Research On Rateless Code Based File Delivery Protocols In Deep Space Communication

Deep space exploration is the most important and inevitable space activitiesto explore the origin of the universe and expand human living space. The deepspace communications systems is the only connection between space probe andground systems. So the development of deep space communications technologydirectly affects the improvement of deep space exploration. The collectedinformation is stored in the form of files before sending to receiver in deep spaceexploration mission, so the merits of the file transfer protocol directly determinesthe performance of deep space communication systems.Due to the extremely long propagation and very high packet loss ratio indeep space communication，the performance of the existing TCP(TransmissionControl Protocol) is very poor in this situation, and it cannot meet the basicrequirements of deep-space communications. Besides, the performance ofCFDP(CCSDS File Delivery Protocols) exhibited excellent performance in someshort delay and low packet loss ratio channel environment. However, when thechannel propagation and packet loss rate increased to a certain threshold, CFDPhave to send more and more information to recovery the lost packets. So the filetransmission of CFDP delay has significantly increased.It is obviously that the reason caused the performance of file deliveryprotocols decreased is the retransmission of feedback information. So thetechnology based forward error correction codes can be introduced to filedelivery protocol to reduce the number of feedback. Combining the research asfront, this paper proposed a kind of LT codes based file delivery protocol to solvethe problem of performance decreased caused by the high packets loss ratio andlong transmission propagation. It can reduce the transmission time of the filedelivery task and improve throughput of the communication link. Before thestarting of design LT-P protocol, this paper analysis the factors that may affectthe performance of LT-P, including the selection of the decoding algorithm andthe degree distribution function and the overhead of decoding progress and so on.Finally, this paper built up the deep space communications test bed for filetransfer protocols, including TCP, CFDP and LT-P. From the result of the test bed,we found that in the single transmission path delay longer than the1s, TCP hasthe worst performance. When the single path transmission delay and packet lossrate of were less than a certain threshold, as the LT-P protocol still needs to sendmore additional overhead to ensure that the probability of successfully decoding,So the performance of CFDP protocol is better than LT-P protocol; However, in the large path in the transmission delay, as CFDP protocols need to send morefeedback of retransmission, so the performance of CFDP significantly decreased.And LT-P protocol showed the best performance at this time.