Low Complexity Ultra-Wideband (UWB) Communication Systems in Presence of Multiple-Access Interference

Ultra-wideband (UWB) communication systems use radio signals with a bandwidth in the range of some hundred MHz to several GHz. Radio channels with dense multipath propagation achieve high multipath diversity, which can be used to improve the robustness and capacity of the communication channel. Furthermore the large bandwidth allows to transmit signals with a small power spectral density such that the interference to other radio signals will be negligible, even if they lie within the same frequency band. In this work the focus is on low-complexity receiver architectures for communication systems in presence of multiple-access interference (MAI). The main objective of this thesis is to develop and to study a framework for communications for transmitted reference (TR) UWB systems and energy detection UWB systems. First, we study the hybrid matched-filter (HMF) receiver for TR UWB systems, which employs matched filters in front of the autocorrelation receiver (AcR). We investigate optimization of the combining weights in the matched filters with the purpose of suppressing MAI. For that goal, we included MAI contributions in an equivalent system model for the HMF-TR UWB receiver and derived a modified pre-combining minimum mean-square error solution for multiuser detection. The obtained solution is novel, due to the non-linear behavior of the autocorrelation operation. The proposed detectors are shown to yield improved performance over the multi-channel autocorrelation receiver. Second, the performance of a dual-pulse TR UWB system is presented in presence of MAI. We derive an analytical expression of the channel-averaged signal-to-interference ratio for a TR UWB receiver in two asynchronous scenarios, based on random time-hopping codes. Analytical results and numerical results are presented for illustration. We further show the impact of the chosen system parameters (e.g., symbol duration and delay hopping code) to better understand their influence on the multi-user performance. Third, we introduce optimization of the energy detection UWB receiver system. We have considered a weighted energy detection receiver that alleviates the noise effect in a single user scenario and the multiple-access influence in a multiple-access environment. We have demonstrated that the weighted receiver outperforms the conventional energy detection receiver.