| There is a surging demand for providing ubiquitous and high-speed Internet connectivity with the proliferation of smartphones, tablets, and other mobile devices. Nevertheless, existing wireless spectrum for mobile access has become overcrowded to meet such demand. To alleviate the spectrum crunch, regulatory agencies worldwide has started embracing a dynamic spectrum access model, which allows opportunistic communications in the unused spectral blocks. A key requirement therein is to protect existing wireless services, leading to various inefficiencies in the unlicensed, secondary applications.;To address this problem, this dissertation makes contributions in building measurement infrastructures, network architectures, and communication protocols to enhance this dynamic spectrum access model in the specific context of TV whitespaces (unused television channels).;We start by deploying a vehicle-based measurement system called V-Scope to enhance existing approaches for whitespace determination. V-Scope leverages spectrum sensors on public vehicles to collect measurements from the road. These measurements are used to refine various propagation models that can better determine whitespace spectrum, estimate its channel quality, and localize primary and secondary devices. Given the improved spectrum knowledge, we then focus on extending the coverage of whitespace networks to provide vehicular Internet connectivity. We present a heterogeneous network called Scout, which leverages TV whitespaces for downlink communications and a traditional cellular path for uplink to address the power asymmetry issue. Scout further uses an additional radio to "foresee" the channel condition to improve the transmission decisions under delayed feedback. It can also coordinate multiple base stations to enhance the network coverage and throughput.;In the last part of the thesis, we focus on improving the bandwidth efficiency of whitespace networks. We present an edge computing system Vigil to provide intelligent video surveillance in real-time. Vigil uses TV whitespaces to connect edge computing nodes co-located with camera sensors, which can filter video traffic locally to conserve wireless bandwidth.;We believe that our measurement infrastructure, network architectures, and wireless protocols are useful in enhancing the performance of TV whitespace networks. Furthermore, most of the concepts and techniques can have broader applications to dynamic spectrum access beyond TV whitespaces. |
