Wireless Local Area Networks (WLANs) are becoming increasingly popular due to the recent availability of affordable devices providing multiple and high rate capabilities. New PHY and MAC layer enhancements have been introduced in different IEEE 802.11 WLAN standards. These improvements have given birth to a wide range of bandwidth channels (up to 160MHz) and very high transmission data rates ( 1Gbps) to keep up with current and upcoming multimedia applications. Optimizing the performance of different wireless networks for emerging network applications is an important and highly challenging issue.

QoS is very important for high throughput WLANs. Scheduling the access of flows in a non-interfering manner to avoid packet loss and adapting rates to changing channel conditions are i...[ Read more ]

Wireless Local Area Networks (WLANs) are becoming increasingly popular due to the recent availability of affordable devices providing multiple and high rate capabilities. New PHY and MAC layer enhancements have been introduced in different IEEE 802.11 WLAN standards. These improvements have given birth to a wide range of bandwidth channels (up to 160MHz) and very high transmission data rates (> 1Gbps) to keep up with current and upcoming multimedia applications. Optimizing the performance of different wireless networks for emerging network applications is an important and highly challenging issue.

QoS is very important for high throughput WLANs. Scheduling the access of flows in a non-interfering manner to avoid packet loss and adapting rates to changing channel conditions are important aspects of QoS in wireless networks. The goal of the rate adaptation scheme is to select the best set of transmission parameters for a given user considering its channel quality. Similarly, sub-channel scheduling access can be seen as selecting the best set of users to allocate subcarriers according to their channel state information. As data traffic has diverse characteristics and different transmission requests, an advanced version of Multimedia-MAC should exist to dynamically adjust the bandwidth allocation according to the instant traffic load status so that both network channel utilization and QoS for different types of traffic streams are dramatically enhanced.

This thesis makes two main contributions. The first is to design a new practical rate control algorithm for 802.11n WLANs, based on a probing system that guarantees that it is has Long-Term Stability and Short-Term Responsiveness (L3S). We then implement it in commercial devices using the Ath9k driver without modifications to the existing standard. The new rate adaptation classifies transient and sustained changes in the link conditions. Then, it controls both short-term and long-term channel quality variations respectively by continuously monitoring the transmission history and intelligently probing at new data rates that may outperform the current one. Our proposed rate control algorithm adapts rapidly to these changes by adjusting the efficient transmission rate. Thus, it optimizes the throughput (or delay) performance on a wireless link. The second part consequently deals with the major reasons for the inefficiency of different WLANs. The current MAC layer randomly allocates the entire channel to only one user as a single resource. Indeed, one way to significantly improve WLAN performance is to effectively reduce the channel width and create different sized sub-channels. Based on the user’s channel conditions and QoS requirements, the Physical layer resources can be dynamically allocated to several users at the same time. Thus, we present a novel sub-channels access approach, titled MU-Access, with new features suitable for the forthcoming high-speed MIMO-based WLAN products. We shall evaluate its performance compared to state-of-the-art systems, using NS-3 under a variety of network conditions. Our experiments then demonstrate that our scheme does indeed enhance IEEE 802.11 device performance with a much higher degree of throughput. Also, we propose to profit from the sub-channels access approach and adapt the rate separately for each block of subcarriers according to the instantaneous channel conditions, for improvement.