Multi-layer low earth orbit satellite congestion avoidance routing method based on SDN (Software Defined Network)

Abstract

The invention relates to an SDN-based multi-layer low-orbit satellite congestion avoidance routing method. The method comprises the following steps: step 1, constructing a satellite and queuing model and analyzing a satellite routing outage probability; step 2, the gateway station periodically collects satellite information; 3, setting a gateway station as a centralized controller, and calculating a routing hop count and a routing search radius by the gateway station based on the distance between the source satellite and the destination satellite; step 4, the gateway station adjusts the selection of the routing area according to the congestion degree of the current routing area; and step 5, the gateway station calculates a path to generate a routing table according to the delimitation of the current routing area, the queuing time delay and the propagation time delay, and uploads the routing table to the source satellite. The method has the advantages that the gateway station is used for collecting satellite queuing information, the congestion condition of the satellites in the search range is obtained, selection of the next hop of satellites is comprehensively considered according to the queuing time delay and the propagation time delay, the satellites with the short queuing length in the search range are preferentially selected, and load balancing of a certain degree is achieved.

Description

Technical Field

[0001] The present invention relates to a multi-layer low-orbit satellite communication system, and in particular to a multi-layer low-orbit satellite congestion avoidance routing method based on SDN. Background Art

[0002] Compared with the ground communication network, the satellite communication network, as an important means of supplementing it, has the advantages of wide coverage, no geographical restrictions, high reliability, flexible deployment and adjustment, and rich service types. It can provide stable, ubiquitous, reliable, and emergency communication services for emergency situations such as natural disasters and areas that ground communication networks cannot reach. Satellite routing, as one of the key technologies of large-scale satellite networks, is the basis for ensuring interconnection between network nodes, which affects the service quality and transmission rate of the entire network.

[0003] In a multi-layer low-orbit satellite network, considering the different orbital inclinations and constellation configurations of satellites in different layers, the topological relationship between layers is highly dynamic, and the cross-layer routing mechanism problem needs to be solved. In addition, the uneven distribution of ground traffic may lead to problems such as packet loss and excessive delay caused by congestion during routing.

[0004] In response to the above problems, early multi-layer low-orbit satellite cross-layer routing adopted vector segment routing technology, such as the low-overhead vector segment routing technology proposed by Lv Ruochen et al. in "Research on Satellite Network Routing Technology" (Xi'an University of Electronic Science and Technology, 2022.001129), which decomposes the routing process into the same-layer routing zone routing process, the same-layer routing zone routing process and the cross-layer routing process. Zhou Yu et al. adopted a local flooding method in "Research on Distributed Routing of Space-Based Networks and Discussion on Its Autonomy Level" (University of Chinese Academy of Sciences (Institute of Microsatellites, Chinese Academy of Sciences), 2022.000007.), allowing each satellite to periodically collect link information to update the routing table. The multi-layer satellite network architecture proposed by Li Rui et al. in "Multi-layer Space Hybrid Network Architecture and Routing Design" mainly focuses on the laser-microwave technology used in cross-layer links and same-layer links [University of Chinese Academy of Sciences (Institute of Microsatellites, Chinese Academy of Sciences), 2023.000007.]

[0005] Xu Xiaotao et al. used a spatiotemporal evolution graph to accurately describe the continuous changes in the dynamic topology of satellite networks in "A multi-layer low-orbit satellite network routing algorithm for 6G communications" to solve the problem of highly dynamic inter-layer topology (A multi-layer low-orbit satellite network routing algorithm for 6G communications, Mobile Communications, 2024, 48(01):56-64+87.)

[0006] Recently, some scholars have also used stochastic geometry to analyze the cross-layer routing process of low-orbit satellites and proposed corresponding algorithms. Ruibo Wang et al. first used stochastic geometry to analyze the routing process in "Stochastic Geometry-Based Low Latency Routing in Massive LEO Satellite Networks" and obtained an analytical expression for the probability of routing interruption ("Stochastic Geometry-Based Low Latency Routing in Massive LEO Satellite Networks," IEEE Transactions on Aerospace and Electronic Systems., vol. 58, no. 5, pp. 3881-3894, Oct. 2022.).

[0007] Mustafa A. Kishk et al. extended the performance analysis of routing to multiple layers and analyzed the reliability of the routing process in the article "Reliability Analysis of Multi-hop Routing in Multi-tier LEO Satellite Networks," (IEEE Transactions on Wireless Communications., vol. 23, no. 3, pp. 1959-1973, March 2024.) The above study also proposed a NearestNeighbor routing strategy that can make the propagation delay close to the optimal. )

[0008] In the above-mentioned prior art, when considering routing between multiple layers of satellites, due to the uncertainty of the connection relationship between satellites and satellites in different layers, it is necessary to calculate the routing table with the help of ephemeris or through centralized ground control. Some studies use MEO satellites to manage multiple layers of satellites in the area and calculate routing tables. However, during the routing process, LEO satellites need to temporarily request cross-layer routing tables from MEO satellites, causing additional delays. In addition, MEO satellites are required to collect link status information for the entire network, resulting in large signaling overhead.

[0009] When designing cross-layer routing for multi-layer LEO satellites, it is necessary to consider the queue length of the routing relay satellite to avoid large queuing delays or even packet loss. The traffic detour scheme proposed in the current study is mainly based on the orbital connection relationship of single-layer LEO satellites, and there are fewer detour options. In addition, due to the uneven distribution of ground services, the route may need to detour multiple times when passing through these areas, or even form a loop. The routing strategy and congestion avoidance scheme given in this scheme can ensure low queuing delays without forming loops. Summary of the invention

[0010] The present invention provides a multi-layer low-orbit satellite congestion avoidance routing method based on SDN. Based on the routing scenario of the multi-layer low-orbit satellite network, a routing strategy is proposed for load balancing and congestion avoidance in the routing process. In the network, a gateway station serves as a control plane. Before routing starts, the gateway station collects data packets of ground users. Due to the uneven distribution of global services and the existence of burst services, the queue lengths of relay satellites vary greatly. The gateway station needs to periodically collect satellite queuing information to obtain the queue length of the satellite selected by the next hop to reduce queuing delay and congestion probability. Afterwards, the gateway station routing table uploads the data packets together to the source satellite. In the routing process, the satellite only serves as a data plane and forwards the data packets according to the routing table until the data packets reach the satellite.

[0011] The SDN-based multi-layer low-orbit satellite congestion avoidance routing method of the present invention comprises the following steps:

[0012] Step 1. Construct satellite and queuing model and satellite routing interruption probability analysis;

[0013] Step 2. The gateway periodically collects satellite information;

[0014] Step 3. Set the gateway as the centralized controller, and the optical station calculates the number of routing hops and routing search radius based on the distance between the source and destination satellites;

[0015] Step 4. The gateway adjusts the selection of the routing area according to the congestion level of the current routing area;

[0016] Step 5. The gateway generates a routing table based on the demarcation of the current routing area, the queuing delay, and the propagation delay, and uploads the routing table to the source satellite;

[0017] Furthermore, in step 1, the construction of the satellite and queuing model and the satellite routing interruption probability analysis specifically includes:

[0018] Step 1.1 Build satellite distribution model

[0019] The satellite network is modeled using the Poisson point process on the sphere. According to the definition of the Poisson point process, the probability that an area of ​​S has n satellites is calculated according to the following formula (1):

[0020]

[0021] Among them, λ is the satellite density, for the i-th layer of satellites, assuming that its orbital height is h i , the total number of satellites is N s,i , the radius of the earth is Then at a radius of r search The number of satellites in range is n i The probability is calculated by the following formula (2):

[0022]

[0023] Step 1.2 Build a satellite queuing model

[0024] The M / M / 1 / N model in queuing theory is used to model the satellite queue length. Assuming that the maximum queue length on the satellite is L, the satellite data packet processing speed is μ, and the satellite data packet receiving speed is λ, the probability that the queue length on the satellite is n is calculated according to the following formula (3):

[0025]

[0026] When n = L, the satellite is considered to be in a congested state and cannot receive data packets sent by other satellites;

[0027] Step 1.3 Satellite routing outage probability analysis

[0028] When the interruption caused by satellite congestion is not considered, the probability that there is no satellite in the i-th layer is as follows (4):

[0029]

[0030] Then, in a single routing search area, the probability of not finding a satellite is the probability that there is no satellite in all layers, as shown in the following equation (5):

[0031]

[0032] Furthermore, in step 2, the gateway periodically collects satellite information:

[0033] The gateway needs to collect the port queue length of the satellite after it enters the search range of the routing, and use it as the queue delay when the routing task arrives at the gateway and selects the satellite.

[0034] Furthermore, step 3 specifically includes:

[0035] The gateway serves as a centralized controller to obtain link status information of low-orbit satellites and calculate routing tables to alleviate congestion in the low-orbit satellite network. The multi-layer low-orbit satellite (Low Earth orbit, LEO) network serves as the data plane to complete the end-to-end forwarding of data packets. First, the gateway calculates the network parameters, i.e., the orbital height h of each layer of satellites. i , Maximum communication distance between satellites d max 、Number of satellites per layer s,i , calculate the expected number of routing hops, routing interruption probability, determine the number of routing hops and routing search radius, specifically including the following steps:

[0036] Step 3.1 Calculation of routing hops Based on the geometric relationship, the minimum routing hop number N that satellites can communicate with within the adjacent search range is hop for:

[0037] Step 3.2 According to the above formula (5), calculate the interruption probability when the current hop number is n, denoted as P out (n), the probability that there is no satellite in the i-th layer when the interruption caused by satellite congestion is not considered, as shown in equation (4) above;

[0038] In a single routing search area, the probability of not finding a satellite is the probability that there is no satellite in all layers, as shown in formula (5);

[0039] Step 3.3 If the interruption probability of the current hop number is P out (n) is less than the interruption probability P calculated last time out (n-1), the routing hop count is determined to be n-1, otherwise n=n+1, and return to step 3.2;

[0040] After the routing hop number n is obtained in step 3.4, the center coordinates and search radius of the search range are determined. Assuming that the routing hop number is n, there are n-1 search ranges in total, and their center coordinates are shown in the following formula (6):

[0041]

[0042] The search radius is shown in the following formula (7):

[0043]

[0044] Furthermore, in step 4, the gateway adjusts the selection of the routing area according to the congestion level of the current routing area:

[0045] like Figure 4As shown, the search range is a "main search range", and the extended search ranges on both sides are "extended search range A" and "extended search range B" in the main search range, respectively. Due to the consideration of propagation delay, the satellite in the main search range is prioritized as the next hop;

[0046] When all satellites in the main search range are congested or there are no satellites, the satellite with the shortest queue length is selected in the extended search ranges A and B; if there are still no satellites in the extended search range or all satellites in the search range are congested, the route is considered to be interrupted;

[0047] Since the maximum communication distance is limited between satellites, the search radius of the extended search is smaller. If the satellite is within the main search range, the next-hop satellite is selected from the main search range or the extended search range A and B. If the satellite is within the extended search area A(B), the next-hop satellite can only be selected from the main search area or the extended search area A(B);

[0048] The center of the extended search range is set to be at the same altitude as the source satellite and the target satellite. The line connecting the center of the main search range and the extended search range is perpendicular to the routing direction, that is, the AOC plane is perpendicular to the AOB plane. The central angle between the center of the main search range and the extended search range is denoted as α;

[0049] Set the radius of the Earth to The distance between the source and destination satellites is d routing , the orbital height of the source and destination satellites is h k , the maximum communication distance between two satellites is d max , taking the center of the earth as the origin, a three-dimensional coordinate system is established. In this coordinate system, the coordinates of the source and destination satellites are (x s ,y s ,z s )、(x d ,y d ,z d );

[0050] Input of the routing calculation process: The distance between the source and destination satellites is d routing , source and destination satellite coordinates (x s ,y s ,z s )、(x d ,y d ,z d ), the orbital heights of the source and destination satellites h k , the maximum communication distance between two satellites d max , the number of satellites in each layer N s,i , the orbital height of each layer of satellites h i ;

[0051] Input and output of the routing calculation process: search range center coordinates, search radius r search， The search radius r of the expanded search range extend (α), the specific routing area update steps are as follows:

[0052] The gateway collects satellite queuing information and obtains the congestion status of satellites within the search range of the routing task;

[0053] The gateway predicts that a satellite within a certain search range is congested. Let the coordinates of the center point of the area be (x, y, z) and the search radius be r. search The extended search range can be set on both sides of this search range. The direction vectors of the source and destination satellites are The deflection angle of the search range is shown as α, denoted as search range A, B. According to the geometric relationship, the coordinates of the center points of the search ranges A and B are respectively as follows (8)-(9):

[0054] To ensure that the satellites in the search range A and B can communicate with the satellites in the original search range, the search radius of the search range extended by geometric relationship is as follows (10):

[0055]

[0056] Furthermore, in step 5, the gateway generates a routing table based on the demarcation of the current routing area, the queuing delay, and the propagation delay, and uploads the routing table to the source satellite:

[0057] Within the selection range of each hop route, the satellite with the shortest queue length is given priority. If there are multiple satellites with the same queue length, the satellite closest to the optimal relay position is selected.

[0058] Furthermore, in step 5, the gateway generates a routing table based on the demarcation of the current routing area, the queuing delay, and the propagation delay, and uploads the routing table to the source satellite:

[0059] Assume that the satellite queue length collected in a single search range in step 2 is L1, L2, ... L n , where the queue with the shortest length is L i , then satellite i is selected as the next hop satellite. If there are multiple satellites with the same queue length, their distances from the optimal relay are D1, D2, ... D n , where the shortest distance is D i , then satellite i is selected as the next hop satellite.

[0060] The SDN-based multi-layer low-orbit satellite congestion avoidance routing method of the present invention has the following superior technical effects:

[0061] 1. The SDN-based multi-layer low-orbit satellite congestion avoidance routing method described in the present invention uses a gateway to collect satellite queuing information, obtains the congestion status of satellites within the search range, comprehensively considers the selection of the next-hop satellite based on the queuing delay and the propagation delay, and gives priority to satellites with shorter queue lengths within the search range to achieve a certain degree of load balancing.

[0062] 2. The SDN-based multi-layer low-orbit satellite congestion avoidance routing method described in the present invention sets an extended search range to allow more routing options, and can actively detour when the route passes through a high-congestion area. When the satellite queue within the original route search range exceeds a certain threshold, the original search range is disabled and the extended search ranges on both sides are used, which can achieve load balancing to a certain extent and ensure low routing delay.

[0063] 3. The SDN-based multi-layer low-orbit satellite congestion avoidance routing method described in the present invention and the proposed routing strategy, by reasonably setting the search range, make each hop routing closer to the destination satellite, thus avoiding the generation of loops.

[0064] 4. The SDN-based multi-layer low-orbit satellite congestion avoidance routing method described in the present invention, the proposed routing strategy, the calculation of the routing hop count and the search range are based on random geometry theory, and do not require a lot of convergence time. After the gateway calculates the routing table, the satellite can forward the data packet according to the routing table.

[0065] 5. The SDN-based multi-layer low-orbit satellite congestion avoidance routing method described in the present invention proposes a congestion avoidance routing method with separation of data plane and control plane, which can realize cross-layer routing while reducing the packet loss rate and queuing delay caused by congestion, and at the same time ensure a low packet loss rate under low load conditions, and is suitable for multi-layer low-orbit satellite networks.

[0066] 6. The SDN-based multi-layer low-orbit satellite congestion avoidance routing method described in the present invention uses ephemeris to predict the positions of satellites in different layers to achieve cross-layer routing, and uses a gateway to periodically collect satellite information to predict the congestion level of satellites within the search range, thereby achieving flexible adjustment of the routing search range and avoiding high congestion areas.

[0067] 7. The SDN-based multi-layer low-orbit satellite congestion avoidance routing method of the present invention designs a search range expansion method, which adds two additional extended search ranges on both sides of the original search range. When the original search range is severely congested, the extended search range can be used. According to the satellite queuing information collected by the gateway, the routing selection area in the ground service concentration area is adjusted to avoid the congested area. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Figure 1A schematic diagram of a routing scenario of the SDN-based multi-layer low-orbit satellite congestion avoidance routing method of the present invention;

[0069] Figure 2 It is a flow chart of the SDN-based multi-layer low-orbit satellite congestion avoidance routing method of the present invention;

[0070] Figure 3 A schematic diagram of the calculation process of the routing hop count for the multi-layer low-orbit satellite congestion avoidance routing method based on SDN according to the present invention;

[0071] Figure 4 A schematic diagram of search range expansion for the multi-layer low-orbit satellite congestion avoidance routing method based on SDN according to the present invention;

[0072] Figure 5 This is a schematic diagram of the average end-to-end delay at different data transmission rates for the multi-layer low-orbit satellite congestion avoidance routing method based on SDN described in the present invention. DETAILED DESCRIPTION

[0073] In order to make the above-mentioned objects, features and advantages of the present invention more clear, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0074] The multi-layer low-orbit satellite congestion avoidance routing method based on SDN of the present invention is as follows: Figure 1-2 As shown, the following steps are included:

[0075] Step 1. Construct satellite and queuing model and satellite routing interruption probability analysis;

[0076] Step 2. The gateway periodically collects satellite information;

[0077] Step 3. Set the gateway as the centralized controller, and the optical station calculates the number of routing hops and routing search radius based on the distance between the source and destination satellites;

[0078] Step 4. The gateway adjusts the selection of the routing area according to the congestion level of the current routing area;

[0079] Step 5. The gateway generates a routing table based on the demarcation of the current routing area, the queuing delay, and the propagation delay, and uploads the routing table to the source satellite;

[0080] As an example of specific steps, in step 1, the construction of the satellite and queuing model and the satellite routing interruption probability analysis specifically includes:

[0081] Step 1.1 Build satellite distribution model

[0082] The satellite network is modeled using the Poisson point process on the sphere. According to the definition of the Poisson point process, the probability that an area of ​​S has n satellites is calculated according to the following formula (1):

[0083]

[0084] Among them, λ is the satellite density. For the i-th layer of satellites, assume that its orbital height is hi and the total number of satellites is N. s,i , the radius of the earth is Then at a radius of r search The number of satellites in range is n i The probability is calculated by the following formula (2):

[0085]

[0086] Step 1.2 Build a satellite queuing model

[0087] The M / M / 1 / N model in queuing theory is used to model the satellite queue length. Assuming that the maximum queue length on the satellite is L, the satellite data packet processing speed is μ, and the satellite data packet receiving speed is λ, the probability that the queue length on the satellite is n is calculated according to the following formula (3):

[0088]

[0089] When n = L, the satellite is considered to be in a congested state and cannot receive data packets sent by other satellites;

[0090] Step 1.3 Satellite routing outage probability analysis

[0091] When the interruption caused by satellite congestion is not considered, the probability that there is no satellite in the i-th layer is as follows (4):

[0092]

[0093] Then, in a single routing search area, the probability of not finding a satellite is the probability that there is no satellite in all layers, as shown in the following equation (5):

[0094]

[0095] As an example of specific steps, in step 2, the gateway periodically collects satellite information:

[0096] The gateway needs to collect the port queue length of the satellite after it enters the search range of the routing, and use it as the queue delay when the routing task arrives at the gateway and selects the satellite.

[0097] As an example of specific steps, step 3 specifically includes:

[0098] The gateway serves as a centralized controller to obtain link status information of low-orbit satellites and calculate routing tables to alleviate congestion in the low-orbit satellite network. The multi-layer low-orbit satellite (Low Earth orbit, LEO) network serves as the data plane to complete the end-to-end forwarding of data packets. First, the gateway calculates the network parameters, i.e., the orbital height h of each layer of satellites. i , Maximum communication distance between satellites d max 、Number of satellites per layer s,i , calculate the expected number of routing hops, routing interruption probability, determine the number of routing hops and routing search radius, specifically including the following steps:

[0099] Step 3.1 Calculation of routing hops Based on the geometric relationship, the minimum routing hop number N that satellites can communicate with within the adjacent search range is hop for:

[0100] Step 3.2 According to the above formula (5), calculate the interruption probability when the current hop number is n, denoted as P out (n), the probability that there is no satellite in the i-th layer when the interruption caused by satellite congestion is not considered, as shown in equation (4) above;

[0101] In a single routing search area, the probability of not finding a satellite is the probability that there is no satellite in all layers, as shown in formula (5);

[0102] Step 3.3 If the interruption probability of the current hop number is P out (n) is less than the interruption probability P calculated last time out (n-1), the routing hop count is determined to be n-1, otherwise n=n+1, and return to step 3.2;

[0103] After the routing hop number n is obtained in step 3.4, the center coordinates and search radius of the search range are determined. Assuming that the routing hop number is n, there are n-1 search ranges in total, and their center coordinates are shown in the following formula (6):

[0104]

[0105] The search radius is shown in the following formula (7):

[0106]

[0107] As an embodiment of the specific steps, in step 4, the gateway adjusts the selection of the routing area according to the congestion level of the current routing area:

[0108] like Figure 3As shown, the search range is a "main search range", and the extended search ranges on both sides are "extended search range A" and "extended search range B" in the main search range, respectively. Due to the consideration of propagation delay, the satellite in the main search range is prioritized as the next hop;

[0109] When all satellites in the main search range are congested or there are no satellites, the satellite with the shortest queue length is selected in the extended search ranges A and B; if there are still no satellites in the extended search range or all satellites in the search range are congested, the route is considered to be interrupted;

[0110] Since the maximum communication distance is limited between satellites, the search radius of the extended search is smaller. If the satellite is within the main search range, the next-hop satellite is selected from the main search range or the extended search range A and B. If the satellite is within the extended search area A(B), the next-hop satellite can only be selected from the main search area or the extended search area A(B);

[0111] The center of the extended search range is set to be at the same altitude as the source satellite and the target satellite. The line connecting the center of the main search range and the extended search range is perpendicular to the routing direction, that is, the AOC plane is perpendicular to the AOB plane. The central angle between the center of the main search range and the extended search range is denoted as α;

[0112] Set the radius of the Earth to The distance between the source and destination satellites is d routing , the orbital height of the source and destination satellites is h k , the maximum communication distance between two satellites is d max , taking the center of the earth as the origin, a three-dimensional coordinate system is established. In this coordinate system, the coordinates of the source and destination satellites are (x s ,y s ,z s )、(x d ,y d ,z d );

[0113] Input of the routing calculation process: The distance between the source and destination satellites is d routing , source and destination satellite coordinates (x s ,y s ,z s )、(x d ,y d ,z d ), the orbital heights of the source and destination satellites h k , the maximum communication distance between two satellites d max , the number of satellites in each layer N s,i , the orbital height of each layer of satellites h i ;

[0114] Input and output of the routing calculation process: search range center coordinates, search radius r search， The search radius r of the expanded search range extend (α), the specific routing area update steps are as follows:

[0115] The gateway collects satellite queuing information and obtains the congestion status of satellites within the search range of the routing task;

[0116] The gateway predicts that a satellite within a certain search range is congested. Let the coordinates of the center point of the area be (x, y, z) and the search radius be r. search , the extended search range can be set on both sides of this search range, and the direction vectors of the source and destination satellites are The deflection angle of the search range is shown as α, denoted as search range A, B. According to the geometric relationship, the coordinates of the center points of the search ranges A and B are respectively as follows (8)-(9):

[0117] To ensure that the satellites in the search range A and B can communicate with the satellites in the original search range, the search radius of the search range extended by geometric relationship is as follows (10):

[0118]

[0119] As an example of specific steps, in step 5, the gateway generates a routing table based on the delineation of the current routing area, the queuing delay, and the propagation delay to calculate the path, and uploads the routing table to the source satellite:

[0120] Within the selection range of each hop route, the satellite with the shortest queue length is given priority. If there are multiple satellites with the same queue length, the satellite closest to the optimal relay position is selected.

[0121] As an example of specific steps, in step 5, the gateway generates a routing table based on the delineation of the current routing area, the queuing delay, and the propagation delay to calculate the path, and uploads the routing table to the source satellite:

[0122] Assume that the length of the satellite queue collected in a single search range in step 2 is L1, L2, ... L n , where the queue with the shortest length is L i , then satellite i is selected as the next hop satellite. If there are multiple satellites with the same queue length, their distances from the optimal relay are D1, D2, ... D n , where the shortest distance is D i , then satellite i is selected as the next hop satellite.

[0123] Example 2

[0124] In this embodiment, three layers of low-orbit satellite networks are deployed. Each layer of LEO satellite network contains 1,800 satellites, the satellite queue length is 200, and the orbital altitudes are 500 kilometers, 550 kilometers, and 600 kilometers respectively. The ground gateway is responsible for collecting satellite queue information and calculating the number of routing hops, routing search range, and routing table.

[0125] like Figure 4 , Figure 5 As shown, this embodiment simulates different degrees of congestion in the LEO satellite network by changing the data packet generation rate, and evaluates the reliability of the present invention by averaging end-to-end delay and packet loss rate. The data processing rate of this embodiment is 10000 packet / s. Compared with the traditional method, when the data transmission rate is 10000 packet / s, the percentage of average end-to-end delay reduction is the largest, and when the data transmission rate is greater than 10000 packet / s, the packet loss rate is significantly reduced.

[0126] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with the technical field within the scope disclosed in the present invention should be covered by the protection scope of the claims of the present invention.

Claims

1. A multi-layer low-orbit satellite congestion avoidance routing method based on SDN, comprising the following steps: Step 1. Construct satellite and queuing model and satellite routing interruption probability analysis; Step 2. The gateway periodically collects satellite information; Step 3. Set the gateway as a centralized controller, and the gateway calculates the number of routing hops and the routing search radius based on the distance between the source and destination satellites; Step 4. The gateway adjusts the selection of the routing area according to the congestion level of the current routing area; Step 5. The gateway calculates the path based on the queuing delay and propagation delay according to the delineation of the current routing area, generates a routing table, and uploads the routing table to the source satellite.

2. According to the SDN-based multi-layer low-orbit satellite congestion avoidance routing method of claim 1, in step 1, the construction of the satellite and queuing model and the satellite routing interruption probability analysis specifically includes: Step 1.1 Build satellite distribution model The satellite network is modeled using the Poisson point process on the sphere. According to the definition of the Poisson point process, the probability that an area of ​​S has n satellites is calculated according to the following formula (1): Among them, λ is the satellite density, for the i-th layer of satellites, assuming that its orbital height is h i , the total number of satellites is N s,i , the radius of the earth is Then at a radius of r search The number of satellites in range is n i The probability is calculated by the following formula (2): Step 1.2 Build a satellite queuing model The M / M / 1 / N model in queuing theory is used to model the satellite queue length. Assuming that the maximum queue length on the satellite is L, the satellite data packet processing speed is μ, and the satellite data packet receiving speed is λ, the probability that the queue length on the satellite is n is calculated according to the following formula (3): When n = L, the satellite is considered to be in a congested state and cannot receive data packets sent by other satellites; Step 1.3 Satellite routing outage probability analysis When the interruption caused by satellite congestion is not considered, the probability that there is no satellite in the i-th layer is as follows (4): Then, in a single routing search area, the probability of not finding a satellite is the probability that there is no satellite in all layers, as shown in the following equation (5):

3. According to the SDN-based multi-layer low-orbit satellite congestion avoidance routing method of claim 1, in step 2, the gateway periodically collects satellite information: The gateway needs to collect the port queue length of the satellite after it enters the search range of the routing, and use it as the queue delay when the routing task arrives at the gateway and selects the satellite.

4. According to the SDN-based multi-layer low-orbit satellite congestion avoidance routing method of claim 1, step 3 specifically includes: The gateway serves as a centralized controller to obtain link status information of low-orbit satellites and calculate routing tables to alleviate congestion in the low-orbit satellite network. The multi-layer low-orbit satellite network serves as the data plane to complete the end-to-end forwarding of data packets. First, the gateway calculates the network parameters, i.e., the orbital height h of each layer of satellites. i , Maximum communication distance between satellites d max 、Number of satellites per layer s,i , calculate the expected number of routing hops, routing interruption probability, determine the number of routing hops and routing search radius, specifically including the following steps: Step 3.1 Calculation of routing hops Based on the geometric relationship, the minimum routing hop number N that satellites can communicate with within the adjacent search range is hop for: Step 3.2 According to the above formula (5), calculate the interruption probability when the current hop number is n, denoted as P out (n), the probability that there is no satellite in the i-th layer when the interruption caused by satellite congestion is not considered, as shown in equation (4) above; In a single routing search area, the probability of not finding a satellite is the probability that there is no satellite in all layers, as shown in formula (5); Step 3.3 If the interruption probability of the current hop number is P out (n) is less than the interruption probability P calculated last time out (n-1), the routing hop count is determined to be n-1, otherwise n=n+1, and return to step 3.2; After the routing hop number n is obtained in step 3.4, the center coordinates and search radius of the search range are determined. Assuming that the routing hop number is n, there are n-1 search ranges in total, and their center coordinates are shown in the following formula (6): The search radius is shown in the following formula (7):

5. According to the SDN-based multi-layer low-orbit satellite congestion avoidance routing method of claim 1, in step 4, the gateway adjusts the selection of the routing area according to the congestion level of the current routing area as follows: The search range is "main search range", and the extended search ranges on both sides are "extended search range A" and "extended search range B" in the main search range, respectively. Due to the consideration of propagation delay, the satellite in the main search range is prioritized as the next hop; If all satellites in the main search range are congested or there are no satellites, the satellite with the shortest queue length is selected in the extended search ranges A and B; if there are still no satellites in the extended search range or all satellites in the search range are congested, the route is considered to be interrupted; Since the maximum communication distance is limited between satellites, the search radius of the extended search is small. If the satellite is within the main search range, the next-hop satellite is selected from the main search range or the extended search range A and B. If the satellite is within the extended search area A(B), the next-hop satellite can only be selected from the main search area or the extended search area A(B); The center of the extended search range is set to be at the same altitude as the source satellite and the target satellite. The center connecting the main search range center and the extended search range is perpendicular to the routing direction, that is, the AOC plane is perpendicular to the AOB plane. The central angle between the main search range center and the extended search range is expressed as α. Set the radius of the Earth to The distance between the source and destination satellites is d routing , the orbital height of the source and destination satellites is h k , the maximum communication distance between two satellites is d max , taking the center of the earth as the origin, a three-dimensional coordinate system is established. In this coordinate system, the coordinates of the source and destination satellites are (x s ,y s ,z s )、(x d ,y d ,z d ); Input of the routing calculation process: The distance between the source and destination satellites is d routing , source and destination satellite coordinates (x s ,y s ,z s )、(x d ,y d ,z d ), the orbital heights of the source and destination satellites h k , the maximum communication distance between two satellites d max , the number of satellites in each layer N s,i , the orbital height of each layer of satellites h i ; Input and output of the routing calculation process: search range center coordinates, search radius r search， The search radius r of the expanded search range extend (α), the specific routing area update steps are as follows: The gateway collects satellite queuing information and obtains the congestion status of satellites within the search range of the routing task; The gateway predicts that a satellite within a certain search range is congested. Let the coordinates of the center point of the area be (x, y, z) and the search radius be r. search , set the extended search range on both sides of this search range, and the direction vectors of the source and destination satellites are The deflection angle of the search range is α, which is denoted as search range A and B. According to the geometric relationship, the coordinates of the center points of the search ranges A and B are respectively as follows (8)-(9): In order to ensure that the satellites in the search range A and B communicate with the satellites in the original search range, the search radius of the search range extended by the geometric relationship is as follows (10):

6. According to the SDN-based multi-layer low-orbit satellite congestion avoidance routing method of claim 1, in step 5, the gateway generates a routing table according to the delineation of the current routing area, the queuing delay, and the propagation delay to calculate the path, and uploads the routing table to the source satellite: within the selection range of each hop route, the satellite with the shortest queue length is preferentially selected; if there are multiple satellites with the same queue length, the satellite closest to the optimal relay position is selected.

7. According to the SDN-based multi-layer low-orbit satellite congestion avoidance routing method of claim 1, in step 5, the gateway generates a routing table based on the delineation of the current routing area, the queuing delay, and the propagation delay calculation path, and uploads the routing table to the source satellite: Assume that the length of the satellite queue collected in a single search range in step 2 is L1, L2, ... L n , where the queue with the shortest length is L i , then satellite i is selected as the next hop satellite. If there are multiple satellites with the same queue length, their distances from the optimal relay are D1, D2, ... D n , where the shortest distance is D i , then satellite i is selected as the next hop satellite.

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