Cross-layer optimization in wireless local area networks

This thesis studies several research problems in the area of wireless local area networks (WLANs) with an objective of improving network efficiency, quality-of-service and user satisfactions. The I E E E 802.11 Working Group has been under rapid development and expansion in recent years following the successful deployment of the 802.11 network around the globe. The thesis work has been striving to study several key problems in these developments and propose effective schemes to improve network performance. The original 802.11 standard presents a simple and robust design, but has relatively low data rate and lacks QoS support. The recent 802.11e standard and the 8 0 2 . l ln proposals aim to significantly improve the network performance in terms of QoS and throughput. In this thesis, an analytical model of I E E E 802.11e WLANs is first presented. With the help of this throughput model, an admission control scheme for a multi-hop 802.11e W L A N is proposed. To fully utilize the high data rate provided by 802.11n, the performance improvement of the M A C protocol by frame aggregation is studied. Two frame aggregation techniques, namely A - M P D U (MAC Protocol Data Unit Aggregation) and A - M S D U (MAC Service Data Unit Aggregation) are considered. Furthermore, a comprehensive network setup is studied where the QoS requirements of the 802.11e M A C and the MIMO physical layer of 8 0 2 . l ln are both considered. Cross-layer design schemes are proposed for WLANs under two different M A C protocols: the carrier sense multiple access with collision avoidance (CSMA/CA)-based 802.11e M A C , and the slotted Aloha M A C . Lastly, the thesis studies the problem of cooperative transmission in a wireless ad-hoc network with extensions to the 802.11 M A C protocols. A complete system framework is proposed for wireless adhoc networks utilizing two different cooperative relaying techniques at the physical layer: the repetition coding and the space-time coding. In the data link layer, two medium access control protocols are proposed to accommodate the corresponding physical layer cooperative diversity schemes. In the network layer, diversity-aware routing protocols are proposed to determine the routing path and the relaying topology. Improvements in network performance for the proposed schemes are validated with numerical and simulation tests.Applied Science, Faculty ofElectrical and Computer Engineering, Department ofGraduat