Acquisition of direct-sequence ultra-wideband signals

Very high rate packet data systems, such as those based on ultra-wideband (UWB) signaling, face an increasingly important challenge - achieving fast timing acquisition and synchronization (which must be done typically on an individual packet basis) to minimize preamble overhead and optimize (packet) throughput. Impulse based UWB modulation schemes use short (nano-second) time-duration pulses that are appropriately shaped - the resulting high resolution in time implies that the acquisition algorithm must employ sub-pulse duration steps, thereby leading to a large search space if a serial timing acquisition approach is used. Moreover, owing to the strict average transmit power limitations on UWB transmissions resulting from the Part 15 limits imposed by the FCC, a large number of pulses need to be integrated for reliable acquisition decisions, which consequently leads to large mean acquisition times (MAT). We investigate the performance of the conventional serial search and random search schemes applied to the acquisition of UWB signals in multipath environments. It is shown that over typical UWB multipath channels, a random search scheme may yield lower MAT than serial search.