Load balancing dynamic access method under multi-satellite coverage

Abstract

The invention discloses a load balancing dynamic access method under multi-satellite coverage, which comprises the following steps of: classifying user terminal services at a user side according to QoS (Quality of Service) requirements, generating a service multi-target utility function according to service indexes, and generating a multi-target weight coefficient for the importance degrees of different services; a terminal visible satellite set and an adjacent satellite set of each satellite are constructed on a satellite side, and a load balance degree parameter and a load adjustment method of the terminal visible satellite set and the adjacent satellite set of each satellite are provided, so that a satellite network corresponding to a current user terminal within a certain time reaches dynamic load balance. According to the method, the actual capability of the satellite network is considered while the multi-target requirements of different types of services of the ground user terminal are met, so that the satellite network corresponding to the current user terminal within a certain time and a certain range can achieve local dynamic load balancing, and the method can be applied to service access of low-orbit satellite networks such as a Chinese satellite network.

Description

Technical Field

[0001] The present invention relates to the field of network and information processing, and in particular to a load balancing dynamic access method under multi-satellite coverage. Background Art

[0002] Since the low-orbit satellite constellation needs to provide global seamless coverage of satellite communication services, the number of low-orbit satellites will inevitably increase significantly, and at the same time, the multi-satellite coverage rate of ground user terminals will be greatly increased. Taking the global star communication system as an example, its dual-satellite coverage rate reaches 90%. At present, with the sharp increase in the number of satellites in the planned low-orbit satellite constellation, user terminals will generally be in the overlapping coverage area of ​​the low-orbit satellite constellation. User terminals in the multi-satellite overlapping area can receive broadcast information from multiple satellites at the same time within a certain period of time. Therefore, user terminals in the overlapping area face the access selection problem under multi-satellite coverage. In addition, when the user terminal leaves the coverage area of ​​the currently connected communication node, it needs to switch to the next satellite communication node for communication to ensure service continuity. Whether it is a new call access or call switching, the user terminal faces the access selection problem under multi-satellite coverage. At the same time, user terminal access is a dynamic balancing problem for the satellite network load. By obtaining the network load conditions of satellites in a certain range, the distributed dynamic load balancing of the satellite network can be achieved.

[0003] Access selection methods under multi-satellite coverage of satellite networks have also been proposed in existing research, which mainly focus on the following aspects: for satellite parameters corresponding to service indicators, such as satellite-to-ground distance, satellite serviceable time, satellite remaining load, etc., the impact of service access on load balancing and the impact of load balancing related parameters on service access are not considered; for multi-service intelligent access selection strategies, the state variables, action space and feedback functions in the dual-satellite coverage scenario are designed. This method assumes that each satellite can obtain the global state information of the satellite network. Its calculation complexity is high and the convergence time is long, which is not conducive to dynamic load balancing on the satellite; for the service QoS requirements in high and low orbit satellite networks, the satellite transmission delay, delay jitter and cost are used as weighted values ​​to calculate the comprehensive weighted value of service QoS and the load value of the satellite set, but it only considers the load value of the accessible satellite set, and does not judge the load balancing situation of the visible satellites and related satellite local networks, and does not make corresponding load balancing adjustments. Summary of the invention

[0004] The technical problem solved by the present invention is: aiming at the comprehensive access demand for service QoS demand and satellite network load balancing performance in a multi-satellite coverage scenario, overcoming the problem that it is difficult for satellites to obtain the global resource usage of the satellite network in real time, and proposing a load balancing dynamic access method under multi-satellite coverage. According to the importance of satellite parameters corresponding to the service QoS demand of the user-side terminal and the satellite load usage, a terminal service access objective function based on weight coefficients and load adjustment factors is constructed, and the user terminal service demand and the satellite network load balancing characteristics are considered at the same time; it is proposed to construct two satellite sets, namely a visible satellite set and an adjacent satellite set, on the satellite side, and by adjusting the load balancing parameters of the two types of satellite sets, the satellite network corresponding to the current user terminal within a certain time and a certain range can achieve local dynamic load balancing.

[0005] The technical solution provided by the present invention is:

[0006] A load balancing dynamic access method under multi-satellite coverage comprises: classifying user terminal services according to QoS requirements on the user side, generating a service multi-objective utility function according to service indicators, and generating multi-objective weight coefficients for the importance of different services; constructing a terminal visible satellite set and an adjacent satellite set of each satellite on the satellite side, proposing load balancing parameters and a load adjustment method for the terminal visible satellite set and the adjacent satellite set of each satellite, so that the satellite network corresponding to the current user terminal within a certain period of time achieves dynamic load balancing.

[0007] Optionally, the specific steps include:

[0008] Step 1: Ground user terminal UE j Generate the business utility function f according to the business indicators and their corresponding satellite-to-ground distance, satellite service time and satellite load utilization parameters j , the subscript j indicates the number of different ground user terminals, specifically:

[0009] f j =α j f 1j +β j f 2j +γ j f 3j ;

[0010] Among them, α j ,β j ,γ j are the satellite-to-ground distance, satellite service time and satellite load utilization parameter weight coefficients, respectively. 1j Characterize the utility function of the satellite-to-ground distance, f 2j Characterize the satellite service time utility function, f 3j Characterize the satellite load balancing utility function;

[0011] Step 2: Satellite LEO i Calculate the current local load utilization based on the local physical channel resource block load The subscript i indicates different satellite numbers, which are calculated as follows;

[0012]

[0013] Among them, n represents the different services of the satellite, Indicates the number of resource blocks occupied by the nth service at time t in the current satellite, Represents the sum of the number of resource blocks occupied by all services at the current satellite time t, represents the number of services that the current satellite accesses to the user terminal at time t, Indicates the total number of resource blocks currently available to the satellite;

[0014] ρ h To characterize the satellite load utilization threshold, if the satellite LEO i If the current load utilization is greater than or higher than the threshold, the satellite cannot access new services, otherwise it can access;

[0015] Step 3. Define satellite LEO i The set of adjacent satellites at time t, K is the satellite LEO i The number of adjacent satellites, K+1 is the set The number of satellites in

[0016] The satellite load utilization variance is used to characterize the discrete degree of satellite load utilization. Satellite load utilization variance Var LEO (t), by calculating the average value Var of the square of the difference between each value in the set and the mean LEO (t) is obtained, and the calculation formula is as follows:

[0017]

[0018] Where K+1 is the set The number of satellites in is the average of all satellite load utilizations in the satellite set; Satellite set Satellite load utilization variance threshold The satellite load utilization variance threshold in the satellite set calculated at the characterization time t is used as the threshold for measuring the satellite load balance;

[0019] Step 4: User terminal UE jReceive satellite broadcast signals and obtain the visible satellite set at time t Defined as I is a collection The number of satellites in

[0020] Step 5: The ground user terminal determines whether the currently accessible satellite meets the service requirements based on the feedback parameters from the satellite side, and sets the satellite load adjustment factor li, and adjusts the value of the parameter li based on the satellite load utilization rate feedback from the satellite side;

[0021] Step 6: Normalize the satellite-to-ground distance, satellite service time, and satellite load utilization index, and calculate the utility function weight coefficient α j ,β j ,γ j Calculate the utility function value of the satellites in the visible satellite set;

[0022] Step 7: Define the satellite objective function as F j =α j f 1j +β j f 2j +γ j f 3j ·l j , according to the satellite load adjustment factor l obtained in step 5 i And the satellite utility function value f obtained in step 6 1j ,f 2j ,f 3j , calculate the target value of accessible satellites; select the satellite corresponding to the maximum target value as the optimal access satellite;

[0023] Step 8. Satellite LEO i After receiving the service application message and successfully accessing, update the local physical channel resource block load and update the load utilization parameter And the load utilization variance Var of the adjacent satellite set LEO (t) Information.

[0024] Optionally, the step 1 specifically includes:

[0025] Step 1a, listing the importance of service utility function parameters under different ground user terminal service types, and the importance of service utility function parameters can be divided into five levels: extremely high, high, medium, general and low;

[0026] Step 1b: Use the analytic hierarchy process to analyze the importance of satellite-to-ground distance, satellite service time, and satellite load utilization for different services; define the importance scales of different indicators, and correspond the three types of service indicator parameters to different importance scales of 1 to 9;

[0027] Step 1c, according to the indicator importance scale given in steps 1a and 1b, respectively calculate the importance of the utility function parameters of voice services, streaming media services, interactive services and background services;

[0028] Step 1d: Use the hierarchical analysis method to calculate the weight coefficients of different businesses. First, obtain the normalized proportion of each column of each indicator, and then calculate the average value of each indicator by row to obtain the utility function weight coefficient α of different businesses. j ,β j ,γ j .

[0029] Optional, satellite load utilization variance threshold The settings include:

[0030] Set satellite load utilization The range is [0,ρ h ],ρ h is the set satellite load utilization threshold, and the number of load utilization values ​​in the set is K+1; given the number of set values ​​and the range of values, the maximum value of the load utilization variance max(Var LEO ) corresponds to a set value that contains only the maximum value ρ h The dispersion is highest when the maximum value difference in the set is less than ρ h / 2, it indicates that the load balancing is good at this time. When the maximum data value difference in the set is greater than or equal to ρ h / 2, it indicates that the load balancing degree is weak and load balancing adjustment is needed; define the load utilization set value range [0, ρ h / 2], the satellite load utilization value only takes the maximum value ρ h / 2 and the minimum value is 0, the calculated variance is the maximum variance of the set As a threshold to measure satellite load balance.

[0031] Optionally, the step 6 specifically includes:

[0032] Step 6a: The ground user terminal obtains the low-orbit satellite-to-ground distance range [D min ,D max ] and the current distance D between the user terminal and the satellite ij , where D min ≤D ij ≤D max ,but

[0033]

[0034] Calculate the set of satellites that can be accessed by the service separately The function value f of the satellite in1j ;

[0035] Step 6b: The ground user terminal obtains the satellite service time range [Ts min ,Ts max ] and the current terminal and satellite service time Ts i,j , where Ts min ≤Ts i,j ≤Ts max ,but Calculate the set of satellites that can be accessed by the service separately The function value f2j of the satellite in the middle;

[0036] Step 6c: The ground user terminal receives the current load utilization parameter fed back by the satellite calculate Calculate the set of satellites that can be accessed by the service separately The function value of the satellite in f3j.

[0037] Optionally, the step 5 specifically includes:

[0038] Step 5a: First, the user terminal sets the currently accessible satellites. Load situation, determine the available load utilization of the satellites in the set in turn Whether the current business load requirement is met, if yes, proceed to step 5c, if not, proceed to step 5b;

[0039] Step 5b: Gather at the Satellite Delete the satellite and go to step 5c. If the updated satellite set If it is an empty set, go to step 5g;

[0040] Step 5c: Updated satellite set Calculate the updated satellite set Load utilization variance Var L ' EO (t), and according to the satellite load utilization variance threshold calculation method, calculate Satellite load utilization variance threshold Among them, Var′ LEO (t) and Refer to Var in step 3 LEO (t) and Calculation method of

[0041] Step 5d: Determine the load utilization variance Var′ LEO (t) Is it greater than or equal to the load utilization variance threshold? If it is greater than or equal to the threshold, go to step 5e;

[0042] Receive updated satellite set The set of neighboring satellites for each satellite in The load utilization variance Var LEO (t), determine its load utilization variance threshold calculated in step 4 If the size is greater than or equal to the threshold, go to step 5e;

[0043] If the resource utilization variances of the two satellite sets are both less than the corresponding threshold values, go to step 5f;

[0044] Step 5e: The satellite load adjustment factor l needs to be adjusted i ; l i The default value is 1, and the value range is defined as [0,2]. The value range of satellite load utilization can be divided into [0,ρ h / 2] and [ρ h / 2,ρ h ]; Compare satellite collections The load utilization of each satellite and ρ h / 2 size;

[0045] like This indicates that the satellite has a small load and needs to increase the satellite's load adjustment factor l i , increase the satellite access target value, l i The adjustment factor is:

[0046] like This indicates that the satellite has a large load and needs to reduce the satellite's load adjustment factor l i , reduce the satellite access target value, l i The adjustment factor is:

[0047] Step 5f: No need to adjust the satellite's load adjustment factor l i ;

[0048] Step 5g: If there is no satisfactory satellite to choose from, wait for the next time period to reselect.

[0049] The advantages of the present invention compared with the prior art are:

[0050] (1) The present invention maps the QoS indicator requirements of terminal services on the user side to the importance of satellite parameters, constructs a multi-objective utility function of terminal services based on weight coefficients and load adjustment factors, and constructs a satellite access objective function according to the load balancing parameters of two types of satellite sets on the satellite side. While meeting the QoS requirements of low-orbit satellite network services, the load balancing requirements of the satellite network are comprehensively considered.

[0051] (2) The present invention adjusts the satellite network load balancing influencing factor by judging the numerical value of the load utilization variance and the load utilization variance threshold in the visible satellite set and the adjacent satellite set, so that the satellite network corresponding to the current user terminal within a certain time and a certain range can achieve local dynamic load balancing. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The accompanying drawings are used to provide a further understanding of the present disclosure and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present disclosure but do not constitute a limitation of the present disclosure. In the accompanying drawings:

[0053] Figure 1 Load balancing dynamic access flow chart under multi-satellite coverage;

[0054] Figure 2 Satellite load adjustment factor calculation flow chart;

[0055] Figure 3 Schematic diagram of multi-satellite coverage scenario and satellite collection. DETAILED DESCRIPTION

[0056] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0057] The load balancing dynamic access method under multi-satellite coverage proposed in the present invention classifies terminal services according to QoS requirements on the user side, generates a multi-objective utility function of the service according to parameters such as satellite-to-ground distance, service service time, and satellite load utilization corresponding to the service indicators, and generates multi-objective weight coefficients according to the importance of the indicators to different services; constructs two types of satellite sets on the satellite side, namely, the terminal visible satellite set and the adjacent satellite set of each satellite, and proposes load balancing parameters and load adjustment methods for these two types of local satellite sets, so that the satellite network corresponding to the current user terminal within a certain period of time achieves dynamic load balancing. While meeting the multi-objective requirements of different types of services of ground user terminals, the method of the present invention also takes into account the dynamic load balancing requirements of satellite sets.

[0058] On the user side, terminal services can be classified according to QoS requirements: QoS service requirements refer to delay requirements, delay jitter requirements, and packet loss rate requirements. Service classification mainly includes four categories: voice services, streaming media services, interactive services, and background services. Among them, voice services are more sensitive to delay, streaming media services are more sensitive to delay jitter and packet loss rate, and background services and interactive services are sensitive to packet loss rate.

[0059] The delay (mainly transmission delay) in low-orbit satellite networks is mainly related to the transmission distance between the satellite and the ground; the delay jitter is mainly related to the difference in the processing queue time of satellite data streams and the satellite service time, and in the access link it is mainly related to the satellite customer service time; the packet loss rate is related to the satellite-to-ground channel quality, processing queue time, and satellite load rate. According to the demand for QoS indicators for ground user services, the importance of three parameters, namely, satellite-to-ground distance, satellite service time, and satellite load utilization, for different services are listed.

[0060] In the present invention, t refers to the moment, indicating that the information is related to the moment but not to the time unit. The following are the meanings of the letters in the present invention:

[0061] UE j : represents the ground user terminal, where the subscript j indicates different terminal numbers.

[0062] LEO i : represents the satellites visible to a terminal at time t, where the subscript i indicates different satellite numbers.

[0063] Characterize User Terminal UE j The set of visible satellites at time t,

[0064] I is a collection The number of satellites in

[0065]

[0066] Characterizing terrestrial user terminals UE j The updated visible satellite set at time t.

[0067] Characterizing LEO Satellites i The set of adjacent satellites at time t, K is the satellite LEO i The number of adjacent satellites, K+1 is the set The number of satellites in

[0068] The satellite LEO at time t i The sum of the time domain and frequency domain physical resource blocks used by the accessed services is used as the numerator, and the satellite LEO i The total amount of available physical resource blocks is used as the denominator to characterize the load utilization of the satellite.

[0069]

[0070] in, Indicates the number of resource blocks occupied by the nth service at time t in the current satellite, Represents the sum of the number of resource blocks occupied by all services at the current satellite time t, Indicates the total number of resource blocks available for the current satellite. When the value of this parameter is high, it means that the current load is large and the access service volume needs to be reduced. When the load is low, the access service volume can be increased. n Indicates the different services of the satellite.

[0071] ρ h : represents the maximum load utilization threshold of the satellite under normal conditions, and the subscript h is the abbreviation of high. i If the load utilization rate at time t is greater than or higher than the threshold, the satellite can no longer access new services. (This value is a constant and is not related to time t)

[0072] Var' LEO (t): represents the updated visible satellite set at time t The satellite load utilization variance in .

[0073] Represents the updated visible satellite set calculated at time t The satellite load utilization variance threshold in .

[0074] Var LEO (t): represents the set of adjacent satellites at time t The satellite load utilization variance in .

[0075] Characterizes the set of adjacent satellites calculated at time t The satellite load utilization variance threshold in .

[0076] α j ,β j ,γ j :respectively represent the user terminal UE j The weight parameters of three objective functions are based on the satellite-to-ground distance, satellite service time, and satellite load balance. The subscript j represents different user terminals.

[0077] l i : Satellite LEO i The load adjustment factor. After the satellite calculates the effect value according to the business utility function, the final effect value of each satellite needs to be adjusted according to the load adjustment factor.

[0078] f j : User terminal UE j The service utility function that needs to be calculated when accessing the satellite, f j =α j f1j +β j f 2j +γ j f 3j , where f 1j Characterize the utility function of the satellite-to-ground distance, f 2j Characterize the satellite service time utility function, f 3j Utility function to characterize satellite load balancing.

[0079]

[0080] F j : User terminal UE j Accessible satellite objective function F j =α j f 1j +β j f 2j +γ j f 3j ·l j , l i To correct f 3j Utility function.

[0081] [D min ,D max ]: Low-orbit satellite distance range from the earth.

[0082] D ij : The current distance between the terminal and the satellite, D min ≤D ij ≤D max .

[0083] [Ts min ,Ts max ]: Satellite service time range.

[0084] Ts i,j : Current terminal and satellite service time, Ts min ≤Ts i,j ≤Ts max

[0085] Combination Figure 1 The load balancing dynamic access method under multi-satellite coverage of the present invention comprises the following steps:

[0086] Step 1: First, the ground user terminal generates a service utility function f according to the service indicators and their corresponding satellite-to-ground distance, satellite service time and satellite load utilization parameters. j =α j f 1j +β j f 2j +γ j f 3j, where α j ,β j ,γ j are the satellite-to-ground distance, satellite service time and satellite load utilization parameter weight coefficients, respectively. 1j ,f 2j ,f 3j The parameters of the business utility function are represented respectively, and the weight coefficient of the business utility function is generated by the hierarchical analysis method.

[0087] Step 1a, listing the importance of service utility function parameters under different ground user terminal service types, and the importance of service utility function parameters can be divided into five levels: extremely high, high, medium, general and low;

[0088] Table 1 Importance of business characteristics

[0089]

[0090] Note: Table 1 only gives examples of importance, and the importance can be adjusted according to business requirements.

[0091] Step 1b: Use the analytic hierarchy process to analyze the importance of satellite-to-ground distance, satellite service time, and satellite load utilization for different services. First, define the importance scale of different indicators and correspond the three types of service indicator parameters to different importance scales of 1 to 9.

[0092] Table 2 Index importance scale

[0093] Scale Meaning of scale difference 1 Indicates that the two indicators are equally important. 3 Indicates that one of the two indicators is slightly more important than the other 5 Indicates that one of the two indicators is more important than the other 7 Indicates that one of the two indicators is more important than the other. 9 Indicates that one of the two indicators is extremely more important than the other 2,4,6,8 The median of the above two adjacent judgments reciprocal If the scale of indicator A is 3 compared to B, then the scale of B compared to A is 1 / 3

[0094] Step 1c: According to the indicator importance scale given in steps 1a and 1b, respectively calculate the importance of utility function parameters of different types of services, namely, voice services, streaming media services, interactive services, and background services.

[0095] Step 1d: Use the hierarchical analysis method to calculate the weight coefficients of different businesses. First, obtain the normalized proportion of each column of each indicator, and then calculate the average value of each indicator by row to obtain the utility function weight coefficient α of different businesses. j ,β j ,γ j .

[0096] Step 2: Satellite LEO i According to the local physical channel resource block load, calculate the current local load utilization parameter The calculation method is as follows.

[0097] The satellite LEO at time t i The sum of the time domain and frequency domain physical resource blocks used by the accessed services is used as the numerator, and the satellite LEO iThe total amount of available physical resource blocks is used as the denominator to characterize the load utilization of the satellite.

[0098]

[0099] in, Indicates the number of resource blocks occupied by the nth service at time t in the current satellite, Represents the sum of the number of resource blocks occupied by all services at the current satellite time t, represents the number of services that the current satellite accesses to the user terminal at time t, Characterizes the total number of resource blocks that can be used by the current satellite. When the value of this parameter is high, it means that the current load is large and the access business volume needs to be reduced. When the load is low, the access business volume can be increased.

[0100] ρ h :Represents the satellite load utilization threshold. If the satellite LEO i If the current load utilization is greater than or higher than the threshold, the satellite can no longer access new services.

[0101] Step 3: Satellite LEO i Statistics on the load utilization information of its adjacent satellites, and calculate the satellite load utilization variance Var in the set Lin (t), and the satellite load utilization variance threshold Used to measure the load balance degree of the satellite set;

[0102] Defining Satellite LEO i The adjacent satellite set LEO in (t) = {LEO i ,LEO1,…,LEO n}, n≤N, n is the satellite LEO i The number of adjacent satellites.

[0103] Satellite LEO i There are two ways to obtain the load utilization of its adjacent satellites: one is to define the set as the satellite LEO i A set of satellites with inter-satellite links. In this mode, satellite status information is exchanged through inter-satellite links to obtain relevant load information of adjacent satellites. The second is to define the set as a set of satellites within a certain spatial distance range. In this mode, the satellites do not necessarily have inter-satellite links. The ground station receives the satellite load status information and regularly sends the load utilization information of the adjacent satellite set to each satellite.

[0104] Satellite load utilization variance: Use satellite load utilization variance Var Lin (t) represents the discrete degree of satellite load utilization, which is obtained by calculating the average of the square of the difference between each value in the set and the mean value. The formula is as follows:

[0105]

[0106] Satellite load utilization variance threshold Set satellite load utilization The range is [0,ρ h ],ρ h is the set satellite load utilization threshold, for The mean value is n, and the number of load utilization values ​​in the set is n. Given the number of set values ​​n and the range of values, the maximum value of the load utilization variance max(Var Lin ) The corresponding set value only contains the maximum value ρ h and the minimum value is 0, at which point the dispersion is the highest; when the maximum value difference in the set is less than ρ h / 2, it indicates that the load balancing is good at this time. When the maximum data value difference in the set is greater than or equal to ρ h / 2, it indicates that the load balancing degree is weak and load balancing adjustment is needed. Define the load utilization set value range [0,ρ h / 2], and the variance corresponding to the maximum and minimum values ​​is the maximum variance of the set As a threshold to measure satellite load balance.

[0107] It can be seen that the satellite set load utilization variance threshold needs to be calculated based on the current accessible satellite situation, and the adjacent satellite set load utilization variance threshold is calculated based on the adjacent satellite situation. Assuming that the number of adjacent satellites of each satellite is the same, since the load utilization threshold is the same, the adjacent satellite set load utilization variance threshold is the same. There are only two types of load utilization variance thresholds in the present invention.

[0108] Step 4: The ground user terminal receives the broadcast signal from the satellite side, including satellite number information and current load utilization of the satellite network. Satellite LEO i The load utilization variance Var of the adjacent satellite set Lin The known satellite ephemeris information can be used to calculate the current satellite-to-ground distance of the corresponding satellite, the satellite service time and other information to simplify the satellite-to-ground interaction information.

[0109] User terminal UE j Receive satellite broadcast signals and obtain relevant parameter information of visible satellites at time t. Define user terminal UE j The visible satellite set Where k is the number of satellites in the set.

[0110] Combination Figure 2Step 5: The ground user terminal determines whether the currently accessible satellite meets the service requirements based on the satellite side feedback parameters, and sets the satellite load adjustment factor l i , according to the satellite load utilization rate feedback from the satellite side, adjust the parameter l i Numeric value.

[0111] The satellite network load adjustment method has the following steps:

[0112] The ground user terminal determines whether the currently accessible satellite meets the service requirements based on the satellite feedback parameters and sets the satellite load adjustment factor l. i , according to the satellite load utilization rate feedback from the satellite side, adjust the parameter l i Numeric value.

[0113] Step 5a: First, the user terminal sets the currently accessible satellites. Load situation, determine the available load utilization of the satellites in the set in turn Whether the current business load requirement is met, if yes, proceed to step 5c, if not, proceed to step 5b;

[0114] Step 5b: Gather at the Satellite Delete the satellite and go to step 5c. If the updated satellite set If it is an empty set, go to step 5g;

[0115] Step 5c: Updated satellite set According to step 3 formula 2, calculate the updated satellite set Load utilization variance Var Lik (t), and according to the satellite load utilization variance threshold calculation method in step 3, calculate Satellite load utilization variance threshold

[0116] Step 5d: Determine the load utilization variance Var Lik (t) Is it greater than or equal to the load utilization variance threshold? If it is greater than or equal to the threshold, go to step 5e;

[0117] Receive updated satellite set The set of neighboring satellites for each satellite in The load utilization variance Var Lin (t), determine its load utilization variance threshold calculated in step 4 If the size is greater than or equal to the threshold, go to step 5e;

[0118] If the resource utilization variances of the two satellite sets are both less than the corresponding threshold values, go to step 5f;

[0119] Step 5e: The satellite load adjustment factor l needs to be adjusted i ;

[0120] l i The default value is 1, and the value range is defined as [0,2]. The value range of satellite load utilization can be divided into and [ρ h / 2,ρ h ] Compare satellite collections The load utilization of each satellite and ρ h / 2 size;

[0121] like This indicates that the satellite has a small load and needs to increase the satellite's load adjustment factor l i , increase the satellite access target value, l i The adjustment factor is:

[0122] like This indicates that the satellite has a large load and needs to reduce the satellite's load adjustment factor l i , reduce the satellite access target value, l i The adjustment factor is:

[0123] Step 5f: No need to adjust the satellite's load adjustment factor l i ;

[0124] Step 5g: If there is no satisfactory satellite to choose from, wait for the next time period to reselect.

[0125] Step 6: Normalize the satellite-to-ground distance, satellite service time, and satellite load utilization index, and calculate the utility function weight coefficient α j ,β j ,γ j Calculate the utility function value of the satellites in the visible satellite set.

[0126] Step 6a: The ground user terminal obtains the low-orbit satellite-to-ground distance range [D min ,D max ] and the current distance D between the terminal and the satellite ij , where D min ≤D ij ≤D max ,but Calculate the set of satellites that can be accessed by the service separately The function value f of the satellite in 1j .

[0127] Step 6b: The ground user terminal obtains the satellite service time range [Ts min ,Ts max ] and the current terminal and satellite service time Ts i,j , where Ts min ≤Ts i,j ≤Ts max ,but Calculate the set of satellites that can be accessed by the service separately The function value f of the satellite in 2j ;

[0128] Step 6c: The ground user terminal receives the current load utilization parameter fed back by the satellite calculate Calculate the set of satellites that can be accessed by the service separately The function value f of the satellite in 3j .

[0129] Step 7: Define the satellite objective function as F j =α j +f 1j +β j f 2j +γ j f 3j ·l j , according to the satellite load adjustment factor l obtained in step 5 i And the satellite utility function value f obtained in step 6 1j ,f 2j ,f 3j , calculate the target value of the accessible satellites. Select the satellite corresponding to the maximum target value as the optimal access satellite.

[0130] Step 8. Satellite LEO i After receiving the service application message and successfully accessing, update the local physical channel resource block load and update the load utilization parameter And the load utilization variance Var of the adjacent satellite set Lin (t) Information.

[0131] Embodiment 1:

[0132] The load balancing dynamic access method under multi-satellite coverage of the present invention has the following specific embodiments:

[0133] like Figure 3 The figure shows a multi-satellite coverage scenario and a schematic diagram of a satellite collection.

[0134] Combination Figure 1 and Figure 2 Specific process, set the ground user terminal parameters: set the ground user terminal UE jThere are four types of transmission services, namely voice service 1, streaming media service 2, interactive service 3, and background service 4. Their resource requirements (calculated according to the satellite resource ratio) are: {0.001, 0.005, 0.0001, 0.0005};

[0135] Ground User Terminal UE j The set of visible satellites is Includes satellite nodes {A, B, C}.

[0136] Set satellite network parameters:

[0137] Star-to-Earth Distance Range: [D min ,D max ] = [600km, 1200km];

[0138] Satellite nodes {A, B, C} communicate with ground user terminal UE at time t j The satellite-to-earth distance is: {800km, 660km, 900km};

[0139] Satellite service time range: [Ts min ,Ts max ]=[5min,15min];

[0140] Satellite nodes {A, B, C} communicate with ground user terminal UE at time t j The serviceable time is: {8min, 10min, 12min};

[0141] The set of adjacent satellites of satellite A is: {A, M, B, I, Q};

[0142] The set of satellite B's neighboring satellites is: {B, A, C, E, F};

[0143] The set of adjacent satellites of satellite C is: {C, B, N, G, H};

[0144] Step 1: First, the ground user terminal generates a service utility function f according to the service indicators and their corresponding satellite-to-ground distance, satellite service time and satellite load utilization parameters. j =α j f 1j +β j f 2j +γ j f 3j , where α j ,β j ,γ j are the satellite-to-ground distance, satellite service time and satellite load utilization parameter weight coefficients, respectively. 1j ,f 2j ,f 3jThe parameters of the business utility function are represented respectively, and the weight coefficient of the business utility function is generated by the hierarchical analysis method.

[0145] Step 1a, listing the importance of service utility function parameters under different ground user terminal service types, and the importance of service utility function parameters can be divided into five levels: extremely high, high, medium, general and low;

[0146] Table 1 Importance of business characteristics

[0147]

[0148] Step 1b: Use the analytic hierarchy process to analyze the importance of satellite-to-ground distance, satellite service time, and satellite load utilization for different services. First, define the importance scale of different indicators and correspond the three types of service indicator parameters to different importance scales of 1 to 9.

[0149] Table 2 Index importance scale

[0150] Scale Meaning of scale difference 1 Indicates that the two indicators are equally important. 3 Indicates that one of the two indicators is slightly more important than the other 5 Indicates that one of the two indicators is more important than the other 7 Indicates that one of the two indicators is more important than the other. 9 Indicates that one of the two indicators is extremely more important than the other 2,4,6,8 The median of the above two adjacent judgments reciprocal If the scale of indicator A is 3 compared to B, then the scale of B compared to A is 1 / 3

[0151] Step 1c: According to the indicator importance scale given in steps 1a and 1b, respectively calculate the importance of utility function parameters of different types of services, namely, voice services, streaming media services, interactive services, and background services.

[0152] Table 3 Importance of voice service indicator parameters

[0153] Voice service / index Distance between star and earth Satellite service time Load Utilization Distance between star and earth 1 3 5 Satellite service time 1 / 3 1 3 Load Utilization 1 / 5 1 / 3 1

[0154] Table 4 Importance of streaming media service indicator parameters

[0155]

[0156]

[0157] Table 5 Importance of interactive business indicator parameters

[0158] Interactive business / indicators Distance between star and earth Satellite service time Load Utilization Distance between star and earth 1 1 / 3 1 / 3 Satellite service time 3 1 1 Load Utilization 3 1 1

[0159] Table 6 Importance of backend business indicator parameters

[0160] Backend business / indicators Distance between star and earth Satellite service time Load Utilization Distance between star and earth 1 1 / 3 1 / 6 Service time 3 1 1 / 3 Load Utilization 6 3 1

[0161] Step 1d: Use the hierarchical analysis method to calculate the weight coefficients of different businesses. First, obtain the normalized proportion of each column of each indicator, and then calculate the average value of each indicator by row to obtain the utility function weight coefficient α of different businesses. j ,β j ,γ j .

[0162] Table 7 Weights of indicators for different businesses

[0163] Distance between star and earth Service time Load Utilization Voice service 0.6334 0.2605 0.1061 Streaming media services 0.1022 0.6865 0.2113 Interactive business 0.1428 0.4286 0.4286 Backstage business 0.0960 0.2510 0.6530

[0164] According to Table 7, the weight parameters of different services regarding satellite-to-ground distance, satellite service time and satellite load utilization can be obtained:

[0165] Service 1 weight parameter α j =0.6334,β j =0.2605,γ j =0.1061;

[0166] Service 2 weight parameter α j =0.1022,β j =0.6865,γ j =0.2113;

[0167] Business 3 weight parameter α j =0.1428,β j =0.4286,γ j =0.4286;

[0168] Business 4 weight parameter α j =0.0960,β j =0.2510,γ j =0.6530.

[0169] Step 2: Satellite LEO i According to the local physical channel resource block load, calculate the current local load utilization parameter

[0170] Load utilization threshold ρ h =0.9;

[0171] Load utilization of satellite nodes {A, B, C, E, F, M, N, G, H, I, Q} They are {0.35, 0.55, 0.7, 0.3, 0.4, 0.55, 0.2, 0.15, 0.1, 0.7, 0.8} respectively.

[0172] Step 3: Satellite LEO i Statistics on the load utilization information of its adjacent satellites, and calculate the satellite load utilization variance Var in the set Lin (t), and the satellite load utilization variance threshold

[0173] The number of satellites in the adjacent satellite set is 5, ρ h / 2=0.45, set the satellite load utilization rate in the adjacent satellite set in the extreme case to {0,0,0,0.45,0.45}, and calculate the satellite load utilization variance threshold through formula 2

[0174] The variance of load utilization of satellite A's neighboring satellites is Var LAn (t) = 0.02865;

[0175] The variance of load utilization of satellite B's neighboring satellites is Var LBn (t) = 0.02648;

[0176] The load utilization variance Var of satellite C's neighboring satellites LCn (t) = 0.07175.

[0177] Step 4: Ground user terminal UE j Receive broadcast signals from the satellite side and obtain the current visible satellite set

[0178] Step 5: The ground user terminal determines whether the currently accessible satellite meets the service requirements based on the satellite feedback parameters, and sets the satellite load adjustment factor l. i , according to the satellite load utilization rate feedback from the satellite side, adjust the parameter l i Numeric value.

[0179] Step 5a: Visible satellite set Satellite available load utilization The current business load requirement can be met, and the process goes to step 5c.

[0180] Step 5c: Visible satellite set No update is required. According to formula 2 in step 3, the load utilization variance Var in the satellite set is Lik (t) = 0.02992. In the extreme case, the satellite load utilization rate in the visible satellite set is set to {0, 0, 0.45}. The satellite load utilization variance threshold can be calculated by formula 2.

[0181] Note: When the satellite load utilization is set to {0, 0, 0.45} or {0, 0.45, 0.45}, the load utilization variance is 0.0675.

[0182] Step 5d: Determine the visible satellite set The load utilization variance Var Lik (t) and variance threshold The size of Var Lik (t) = 0.02992 less than

[0183] Determine the load utilization variance Var of the adjacent satellites of satellites A, B, and C respectively LAn (t), Var LBn (t), Var LCn (t) and variance threshold The size of Var LAn (t)=0.02865,Var LBn (t)=0.02648are all less than Var LCn (t) = 0.07175 greater than Go to step 5e, and adjust the load adjustment factor parameter according to the load utilization rate of the set of adjacent satellites of satellite C;

[0184] Step 5e: The satellite load adjustment factor l needs to be adjusted i . Comparing the adjacent satellite set of satellite C, both satellite B and satellite C are in the terminal visible satellite set, and the load adjustment factors of satellite B and satellite C can be adjusted.

[0185] Satellite B l i The adjustment factor is:

[0186] Satellite C l i The adjustment factor is:

[0187] Step 6: Normalize the satellite-to-ground distance, satellite service time, and satellite load utilization index, and calculate the utility function weight coefficient α j ,β j ,γ j Calculate the utility function value of the satellites in the visible satellite set.

[0188] Step 6a: According to the satellite-to-ground distance range [D min ,D max ] and the current distance D between the terminal and the satellite ij , calculate the utility function value f 1j Satellite A: f 1j ={0.6334*0.6667, 0.1022*0.6667, 0.1428*0.6667, 0.0960*0.6667}; Satellite B: f 1j ={0.6334*0.9, 0.1022*0.9, 0.1428*0.9, 0.0960*0.9}; Satellite C: f 1j={0.6334*0.5, 0.1022*0.5, 0.1428*0.5, 0.0960*0.5}.

[0189] Step 6b: According to the satellite service time range [Ts min ,Ts max ] and the current terminal and satellite service time Ts i,j , calculate the utility function value f 2j Satellite A: f 2j ={0.2605*0.3, 0.6865*0.3, 0.4286*0.3, 0.2510*0.3}; Satellite B: f 2j ={0.2605*0.5, 0.6865*0.5, 0.4286*0.5, 0.2510*0.5}; Satellite C: f 2j ={0.2605*0.7, 0.6865*0.7, 0.4286*0.7, 0.2510*0.7}.

[0190] Step 6c: Based on the satellite current load utilization parameter Calculate the utility function value f 3j Satellite A: f 3j ={0.1061*0.65, 0.2113*0.65, 0.4286*0.65, 0.6530*0.65}; Satellite B: f 3j ={0.1061*0.45, 0.2113*0.45, 0.4286*0.45, 0.6530*0.45}; Satellite C: f 3j ={0.1061*0.3, 0.2113*0.3, 0.4286*0.3, 0.6530*0.3}.

[0191] The utility function values ​​f of satellites A, B, and C corresponding to different services j =α j f 1j +β j f 2j +γ j f 3j They are:

[0192] Satellite A: f j ={0.5694, 0.4114, 0.5023, 0.5637}

[0193] Satellite B: f j ={0.7481, 0.5303, 0.5357, 0.5057}

[0194] Satellite C: f j={0.5468, 0.5950, 0.5000, 0.4196}

[0195] Step 7: According to the satellite objective function F j =α j f 1j +β j f 2j +γ j f 3j ·l j , calculate the target values ​​of accessible satellites corresponding to different services respectively.

[0196] Service 1: Satellite AF j =0.5694, Satellite BF j =0.7361, satellite CF j =0.5152;

[0197] Service 2: Satellite AF j =0.4114, Satellite BF j =0.5065, satellite CF j =0.5598;

[0198] Service 3: Satellite AF j =0.5023, Satellite BF j =0.4875, satellite CF j =0.4283;

[0199] Service 4: Satellite AF j =0.5637, Satellite BF j =0.4322, satellite CF j =0.3107.

[0200] Therefore, terminal service 1 can choose to access satellite B, service 2 can choose to access satellite C, and services 3 and 4 can choose to access satellite A.

[0201] Step 8. Satellite LEO i After receiving the service application message and successfully accessing, update the load utilization parameter of satellite A The load utilization variance Var of its adjacent satellite set Lin (t) = 0.0291; Satellite B load utilization parameter The load utilization variance Var of its adjacent satellite set Lin (t) = 0.0273; load utilization parameter of satellite C The load utilization variance Var of its adjacent satellite set Lin (t) = 0.0727.

[0202] It can be seen that service 3 optimally accesses satellite B according to the utility function value calculated in step 6, and optimally accesses satellite A after load balancing adjustment in step 7. At the same time, the load utilization variance of the satellite set {A, B, C, E, F, M, N, G, H, I, Q} is reduced from 0.057827 to 0.057823, indicating that the load utilization variance of the satellite network within a certain range is reduced while the service is accessed.

[0203] In summary, the load balancing dynamic access method under multi-satellite coverage of the present invention takes into account the satellite network load balancing requirements while considering the business requirements for satellite parameters. The access method based on the service QoS requirements and the network dynamic load balancing requirements, according to the importance of the satellite parameters corresponding to the user side terminal service QoS requirements and the satellite load usage, constructs the terminal service access objective function based on the weight coefficient and the load adjustment factor, and considers the user terminal service requirements and the satellite network load balancing characteristics at the same time, and solves the access decision problem of the user side and the satellite side when the service accesses the satellite; the satellite load adjustment method constructs two satellite sets, namely the visible satellite set and the adjacent satellite set, on the satellite side, to determine whether the currently accessible satellite meets the business requirements, and adjusts the satellite load adjustment factor and the target value of the service accessible satellite by adjusting the load balancing parameters of the two types of satellite sets. While meeting the multi-objective requirements of different types of services of ground user terminals, the method of the present invention takes into account the actual capabilities of the satellite network, so that the satellite network corresponding to the current user terminal within a certain time and a certain range can achieve local dynamic load balancing. It can be used in the service access of low-orbit satellite networks such as China Star Network, and is creative and practical.

[0204] Parts of the present invention that are not described in detail belong to common knowledge among those skilled in the art.

[0205] Although the present invention has been described in detail above with general descriptions and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements can be made on the basis of the present invention. Therefore, these modifications or improvements made on the basis of not departing from the spirit of the present invention all belong to the protection scope of the present invention.

Claims

1. A load balancing dynamic access method under multi-satellite coverage, characterized in that: include: On the user side, user terminal services are classified according to QoS requirements, a multi-objective utility function is generated based on service indicators, and multi-objective weight coefficients are generated for the importance of different services; On the satellite side, a set of satellites visible to the terminal and a set of adjacent satellites for each satellite are constructed, and load balancing parameters and load adjustment methods for the set of satellites visible to the terminal and the set of adjacent satellites for each satellite are proposed, so that the satellite network corresponding to the current user terminal within a certain period of time can achieve dynamic load balancing.

2. The load balancing dynamic access method under multi-satellite coverage according to claim 1 is characterized in that: The specific steps include: Step 1: Ground user terminal UE j Generate the business utility function f according to the business indicators and their corresponding satellite-to-ground distance, satellite service time and satellite load utilization parameters j , the subscript j indicates the number of different ground user terminals, specifically: f j =a j f 1j +b j f 2j +g j f 3j ; Among them, α j ,β j ,γ j are the satellite-to-ground distance, satellite service time and satellite load utilization parameter weight coefficients, respectively. 1j Characterize the utility function of the satellite-to-ground distance, f 2j Characterize the satellite service time utility function, f 3j Characterize the satellite load balancing utility function; Step 2: Satellite LEO i Calculate the current local load utilization based on the local physical channel resource block load The subscript i indicates different satellite numbers, which are calculated as follows; in, n Characterize the different services of satellites, Represents the current satellite at time t n The number of resource blocks occupied by each service, Represents the sum of the number of resource blocks occupied by all services at the current satellite time t, represents the number of services that the current satellite accesses to the user terminal at time t, Indicates the total number of resource blocks currently available to the satellite; ρ h To characterize the satellite load utilization threshold, if the satellite LEO i If the current load utilization is greater than or higher than the threshold, the satellite cannot access new services, otherwise it can access; Step 3. Define satellite LEO i The set of adjacent satellites at time t, K is the satellite LEO i The number of adjacent satellites, K+1 is the set The number of satellites in The satellite load utilization variance is used to characterize the discrete degree of satellite load utilization. Satellite load utilization variance Var LEO (t), by calculating the average value Var of the square of the difference between each value in the set and the mean LEO (t) is obtained, and the calculation formula is as follows: Where K+1 is the set The number of satellites in is the average of all satellite load utilization in the satellite set; satellite set Satellite load utilization variance threshold The satellite load utilization variance threshold in the satellite set calculated at the characterization time t is used as the threshold for measuring the satellite load balance; Step 4: User terminal UE j Receive satellite broadcast signals and obtain the visible satellite set at time t Defined as I is a collection The number of satellites in Step 5: The ground user terminal determines whether the currently accessible satellite meets the service requirements based on the satellite feedback parameters, and sets the satellite load adjustment factor l. i , according to the satellite load utilization rate feedback from the satellite side, adjust the parameter l i Numeric value; Step 6: Normalize the satellite-to-ground distance, satellite service time, and satellite load utilization index, and calculate the utility function weight coefficient α j ,β j ,γ j Calculate the utility function value of the satellites in the visible satellite set; Step 7: Define the satellite objective function as F j =α j f 1j +β j f 2j +γ j f 3j ·l j , according to the satellite load adjustment factor l obtained in step 5 i And the satellite utility function value f obtained in step 6 1j ,f 2j ,f 3j , calculate the target value of accessible satellites; select the satellite corresponding to the maximum target value as the optimal access satellite; Step 8. Satellite LEO i After receiving the service application message and successfully accessing, update the local physical channel resource block load and update the load utilization parameter And the load utilization variance Var of the adjacent satellite set LEO (t) Information.

3. The load balancing dynamic access method under multi-satellite coverage according to claim 2 is characterized in that: The step 1 specifically includes: Step 1a, listing the importance of service utility function parameters under different ground user terminal service types, and the importance of service utility function parameters can be divided into five levels: extremely high, high, medium, general and low; Step 1b: Use the analytic hierarchy process to analyze the importance of satellite-to-ground distance, satellite service time, and satellite load utilization for different services; define the importance scales of different indicators, and correspond the three types of service indicator parameters to different importance scales of 1 to 9; Step 1c, according to the indicator importance scale given in steps 1a and 1b, respectively calculate the importance of the utility function parameters of voice services, streaming media services, interactive services and background services; Step 1d: Use the hierarchical analysis method to calculate the weight coefficients of different businesses. First, obtain the normalized proportion of each column of each indicator, and then calculate the average value of each indicator by row to obtain the utility function weight coefficient α of different businesses. j ,β j ,γ j .

4. The load balancing dynamic access method under multi-satellite coverage according to claim 2 or 3, characterized in that: Satellite load utilization variance threshold The settings include: Set satellite load utilization The range is [0,ρ h ],ρ h is the set satellite load utilization threshold, and the number of load utilization values ​​in the set is K+1; given the number of set values ​​and the range of values, the maximum value of the load utilization variance max(Var LEO ) corresponds to a set value that contains only the maximum value ρ h The dispersion is highest when the maximum value difference in the set is less than ρ h / 2, it indicates that the load balancing is good at this time. When the maximum data value difference in the set is greater than or equal to ρ h / 2, it indicates that the load balancing degree is weak and load balancing adjustment is needed; define the load utilization set value range [0, ρ h / 2], the satellite load utilization value only takes the maximum value ρ h / 2 and the minimum value is 0, the calculated variance is the maximum variance of the set As a threshold to measure satellite load balance.

5. The load balancing dynamic access method under multi-satellite coverage according to claim 2 or 3, characterized in that: The step 6 specifically includes: Step 6a: The ground user terminal obtains the low-orbit satellite-to-ground distance range [D min ,D max ] and the current distance D between the user terminal and the satellite ij , where D min ≤D ij ≤D max ,but Calculate the set of satellites that can be accessed by the service separately The function value f of the satellite in 1j ; Step 6b: The ground user terminal obtains the satellite service time range [Ts min ,Ts max ] and the current terminal and satellite service time Ts i,j , where Ts min ≤Ts i,j ≤Ts max ,but Calculate the set of satellites that can be accessed by the service separately The function value f2j of the satellite in the middle; Step 6c: The ground user terminal receives the current load utilization parameter fed back by the satellite calculate Calculate the set of satellites that can be accessed by the service separately The function value of the satellite in f3j.

6. The load balancing dynamic access method under multi-satellite coverage according to claim 2 or 3, characterized in that: The step 5 specifically includes: Step 5a: First, the user terminal sets the currently accessible satellites. Load situation, determine the available load utilization of the satellites in the set in turn Whether the current business load requirement is met, if yes, proceed to step 5c, if not, proceed to step 5b; Step 5b: Gather at the Satellite Delete the satellite and go to step 5c. If the updated satellite set If it is an empty set, go to step 5g; Step 5c: Updated satellite set Calculate the updated satellite set Load utilization variance Var L ' EO (t), and according to the satellite load utilization variance threshold calculation method, calculate Satellite load utilization variance threshold Among them, Var′ LEO (t) and Refer to Var in step 3 LEO (t) and Calculation method of Step 5d: Determine the load utilization variance Var L ' EO (t) Is it greater than or equal to the load utilization variance threshold? If it is greater than or equal to the threshold, go to step 5e; Receive updated satellite set The set of neighboring satellites for each satellite in The load utilization variance Var LEO (t), determine its load utilization variance threshold calculated in step 4 If the size is greater than or equal to the threshold, go to step 5e; If the resource utilization variances of the two satellite sets are both less than the corresponding threshold values, go to step 5f; Step 5e: The satellite load adjustment factor l needs to be adjusted i ; l i The default value is 1, and the value range is defined as [0,2]. The value range of satellite load utilization can be divided into [0,ρ h / 2] and [ρ h / 2,ρ h ]; Compare satellite sets The load utilization of each satellite and ρ h / 2 size; like This indicates that the satellite has a small load and needs to increase the satellite's load adjustment factor l i , increase the satellite access target value, l i The adjustment factor is: like This indicates that the satellite has a large load and needs to reduce the satellite's load adjustment factor l i , reduce the satellite access target value, l i The adjustment factor is: Step 5f: No need to adjust the satellite's load adjustment factor l i ; Step 5g: If there is no satisfactory satellite to choose from, wait for the next time period to reselect.

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