Utility Based Backoff (UBB) Algorithm for Initial Ranging Procedure in WiBro

In this paper, a contention resolution backoff algorithm termed Utility Based Backoff (UBB) is proposed for initial ranging procedure in IEEE 802.16e based WiBro (Wireless Broadband) system. In UBB algorithm, whenever an active Subscriber Station (SS) experiences a collision during ranging request transmission, it accomplishes its new contention window size based on the utility (satisfaction) upon its randomly selected backoff value on the previous transmission attempt. Higher the deferred backoff value lower will be the utility and vice versa. The contention window will be larger for higher utility and vice versa. The process is repeated unless the request is transmitted successfully, or until the maximum retransmission attempt is reached. UBB algorithm applied to WiBro reduces the average medium access delay for the successful request transmission compared to Binary Exponential Backoff (BEB). Even more, throughput for lower offered load is higher in UBB than BEB.