In transmitted-reference (TR) and frequency-shifted reference (FSR) ultrawideband (UWB) systems, data and reference signals are shifted relative to each other in time and frequency domains, respectively. The main advantage of these systems is that they remove strict requirements of channel estimation. In order to implement TR UWB systems, an analog delay line, which is difficult to build in an integrated fashion, is needed. Although FSR systems require frequency conversion at the receiver, which is much simpler in practice, they have data rate limitations. Instead, a code-multiplexed transmitted-reference (CM-TR) UWB system that transmits data and reference signals using two distinct orthogonal codes can be considered. This system requires a simpler receiver and has better performance than TR and FSR. In the first part of the thesis, CM-TR systems are investigated and probability of error expressions are obtained. For the single user case, a closed-form expression for the exact probability of error is derived. For the multiuser case, a closed-form expression is derived based on the Gaussian approximation, and the

results are compared in different scenarios. In the second part of the thesis, some optimal and suboptimal receivers are studied. First, low complexity receivers, such as the blinking receiver (BR) and the chip discriminator, are presented. The requirements for these types of receivers are explained, and the conditions under which their performance can be improved are discussed. Then, an analytical analysis of the linear minimum mean-squared error (MMSE) receiver and the requirements to implement this MMSE receiver are provided. Lastly, the optimal maximum-likelihood (ML) detector is derived, which has higher computational complexity and more strict requirements than the other receivers. Finally, simulation results are presented in order to verify the theoretical results and to compare the performance of the receivers.