Antenna and synchronization design issues for the ultra-wideband systems

This dissertation focuses on antenna and synchronization challenges in the design of ultra-Wideband (UWB) systems. Motivated by short-range, high-data-rate applications, we seek practical solutions of modest complexity.; The first part of the dissertation (Chapter 2-5) explores antenna and signal design challenges when transmitting and receiving impulse-type UWB signals. We establish general conditions under which the antenna transmit impulse response is proportional to the time derivative of the receive impulse response of the same antenna. This fact enables study of UWB signal designs meeting the FCC Mask, which mandates the maximum allowable transmitted power spectrum density. We consider design; modeling, and measurement of small; low-cost; two-dimensional antennas, with a particular focus on the diamond antenna and its variations. Based on simulated current distributions, a simplified model composed of only linear elements is proposed to predict the diamond antenna radiation patterns. Simulations and measurements established that the model predicts well the somewhat surprising significant frequency-dependency of the radiation patterns. This pattern frequency dependency has motivated our study of the direction-dependent impulse responses and corresponding receiver filter design. The insights from the model study have encouraged two design modifications of the diamond antenna: a rounded diamond and the house-shaped planar antenna (house antenna). The rounded diamond antenna is of an increased bandwidth relative to its diamond counterpart. The house-shaped planar antenna is shown to be a promising design for multi-band OFDM UWB type-systems.; The second part of the dissertation (Chapter 6-7) explores packet detection and synchronization challenges with a particular emphasis on OFDM UWB systems operating at very low SNR. (down to 4 dB). We first consider four packet detection methods and their performance in both AWGN and multipath channels. We facilitate analysis of the Schmidl and Cox packet detection method by deriving a significantly improved approximation for the probability density function (PDF) of its detection decision variable. In addition, we explore methods for correcting UWB frame synchronization errors. An adaptive time shift scheme is proposed and its performance relative to "non-adaptive" schemes is quantified.; Finally; we describe our design of a multiband OFDM based UWB system simulator. Some applications are exemplified.