On equal-gain combining for acquisition of time-hopping ultra-wideband signals

The acquisition of ultra-wideband (UWB) signals is a potential bottleneck for system throughput in a packet-based network employing UWB signaling format in the physical layer. The problem is mainly due to the low received signal power and the fine time resolution which forces the acquisition system to process the signal over long periods of time before getting a reliable estimate of the timing of the signal. Hence, there is a need to develop more efficient acquisition schemes by taking into account the signal and channel characteristics. In this paper, we investigate two approaches, the square-and-integrate and the integrate-and-square, which collect the energy in the multipaths by performing equal-gain combining (EGC) to improve the acquisition performance. We define the hit set as the set of hypothesized phases which can guarantee adequate system performance after acquisition, and also study the effect of the EGC window length on the acquisition performance.     

SALDEFT: Self-Adaptive Learning Differential Evolution Based Optimal Physical Machine Selection for Fault Tolerance Problem in Cloud

Wireless Personal Communications - In recent years, cloud computing plays a significant role in offering several applications with high-level reliability, availability, and security as well as...     

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.     

Maximum Likelihood Localization of a Diffusive Point Source Using Binary Observations

In this paper, we investigate the problem of localization of a diffusive point source of gas based on binary observations provided by a distributed chemical sensor network. We motivate the use of the maximum likelihood (ML) estimator for this scenario by proving that it is consistent and asymptotically efficient, when the density of the sensors becomes infinite. We utilize two different estimation approaches, ML estimation based on all the observations (i.e., batch processing) and approximate ML estimation using only new observations and the previous estimate (i.e., real time processing). The performance of these estimators is compared with theoretical bounds and is shown to achieve excellent performance, even with a finite number of sensors     

On the asymptotic performance of threshold-based acquisition systems in multipath fading channels

The asymptotic performance of timing acquisition systems having fixed dwell time in multipath fading channels is investigated. The detrimental effect of the multipath channel fading on the acquisition performance is isolated by considering the asymptotic performance as the average signal-to-noise ratio (SNR) increases. It is found that for any threshold such that the average probability of false alarm is less than a given tolerance, the channel fading results in a lower bound on the asymptotic average probability of miss which is nontrivial for a variety of fading scenarios. A threshold-based direct-sequence spread-spectrum signal acquisition system is considered and it is found that the detrimental effect of channel fading on asymptotic acquisition performance, albeit nontrivial, is not very significant. The asymptotic acquisition performance of two threshold-based acquisition schemes for ultra-wideband (UWB) signals with time-hopping (TH) spreading are also evaluated and compared. For both schemes, the detrimental effect of the channel fading on the asymptotic acquisition performance turns out to be significant.     

Sea Turtle Foraging and Hydrozoan Optimization Algorithm-based NLOS Node Positioning Scheme for Reliable Data Dissemination in Vehicular Ad hoc Networks

Wireless Personal Communications - Wireless sensor networks have become one of the prominent and persuasive methods for surveillance of inaccessible physical areas and are employed in innumerable...