Development of efficient medium access schemes for wireless local area networks.

摘要

Though the WLAN performance has improved tremendously, all the revisions and fixes have resulted in the standard becoming difficult to analyse. As the endeavour to reach gigabit speeds over WLANs keeps growing, the time to reflect on the direction we are headed dawns upon us. This dissertation presents efficient schemes to optimize performance factors like throughput and latency while obtaining energy efficient communication.;First, we design a MAC protocol which is completely distributed but yet is completely contention free. New applications like VOIP and streaming video have specific requirements which the 802.11 is unable to handle. Collisions in 802.11 also drain energy and increase latency. Our adaptive, contention free protocol can meet the requirements of future services that demand high data rates. The protocol statistically multiplexes opportunities for transmission for every node. The protocol is analysed mathematically and optimized for performance and shows much lower latency as compared to 802.11. Since our system is mathematically tractable, simulation results for our system completely agree with our analytical results.;Second, we investigate characteristics of various real world applications like VOIP, video streaming etc. and their impact on mobile platforms in terms of power consumption and energy. Based on the study, we develop a traffic shaping scheme using interrupt coalescing. The scheme is shown to reduce the wakeups of platform components thus saving energy. The measurements shows that the suggested scheme is able to obtain significant power savings without impacting the user experience.;802.11 provides different modulation schemes like BPSK, QPSK, 16QAM etc. schemes offer varying bit rates and have varying constellation densities. The modulation schemes with higher constellation densities normally offer higher data rates but are also more susceptible to errors. Thus, Rate Adaptation allows a device to take advantage of higher data rates when the channel conditions are good and switch back to lower data rates when conditions deteriorate. In addition in 802.11 systems, the rate adaptation algorithm has to distinguish a packet loss due to collisions from that of environmental errors. Our scheme uses information collected from the protocol specification to identify the cause of the packet loss before deciding on the best rate to transmit. The information collected is local to the device and does not need any changes to the protocol.