Multicast Transmission for Asynchronous Data Requests

This paper considers a two-user asynchronous multicast scenario where both users request the same content at different time instances, and a base station simultaneously serves them with nonorthogonal transmission. To serve the asynchronous requests of the same content, we develop three nonorthogonal transmission schemes. The first scheme serves the asynchronous requests by unicast transmission and the second scheme enables multicast transmission for the asynchronous requests based on interference decoding capability at receiver. The third scheme combines the first and second schemes. For the three proposed schemes, we formulate completion time minimization problems that aim to minimize the time required to complete serving users, while ensuring a given quality constraint of streaming content. For each scheme, the feasibility condition in terms of transmit power and optimal rate control are investigated. In addition, we analytically compare the performance of the proposed schemes, and additionally, propose an opportunistic transmission that opportunistically switches three proposed schemes depending on the channel and power conditions.