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UBC Theses and Dissertations

Multiuser pre-filtered ultra-wideband systems Ahmadian, Zahra


Ultra-wideband (UWB) communication enables license-exempt transmission with very low power over large bandwidths. The technology can provide very high data rates over short transmission ranges to support applications such as real-time data streaming, interchip communication and wireless memory. The work in this thesis considers a particular type of high data-rate multiuser direct-sequence UWB (DS-UWB) with popular and commonly used binary UWB signalling. The system consists of multiple low-complexity DS-UWB transceivers (nodes) and a central unit that is more powerful in terms of signal processing capabilities. We mostly focus on the transmission from the central unit to the nodes. We address the following main questions: (1) What signal processing should be applied at the central unit to enable simple yet reliable detection at low-complexity nodes? (2) How can the system performance be optimized in the presence of imperfect channel estimation? (3) Is it possible to improve the system performance by incorporating the binary detector structure in the transmitter design? (4) How can the performance of a network of multiple UWB nodes communicating through a central relay be optimized? For question (1), we propose to shift the signal processing load from the nodes to the central unit via pre-filtering (the combination of pre-rake and pre-equalization) of the transmit signal at the central node, and we provide filter design strategies for the downlink communication. Questions (2) is addressed by studying the impact of errors in estimation of the channel impulse response at the central unit. Two mathematical models are proposed to represent the channel estimation error and robust strategies are formulated for the design of downlink pre-equalization filters (PEFs). For the popular binary UWB signalling, the real-part of the received signal contains sufficient statistics for signal detection. Hence the widely linear design of PEFs is proposed to answer question (3). As for question (4), we extend our design methods to multi-way internode communication via a central relay. Two relaying strategies namely, detect-and-forward relaying and filter-and-forward relaying with partial and full self-interference cancellation are devised.

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