CN110809292B - Combined switching method based on load balance in low-orbit satellite communication - Google Patents

Combined switching method based on load balance in low-orbit satellite communication Download PDF

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CN110809292B
CN110809292B CN201911102886.XA CN201911102886A CN110809292B CN 110809292 B CN110809292 B CN 110809292B CN 201911102886 A CN201911102886 A CN 201911102886A CN 110809292 B CN110809292 B CN 110809292B
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satellite
switching
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mobile user
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CN110809292A (en
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费泽松
王统
张亚生
蒋逸凡
赵海峰
刘昊昱
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Beijing Institute of Technology BIT
CETC 54 Research Institute
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CETC 54 Research Institute
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W28/00—Network traffic management; Network resource management
    • H04W28/02—Traffic management, e.g. flow control or congestion control
    • H04W28/08—Load balancing or load distribution
    • 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
    • H04B7/18519—Operations control, administration or maintenance
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W36/00—Hand-off or reselection arrangements
    • H04W36/0005—Control or signalling for completing the hand-off
    • H04W36/0055—Transmission or use of information for re-establishing the radio link
    • H04W36/0058—Transmission of hand-off measurement information, e.g. measurement reports

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Abstract

The invention relates to a combined switching method based on load balancing in low-orbit satellite communication, and belongs to the technical field of satellite communication switching. The method comprises the following steps: 1) judging whether an overload satellite exists or not to decide whether to trigger switching, and selecting a proper target satellite by a target satellite selection method based on the multi-attribute decision of the signal intensity of the adjacent satellite received by the mobile user and the load condition of the adjacent satellite; 2) judging whether the reference signal receiving power and the reference signal receiving quality of the source satellite and the target satellite meet the switching triggering condition or not to determine whether to trigger switching or not; 3) if the steps 1) and 2) meet the switching triggering condition, switching is executed through the inter-satellite switching signaling flow provided by the invention. The switching method reduces the switching failure rate and the call drop rate, and also reduces the probability of occurrence of ping-pong switching to a certain extent; and after the switching is finished, the mobile user can obtain better service quality.

Description

Combined switching method based on load balance in low-orbit satellite communication
Technical Field
The invention relates to a combined switching method based on load balancing in low-earth orbit satellite communication, in particular to a switching method, a switching flow and a selection method of a switching target satellite in low-earth orbit satellite communication, and belongs to the technical field of satellite communication switching.
Background
The switching technology in the satellite communication system is always a hot point of research, and when a user is in a connection state with a network, because a satellite moves rapidly relative to the ground, the strength of a signal received by the user may be weakened due to the fact that the original service satellite of the mobile user is too far away from a satellite sub-satellite point. When the mobile subscriber receives signals of strength which do not meet the service requirements, the network selects another suitable satellite for the subscriber to ensure the continuity of the communication, and switches the mobile subscriber to the satellite and establishes a wireless connection. If the handover is not performed, the mobile subscriber may drop the call due to the received signal strength being too weak.
The switching process of the satellite communication system is divided into three stages: the first phase is handover measurement, which is performed by the mobile User (UE) and the serving satellite through signaling interaction of measurement control and measurement reporting. The second phase is handover decision, which refers to a handover decision method, and is completed in the satellite. The third stage is a switching completion stage, which means that the switching process is completed through signaling interaction and is completed by UE, a satellite and a ground gateway station together. The common-frequency switching generally adopts a switching method based on an A3 event, and when the signal intensity of the neighboring cell measured by the UE is greater than the signal intensity of the current cell and the difference value is greater than a certain threshold value (Hyst), an A3 event is triggered. If the duration time after triggering the A3 event is greater than a hysteresis threshold (TTT), the UE sends a measurement report of the A3 event to the satellite, the satellite performs switching judgment according to the measurement report, if the condition is met, switching is initiated, and the whole switching process is executed.
Because of the high speed of satellite movement relative to the ground, mobile users are confronted with frequent inter-beam and inter-satellite handovers, and the conventional handover method based on the a3 event has not been able to meet the requirements of the low earth orbit satellite system. In the traditional switching method, only the reference signal receiving limit power is taken as a judgment condition, and noise interference caused by channel change is ignored. For example: when the serving satellite RSRP is large and the channel noise is also large, the conventional handover method does not initiate handover but is affected by noise, and the communication quality is necessarily poor. In addition, the satellite load capacity is limited, and another obvious defect of the conventional method is that the condition of load balancing cannot be considered, for example, when a certain satellite is overloaded, the system cannot adjust the load in time, and at this time, the satellite wireless resources cannot meet the requirements of a large number of users, so that the switching failure rate and the call drop rate are improved. And the adjacent satellite is likely to have a smaller access user, the utilization rate of wireless resources is lower, and a large amount of resources are wasted.
The Reference Signal Receiving limit power is referred to as Reference Signal Receiving Quality, which is called RSRP for short.
The traditional switching method ignores the situations of noise interference and satellite load balancing and has little influence on the overall performance of the system, so that the improvement of the traditional method has a larger promotion space. The invention provides a joint switching judgment method based on satellite load balance and a switching target satellite selection method based on multi-attribute decision of satellite load and mobile user received signal strength to solve the two defects of the traditional method.
Disclosure of Invention
The invention aims to solve the technical defect that the traditional switching method does not consider the channel noise interference and the load balance and cannot be applied to a low-orbit satellite communication system, provides a combined switching method based on the load balance in the low-orbit satellite communication, and realizes the target satellite selection based on the multi-attribute decision of the signal intensity of the adjacent satellite received by a mobile user and the load condition of the adjacent satellite.
The combined switching method comprises the following specific steps:
the method comprises the following steps: calculating the load condition of each satellite, judging whether an overload satellite exists or not, entering the step two if the overload satellite exists, and jumping to the step eight if the overload satellite does not exist;
step two: generating a switching user list according to the sequence from small to large of the signal intensity received by the mobile user in the overload satellite;
step three: calculating the signal strength of the mobile user received by the adjacent satellite by the formula (1):
P＝Pt-Lr(d)-Ls(d)-Lf(d)-LRa(d) (1)
wherein, PtIs the transmission power of the adjacent satellite, P is the signal strength received by the mobile subscriber, Lr(d) To the path loss, Ls(d) For shadow fading, Lf(d) For fast fading, LRa(d) D is the linear distance from the satellite to the mobile user;
the process for calculating the linear distance d from the satellite to the mobile user comprises the following steps:
a the satellite coverage radius R is calculated by formula (2):
R＝Re·sinθ (2)
wherein R iseIs the radius of the earth, theta is the geocentric angle;
and 3.B, calculating the linear distance d from the satellite to the mobile user by the formula (3):
Figure BDA0002270382720000031
wherein, alpha is the lower angle of the satellite, and R is the satellite coverage radius;
step four: inter-satellite load information interaction specifically comprises the following steps: the satellite A sends RESOURCE STATUS REQUEST information to the satellite B to trigger a load information interaction process, and the satellite B periodically reports the load condition to the satellite A through RESOURCE STATUS UPDATE information;
so far, the signal strength of the adjacent satellite received by the mobile user and the load condition of the adjacent satellite are obtained through the third step and the fourth step;
step five: calculating a weight value of a mobile user by using the signal intensity of the adjacent satellite received by the mobile user and the load condition of the adjacent satellite as variables through a standard deviation distance method, and selecting an optimal switching target satellite based on a good-bad solution distance method, wherein the method specifically comprises the following substeps:
step 5.1: calculating weight values by a standard deviation method, assuming that N target satellites to be switched exist, and standardizing the signal intensity of adjacent satellites received by a mobile user and the load condition of the adjacent satellites according to a formula (4):
Figure BDA0002270382720000041
wherein, bijNormalized value, x, of the ith variable representing the jth neighbor satelliteijValue of i variable, x, representing the j adjacent satelliteiminDenotes the minimum value, x, of the variable iimaxThe maximum value in the variable i is represented, i is 1,2, j is 1,2,3 … N, i is 1 corresponding to the signal strength of the mobile user received by the adjacent satellite, and i is 2 corresponding to the load condition of the adjacent satellite;
step 5.2: calculating the mean of two variables
Figure BDA0002270382720000042
Figure BDA0002270382720000043
Wherein N is the number of target satellites;
step 5.3: calculating the standard deviation sigma of two variablesi：
Figure BDA0002270382720000044
Wherein the content of the first and second substances,
Figure BDA0002270382720000045
is the mean of the two variables calculated in step 5.2;
step 5.4: calculating the weights ω of two variablesi：
Figure BDA0002270382720000046
Wherein σiThe standard deviation of the two variables calculated for equation (6);
step 5.5: calculating the optimal switching target by a good-bad solution distance method, and calculating the values v of the two weighted variables by a formula (8)ij：
vij＝ωi·bij (8)
Step 5.6: and calculating the Euler distance between the parameters acquired by each satellite and the optimal value and the worst value:
Figure BDA0002270382720000047
Figure BDA0002270382720000048
wherein D ismax,jEuler distance, D, representing adjacent satellite parameters and an optimum valuemin,jEuler distance, V, representing the parameters of adjacent satellites and the worst value1,jReceiving the signal strength, V, of the j-th satellite for the mobile subscriber1,maxFor a mobile user receiving an optimum value of the signal strength of the adjacent N satellites, V2,jLoad condition of jth satellite, V2,maxIs the optimal value of the load conditions of the adjacent N satellites, V1,minWorst value of signal strength, V, for mobile users receiving adjacent N satellites2,minThe worst value of the load conditions of the adjacent N satellites is obtained;
step 5.7: calculating the relative distance L between each adjacent satellite and the optimal value according to the (11)j：
Figure BDA0002270382720000051
Wherein D ismax,jAnd Dmin,jEuler distances of the adjacent satellite parameters and the optimal value and the worst value calculated by the formulas (9) and (10) respectively;
step 5.8: taking the relative distance L from the optimal valuejThe smallest satellite is used as a switching target satellite;
step six: executing an inter-satellite switching process according to the switching user list generated in the step two and the target satellite selected in the step five, and sequentially switching the mobile users in the overloaded satellite to the adjacent satellites;
step seven: judging whether the switched source satellite and the switched target satellite are overloaded, if the overload condition still exists, entering a second step, and if the overload condition does not exist, entering an eighth step;
step eight: the satellite receives a measurement report sent by a mobile user, acquires the RSRP of a source satellite and a target satellite, judges whether the RSRP of the source satellite and the target satellite meets the triggering condition of an A3 event or not, jumps to the tenth step if the RSRP of the source satellite and the target satellite meets the triggering condition of the A3 event, and jumps to the ninth step if the RSRP of the source satellite and the target satellite does not meet the condition;
the event A3 is when the UE measures a signal strength of a neighboring satellite greater than a signal strength of a current serving satellite and a difference is greater than a threshold, and then an event A3 is triggered.
Step nine: judging whether the RSRQ of the source satellite and the target satellite meets the switching triggering condition of the A3 event, if so, entering a step ten, and if not, jumping to a step eight;
wherein, the RSRQ, i.e. Reference Signal Receiving Quality, is the Reference Signal Receiving Quality;
step ten: judging whether the time when the RSRP or the RSRQ meets the condition is larger than a time delay threshold TTT or not, if so, triggering inter-satellite switching, otherwise, jumping to the step eight;
wherein, the Time delay threshold, i.e. Time To Trigger, is abbreviated as TTT.
Advantageous effects
Compared with the traditional switching method based on the A3 event, the joint switching judgment method based on the satellite load balancing has the following beneficial effects:
1. the RSRQ is added in the switching judgment condition, so that the problems that the noise interference is large, the switching is not timely and the communication quality is influenced due to the change of the channel environment under the single judgment condition are solved;
2, the combined switching method adds a load balancing mechanism, so that the switching failure rate and the call drop rate are reduced, and the probability of occurrence of ping-pong switching is also reduced to a certain extent;
3. the combined switching method comprehensively considers the signal intensity of the target satellite received by the mobile user and the load of the target satellite through the selection of the multi-attribute decision target satellite, thereby improving the switching success rate; and after the switching is finished, the mobile user can obtain better service quality, and the condition that the satellite is overloaded is reduced to a certain extent.
Drawings
FIG. 1 is a diagram of a low earth orbit satellite communication system architecture in which a joint handover method based on load balancing in low earth orbit satellite communication is relied on;
FIG. 2 is a flowchart of a joint handover method based on load balancing in low earth orbit satellite communication according to the present invention;
fig. 3 is a flowchart of inter-satellite handover corresponding to step six and step ten of the combined handover method based on load balancing in low earth orbit satellite communication according to the present invention;
FIG. 4 is a graph comparing ping-pong handover occurrence probability simulation results of a conventional handover method and a handover method of the present invention when a power threshold parameter is taken as 1;
fig. 5 is a comparison graph of the RLF transition probability occurrence simulation results of the conventional switching method and the switching method of the present invention when the power threshold parameter is 4.
Detailed Description
The joint handover decision method and inter-satellite handover procedure based on satellite load balancing according to the present invention will be further described and illustrated in detail with reference to the accompanying drawings and embodiments.
Example 1
The embodiment describes a specific implementation of a combined handover method based on load balancing in low earth orbit satellite communication in a low earth orbit satellite communication system, as shown in fig. 1, the whole low earth orbit satellite communication system is divided into three parts, namely a space section, a ground section and a user section. The user segment is various mobile users; the ground section comprises a system control center, a network control center, a gateway station and the like; the space segment is comprised of low earth orbit satellites that communicate with each other via communication links. Switching occurs between low orbit satellites in a space section, whether inter-satellite switching triggering conditions are met or not is judged firstly, when the switching triggering conditions are met, a target satellite is selected through the multi-attribute decision target satellite selection method, and a mobile terminal, a source satellite, the target satellite and a ground gateway station complete a switching process through signaling interaction.
Two conditions for inter-satellite handover triggering:
1. calculating the load condition of each satellite, if the overload satellite exists, initiating switching to transfer a user with lower received signal strength in the overload satellite to an adjacent satellite with lower load, and repeating the process until the overload satellite does not exist;
2. a base station deployed on a low earth orbit satellite acquires RSRP values of a source satellite and a target satellite station through a measurement report transmitted from a ground mobile user, compares whether the RSRP of the source satellite and the target satellite meets a switching triggering condition in a switching method, judges whether the duration of the RSRP meeting the switching triggering condition is greater than a set time delay threshold under the condition of yes, executes switching if the duration is greater than TTT, compares whether the RSRQ of the source satellite and the target satellite meets the switching triggering condition in the switching method under the condition of no, judges whether the duration of the RSRQ meeting the switching triggering condition is greater than the set time delay threshold if the RSRQ meets the switching triggering condition, triggers switching if the RSRQ meets the switching triggering condition, and otherwise waits for a next measurement report to continue to execute the flow of the method;
fig. 2 is a flowchart of a joint switching method based on load balancing, which specifically includes the steps of:
step 1: calculating the load condition of each satellite, judging whether an overload satellite exists or not, entering the step 2 under the condition of yes, and otherwise, jumping to the step 6;
step 2: generating a list of users to be switched according to the strength of signals received by mobile users in the overload satellite;
and step 3: selecting a proper target satellite according to a target satellite selection method of multi-attribute decision in the invention content;
and 4, step 4: triggering switching, selecting a proper target satellite according to the switching user lists generated in the step 2 and the step 3, executing a switching process, and sequentially switching the mobile users in the overloaded satellite to the adjacent satellites;
and 5: and judging whether the switched source satellite and the switched target satellite are overloaded, if the overload condition still exists, entering the step 2 until the overload satellite does not exist, and entering the step 6.
Step 6: determining a power threshold parameter to judge whether the RSRP of the source satellite and the target satellite meets a switching trigger condition, and determining a time lag parameter to judge whether the time duration that the RSRP and the RSRQ meet the switching trigger condition meets the switching trigger condition and a received signal quality threshold parameter (H) whether the RSRQ of the source satellite and the target satellite meets the switching trigger condition. The three parameters are set to prevent the ping-pong effect caused by the early switching;
and 7: the base station carried on the low earth orbit satellite sends down the 'measurement control' message to the ground mobile user, the mobile user measures according to the requirement in the 'measurement control' message, and the measurement result is generated into the measurement report. The measurement control message includes: measurement signaling, the amount that the UE needs to measure, such as the reference signal received power, etc., the measurement report includes: a source satellite identification number, a target satellite identification number, RSRP, RSSI, RSRQ and the like, wherein the RSRQ is calculated by the formula (12);
Figure BDA0002270382720000091
where N is the number of resource blocks RB in the measurement bandwidth of the RSSI, which is an indication of the strength of the received signal, including the desired signal and the interfering signal.
Wherein, the RSSI, namely Reference Signal Receiving Quality, is the received Signal strength indication;
and 8: the mobile user uploads a measurement report obtained by measurement to a satellite;
Mt≥Ms+Hyst (13)
wherein M istReceiving target satellite RSRP, M for mobile userssReceiving RSRP of a source satellite by a mobile user, wherein Hyst is a power hysteresis threshold;
and step 9: the satellite judges whether the RSRP of the source satellite and the target satellite meets the condition of the formula (13) or not according to the measurement report, and if the RSRP of the source satellite and the target satellite meets the condition, the step 11 is carried out; if the condition is not met, entering the step 10;
RSRQj-RSRQi＞H (14)
wherein, RSRQjReceiving a target satellite RSRQ for a mobile useriA mobile user receives RSRQ of a source satellite and an H hysteresis threshold;
step 10: the satellite judges whether the RSRQ of the source satellite and the target satellite meets the condition (14) or not according to the measurement report, and if the RSRQ of the source satellite and the target satellite meets the condition, the step 11 is carried out; if the condition is not met, waiting for the next measurement report;
step 11: judging whether the time duration that the RSRP and the RSRQ of the source satellite and the target satellite meet the condition is longer than a time lag parameter or not; under the condition of 'yes', triggering the switching; otherwise, waiting for the next measurement report;
fig. 3 is a signaling flow chart for inter-satellite handover, which includes the following steps:
step (1): the service satellite transmits a measurement control message to the mobile user to request the mobile user to measure the related parameters;
step (2): the mobile user completes measurement according to the measurement control message and reports a measurement report;
and (3): the service sends RESOURCE STATUS REQUEST message to the adjacent satellite to trigger the load information interaction process;
and (4): if the adjacent satellite can successfully complete the corresponding measurement, sending a resource state response confirmation message to the service satellite;
and (5): if the adjacent satellite fails to complete the measurement, a resource state response failure message is sent to the service satellite;
and (6): after the adjacent satellite sends a RESOURCE state response confirmation message to the service satellite, the load condition is periodically reported to the service satellite through a RESOURCE STATUS UPDATE message;
and (7): the service satellite executes switching judgment, and the judgment conditions are divided into two types: whether a service satellite is overloaded and whether the RSRP and the RSRQ of the service satellite and the target satellite meet the switching condition required by the method or not;
and (8): selecting a proper target satellite to initiate a switching request according to the multi-attribute decision-making target satellite selection method;
and (9): the target satellite performs admission control and judges whether a mobile user is allowed to access the satellite or not;
step (10): if the target satellite allows the mobile user to access the satellite, a handoff request acknowledge message is sent to the serving satellite.
Step (11): the service satellite sends a switching command containing an RRC connection reconfiguration message to the mobile user;
step (12): the service satellite sends a serial number state transmission message to the target satellite;
wherein, the serial Number is SN for short;
step (13): the mobile user is detached from the service satellite and performs synchronization with the target satellite;
step (14): the target satellite returns uplink resource allocation and timing information of the mobile user;
step (15): the mobile user confirms that the switching process is completed to the target satellite;
step (16): the target satellite sends a path switching request to the gateway station to inform the gateway station that the mobile user is switched to another satellite;
step (17): the target satellite sends a user plane updating request to the gateway station to request to switch a downlink user plane data path to the target satellite;
step (18): the gateway station converts a downlink data path, does not send user plane data to the source satellite any more, and sends downlink data to the target satellite;
step (19): the gateway station sends a user plane updating response to the target satellite to confirm that the user plane updating is completed;
step (20): the gateway station sends a path switching request confirmation message to the target satellite to inform the target satellite that the path switching is completed;
step (21): the target satellite informs the service satellite to release the control plane resource related to the user context;
step (22): and after receiving the user context release message sent by the target satellite, the service satellite releases the radio bearer and the resources related to the user.
In order to better show the comparison effect of the improved method and the original method, the power threshold parameter with the most obvious ping-pong switching probability and the most obvious change of the wireless link failure occurrence probability is selected for simulation. In the two methods, the power threshold parameter is selected to be 1dB in the simulation of the ping-pong switching probability comparison result, and the power threshold parameter is selected to be 4dB in the simulation of the RLF probability comparison result. The results of comparing the ping-pong handover occurrence probability and the RLF occurrence probability of the two methods are shown in fig. 4 and 5, respectively.
The ping-pong effect is a situation that a mobile user switches back to a source satellite within a short time after switching from the source satellite to the target satellite, and even switches back and forth between the target satellite and the source satellite for many times. Radio Link Failure, RLF for short, refers to a phenomenon of communication interruption due to some reasons, and if handover is initiated too late, signal quality between the UE and the source satellite is too poor, which may result in Radio Link Failure.
Fig. 4 is a comparison graph of simulation results of the improved method and the conventional method on ping-pong handover probability, and RSRQ and load balancing determination conditions are added in the improvement of the method, so that the occurrence probability of ping-pong handover is reduced. From the results in the figure, it can be seen that the probability of ping-pong handover is reduced by about 6-8% in the improved method compared to the conventional method.
Fig. 5 is a comparison graph of simulation results of the improved method and the conventional method with respect to the RLF probability, where the power threshold parameter selected in the ping-pong handover probability comparison result simulation of the two methods is 4dB, a decision condition for load balancing is added, and a selection method of a target satellite for multi-attribute decision is designed, and the received signal strength and the load condition of the target satellite are comprehensively considered in selecting the handover target satellite, thereby avoiding the access rejection of the target satellite due to overload, and thus reducing the probability of the RLF occurrence, and the simulation results also confirm this. From the results in the figure, it can be seen that the probability of RLF occurrence is also continuously increased with the increase of the time lag parameter, and the improvement of the RLF occurrence probability by the improved method is more obvious. The probability of RLF is greatest when the time lag parameter is 240ms, where the improved method reduces the probability of occurrence of RLF by approximately 17%.
In view of the two points, compared with the traditional switching method, the joint switching judgment method based on satellite load balancing simultaneously reduces the probability of ping-pong switching and the probability of RLF, simultaneously improves the resource utilization rate through the load balancing technology, and improves the overall performance of the system.
While the foregoing is directed to the preferred embodiment of the present invention, it is not intended that the invention be limited to the embodiment and the drawings disclosed herein. Equivalents and modifications may be made without departing from the spirit of the disclosure, which is to be considered as within the scope of the invention.

Claims (2)

1. A combined switching method based on load balance in low earth orbit satellite communication is characterized in that:
the method comprises the following steps: calculating the load condition of each satellite, judging whether an overload satellite exists or not, entering the step two if the overload satellite exists, and jumping to the step eight if the overload satellite does not exist;
step two: generating a switching user list according to the sequence from small to large of the signal intensity received by the mobile user in the overload satellite;
step three: calculating the signal strength of the mobile user received by the adjacent satellite by the formula (1):
P＝Pt-Lr(d)-Ls(d)-Lf(d)-LRa(d) (1)
wherein, PtIs the transmission power of the adjacent satellite, P is the signal strength received by the mobile subscriber, Lr(d) To the path loss, Ls(d) For shadow fading, Lf(d) For fast fading, LRa(d) D is the linear distance from the satellite to the mobile user;
the process for calculating the linear distance d from the satellite to the mobile user comprises the following steps:
a the satellite coverage radius R is calculated by formula (2):
R＝Re·sinθ (2)
wherein R iseIs the radius of the earth, theta is the geocentric angle;
and 3.B, calculating the linear distance d from the satellite to the mobile user by the formula (3):
Figure FDA0002788495540000011
wherein, alpha is the lower angle of the satellite, and R is the satellite coverage radius;
step four: inter-satellite load information interaction specifically comprises the following steps: the satellite A sends RESOURCE STATUS REQUEST information to the satellite B to trigger a load information interaction process, and the satellite B periodically reports the load condition to the satellite A through RESOURCE STATUS UPDATE information;
so far, the signal strength of the adjacent satellite received by the mobile user and the load condition of the adjacent satellite are obtained through the third step and the fourth step;
step five: calculating a weight value of a mobile user by using the signal intensity of the adjacent satellite received by the mobile user and the load condition of the adjacent satellite as variables through a standard deviation distance method, and selecting an optimal switching target satellite based on a good-bad solution distance method, wherein the method specifically comprises the following substeps:
step 5.1: calculating weight values by a standard deviation method, assuming that N target satellites to be switched exist, and standardizing the signal intensity of adjacent satellites received by a mobile user and the load condition of the adjacent satellites according to a formula (4):
Figure FDA0002788495540000021
wherein, bijNormalized value, x, of the ith variable representing the jth neighbor satelliteijValue of i variable, x, representing the j adjacent satelliteiminDenotes the minimum value, x, of the variable iimaxThe maximum value in the variable i is represented, i is 1,2, j is 1,2,3 … N, i is 1 corresponding to the signal strength of the mobile user received by the adjacent satellite, and i is 2 corresponding to the load condition of the adjacent satellite;
step 5.2: calculating the mean of two variables
Figure FDA0002788495540000022
Figure FDA0002788495540000023
Wherein N is the number of target satellites;
step 5.3: calculating the standard deviation sigma of two variablesi：
Figure FDA0002788495540000024
Wherein the content of the first and second substances,
Figure FDA0002788495540000025
is the mean of the two variables calculated in step 5.2;
step 5.4: calculating the weights ω of two variablesi：
Figure FDA0002788495540000026
Wherein σiThe standard deviation of the two variables calculated for equation (6);
step 5.5: calculating the optimal switching target by a good-bad solution distance method, and calculating the values v of the two weighted variables by a formula (8)ij：
vij＝ωi·bij (8)
Step 5.6: and calculating the Euler distance between the parameters acquired by each satellite and the optimal value and the worst value:
Figure FDA0002788495540000031
Figure FDA0002788495540000032
wherein D ismax,jEuler distance, D, representing adjacent satellite parameters and an optimum valuemin,jEuler distance, V, representing the parameters of adjacent satellites and the worst value1,jReceiving the signal strength, V, of the j-th satellite for the mobile subscriber1,maxFor a mobile user receiving an optimum value of the signal strength of the adjacent N satellites, V2,jLoad condition of jth satellite, V2,maxIs the optimal value of the load conditions of the adjacent N satellites, V1,minWorst value of signal strength, V, for mobile users receiving adjacent N satellites2,minThe worst value of the load conditions of the adjacent N satellites is obtained;
step 5.7: calculating the relative distance L between each adjacent satellite and the optimal value according to the (11)j：
Figure FDA0002788495540000033
Wherein D ismax,jAnd Dmin,jEuler distances of the adjacent satellite parameters and the optimal value and the worst value calculated by the formulas (9) and (10) respectively;
step 5.8: taking the relative distance L from the optimal valuejThe smallest satellite is used as a switching target satellite;
step six: executing an inter-satellite switching process according to the switching user list generated in the step two and the target satellite selected in the step five, and sequentially switching the mobile users in the overloaded satellite to the adjacent satellites;
step seven: judging whether the switched source satellite and the switched target satellite are overloaded, if the overload condition still exists, entering a second step, and if the overload condition does not exist, entering an eighth step;
step eight: the satellite receives a measurement report sent by a mobile user, acquires the RSRP of a source satellite and a target satellite, judges whether the RSRP of the source satellite and the target satellite meets the triggering condition of an A3 event or not, jumps to the tenth step if the RSRP of the source satellite and the target satellite meets the triggering condition of the A3 event, and jumps to the ninth step if the RSRP of the source satellite and the target satellite does not meet the condition;
the event A3 is that when the signal strength of the neighboring satellite measured by the UE is greater than the signal strength of the current serving satellite and the difference is greater than a certain threshold, the event A3 is triggered;
step nine: judging whether the RSRQ of the source satellite and the target satellite meets the switching triggering condition of the A3 event, if so, entering a step ten, and if not, jumping to a step eight;
step ten: and judging whether the time when the RSRP or the RSRQ meets the condition is greater than a time delay threshold TTT or not, if so, triggering inter-satellite switching, and otherwise, jumping to the step eight.
2. The method according to claim 1, wherein the method comprises: the RSRQ, namely Reference Signal Receiving Quality, is the Reference Signal Receiving Quality; the Time delay threshold, namely Time To Trigger, is abbreviated as TTT.
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