A Novel Retransmission Scheme for Hierarchical Modulation Based MBMS

In this paper we focus on efficient retransmission strategy for MBMS that employs hierarchical modulation. Hierarchical modulation offers a mechanism to enable the transmission of several data streams on one single frequency channel, with different transmission qualities, which requires more efficient HARQ strategy for MBMS. Constellation rearrangement and symbol bits rearrangement based HARQ are two kinds of methods to improve the efficiency of MBMS transmission from the perspective of constellation diversity. To further improve the performance, we proposed a novel retransmission method, including two constellations designed for transmission and retransmission, the transmitter algorithm to select the constellation to be used based on feedback information and the receiver algorithm to combine the retransmission packets. The merit of the proposal is to obtain the benefits from constellation rearrangement and symbol bits rearrangement simultaneously via once retransmission so as to save retransmission number, resulting in improved spectrum efficiency. Simulation results show our algorithm can provide about 21.5% cell throughput gain and 23% cell edge throughput gain than other HARQ methods.