Two-stage acquisition for UWB in dense multipath

Traditional synchronization techniques applied to impulse-radio ultra-wideband (UWB) result in prohibitively long acquisition times, due to the extremely large search space. Additionally, in dense multipath environments, there exist a larger number of cells within the uncertainty region that can lead to acquisition lock. Locking to an arbitrary multipath component may result in unacceptable performance for many applications (range error in positioning systems for example). In this paper, we present a modified framework for the analysis of UWB acquisition which accommodates multiple lock cells. The framework divides the acquisition process into two distinct phases. The two phases are termed "coarse" and "fine" acquisition. The coarse acquisition phase is a fast implementation of traditional serial search which takes advantage of the large number of cells which can terminate the search process. Fine acquisition exploits statistics derived from the first phase and the clustered nature of multipath arrivals to determine the earliest arriving path, even when it is severely attenuated. We show that the first phase provides a substantial improvement in mean acquisition time compared with traditional serial search and that the second phase provides robust estimation of the first arriving path in ranging applications.