Performance analysis of IEEE 802.16 multicast and broadcast polling based bandwidth request

Recently, IEEE has standardized the 802.16 protocol for Wireless Metropolitan Area Networks. In the point-to-multipoint (PMP) mode of the medium access control (MAC), the subscriber stations (SSs) request bandwidth based upon unicast, multicast and broadcast polling by the base station (BS). Polling is the process by which the BS allocates to the SSs bandwidth specifically for the purpose of making bandwidth requests. The SSs contend for the transmission opportunities which are allocated by the BS when they want to transmit the bandwidth request. Generally speaking, the contention intensity heavily influences the network performance. However, no attention is paid to investigate the impact of the system parameters to the utilization of transmission opportunity. This paper provides a simple, but nevertheless accurate, analytical model to compute the utilization of transmission opportunity, in the assumption of finite number of subscriber stations and ideal channel conditions. The proposed analysis applies to multicast and broadcast polling mechanisms. The analytical results match with the simulation results very well and the performance evaluation reveals that the utilization of transmission opportunity mainly depends on the initial contention window size, the network size and the average number of transmission opportunities in one frame. The simulation data also show that multicast polling can achieve higher utilization than broadcast polling especially when the network size is large.