Ultra-Wideband (UWB) is a new technology with promising features which enable various applications in wireless communication, radar, imaging and localization systems. This paper first presents basic concepts of UWB, its prospects and challenges, then focuses on signal processing aspects in the physical layer of Impulse-Radio UWB communication systems, in which popular modulation schemes and receiver algorithms are explored and evaluated. More specifically, the authors investigate, develop algorithms for PRAKE and SRAKE receivers frequently used in high rate applications. A simple Transmit-Reference UWB transceiver scheme, proposed for low rate applications, is also discussed and simulated.