Unisource and Multisource Tree Schemes for Collision Resolution in Wireless MAN

Abstract

IEEE 802.16 wireless MAN standard specifies the air interface of broadband wireless access systems providing multiple services. In the wireless MAN, the best effort service class is ranked on the lowest position in priority and is assisted by a MAC scheme based on reservation ALOHA. In such a MAC scheme, a collision of resource requests is unavoidable so that the wireless MAN standard adopted a truncated binary exponential back-off scheme to arbitrate request attempts. While an exponential back-off scheme is simple to implement, its capture or starvation effect was revealed to deteriorate the fairness in short-term throughput and delay variance in the long term. Aiming at improving the throughput and delay performance, we thus propose the unisource and multisource m-ary tree schemes as alternatives for resolving request collisions in a wireless MAN. For the unisource tree scheme, we first develop an analytical method to exactly calculate the throughput in the saturated environment. Using the analytical method and simulation method as well, we then evaluate the saturated throughput, mean of MAC PDU delay and variance of MAC PDU delay in each proposed scheme. From the numerical examples, we confirm that the unisource and multisource m-ary tree schemes invoke superior throughput and delay performance to a truncated binary exponential back-off scheme.