A Beaconless Asymmetric Energy-Efficient Time Synchronization Scheme for Resource-Constrained Multi-Hop Wireless Sensor Networks

The ever-increasing number of WSN deployments based on a large number of battery-powered, low-cost sensor nodes, which are limited in their computing and power resources, puts the focus of WSN time synchronization research on three major aspects, i.e., accuracy, energy consumption and computational complexity. In the literature, the latter two aspects have not received much attention compared to the accuracy of WSN time synchronization. Especially in multi-hop WSNs, intermediate gateway nodes are overloaded with tasks for not only relaying messages but also a variety of computations for their offspring nodes as well as themselves. Therefore, not only minimizing the energy consumption but also lowering the computational complexity while maintaining the synchronization accuracy is crucial to the design of time synchronization schemes for resource-constrained sensor nodes. In this paper, focusing on the three aspects of WSN time synchronization, we introduce a framework of reverse asymmetric time synchronization for resource-constrained multi-hop WSNs and propose a beaconless energy-efficient time synchronization scheme based on reverse one-way message dissemination. Experimental results with a WSN testbed based on TelosB motes running TinyOS demonstrate that the proposed scheme conserves up to 95% energy consumption compared to the flooding time synchronization protocol while achieving microsecond-level synchronization accuracy.Comment: 12 pages, 16 figure

Testing two-phase transition signaling based self-timed circuits in a synthesis environment

Journal ArticleThe problem of testing self-timed circuits generated by an automatic synthesis system is studied. Two-phase transition signalling is assumed and the circuits are targetted for an asynchronous macromodule based implementation as in [?, ?, ?, ?]. The partitioning of the circuits into control blocks, function blocks, and predicate (conditional) blocks, originally conceived for synthesis purpose, is found to be very elegant and appropriate for test generation. The problem of data dependent control flow is solved by introducing a new macromodule called SCANSELECT (SELECT with scan). Algorithms for test generation are based on the Petri-net like representation of the physical circuit. The techniques are illustrated on the high-level synthesis system called SHILPA being developed by the Author's

The limits of statistical significance of Hawkes processes fitted to financial data

Many fits of Hawkes processes to financial data look rather good but most of them are not statistically significant. This raises the question of what part of market dynamics this model is able to account for exactly. We document the accuracy of such processes as one varies the time interval of calibration and compare the performance of various types of kernels made up of sums of exponentials. Because of their around-the-clock opening times, FX markets are ideally suited to our aim as they allow us to avoid the complications of the long daily overnight closures of equity markets. One can achieve statistical significance according to three simultaneous tests provided that one uses kernels with two exponentials for fitting an hour at a time, and two or three exponentials for full days, while longer periods could not be fitted within statistical satisfaction because of the non-stationarity of the endogenous process. Fitted timescales are relatively short and endogeneity factor is high but sub-critical at about 0.8

How much can large-scale Video-On-Demand benefit from users' cooperation?'

International audienceWe propose an analytical framework to tightly characterize the scaling laws for the additional bandwidth that servers must supply to guarantee perfect service in peer-assisted Video-on-Demand systems, taking into account essential aspects such as peer churn, bandwidth heterogeneity, and Zipf-like video popularity. Our results reveal that the catalog size and the content popularity distribution have a huge effect on the system performance. We show that users' cooperation can effectively reduce the servers' burden for a wide range of system parameters, confirming to be an attractive solution to limit the costs incurred by content providers as the system scales to large populations of users

Reliable interface design for combining asynchronous and synchronous circuits

Journal ArticleAbstract: In order to successfully integrate asynchronous and synchronous designs, great care must be taken at the interface between the two types of systems. Synchronizing asynchronous inputs with a free running clock can cause well-known problems with metastability in the synchronization circuits. Stretchable clocks allow a clock cycle to expand dynamically in response to the metastability effects of sampling asynchronous inputs. We use an interface organization where the special circuitry for detecting metastability and for stretching the clock that is delivered to the synchronous part of the system is encapsulated in a Q-flop-based interface. This provides a very convenient method for interfacing mixed systems, as the interface and clock generation circuitry are isolated into one special module, and neither the asynchronous nor the synchronous system need be modified internally to accommodate the interface. This is especially important when standard synchronous components are used as there is no opportunity to modify these parts. We show that this interface module is suitable for most mixed design needs and conclude with an example

Research on Mobile Phone Data in the Global South: Opportunities and Challenges

The rapid uptake of mobile phones in the global South—that is, developing countries located primarily in the Southern Hemisphere—is a fact that is often repeated in popular discourse as well as academic research. In the years since it became a favorite factoid, there have been shifts in some of the most well-known patterns of use, with new data being created and collected. To a large extent, communication and information researchers have yet to fully address the opportunities and challenges regarding these changes. This chapter outlines some of the shifts in usage trends, what kinds of data they generate, and what kinds of questions they can help answer about social and economic ties, mobility and location, and innovation and design. These can strengthen theorizing new communication practices and generate greater knowledge about life in a networked age for those in resource-constrained environments

Demonstration of a Standalone, Descriptive, and Predictive Digital Twin of a Floating Offshore Wind Turbine

Digital Twins bring several benefits for planning, operation, and maintenance of remote offshore assets. In this work, we explain the digital twin concept and the capability level scale in the context of wind energy. Furthermore, we demonstrate a standalone digital twin, a descriptive digital twin, and a prescriptive digital twin of an operational floating offshore wind turbine. The standalone digital twin consists of the virtual representation of the wind turbine and its operating environment. While at this level the digital twin does not evolve with the physical turbine, it can be used during the planning-, design-, and construction phases. At the next level, the descriptive digital twin is built upon the standalone digital twin by enhancing the latter with real data from the turbine. All the data is visualized in virtual reality for informed decision-making. Besides being used for data bundling and visualization, the descriptive digital twin forms the basis for diagnostic, predictive, prescriptive, and autonomous tools. A predictive digital twin is created through the use of weather forecasts, neural networks, and transfer learning. Finally, digital twin technology is discussed in a much wider context of ocean engineering