Optimization Of Space DTN Network Bundle Protocol Based On LDPC Code

The space communication environment faces the problems of long transmission delay,high error rate,frequent link interruption and bidirectional asymmetric data rate etc,this makes it difficult for the traditional TCP/IP communication protocol to work properly.So we need to put forward a kind of network communication protocol which can adapt to the characteristics of this kind of communication environment.In 2002,scientists put forward the DTN(Delay Tolerant Network)protocol system,which is applied to the limited network,as a new type of network architecture.In the DTN protocol,the Bundle protocol adopts the "custody transmission" mechanism,which guarantees the reliable transmission of end to end.But when the space communication environment in the long transmission delay and high bit error rate,although Bundle protocol can guarantee the data reliable for the end-to-end delivery of data packets,often require many times of retransmission,not only increases the file transmission time,but also very be vulnerable to congestion.The performance of LDPC(Low Density Parity Check)code in the AWGN(Additive White Gaussian Noise)channel closes to the Shannon limit,besides very good error correction performance and low complexity,so it is gradually applied to the channel.In this dissertation,the LDPC code will be applied to the Bundle protocol,we hope it to optimize the performance of space communication,to reduce packet retransmission,to improve the utilization of link resources.According to the tranditional transmission process of Bundle,new retransmission mechanism was proposed.According to the retransmission contents of the sender end,we present 2 retransmission mechanism,namely retransmitting original Bundle and retransmitting original Bundle and redundant Bundle,and the file transmission time of each retransmission mechanism is analyzed and deduced.Experiments show that when the space network path is short(ms level),and the packet loss rate is high,the new proposed method has very good performance,besides we find a critical delay point in the three transmission mechanism.When the transmission path is less than that value,the performance of traditional Bundle transmission mechanism is better.When the transmission path is greater than this value,the performance of retransmission mechanism is better.In this dissertation,the release rate of the node memory in the BP(Bundle Protocol)layer is studied.Based on this,a new release model of the LDPC code combined with the BP layer is proposed,And 3 kinds of the release of memory storage are simulated.Experiments show that the Bundle protocol combined with the LDPC code,the release rate is significantly accelerated.