Research On Digital Fountain Codes And Their Applications

In recent years, with the rapid development of the Internet, the packet network has been playing leading role in data transmission. In order to protect the transmission of information, the error control coding technique has been applied to lots of applications. The retransmission mechanism based on TCP is applicable in most scenarios except for some specific cases such as broadcast transmission. In this situation the sender needs to keep track of the reception of every individual receiver and handle the requirement for retransmission. It may reduce the efficiency if the channels between sender and receivers are bad. Different with the physical layer FEC, the application layer FEC in which the packets are be encoded and decoded in the application layer provides protection for data packets. The receiver can recover all the information packets with a great probability as long as the number of encoded packets that it has correctly received is slightly larger than that of the original information packets. This thesis focuses on the research of key technologies and applications of the digital fountain codes.Firstly, this thesis studies two major digital fountain codes, i.e., LT (Luby transform) codes and Raptor codes. We describe the encoding process with the degree distribution and the BP decoding algorithm of LT codes. The performance of LT codes under different lengths and decoding methods is shown in this thesis. The principle of Raptor codes is described and we give a detailed description of the coding and decoding process of R10 Raptor codes according to IETF RFC 5053. The performance of R10 Raptor codes over erasure channels is given in this thesis, along with the performance of LT codes with Gaussian elimination decoding algorithm.Additionally, the distributed LT codes applied to the multiple-access relay networks are investigated. We introduce the network model and the original scheme of distributed LT codes, i.e., DLT, along with the coding method adopted by the sources and the operation carried out at the relay. Performance comparison between DLT scheme and traditional LT scheme is given in this thesis. So far, several efforts have been devoted to constructing well-performed LT codes for multiple-access relay networks and we give a detailed description of the SLRC scheme and ISLRC scheme. And then we propose a novel approach named hybrid soliton distribution coding (HSDC) scheme, which is specially optimized for the scenario where source-relay links are subject to erasures. We develop a kind of new degree distribution by exploiting the properties of the RSD and the DSD and design a practical encoding algorithm for the relay. Moreover, we utilize the AND-OR tree analysis to study the asymptotic performance of our proposed HSDC strategy. The simulation results show that the proposed HSDC noticeably outperforms conventional schemes under lossy source-relay links with equal and unequal erasure probabilities.Furthermore, a hybrid method in which the R10 Raptor codes are adopted in LTE system to protect data transmission is proposed. We investigate the code block segmentation and HARQ process as they are relate to the method. The method is described in detail and the performance comparison between this method and original LTE scheme is given. Simulation results show that the probability of correct transmission increases significantly and about 0.25 to 1.25dB performance gain can be achieved in some specific scenarios with this method.Finally, we study a network coding method in the star network as it is a fountain scheme. We introduced the network model and data transmission service. Then two different methods, i.e., RLNC and TDMA are analyzed separately to obtain the optimal values for the adjustable parameters. The theoretical result and simulated result of the two methods is also given in this thesis and the best performance of RLNC scheme can be achieved by setting the adjustable parameters to the optimal values obtained from theoretical analysis.