Ultra-Wideband (UWB) communication is a promising technology for short-distance, low power, and high data rate wireless communication systems. The data are carried by short duration pulses in UWB systems. The popular modulation schemes are based on changing pulse positions and amplitudes. In this book, two new modulation and receiver structures are developed for energy detection UWB systems. The modulation schemes of these two new technologies are based on changing pulse widths and using different-order derivatives of the Gaussian pulse. These two new technologies exhibit better performance than the existing ones. Also the multiple access schemes for these two technologies are discussed in this book. This book also includes the general knowledge of UWB systems. It is suitable for academic researchers, engineers, and students who are interested in developping new solutions for UWB systems.