This paper deals with the issue of monitoring physical phenomena using wireless sensor networks. It provides principal component analysis for the time series of sensors' measurements. Without the need to compute the sample covariance matrix, we derive several in-network strategies to estimate the principal axis, including noncooperative and diffusion strategies. The performance of the proposed strategies is illustrated in the issue of monitoring gas diffusion.

Cloud computing has gained an important role in providing high quality and cost-effective IT services by outsourcing part of their operations to dedicated cloud providers. If intrinsic security issues of this architecture have been extensively studied, it has recently been considered as a ready-to-use platform able to perform malicious activities, thus offering new targets for indirect threats. However, its large scale, the heterogeneous and dynamic nature of the activities it executes, as well as multitenancy and privacy-related issues, make the security operation complex. Consequently, cloud providers can hardly detect and mitigate malicious activities they unknowingly host. Leveraging the autonomic paradigm represents a promising solution to face such a complexity, but it requires efficient grounded monitoring and analysis functions to efficiently detect malicious activities hidden within the large number of legitimate ones. In this effort, this paper presents a robust and cost-effective solution to detect malicious activities in a public virtualized environment. Its contribution is twofold: (1) a scalable and robust workload estimation of the virtual host activities in a cloud and (2) a detection algorithm able to discriminate infected hosts with low malicious activities hidden within their legitimate workload and potentially scattered on several tenants. For both of these contributions, we establish their theoretical performance, which demonstrates their optimality, and we evaluate their efficiency on a dataset made of real data collected on PlanetLab. Finally, we study the scalability on a large dataset that consists of simulated data resulting from the real dataset modeling. This demonstrates

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This paper deals with the issues of the dimensionality reduction and the extraction of the structure of data using principal component analysis for the multivariable data in large-scale networks. In order to overcome the high computational complexity of this technique, we derive several in-network strategies to estimate the principal axes without the need for computing the sample covariance matrix. To this aim, we propose to combine Oja's iterative rule with average gossiping algorithms. Gossiping is used as a solution for communication between asynchronous nodes. The performance of the proposed approach is illustrated on time series acquisition in wireless sensor networks.