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Total 229 records

    Achievable rate regions for many-to-one Gaussian interference channel with a fusion centre

    , Article IET Communications ; Volume 9, Issue 6 , April , 2015 , Pages 880-887 ; 17518628 (ISSN) Baianifar, M ; Behroozi, H
    Institution of Engineering and Technology  2015
    Abstract
    This paper considers a many-to-one Gaussian interference channel with a fusion centre (FC) where there is a K -user interference channel in which only one relay (receiver) faces interference while the remaining K-1 receivers are interference free. All the relays communicate information about their observed sequence to the FC through noiseless links at communication rate R0. First, by analysing traditional relaying schemes, i.e., Decode and Forward, Compress and Forward and Compute and Forward, three rate-regions for this setting are derived. Then, based on nested lattice codes, a new achievable rate-region is provided. Based on the proposed scheme, one can design a transmission scheme that... 

    Bayesian denoising framework of phonocardiogram based on a new dynamical model

    , Article IRBM ; Volume 34, Issue 3 , 2013 , Pages 214-225 ; 19590318 (ISSN) Almasi, A ; Shamsollahi, M. B ; Senhadji, L ; Sharif University of Technology
    2013
    Abstract
    In this paper, we introduce a model-based Bayesian denoising framework for phonocardiogram (PCG) signals. The denoising framework is founded on a new dynamical model for PCG, which is capable of generating realistic synthetic PCG signals. The introduced dynamical model is based on PCG morphology and is inspired by electrocardiogram (ECG) dynamical model proposed by McSharry et al. and can represent various morphologies of normal PCG signals. The extended Kalman smoother (EKS) is the Bayesian filter that is used in this study. In order to facilitate the adaptation of the denoising framework to each input PCG signal, the parameters are selected automatically from the input signal itself. This... 

    General noise considerations of amplified photons in lightwave systems with optically bistable elements

    , Article Proceedings - 10th International Conference on Laser and Fiber-Optical Networks Modeling, LFNM 2010, 12 September 2010 through 14 September 2010 ; 2010 , Pages 93-95 ; 9781424469970 (ISBN) Abediasl, H ; Naqavi, A ; Mehrany, K ; Mousavi, S. M ; Aliakbar, J ; Mousavi, S. M ; Sharif University of Technology
    Abstract
    An optical amplifier followed by a bistable element has been statistically analyzed before [1]. In this manuscript, output noise analysis represents, then signal to noise ratios (SNR) are calculated either for input or output. It will be shown that noise reduction, can be achieved by a proper selection of parameters  

    Gain ripple minimization in fiber Raman amplifiers based on variational method

    , Article Optics Communications ; Volume 281, Issue 6 , 2008 , Pages 1545-1557 ; 00304018 (ISSN) Bahrampour, A. R ; Ghasempour, A ; Rahimi, L ; Sharif University of Technology
    2008
    Abstract
    In this paper, the variational method is employed for minimizing the gain ripple of multi-wavelength fiber Raman amplifiers. The variance of gain spectrum of the fiber Raman amplifier is regarded as the cost function, restriction on total pump power and average gain is given as the constraints of the minimization problem. It is shown that the minimization problem with any necessary constraints on the pump powers, average gain and signal to noise ratio, is reduced to a two-point boundary value problem. The method gives the entire possible local and global solutions. The method is applied to different examples of fiber Raman amplifiers with different lengths from 25 km to 100 km and different... 

    A simple and fast analysis of SNR in non-coherent integrators

    , Article 2005 1st International Conference on Computers, Communications and Signal Processing with Special Track on Biomedical Engineering, CCSP 2005, Kuala Lumpur, 14 November 2005 through 16 November 2005 ; 2005 , Pages 5-9 ; 1424400112 (ISBN); 9781424400119 (ISBN) Esfandyarpour, R ; Norouzi, Y ; Parizi, K. B ; Esfandyarpour, H ; Nayebi, M. M ; Sharif University of Technology
    2005
    Abstract
    In this paper, an approximate analysis for SNR improvement factor in non-coherent integrators for communication channels is introduced. The SNR improvement factor and loss function of the non-coherent integrator are calculated. Our results are very simple and illustrative. Although calculations are with some approximations and therefore the results are not exact, but the error is negligible, as it is shown. © 2005 IEEE  

    An improved spectral subtraction speech enhancement system by using an adaptive spectral estimator

    , Article Canadian Conference on Electrical and Computer Engineering 2005, Saskatoon, SK, 1 May 2005 through 4 May 2005 ; Volume 2005 , 2005 , Pages 261-264 ; 08407789 (ISSN) Ayat, S ; Manzuri, M. T ; Dianat, R ; Kabudian, J ; Sharif University of Technology
    2005
    Abstract
    Spectral subtraction is one of the most famous and common-used methods for speech enhancement. The main weakness of this method is the production of an annoying noise called musical noise. In this paper, we have reduced the musical noise and improved the quality of enhanced speech by increasing the accuracy of the system spectral estimator. This method is useful for speech enhancement systems in which the speech signal is degraded by stationary or near-stationary noises. Different experimental results in different SNRs confirmed the better performance of our system from both objective and subjective views, which means better quality and more SNR improvement. © 2005 IEEE  

    A modified pressure-based algorithm to solve flow fields with shock and expansion waves

    , Article Numerical Heat Transfer, Part B: Fundamentals ; Volume 46, Issue 5 , 2004 , Pages 497-504 ; 10407790 (ISSN) Darbandi, M ; Mokarizadeh, V ; Sharif University of Technology
    2004
    Abstract
    The use of collocated grid schemes in control-volume-based methods has resulted in developing different strategies for coupling mass and momentum governing equations. Defining two different velocity components at cell faces is one remedy to suppress the possible checkerboard problem in the solution domain. These velocity components are widely known as convected and convecting velocities which are normally used in the momentum and mass governing equations, respectively. However, the linearization of the nonlinear governing equations generates a number of lagged velocity components which must be carefully treated in a manner to preserve the conceptual definition of the convected and convecting... 

    Design optimisation of aluminium recycling processes using Taguchi technique

    , Article Journal of Materials Processing Technology ; Volume 127, Issue 1 , 2002 , Pages 96-106 ; 09240136 (ISSN) Khoei, A. R ; Masters, I ; Gethin, D. T ; Sharif University of Technology
    2002
    Abstract
    In this paper, a robust design method is developed for reducing cost and improving quality in aluminium recycling. An experimental investigation into the process parameter effects is presented to determine the optimum configuration of design parameters for performance, quality and cost. The Taguchi method is applied initially to plan a minimum number of experiments. Orthogonal array techniques are used to investigate the simultaneous variation of several parameters and the investigation of interactions between parameters. Matrix experiments using standard L4 and L9 orthogonal arrays are employed to evaluate the effects of parameters in recycling of aluminium dross and scrap materials. A... 

    Sparse representation-based super-resolution for diffusion weighted images

    , Article 21st Iranian Conference on Biomedical Engineering, ICBME ; 26-28 November , 2014 , pp. 12-16 ; ISBN: 9781479974177 Afzali, M ; Fatemizadeh, E ; Soltanian-Zadeh, H ; Sharif University of Technology
    Abstract
    Diffusion weighted imaging (DWI) is a non-invasive method for investigating the brain white matter structure. It can be used to evaluate fiber bundles in the brain. However, clinical acquisitions are often low resolution. This paper proposes a method for improving the resolution using sparse representation. In this method a non-diffusion weighted image (bO) is utilized to learn the patches and then diffusion weighted images are reconstructed based on the trained dictionary. Our method is compared with bilinear, nearest neighbor and bicubic interpolation methods. The proposed method shows improvement in terms of Peak Signal-to-Noise Ratio (PSNR) and Structural SIMilarity (SSIM)  

    Colour image steganography method based on sparse representation

    , Article IET Image Processing ; Volume 9, Issue 6 , 2015 , Pages 496-505 ; 17519659 (ISSN) Ahani, S ; Ghaemmaghami, S ; Sharif University of Technology
    Institution of Engineering and Technology  2015
    Abstract
    The authors address the use of sparse representation to securely hide a message within non-overlapping blocks of a given colour image in the wavelet domain. All four sub-images of the two-dimensional wavelet transform of two colour bands are used for data embedding without affecting the image perceptibility. Bit error rate of hidden data extraction is reduced to zero by introducing a novel refinement procedure in the proposed algorithm. The refinement procedure introduced solves the hidden bit extraction errors caused by the rounding process, the overflows and the nature of approximation in sparse decomposition. Capacity of the proposed method is calculated using necessary conditions for... 

    A novel image hiding scheme using content aware seam carving method

    , Article ARES 2010 - 5th International Conference on Availability, Reliability, and Security, 15 February 2010 through 18 February 2010 ; Feb , 2010 , Pages 702-707 ; 9780769539652 (ISBN) Toony, Z ; Jamzad, M ; Sharif University of Technology
    2010
    Abstract
    In image hiding we embed a secret image into a cover image. In order to minimize the distortion of secret image, we presented a novel steganographic method based on content-aware seam carving. In this paper, we propose a new image hiding method in which, the secret image is initially classified based on image complexity measure. Then it is resized to an appropriate smaller size, but for having the important objects of the image in resized image we use seam carving method that resizes an image whereas the important content of it remains. By applying the seam carving, we have an image that is smaller than the original one, and then we hide it in a cover image. Obviously hiding a smaller secret... 

    On the use of compressive sensing for image enhancement

    , Article Proceedings - 2016 UKSim-AMSS 18th International Conference on Computer Modelling and Simulation, UKSim 2016, 6 April 2016 through 8 April 2016 ; 2016 , Pages 167-171 ; 9781509008889 (ISBN) Ujan, S ; Ghorshi, S ; Khoshnevis, S. A ; Pourebrahim, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2016
    Abstract
    Compressed Sensing (CS), as a new rapidly growing research field, promises to effectively recover a sparse signal at the rate of below Nyquist rate. This revolutionary technology strongly relies on the sparsity of the signal and incoherency between sensing basis and representation basis. Exact recovery of a sparse signal will be occurred in a situation that the signal of interest sensed randomly and the measurements are also taken based on sparsity level and log factor of the signal dimension. In this paper, compressed sensing method is proposed to reduce the noise and reconstruct the image signal. Noise reduction and image reconstruction are formulated in the theoretical framework of... 

    Improved CT image reconstruction through partial Fourier sampling

    , Article Scientia Iranica ; Volume 23, Issue 6 , 2016 , Pages 2908-2916 ; 10263098 (ISSN) Abbasi, H ; Kavehvash, Z ; Shabany, M ; Sharif University of Technology
    Sharif University of Technology  2016
    Abstract
    A novel CT imaging structure based on Compressive Sensing (CS) is proposed. The main goal is to mitigate the CT imaging time and, thus, X-ray radiation dosage without compromising the image quality. The utilized compressive sensing approach is based on radial Fourier sampling. Thanks to the intrinsic relation between captured radon samples in a CT imaging process and the radial Fourier samples, partial Fourier sampling could be implemented systematically. This systematic compressive sampling helps in better control of required conditions such as incoherence and sparsity to guarantee adequate image quality in comparison to previous CS-based CT imaging structures. Simulation results prove the... 

    K-Space aware multi-static millimeter-wave imaging

    , Article IEEE Transactions on Image Processing ; Volume 28, Issue 7 , 2019 , Pages 3613-3623 ; 10577149 (ISSN) Kazemi, M ; Kavehvash, Z ; Shabany, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2019
    Abstract
    This paper focuses on an efficient approach for designing multi-static arrays for millimeter-wave imaging, based on the k -space or Fourier-spatial domain characteristic of imaging systems. Our goal is to decrease the redundancy of the data measured by each antenna and to improve the resolution of the reconstructed image. The proposed technique is based on determining the role of each transmitter and receiver, in collecting the data from each voxel of the target in k -space domain and then rotating the transmitters' beams to measure the desirable information. The effect of non-uniform redundant k -space domain frequency samples that act as an undesirable filter is compensated using a... 

    Outage performance in secure cooperative NOMA

    , Article 2019 Iran Workshop on Communication and Information Theory, IWCIT 2019, 24 April 2019 through 25 April 2019 ; 2019 ; 9781728105840 (ISBN) Abolpour, M ; Mirmohseni, M ; Aref, M. R ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2019
    Abstract
    Enabling cooperation in a NOMA system is a promising approach to improve its performance. In this paper, we study the cooperation in a secure NOMA system, where the legitimate users are distributed uniformly in the network and the eavesdroppers are distributed according to a homogeneous Poisson point process. We consider a cooperative NOMA scheme (two users are paired as strong and weak users) in two phases: 1) Direct transmission phase, in which the base station broadcasts a superposition of the messages, 2) Cooperation phase, in which the strong user acts as a relay to help in forwarding the messages of the weak user. We study the secrecy outage performance in two cases: (i) security of... 

    Fast wavelet-based photoacoustic microscopy

    , Article Journal of the Optical Society of America A: Optics and Image Science, and Vision ; Volume 38, Issue 11 , 2021 , Pages 1673-1680 ; 10847529 (ISSN) Abbasi, H ; Mostafavi, S. M ; Kavehvash, Z ; Sharif University of Technology
    The Optical Society  2021
    Abstract
    A novel photoacoustic microscopy (PAM) structure, based on Haar wavelet patterns, is proposed in this paper. Its main goal is to mitigate the PAM imaging resolution and thus the time of its sampling process without compromising the image quality. Owing to the intrinsic nature of wavelet transform, this structure collects spatial and spectral components simultaneously, and this feature speeds up the sampling process by 33%. The selection of these patterns helps in better control of required conditions, such as multi-resolution imaging, to guarantee adequate image quality in comparison to previous microscopic structures. Simulation results prove the superior quality of the proposed approach... 

    Fast wavelet-based photoacoustic microscopy

    , Article Journal of the Optical Society of America A: Optics and Image Science, and Vision ; Volume 38, Issue 11 , 2021 , Pages 1673-1680 ; 10847529 (ISSN) Abbasi, H ; Mostafavi, S. M ; Kavehvash, Z ; Sharif University of Technology
    The Optical Society  2021
    Abstract
    A novel photoacoustic microscopy (PAM) structure, based on Haar wavelet patterns, is proposed in this paper. Its main goal is to mitigate the PAM imaging resolution and thus the time of its sampling process without compromising the image quality. Owing to the intrinsic nature of wavelet transform, this structure collects spatial and spectral components simultaneously, and this feature speeds up the sampling process by 33%. The selection of these patterns helps in better control of required conditions, such as multi-resolution imaging, to guarantee adequate image quality in comparison to previous microscopic structures. Simulation results prove the superior quality of the proposed approach... 

    Investigation of the Photonic Scattering Error in Radiography of Pipes and its Evaluation by Mote- carlo Simulation

    , M.Sc. Thesis Sharif University of Technology Masoumi Kolvanaq, Hojjat (Author) ; Vossoughi, Nasser (Supervisor) ; Movafeghi, Amir (Co-Advisor) ; Kermani, Abotaleb (Co-Advisor)
    Abstract
    Non-destructive testing method is for detect specimen flaws such as (crack, porosity, impure, welding defects, corrosion etc.) without destruction the specimen under inspection. Particular characteristic of radiography is an image product from specimen inside under testing where help to identity and better comprehend at flaw nature. Photon scattering is one of important factor to reduce image quality and signal to noise ratio. Scattered photons can due toexistent ingredient in the radiography environment and curvature of material transmission pipe where cause the disorder creation in the radiography images. In this research, pipe radiography simulated using the TIC and TIR radiography... 

    Design and Optimization of Magnetic Resonance Signal Detector to Enhancement of Sensitivity and SNR in Proton Precession Sensor

    , M.Sc. Thesis Sharif University of Technology Mazaheri Karvani, Jamal (Author) ; Fardmanesh, Mahdi (Supervisor)
    Abstract
    Proton precession is used in measurement of scalar magnetic field intensity. In this sensor, the magnetic field intensity is calculated through Larmor frequency using the proton precession frequency around the magnetic field. The accuracy of this sensor is in the range of picoTesla which is used for magnetic field measurement as well as the calibration of vector magnetic sensors. The signal to noise ratio in this sensor is due to the dimension and resistances of the wires and is a kind of RMS random noise. Although, changing the dimension of the wires for noise reduction and increasing the signal amplitude requires the fabrication of a bulky sensor with low power consumption. Therefore, it... 

    Compensating interpolation distortion by new optimized modular method

    , Article 2011 18th International Conference on Telecommunications, ICT 2011 ; 2011 , Pages 346-350 ; 9781457700248 (ISBN) Ayremlou, A ; Tofighi, M ; Marvasti, F ; IBM Cyprus; University of Cyprus; Cyprus Tourism Organisation ; Sharif University of Technology
    Abstract
    A modular method was suggested before to recover a band limited signal from the sample and hold and linearly interpolated (or, in general, an nth-order-hold) version of the regular samples. In this paper a novel approach for compensating the distortion of any interpolation based on modular method has been proposed. In this method the performance of the modular method is optimized by adding only some simply calculated coefficients. This approach causes drastic improvement in terms of signal-to-noise ratios with fewer modules compared to the classical modular method. Simulation results clearly confirm the improvement of the proposed method and also its superior robustness against additive...