Fair and efficient access provisioning in wireless local area networks

IEEE 802.11 Wireless Local Area Network (WLAN) technology is experiencing impressive market success due to inexpensive and easy-to-install components, unlicensed spectrum, broadband capabilities, and interoperability granted by standards and certifications. The WLANs have become prevalent almost everywhere such as at offices, homes, coffee shops, hotels, airports, campuses, conference venues, etc.;Most of the deployed IEEE 802.11 WLANs use the infrastructure Basic Service Set (BSS) architecture in which an Access Point (AP) serves as a gateway between wired and wireless domains. This architecture simply defines a downlink where the packet flow direction is from the AP to a mobile station and an uplink where the packet flow direction is from the mobile station to the AP. In this dissertation, we present that the assignment of IEEE 802.11 Medium Access Control (MAC) layer parameters as suggested in the 802.11 standards results in unfair access among competing stations and inefficient channel utilization in the downlink and the uplink of WLANs. We also illustrate how unfair access is exacerbated by the specific interactions of the MAC layer mechanisms and transport layer protocols. Aiming to resolve these issues, this dissertation concentrates on the design of congestion control, scheduling, and resource allocation schemes that would provide high channel efficiency, fair access, and low packet delay.;The first part of the dissertation focuses on fair and efficient Transmission Control Protocol (TCP) access in the IEEE 802.11 BSS as the network traffic is currently dominated by data traffic mainly using TCP in the transport layer. We propose a novel and simple analytical model to approximately calculate the per-flow TCP congestion window limit that provides fair and efficient TCP access in a heterogeneous wired-wireless scenario. The proposed analysis is unique in that it considers the effects of varying number of uplink and downlink TCP flows, differing Round Trip Times (RTTs) among TCP connections, and the use of delayed TCP Acknowledgment (ACK) mechanism. Motivated by the findings of this analysis, we design a link layer access control block to be employed only at the AP in order to resolve the unfair access problem. The novel and simple idea of the proposed link layer access control block is employing a congestion control and filtering algorithm on TCP ACK packets of uplink flows, thereby prioritizing the access of TCP data packets of downlink flows at the AP. Via simulations, we show that short- and long-term fair access can be provisioned with the introduction of the proposed link layer access control block to the protocol stack of the AP while improving channel utilization and access delay.;In the second part of the dissertation, we design a simple, practical, and standard-compliant MAC layer framework to be employed at the AP for fair and efficient access provisioning. A dynamic measurement-based EDCA parameter adaptation block lies in the core of this framework. The proposed framework is unique in the sense that it considers the characteristic differences of TCP and User Datagram Protocol (UDP) flows and the coexistence of stations with varying bandwidth or Quality-of-Service (QoS) requirements. Via simulations, we show that our solution provides short- and long-term fair access for all stations in the uplink and downlink employing TCP and UDP flows with non-uniform packet rates in a wired-wireless heterogeneous network. In the meantime, the QoS requirements of coexisting real-time flows can also be maintained.