Joint Power and Constellation Size Adaptation for Mobile Multicast Employing MQAM Over Wireless Fading Channels

We propose a power and constellation-size adaptation scheme for the multicast system employing multilevel quadrature amplitude modulation (MQAM) with discrete constellation sizes, which aims at achieving high multicast goodput over wireless fading channels. Specifically, we formulate the optimization problem to maximize multicast goodput via adaptive transmission-mode selection, including power and constellation-size adaptation, and then solve for the optimal adaptation policy through two steps. We first investigate the goodput variation with the transmission-mode selection and equivalently convert the optimization problem into a concave-like form by introducing the concepts of effective marginal goodput gain (EMGG) and adjacent EMGG. Then, we derive the optimal transmission adaptation policy by using a global adjacent EMGG threshold. Finally, simulation results are provided to show the significant multicast goodput improvement gained by applying the optimal power and constellation-size adaption.