Ultra wideband (UWB) is a promising technology for short range and high-speed wireless communications such as home entertainment, wireless video downloading, wireless LAN, wireless USB and so on. This dissertation studied several important issues in the application of UWB technology and its contributions are summarized as follows. First, a 2-stage optimal UWB pulse shaping filter design procedure is proposed, which not only satisfies the FCC transmission spectral masks but also suppress the multiple access interference (MAI). The major advantages of the proposed joint optimization method are: (1) it has superior MAI suppression capability; (2) it can achieve the best system performance by optimizing transmitting and receiving filters jointly. Second, a pulse shaping optimizer is proposed to achieve the best received signal-to-noise ratio (SNR). Since the objective function of the SNR optimization has multiple maxima, genetic algorithms are adopted in this all-pass filter optimization. Third, a novel analytical method of assessing the narrowband performance degradation due to UWB interferences is proposed. This method models the UWB interferences as a composite signal of white Gaussian noise and jamming tones. Finally, a RAKE receiver simulation model under a realistic UWB channel is proposed and numerical results are presented. Overall, this dissertation investigates several important issues in the application of UWB technology, and provides some insights on the role of UWB technology in the evolving course of wireless communications. / Ph. D.