Quality-of-service and performance optimization in broadband wireless access networks -- a cross-layer study

The emergence of broadband wireless access technology is rapidly extending the data-centric and bandwidth intensive Internet services from traditional wired networks into the ubiquitous wireless domain. However, coexistence of heterogeneous applications such as circuit-quality voice transfer, interactive video gaming and inherently bursty data streaming over the shared wireless access platform exposes the compliance with service level agreement (SLA) of individual applications under substantial challenge, due to the frequent transmission errors, limited radio resource, broadcast oriented propagation, as well as energy constraint in wireless communication systems. The objective of this thesis is to study the parameterized service guarantee for diverse resource-competing applications, commonly referred to as quality of service (QoS) provisioning technologies, under various design contexts in broadband wireless access networks using cross-layer optimization technique. The first topic of this thesis addresses the minimization of average packet loss probability in a single-input-single-out wireless transmission system with constant transmission power. Both packet losses at the physical (PHY) layer due to transmission errors and the media access control (MAC) layer incurred by buffer overflow are considered. The proposed cross-layer optimization design includes two stages, namely, the policy domain optimization and the channel domain improvement. The policy domain optimization aims to search on the optimal transmission scheduling strategy for the adaptive modulation and coding application with a particular channel partition method, based on classical Markov decision process theories. The channel domain improvement, on the other hand, targets defining the most appropriate partition method that discretizes the continuous channel fading process with a Markovian estimation. This two-dimensional optimization proposal is shown to be capable of rendering lower cross-layer average packet loss probability compared with the one-dimensional design in the literature. In the first topic depicted above, transmission power consumption is not considered in the protocol design. To extend this topic with further effort to optimize the power consumption of the system, the second topic of this thesis focuses on minimizing long-term average power consumption for the uplink transmission from a mobile station to the base station via a wireless fading channel. The optimization problem is conditioned upon the QoS requirements set by cross layer average packet loss probability and average packet queuing delay. This leads to a constrained Markov decision process formulation of the problem. With this formulation, a linear programming based solution is proposed and validated by simulations. The results firmly verify the minimized average power consumption as well as the strict compliance with predefined QoS metrics. Being slightly different from the first and second topics, the third topic of this thesis deals with the radio resource management issue for providing robust QoS support in a networked scenario. Particularly, an efficient QoS control scheme for the IEEE 802.16 standard based WiMAX system is designed and experimentally verified. This scheme distributes the centralized QoS control functionalities performed by the base station to each subscriber station, thereby significantly reduces signaling overhead. Moreover, the MAC-PHY cross-layer resource allocation proposal spreads the capacity loss due to particular wireless link degradation over the entire network, which substantially improves the robustness of the proposed design. Keywords. broadband wireless access network, quality of service, cross-layer optimization, IEEE 802.16, modeling and simulation, finite state Markov channel, Markov decision process, linear programming.

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