Indoor positioning has grasped great attention in recent years. A number of efforts have been exerted to achieve high positioning accuracy. However, there exists no technology that proves its efficacy in various situations. In this paper, we propose a novel positioning method based on fusing trilateration and dead reckoning. We employ Kalman filtering as a position fusion algorithm. Moreover, we adopt an Android device with Bluetooth Low Energy modules as the communication platform to avoid excessive energy consumption and to improve the stability of the received signal strength. To further improve the positioning accuracy, we take the environmental context information into account while generating the position fixes. Extensive experiments in a testbed are conducted to examine the performance of three approaches: trilateration, dead reckoning and the fusion method. Additionally, the influence of the knowledge of the environmental context is also examined. Finally, our proposed fusion method outperforms both trilateration and dead reckoning in terms of accuracy: experimental results show that the Kalman-based fusion, for our settings, achieves a positioning accuracy of less than one meter.

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Replicating data in a distributed system is a suitable means for increasing the availability as well as the performance of data access operations. Unfortunately, there exists a trade-o between these two properties: a replica control protocol which exhibits, e.g., a high read availability and low read operation costs usually su ers from low write availability and high write operation costs. This trade-o is visible for protocols like Weighted Voting for which the above characteristics can be customized by adjusting certain protocol parameters. Changing the read and write quorums of a Weighted Voting protocol while preserving the protocol's correct behavior increases either the read availability and the write operation costs or the write availability and the read operation costs but not both a the same time. In this paper, we prove that for a large class of replica control protocols, a certain symmetry between the read and write operation availability exists. We further demonstrate how a protocol without this symmetry property can be optimized such that the resulting protocol has identical cost but a higher read or write availability or both. We present two design strategies which lead to those optimized replica control protocols. By using the well-known Grid Protocol which lacks symmetry as an example, we apply our ndings to derive two di erent replica c ontrol protocols with superior characteristics.

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