Ranging in multiband ultrawideband communication systems

In this paper, we consider the problem of providing highly accurate time-delay or ranging estimates using multiple receptions of ranging signals in multiband communication systems. Specifically, we propose an algorithm to enhance the resolution of range and time-delay estimation in a multiband orthogonal frequency-division multiplexing system that has been proposed for the IEEE 802.15.3a wireless personal area networks. While this paper does not specifically address the problem of accurate localization in multipath nonline-of-sight environments, the proposed approach enhances the resolution and can be combined with any of the known techniques designed for such environments to provide an enhanced localization performance. Prior research has shown that the variance of the time-delay estimation error in white Gaussian noise is inversely proportional to the energy of probe signal and the square of its mean square bandwidth. In a multiband system with M subbands, traditional ranging techniques reduce the variance of the delay estimation from a single subband signal by a factor of M by properly combining M probing signals from all subbands. In contrast, we describe a new approach that synthesizes the return corresponding to a virtual large-bandwidth signal by appropriately merging the returns of M low-bandwidth ranging signals at the receiver. We show that using this technique, the variance of the delay estimation is reduced by a factor of [M.sup.3]. We also show that the proposed scheme achieves the Cramer-Rao lower bound under the high signal-to-noise ratio condition. Index Terms--Cramer-Rao lower bound (CRLB), multiband systems, ranging, ultrawideband (UWB) communications.