In this paper, we propose two time of arrival estimators for ultra wideband signals based on the phase difference\r\nbetween the discrete Fourier transforms (DFT) of the transmitted and received signals. The first estimator is based\r\non the slope of the unwrapped phase and the second one on the absolute unwrapped phase. We derive the\r\nstatistics of the unwrapped phase. We show that slope-based estimation almost achieves asymptotically the\r\nbaseband Cramer-Rao lower bound (CRLB), while the absolute-phase-based estimator achieves asymptotically the\r\npassband CRLB. We compare the proposed estimators to the time-domain maximum likelihood estimator (MLE).\r\nWe show that the MLE achieves the CRLB faster than the DFT-based estimator, while the DFT-based estimator\r\noutperforms the MLE for low signal to noise ratios. We describe also how to use the proposed estimators in\r\nmultipath UWB channels.
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