Wireless Coexistence for Spectrum Sharing

Abstract

Much of the spectrum licensed for usage by the regulatory authorities remains idle or heavily underutilized. By allowing opportunistic access to these dormant resources, spectrum sharing promises to dramatically boost the supply of spectrum that is available for high bandwidth wireless communications. This shared access arrangement will lead to the expected coexistence of multiple wireless systems within the same frequency band giving rise to the study undertaken in this dissertation. Our work begins by considering TV Whitespaces (TVWS) which were the first major instance of spectrum sharing to be considered. We look at adapting the 802.11 WLAN standard for operation in TVWS bands by incorporating sensing into the Wi-Fi MAC layer. We use this study to explore the potential of Software Defined Radio systems and the role they play in spectrum sharing systems while identifying the challenges and pitfalls inherent in such implementations. Our focus then shifts to spectrum sharing in radar bands. First, we aim to shrink the exclusion regions (as defined by the NTIA) by inheriting from the techniques developed for TVWS. The key outcome of this work is to provide an analytic framework for the selection of Wi-Fi parameters than can deliver the desired radar protection performance. This framework supports the aim of maximum spectrum utilization by reducing the areas which are deprived of shared access to radar spectrum. The last major result in this dissertation is a detailed study into the impact of radars on communication systems. We present what is to our knowledge the first detailed look at the physical layer obstacles that hinder network throughput for devices deployed in radar bands. Looking at the two major broadband standards (IEEE 802.11 WLAN and 3GPP LTE), we identify vulnerabilities that would render networks inoperable in close proximity to radars before providing effective solutions to recover the desired performance. The line of investigation in this thesis furnishes some of the solutions that are necessary for the future success of spectrum sharing systems.