The conventional ultra-wideband (UWB) synchronization schemes could cause poor performance in receiver operations such as demodulation after the synchronization, since unreliable timing information corresponding to low-power multipath components might be transferred to the next stage. To solve this problem, in this paper, we propose novel synchronization schemes for UWB systems. We first derive an optimal scheme based on the maximum likelihood (ML) criterion and then develop a simpler suboptimal scheme. Simulation results show that both proposed schemes provide a better synchronization performance than the conventional scheme.
[Show abstract][Hide abstract] ABSTRACT: The problem of initial acquisition of ultrawideband (UWB)
signals in the dense multipath channel is addressed. We demonstrate the
advantages of designing the acquisition system so that the size of the uncertainty
region is a Fibonacci number and propose a simple search strategy
for coarse synchronization that uses no channel knowledge, extending a
previous work where we proposed a method based on the golden section,
which practically achieved the minimum mean acquisition time (MAT)
under a simplistic model. We derive the MAT of the new strategy for this
model and compare it with simulation results for a realistic propagation
scenario with a high signal-to-noise ratio (SNR). There is an agreement
between the theoretical and simulated MATs, which is limited by the
differences between the two models. Simulations from moderate to high
SNRs confirm that the proposed strategy provides a simple way to achieve
the performance of the best strategies for acquisition of wide-bandwidth
signals. In particular, it is similar in terms of complexity and performance
to the popular bit reversal search, thus providing alternatives in the choice
of design parameters wherever the bit reversal search is advisable.
[Show abstract][Hide abstract] ABSTRACT: Very high rate packet data systems such as those based on wideband spread-spectrum (SS) signaling face an important challenge - achieving fast and reliable acquisition to minimize preamble overhead and optimize packet throughput. Such wideband modulation schemes undergo frequency selective fading, implying a very large number of resolved multipath components. Thus, the conventional analyses of serial search acquisition schemes based on simplifying assumptions that are valid in narrow(er) band systems (and are invalid for sufficiently wideband systems) need to be revamped. Also, there is a need to devise new schemes that exploit the presence of multipath components for faster acquisition over simple serial search. Our work provides novel contributions in both these aspects: we analyze serial and random search acquisition schemes and compare their performances in several multipath environments. It is shown that over many typical indoor channels, random search offers significantly lower mean acquisition times
[Show abstract][Hide abstract] ABSTRACT: 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.
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