Performance analysis of backoff algorithms under unsaturated conditions

This paper is concerned with the backoff algorithm for a random access system on the basis of slotted ALOHA. The performance of the algorithm in which the backoff counter is reset after the packet transmission success (conventional scheme), and the performance of the algorithm in which the backoff counter is successively decremented (modified scheme), are analyzed for the unsaturated condition. Based on the concept of equilibrium point analysis, the packet transmission failure probability, the throughput, the average transmission delay, and the uniformity of the transmission delay variation are evaluated. It is shown by a numerical example that the modified scheme exhibits better performance than the conventional scheme, even in the unsaturated condition, as well as in the saturated condition, with appropriate setting of the backoff window width. In addition, the modified scheme is shown to be better from the viewpoint of uniformity, in the sense that the packet transmission delay variation is smaller, even if the parameters are set to values that degrade the throughput. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(4): 32–43, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20176