Optimal Opportunistic Multicast for Minimizing Broadcast Latency in Wireless Networks

In this paper, we study opportunistic multicast scheduling (OMS) in a wireless network with a central base station (BS) broadcasting a common packet to multiple users with different instantaneous channel conditions. Our objective is to minimize the broadcast latency, which is defined as the total transmission time required for all intended users in a multicast group to receive the packet. Based on the instantaneous channel conditions, BS can send a packet at different transmission rates. Sending at a higher rate allows a shorter packet transmission time, but only a limited number of users with sufficient channel quality can receive the packet. To reach all users in a multicast group, the packet must be transmitted multiple times. We can see that the broadcast latency depends on the transmission rate used and the number of transmissions required. In this paper, we formulate the problem of minimizing broadcast latency as a dynamic programming problem, and a close-loop optimal opportunistic multicast scheduling scheme (OOMS) is derived.