Medium Access Control and Adaptive Transmission Techniques in Wireless Networks

Abstract

Efficient utilization of the limited wireless spectrum while satisfying applications’ quality of service requirements is an essential design goal of forthcoming wireless networks and a key to their successful deployment. The need for spectrally efficient systems has motivated the development of adaptive transmission techniques. Enabling this adaptation requires protocols for information exchange as well as mathematical tools to optimize the controllable parameters. In this dissertation, we provide insights into such protocols and mathematical tools that target efficient utilization of the wireless spectrum. First, we propose a distributed CDMA-based medium access protocol for mobile ad hoc networks (MANETs). Our approach accounts for multiple access interference at the protocol level, thereby addressing the notorious near-far problem that undermines the throughput performance in MANETs. Second, we present a novel power-controlled MAC protocol, called POWMAC, which enjoys the same single-channel, single-transceiver design of the IEEE 802.11 Ad Hoc MAC protocol, but which achieves a significant throughput improvement over the 802.11 protocol. Third, we consider joint power/rate optimization in the context of orthogonal modulation (OM) and investigate the performance gains achieved through adaptation of the OM order using recently developed optimization techniques. We show that such adaptation can significantly increase network throughput while simultaneously reducing the per-bit energy consumption relative to fixed-order modulation systems. Finally, we determine the maximum achievable “performance” of a wireless CDMA network that employs a conventional matched filter receiver and that operates under optimal link-layer adaptation where each user individually achieves the Shannon capacity. The derived bounds serve as benchmarks against which adaptive CDMA systems can be compared.