Cooperation Based Efficient Transmission Mechanism For LEO Satellite Networks

Because of its global coverage,long communication distance and limited terrain restrictions,satellite network plays a vital role in the global communication system.The low earth orbit satellite is close to the ground and the transmission loss is small so it can be applied to the remote sensing monitoring,earth observation and so on.Such applications require satellites to provide broadband data services while ensuring low end-to-end delay.We propose a multi-path cooperative routing based on network coding to provide high network throughput and low end-to-end delay.Multi-path routing can improve throughput performance and end-to-end delay performance of the network by simultaneously transmitting data over multiple paths.Due to the uneven distribution of traffic in satellite networks,cooperative traffic distribution algorithm is proposed to control the number of forwarding packets for each satellite according to the duration of ISLs and length of the queue.Multi-path routing also needs to allocate data among paths and network coding can avoid complex negotiation overhead between paths,thus further improving the performance of the network.Traditional network coding based multi-path routing is not applicable to low earth orbit satellite networks because of its long delay of ISL links.In this paper,we propose a no-stop-wait ACK scheme for network coding in low earth orbit satellite networks.The main contributions of this thesis are listed as follows:1.A formal description of network coding based multi-path cooperative routing is given. Through the formalization of research problems,the research content can not only be more accurately expressed,but also make the research results more general.2.Based on the characteristics of the regular topology,multi-path routing discovery algorithms based on source and destination are designed and developed respectively.The former is a centralized routing discovery algorithm,which can quickly generate the multiple paths.The latter is a distributed route discovery algorithm,which can be easily scaled with the increasing of the size of satellite networks.3.Under the framework of multi-path routing,a cooperative traffic distribution algorithm is proposed.Due to the uneven distribution of satellite network traffic and the dynamic change of satellite position,each satellite has different forward capacities.According to the current queue length and geographical position of each satellite,the source estimates the number of packets that can be forwarded by the satellite,thus improving the network resources usage.4.According to the characteristics of long ISL delay,a no-stop-wait ACK mechanism is proposed to reduce the overhead of waiting for the ACK.Due to the long delay of each ISL,the traditional ACK mechanism causes a very long end-to-end delay in the satellite network.The no-stop-wait ACK scheme makes the network resources be used more efficiently by trading off between delivery ratio and decode ratio.The network coding based multi-path cooperative routing is implemented using NS2 and compared with the representative multi-path protocols and satellite routing protocols.The experiment results show that the performance of the proposed routing protocol is improved in terms of throughput and end-to-end delay.