Ultra-Wideband (UWB) Communications: Performed pioneering work on UWB radio as well as provided foundations for the design and analysis of UWB networks. Devised the first statistical UWB propagation channel model, proposed a network experimentation methodology, and developed low complexity transmission systems, which enabled the efficient design and accurate performance prediction of UWB wireless networks. UWB signals enable robust communications and high-resolution ranging capabilities even in harsh environments. Specific contributions include:
- Propagation Measurement and Statistical Modeling: Conducted a widely recognized UWB signal propagation experiment and devised the first statistical propagation channel model based on an extensive measurement campaign. Experimentally demonstrated the robustness of UWB signals in multipath environments.
- Network Experimentation: Established a network experimentation methodology to characterize the phenomena affecting communication, localization, and navigation networks. Performed a measurement campaign based on the proposed methodology and evaluated the performance of cooperative network localization in realistic settings.
- Optimal Search Strategies: Established a framework and determined the fundamental limits of search strategies by bringing together ideas from the disciplines of engineering and mathematics, involving communication, signal processing, convexity, and optimization theories. Specific contributions include:
- η-optimal Search: Developed methodologies for the design of deterministic search that approach the fundamental limits.
- Randomized Search: Proposed and analyzed a search strategy that is robust to variation in channel.
This work is applicable to a broad class of search scenarios including minimal-time search algorithms that exploit multipath for acquisition of wide bandwidth wireless signals. In particular, it provides the fundamental basis for the design and analysis of UWB fast synchronization systems, which are essential for the rapid deployment and operation of future communication and sensor networks.
- Local-Reference (LR) Systems: Devised reduced-complexity UWB LR systems based on partial combining (PRake) and selective combining (SRake). Analyzed their performance in multipath environments. Characterized the performance vs. complexity trade-off for these systems based on extensive propagation measurements.
- Transmitted-Reference (TR) Systems: Developed an analytical framework, based on a sampling expansion approach, to evaluate the performance of UWB TR and differential TR systems with autocorrelation receivers. Characterized the effects of narrowband interference for a broad class of fading channels. Obtained the scientific basis for comparing simple TR systems with ideal LR systems in terms of the asymptotic SNR penalty.
- Unified Spectral Analysis: Derived general expressions for the power spectral density (PSD) of a variety of time-hopping spread-spectrum signaling schemes in the presence of timing jitter using stochastic theory.