A centralized and active coordinated low-orbit satellite system switching method

Abstract

The present invention discloses a centralized and active coordinated low-orbit satellite system switching method. Compared with the centralized switching, the proposed coordinated low-orbit satellite system switching method has a low signal strength at the edge of the access satellite coverage area, which is likely to cause unsuccessful satellite switching. The user actively sends a switching request to the destination satellite and switches to the destination satellite in time, which effectively improves the user switching success rate and the quality of experience when performing satellite switching. Compared with the active switching, the proposed coordinated switching method can aggregate multiple users with similar geographical locations into a group and send a group request message, which greatly reduces the repeated transmission of signaling and reduces the system signaling overhead. Compared with the existing centralized switching algorithm and active switching algorithm, this method can improve the user switching success rate, and at the same time reduce the system signaling overhead compared with the active switching algorithm, which can effectively improve the user's experience quality when performing satellite switching.

Description

Technical Field

[0001] The invention relates to a centralized and actively coordinated low-orbit satellite system switching method, belonging to the technical field of satellite switching in satellite communications. Background Art

[0002] Low-orbit satellites have received extensive research and attention in recent years. Starlink abroad and Hongyun and Hongyan projects in China have launched their own low-Earth orbit communication satellite constellations. Compared with medium- and high-orbit satellites, low-orbit satellites have the advantages of low latency, low power consumption and low cost, and have broad development prospects. However, due to the characteristics of LEO satellites such as fast movement speed, low orbit altitude and small coverage area, users switch between different satellites more frequently. The satellite switching strategy has a huge impact on user communication quality and satellite network load.

[0003] The common methods of satellite switching at present are centralized switching and active switching. In the centralized switching strategy, all access and switching requests are collected and managed by the ground station to make decisions, but in the scenario of large-scale user switching, there is a problem of low user switching success rate; in the active switching strategy, the switching request is executed by the user, and the target satellite can be switched in time, which improves the user switching success rate, but there are a lot of repeated transmission signaling in the network.

[0004] It can be seen from the above that the above two satellite switching methods have the problem that the user switching success rate and the system signaling overhead cannot be well balanced. Therefore, it is necessary to propose a reasonable and effective low-orbit satellite switching method to improve the existing switching method. Summary of the invention

[0005] The purpose of the present invention is to propose a centralized and actively coordinated low-orbit satellite system switching method suitable for large-scale user switching, which aims to improve the user's switching success rate, balance the satellite network load, and thus enhance the service experience of ground users during satellite switching.

[0006] The system architecture of the present invention is a centralized and active coordinated low-orbit satellite system switching system architecture. All ground users are divided into two parts. Users at the center of the access satellite coverage area perform centralized switching, while users at the edge of the access satellite coverage area or blocked users perform active switching. The switching of the two parts of users cooperates with each other, which improves the overall user switching experience.

[0007] Centralized switching is when a large number of users send switching requests to connected satellites. Satellites group users according to geographic information and send group switching messages to ground stations. Ground stations uniformly collect and manage access and switching requests from all LEO satellites, comprehensively consider user performance and satellite network load balancing indicators, perform centralized switching, and determine whether users need to perform inter-satellite switching. If users need to switch, the ground station notifies the destination satellite and users to prepare for the switch.

[0008] Active switching is when users at the edge of a cell or blocked users collect satellite information, select the satellite with the largest utility function as the destination satellite through a utility function consisting of the remaining visible time of the satellite and the satellite elevation angle, and send a switching request to the destination satellite, thereby ensuring that the user can switch to the destination satellite in a timely manner.

[0009] The proposed coordinated switching method allows most users with good communication quality to perform centralized switching, effectively reducing the system signaling overhead; and allows a small number of users who are prone to communication interruption to perform active switching, avoiding reducing the user switching success rate. The two complement each other, optimize the overall performance of the satellite communication network, and reduce switching delay and energy consumption.

[0010] The switching method of the centralized and active coordinated low-orbit satellite system is as follows:

[0011] S1 Network Modeling:

[0012] Assume that there are M satellites and N users who need satellite switching in the satellite communication system. The satellite set is S = {s j |j=1,…,M}, the user set is U={u i |i=1,…,N}. The angle θ between user i and satellite j i,j , user i’s business requirement is b i , signal strength is rssi i,j , the remaining visible time is t i,j , the signal strength tolerance threshold for communication between the satellite and the user is rssi0, and the maximum bandwidth of satellite j is B jmax , start switching satellite j, the bandwidth provided is c j0 , the bandwidth resource in switching is c j .

[0013] All users are divided into two categories according to the relationship between the user signal strength and the tolerance threshold: if the user's signal strength is greater than the tolerance threshold, the user belongs to the centralized switching user u c , otherwise the user is an active switching user u a .

[0014] The S2 coordinated low-orbit satellite system switching method has the following steps:

[0015] 1) At the beginning of each cycle, connect to the users in the satellite coverage area to measure their signal strength and determine whether the signal strength is less than the tolerance threshold. If yes, go to 2). If not, go to 3).

[0016] 2) The user executes the active switching algorithm and sends a switching request message to the destination satellite, and the destination satellite determines whether it has any remaining bandwidth resources. If yes, the switching is successful, and go to 4). If no, the switching fails, and go to 4).

[0017] 3) The access satellite uses the K-means algorithm to group users according to their geographic location information and sends a group switching request message to the ground station. The ground station executes the centralized switching algorithm and sends a group switching request message to the destination satellite. The destination satellite determines whether it has any remaining bandwidth resources. If yes, the switching is successful, then go to 4). If no, the switching fails, then go to 2).

[0018] 4) Increase the number of users to start a new cycle and determine whether the number of users is a predetermined maximum value.

[0019] If not, go to 1). If yes, the method ends.

[0020] In step 2), the cell edge user or the blocked user executes the active algorithm, and the objective function and constraints are as follows:

[0021] Objective function:

[0022]

[0023] Constraints:

[0024] b i <c j0 ,i∈U,j∈S (2)

[0025] θ i,j >0,t i,j >0 (3)

[0026] Formula (1) selects the satellite s that makes F1 the largest j , where w a1 and w a2 are the weights of satellite elevation angle and remaining visible time respectively.

[0027] Formula (2) limits the bandwidth required for single user switching to be smaller than the bandwidth provided by the satellite during switching.

[0028] Formula (3) limits the satellite elevation angle and the remaining visible time to be greater than zero.

[0029] If c j -b i >0, the switch is successful, and c is updated j =cj -b u ; Otherwise the switch fails.

[0030] In step 3), users with better signal strength execute the centralized algorithm. Considering the need to reduce the signaling overhead of the system, the K-means algorithm is used on the satellite to group users and send group request messages to the ground station for unified processing. The objective function and constraints are as follows:

[0031] Objective function:

[0032]

[0033] Constraints:

[0034] b i <c j0 ,i∈U,j∈S (5)

[0035] θ i,j >0,t i,j >0 (6)

[0036] Formula (4) selects the satellite s that makes F2 the largest j , where cluster i represents the number of users in the i-th group, w c1 、w c2 、w c3 are the weights of satellite elevation angle, remaining visible time and fairness factor respectively.

[0037] The fairness factor ensures that the load of each satellite is as balanced as possible, and is defined as follows:

[0038] f j =c j / B jmax (7)

[0039] like If the switch is successful, update Otherwise go to 2).

[0040] S3 system signaling overhead analysis:

[0041] The coordinated switching method can group users according to their geographical locations and send switching request messages in the form of groups, which greatly reduces the signaling overhead of the system. The signaling overhead can be given by formula (8):

[0042]

[0043] Among them, M cs and M cf are the number of groups that successfully switched and failed to switch in centralized switching, and similarly Mas and M af are the number of users who successfully switched and failed to switch in active switching; N cs and N cf are the signaling overheads of a single centralized handover success and failure, respectively. Similarly, N as and N af They are the signaling overhead of a single successful and failed active handover.

[0044] The effects of the present invention are as follows: compared with the existing centralized switching algorithm and active switching algorithm, this method can improve the user switching success rate, and at the same time reduce the system signaling overhead compared with the active switching algorithm, which can effectively improve the user's experience quality when performing satellite switching. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 . Architecture diagram of the centralized and active coordinated low-orbit satellite system switching system.

[0046] Figure 2 .Flowchart of the centralized and active coordinated low-orbit satellite system switching method.

[0047] Figure 3 .Comparison chart of user switching success rates.

[0048] Figure 4. System signaling overhead comparison diagram. DETAILED DESCRIPTION

[0049] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0050] The present invention provides a centralized and active collaborative low-orbit satellite system switching architecture, and proposes a method for collaborative switching of a low-orbit satellite system. Compared with centralized switching, the proposed collaborative low-orbit satellite system switching method has a weak signal strength for users at the edge of the access satellite coverage area, and it is very likely that satellite switching will fail. The user will actively send a switching request to the destination satellite and switch to the destination satellite in time, which can effectively improve the user switching success rate and the quality of experience when performing satellite switching; compared with active switching, the proposed collaborative switching method can aggregate multiple users with similar geographical locations into one group, send a group request message, greatly reduce repeated transmission of signaling, and reduce system signaling overhead.

[0051] The system architecture of the present invention is a centralized and active coordinated low-orbit satellite system switching system architecture. All ground users are divided into two parts. Users at the center of the access satellite coverage area perform centralized switching, while users at the edge of the access satellite coverage area or blocked users perform active switching. The switching of the two parts of users cooperates with each other, which improves the overall user switching experience.

[0052] Centralized switching is when a large number of users send switching requests to connected satellites. Satellites group users according to geographic information and send group switching messages to ground stations. Ground stations uniformly collect and manage access and switching requests from all LEO satellites, comprehensively consider user performance and satellite network load balancing indicators, perform centralized switching, and determine whether users need to perform inter-satellite switching. If users need to switch, the ground station notifies the destination satellite and users to prepare for the switch.

[0053] Active switching is when users at the edge of a cell or blocked users collect satellite information, select the satellite with the largest utility function as the destination satellite through a utility function consisting of the remaining visible time of the satellite and the satellite elevation angle, and send a switching request to the destination satellite, thereby ensuring that the user can switch to the destination satellite in a timely manner.

[0054] The proposed coordinated switching method allows most users with good communication quality to perform centralized switching, effectively reducing the system signaling overhead; and allows a small number of users who are prone to communication interruption to perform active switching, avoiding reducing the user switching success rate. The two complement each other, optimize the overall performance of the satellite communication network, and reduce switching delay and energy consumption.

[0055] The switching method of the centralized and active coordinated low-orbit satellite system is as follows:

[0056] S1 Network Modeling:

[0057] Assume that there are M satellites and N users who need satellite switching in the satellite communication system. The satellite set is S = {s j |j=1,…,M}, the user set is U={u i |i=1,…,N}. The angle θ between user i and satellite j i,j , user i’s business requirement is b i , signal strength is rssi i,j , the remaining visible time is t i,j , the signal strength tolerance threshold for communication between the satellite and the user is rssi0, and the maximum bandwidth of satellite j is B jmax , start switching satellite j, the bandwidth provided is c j0 , the bandwidth resource in switching is c j .

[0058] All users are divided into two categories according to the relationship between the user signal strength and the tolerance threshold: if the user's signal strength is greater than the tolerance threshold, the user belongs to the centralized switching user u c , otherwise the user is an active switching user u a .

[0059] S2 coordinated low-orbit satellite system switching method:

[0060] Figure 2 The flowchart of the low-orbit satellite system switching method based on centralized and active coordination is as follows:

[0061] 5) At the beginning of each cycle, connect to the users in the satellite coverage area to measure their signal strength and determine whether the signal strength is less than the tolerance threshold. If yes, go to 2). If not, go to 3).

[0062] 6) The user executes the active switching algorithm and sends a switching request message to the destination satellite, and the destination satellite determines whether it has any remaining bandwidth resources. If yes, the switching is successful, and go to 4). If no, the switching fails, and go to 4).

[0063] 7) The access satellite uses the K-means algorithm to group users according to their geographic location information and sends a group switching request message to the ground station. The ground station executes the centralized switching algorithm and sends a group switching request message to the destination satellite. The destination satellite determines whether it has any remaining bandwidth resources. If yes, the switching is successful, then go to 4). If no, the switching fails, then go to 2).

[0064] 8) Increase the number of users to start a new cycle and determine whether the number of users is a predetermined maximum value.

[0065] If not, go to 1). If yes, the method ends.

[0066] In step 2), the cell edge user or the blocked user executes the active algorithm, and the objective function and constraints are as follows:

[0067] Objective function:

[0068]

[0069] Constraints:

[0070] b i <c j0 , i∈U,j∈S (2)

[0071] θ i,j >0,t i,j >0 (3)

[0072] Formula (1) selects the satellite s that maximizes F1 j , where w a1 and w a2 are the weights of satellite elevation angle and remaining visible time respectively.

[0073] Formula (2) limits the bandwidth required for single user switching to be smaller than the bandwidth provided by the satellite during switching.

[0074] Formula (3) limits the satellite elevation angle and the remaining visible time to be greater than zero.

[0075] If c j -b i >0, the switch is successful, and c is updated j =c j -b u ; Otherwise the switch fails.

[0076] In step 3), users with better signal strength execute the centralized algorithm. Considering the need to reduce the signaling overhead of the system, the K-means algorithm is used on the satellite to group users and send group request messages to the ground station for unified processing. The objective function and constraints are as follows:

[0077] Objective function:

[0078]

[0079] Constraints:

[0080] b i <c j0 ,i∈U,j∈S (5)

[0081] θ i,j >0,t i,j >0 (6)

[0082] Formula (4) selects the satellite s that makes F2 the largest j , where cluster i represents the number of users in the i-th group, w c1 、w c2 、w c3 are the weights of satellite elevation angle, remaining visible time and fairness factor respectively.

[0083] The fairness factor ensures that the load of each satellite is as balanced as possible, and is defined as follows:

[0084] f j =c j / B jmax (7)

[0085] like If the switch is successful, update Otherwise go to 2).

[0086] S3 system signaling overhead analysis:

[0087] The coordinated switching method can group users according to their geographical locations and send switching request messages in the form of groups, which greatly reduces the signaling overhead of the system. The signaling overhead can be given by formula (8):

[0088]

[0089] Among them, M cs and M cf are the number of groups that successfully switched and failed to switch in centralized switching, and similarly M as and M af are the number of users who successfully switched and failed to switch in active switching; N cs and N cf are the signaling overheads of a single centralized handover success and failure, respectively. Similarly, N as and N af They are the signaling overhead of a single successful and failed active handover.

[0090] The solution is applied in Figure 1 In the switching architecture of the low-orbit satellite system shown in the figure, the carrier frequency of the system is 1500MHz, the number of satellites is 5, the altitude is 780km, and the satellite system bandwidth is 500MHz. The number of users is continuously increased during the simulation process, and the user success switching rate is obtained through the proposed cooperative switching algorithm.

[0091] Under the above simulation conditions, this example simulates the number of system users from 10 to 400, with an interval of 10, and obtains the switching success rate of system users. The performance of the proposed satellite switching method based on centralized and active coordination is compared with the existing centralized switching method and active switching method. The comparison results are shown in Figure 2. Figure 3 As shown in the figure, the square curve fluctuates because the user grouping results are relatively random. The proposed coordinated switching algorithm will divide the users who perform satellite switching at the same time into different groups and switch to different satellites, avoiding the problem that a large number of users may send switching requests to the same satellite in a short period of time, resulting in a shortage of satellite resources and the failure of some users to switch. It can be seen that the proposed algorithm is superior to other algorithms in terms of user switching success rate. Figure 4 System signaling overhead under different numbers of users. Compared with active switching, the coordinated switching strategy based on user grouping aggregates the switching requests of multiple users into one group switching request, thereby reducing the signaling overhead of the system.

Claims

1. A centralized and active coordinated low-orbit satellite system switching method, the system architecture for implementing the method is a centralized and active coordinated low-orbit satellite system switching system architecture, all ground users are divided into two parts, users at the center of the access satellite coverage area perform centralized switching, and users at the edge of the access satellite coverage area or blocked users perform active switching; the switching of the two parts of users is coordinated with each other; It is characterized in that The switching method of the centralized and active coordinated low-orbit satellite system is as follows: S1 Network Modeling: There are M satellites and N users who need satellite switching in the satellite communication system; the satellite set is S = {s j |j=1,…,M}, the user set is U={u i |i=1,…,N}; the angle θ between user i and satellite j i,j , user i’s business requirement is b i , signal strength is rssi i,j , the remaining visible time is t i,j , the signal strength tolerance threshold for communication between the satellite and the user is rssi0, and the maximum bandwidth of satellite j is B jmax , start switching satellite j, the bandwidth provided is c j0 , the bandwidth resource in switching is c j ; All users are divided into two categories according to the relationship between the user signal strength and the tolerance threshold: if the user's signal strength is greater than the tolerance threshold, the user belongs to the centralized switching user u c , otherwise the user is an active switching user u a ; The steps of the S2 coordinated low-orbit satellite system switching method are as follows: 1) At the beginning of each cycle, connect to the users in the satellite coverage area to measure their signal strength and determine whether the signal strength is less than the tolerance threshold; if so, go to 2); if not, go to 3); 2) The user executes the active switching algorithm and sends a switching request message to the destination satellite. The destination satellite determines whether it has remaining bandwidth resources. If so, the switching is successful, and then go to 4); If not, the switch fails, then go to 4); 3) The access satellite uses the K-means algorithm to group users according to the geographic location information and sends a group switching request message to the ground station. The ground station executes the centralized switching algorithm and sends a group switching request message to the destination satellite. The destination satellite determines whether it has remaining bandwidth resources. If so, the switching is successful, and then go to 4); If not, the switch fails, then go to 2); 4) Increase the number of users to start a new cycle and determine whether the number of users reaches a predetermined maximum value; If not, go to 1); if so, the method ends; S3 system signaling overhead analysis: The coordinated switching method groups users according to their geographical locations and sends switching request messages in the form of groups to reduce signaling overhead. The signaling overhead is given by formula (8): Among them, M cs and M cf are the number of groups with successful switching and failed switching in centralized switching, M as and M af are the number of users who successfully switched and failed to switch in active switching; N cs and N cf are the signaling overhead of a single centralized handover success and failure, N as and N af They are the signaling overheads for a single successful and failed active handover, respectively; In step 2) of the S2 coordinated low-orbit satellite system switching method, the cell edge user or the blocked user executes the active algorithm, and the objective function and constraints are as follows: Objective function: Constraints: b i <c j0 , i∈U,j∈S (2) i i,j >0,t i,j >0 (3) Formula (1) selects the satellite s that makes F1 the largest j , where w a1 and w a2 are the weights of satellite elevation angle and remaining visible time respectively; Formula (2) limits the bandwidth required for a single user switching to be smaller than the bandwidth provided by the satellite when switching; Formula (3) limits the satellite elevation angle and remaining visible time to be greater than zero; If c j -b i >0, the switch is successful, and c is updated j =c j -b u ; Otherwise the switch fails; In step 3 of the S2 coordinated low-orbit satellite system switching method, users with better signal strength execute a centralized algorithm. Considering the reduction of the system's signaling overhead, the K-means algorithm is used on the satellite to group users and send group request messages to the ground station for unified processing; the objective function and constraints are as follows: Objective function: Constraints: b i <c j0 ,i∈U,j∈S (5) i i,j >0,t i,j >0 (6) Formula (4) selects the satellite s that makes F2 the largest j , where cluster i represents the number of users in the i-th group, w c1 、w c2 、w c3 are the satellite elevation angle, remaining visible time and the weights of the fairness factor respectively; The fairness factor ensures that the load of each satellite is as balanced as possible, and is defined as follows: f j =c j / B jmax (7) like If the switch is successful, update Otherwise go to 2).

2. The centralized and active coordinated low-orbit satellite system switching method according to claim 1, characterized in that: Centralized switching is when the user sends a switching request to the connected satellite. The satellite groups the users according to geographic information and sends group switching messages to the ground station. The ground station uniformly collects and manages the access and switching requests of all LEO satellites, comprehensively considers user performance and satellite network load balancing indicators, executes centralized switching and determines whether the user needs to perform inter-satellite switching. If the user needs to switch, the ground station notifies the destination satellite and the user to prepare for the switch.

3. The centralized and active coordinated low-orbit satellite system switching method according to claim 1, characterized in that: Active switching is when users at the edge of the cell or blocked users collect satellite information, select the satellite with the largest utility function as the destination satellite through a utility function composed of the remaining visible time of the satellite and the satellite elevation angle, and send a switching request to the destination satellite, thereby ensuring that the user switches to the destination satellite in time.

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