Research And Application Of Rateless Codes In NGB-W System

With the rapid development of wireless broadcast and multicast service, the traditional transmission technology could hardly meet the demands. As a new type of adaptive codes designed for the broadcast service, Rateless Codes have significant advantages such as low cost and low complexity of encoding and decoding. The next generation broadcast (NGB) system will be the future network for broadcasting system in China. In order to improve the data transmission efficiency in the NGB wireless network (NGB-W) system, this paper focuses on the application of Rateless Codes in the NGB-W system. In this paper, a new class of feedback Rateless Codes and cooperative Rateless Codes are proposed for two different networking schemes of NGB-W system.In this paper, the developing process, characteristics, research orientations and achievements of the Rateless Codes are introduced firstly. Then, the LT codes are used to analyze the encoding and decoding process, different kinds of degree distribution functions and several kinds of decoding algorithms. The discrete degree distribution function and BP soft decision decoding algorithm are adopted in the following research. Addionally, to improve the decoding efficiency, joint coding of Rateless Codes and common error-correcting codes which is the combination of LDPC codes and Turbo codes is achieved.Then, two types of feedback schemes are provided according to the different network structure of NGB-W system. The indexes of original packets with large degree value will be fed back in the case of large area broadcast network. However, in the case of bidirectional communication network, indexes of all the original packets will be fed back. Simulation results show that the proposed Rateless Codes with feedback have better BER performances in the both networks than the Rateless Codes without feedback. Furthermore, in order to avoid the feedback storm, the modified users grouping method is considered, and two consolidation modes for feedback information are proposed. In addition, the effect of the service priorities on the performance of the feedback system is discussed.At last, two types of cooperation modes based on users and base stations are established respectively, and in order to reduce encoding complexity, a simplified implementation of discrete degree distribution function for the multiple relay coordination schemes is also introduced. Simulation results indicate that cooperative Rateless Codes can effectively improve the quality of service for the edge users. Additionally, the simplified degree distribution function can reduce encoder complexity significantly and speed up the decoding process effectively.