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

Abstract

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.

Enhancing MAC performance of DCF protocol for IEEE 802.11 wireless LANs

“…In the literature, the optimization of contention window and the number of backoff stages has been studied to enhance the performance of the DCF [6][7][8]. However, because the boundary of candidates for the optimization of the parameters converges to infinite limit as the number of nodes participating in the DCF transmission procedure increases, it is difficult to develop an efficient method for optimizing the parameters.…”

“…However, because the boundary of candidates for the optimization of the parameters converges to infinite limit as the number of nodes participating in the DCF transmission procedure increases, it is difficult to develop an efficient method for optimizing the parameters. According to [6], the joint optimization of the parameters of contention window and the number of backoff stages yields no additional performance gain over the simple optimization of contention window.…”

Performance analysis of distributed cluster-based MAC protocol for multiuser MIMO wireless networks

“…The cause of failure, however, cannot be distinguished in current WLAN systems [12,13]. Hence, in both cases, the backoff interval increases exponentially up to a maximum value which is specified by the standard.…”

“…Accordingly, the transmission probability of synchronous and asynchronous STAs in each C i can be calculated as follows: Here and in the following, for simplicity we denote the superscript (k 1 , k 2 , ..., k n c ) by (k) . The probability that k i out of N nc i STAs are asynchronous can be obtained from (13), however, here k may take different values in different clusters. In this scenario, the probability that only members of one cluster transmit also depends on (k) and can be obtained as follows:…”

“…In order to do so we can either calculate throughput results for different values of τ and find the τ* which maximises the throughput or find τ* as explained in [13] by applying the following equation:…”