Research On Reliable Transmission Based On Network Coding In Aerospace Relayed Network

The relay satellite system between the user spacecraft and ground stations is able to effectively alleviate the problem of limited ground network coverage and provide users with data relay service, which plays a pivotal role in aerospace communications. However, there are serious delay and packet loss ratio and other inherent shortcomings in space relay network, which makes it challenge to achieve reliable data transmission. In order to solve the problems above, in this paper, we intend to study and achieve the method that uses network coding(NC) to improve the transmission reliability of relay satellite link.In this paper, we use the idea of reliable transmission of network coding to design a transport protocol for aerospace network after analyzing the existing methods of enhancing transmission reliability and the characteristics about aerospace link. In the protocol, network coding is an independent sub-layer added between the network layer and data link layer of the original TCP/IP protocol. It sends redundant packets at the network coding layer to cover occurs of packet loss that is perceived by TCP and reduces the frequency of its access to congestion control so that it can enhance the transmission performance of TCP in aerospace network. To further reduce coding latency, we design a sparse part network coding scheme after optimizing the traditional network coding combinations we have. It can enhance the codding and decoding speed effectively by reducing the times of operation on the original packet. When the coding window size is 4, generation size is 50, the encoding and decoding speed of sparse part network coding scheme is 5.88 and 6.60 respectively compared with part network coding. In redundancy, we design an adaptive control algorithm whose redundancy factor can be changed through real-time monitoring the status of channel packet loss to control the amount of redundancy packet. When the packet loss decreased we reduce the amount of redundancy packet and can make full use of channel resources.In the end, we build an actual system testing environment to test our design. When packet loss rate is 1%, RTT is 100 ms, and transmission bandwidth is 100Mbits/s, the throughput can still achieve 69.2Mbits/s, while the traditional TCP(Vegas) can achieve just 0.87Mbits/s, which is improved by 78.5 times. Thus, the designed protocol can ensure the transmission reliability and effectively improve the system throughput simultaneously, making relay satellite system can provide more reliable and efficient service for users.