Performance Evaluation of Contention-Based Access in IEEE 802.16 Networks with Subchannelization

IEEE 802.16 wireless networks, known as WiMAX, employ a mechanism for guaranteed time allocation to mobile stations in order to meet the different quality of service requirements for service flows. The base station allocates contention-based time slots for the stations to transmit their requests for additional bandwidth. Each contention time slot can accommodate a single transmission if there is no sub-channelization or multiple concurrent transmissions if the base station enables sub-channelization during the contention period. For transmission during this period, each station employs a contention-resolution mechanism. In this paper, we develop an analytical model for the bandwidth request and resolution mechanism during this contention period when sub-channelization is employed. The model is shown to accurately model the contention period when sub-channelization is enabled. Performance metrics, such as throughput and capacity, show that adding more subchannels to the contention time slots increases both the throughput and the capacity of the contention period carrying more successful bandwidth requests. Simulations with different parameter sets are carried out to validate the proposed model.