Joint drift analysis for multigroup slotted ALOHA: stability with maximum utilization

In this paper, a slotted ALOHA system is considered where the users in the system are divided into two power groups. At the mobile base station, members of one group are received at a higher power level than those in the second group. This power division can be used to increase the overall throughput of the ALOHA system from 0.368 to 0.53. The two-group ALOHA system is stabilized by extending the idea of joint drift analysis, originally devised for a single group to the two-group case and the paper proposes a criterion for choosing a set of control parameters. The control parameter selection criterion guarantees one stable equilibrium point for each group, which enables the system to operate at the maximum throughput point. Combinations of the "optimal" control parameters are used to update the estimated number of users in the backlog, which is required in calculating the retransmission probability for users in each group. Simulation results demonstrate the superiority of the proposed control strategy over existing stability schemes.