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Wireless communication network is an important area of modern technology. To ensure reliable communications in an inevitably uncertain and ever-changing environment, link adaptation is necessary. In addition, since wireless devices typically have limited power supply and mobile users often want to communicate regardless of their locations, power-efficient and location-fair link adaptation is highly desirable. This dissertation is devoted to the analysis and design of power-efficient and location-fair link adaptation protocols for wireless networks. It addresses fundamental issues in data rate control and power management, develops practical adaptation protocols, and analyzes their performance. More specifically, in data rate control, the maximum achievable average throughput of feedforward controllers is derived. The optimal controller is found to be channel-independent but non-causal. A suboptimal implementable controller, which yields significant increase in average throughput over fixed data rate operation in Rician fading channels, is designed and shown to outperform existing protocols. In power management, both TDMA and CDMA systems are considered. For TDMA systems, the optimal transmission policy, which maximizes power-efficiency, is proved to be of threshold nature. This policy is simplified, resulting in a suboptimal threshold policy that is 11 dB more power-efficient than traditional TDMA. It is however location-unfair and, thus, is suitable only for delay-insensitive applications. To overcome this limitation, we develop a location-fair adaptive threshold policy that offers 3.6 dB power-efficiency improvement over traditional TDMA. For CDMA systems, an N-choose-n operation, where n out of N users are chosen to transmit at a time, is introduced. The set of feasible pairs (N, n), which ensures every user a desired average throughput, is characterized. The optimal N-choose-n operation is proved to be ranking-based, i.e., selecting the n users with the largest channel gains maximizes power-efficiency. The resulting system, referred to as Ranking CDMA, is 14 dB more power-efficient than traditional CDMA, but lacks location-fairness. This deficiency is alleviated by a location-fair Adaptive Ranking CDMA that is still 5 dB more power-efficient than traditional CDMA.

The methodology of variable structure with sliding mode is proven to be very successful in controlling uncertain continuous-time dynamical systems. When the system is sampled or purely discrete, the invariance property of sliding mode, which is originally a continuous-time concept, no longer hold and the reaching condition has to be modified to allow a pseudo-sliding mode. Moreover, the state dependency of parametric uncertainties makes the satisfaction of reaching condition considerably more difficult especially in multivariable systems. These difficulties have offered challenges that attracted a great deal of research interests. This thesis presents theoretical results on the discrete variable structure control of uncertain linear multivariable systems using the concepts of sliding mode and switching sector. It considers both the stale and output feedback cases for systems with addictive uncertainties and the state feedback case for systems with parametric uncertainties. The thesis also presents a sliding surface design procedure for single-input systems based on the version of discrete variable structure control developed by OJ'. Eduardo Misawa.