Browsing by Subject "Maximum a posteriori"
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Item Open Access Data imputation through the identification of local anomalies(Institute of Electrical and Electronics Engineers Inc., 2015) Ozkan, H.; Pelvan, O. S.; Kozat, S. S.We introduce a comprehensive and statistical framework in a model free setting for a complete treatment of localized data corruptions due to severe noise sources, e.g., an occluder in the case of a visual recording. Within this framework, we propose: 1) a novel algorithm to efficiently separate, i.e., detect and localize, possible corruptions from a given suspicious data instance and 2) a maximum a posteriori estimator to impute the corrupted data. As a generalization to Euclidean distance, we also propose a novel distance measure, which is based on the ranked deviations among the data attributes and empirically shown to be superior in separating the corruptions. Our algorithm first splits the suspicious instance into parts through a binary partitioning tree in the space of data attributes and iteratively tests those parts to detect local anomalies using the nominal statistics extracted from an uncorrupted (clean) reference data set. Once each part is labeled as anomalous versus normal, the corresponding binary patterns over this tree that characterize corruptions are identified and the affected attributes are imputed. Under a certain conditional independency structure assumed for the binary patterns, we analytically show that the false alarm rate of the introduced algorithm in detecting the corruptions is independent of the data and can be directly set without any parameter tuning. The proposed framework is tested over several well-known machine learning data sets with synthetically generated corruptions and experimentally shown to produce remarkable improvements in terms of classification purposes with strong corruption separation capabilities. Our experiments also indicate that the proposed algorithms outperform the typical approaches and are robust to varying training phase conditions. © 2015 IEEE.Item Open Access On capacity and coding for segmented deletion channels(IEEE, 2011) Wang, F.; Aktaş, Defne; Duman, T. M.We consider binary deletion channels with a segmentation assumption which appears to be suited for more practical scenarios. Unlike the binary independent and identically distributed (i.i.d.) deletion channel where each bit is independently deleted with an equal probability, the segmentation assumption prohibits certain transmitted bits to be deleted, i.e., in a block of bits of a certain length, only a limited number of deletions can occur. We first propose several upper and lower capacity bounds for the segmented deletion channel. Then we focus on an interleaved concatenation of an outer low-density parity check (LDPC) code with error-correction capabilities and an inner marker code with synchronization capabilities over these channels. With the help of a specifically designed maximum-a-posteriori (MAP) detector, we demonstrate reliable transmission at higher code rates than the existing ones reported in the literature.