| Ultra-wideband (UWB) communication systems have been considered for future short-range wireless communications due to a number of advantages. However, the high multipath resolution of a conventional UWB system makes receiver design challenging. In particular, the huge number of resolvable paths of a multipath fading channel makes a rake receiver type architecture difficult due to the realization complexity and the problems arising from channel estimation. The transmitted-reference (TR) scheme has been proposed to ease this burden on the receiver for an impulse radio UWB system. However, despite the simplicity at first glance of the architecture of the TR-UWB system, practical implementation is challenging due to the difficulty of building an ultra-wideband delay element in a low power circuit.;In this dissertation, a new type of transmitted-reference ultra-wideband system is proposed. Rather than separating the data and reference signals by a time delay as in a standard TR-UWB system, the proposed scheme uses a slightly frequency-shifted reference (FSR) that is orthogonal to the data-bearing signal over the symbol interval. The proposed FSR-UWB system not only significantly simplifies the receiver design by successfully avoiding the delay element, but also outperforms the standard TR-UWB system in error performance. A multi-differential (MD) FSR-UWB system is also introduced in this dissertation, where multiple data carriers employ a common reference carrier. Compared to the original single-differential FSR-UWB system, this modification essentially increases the number of (differential) degrees of freedom available for signaling in the system with only a negligible increase in bandwidth. Moreover, a higher data rate and an improved error performance are also achieved. Finally, a multiple-access (MA) FSR-UWB system is introduced. It will be shown in this dissertation that the receiver of the proposed MA FSR-UWB system achieves processing gain but does not require knowledge of the spreading code of the user of interest. Therefore, an extremely simple receiver structure can be implemented by avoiding the need for a costly de-spreading circuitry. In addition, synchronization of the proposed schemes is discussed. It is shown that the FSR-UWB systems can realize synchronization without difficulty - even in a multiple access environment. |
