Performance evaluation and enhancements of the MAC layer for multi-rate SISO and MIMO IEEE 802.11 wireless LANs

This thesis deals with the Medium Access Control (MAC) layer of the IEEE 802.11 standard. Specifically, it addresses the MAC layer in SISO (Single-Input Single-Output) and MIMO (Multi-Input Multi-Output) networks with the goal of achieving higher data rates and higher performance in throughput and fairness for best effort and QoS applications. We also study the impact of the physical (PHY) layer on the performance of the MAC.; A complete study of the multi-rate capability of the standard is provided in this thesis. An accurate mathematical model for the Distributed Coordination Function (DCF) access mechanism in a multi-rate environment is introduced. The mathematical analysis is supported by experiments and simulations. The model is capable of capturing the performance anomaly of the standard in terms of throughput when stations transmit at different data rates. Practical and simple-to-apply solutions are proposed to prevent the severe degradation in throughput.; Quality of service in wireless LANs is addressed in this thesis by studying the performance of the IEEE 802.11e standard. A mathematical model which is consistent with the Enhanced Distributed Channel Access (EDCA) of the standard is introduced. The model includes all the mandatory QoS parameters that differentiate between priority classes. It also implements many lesser known details of the EDCA such as the management of the backoff counter which is technically different from the one used in the legacy DCF.; This thesis also addresses the addition of multiple antennas to wireless LANs. Performance analysis is conducted analytically and by simulations to evaluate this addition. Throughput enhancements and QoS differentiation mechanisms using MIMO links are introduced. Anew MAC protocol that enables the spatial reuse of the channel by employing the infrastructure and ad-hoc modes concurrently is also proposed.