Adaptive modulation for completion time minimization in wireless broadcast networks

In this work we study the effect of hierarchical modulation on completion time minimization in wireless broadcast channels. Time needed to transmit all bits intended for a particular user is defined as its completion time. In this work we investigate minimizing the maximum completion time over all users in a broadcast channel using hierarchical modulation. We compare time division, opportunistic scheduling, and three different adaptive modulation schemes: rate adaptive hierarchical modulation assisted transmission (HA), modified HA (MHA) and optimal HA (OHA). While HA aims at maximizing total throughput, OHA minimizes the maximum completion time, and MHA provides an intermediate solution. It is observed that OHA always chooses the best superposition order and the constellation size to minimize the maximum completion time.