Optimization Design Of LTP Based On Erasure Code

Features of deep space channel such as long propagation delay, high bit error rate, frequently interruption, differs from the ones of terrisal communication channel, and thease features really challenge the communication system working on the deep space channel. As to communication protocols, these features challenge the working process, feedback mechanism, and error control manner of the protocol. Now days the protocols are widely used in deep space channel are CCSDS Space Communication Protocol Reference Model and DTN protocol stack, and DTN protocol stack can be treated as the extension of CCSDS protocol family in a relay deepspace network or in IPN. LTP is the convergence layer protocol and the transmission protocol of DTN protocol stack and it can provide reliable transmission between tow entities in deepspace channel, but the transmission delay will be huge. The reason of this problem is that LTP uses ARQ mechanism to provide reliable transmission and which will go through a number of retransmission events that having long propagation delay.This paper consider introducing packed–oriented, systematic form long erasure codes into LTP. The sender will send encoded packets and the receiver will not start restransmission process until finishing the decoding operation of the received packets and the decoding process will recover some packets. By means of this, the original ARQ mechanism in LTP has already been replaced to H-ARQ mechanism. Using H-ARQ mechanism in LTP can reduce the retransmission rounds and therefore decrease the total transmission delay.Common used erasure codes are RS codes, LDPC codes, and fountain codes. This paper choose LDPC codes to be the long erasure codes used in LTP because of RS codes have a higher coding and decoding complexity and fountain codes do not have mature theories. This paper keep the segment types of the optimized protocol as the same of the segments of the original LTP, and only modifies the DS and RS structure to convey long erasure codes’ information. And the related information will be stored in the extensions of original LTP’s segments. These works keep a good compatibility for the original LTP and optimized protocol.This paper implements the original LTP and optimized protocol and takes a searies of simulation experiments. The results of experiments show that the optimized protocol has a better performance than the original LTP in transmission delay, and these results validate the effectiveness and feasibility of the optimizing approach. By analyzing the experiment results, this paper has conclusions of suitable condition of the optimized protocol, how different long erasure codes will affect the performance, and the optimal parameters of the optimized protocol. This paper also discusses the reliability of transmitted data and the optimal transmission mode when considering data link layer’s performance.