Date of Award

January 2015

Degree Type


Degree Name

Doctor of Philosophy (PhD)


Electrical Engineering and Computer Science


Biao Chen


authentication, cognitive radio, communication system, MIMO, software-defined radio, wireless communication

Subject Categories



This dissertation is composed of three parts: airborne multi input multi output (MIMO) communications, physical layer authentication, and software radio design for DARPA Spectrum Challenge. A common theme for the three distinct problems is the system perspective that we have adopted throughout this dissertation. Instead of considering isolated issues within these problems, we have provided a holistic design approach to the three problems and have implemented all three systems using the GNU Radio/USRP (Universal Software Radio Peripheral) platform.

In the first part, we develop a MIMO communication system for airborne platforms. MIMO communication has long been considered to be suitable only for environment that is rich in scatterers. This, unfortunately is not the case for airborne platforms. However, this lack of scattering can be compensated by the large aperture of the airborne MIMO platform; this is corroborated by our careful analysis using real measurement data. Our analysis of the airborne MIMO channels leads to the development of a variable rate MIMO transceiver architecture. This architecture is numerically shown to improve the bit error rate (BER) over conventional transceiver architectures that are developed for rich scattering environments. A software radio based MIMO system is then implemented to demonstrate experimentally the efficacy of the developed architecture.

In the second part, we develop a physical layer authentication scheme as a counter measure to primary user emulation attack (PUEA) in cognitive radio (CR) networks. In this attack, a malicious user emulates the signal characteristics of the primary user (PU) when it is silent which prevents unsuspecting secondary user (SU) from utilizing the network. The developed physical layer authentication is based on embedding cryptographic hash signatures, referred to as authentication tags, within PU's signal constellations. The embedding is performed such that the legacy receivers are not affected. We analyze the scheme using the fast fading Rayleigh channel model and present an optimal scheme to embed signals in PU's constellations which minimizes the tag BER. Experimental results are obtained that corroborate our theoretical claims, thereby establish that reliable authentication can be achieved without sacrificing signal quality at the primary receivers.

In the final part, we describe in detail our design of software radios developed as part of the DARPA Spectrum Challenge (DSC), a year long competition that started in January 2013 and concluded in March 2014 with the final tournament held in Arlington, VA at the DARPA headquarter. DSC was comprised of two tournaments, competitive and cooperative. In the competitive mode two radio pairs, each composed of a transmitter and a receiver, are pitted against each other to transmit the most amount of data error-free while operating concurrently in the same frequency band. In the cooperative mode, three radio pairs have to share a frequency band in a cooperative manner wherein the goal is to maximize the throughput of all the three pairs. We describe the design of our software radio system that integrates some key technologies crucial in operating in an environment that does not allow user coordination and spectrum pre-planning, including: spectrum sensing, adaptive transmission both in spectrum utilization and transmission rate, opportunistic jamming, and sliding window feedback. The developed radio is robust in the presence of unknown interference and achieves the desired balance between throughput and reliability in an uncoordinated transmission environment.


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