Research On The Efficient File Delivery Strategies For Deep Space Communications Network

Deep space communications is an important component to guarantee the successful implementation of space scientific activities.As deep space exploration missions become more fine-grained,payloads performance constantly continues to improve,and infrastructures gradually increase.In addition,diversified services,massive scientific data,and networked transfer shape the development trend of deep space communications,and greatly challenge the improvement of data transmission efficiency.This dissertation aims to address the development trend and the need of deep space communications,on a basis of transmission performance restricted by long distance,time-variant,and multi-hop transmission systems.By means of optimization of transfer mechanisms for CFDP(CCSDS File Delivery Protocol)and LTP(Licklider Transmission Protocol),CFDP-based double retransmission deferred NAK(Negative Acknowledgement)protocol is proposed.In additon,an adaptive transmission strategy of CFDP matching time-varying channel is designed.LTP asynchronous accelerated retransmission scheme and multi-sessions data aggregation method are also given.The transfer mechanisms and optimization methods of deep space file delivery protocols are expl ored.The data transmission efficiency in deep space environment is enhanced.Main research issues of this work are as follows:Firstly,the dissertation studies the effective transmission problem of CFDP in AWGN(Additive White Gaussian Noise)channels.On the basis of Ka-band channel characteristics and channel modeling methods,considering the problem of too long file transfer time caused by long delay and frequent retransmission,the transmission procedure of CFDP deferred NAK mode in AWGN channel is mod elled and the transmission model is validated.It is found that the file delivery time under deep space environment is dominated by the propagation delay and retransmission spurts.Based on the constructed network model and transmission model,CFDP double retransmission deferred NAK transmission strategy is proposed.In GEO(Geostationary Earth Orbit),cislunar and cismartian scenarios,transmission performance is compared to verify the proposed protocol,whereas communication links are characterized by long distance,and high packet loss rate.Secondly,the dissertation studies the adaptive transmission of CFDP protocol in deep space time-varying channels.Ka-band transfer will be widely used in future deep space communications,while the quality of communi cation is seriously infulenced by rain attenuation.Since the poor performance of CFDP is caused by the time-variant of channel,both time-varying channel model and weather forecasting model are therefore established.An adaptive transmission strategy base d on feedback channel state is designed.Combined with a weather forecasting model,the transmission strategy is modelled as a partially observable Markov decision process.The optimality of strategy and its selection principle are proved,and the existenc e of thresholds and the space of alternative strategies are determined.The gains in closed-form are given for the one or two threshold strategy,and the optimalities of transmission strategy under two threshold strategies are verified using value iteration algorithm.In a cismartian scenario,the effectiveness of adaptive transmission strategy is tested by comparisons of four transfer schemes in deep space time-varying channel.Thirdly,the dissertation studies the asynchronous accelerated retransmission issue in an LTP session.As LTP inherited the design idea of CFDP deferred NAK mode,in view of the problem caused by the deferred mechanism in extremely long link that the retransmitted data cannot be timely recovered,the transmission procedure of an LTP data block is modelled under an AWGN channel.Based on the validation of transmission model,the mechanism of LTP single session and the factors restricting the transmission of data block are analyzed.For recovering the lost data sooner,an asynchronous accelerated retransmission scheme triggered by receiver is proposed.The expected transfer time of five kinds of asynchronous accelerated retransmission cases are derived,and performance of asynchronous accelerated retransmission scheme is analyzed under both cislunar and cismartian scenarios,which can speed up retransmission start and shorten file transfer time.Finally,the dissertation studies the LTP multi-sessions transmission and data aggregation issue.Because of the precious deep space channel,aim ing at the low channel utilization in LTP single session transmission,multi-sessions transmission mechanism using multiple concurrent sessions to improve channel utilization is put forward.By joining link asymmetric characteristics and multi-sessions transmission mechanism together,an LTP multi-sessions data aggregation method is designed.Based on the modeling of multi-sessions data aggregation process and the numerical simulation of the factors restricting the data aggregation,the lower bound of the aggregation number and the principle of data aggregation are given.The effect of EORP(End of Red-Part)loss on the delay of reception report is simulated,and the delay mechanism of data segment loss to the reception report is clarified.