Research On Datagram Routing Protocols In LEO Satellite Networks

LEO(Low Earth Orbit) satellite network is a kind of constellation network composed by certain number of LEO-communication-satellite nodes. The LEO satellite network has the characteristics such as wide coverage, shorter round-trip delay, low communication power consumption from user terminals to satellites, and high efficient reuse of radio spectrum. It provides an effective solution for global real-time and seamless information transfer service. With all the features, the LEO satellite network has a broad application prospects and research value on areas such as video-on-demand, multimedia broadcasting, telemedicine, tele-education, high-speed Internet access, and so on.The core technology of LEO satellite network to carry Internet data communications lay on the routing technology, which plays an important role on the efficient real-time delivery of information. However, the LEO-satellite network has its own limitations, which includes: the network topology and the access connections between the mobile user and the satellite are always changing; the processing capability and power consumption of each satellite is limited; and the hardware resources of satellite can merely be upgraded. Therefore, implementing an efficient datagram routing in the LEO-satellite constellation based network is an exoteric challenging research topic. Addressing the problems above, this dissertation focuses on the LEO satellite network routing protocol design in reality, with in-depth study carried out on the mobility management, unicast and multicast routing and other key technologies. The main achievements and contributions are as follows:1. We propose a GEO(GEostationary Orbit) satellite-aided mobility management protocol called GSAMM(GEO-Ssatellites-Aided Mobility Management).In order to achieve point-to-point datagram forwarding, the mobile communication network should be able to do not only routing function but also mobility management to update the location information in response to user mobility, and to ensure the continuity of an on-going connection. The relationship between mobile user node and the accessing satellite keep on changing, and there are some special areas such as "seam" area and Polar Regions, in which the space-based mobility management of LEO satellite network will induce great communication overhead due to binding update and locating. To solve these problems, the GEO-Satellite-Aided Mobility Management(GSAMM) is proposed. GSAMM utilizes the GEO satellites to complete the major work of mobile management, taking advantage of the large coverage of GEO satellites. Meanwhile, a local distance-based location updating algorithm is proposed as well to reduce the complexity and signaling overhead of mobility management procedures. In the proposed scheme, the LEO satellites are only responsible for the auxiliary work, and the overlap problems that whether the location area overlaps with the coverage area of current satellite, and also overlaps with its neighbor LEO satellite coverage are eliminated in our proposal. Furthermore, the neighboring LEO satellites have no necessary to interact with each other’s coverage information, thus it greatly reduces the mobile management overhead of the LEO satellite nodes. Experimental results show that compared with other related work, our proposal can reduce more than 70% administrative overhead.2. We propose a distributed routing protocol based on relatively-unchanged attributes of users – RBRUAU(Routing Based on Relatively-Unchanged Attributes of Users).Due to the time-varying topology characteristics and the always-changing access connection between the mobile user and the satellite, it is difficult to implement a point-to-point routing protocol for LEO satellite network because it is hard to maintain routing information consistent with network topology and the relationship of access connections. To address this problem, a new distributed routing protocol called RBRUAU is proposed. RBRUAU is based on a location-based routing algorithm that the need not to maintain the consistency of routing information, and it can be quickly adapted to the network topology changes, and it has a smaller signaling and processing overhead, and good scalability. In RBRUAU, firstly, it classifies the local maximum situations for the location-based routing algorithm; then, it utilizes the satellite network topology regularity, and combines the relatively-unchanged attributes of users and trajectory-based forwarding method to dealing with different types of local maximum problem. Experimental results show that compared with datagram forward delay of the shortest path between two mobile nodes, the average delay of the proposed routing protocol increases less than 9.2%.3 We propose a group-members position based multicast routing protocol-GMPBMR(Group-Members Position Based Multicast Routing).The time-varying topology and the always-changing access connections of LEO satellite network introduce difficulties to implement a multicast routing protocol in LEO satellite network as well; because it is difficult to maintain multicast state information. To solve this problem, a new multicast protocol called GMPBMR is proposed. The proposed protocol does not need "multicast tree" to forward multicast datagrams. Instead, GMPBMR divides satellite nodes of LEO satellite network into clusters according to the satellite-orbital planes, and the group user and the satellite relationship changing information is limited among the satellite nodes in the cluster; using location-based routing multicast datagrams, GMPBMR can quickly adapt to network topology changes. Since GMPBMR eliminates the overhead of maintaining multicast state information and utilizes the location-based routing algorithm to forward multicast datagrams, it has a smaller signaling and processing overhead and better scalability. Experimental results show that compared with other related work, our proposal can reduce more than 20% of the average delay of the shortest-path from the multicast source to the end user node.