Multicast Transmission Optimization over Hybrid DVB-SH Systems

Research interest related to hybrid networks for mobile users has rapidly evolved in order to extend service to all users. In particular, DVB-SH provides an efficient way of carrying multimedia services over hybrid satellite and terrestrial networks for a big diversity of terminals. Also a variety of possible hybrid system architectures can be chosen due to the two different physical layers specified: OFDM and TDM. Although DVB-SH has been designed for broadcast transmission, we propose to use it for multicast applications, which is more competitive over satellite systems. New system techniques implemented in the hybrid scheme, such as ACM and resource allocation, make the system strongly dependent on the channel conditions. Thus the capacity optimization in a multicast scenario becomes a powerful research challenge, mainly in mobile scenarios. In this paper, we aim at optimizing the multicast transmission over the satellite link and the terrestrial link of a DVB-SH based system. The architecture proposed includes resource allocation techniques depending on the scenarios considered (mobility and transmission mode). We first investigate a Hierarchical Allocation algorithm based on SC (HA-SC) for the OFDM air interface of DVB-SH, which is constrained to serve a minimum rate to all users. We later propose a Time Scheduling (TS) algorithm, more appropriate for TDM satellite-based systems, which finds the optimal number of users to be served in order to achieve the highest throughput in the multicast group. We show that with the TS algorithm, the spectral gain is 20-40% with respect to the worst case user. Moreover, the HA-SC is more suitable for the satellite since it outperforms TS in 300%.