Optimization of efficiency and energy consumption in p-persistent CSMA-based wireless LANs

Wireless technologies in the LAN environment are becoming increasingly important. The IEEE 802.11 is the most mature technology for wireless local area networks (WLANs). The limited bandwidth and the finite battery power of mobile computers represent one of the greatest limitations of current WLANs. In this paper, we deeply investigate the efficiency and the energy consumption of MAC protocols that can be described with a p-persistent CSMA model. As already shown in the literature, the IEEE 802.11 protocol performance can be studied using a p-persistent CSMA model (Cali et al. 2000). For this class of protocols, in the paper, we define an analytical framework to study the theoretical performance bounds from the throughput and the energy consumption standpoint. Specifically, we derive the p values (i.e., the average size of the contention window in the IEEE 802.11 protocol (Cali et al.)) that maximizes the throughput, p_opt^C, and minimizes the energy consumption, p_opt^E. By providing analytical closed formulas for the optimal p values, we discuss the trade-off between efficiency and energy consumption. Specifically, we show that power saving and throughput maximization can be jointly achieved. Our analytical formulas indicate that the optimal p values depend on the network configuration, i.e., number of active stations and length of the messages transmitted on the channel. As network configurations dynamically change, the optimal p values must be dynamically updated. In this paper, we propose and evaluate a simple but effective feedback-based distributed algorithm for tuning the p parameter to the optimal values, i.e., p_opt^E and p_opt^C. The performance of the p-persistent IEEE 802.11 protocol, enhanced with our algorithm, is extensively investigated by simulation. Our results indicate that the enhanced p-persistent IEEE 802.11 protocol is very close to the theoretical bounds both in steady-state and in transient conditions.