Applications Of Raptor Codes In Video Communications

In recent years, the multimedia applications over IP networks, such as video on demand, IPTV, are becoming increasingly widespread. The phenomena of packet loss is unavoidable for IP network, so an error control strategy, which is used to improve QoS of multimedia applications, has been one of an important issue. Common error control strategy that used to overcome packet loss include automatic repeat request (ARQ) and forward error correction (FEC). ARQ is based on the cost of delay and throughput for transmission reliability ,and is not conducive to real-time multimedia data transmission in IP networks. As a flexible, scalable erasure codes, Fountain codes has drawn increasing attention in academia and industry. In this paper, we focus on the second practical realizations of Fountain codes--Raptor codes. Specific tasks as follows:Firstly, after illustrating the background and status, this paper gives a brief introduction to the concept of erasure channel and erasure codes, and next systematically introduces several common erasure codes, including RS codes, LDPC codes and LDGM codes, among which we lay emphasis on LDGM codes.Secondly, on the base of researching the codec algorithm of LT codes, we propose an implementations of Raptor codes with a concatenation of LDGM codes and LT codes. Then we discuss the factors that influencing the performance of Raptor Codes, including the degree distribution, the pre-coding scheme and pseudo-random number generator. Last, the realization of The codec algorithm of Raptor codes is given in the form of C language, and a simulation experiment is held to measure the performance of Raptor codes.Thirdly, we propose an unequal error protection strategy based on Raptor codes, which privides higher priority data with strong degree of protection and privides lower priority data with strong degree of protection, in order to achieve the purposes of prividing unequal error protection for different priority data. The simulation result shows that the proposed unequal error protection strategy based on Raptor codes can restore larger number of the higher priority data.Finally, against packet loss of video transmission in IP network, we take Raptor code as the application layer erasure codes, provide an error control strategy for video transmission system, and then give a detailed description of system design and system implementation. The implementation result shows that the video transmission system with Raptor codes is running well, which can overcome the packet loss effectively and improve the playback quality significantly.