Wireless Local area networks (WLANs) have become more and more popular today. Through WLAN, people can access the Internet anytime, anywhere, as WLANs are deployed in different areas such as malls, cafes, airports and so on. Wireless Lans suffer dramatically from Path loss and interferences and as a result channel errors rates are very high and are known to be location dependent and bursty in nature. As a consequence, due to the fairness of the medium access control protocol in sharing access opportunities in WLANs, when one of the station observes a bad channel state and continues to access attempt transmission the throughput of the whole network is greatly degraded....[ Read more ]

Wireless Local area networks (WLANs) have become more and more popular today. Through WLAN, people can access the Internet anytime, anywhere, as WLANs are deployed in different areas such as malls, cafes, airports and so on. Wireless Lans suffer dramatically from Path loss and interferences and as a result channel errors rates are very high and are known to be location dependent and bursty in nature. As a consequence, due to the fairness of the medium access control protocol in sharing access opportunities in WLANs, when one of the station observes a bad channel state and continues to access attempt transmission the throughput of the whole network is greatly degraded.

In order to address this problem, link adaptation schemes and wireless schedul-ing algorithms are proposed. The idea of link adaptation is to improve the network throughput by adjusting some network parameters, such as the frame size, the tran-smission rate, or the rate of error correcting codes, to adapt to different channel con-ditions. Wireless scheduling is based on swapping transmission opportunities among stations in order to enable the stations with good channel to transmit first and postpone the transmissions of the bad channel stations to a later time when their channels be-come good. This reduces the number of frame errors and thus improves the network throughput.

In this thesis, we study different link adaptation schemes and wireless scheduling algorithms to improve the network throughput while providing QoS guarantees. We propose a per-fragment link adaptation system with a credit based scheduler that allows every fragment of a frame to be transmitted at the best transmission rate and fragment size, and good channel flows are allowed to transmit more than the bad channel flows. This can greatly improve the network throughput. We also propose a delay aware wire-less scheduling algorithm which targets the support multimedia traffic in WLAN. The scheduler improves the network throughput when the traffic has a deadline constraint. The scheduler uses both the information of the packet deadlines and the underlying link adaptation scheme to swap the transmission opportunities based on different channel conditions without violating the delay requirements of the packets.