Satellite Internet distributed mobility management method and system

Abstract

The present invention discloses a satellite Internet distributed mobility management method and system, belonging to the technical field of low-orbit satellite network mobility management. The method hides the mobility of satellites through VIP and subVIP management mechanisms, and synchronizes the connection management information and satellite routing of online users from old satellites to new satellites in real time, so that users can maintain the same IP address before and after satellite switching. The method specifically includes: cluster-based satellite node topology management and routing management, user registration, UE host routing of satellite-borne routers and satellite gateway SIP subnet loading, information synchronization between satellite-borne UDM and ground UDM, UE data access to the Internet through ground UPF, Internet data return, and satellite switching based on predictive networking control. The present invention can greatly reduce the online delay of mobile users and the signaling overhead of satellite switching.

Description

Technical Field

[0001] The present invention relates to the technical field of low-orbit satellite network mobility management, and in particular to a satellite Internet distributed mobility management method and system. Background Art

[0002] With the development of the global fifth generation mobile communication technology (5th Generation Mobile Communication Technology, referred to as 5G) network and satellite communication technology, satellite Internet has become one of the key means to achieve global seamless network coverage and wide application. Satellite Internet is a communication method that provides Internet access services to the ground through satellites operating in Earth orbit. It can provide Internet connectivity worldwide, especially in remote and oceanic areas that are difficult to cover by ground communication networks. According to the 3GPP TR 38.821 standard, satellite communications can be divided into multiple architectures, including data transmission of non-terrestrial networks (NTN) through satellites. Satellite Internet mainly consists of several connections: space segment, ground segment and user segment. User Equipment (UE) directly connected to satellite to access the Internet is the future development trend of satellite Internet. When uploading data, UE sends data to the satellite, the satellite forwards the data to the ground station, and then the ground station sends it to the Internet backbone network; when downloading data, the data is transmitted from the Internet backbone network to the satellite through the ground station, and then back to the UE by the satellite.

[0003] Today, satellite Internet is developing from traditional geostationary Earth Orbit (GEO) satellites to low Earth Orbit (LEO) satellite networks, mainly due to the advantages of low-orbit satellites. Due to its low orbit altitude, usually between 200 and 2000 kilometers, LEO satellite networks have the advantages of low latency, global coverage and high bandwidth. However, due to the fast movement speed of low-orbit satellites, UEs need to frequently switch connected satellites, which increases the complexity of communication protocols and switching delays. Therefore, satellite Internet faces many technical challenges in mobility management. In particular, how to ensure uninterrupted data transmission when the satellites accessed by UEs are frequently switched is an industry problem.

[0004] The rapid mobility of satellite networks has caused great difficulties for traditional IP address-based routing and forwarding mechanisms in satellite network communications. IP addresses have the property of being bound to locations, and are highly plannable and secure in ground networks, but they have obvious defects in high-mobility satellite networks. If the gateway accessed by the terminal is set on the satellite, then the network segment of its IP address should be the address in the IP address network segment of the access satellite. The rapid movement of the satellite will cause its gateway address segment to change with the switching of the access satellite. At the same time, due to the change of the satellite accessed by the terminal, the host route of the terminal needs to be re-flooded so that all satellites can refresh the host route of the access terminal. Therefore, this traditional IP routing mechanism is very likely to cause frequent routing fluctuations, affecting the stability and availability of the satellite network.

[0005] The existing 5G network architecture includes components such as the core network (CN), the radio access network (RAN), the IP radio access network (IPRAN), and the UE. The core network includes modules such as the access and mobility management function (AMF), the session management function (SMF), the unified data management (UDM), the user plane function (UPF), and the policy control function (PCF). RAN is responsible for connecting the UE and transmitting wireless data through the base station. IPRAN is responsible for connecting the base station and the CN. Each module works together to realize functions such as access and mobility management, connection management, session management, and policy control.

[0006] In the centralized mobility management architecture, the UE is directly connected to the satellite, and the UE registration and switching need to go through the ground core network. Although this method simplifies the network design to a certain extent, the UE registration requires multiple signaling interactions between the satellite and the ground, resulting in very long user registration time and a lot of signaling interactions between the UE and the core network during satellite switching. The application of centralized mobility management to satellite Internet has exposed problems such as poor scalability and low efficiency. Summary of the invention

[0007] Purpose of the invention: In view of the frequent oscillations in the existing IP routing mechanism in the above-mentioned satellite Internet, the centralized mobility management faces the problems of long user registration time, and a lot of interactive signaling between UE and the core network when the satellite is switched. The present invention discloses a satellite Internet distributed mobility management method and system. Based on the 5G core network architecture, the present invention proposes a routing management mechanism based on a virtual cluster grid (Grid) and cluster (Cluster), and deploys the core network function on each satellite, so that the IP address of the UE can remain unchanged when the satellite moves, so that the UE data transmission remains connected when the access satellite is frequently switched. The core idea of ​​the virtual IP management mechanism proposed in the present invention is to hide the mobility of the satellite through the management mechanism of the Cluster's aggregate routing and subnet routing, so that the UE's IP address remains unchanged when the satellite is frequently switched, and the core network's mobility management and session management are deployed on each satellite, and the IP address is directly allocated to the UE in the subnet of the satellite Cluster, thereby reducing the user registration overhead and the satellite switching signaling overhead.

[0008] The present invention first provides a satellite Internet distributed mobility management method, which hides the mobility of satellites through virtual cluster Cluster / Grid aggregation routing (virtual cluster Cluster / Grid aggregation routing is referred to as VIP) and subnet routing (subnet routing is referred to as subVIP) management mechanisms, and synchronizes the connection management information and satellite routing of online users from the old satellite to the new satellite in real time, so that the user can keep the same IP address before and after the satellite is switched. The method specifically includes the following steps:

[0009] S1. Cluster-based satellite node topology management and routing management, routing management includes VIP management and subVIP management, as well as VIP network segment routing loading and publishing;

[0010] S2. User registration, assigning an IP address to the UE from the subVIP address pool (the IP address assigned to the UE is referred to as UEIP), assigning a floating IP address / network prefix length and a VMAC address to the satellite gateway, where the floating IP address / network prefix length is referred to as SIP, and the floating IP address / network prefix length and VMAC address assigned by the satellite gateway are subVIP network segments;

[0011] S3. The UE host routing of the satellite router and the satellite gateway SIP subnet are loaded. The satellite router establishes a packet radio service tunnel protocol tunnel (packet radio service tunnel protocol tunnel referred to as GTP tunnel) to the user plane function module in the ground core network, namely UPF, through SIP;

[0012] S4. Information synchronization between onboard UDM and ground UDM: UE connection management information, satellite SSP information and routing information in onboard UDM are synchronized to ground UDM;

[0013] S5.UE data accesses the Internet through the ground UPF: UE establishes a connection with the satellite base station. The satellite base station receives the RF signal from the UE and converts it into an IP packet message and transmits it to the satellite router. The UE uses the assigned UEIP as the source IP address, the satellite router SIP as the next-hop gateway address, and VMAC as the gateway MAC address to send the message; after receiving the UE packet message, the satellite router sends it to the ground UPF through the GTP tunnel to access the Internet. The satellite router transmits data to the NTN gateway through the space IP network;

[0014] S6. Internet data return: Internet messages reach the NTN gateway with the help of VIP network segment routing. The NTN gateway looks up SIP to obtain the beam channel and routes the packet message to the satellite connected to it. The satellite router looks up the UEIP host route and transmits the message back to the UE.

[0015] S7. Satellite switching based on predictive networking control.

[0016] Furthermore, the cluster-based satellite node topology management and routing management in step S1 is a cluster-based satellite node topology management that realizes routing aggregation by dividing the satellite orbit into several cellular-like clusters according to the spatial distribution topology and coverage range, specifically including:

[0017] 1) Divide the satellite orbits into several honeycomb-like clusters (the honeycomb-like clusters are called Clusters) according to the spatial distribution topology and coverage range, and assign a cluster unique identifier (CID for short) to each Cluster;

[0018] 2) VIP aggregation routing management and subVIP subnet routing management: The earth's surface is divided into multiple grids according to longitude and latitude. Each grid is called a Grid. Each Grid has a unique identifier (GID) and a VIP address pool (VIP address pool is also called a VIP network segment). The VIP network segment is further subdivided into several subnets (called SubVIP address pools or SubVIP network segments) for assigning IP addresses when users register. Each Grid is mapped to a satellite Cluster, which contains all satellites visible within a time period in the Grid. The Cluster obtains the corresponding VIP network segment and assigns the SubVIP network segment to each satellite. At the same time, each Cluster also has a virtual media access control address (virtual media access control address is abbreviated as VMAC), so as to establish a mapping relationship between the ground Grid and the satellite Cluster in the sky.

[0019] 3) Loading and publishing VIP network segment routes: The NTN gateway loads the Cluster’s VIP address pool and SubVIP address pool group to all satellites and stores them in the onboard UDM. At the same time, the NTN gateway publishes the Cluster’s VIP network segment to the Internet.

[0020] Furthermore, the user registration in step S2 specifically includes:

[0021] The UE sends a registration request message to the access and mobility management function module in the satellite core network (the access and mobility management function module in the satellite core network is the satellite AMF); the satellite AMF registers the UE information and then sends a session request to the session management function module in the satellite core network, that is, the satellite SMF;

[0022] The onboard SMF allocates an IP address to the UE from the SubVIP address pool stored in the unified data management system in the onboard core network (the unified data management system in the onboard core network is the onboard UDM) (allocating an IP address to the UE is called UEIP), and allocates a virtual media access control address to the satellite. The virtual media access control address includes VMAC and an IP address. The IP address here is called SIP, and then returns a registration response message to the onboard AMF carrying UEIP, SIP, and VMAC information;

[0023] The onboard AMF confirms the registration and returns it to the UE. The UE obtains the UE IP address assigned to it and the gateway SIP and VMAC addresses of the onboard router.

[0024] Furthermore, the satellite switching based on predictive networking control described in step S7 first performs information synchronization of satellite switching based on the ephemeris, and synchronizes the routing information and user connection information on the old satellite to the new satellite. When the satellite moves out of the current Cluster, the switching process will be triggered, and the old satellite will synchronize the SIP, VMAC, UEIP host routing, and UE steady-state connection management information in its UDM to the UDM of the new satellite, so that the routing information and user connection information on the new satellite are consistent with those of the old satellite after the satellite switching, and the user connection is not interrupted.

[0025] Furthermore, the information synchronization of satellite switching based on ephemeris is that the satellites in the Cluster corresponding to a Grid are switched once every several minutes. Through the preset time nodes and switching rhythm, a Cluster set time diagram of 24 hours a day is obtained to form a predictable satellite switching set, i.e., ephemeris. The control of information synchronization of satellite switching based on the ephemeris specifically includes:

[0026] Satellite state definition: Four states are defined for satellite switching processing, namely, initial state, routing synchronization state, switching state and switching completion state, to achieve synchronous control of user data and satellite routing during satellite switching;

[0027] Route synchronization: Route synchronization is divided into Cluster position awareness, Cluster ephemeris cycle awareness, Cluster pre-switching start, route synchronization, data packet forwarding, and deletion of routing information and connection management information to achieve smooth switching of satellites.

[0028] Furthermore, the satellite status definition includes:

[0029] Initial state: When the satellite is about to enter a new cluster, the satellite marks the route as synchronized, which does not affect the data transmission and session of the currently connected users;

[0030] Routing synchronization state: In this state, the satellite does not accept new user registrations, but accepts users going offline, and synchronizes the user's host routing information and data packets to the new satellite that is about to enter the current Cluster;

[0031] Switching state: In this state, the satellite actually starts to perform the Cluster switching operation, migrating the current user to the new satellite. The new satellite can accept new users, including registering the user's context and session information to the new satellite.

[0032] Switching completed state: In this state, the satellite has successfully completed the Cluster switching operation, all users have been migrated to the new satellite, and the old satellite deletes the previous Cluster information to release resources.

[0033] Furthermore, the specific process of the routing synchronization includes:

[0034] Cluster location awareness: The old satellites in the cluster sense the current geographic location (the current geographic location is the SSP);

[0035] Cluster ephemeris cycle perception: The old satellite perceives the ephemeris cycle of the current Cluster (the ephemeris cycle of the current Cluster is TLE);

[0036] Cluster pre-switching starts: the old satellite starts pre-switching and synchronizes the routing with the new satellite that is about to enter the cluster;

[0037] Route synchronization: Route synchronization is performed in the onboard core network and the UDM in the ground core network. The synchronized data includes: UE connection management information<Location,MAC,UEIP> , UEIP host routing, satellite<SSP,SIP,VMAC> , SIP / network prefix length and VMAC address, GTP tunnel information;

[0038] Deletion of routing information and connection management information: The old satellite deletes the data that has been synchronized from the previous Cluster.

[0039] The present invention also provides a satellite Internet distributed mobility management system, which is used to run the above-mentioned satellite Internet distributed mobility management method. The system includes a satellite base station, a satellite router, a satellite core network, an NTN gateway and a ground core network, wherein:

[0040] The gNB uses the radio resource control protocol, or RRC protocol, to manage UE access.

[0041] The onboard router is responsible for establishing a GTP tunnel with the UPF in the ground core network and forwarding IP data packets;

[0042] The satellite core network includes AMF, SMF, and UDM functions. AMF is responsible for user registration and mobility management, SMF is responsible for user and satellite IP address allocation and connection management, and UDM is responsible for storing VIP address pools, subVIP address pools, Cluster and Grid location information, and user connection management information.

[0043] NTN gateway, usually located at the ground station, is responsible for the interface and data conversion between the ground network including the ground core network and the satellite network including the satellite core network;

[0044] Ground core network, responsible for mobile Internet data transmission

[0045] Beneficial effects:

[0046] 1. The present invention provides a satellite Internet distributed mobility management method, which is based on the Cluster mobility management solution, realizes the aggregation routing and subnet routing allocation mechanism through satellite virtual cluster technology, allocates floating IP gateway addresses to satellites, thereby hiding the mobility of satellites and converting them into fixed Clusters. According to this method, all communication data will be allocated to the satellite of the corresponding Cluster according to VIP, and fast IP address resolution and data forwarding can be performed within the Cluster, which improves the efficiency and stability of data transmission.

[0047] 2. Since the VIP network segment of each Grid and its mapped Cluster is fixed, the satellite always inherits the VIP of the ground Grid. When the satellite switches, the gateway address segment of the UE in the Grid will not change with the switch of the access satellite. Then the assigned IP address is fixed, so that when the UE roams only within the Grid, the IP address can remain unchanged, reducing the risk of IP conflict and IP reallocation during the switching process, and ensuring continuous and uninterrupted data transmission.

[0048] 3. The method timely controls the user information and route synchronization during satellite switching by predicting the networking, and forms a predictable satellite switching set by preset time nodes and switching rhythm, thereby improving the reliability of the service. Moreover, when the satellite accessed by the UE changes, the host route has been synchronized and does not need to be re-flooded. All satellites do not need to refresh the host route of the accessed UE, which will not cause frequent route fluctuations, thereby improving the stability and availability of the satellite network.

[0049] 4. AMF, SMF, UDM and other core network functions are distributed on each satellite. UE registration and switching do not need to go through the ground core network, which greatly shortens the user registration time and the mobile user online delay, and reduces the interactive signaling between the UE and the ground core network during satellite switching. At the same time, the core network functions are deployed on each satellite to improve the scalability of satellite Internet and can flexibly respond to the dynamic nature of satellite Internet. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 A schematic diagram of a Cluster-based satellite Internet networking method provided in an embodiment of the present invention;

[0051] Figure 2 4 is a diagram showing the architecture of a distributed LEO satellite network mobility management system in an embodiment of the present invention;

[0052] Figure 3 A schematic diagram of the division method of the Cluster and its mapping relationship with the ground Grid provided in an embodiment of the present invention;

[0053] Figure 4 A schematic diagram of a satellite switching mechanism based on predictive networking control provided in an embodiment of the present invention;

[0054] Figure 5 A schematic diagram of a satellite state machine during satellite switching provided in an embodiment of the present invention;

[0055] Figure 6 A schematic diagram of the routing synchronization process when a satellite switches a Cluster provided in an embodiment of the present invention;

[0056] Figure 7The figure is a schematic diagram of a data forwarding process provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0057] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the embodiments of the present invention are described in detail below in conjunction with the accompanying drawings: This embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation method and a specific operation process are given. It should be understood that the specific examples described here are only used to explain the present invention, but the protection scope of the present invention is not limited to the following embodiments.

[0058] In the low-orbit satellite network scenario, the present invention proposes a satellite Internet distributed mobility management method in combination with the satellite motion law. First, considering the unique characteristics of low-orbit satellite networks (LEO satellite networks, LSN), the challenges faced by centralized mobility management include: high mobility and frequent switching, single point failure, high latency, poor scalability and low efficiency; and distributed network element deployment brings opportunities to low-orbit satellite network mobility management: low latency, high reliability and elasticity, seamless mobility, optimized resource management and strong disaster recovery capabilities.

[0059] The present invention comprises the following main steps:

[0060] S1. Cluster-based satellite node topology management and routing management, including the following sub-steps:

[0061] S1.1 Cluster-based satellite node topology management:

[0062] The satellite orbits are divided into several honeycomb-like clusters according to the spatial distribution topology and coverage range, called Clusters. Each Cluster is assigned a unique identifier (Cluster Unique Identifier, CID for short). The starry sky range covered by a Cluster is C(i,j), where i is the latitude index and j is the longitude index. C(i,j) represents the latitude projection from i to i+1 and the longitude projection from j to j+1, and the projection comes from the ground Grid.

[0063] S1.2 Routing management, specifically including:

[0064] 1) VIP aggregation routing management and subVIP subnet routing management: The earth's surface is divided into several grids according to longitude and latitude. The ground range covered by a grid is G(i,j), where i is the latitude index and j is the longitude index. The ground range represented by G(i,j) is the area from latitude i to latitude i+1, and the area from j to j+1. Each grid is assigned a grid unique identifier (Grid Unique Identifier, referred to as GID) and an IP address segment, which is called a VIP address pool, expressed as VIP address / network prefix length n, also called a VIP segment. At the same time, the VIP address pool segment is split into several small subnet segments / network prefix length m, referred to as SubVIP address pools. A VIP address pool contains 2 m-n SubVIP subnet address pools are called SubVIP address pool groups. Users obtain an IP address from the SubVIP address pool when registering. The purpose of dividing subIP subnets is to match the number of users that can be accessed concurrently by each satellite. m and n are divided based on the actual satellite network capacity.

[0065] 2) Cluster and Grid mapping: According to the ground Grid mapping to the satellite Cluster at a fixed position in the air, there is at least one ground station in a Grid. A Cluster contains all visible satellites in the Grid within a time period, so that each Cluster can obtain the VIP network segment of the corresponding Grid. The VIP network segment is the aggregated route of all satellites in the Cluster. Each satellite in the Cluster can obtain a SubVIP subnet segment. Each Cluster is assigned a virtual media access control address (Virtual Media Access Control Address, referred to as VMAC address), so as to establish a spatial Cluster and the corresponding ground Grid mapping table CGMap. The data structure of the mapping table includes {GID, CID, G(i,j), C(i,j), VIP address pool, VMAC, SubVIP address pool group};

[0066] S1.3 VIP address pool route loading and publishing: NTN gateway loads the Cluster’s VIP address pool and SubVIP address pool group, CGMap, to all satellites and stores them in the onboard UDM. At the same time, NTN gateway only publishes the Cluster’s VIP address pool network segment to the Internet. Since the VIP network segment is stable for ground stations, the Internet cannot see the mobility of the satellite.

[0067] S2, user registration, allocates an IP address (UEIP) to the UE from the subVIP address pool, allocates a floating IP address / network prefix length (SIP for short, i.e., the subVIP network segment) and VMAC address to the satellite gateway, including the following sub-processes:

[0068] S2.1 The user registration request message is sent to the satellite AMF. The request message contains the user's subscription permanent identifier (SUPI) and the UE's media access control address (MAC). The satellite AMF module issues a G-GUTI (a globally unique temporary UE identifier in the 5G system) to the UE to register the UE.<Location,MAC,G-GUTI> , S <ssp>Information, where Location is the user's location, expressed in longitude and latitude (x, y), and SSP is the sub-satellite point (SSP) of the vertical projection of the satellite on the ground, also expressed in longitude and latitude (x, y);

[0069] S2.2 The satellite AMF sends a session request to the satellite SMF. The session request parameters include UE<Location,MAC,G-GUTI> , S <ssp>The onboard SMF is based on S <ssp>Obtain the CID and SubVIP address pool from the Cluster and Grid mapping table CGMap stored in the on-board UDM. Allocate an IP address for the UE in the SubVIP address pool of the Cluster containing the SSP, which is called UEIP. Allocate an IP address for the satellite, which is the IP address of the satellite as the user gateway. Since it is dynamically allocated during user registration, it is also called the floating IP address, simply referred to as SIP.

[0070] S2.3 The on-board SMF returns a registration response message to the on-board AMF module. The message contains parameters such as UE <Location, MAC, G-GUTI, UEIP>, S <SSP, SIP / network prefix length m, VMAC>.

[0071] S2.4 After the on-board AMF module confirms the successful registration of the UE, it returns to the UE. The UE obtains the IP address assigned to it, the gateway SIP / network prefix length m and the VMAC address of the on-board router.

[0072] S3. On-board router UE host routing and satellite subnet loading:

[0073] After the on-board AMF module confirms the successful registration of the user UE, it notifies the on-board router to register UE <Location, MAC, G-GUTI, UEIP>, satellite <SSP, SIP, VMAC>. VMAC is the MAC address of the satellite, register the SubVIP network segment and the VMAC address. At the same time, the on-board router establishes a General Packet Radio Service Tunneling Protocol (GPRSTunneling Protocol) tunnel, simply referred to as GTP tunnel, to the UPF module in the ground core network.

[0074] S4. Synchronize the connection information and routing information in the on-board UDM to the ground UDM:

[0075] Including UE <Location, MAC, G-GUTI, UEIP>, satellite <SSP, SIP, VMAC, beam channel>. VMAC is the MAC address of the satellite, register the SubVIP network segment and the VMAC address, and GTP tunnel information.

[0076] S5. UE data accesses the Internet through the ground UPF:

[0077] The UE establishes a connection with the satellite base station. The satellite base station receives the RF signal from the UE and converts it into an IP packet message and transmits it to the satellite router. The UE uses the assigned UEIP as the source IP address, the satellite router SIP as the next-hop gateway address, and VMAC as the gateway's MAC address to send the message. After receiving the UE packet message, the satellite router sends it to the ground UPF through the GTP tunnel to access the Internet. The satellite router transmits data to the NTN gateway through the space IP network.

[0078] S6. Internet data returns to UE: Internet packet messages reach the NTN gateway with the help of VIP network segment routing. The NTN gateway searches SIP to obtain the beam channel and routes the packet messages to the satellite connected to it. The satellite sends the messages to the UE based on the UEIP host routing.

[0079] S7. Control satellite switching based on predictive networking: When a satellite moves out of the current Cluster, the switching process will be triggered. The old satellite will synchronize its SIP / network prefix length and VMAC, UE routing information and steady-state information in UDM to the new satellite. The steady-state information includes VIP network segment, SubVIP network segment, SIP, VMAC, and UEIP host routing table of all registered UEs. The new satellite will take over as the new UE gateway, so that the UE's IP address remains unchanged, thereby ensuring that the user's IP connection is not interrupted.

[0080] Furthermore, the method controls satellite switching by predictive networking. The satellites in the Cluster corresponding to a Grid are switched every several minutes. Through preset time nodes and switching rhythms, a predictable satellite switching set is formed, thereby obtaining a 24-hour Cluster set time map. Based on the ephemeris, information synchronization is controlled during satellite switching to achieve real-time control of new and old satellite data synchronization, so that after the satellite is switched, the routing information and user connection information on the old satellite are all synchronized to the new satellite, and the synchronization of user data and satellite routing is achieved during satellite switching, so that user connections are not interrupted after the satellite is switched. Specifically including:

[0081] 1) Satellite state definition: Four states are defined for satellite switching processing, namely, initial state, routing synchronization state, switching state and switching completion state, to achieve synchronous control of user data and satellite routing during satellite switching;

[0082] 2) Routing synchronization: Routing synchronization is divided into several processes, including Cluster location awareness, Cluster ephemeris cycle awareness, Cluster pre-switching start, routing synchronization, satellite switching, data packet forwarding, and deletion of routing information and connection management information, to achieve smooth switching of satellites.

[0083] S7.1 Satellite state definition: Four states are defined for satellite switching processing, namely, initial state, routing synchronization state, switching state, and switching completion state. The state machine is used to achieve synchronous control of user data and satellite routing during satellite switching, including:

[0084] 1) Initial state: When the old satellite is about to leave the Cluster and be replaced by the new satellite, the old satellite marks the route as synchronized. This state does not affect the data transmission and session of the currently connected users.

[0085] 2) Routing synchronization state: In this state, the old satellite does not accept new user registrations, but accepts users going offline, and synchronizes all user information and routing information in the UDM to the new satellite entering the current Cluster;

[0086] 3) Switching state: In this state, the old satellite actually starts to perform the Cluster switching operation and migrate the current user session to the new satellite, including registering the user's context and session information to the UDM of the new satellite;

[0087] 4) Switching completed state: In this state, the satellite has successfully completed the Cluster switching operation, all users have been migrated to the new satellite, and the old satellite deletes all user information and routing information in the previous UDM in the Cluster, releasing AMF and SMF connection resources.

[0088] S7.2 Routing synchronization: Routing synchronization is divided into several processes, including Cluster position perception, Cluster ephemeris cycle perception, Cluster pre-switching start, routing synchronization, and deletion of routing information and connection management information, to achieve smooth switching of satellites.

[0089] 1) Cluster location awareness: Before the switch begins, the old satellite in the cluster uses its own sensors, ephemeris data, and the assistance of the ground station to determine its current geographic location, namely the SSP, which represents the projection point of the satellite on the earth's surface;

[0090] 2) Cluster ephemeris cycle perception: After determining the position, the old satellite calculates the ephemeris cycle information of itself and the satellite that is about to enter the Cluster by receiving the Two-Line Element Set (TLE) sent by the ground station and using the SGP4 model (Simplified General Perturbations model, SGP4);

[0091] 3) Cluster pre-switching: After obtaining the position and ephemeris cycle information, the old satellite starts the pre-switching operation, marks the route as synchronized, prepares to synchronize the route data, and negotiates with the new satellite that is about to enter the Cluster, preparing to start the synchronization operation;

[0092] 4) Route synchronization: Perform route synchronization operations on the UDM, including subVIP address pool, SIP address / network prefix length, UE host routing table, UE identity information and location information, etc., which describe the steady-state information of routing and UE connection management on the satellite, and synchronize all UE host routing information of the old satellite to the new satellite. In this process, the UE host routing of the new satellite is marked as inactive, which means that it cannot be used to forward packets temporarily;

[0093] 5) Deletion of routing information and connection management information: After the old satellite confirms that all UEs have successfully switched to the new satellite and are operating normally, the data previously successfully synchronized to the new satellite is deleted; the old satellite prepares to enter the next Cluster pre-switching phase and waits for future switching tasks; the UE host routes of the new satellite are all marked as active, indicating that they are activated and can be used to forward packet messages.

[0094] The present invention also provides a satellite Internet distributed mobility management system for running the above method. The satellite Internet distributed mobility management system of the present invention is also called a distributed mobility management architecture (Distributed Mobility Management, DMMA). DMMA is a cluster-based network management architecture that adopts a LEO satellite / ground network collaborative working mechanism. Specifically, the core network network elements are deployed to the satellite and the ground respectively to form a distributed system in which the satellite core network and the ground core network work together. The architecture includes a satellite base station, a satellite router, a satellite core network, an NTN gateway and a ground core network. Among them, the satellite base station uses the Radio Resource Control (RRC) protocol to manage the user equipment UE, which is also referred to as the connection between the UE and the satellite base station; the satellite router is responsible for processing the communication data path through the satellite.

[0095] The onboard core network is responsible for UE registration, IP address allocation and resource allocation, mobility management and recording of user information, including SUPI and IP address; the NTN gateway is responsible for the interface and data conversion between the ground network including the ground core network and the satellite network including the onboard core network; the ground core network is responsible for establishing a GTP tunnel between the onboard router and the UPF module in the ground core network, so that the UE can transmit data with the Internet.

[0096] The following describes a specific implementation case of the present invention for a LEO mobile scenario, including a network element architecture for distributed mobility management and the operation process of S1 to S7 of the method proposed in the present invention.

[0097] S1. Cluster-based satellite node topology management and routing management:

[0098] S1.1 Cluster-based satellite node topology management, such as Figure 1 As shown in the figure, the satellite orbits are divided into several honeycomb-like clusters according to the spatial distribution topology and coverage range, and each cluster is assigned a CID, such as CID001. The starry sky range covered by a Cluster is C(i,j), where i is the latitude index and j is the longitude index. C(i,j) represents the latitude projection from i to i+1 and the longitude projection from j to j+1. The projection comes from the ground Grid, such as C(30,-90), which means mapping from the ground surface G(30,-90) to the spatial Cluster.

[0099] S1.2 Routing management, such as Figure 3 As shown in the figure, the earth's surface is divided into several Grids according to longitude and latitude. The ground range covered by a Grid is G(i,j), where i is the latitude index and j is the longitude index. The ground range represented by G(i,j) is the area from latitude i to latitude i+1, and the area from j to j+1. For example, G(30,-90) represents the ground area from latitude 30 degrees to 31 degrees, and longitude -90 degrees to -89 degrees. Each Grid is assigned a GID, such as GID001 and an IP address segment, which is called a VIP address pool, expressed as VIP address / network length, also called a VIP segment. For example, it can be assumed that the size of each Grid is 1996km×1996km, GID001: the corresponding VIP1 is 192.168.0.0 / 16, GID002: the corresponding VIP2 is 192.2.0.0 / 16, GID003: the corresponding VIP3 is 192.3.0.0 / 16, and so on. At the same time, the VIP segment is divided into several small subnet segments, referred to as SubVIP segments, such as SubVIP1: 192.168.0.0 / 24. A VIP segment contains 256 SubVIP subnet address pools. When a user registers, he obtains an IP address from the SubVIP segment, such as 192.168.0.1. According to the ground grid mapping to the satellite cluster at a fixed position in the sky, a cluster contains all the visible satellites in the grid within a time period. For example, Cluster 1 includes Orbit1 to Orbit3, Cluster 2 includes Orbit4 to Orbit6, and Cluster 3 includes Orbit7 to Orbit9. Therefore, each cluster can obtain the VIP network segment of the corresponding grid, which is the aggregate route of all satellites in the cluster. Each satellite in the cluster can obtain a SubVIP subnet segment. Each cluster is assigned a VMAC address, such as VMAC1:00:0c:29:72:ed:79. In this way, a spatial Cluster and the corresponding ground Grid mapping table CGMap are established. The data structure of the mapping table includes {GID, CID, G(i,j), C(i,j), VIP address, VMAC, SubVIP address pool group}, for example {GID001, CID001, C(30,-90), G(30,-90), 192.168.0.0 / 16, 00:0c:29:72:ed:79, 192.168.0.0 / 24}.

[0100] S1.3 VIP address pool route loading and publishing: VIP network segment route loading and publishing: NTN gateway loads the Cluster’s VIP network segment address pool, such as VIP1: 192.168.0.0 / 16 and SubVIP groups SubVIP1 to SubVIP256, to all satellites and stores them in the onboard UDM module. At the same time, NTN gateway publishes the Cluster’s VIP network segment 192.168.0.0 / 16 to the Internet.

[0101] S2. User registration: Allocate an IP address (UEIP) to the UE from the subVIP address pool, allocate a floating IP address / network prefix length (SIP for short, i.e., the subVIP network segment) and a VMAC address to the satellite gateway. The specific steps for the UE to perform initial registration are as follows: The UE starts the registration process, generates a registration request containing its identity information, such as SUPI: imsi-208930000000004, location information Location1, such as (30.5, -89.5) and MAC address, such as 02:42:8d:75:c2:e4, and sends the request message to the onboard AMF. The onboard AMF registers the UE<Location1,MAC> , S1 <ssp>Information, for example, SSP1: (30.75, -89.25). Then send a session request to the satellite SMF, the session request parameters contain UE<Location1,MAC> , S1 <ssp>; Onboard SMF based on S1 <ssp1>Obtain CID1, subVIP1192.168.0.0 / 24 from the onboard UDM, assign a UEIP1 address to the UE from subVIP1, such as 192.168.0.1, assign a SIP1 address to the satellite, such as 192.168.0.133 / 24, and then return a registration response message to the onboard AMF, which contains the UE<Location1,MAC,UEIP1> , S<SSP1,SIP1> And other parameters.

[0102] S3, onboard router UE host routing and satellite subnet loading:

[0103] After confirming that the user UE has successfully registered, the onboard AMF module notifies the onboard router to register the UE.<Location1,MAC,UEIP1> ,satellite<SSP1,SIP1,VMAC> , register the SubVIP network segment and VMAC address; at the same time, the onboard router establishes a GTP tunnel to the UPF module in the ground core network, for example uesimtun0 (SIP = 192.168.0.133 / 24, ground UPFIP = 192.168.111.132), where the ground UPFIP represents the IP address of the UPF module in the ground core network.

[0104] S4. The connection information and routing information in the satellite UDM are synchronized to the ground UDM: the connection information is the connection information between the user and the satellite, including the UE's identity information SUPI, such as imsi-2089300000000, and the routing information includes the UE's IP address (192.168.0.1) and MAC address (02:42:8d:75:c2:e4), the satellite's SIP (192.168.0.133 / 24) and VMAC address (00:0c:29:72:ed:79).

[0105] S5, UE data accesses the Internet through the ground UPF: Figure 7 As shown, the UE establishes a connection with the satellite base station. The satellite base station receives the RF signal from the UE and converts it into an IP packet message and transmits it to the satellite router. The UE uses the assigned UEIP 192.168.0.1 as the source IP address, the satellite router SIP 192.168.0.133 / 24 as the next-hop gateway address, and VMAC 00:0c:29:72:ed:79 as the gateway MAC address to send the message. After receiving the packet message, the satellite router sends it to the UPF in the ground core network through the GTP tunnel uesimtun0, such as 192.168.111.132, to achieve Internet access.

[0106] S6. Internet data returns to UE: Internet packet messages reach the NTN gateway with the help of VIP network segment 192.168.0.0 / 16 routing. The NTN gateway looks up SIP (192.168.0.133 / 24) to obtain the beam channel and routes the packet messages to the satellite connected to it. The satellite sends the messages to the UE based on the UEIP 192.168.0.1 host routing.

[0107] S7. Control satellite switching based on predictive networking: When a satellite moves out of the current Cluster, the switching process will be triggered. The old satellite will synchronize its SIP / network prefix length and VMAC, UE routing information and steady-state information in UDM to the new satellite. The steady-state information includes VIP network segment, SubVIP network segment, SIP, VMAC, and UEIP host routing table of all registered UEs. The new satellite will take over as the new UE gateway, so that the UE's IP address remains unchanged, thereby ensuring that the user's IP connection is not interrupted.

[0108] Figure 4 The figure shows the satellite switching process in the satellite cluster corresponding to GID001. The whole process achieves continuous coverage across 24 hours through predefined time nodes and switching rhythm. Here, it is assumed that the satellite switches every 5 minutes to form a predictable satellite set. The cluster set time diagram of 1 day and 24 hours can be obtained, and the IP address synchronization during satellite switching is performed based on the ephemeris. At time T0, Orbit1 is satellite 1 and 2, Orbit2 is satellite 5 and 6, and Orbit3 is satellite 1 and 2. The satellite cluster at this time determines the data transmission path within the Grid and provides services for the UE. At time T0+5, Orbit1 switches to satellite 2 and 3, Orbit2 switches to satellite 6 and 7, and Orbit3 switches to satellite 2 and 3. These satellites constitute the new data path within the Cluster, and the system automatically updates the data transmission path within each Grid. Although the physically connected satellite changes, the UE's IP address remains unchanged. The switching process at subsequent moments is as above. According to this periodic interval and switching mechanism, a complete satellite switching cycle is completed every 24 hours. Through (24*60) / 5=288 switches, seamless connection and service at different time points in a day can be achieved.

[0109] S7.1 Satellite switching state machine processing, such as Figure 5 As shown:

[0110] 1) Initial state: normal satellite data transmission state;

[0111] 2) Routing synchronization state: When the old satellite is about to leave Cluster 1 and be replaced by a new satellite, the satellite state is migrated from the initial state to the synchronization state. In this state, the satellite does not accept new user registrations, but accepts users going offline. At the same time, all user information and routing information in the UDM are synchronized to the new satellite entering the current Cluster;

[0112] 3) Switching state: In this state, the old satellite actually starts to perform the Cluster switching operation and migrate the current user session to the new satellite, including registering the user's context and session information to the UDM of the new satellite;

[0113] 4) Switching completed state: In this state, the satellite has successfully completed the Cluster switching operation, all users have been migrated to the new satellite, and the old satellite deletes all user information and routing information in the previous UDM in the Cluster, releasing AMF and SMF connection resources.

[0114] S7.2 Routing Synchronization: Figure 6 As shown, routing synchronization is required when the satellite switches the Cluster. The steps are as follows:

[0115] 1) Cluster position awareness: Before the switch begins, the old satellite in the cluster uses its own sensors, ephemeris data, and the assistance of the ground station to determine its projection point SSP1 on the earth's surface;

[0116] 2) Cluster ephemeris cycle perception: After determining the position, the old satellite receives the TLE sent by the ground station and uses the SGP4 model to calculate the ephemeris cycle information of itself and the satellite that is about to enter the Cluster;

[0117] 3) Cluster pre-switching: After obtaining the position and ephemeris cycle information, the old satellite starts the pre-switching operation, marks the route as synchronized, prepares to synchronize the route data, and negotiates with the new satellite that is about to enter the Cluster, preparing to start the synchronization operation;

[0118] 4) Route synchronization: Perform route synchronization operations on UDM, including subVIP address pool, SIP address / network prefix length, UE host routing table, UE identity information and location information, etc., which describe the steady-state information of routing and UE connection management on the satellite, and synchronize all UE host routing information of the old satellite to the new satellite. In this process, the UE host routing of the new satellite is marked as inactive, indicating that it cannot be used to forward packets temporarily;

[0119] 5) Deletion of routing information and connection management information: After the old satellite confirms that all UEs have been successfully switched to the new satellite and are operating normally, it deletes the data that was previously successfully synchronized to the new satellite; the old satellite prepares to enter the next Cluster pre-switching phase and waits for future switching tasks.

[0120] The present invention also provides a satellite Internet distributed mobility management system for running the above method. The DMMA of the present invention is a cluster-based network management architecture that adopts a LEO satellite / ground network collaborative working mechanism. Figure 2 As shown in FIG. 1 , the architecture includes a satellite base station, a satellite router, a satellite core network, an NTN gateway and a ground core network. The satellite base station uses the RRC protocol to manage the user equipment UE, which is also called the connection between the UE and the satellite base station; the satellite router is responsible for processing the communication data path through the satellite.

[0121] The onboard core network is responsible for UE registration, IP address allocation and resource allocation, mobility management and recording of user information, including SUPI and IP address; the NTN gateway is responsible for the interface and data conversion between the ground network including the ground core network and the satellite network including the onboard core network; the ground core network is responsible for establishing a GTP tunnel between the onboard router and the UPF module in the ground core network, so that the UE can transmit data with the Internet.

[0122] The above is only an implementation example of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements can be made without departing from the principle of the present invention. These improvements should also be regarded as the protection scope of the present invention. < / ssp> < / ssp> < / ssp> < / ssp> < / ssp>

Claims

1. A satellite Internet distributed mobility management method, characterized in that: The method hides the mobility of satellites through virtual cluster Cluster / Grid aggregation routing VIP management and subnet routing subVIP management mechanism. The old satellite synchronizes the connection management information and satellite routing of online users to the new satellite in real time, so that users can keep the same IP address before and after satellite switching. The method specifically includes the following steps: S1. Cluster-based satellite node topology management and routing management, routing management includes VIP aggregation routing management and subVIP subnet routing management as well as VIP network segment routing loading and publishing; S2. User registration, assigning an IP address UEIP to the UE from the subVIP address pool, and assigning a floating IP address / network prefix length SIP and a virtual media access control address VMAC to the satellite gateway, where SIP is the subVIP network segment; S3. The UE host routing of the satellite router and the satellite gateway SIP subnet are loaded, and the satellite router establishes a GTP tunnel to the UPF in the ground core network through SIP; S4. Information synchronization between onboard UDM and ground UDM: UE connection management information, satellite geographic location SSP information and routing information in onboard UDM are synchronized to ground UDM; S5. UE data accesses the Internet through the ground UPF: UE establishes a connection with the satellite base station. The satellite base station receives the RF signal from the UE and converts it into an IP packet message and transmits it to the satellite router. The UE uses the assigned UEIP as the source IP address, the satellite router SIP as the next-hop gateway address, and VMAC as the gateway's MAC address to send the message; After receiving the UE packet message, the satellite router sends it to the ground UPF through the GTP tunnel to access the Internet. The satellite router transmits data to the NTN gateway through the space IP network; S6. Internet data return: Internet messages reach the NTN gateway with the help of VIP network segment routing. The NTN gateway looks up SIP to obtain the beam channel and routes the packet message to the satellite connected to it. The satellite router looks up the UEIP host route and transmits the message back to the UE. S7. Satellite switching based on predictive networking control; The cluster-based satellite node topology management and routing management in step S1 is based on cluster-based satellite node topology management, which realizes routing aggregation by dividing the satellite orbit into several cellular-like clusters according to the spatial distribution topology and coverage range, and specifically includes: 1) Divide the satellite orbit into several cellular-like clusters according to the spatial distribution topology and coverage, and assign a unique cluster identifier CID to each cluster; 2) VIP aggregation routing management and subVIP subnet routing management: The earth's surface is divided into multiple grids according to longitude and latitude. Each grid has a unique GID and a VIP network segment. The VIP network segment is further subdivided into several subnets called SubVIP network segments, which are used to allocate IP addresses when users register. Each grid is mapped to a satellite cluster, which contains all satellites visible in the grid within a time period. The cluster obtains the corresponding VIP network segment and allocates the SubVIP network segment to each satellite. At the same time, each cluster also has a VMAC, so as to establish a mapping relationship between the ground grid and the satellite cluster in the sky. 3) Loading and publishing VIP network segment routes: The NTN gateway loads the Cluster’s VIP address pool and SubVIP address pool group to all satellites and stores them in the onboard UDM. At the same time, the NTN gateway publishes the Cluster’s VIP network segment to the Internet. The user registration in step S2 specifically includes: The UE sends a registration request message to the onboard AMF; the onboard AMF registers the UE information and then sends a session request to the onboard SMF; The onboard SMF allocates a UEIP to the UE from the SubVIP address pool stored in the onboard UDM, allocates a VMAC and a SIP to the satellite, and then returns a registration response message to the onboard AMF carrying the UEIP, SIP, and VMAC information; After the onboard AMF confirms the registration, it returns it to the UE, and the UE obtains the UEIP address assigned to it and the gateway SIP and VMAC addresses of the onboard router; The satellite switching based on predictive networking control described in step S7 first performs information synchronization of satellite switching based on the ephemeris, and synchronizes the routing information and user connection information on the old satellite to the new satellite. When the satellite moves out of the current Cluster, the switching process will be triggered, and the old satellite will synchronize the SIP, VMAC, UEIP host routing, and UE steady-state connection management information in its UDM to the UDM of the new satellite, so that the routing information and user connection information on the new satellite are consistent with those of the old satellite after the satellite switching, and the user connection is not interrupted.

2. The satellite Internet distributed mobility management method according to claim 1, characterized in that: The information synchronization of satellite switching based on ephemeris is that the satellites in the Cluster corresponding to a Grid are switched every several minutes. Through the preset time nodes and switching rhythm, a 24-hour Cluster set time diagram is obtained to form a predictable satellite switching set, i.e., ephemeris. The control of information synchronization of satellite switching based on the ephemeris specifically includes: Satellite state definition: Four states are defined for satellite switching processing, namely, initial state, routing synchronization state, switching state and switching completion state, to achieve synchronous control of user data and satellite routing during satellite switching; Route synchronization: Route synchronization is divided into Cluster location awareness, Cluster ephemeris cycle awareness, Cluster pre-switching start, route synchronization, data packet forwarding, and deletion of routing information and connection management information to achieve smooth switching of satellites.

3. The satellite Internet distributed mobility management method according to claim 2, characterized in that: The satellite status definition includes: Initial state: When the satellite is about to enter a new cluster, the satellite marks the route as synchronized, which does not affect the data transmission and session of the currently connected users; Routing synchronization state: In this state, the satellite does not accept new user registrations, but accepts users going offline, and synchronizes the user's host routing information and data packets to the new satellite that is about to enter the current Cluster; Switching state: In this state, the satellite actually starts to perform cluster switching operations, migrating current users to the new satellite, and the new satellite can accept new users, including registering the user's context and session information to the new satellite; Switching completed state: In this state, the satellite has successfully completed the Cluster switching operation, all users have been migrated to the new satellite, and the old satellite deletes the previous Cluster information to release resources.

4. The satellite Internet distributed mobility management method according to claim 2, characterized in that: The specific process of the routing synchronization includes: Cluster location awareness: The old satellites in the cluster sense the current geographical location, i.e. SSP; Cluster ephemeris cycle perception: The old satellite perceives the ephemeris cycle of the current Cluster, i.e. TLE; Cluster pre-switching starts: the old satellite starts pre-switching and synchronizes the routing with the new satellite that is about to enter the cluster; Route synchronization: Route synchronization is performed in the onboard core network and the UDM in the ground core network. The synchronized data includes: UE connection management information<Location,MAC,UEIP> , UEIP host routing, satellite<SSP,SIP,VMAC> , SIP / network prefix length and VMAC address, GTP tunnel information; Deletion of routing information and connection management information: The old satellite deletes the data that has been synchronized from the previous Cluster.

5. A satellite Internet distributed mobility management system, the system being used to run the satellite Internet distributed mobility management method according to any one of claims 1 to 4, characterized in that: The system includes a satellite base station, a satellite router, a satellite core network, an NTN gateway and a ground core network, wherein: The satellite base station uses the RRC protocol to manage UE access; The onboard router is responsible for establishing a GTP tunnel with the UPF in the ground core network and forwarding IP data packets; The satellite core network includes AMF, SMF, and UDM functions. AMF is responsible for user registration and mobility management, SMF is responsible for user and satellite IP address allocation and connection management, and UDM is responsible for storing VIP address pools, subVIP address pools, Cluster and Grid location information, and user connection management information. NTN gateway, located on the ground station, is responsible for the interface and data conversion between the ground network including the ground core network and the satellite network including the satellite core network; The ground core network is responsible for mobile Internet data transmission.

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