NACK-based retransmission schemes for MBMS over single frequency network in LTE

In this paper, we propose NACK-based retransmission schemes for multimedia broadcast and multicast service over single frequency network (MBSFN) in LTE systems to enhance goodput and reduce retransmission rate. It is known that more retransmissions in MBSFN will reduce the spectrum efficiency. Hence, to provide a reliable broadcast/multicast service in LTE systems is an important issue. We first group mobile users into three sets according to their SNRs. Each set can report NACK messages on dedicated or shared feedback channel. The retransmission is triggered by pre-defined probability or pre-defined threshold. By applying different retransmission trigger schemes on different feedback channels, we have four kinds of NACK-based retransmission schemes. Simulation results show that, the proposed retransmission schemes can enhance the goodput by up to 28.3% and reduce the retransmission rate by up to 37.8% compared to the conditional HARQ scheme [12].