Performance Evaluation and Enhancement of the CSMA/CA MAC Protocol for 802.11 Wireless LANs

ABSTRACT. The IEEE 802.11 protocol for Wireless Local Area Networks adopts a CSMA/CA protocol with exponential backoff as medium access control technique. As the throughput performance of such a scheme becomes critical when the number of mobile stations increases, in this paper we propose an Adaptive Contention Window mechanism, which dynamically selects the optimal backoff window according to the estimate of the number of contending stations. We show that this technique leads to stable behavior,and it outperforms the standard protocol when the network load and the number of mobile stations are high. We also investigate the CSMA/CA with the optional RTS/CTS technique, and we show that our adaptive technique reaches better performance only when the packet size is short. Finally, the performance of a system environment with hidden terminals show that the RTS/CTS mechanism, which can also be used in conjunction with the adaptive contention window mechanism, provides significant improvements.