Distributed Network-coded Fountain Codes In Deep Space Dynamic Topology

Since the beginning of the 21 st century,the great idea of Interplanetary Internet provides important supports for deep space exploration and investigation.At present,power nations including the United States,China,Russia,and Europe are all exploring the structure of the Interplanetary Internet.In many deep space exploration activities,the "Earth-Mars" Interplanetary Internet becomes a hot spot.In April 2016,China’s Mars exploration mission has been formally established,and the goal is to achieve "surround,landing,inspection" in a one-time task in 2020.The relevant project is being developed,and China’s first Mars detector is expected to launch in 2020.At present,the main business of "Earth-Mars" communications include large amount of scientific research data and high-definition images.The traditional point-to-point transmission cannot satisfy the large-scale data transmission because of long transmission distance,huge delay and poor channel quality.The emergence of orbiting relay satellites provides a great deal of convenience for data transmission.On the one hand,relay satellites provide energy gain for data transmission,in order to combat the path losses caused by long-haul transmission.On the other hand,relay satellites can provide available links when the planetary revolution causes point-to-point direct links to be unavailable,which increase the effective transmission time.In this paper,a dynamic topology network consisting of multiple Mars Landing Detectors,periodic mobile relay satellites and groun d stations is established.Based on the rateless characteristic and forward correction characteristic of fountain codes,an asynchronous network distributed fountain code is designed.Moreover,the unequal protection transmission mechanism is studied to ensure the high reliability of the important data,which improve the flexibility of deep space communication.The main research work of this thesis includes:Firstly,based on the analyses of the actual network architecture of "Earth-Mars",a dynamic topology network model based on multiple access relay network is established,and the functions of each node in the model are explained.The importance of LT codes to deep space communication is proved by analyzing the theory of LT codes.It is determined as the main coding method in this thesis.The analysis of network coding proves the importance of network coding to relay satellites.Which determine the operation mode of the relay satellite.Thus,it is determined to use distributed fountain code in this thes is.Then,a cooperative scheme of distributed fountain codes is proposed for the dynamic network model,and the different characteristics of its primary and secondary links are optimized.And-Or Tree analysis is used to derive the asymptotic decoding performance formula.Compared to the existing programs "forward" operation,"XOR" operation and Soliton-like fountain code cooperation,higher successful decoding probability and system throughput are obtained with the same redundancy.System utilization is improved,and resources are saved further.Finally,a scheme of unequal protection based on weighting method is designed for the cooperative scheme of distributed fountain codes.The asymptotic decoding performance formula of different important information i s deduced by AND-OR tree analysis and simulation is also provided.The scheme improves the transmission reliability of the important data and completes the preliminary exploration of the unequal protection distributed network fountain code in the dynamic t opology.