Throughput Optimal Multi-User Scheduling via Hierarchical Modulation

We investigate the network stability problem when two users are scheduled simultaneously. The key idea is to simultaneously transmit to more than one users experiencing different channel conditions by employing hierarchical modulation. For two-user scheduling problem, we develop a throughput-optimal algorithm which can stabilize the network whenever traffic load is stabilizable (i.e., it is within the achievable rate region.) In addition, we analytically prove that the proposed algorithm achieves larger achievable rate region compared to the conventional Max-Weight algorithm which employs uniform modulation and transmits to a single user. We demonstrate the efficacy of the algorithm on a realistic simulation environment using the parameters of High Data Rate protocol in a Code Division Multiple Access system. Simulation results show that with the proposed algorithm, the network can carry higher traffic load with lower delays.