To effectively maintain and analyze a large amount of real-time sensor data, one often uses a filtering technique that reflects characteristics of original data well. This paper proposes a novel method for recommending the measurement noise for Kalman filtering, which is one of the most representative filtering techniques. Kalman filtering corrects inaccurate values of input sensor data, and its filtering performance varies depending on the input noise parameters. In particular, if the noise parameters determined based on the user’s experience are incorrect, the accuracy of Kalman filtering may be reduced significantly. Based on this observation, this paper addresses how to determine the measurement noise variance, a major input parameter of Kalman filtering, by analyzing past sensor data and how to use the estimated noise to improve the filtering accuracy. More specifically, to estimate the measurement noise variance, two analytical methods are proposed: one a transform-based method using a wavelet transform and the other a learning-based method using a denoising autoencoder. Experimental results show that the proposed methods estimated the measurement noise variance accurately and were superior to the experience-based method in the filtering accuracy.

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As a large amount of data streams occur rapidly in many recent applications such as social network service, Internet of Things, and smart factory, sampling techniques have attracted many attentions to handle such data streams efficiently. In this article, we address the performance improvement of binary Bernoulli sampling in the multi-source stream environment. Binary Bernoulli sampling has the n:1 structure where n sites transmit data to 1 coordinator. However, as the number of sites increases or the input stream explosively increases, the binary Bernoulli sampling may cause a severe bottleneck in the coordinator. In addition, bidirectional communication over different networks among the coordinator and sites may incur excessive communication overhead. In this article, we propose a novel distributed processing model of binary Bernoulli sampling to solve these coordinator bottleneck and communication overhead problems. We first present a multiple-coordinator structure to solve the coordinator bottleneck. We then present a new sampling model with an integrated framework and shared memory to alleviate the communication overhead. To verify the effectiveness and scalability of the proposed model, we perform its actual implementation in Apache Storm, a real-time distributed stream processing system. Experimental results show that our Storm-based binary Bernoulli sampling improves performance by up to 1.8 times compared with the legacy method and maintains high performance even when the input stream largely increases. These results indicate that the proposed distributed processing model is an excellent approach that solves the performance degradation problem of binary Bernoulli sampling and verifies its superiority through the actual implementation on Apache Storm.

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