Near-far resistant ultra-wideband communications in multiple-access environments

LI, LIPING. Near-Far Resistant Ultra-Wideband Communicat ions in Multiple-Access Environments. (Under the direction of Dr. J. Keith Townsend ). Ultra-Wideband (UWB) systems promise high data rate and acc ur te localization capabilities for communications, imaging, sensor networks, an d vehicular systems. The simple UWB receiver structure is especially attractive to applica tions which require low cost and low power consumption. However, the envisioned simple rece iv r designs are also fraught with challenges ranging from estimation of highly frequenc y-selective multipath channels to synchronization of received signals consisting of very n arrow pulses. In this context, transmitted reference (TR) UWB systems have been proposed i n the literature as one way to avoid computationally intensive channel estimation whi le still maintaining a relatively simple receiver structure. In this dissertation, we investigate the performance of TR U WB communication systems in multiple-access environments. We remove the common ly invoked assumption of perfect power control and include in our analysis an additio nal group of users which have power levels much higher than the desired user. The detrimen tal ffects of high-power users are suppressed by chip discrimination in this dissert ation. To yield a straightforward mapping between the number of equal-power users and the vari ance 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 techn ique of using PDP is also applied to analyze the MAI in frequency-shifted reference (FSR) UWB sy stems. The near-far problem also arises for synchronization when h igh-power users are included in the network. In this dissertation, we propose and i nvestigate a synchronization procedure which is near-far resistant. By exploiting the st ructure of interfering power levels, we devise an efficient suppression technique which only requires the knowledge of the spreading code of the desired user. Complex matrix operatio ns required by other techniques found in the CDMA literature are not required in our suppress ion process. We also propose a new dimension-based technique for the detection of the cod phase based on the suppressed signal. Simulation results validate our proposed n ear-far resistant synchronization technique and the superior performance is shown when compar ed to the current literature. Near-Far Resistant Ultra-Wideband Communications in Mult iple-Access Environments by Liping Li A dissertation submitted to the Graduate Faculty of North Carolina State University in partial fullfillment of the requirements for the Degree of Doctor of Philosophy Electrical Engineering Raleigh, North Carolina 2009