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A new on-line signature verification algorithm using variable length segmentation and hidden markov models
, Article 7th International Conference on Document Analysis and Recognition, ICDAR 2003, 3 August 2003 through 6 August 2003 ; Volume 2003-January , 2003 , Pages 443-446 ; 15205363 (ISSN); 0769519601 (ISBN) ; Rabiee, H. R ; Sharif University of Technology
IEEE Computer Society
2003
Abstract
In this paper, a new on-line handwritten signature verification system using Hidden Markov Model (HMM) is presented. The proposed system segments each signature based on its perceptually important points and then computes for each segment a number of features that are scale and displacement invariant. The resulted sequence is then used for training an HMM to achieve signature verification. Our database includes 622 genuine signatures and 1010 forgery signatures that were collected from a population of 69 human subjects. Our verification system has achieved a false acceptance rate (FAR) of 4% and a false rejection rate (FRR) of 12%. © 2003 IEEE
Improvements of image-steganalysis using boosted combinatorial classifiers and gaussian high pass filtering
, Article 2008 4th International Conference on Intelligent Information Hiding and Multiedia Signal Processing, IIH-MSP 2008, Harbin, 15 August 2008 through 17 August 2008 ; 2008 , Pages 1508-1511 ; 9780769532783 (ISBN) ; Jamzad, M ; Sajedi, H ; Sharif University of Technology
2008
Abstract
Powerful universal steganalyzers were proposed in the literature during the past few years. In addition some studies have been conducted on improvements of current steganalysis results using information fusion techniques, merging available feature vectors, etc. This paper presents two independent ideas, which can be used together, to obtain higher accuracy in detecting stego images. First, we propose the use of boosted fusion methods to aggregate outputs of multiple steganalyzers. Second, we investigate how passing high frequencies through filtering can enhance the results of steganalysis techniques. In this work, it is shown that, through different tests over the state-of-the-art...
Turbulencelike behavior of seismic time series
, Article Physical Review Letters ; Volume 102, Issue 1 , 2009 ; 00319007 (ISSN) ; Saberi, S ; Sahimi, M ; Peinke, J ; Pacheco, A. F ; Rahimi Tabar, M. R ; Sharif University of Technology
2009
Abstract
We report on a stochastic analysis of Earth's vertical velocity time series by using methods originally developed for complex hierarchical systems and, in particular, for turbulent flows. Analysis of the fluctuations of the detrended increments of the series reveals a pronounced transition in their probability density function from Gaussian to non-Gaussian. The transition occurs 5-10 hours prior to a moderate or large earthquake, hence representing a new and reliable precursor for detecting such earthquakes. © 2009 The American Physical Society
Rigorous vectorial gaussian beam modeling of spectral dispersing performance of virtually imaged phased arrays
, Article Journal of the Optical Society of America B: Optical Physics ; Volume 26, Issue 2 , 2009 , Pages 272-278 ; 07403224 (ISSN) ; Shishegar, A. A ; Sharif University of Technology
Optical Society of American (OSA)
2009
Abstract
We have developed a generalized closed-form representation of the virtually imaged phased array (VIPA) output profile based on a 3D vectorial Gaussian beam formulation. Tracing the input vectorial elliptic Gaussian beam (GB), the output profile of the VIPA is represented as an array of virtual images. Furthermore, employing GB propagation and summing up all the virtual image profiles, the VIPA output profile has been calculated on a vertical plane at an arbitrary distance from the device. Finally, the derived closed-form representation is applied to the different sources (i.e., circular and elliptic GBs) and the results are compared with previous work. © 2009 Optical Society of America
Implementation and optimization of wavelet modulation in additive gaussian channels
, Article 11th International Conference on Advanced Communication Technology, ICACT 2009, Phoenix Park, 15 February 2009 through 18 February 2009 ; Volume 3 , 2009 , Pages 1940-1943 ; 17389445 (ISSN); 9788955191387 (ISBN) ; Nassirpour, S ; Shamsollahi, M. B ; IEEE Communications Society, IEEE ComSoc ; Sharif University of Technology
2009
Abstract
In this paper, we investigate the implementation of wavelet modulation (WM) in a digital communication system and propose novel methods to improve its performance. We will put particular focus on the structure of an optimal detector in AWGN channels and address two main methods for inserting the samples of the message signal in different frequency layers. Finally, computer based algorithms are described in order to implement and optimize receivers and transmitters
UWB spectrally-encoded spread-time CDMA in the presence of multiple Gaussian interferences: RAKE receiver and three-level codes
, Article IEEE Transactions on Communications ; Volume 56, Issue 12 , December , 2008 , Pages 2178-2189 ; 00906778 (ISSN) ; Salehi, J. A ; Sharif University of Technology
2008
Abstract
In this paper we study and analyze the performance of the RAKE receiver for a typical Ultrawideband (UWB) Spectrally-Encoded Spread-Time (ST) CDMA in the presence of multiple Gaussian Interference (GI) signals. We demonstrate that by combining useful properties of three-level codes, i.e., codes with values of - 1, 0, +1, and RAKE receiver, we can introduce a new strategy in which it can result in superior performance when compared to previous results. In particular, following a discussion on three-level codes we can show that RAKE receiver with optimum multiplicative weights achieves a better performance when compared with simple two-level codes. With the help of an example we show various...
Crowded scene object tracking in presence of Gaussian white noise using undecimated wavelet features
, Article 2007 9th International Symposium on Signal Processing and its Applications, ISSPA 2007, Sharjah, 12 February 2007 through 15 February 2007 ; 2007 ; 1424407796 (ISBN); 9781424407798 (ISBN) ; Rabiee, H. R ; Asadi, M ; Ghanbari, M ; Sharif University of Technology
2007
Abstract
In this paper, we propose a new noise robust algorithm for object tracking in the crowded video scenes. The algorithm exploits the properties of undecimated wavelet packet transform (UWPT) coefficients and texture analysis to track arbitrary objects. The coefficients of the UWPT of a user-specified region at the reference frame construct a Feature Vector (FV) for every pixel in that region. Optimal search for the best match of the region in successive frames is then performed by using the generated FVs inside an adaptive search window. Adaptation of the search window is achieved by inter-frame texture analysis to find the direction and speed of the object motion. Noise robustness has been...
Joint detector & estimator design for widely separated MIMO radars
, Article 2016 IEEE Radar Methods and Systems Workshop, RMSW 2016 - Proceedings, 27 September 2016 through 28 September 2016 ; 2016 , Pages 136-140 ; 9781509010493 (ISBN) ; Nayebi, M. M ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2016
Abstract
This paper considers the detector design and performance analysis in a widely separated multiple input - multiple output (S-MIMO) radar. We studied this subject under some assumptions such as single point target, Swerling models for radar cross section and Gaussian interference. The target is moving in piecewise linear trajectory and multi-scan data is stored. So, the target cell maybe changed through the time. A GLRT detector is derived that employs all data at once in a central unit. The performance of detector is extracted and numerical simulations verify all results
Achievable rates for two interfering broadcast channels with a cognitive transmitter
, Article AEU - International Journal of Electronics and Communications ; Volume 63, Issue 12 , 2009 , Pages 1005-1011 ; 14348411 (ISSN) ; Nasiri Kenari, M ; Sharif University of Technology
Abstract
We introduce a new communication model consisting of two interfering broadcast channels with one cognitive transmitter, who knows the message transmitted by the other non-cognitive transmitter, in a non-causal manner. An achievable rate region is derived for this model. The region is computed based on the Marton region for the general broadcast channel and its extension by Steinberg to the broadcast channel with the states known at the transmitter. By using the region evaluated, an achievable rate for the Gaussian broadcast channel is derived
Improvements in audio classification based on sinusoidal modeling
, Article 2008 IEEE International Conference on Multimedia and Expo, ICME 2008, Hannover, 23 June 2008 through 26 June 2008 ; 2008 , Pages 1485-1488 ; 9781424425716 (ISBN) ; Ghaemmaghami, S ; Razzazi, F ; Sharif University of Technology
2008
Abstract
In this paper, a set of features is presented and evaluated based on sinusoidal modeling of audio signals. Amplitude, frequency, and phase parameters of the sinusoidal model are used and compared as input features into an audio classifier system. The performance of sinusoidal model features is evaluated for classification of audio into speech and music classes using both the Gaussian and the GMM (Gaussian Mixture Model) classifiers. Experimental results show superiority of the amplitude parameters of the sinusoidal model, which could be used for the first time for such an audio classification, as compared to the popular cepstral features. By using a set of 40 sinusoidal features, we achieved...
A rigorous vectorial Gaussian beam modeling of virtually-imaged-phased-array
, Article 2007 Asia Optical Fiber Communication and Optoelectronic Exposition and Conference, AOE, Shanghai, 17 October 2007 through 19 October 2007 ; 2007 , Pages 514-516 ; 0978921739 (ISBN); 9780978921736 (ISBN) ; Shishegar, A. A ; Sharif University of Technology
2007
Abstract
The Virtually-Imaged-Phased-Array (VIPA) is a modified version of etalon used as a hyperfine spectral disperser. We have developed an analytical Gaussian beam tracing formulation which can model the VIPA output pattern and the effects of polarization changes
Detection of Apnea Bradycardia from ECG Signals of Preterm Infants Using Layered Hidden Markov Model
, Article Annals of Biomedical Engineering ; Volume 49, Issue 9 , 2021 , Pages 2159-2169 ; 00906964 (ISSN) ; Shamsollahi, M. B ; Fatemizadeh, E ; Beuchée, A ; Hernández, A. I ; Montazeri Ghahjaverestan, N ; Sharif University of Technology
Springer
2021
Abstract
Apnea-bradycardia (AB) is a common complication in prematurely born infants, which is associated with reduced survival and neurodevelopmental outcomes. Thus, early detection or predication of AB episodes is critical for initiating preventive interventions. To develop automatic real-time operating systems for early detection of AB, recent advances in signal processing can be employed. Hidden Markov Models (HMM) are probabilistic models with the ability of learning different dynamics of the real time-series such as clinical recordings. In this study, a hierarchy of HMMs named as layered HMM was presented to detect AB episodes from pre-processed single-channel Electrocardiography (ECG). For...
Analytical study of multiple access interference and beat noise in polarization-wavelength-time optical CDMA systems
, Article 2011 18th International Conference on Telecommunications, ICT 2011, 8 May 2011 through 11 May 2011, Ayia Napa ; 2011 , Pages 206-210 ; 9781457700248 (ISBN) ; Mehrany, K ; Sharif University of Technology
2011
Abstract
The performance of a three-dimensional optical code-division multiple-access system based on polarization-wavelength-time codes is investigated. The unwanted effects of multiple access interference are first studied and an accurate enough expression is given for the upper bound of the bit error rate. The proposed expression is obtained by decomposing the three-dimensional polarization-wavelength-time codes into horizontally and vertically polarized two-dimensional wavelength-time codes that are assumed to be statistically independent. It is shown by Monte Carlo simulation that the assumption of independence gives accurate enough bit error rate, whenever the number of chips is much larger...
Soft context clustering for F0 modeling in HMM-based speech synthesis
, Article Eurasip Journal on Advances in Signal Processing ; Volume 2015, Issue 1 , January , 2015 ; 16876172 (ISSN) ; Sameti, H ; King, S ; Sharif University of Technology
Springer International Publishing
2015
Abstract
This paper proposes the use of a new binary decision tree, which we call a soft decision tree, to improve generalization performance compared to the conventional ‘hard’ decision tree method that is used to cluster context-dependent model parameters in statistical parametric speech synthesis. We apply the method to improve the modeling of fundamental frequency, which is an important factor in synthesizing natural-sounding high-quality speech. Conventionally, hard decision tree-clustered hidden Markov models (HMMs) are used, in which each model parameter is assigned to a single leaf node. However, this ‘divide-and-conquer’ approach leads to data sparsity, with the consequence that it suffers...
Hidden markov model-based speech enhancement using multivariate laplace and gaussian distributions
, Article IET Signal Processing ; Volume 9, Issue 2 , 2015 , Pages 177-185 ; 17519675 (ISSN) ; Veisi, H ; Sameti, H ; Sharif University of Technology
Institution of Engineering and Technology
2015
Abstract
In this paper, statistical speech enhancement using hidden Markov model (HMM) is studied and new techniques for applying non-Gaussian distributions are proposed. The superiority of using non-Gaussian distributions in online adaptive noise suppression algorithms has been proven; however, in this study, this approach is formulated in an HMM-based mean-square error estimator (MMSE) estimator in which a priori models are trained in an off-line manner. In addition, an analytical study of using different distributions other than autoregressive (AR) Gaussian distribution, such as Laplace, is presented in order to construct an accurate HMM as a priori model for discrete Fourier transform and...
Code design for IMTSC/CEO problem using multilevel Slepian-Wolf coded quantization framework
, Article Proceedings - 2010 18th Iranian Conference on Electrical Engineering, ICEE 2010, 11 May 2010 through 13 May 2010 ; 2010 , Pages 282-287 ; 9781424467600 (ISBN) ; Aghagolzadeh, A ; Rabiee, H. R ; Sharif University of Technology
Abstract
The aim of this paper is introducing coding scheme that can potentially achieve the sum rate-distortion bound of Gaussian IMTSC/CEO problem with arbitrary number of encoders. No previous work has been reported on code design for the IMTSC/CEO problem with the number of encoders greater than two. In this paper the framework of Slepian-Wolf coded quantization is extended to the case with the number of encoders greater than two. On the other hand, we apply the approach to the case of unequal levels of the observation noise at the encoders. Encoding process consists of trellis coded quantization (TCQ) and LDPC codes. The proposed framework can be easily used for any number of active encoders...
Designing a dimmable OPPM-based VLC system under channel constraints
, Article 10th International Symposium on Communication Systems, Networks and Digital Signal Processing, CSNDSP 2016, 20 July 2016 through 23 July 2016 ; 2016 ; 9781509025268 (ISBN) ; Jamali, M. V ; Abdollahramezani, S ; Salehi, J. A ; Dargahi, A ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2016
Abstract
In this paper, we design a dimming compatible visible light communication (VLC) system in a standard office room according to illumination standards under channel constraints. We use overlapping pulse position modulation (OPPM) to support dimming control by changing the code weights. The system parameters such as a valid interval for dimming together with an upper bound for bit rate according to the channel delay spread are investigated. Moreover, considering the dispersive VLC channel and using Monte Carlo (MC) simulations, a method is proposed to determine the minimum code length in different dimming levels in order to achieve a valid bit error rate (BER). Finally, trellis coded modulation...
Noise robust speech recognition using deep belief networks
, Article International Journal of Computational Intelligence and Applications ; Volume 15, Issue 1 , 2016 ; 14690268 (ISSN) ; Halavati, R ; Sharif University of Technology
World Scientific Publishing Co
2016
Abstract
Most current speech recognition systems use Hidden Markov Models (HMMs) to deal with the temporal variability of speech and Gaussian mixture models (GMMs) to determine how well each state of each HMM fits a frame or a short window of frames of coefficients that represents the acoustic input. In these systems acoustic inputs are represented by Mel Frequency Cepstral Coefficients temporal spectrogram known as frames. But MFCC is not robust to noise. Consequently, with different train and test conditions the accuracy of speech recognition systems decreases. On the other hand, using MFCCs of larger window of frames in GMMs needs more computational power. In this paper, Deep Belief Networks...
Fisherposes for human action recognition using kinect sensor data
, Article IEEE Sensors Journal ; 2017 ; 1530437X (ISSN) ; Mohammadzade, H ; Mokari, M ; Sharif University of Technology
Abstract
This article proposes a new method for viewinvariant action recognition that utilizes the temporal position of skeletal joints obtained by Kinect sensor. In this method, the actions are represented as sequences of several pre-defined poses. After pre-processing, which includes skeleton alignment and scaling, the appropriate feature vectors are obtained for recognizing and discriminating the pose of every frame by the proposed Fisherposes method. The proposed regularized Mahalanobis distance metric is used in order to recognize both the involuntary and highly made-up actions at the same time. Hidden Markov Model (HMM) is then used to classify the action related to an input sequence of poses....
Realization of constant envelope OFDM using quantization and CPM technique
, Article AEU - International Journal of Electronics and Communications ; Volume 80 , 2017 , Pages 172-178 ; 14348411 (ISSN) ; Mohammadi, A ; Afrashteh, N ; Sanjaroonpouri, V ; Sharif University of Technology
Abstract
Orthogonal frequency division multiplexing (OFDM) is used in many wireless communication. The important drawback of this modulation is its high peak-to-average power ratio (PAPR). In this paper, a new modulation scheme of constant-envelope OFDM (CE-OFDM) is proposed. This scheme uses a combination of OFDM, quantizer and continuous phase modulation (CPM) to achieves 0 dB PAPR. The statistical signatures of signals, based on system parameters such as the length of discrete Fourier transform (DFT) and the number of quantization levels are presented. There are two sources of noise in proposed CE-OFDM scheme: quantization noise and channel noise. The theoretical analysis of these noises is...