Research And Application Of Improved Raptor Codes In MBMS

With the multimedia mobile communication business,diversified, personalized development and data business emerge in endlessly,3G gradually replaced the2G and will be replaced by the4G. Although3G network brings us a wider bandwidth and faster data transfer rate, however, each user must be assigned an independent channel for data transmission without change. The nature of mobile operators have to be of the base station each user is assigned a dynamic, non-interference in each other’s information transmission channel. When communication carrier sectors are in increasing the number of users, the limited bandwidth will eventually run out. Not only using a mobile phone TV such large capacity data transmission can not be achieved, and even ordinary voice calls will be seriously affected. MBMS(Multimedia Broadcast/Mutticast Servicee) happenes at the moment, becomes a new hot spot of mobile communication. This paper first states the Raptor codes encoding and decoding principles, then studies the MBMS protocols and mechanisms. Finally improvements on Raptor code are provided, and the improved Raptor as MBMS forward error correction code is studied. Improved Raptor codes in MBMS are provided. Specific content is as follows:Fist,study the production of fountain codes and the process of the improvement. It mainly states LT codes encoding and decoding principles and the choice of the degree distribution, Raptor codes decoding process on the base ofLT.Second, study protocols and mechanisms on multicast and broadcast service. Framework, hosting services management and customer service in MBMS have been made the detailed elaboration to.Third, Raptor code is one of the best performances of fountain codes, and is developde on the basis of LT code compiled with linear complexity improvement. In this paper, an improved Raptor decoding algorithm of3GPP MBMS FEC codes is presented. An Improved Algorithm introduces enhanced generator and pre-coding relationships (i.e., a two-stage pre-coding algorithm using LDPC and HDPC codes). A modified in the second encoding step of a new algorithma, more efficient encoding process than this of Raptor, is applied in order to generate the encoding symbols. The key change between the two FEC schemes is that the enhanced new code introduces the use of arithmetic operations on octets, i.e., the GF(256), while the standardized Raptor code operates over GF(2).Finally, we provide several simulations on the relationship between service coverage and AL-FEC transmission overhead, between total number of retransmitted packets and AL-FEC transmission overhead,between tune-in delay and service coverage in the the ns-3environment. Through the experimental results, different performances can be seen among the ideal of fountain codes, Raptor, improved Raptor code.The results demonstrates that an improved algorithm improves the service coverage and decreases total number of retransmitted packets and tune-in delay,so the new one enhances reliable multicasting.