In many mobile wireless applications such as the automated driving of cars, formation flying of unmanned air vehicles, and source localization or target tracking with wireless sensor networks, it is more important to know the precise relative locations of nodes than their absolute coordinates. GPS, the most ubiquitous localization system available, generally provides only absolute coordinates. Furthermore, low-cost receivers can exhibit tens of meters of error or worse in challenging RF environments. This paper presents an approach that uses GPS to derive relative location information for multiple receivers. Nodes in a network share their raw satellite measurements and use this data to track the relative motions of neighboring nodes as opposed to computing their own absolute coordinates. The system has been implemented using a network of Android phones equipped with a custom Bluetooth headset and integrated GPS chip to provide raw measurement data. Our evaluation shows that centimeter-scale tracking accuracy at an update rate of 1 Hz is possible under various conditions with the presented technique. This is more than an order of magnitude more accurate than simply taking the difference of reported absolute node coordinates or other simplistic approaches due to the presence of uncorrelated measurement errors.
Molecular dynamics simulators are indispensable tools in the arsenal of chemical engineers and material scientists. However, they are often difficult to use and require programming skills as well as deep knowledge of both the given scientific domain and the simulation software itself. In this paper, we describe a metaprogramming approach where simulator experts can create a library of simulation components and templates of frequently used simulations. Domain experts, in turn, can build and customize their own simulations and the required input for the various supported simulators is automatically synthesized. The web-based environment also supports setting up a suite of simulation jobs, for example, to carry out automated parameter optimization, via a visual programming environment. The entire simulation setup – including the various parameters, the version of tools utilized and the results – is stored in a database to support searching and browsing of existing simulation outputs and facilitating the reproducibility of scientific results.
We present an analytical framework for formulating partition configuration problems in real-time systems with dependencies, particularly applicable to modeling systems with multiple criticality or security levels. Partition configuration constraints for real-time tasks include affinity and conflict. We also discuss the application of the framework to arbitrary partition schedulers, harmonic partition execution, and round robin partition execution (which is particularly problematic). Our interest is in minimizing end-to-end latency, though the computational complexity of the problem prevents us from finding optimal results. We conclude with some open problems.
Fractionated spacecraft are clusters of small, inde- pendent modules that interact wirelessly to realize the function- ality of a traditional monolithic spacecraft. System F6 (F6 stands for Future, Fast, Flexible, Fractionated, Free-Flying spacecraft) is a DARPA program for fractionated spacecraft. Software applications in F6 are implemented in the context of the F6 Information Architecture Platform (IAP), which provides component-based abstractions for composing distributed applications. The lifecycle of these distributed applications must be managed autonomously by a deployment and configuration (D&C) infrastructure, which can redeploy and reconfigure the running applications in response to faults and other anomalies that may occur during system operation. Addressing these D&C requirements is hard due to the significant fluctuation in resource availabilities, constraints on resources, and safety and security concerns. This paper presents the key architectural ideas that are required in realizing such a D&C infrastructure.
For most wireless sensor network (WSN) applications, the position of the sensor nodes needs to be known. GPS has not t into WSN very well due to its price, power consumption, accuracy, and limitations in its operating environment. Hence, the last decade brought about a large number of proposed methods for WSN node localization. They show tremendous variation in the physical phenomena they use, the signal properties they measure, the resources they consume, as well as their accuracy, range, advantages and limitations. This paper provides a high-level, com- prehensive overview of this very active research area.