Compressed Multicast Retransmission in LTE-A eMBMS

Network coded retransmission without soft combining (NC ARQ) has been studied for multicast or for multiple unicast. Some papers also mentioned that the soft combining with NC information will be the proper way to improve the receiving performance. However, some papers didn´t mention the detailed combining procedure, and most papers on soft combining used extrinsic information for iterative decoding. This paper presents two kinds of NC ARQ, and designs three kinds of chase combining schemes on the network coded packets in very detail for LTE-A eMBMS system. This paper will show soft combining with the soft information on all the code bits is more efficient than just using the extrinsic information. Deducing from the basic MAP principle, the NC HARQ schemes designed in this paper are universal for all the modulation types with certain constellation and for all the Soft-In-Soft-Out channel codes. With proper redundancy factor, NC ARQ saves about 25% of retransmission compared with normal HARQ, while NC HARQ saves further, up to 50%.