A search strategy for ultra-wideband signal acquisition

The ultra-wideband (UWB) channel is characterized by the presence of dense multipath and robustness to multipath fading. By taking system performance subsequent to acquisition into account, it was shown recently that there are multiple phases (called the hit set) where a receiver lock can be considered as successful acquisition. In this case, the serial search may no longer be the optimal choice for the sequential search strategy in the acquisition system. In this letter, we consider the problem of finding better search strategies in the set of all search strategies which are permutations of the search space. The large size of the search space and the absence of any exploitable structure make the problem of finding the permutation search strategy which minimizes the mean detection time prohibitively complex. However, if we take the first-order approximation that the probabilities of detection of all the hit-set phases are equal, then there exists a permutation search strategy which minimizes the mean detection time. Since the actual probabilities of detection are not equal, this search strategy, although not optimal, serves as a useful heuristic solution to an otherwise intractable problem. Furthermore, we see that this search strategy has a simple Jump-by-H structure, and improves the mean detection time by a significant amount compared with the serial search.