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Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Electrical and Computer Engineering

Year Degree Awarded

Summer 2014

First Advisor

Dennis Goeckel

Subject Categories

Electrical and Computer Engineering

Abstract

This dissertation focuses on two important areas in wireless communications: receiver design and security. In the first part of this dissertation we consider low data rate receiver design for ultra-wideband (UWB), a wideband radio technology that promises to help solve the frequency allocation problem that often inhibits narrowband systems. Reference-based receivers are promising candidates in the UWB regime, because the conventional rake receiver designs suffers from complexity limitations and inaccuracies in channel estimation. Many reference-based systems have arisen as viable solutions for receivers. We unify these systems as well as other systems into the general framework for performance analysis to suggest the optimal system for varying constraints. We improve the performance of frequency-shifted reference (FSR-UWB) for an average power constraint by halving the frequency offset and employing a sample-and-hold approach across the frame period. Also, we introduce a novel peak mitigation technique; tone reservation, for the multi-differential (MD) version of FSR-UWB, to reduce the high peak-to-average power ratio observed as the data carriers increase. The next part of this dissertation is about wireless security which is ubiquitous in modern news. Cryptography is widely use for security but it assumes limited computational abilities of an eavesdropper, is based on the unproven hardness of the underlying primitives, and allows for the message to be recorded and decrypted later. In this dissertation we consider an information-theoretic security approach to guaranteeing everlasting secrecy. We contribute a new secrecy rate pair outage formulation, where an outage event is based on the instantaneous rates of the destination and the eavesdropper being below and above desired thresholds, respectively. In our new secrecy rate pair outage formulation, two new unaccounted outage events emerge: secrecy breach, where the eavesdropper is above the targeted threshold; unreliable, where the destination is unable to successfully decode the message. The former case must be carefully avoided, while for the latter case we can exploit automatic retransmissions (ARQ) while maintaining the eavesdropper intercept probability below the target threshold. We look at both ``simple'' receivers and also complex receivers that use a buffer to store previous messages to maximally combine signal-to-noise ratio (SNR). Then we extend these results to the two-hop case where we maximize the end-to-end secure throughput by optimizing the intercept probability at each eavesdropper given a total end-to-end intercept constraint. Lastly, we consider the difficult case in information-theoretic security: the near eavesdropper case, where we contribute an optimal power allocation algorithm that leverages nearby chatter nodes to generate noise to reduce the probability of intercept by the eavesdropper while minimally impeding the source-to-destination communication. As shown in both one-hop and two-hop cases, allowing a slight outage at the destination for cases of when the eavesdropper is above a specific threshold greatly improves secrecy performance.

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