Reconfigurable medium access control protocols for wireless networks

摘要

Wireless networks are becoming ubiquitous. They have numerous applications also outside the cellular systems, for example in agriculture, multi-user games, health monitoring using body area networks, and security surveillance. Wireless networks operate using a limited and unstable radio resource, yet they must provide a reliable service for an array of varying applications and mobility patterns. These challenges are compounded by having to rapidly develop hardware platforms and software stacks as new applications emerge. Medium Access Control (MAC) protocols facilitate access to the shared spectrum by defining rules by which wireless terminals communicate with each other. A runtime reconfigurable MAC protocol is able to change these rules dynamically. Supporting varying application needs, Quality of Service (QoS), available spectrum utilization in accordance to regulatory policies, and fair resource sharing among networks make runtime reconfigurable MAC protocols desirable. Traditionally, MAC protocols are optimized for one or very few specific operating scenarios, and are thus unable to guarantee satisfactory performance in increasingly complex and dynamic wireless environment. The goal of this work is to provide MAC protocols with a high level of runtime reconfigurability for any changing applications and spectral environment. In this dissertation, we present a MAC protocol development framework and an associated toolchain for on-the-fly MAC protocol realization and reconfiguration. MAC functionalities are decoupled into a set of common components which are used to construct MAC protocols. To validate the applicability of our approach, we implemented and evaluated our framework and toolchain in two significantly different application areas: cognitive radio networks and wireless sensor networks. The component-based architecture enabled realization of both classical and new MAC protocols with very low overhead. Runtime MAC protocol reconfiguration is enabled in two ways: small-scale reconfigurations using MAC parameter tuning, and macroscopic reconfigurations through component-based MAC protocol reconstruction. We evaluated our implementations using hardware platforms in realistic environments. The experimental results on MAC protocol reconfiguration show that the developed framework improved throughput and packet delivery ratio up to 400% in an unstable spectral environment. Adapting to varying application requirements is achieved, and seamless QoS is offered under highly varying conditions. In addition, our toolchain enables parallel execution of independent MAC components on many-core architectures. We found parallel execution to improve MAC performance especially for computationally intensive algorithms.