Enhancing access technique for non real time services in 802.16 systems

The access technique of non real time services in 802.16 networks is generally based on multicast or broadcast polling and contentions resolution mechanisms. Thus, the major problem that faces this class of service is the number of collisions that occur between the bandwidth request messages of subscribers´ stations (SSs). These collisions cause waste of bandwidth and increase the access delay. In this paper, we propose a new strategy that aims at reducing to the minimum the collision probability in contention periods. The proposed approach allows to the base station (BS) to select the SSs that can participate to the multicast polling, based on the amount of bandwidth already used by their active connection. Once this selection is made, the considered SSs will adopt a queue status-based contention window (QCW) technique that combines the minimum value sent by the BS and the number of nrtps packets waiting in the queue. Using the simulation results obtained with NS2, we demonstrate the effectiveness of our approach, especially at reducing access delay and collision rate.