Abstract:
One of the key factors that influence the performance of wireless local area networks (WLANs) is the medium access control (MAC) protocol. In WLANs, the MAC protocol is the main element that determines the efficiency of the sharing of the limited wireless channel bandwidth since it coordinates data transmissions on the network. Another factor that influences WLAN performance is the nature of radio signal propagation. Other factors, such as traffic type and their arrival distribution, and signal interference also influence WLAN performance. In this thesis, an empirical investigation of the key factors influencing WLAN performance is described and its results are reported. In the investigation, the key performance-limiting factors are identified and measured by simulation and propagation measurements. A method of increasing WLAN performance by modifying a MAC protocol is reported. A significant network performance gain with respect to higher throughput, lower packet delay, lower packet drop ratio, and better fairness is obtained with the modified MAC protocol under medium-to-high traffic loads. This performance is improved by introducing a temporary buffer at the MAC layer for each active network connection, where multiple packets are combined into one large packet with a single header and trailer for transmissions. The nature of the radio propagation environment is shown to have a significant impact on WLAN performance. For example, line-of-sight blockage in an obstructed office block and a suburban residential house is found to have a significant effect on WLAN throughput. The integration of physical (PHY) layers and MAC layers can further improve WLAN performance. A joint PHY-MAC layer design :framework was proposed for estimating as well as improving WLAN performance. The performance gain is achieved by adjusting MAC layer protocols to suit the changing conditions of the PHY layer. Packet arrival distributions such as Poisson, Pareto ON-OFF, Exponential, and Constant Bit Rate also influence WLAN performance. The combined effect of signal strength and traffic type on a typical WLAN's performance is investigated. Streaming video traffic over a weak wireless link was observed to have a higher latency than voice and data traffic. WLAN design and deployment strategies are outlined and recommendations are made for various system design scenarios.