Research On Distributed Fountain Codes In Deep Space Communicaion

Since the communication distance in the deep space exploration mission isvery far, the received signal becomes extremely weak and propagation delaygreatly increases. The safeguards of end-to-end link based on physical quantitygain become difficulty for future. In order to ensure the reliable communication,Mars missions and the related research have turned to multiplicity of spacecraft permission from end-to-end link. The asynchronous store and forward mechanism ofthe relay orbiter can provide distributed relay transmission for more nodes onsurface of mars. With the development of academic theory, more and more peoplepay attention to distributed digital fountain codes. Fountain codes encode usingdegree distribution, and the original information were randomly dispersed in all theencoded packets. Therefore, for the future multi-rovers can return science datathrough one obiter simultaneously, in this paper, we provide the design of degreedistribution and a randomized decision relaying scheme for distributed fountaincodes, the main research content of this paper is summarized as follows.Firstly, according to the research on distributed LT (Luby Transform) codes,we find that two sources encode using deconvolved RSD and RSD was constructedby XOR at the relay node, in order to recovering all the original information in thesink node by high probability. But RSD need more decode redundancy to recoverall the original information by high probability, which is not suited to deep spacecommunication environment of power limited. Because deep space links easily areinterrupted, the primary goal of remote deep space data transmission is to recoveras much data as possible, rather than to recover all the original information. Thus,we need to improve the traditional distributed fountain codes for meeting thespecial need of the deep space communication.Secondly, in order to ensure the ground station can recover as much originalinformation as possible, we need to design degree distribution at the source node ofdistributed LT codes. Thus, for the future space network scenarios, wheremulti-rovers can return science data through one obiter simultaneously, weproposes a method to decompose weaken robust soliton distribution (WRSD)exploited by relay node into two deconvolved weaken robust soliton distributions(DWSDs), which are used in the sources and have lower average degree thantraditional RSD-based deconvolved soliton distributions (DSDs). When theNDLT-encodes packets are combined at a common relay, the resulted bit streamswhich are transmited to the sink node follow approximate WRSD. The simulationresults show that the proposed NDLT has a higher decoding probability than that of traditional DLT, under the condition of recovering a certain percentage of originalinformation.Thirdly, to improve churn rates of source nodes, the decoding success rate andreduce encoding complexity of distributed fountain codes for Y-network, we designa randomized decision relaying scheme (RDRS), which consisted of forwarding,buffering, XORing and discarding operations at the relay node. The proposedscheme can be suited this scenario, in which the source node randomly is added ordeleted. We provide analytical results about the encoding complexity at the sourcenodes and the relay node. The simulation results show that the proposed RDRS hashigher decoding performance than several distributed fountain coding schemes inrecent years. The improved relaying scheme is presented which has lower decodingfailure probability than SLRC, DLT and RDRS with the total redundancyincreasing.