Browsing by Author "Yar, Ersin"
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Item Open Access A complete framework of radar pulse detection and modulation classification for cognitive EW(Institute of Electrical and Electronics Engineers Inc., 2019) Yar, Ersin; Kocamış, M. B.; Orduyılmaz, A.; Serin, M.; Efe, M.In this paper, we consider automatic radar pulse detection and intra-pulse modulation classification for cognitive electronic warfare applications. In this manner, we introduce an end-to-end framework for detection and classification of radar pulses. Our approach is complete, i.e., we provide raw radar signal at the input side and produce categorical output at the output. We use short time Fourier transform to obtain time-frequency image of the signal. Hough transform is used to detect pulses in time-frequency images and pulses are represented with a single line. Then, convolutional neural networks are used for pulse classification. In experiments, we provide classification results at different SNR levels.Item Open Access Estimating distributions varying in time in a universal manner(IEEE, 2017) Gökçesu, Kaan; Manış, Eren; Kurt, Ali Emirhan; Yar, ErsinWe investigate the estimation of distributions with time-varying parameters. We introduce an algorithm that achieves the optimal negative likelihood performance against the true probability distribution. We achieve this optimum regret performance without any knowledge about the total change of the parameters of true distribution. Our results are guaranteed to hold in an individual sequence manner such that we have no assumptions on the underlying sequences. Apart from the regret bounds, through synthetic and real life experiments, we demonstrate substantial performance gains with respect to the state-of-the-art probability density estimation algorithms in the literature.Item Open Access Online text classification for real life tweet analysis(IEEE, 2016) Yar, Ersin; Delibalta, İ.; Baruh, L.; Kozat, Süleyman SerdarIn this paper, we study multi-class classification of tweets, where we introduce highly efficient dimensionality reduction techniques suitable for online processing of high dimensional feature vectors generated from freely-worded text. As for the real life case study, we work on tweets in the Turkish language, however, our methods are generic and can be used for other languages as clearly explained in the paper. Since we work on a real life application and the tweets are freely worded, we introduce text correction, normalization and root finding algorithms. Although text processing and classification are highly important due to many applications such as emotion recognition, advertisement selection, etc., online classification and regression algorithms over text are limited due to need for high dimensional vectors to represent natural text inputs. We overcome such limitations by showing that randomized projections and piecewise linear models can be efficiently leveraged to significantly reduce the computational cost for feature vector extraction from the tweets. Hence, we can perform multi-class tweet classification and regression in real time. We demonstrate our results over tweets collected from a real life case study where the tweets are freely-worded, e.g., with emoticons, shortened words, special characters, etc., and are unstructured. We implement several well-known machine learning algorithms as well as novel regression methods and demonstrate that we can significantly reduce the computational complexity with insignificant change in the classification and regression performance.Item Open Access Text categorization using syllables and recurrent neural networks(2017-07) Yar, ErsinWe investigate multi class categorization of short texts. To this end, in the third chapter, we introduce highly efficient dimensionality reduction techniques suitable for online processing of high dimensional feature vectors generated from freely-worded text. Although text processing and classification are highly important due to many applications such as emotion recognition, advertisement selection, etc., online classification and regression algorithms over text are limited due to need for high dimensional vectors to represent natural text inputs. We overcome such limitations by showing that randomized projections and piecewise linear models can be efficiently leveraged to significantly reduce the computational cost for feature vector extraction from the tweets. We demonstrate our results over tweets collected from a real life case study where the tweets are freely-worded and unstructured. We implement several well-known machine learning algorithms as well as novel regression methods and demonstrate that we can significantly reduce the computational complexity with insignificant change in the classification and regression performance.Furthermore, in the fourth chapter, we introduce a simple and novel technique for short text classification based on LSTM neural networks. Our algorithm obtains two distributed representations for a short text to be used in classification task. We derive one representation by processing vector embeddings corresponding to words consecutively in LSTM structure and taking average of the produced outputs at each time step of the network. We also take average of distributed representations of the words in the short text to obtain the other representation. For classification, weighted combination of both representations are calculated. Moreover, for the first time in literature we propose to use syllables to exploit the sequential nature of the data in a better way. We derive distributed representations of the syllables and feed them to an LSTM network to obtain the distributed representation for the short text. Softmax layer is used to calculate categorical distribution at the end. Classification performance is evaluated in terms of AUC measure. Experiments show that utilizing two distributed representations improves classification performance by 2%. Furthermore, we demonstrate that using distributed representations of syllables in short text categorization also provides performance improvements.