On Optimization of CSMA/CA based Wireless LANs: Part I - Impact of Exponential Backoff

In this paper, we consider optimization of CSMA/CA based wireless networks such as IEEE 802.11 Wireless LANs. A fundamental component of the MAC layer functionality in such networks is the binary exponential backoff (BEB) of contending nodes which serves as a means of arbitrating distributed channel access. In this paper, we show that the joint optimization of initial contention window (CWmin) and the number of backoff stages in BEB yields, interestingly, no additional gains over a simple CWmin optimization that is performed by considering that BEB is absent. Thus, BEB has negligible impact once CWmin is optimized. While this result holds only for an ideal WLAN, in the presence of channel errors, BEB penalizes performance even when CWmin is optimized. Finally, disabling BEB and optimizing CWmin not only improves short-term fairness significantly but it also stabilizes the system even when there are asymptotically large number of saturated users contending.