Research On Coding And Decoding Technology Of Fountain Codes

After more than half a century development, the field of deep space exploration made many remarkable achievements. The development of deep space communication opens the way for the exploration of deep space. It provides the guarantee for the development and utilization of space resources, at the same time, the rapid development of deep space exploration makes the human’s visual field more and more abroad and also increases its communication technology requirements. The extremely remote communication distance and complex noise environment make the traditional error control scheme not suitable for deep space communication system, for example ARQ and HARQ, M.Luby proposed the digital fountain code whose greatest feature is that the rate is not fixed and it requires no feedback compared with the conventional channel coding, so it applies very well in deep space communication system.Digital fountain code works in data link layer, each of the encoding packet carries on the overall protection of the source of data, and every data packet loss in the transmission process can be recovered by the receiving data packets according to corresponding rules. Similar to the broadcast mode, the sending node continues to send data packets, in the transmission process, the packet constantly being discarded under the influence of the channel noise and other factors, however, the destination node can complete recovery all the source informationas long as it receives a certain number of packets,therefore, the transmission scheme based on the fountain codes need no feedback mechanism, it is suitable for large time delay and long distance communication of deep space communication system. At the same time, the proposal of the distributed transmission scheme based on the digital fountain codes, with shorter length and lower complexity of coding in the relay (especially the middle load limited space) whose performance is better than the normal fountain code. It provides a strong guarantee for further implementation of reliable communication in deep space environment.The related technology of fountain code is analyzed under the background of deep space communication in this thesis. Firstly the basic principle of the fountain codes and distributed fountain codes is analyzed and simulated according to the characteristics of deep space communication.Then considering the different priority source of information, according to the traditional end-to-end and distributed communication model, we analyzed the different unequal error protection strategy of important information, and simulated the transmission performance of unequal error protection strategy in image compression coding standard, confirmed the effectiveness of its protection strategy. Finally, considering the scale-free network has the characteristic of the minimum average path length, we introduced it to the fountain codes degree distribution algorithm, designed the scale-free fountain codes with better decoding performance which is confirmed a better transmission performance through the simulation in the distributed system environment.