A New Search Space Reduction Technique for Rapid Acquisition of UWB Signals in Multipath Channels

Ultra-wideband (UWB) radio is a promising technology for low-cost, high-rate communications at short ranges. However, high bandwidth and low power of the UWB signals impose some difficult challenges in signal processing and implementation of the receiver. Acquisition of the signal timing is the first task to be performed in a coherent receiver. The high bandwidth of UWB signals demand for fine time resolution search of the uncertainty region. Thus, for an accurate acquisition, the uncertainty region must be searched in small step sizes, imposing a large search space. Moreover, the low transmission power of UWB systems requires the receiver to observe the received signal for a long time in order to make a reliable decision. These are the two reasons that cause the receiver to spend a long time for acquisition of the signal timing. The fine time resolution, on the other hand, results in a large number of resolvable multipath components which locking to many of them might be treated as a good estimate of the timing information of the received signal. Hence, in a multipath channel there may be more than one phase that could be considered a reliable estimate of the true signal timing.
In this paper, we propose a new two-stage search space reduction technique which speeds up the acquisition process without adding additional complexity to the conventional serial acquisition method. Specifically, we divide the search space into some groups of consecutive phases and the first stage tries to find a set of possible positions of the true phase relative to the positions of the groups using a special template signal. When a set of phases?one from each group?is declared to include the true phase, the second stage tries to find the absolute position of the true phase by searching the relative positions in each group using a simple template signal. The performance of the proposed method is analytically evaluated in terms of mean acquisition time and the results are validated through computer simulations. For the simulations we performed in this paper, a complete fully parameterized model of the system is designed using MATLAB/Simulink software. The results show a significant improvement in acquisition time with no additional complexity.