Near-Far Resistant Ultra-Wideband Communications in Multiple-Access Environments

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Title: Near-Far Resistant Ultra-Wideband Communications in Multiple-Access Environments
Author: Li, Liping
Advisors: Keith Townsend, Committee Chair
Bojko Bakalov, Committee Member
Brian Hughes, Committee Co-Chair
Huaiyu Dai, Committee Member
Robert Ulman, Committee Member
Abstract: Ultra-Wideband (UWB) systems promise high data rate and accurate localization capabilities for communications, imaging, sensor networks, and vehicular systems. The simple UWB receiver structure is especially attractive to applications which require low cost and low power consumption. However, the envisioned simple receiver designs are also fraught with challenges ranging from estimation of highly frequency-selective multipath channels to synchronization of received signals consisting of very narrow pulses. In this context, transmitted reference (TR) UWB systems have been proposed in the literature as one way to avoid computationally intensive channel estimation while still maintaining a relatively simple receiver structure. In this dissertation, we investigate the performance of TR UWB communication systems in multiple-access environments. We remove the commonly invoked assumption of perfect power control and include in our analysis an additional group of users which have power levels much higher than the desired user. The detrimental effects of high-power users are suppressed by chip discrimination in this dissertation. To yield a straightforward mapping between the number of equal-power users and the variance of the resulting MAI, we incorporate the power delay profile (PDP) of the channel in the analysis, which makes the theoretical analysis tractable. This analytical technique of using PDP is also applied to analyze the MAI in frequency-shifted reference (FSR) UWB systems.The near-far problem also arises for synchronization when high-power users are included in the network. In this dissertation, we propose and investigate a synchronization procedure which is near-far resistant. By exploiting the structure of interfering power levels, we devise an efficient suppression technique which only requires the knowledge of the spreading code of the desired user. Complexmatrix operations required by other techniques found in the CDMA literature are not required in our suppression process. We also propose a new dimension-based technique for the detection of the code phase based on the suppressed signal. Simulation results validate our proposed near-far resistant synchronization technique and the superior performance is shown when compared to the current literature.
Date: 2009-12-04
Degree: PhD
Discipline: Electrical Engineering

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