Date Added: Mar 2012
The authors 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, they 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, they 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.