i,j Azimuth angle of jth beam of ith layer;
213 To earth's sphere with latitude and longitude expressed as
22 Establishing a coverage time model of the single beam to the terminal in the oblique projection mode. Calculating switching time in a satellite network according to known information, namely terminal coordinates, current beam central point coordinates and switching time beam central point coordinates; the time model of the single beam coverage of the terminal in the oblique projection mode comprises the following steps:
221 Fig. 2 shows a multi-beam satellite-to-terminal service duration model in an oblique projection mode in the geocentric earth-fixed coordinate system. O is the geocentric, and S, C, B and U are the satellite, the subsatellite point of the satellite, the central point of any beam and the position of the terminal. Taking S as a vertex, taking a straight line SC as an axis, taking an included angle beta between a bus and BS (namely a half-pitch angle of the satellite antenna) as a cone, and taking the intersection of the cone and the earth as the coverage range of the wave beam, namely a shadow part in the figure;
222 Terminal coordinates can be obtained from GPS U (U) lon ,u lat ) With each beamThe arc distance BU of the center point is represented by the geocentric angle gamma 0 ＝arccos(cos(90°-B lat )cos(90°-u lat )+sin(90°-B lat )sin(90°-u lat )cos(B lon -u lon ) Distance of the terminal from the center point of any beam
223 ) the distance d between the satellite and the center point of the beam can be obtained BS And distance d of satellite to terminal US Then the deviation angle of the terminal from the beam center
224 Replacing the terminal U with any point P in the beam, the included angle between the bus and the axis SC can be obtained as beta, and the central point B and the point Q of the beam can be obtained k Is a function of the argument. All points Q in the beam coverage area can be calculated by setting the step length to meet the point of step 223) k The longitude and latitude coordinates of;
225 From the coordinates of the terminal and the switching boundary Q of the beam, the distance Ω of the terminal from the center point of the beam can be obtained b The shortest arc distance gamma from the terminal to the central point of the wave beam b (t)＝min{2arcsin(Ω b )}；
226 Time of switching
Omega is the angular velocity of the satellite relative to the terminal under the geocentric geostationary coordinate system.
23 Considering the average residence time of the terminal when the terminal is uniformly distributed in the beam, sending a channel resource reservation message to the target beam by taking the average residence time as a reference, and reducing the time for reserving the channel as much as possible so as to avoid occupying the channel resource for a long time and causing resource waste. The process of predicting the resource reservation time comprises the following steps:
231 Terminal at t) 0 Time of day directional beam B 0 Initiating a call application if the source beam B 0 If there is a free channel, directly accessing;
232 ) usersIs generally greater than the coverage duration of one beam, at t 0 +T 0 -t pre At that time, the user can be applied for the next service beam B 1 Of the channel, i.e. advanced by t pre Applying for switching the used channel resources at all times;
233 The terminals are evenly distributed within the beam and newly arriving calls occur with equal probability at any point within the beam. The terminal call duration T follows the exponential distribution with the mean value T. The terminals are randomly distributed on the ground, and the distances from the terminals to the central point of the beam are assumed to be uniformly distributed. Thus, γ 0 Obey U (0-gamma) bmax ) Is uniformly distributed, gamma can be obtained 0 A probability density function of;
234 233) available coverage time t cm Is derived to cover the time t cm A probability density function of (a);
235 To the coverage time t) cm The average coverage time is calculated by the probability density function, and the predicted channel resource reservation time is set as t pre ＝E(t cm ) In advance of t, depending on the network state pre And occupying channel resources for the switching terminal from the target wave beam at the moment.
Step 3, switching preparation, comprising:
31 Ground control center sends pre-switching request message to target satellite beam to request switching;
32 Terminal information contained in the pre-handover request message received by the target satellite, and then forwarding the message to the target beam to perform channel resource reservation;
33 The target beam adds the prepared wireless resources into the pre-switching request response message, and forwards the pre-switching request response message to the ground control center through the target satellite to confirm that the switching preparation is completed;
34 The ground control center adds the satellite, the beam, the channel resource, the frequency resource and the like in the received pre-switching request response message into the pre-switching notification message, adds the switching time in the pre-switching decision into the information, and forwards the information to the terminal through the source beam of the source satellite.
And 4, performing switching, comprising:
1) And when the terminal reaches the switching moment, the terminal initiates switching to the target satellite or the target beam. After the terminal is successfully switched to a target satellite, updating and registering the target satellite to a satellite network;
2) After the switching is successful, the satellite network releases the resource of the source wave beam after receiving the updating message.
The invention provides a method for pre-switching among wave beams based on terminal position information on a multi-wave beam low-orbit satellite communication system. The invention can correlate the messages between the User Equipment (UE), the Source Satellite terminal (S-SAT), the Target Satellite terminal (T-SAT) and the ground Control Center (NCC) in the connection mode to form a complete signaling flow. Fig. 3 and fig. 4 are schematic diagrams of inter-satellite and intra-satellite pre-switching signaling flows, respectively.
As shown in fig. 3, the inter-satellite beam pre-handover signaling procedure includes the following steps:
1) After accessing the satellite network, the user sends a PRE CONNECT NOTIFY message (also called a user registration message) to the source satellite through an uplink channel of the source beam. The message includes information such as UE _ id, latitude and longitude coordinates of the user, and the like. The format of the PRE CONNECT NOTIFY message is shown in table 1.
TABLE 1 PRE CONNECT NOTIFY message format
2) The source satellite judges whether INTER-satellite switching is needed or not, and if the INTER-satellite switching is about to occur, the source satellite sends a PRE INTERCONNECT NOTIFY message (also called an INTER-satellite user registration message) to the ground control center. The format of PRE INTERCONNECT NOTIFY is shown in Table 2.
TABLE 2 PRE INTERINTERCONNECT NOTIFY message Format
3) The ground control center performs pre-switching decision on the received user registration information, which is specifically seen in the step 2 of the invention content.
4) After the decision is completed, the ground control center sends a PRE INTER HANDOVER REQUEST message (also called an INTER-satellite PRE-HANDOVER REQUEST message) to the target satellite. The format of the PRE INTER HANDOVER REQUEST is shown in Table 3.
TABLE 3 PRE INTER HANDOVER REQUEST message format
5) The target satellite allocates radio resources and replies a PRE-INTER HANDOVER REQUEST ACK message (also called PRE-HANDOVER REQUEST response message) to the ground control center. The message includes the newly allocated switchable channel id and the uplink and downlink frequencies allocated to the user by the target beam in the target satellite. The format of the PRE INTER HANDOVER REQUEST ACK is shown in Table 4.
TABLE 4 PRE INTER HANDOVER REQUEST ACK MESSAGE FORMAT
6) The ground control center receives new radio resources prepared by the target satellite for the user, adds the switching time in the PRE-switching decision into a PRE-INTER-HANDOVER NOTIFY message (also called an INTER-satellite PRE-switching notification message), and forwards the message to the user through the source satellite, wherein the format of the PRE-INTER-HANDOVER NOTIFY is shown in table 5.
TABLE 5 PRE INTER HANDOVER NOTIFY message Format
7) When the PRE-switching time is reached, the user sets the uplink frequency and the downlink frequency as the frequency allocated to the target beam in the target satellite, and sends a PRE HANDOVER ACCESS message (also called PRE-switching ACCESS request message) to the target beam in the target satellite to ACCESS the target beam. When the user accesses the target beam, the user still needs to report the own position information so as to provide information for the next pre-switching decision. The format of PRE HANDOVER ACCESS is shown in Table 5.
TABLE 5 PRE HANDOVER ACCESS message format
8) After receiving the PRE-switching access request message of the user, the target satellite verifies whether the accessed user is the user who reserves the channel resource previously through UE _ id, if so, the target satellite sends a PRE INTERCONNECT NOTIFY message (also called an INTER-satellite user registration message) to the ground control center through verification; meanwhile, the satellite continues to make pre-handover decisions for the next pre-handover. The format of PRE INTER CONNECT NOTIFY is shown in table 2.
9) After receiving the user access message reported by the target satellite, the ground control center sends a UE INTER CONTEXT RELEASE message (also called a resource RELEASE message) to the source beam of the source satellite, and the resources occupied by the user in the source beam are eliminated. The format of the UE INTER CONTEXT RELEASE is shown in table 6.
TABLE 6 UE INTER CONTEXT RELEASE message Format
As shown in fig. 4, the intra-satellite inter-beam pre-handover signaling procedure includes the following steps:
1) The user sends PRE CONNECT NOTIFY (also called user registration message) to the satellite via the source beam.
2) And after the satellite judges that the satellite switches the intra-satellite beams, pre-switching decisions are made by using ephemeris information, beam pointing information and other information. See step 2 of the summary of the invention.
3) After the decision is made, the satellite sends a PRE handoff REQUEST message to the target beam, the format of which is shown in table 7.
TABLE 7 PRE HANDOVER REQUEST message format
4) After the target beam allocates the radio resource, a PRE HANDOVER REQUEST ACK message (also called PRE-HANDOVER REQUEST response message) is returned to the satellite, and the format of the PRE HANDOVER REQUEST ACK is shown in table 8.
TABLE 8 PRE HANDOVER REQUEST message Format
5) The satellite receives new radio resources prepared by the target beam for the user, adds the HANDOVER time in the PRE-HANDOVER decision into a PRE HANDOVER NOTIFY message (also called PRE-HANDOVER notification message), and forwards the message to the user through the source beam, where the format of the PRE HANDOVER NOTIFY is shown in table 9.
TABLE 9 PRE HANDOVER NOTIFY message Format
6) When the PRE-switch moment is reached, the user sets the uplink and downlink frequencies as the frequencies allocated to the target beam, so as to send a PRE HANDOVER ACCESS message (also called PRE-switch ACCESS request message) to the target beam and ACCESS the target beam. The format of PRE HANDOVER ACCESS is shown in Table 5.
7) After receiving the PRE-switch access request message of the user, the target beam verifies whether the accessed user is a user who previously reserves channel resources through UE _ id, and if yes, the target beam sends PRE CONNECT NOTIFY message (also called user registration message) to the satellite through verification. The format of the PRE CONNECT NOTIFY message is shown in table 1.
8) The satellite receives the user access information reported by the target wave beam, on one hand, the satellite continues to make a pre-switching decision to perform next pre-switching; on the other hand, the satellite sends a UE CONTEXT RELEASE message (also called resource RELEASE message) to the source beam to clear the resources occupied by the UE in the source beam. The format of UE CONTEXT RELEASE is shown in table 10.
TABLE 10 UE CONTEXT RELEASE message Format
Tables 7-10 may be complementary to some of the messages in fig. 3.
The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and those skilled in the art should cover any modifications, equivalents and improvements within the spirit and principle of the present invention within the technical scope of the present invention.
Finally, the above embodiments are only intended to illustrate the technical solutions of the present invention and not to limit the present invention, and although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions, and all of them should be covered by the claims of the present invention.
Claims (6)
1. A pre-switching method for a multi-beam low-orbit satellite communication system is characterized by comprising the following steps: the method comprises the following steps:
s1: the terminal accesses and registers;
s2: pre-switching decision of the satellite network;
s3: preparing for switching;
s4: switching execution;
the satellite network pre-switching decision in the step S2 comprises the following steps:
s21: the satellite network stores an under-satellite point trajectory equation and ephemeris information of a constellation system, and acquires the beam center point of each beam in each satellite in real time by utilizing the fixed and static property of the beam relative to the direction of the under-satellite point of the satellite;
s22: establishing a coverage time model of a single beam to a terminal in an oblique projection mode, specifically comprising:
s221: o is the geocentric, and S, C, B and U are the positions of the satellite, the satellite subsatellite point, any beam center point and the terminal; taking S as a vertex, taking a straight line SC as an axis, making an included angle between a bus and the BS, namely a half-pitch angle beta of the satellite antenna, as a cone, and taking the intersection of the cone and the earth as the coverage range of the wave beam;
s222: the terminal coordinates are acquired by GPS U (U) lon ,u lat ) Arc distance from the center point of each beam
Expressed as gamma in the geocentric angle 0 ＝arccos(cos(90°-B lat )cos(90°-u lat )+sin(90°-B lat )sin(90°-u lat )cos(B lon -u lon ) Distance of the terminal from the center point of any beam
Wherein R is e Is the radius of the earth;
s223: the synchronization step S222 obtains the distance d between the satellite and the beam center point BS And distance d of satellite to terminal US The deviation angle between the terminal and the beam center point
Wherein h is the satellite orbit height;
s224: replacing the terminal U with any point P in the beam to obtain an included angle beta between a bus and an axis SC, and a beam central point B and a point Q k The longitude and latitude of (a) is a function of the independent variable; calculating all points Q in the beam coverage range by setting the step length to satisfy the points of step S223 k Longitude and latitude coordinates of (c);
s225: obtaining the distance omega of the terminal relative to the central point of the wave beam according to the coordinates of the switching boundary Q of the terminal and the wave beam b Then the shortest arc distance gamma from the terminal to the central point track of the wave beam b (t)＝min{2arcsin(Ω b )}；
S226: switching time
Omega is the angular velocity of the satellite relative to the terminal under the geocentric geostationary coordinate system;
s23: and considering the average residence time of the terminal when the terminal is uniformly distributed in the beam, and sending a channel resource reservation message to the target beam by taking the average residence time as a reference so as to reduce the time for reserving the channel.
2. The multi-beam low-orbit satellite communication system pre-switching method according to claim 1, characterized in that: the step S1 of accessing and registering the terminal specifically includes the following steps:
s11: after the terminal accesses the satellite, the terminal adds the position information of the terminal into a registration signaling by using the GPS function, and registers in a satellite network;
s12: when the terminal registers and registers to the satellite network, whether the terminal is switched among the satellites or not is judged at the satellite terminal according to the beam number accessed by the terminal, and if the terminal is switched among the satellites, the terminal is handed to a ground control center to enter a decision of switching among the satellites; otherwise, the satellite makes the inter-beam switching decision.
3. The multi-beam low-orbit satellite communication system pre-switching method according to claim 1, characterized in that: the obtaining of the beam center point in step S21 includes the following steps:
s211: knowing the longitude and latitude of the satellite and the pointing direction of each antenna in the satellite, namely a half-pitch angle; the geocentric angle of each layer of wave beam is obtained from the space geometric relationship of the satellite and the wave beam
The distance between the center point of each layer of beams and the point under the satellite is expressed as
Wherein alpha is i Is the geocentric angle, beta, of the ith layer beam i Is the half-pitch angle, R, of the ith layer beam e Is the radius of the earth, h is the satellite orbital height, d i The distance between the beam center point of the ith layer of beam and the point under the satellite;
s212: three beams uniformly cover the points under the satellite, and three central points are respectively positioned at the original points d which have the included angles of 30 degrees, 150 degrees and 270 degrees with the X axis and take C as the original point i Is on the circumference of a radius; making the 3 circle centers respectively along X and Y axes as vertical lines to obtain a beam center point B i,j The distances projected to the warp and weft are respectively represented as
Wherein d is i Is the distance between the beam center point of the ith layer beam and the sub-satellite point, az i,j Azimuth, CB, of the ith beam of the ith layer x And CB y Respectively representing the beam center points B i,j The distance projected onto the warp and weft;
s213: conversion to earth sphere with longitude and latitude expressed as
Wherein s is lon And s lat Respectively representing the longitude and latitude, CB of the sub-satellite point x And CB y Respectively represent the beam center points B i,j Distance projected onto the warp and weft, B i,jlon And B i,jlat Respectively representing the beam center points B i,j Latitude and longitude in the earth's sphere.
4. The multi-beam low-orbit satellite communication system pre-switching method according to claim 1, characterized in that: the step S23 of predicting the reservation time of the channel resource reservation message includes:
s231: terminal is at t 0 Time of day directional beam B 0 Initiating a call application if the source beam B 0 If there is a free channel, directly accessing;
s232: the average call duration of the user is greater than the coverage duration of one beam, at t 0 +T 0 -t pre At the moment, the next service beam B is applied for the user 1 Of a channelResources, i.e. advance t pre Applying for switching the used channel resources at any moment;
s233: terminals are uniformly distributed in the wave beam, and newly arrived calls occur at any point in the wave beam at equal probability; the terminal call duration T follows the exponential distribution with the mean value T; terminals are randomly distributed on the ground, and the distances from the terminals to the central point of the wave beam are uniformly distributed; thus, γ 0 Obey U (0-gamma) bmax ) To obtain gamma 0 A probability density function of (a);
s234: the coverage time t is obtained from S233 cm Is derived to cover the time t cm A probability density function of;
s235: for the coverage time t cm The average coverage time is calculated by the probability density function, and the predicted channel resource reservation time is set to be t pre ＝E(t cm ) In advance of t, depending on the network state pre And occupying channel resources for the switching terminal from the target wave beam at the moment.
5. The multi-beam low-orbit satellite communication system pre-switching method according to claim 1, characterized in that: the step S3 specifically includes the following steps:
s31: the ground control center sends a pre-switching request message to a target satellite beam to request switching;
s32: the target satellite receives the terminal information contained in the pre-switching request message and forwards the message to the target wave beam so as to execute channel resource reservation;
s33: the target wave beam adds the prepared wireless resource into the pre-switching request response message, and forwards the pre-switching request response message to the ground control center through the target satellite to confirm that the switching preparation is completed;
s34: and the ground control center adds the satellite, the wave beam, the channel resource, the frequency resource and the like in the received pre-switching request response message into the pre-switching notification message, adds the switching time in the pre-switching decision into the information, and forwards the information to the terminal through the source wave beam of the source satellite.
6. The multi-beam low-orbit satellite communication system pre-switching method according to claim 1, characterized in that: the step S4 specifically includes the following steps:
s41: when the switching time is reached, the terminal initiates switching to a target satellite or a target beam; after the terminal is successfully switched to a target satellite, updating and registering to a satellite network;
s42: after the switching is successful, the satellite network releases the resource of the source wave beam after receiving the updating message.
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