Search for: amplitude-modulation
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    Blind source separation of discrete finite alphabet sources using a single mixture

    , Article IEEE Workshop on Statistical Signal Processing Proceedings, 28 June 2011 through 30 June 2011, Nice ; June , 2011 , Pages 709-712 ; 9781457705700 (ISBN) Rostami, M ; Babaie Zadeh, M ; Samadi, S ; Jutten, C ; Sharif University of Technology
    This paper deals with blind separation of finite alphabet sources where we have n sources and only one observation. The method is applied directly in time (spatial) domain and no transformation is needed. It follows a two stage procedure. In the first stage the mixing coefficients are estimated, and in the second stage the sources are separated using the estimated mixing coefficients. We also study restrictions of this method and conditions for which its performance is acceptable. Simulation results are presented to show the ability of this method to source separation in images and pulse amplitude modulation (PAM) signals  

    Simply decoded efficient full-rate space-time block codes over correlated Rician fading channels

    , Article IET Communications ; Volume 8, Issue 10 , 3 July 2014 , Pages 1684-1695 Kuhestani, A ; Pilaram, H ; Mohammadi, A ; Sharif University of Technology
    A novel technique is presented to design efficient full-rate space-time block codes (STBCs) over correlated Rician fading channels. The authors first derive a formula for the achievable information rate of a linear dispersion coded multi-input single-output system as a function of correlation at the transmitter in a Rician fading channel. In addition, the authors obtain the bit-error-rate (BER) equations for this system, when multiple phase shift keying and multiple quadrature amplitude modulation schemes are used at the transmitter. Therefore with regard to derived formulae and using a genetic algorithm, a method is presented to construct STBCs over correlated Rician fading channels. The... 

    An analytical approach in analysis of local oscillator near-the-carrier AM noise suppression in microwave balanced mixers

    , Article IEEE Transactions on Microwave Theory and Techniques ; Volume 57, Issue 4 , 2009 , Pages 760-766 ; 00189480 (ISSN) Kheirdoost, A ; Banai, A ; Farzaneh, F ; Sharif University of Technology
    In this paper, a new formulation based on conversion matrix method is proposed to analyze near-the-carrier local ocillator (LO) noise down conversion to IF in microwave mixers. This method could be easily applied to analyze LO noise down conversion in any type of mixer. Practical results of this method have been compared with the envelope method and measurement results. It is shown that despite the conventional AM noise suppression in balanced mixers, the near-the-carrier LO noise suppression does not occur necessarily at the center frequency of hybrid in balanced mixers. AM noise suppression values are predicted precisely. © 2006 IEEE  

    Effect of subchannelization in uplink in OFDM PHY of IEEE 802.16d

    , Article 2008 International Conference on High Performance Computing, Networking and Communication Systems, HPCNCS 2008, Orlando, FL, 7 July 2008 through 10 July 2008 ; 2008 , Pages 141-145 ; 9781615677177 (ISBN) Hajipour, J ; Vahdat, B. V ; Sharif University of Technology
    Wireless broadband access has gained so much attention in recent years. IEEE 802.16d as a standard in this field has provided MAC layer and PHY layer specifications. It has adopted OFDM method for one of PHY specifications that uses 256 subcarriers. In this paper we verify the effects of subchannelization option in uplink, on bit error rates in 16QAM modulation. Simulation results show that considerable improvement is obtained using half of the subcarriers  

    Equivalence of the Lagrange interpolator for uniformly sampled signals and the scaled binomially windowed shifted sinc function

    , Article Digital Signal Processing: A Review Journal ; Volume 19, Issue 5 , 2009 , Pages 838-842 ; 10512004 (ISSN) Jahani Yekta, M. M ; Sharif University of Technology
    The maximally flat (MF) fractional delay (FD) filter which is in fact a Lagrange interpolator for uniformly sampled signals, has previously been shown to be equal to the scaled binomially windowed shifted version of the sinc function; the ideal interpolation kernel for band-limited signals. In this paper, another proof for this equivalence is presented. Unlike its counterparts available in the literature, the proof given here is neither strictly algebraic, nor deploys the explicit coefficient formulas of the MFFD filter. It follows a frequency domain approach based on the definition of this filter instead, and aims to provide more insight into the corresponding equivalence. © 2009 Elsevier... 

    Nonlinear dynamic analysis of atomic force microscopy under deterministic and random excitation

    , Article 2006 ASME International Mechanical Engineering Congress and Exposition, IMECE2006, Chicago, IL, 5 November 2006 through 10 November 2006 ; 2006 ; 1096665X (ISSN); 0791837904 (ISBN); 9780791837900 (ISBN) Pishkenari, H. N ; Behzad, M ; Meghdari, A ; Sharif University of Technology
    American Society of Mechanical Engineers (ASME)  2006
    This paper is devoted to the analysis of nonlinear behavior of amplitude modulation (AM) and frequency modulation (FM) modes of atomic force microscopy. For this, the microcantilever (which forms the basis for the operation of AFM) is modeled as a single mode approximation and the interaction between the sample and cantilever is derived from a van der Waals potential. Using perturbation methods such as Averaging, and Fourier transform nonlinear equations of motion are analytically solved and the advantageous results are extracted from this nonlinear analysis. The results of the proposed techniques for AM-AFM, clearly depict the existence of two stable and one unstable (saddle) solutions for... 

    A non-linear neural D/A converter for direct digital frequency synthesizers

    , Article International Joint Conference on Neural Networks 2006, IJCNN '06, Vancouver, BC, 16 July 2006 through 21 July 2006 ; 2006 , Pages 2669-2672 ; 10987576 (ISSN); 0780394909 (ISBN); 9780780394902 (ISBN) Sadati, N ; Sedighi, B ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2006
    In this paper, a new non-linear D/A converter (DAC) is presented. This D/A converter uses neural network to approximate a sine function. It is targeted for direct digital frequency synthesizers in which the phase to sine amplitude conversion is usually performed using a ROM. Utilizing the proposed DAC, the power hungry ROM is removed. A design example is presented and the performance of the DAC is compared to the conventional method. The impact of non-idealities on the performance of the system is also investigated. © 2006 IEEE  

    Fast maximum-likelihood decoder for quasi-orthogonal space-time block code

    , Article Mathematical Problems in Engineering ; Volume 2015 , 2015 ; 1024123X (ISSN) Ahmadi, A ; Talebi, S ; Sharif University of Technology
    Hindawi Publishing Corporation  2015
    Motivated by the decompositions of sphere and QR-based methods, in this paper we present an extremely fast maximum-likelihood (ML) detection approach for quasi-orthogonal space-time block code (QOSTBC). The proposed algorithm with a relatively simple design exploits structure of quadrature amplitude modulation (QAM) constellations to achieve its goal and can be extended to any arbitrary constellation. Our decoder utilizes a new decomposition technique for ML metric which divides the metric into independent positive parts and a positive interference part. Search spaces of symbols are substantially reduced by employing the independent parts and statistics of noise. Symbols within the search... 

    Linear and nonlinear approaches towards amplitude modulation atomic force microscopy

    , Article Current Applied Physics ; Volume 10, Issue 6 , 2010 , Pages 1416-1421 ; 15671739 (ISSN) Delnavaz, A ; Mahmoodi, S. N ; Jalili, N ; Zohoor, H ; Sharif University of Technology
    Frequency response behavior of microcantilever is analytically and experimentally investigated in amplitude modulation Atomic Force Microscopy (AFM). AFM microcantilever probe is modeled as a continuous beam, and tip-sample interaction force is considered to include both attractive and repulsive force regimes. The developed model is compared with the linear lumped-parameters model that has been extensively used in the literature so far. Experimental measurements are also provided for the frequency response of a typical microcantilever-sample system to demonstrate the advantages of the developed model over the linear formulation. The results indicate that the nonlinear continuous model is... 

    Tip geometry effects in surface characterization with amplitude modulation AFM

    , Article Scientia Iranica ; Volume 17, Issue 1 F , 2010 , Pages 27-34 ; 10263098 (ISSN) Nejat Pishkenari, H ; Meghdari, A ; Sharif University of Technology
    In the present work, characterization of the surface trenches and vacancies with Amplitude Modulation AFM (AM-AFM) using Molecular Dynamics (MD) is simulated and the effects of the tip shape on the resulting images are investigated. The simulated system includes a recently developed gold coated AFM probe which interacts with a sample including a surface trench or a single-atom vacancy. In order to examine the behavior of the above system, including different transition metals, a Molecular Dynamics (MD) simulation with Sutton-Chen (SC) interatomic potential is used. Special attention is dedicated to the study of tip geometry effects such as the tip apex radius, the tip cone angle, the probe... 

    Design of Low Phase Noise DCO in All Digital Frequency Synthesizers

    , M.Sc. Thesis Sharif University of Technology Bagherzadeh Sohrabi, Salar (Author) ; Atarodi, Mojtaba (Supervisor)
    A new class of design has been introduced in the RF circuits and Frequency Synthesizers, which is based on the digital circuits. Implementation of the digital synthesizers suppresses the need to use loop filter and thus reduces the loop lock time. In this thesis different topologies of digitally controlled oscillators using inductor and capacitor tank and all digital architectures used in high frequency all digital synthesizers in 0.18um CMOS technology has been inspected and simulated. Novel techniques introduced to improve the ring oscillator-based design’s specifications which doesn’t need inductor. Using the introduced techniques, the phase noise has been lessened acceptably with respect... 

    Analysing of binary PAM systems in digital communication

    , Article International Conference on Communication Technology Proceedings, ICCT ; 2012 , Pages 1240-1246 ; 9781467321013 (ISBN) Roshanzamir, A ; Bastani, M. H ; Sharif University of Technology
    In this era of digital communication systems, different factors are included in efficiency of a transceiver system. Binary PAM systems are one of these transceiver systems. Many aspects of such a system has been considered yet but this field needs more research on because this is the base of any communication system. In this paper, effects of transmitter and receiver filters, noise, duty-cycle and time mismatch between transmitter and receiver in a binary baseband PAM transceiver system is analyzed. Simulation is performed to analyze the above effects on a typical communication system with 10 bits of transmit. MATLAB software is being employed for simulations  

    Reconfigurable infinite impulse response (IIR) microwave-photonic filter with controllable selectivity using tunable delay line

    , Article Conference on Millimeter-Wave and Terahertz Technologies, MMWaTT, 24 December 2012 through 26 December 2012 ; December , 2012 , Pages 37-39 ; 21570965 (ISSN) ; 9781467349567 (ISBN) Mokhtari, A ; Jamshidi, K ; Akbari, M ; Sharif University of Technology
    A tunable IIR microwave-photonic filter (MPF) with controllable selectivity is implemented using an electrically tunable delay line. The proposed method has been experimentally tested and verified. An IIR Microwave-Photonic filter with variable Q factor in the range of 238 - 257 is realized  

    Tip and sample flexibility effects on tapping mode (amplitude modulation) AFM measurements

    , Article Micro and Nano Letters ; Volume 6, Issue 12 , December , 2011 , Pages 1023-1028 ; 17500443 (ISSN) Pishkenari, H. N ; Meghdari, A ; Sharif University of Technology
    This Letter is devoted to the investigation of the tip, substrate and particle flexibility effects on the elastic deformation, the maximum repulsive force and the topography images in tapping mode (amplitude modulation) atomic force microscopy (TM-AFM). Several quantitative comparisons among the different models are presented and the effects of the elastic deformations on TM-AFM measurement are investigated  

    Simulation of imaging in tapping-mode atomic-force microscopy: A comparison amongst a variety of approaches

    , Article Journal of Physics D: Applied Physics ; Volume 44, Issue 7 , February , 2011 ; 00223727 (ISSN) Pishkenari, H. N ; Mahboobi, S. H ; Meghdari, A ; Sharif University of Technology
    Models capable of accurate simulation of microcantilever dynamics coupled with complex tip-sample interactions are essential for interpretation and prediction of the imaging results in amplitude modulation or tapping-mode atomic-force microscopy (AM-AFM or TM-AFM). In this paper, four approaches based on combinations of lumped and finite element methods for modelling of cantilever dynamics, and van derWaals and molecular dynamics for modelling of tip-sample interactions, are used to simulate the precise imaging by AM-AFM. Based on the simulated imaging and force determination, the efficiency of different modelling schemes is evaluated. This comparison is performed considering their... 

    A frequency domain proof for the equivalence of the maximally flat FIR fractional delay filter and the Lagrange interpolator

    , Article Digital Signal Processing: A Review Journal ; Volume 21, Issue 1 , 2011 , Pages 13-16 ; 10512004 (ISSN) Jahani Yekta, M. M ; Sharif University of Technology
    One of the most important properties of the maximally flat (MF) FIR fractional delay (FD) filter is its equivalence with the Lagrange interpolator for uniformly sampled signals. In this article, to provide the required background for the reader, we first propose a straightforward algebraic proof for this equivalence. This proof is given by simply demonstrating that the system of linear equations governing the maximally flatness property of this filter is the same as the one from which the coefficients of the Lagrange interpolator are computed. We then present the main contribution of the paper, which is a frequency domain proof for the same equivalence. In contrast with its classic... 

    Numerical investigation of the performance of a U-shaped pulsating heat pipe

    , Article Heat Transfer Engineering ; Volume 31, Issue 14 , Oct , 2010 , Pages 1155-1164 ; 01457632 (ISSN) Arabnejad, S ; Rasoulian, R ; Shafii, M. B ; Saboohi, Y ; Sharif University of Technology
    In this research the performance of a U-shaped pulsating heat pipe (PHP) was investigated using numerical methods. This heat pipe consists of two sections: The evaporator is set at the two ends of the pipe, and the middle part of the pipe comprises the condenser section. This heat pipe is a type of open looped pulsating heat pipe. The governing equations are derived analytically from the continuity, momentum, and energy equations and are solved implicitly. In this model, considering the liquid mesh, the rate of convection and boiling heat transfer in the U-shaped PHP, which has not been investigated as of yet, are examined. The effect of the evaporator temperature on the pulse amplitude and... 

    Investigation of the modulation between EEG alpha waves and slow/fast delta waves in children in different depths of Desflurane anesthesia

    , Article IRBM ; Volume 31, Issue 1 , 2010 , Pages 55-66 ; 19590318 (ISSN) Molaee Ardekani, B ; Shamsollahi, M. B ; Tirel, O ; Vosoughi Vahdat, B ; Wodey, E ; Senhadji, L ; Sharif University of Technology
    Objectives: Investigation of the amplitude modulation of alpha-band EEG oscillations (i.e., grouping of alpha-band activities) by delta-band EEG activities in various depths of anesthesia (DOA). Methods: This modulation, which is a sort of phase dependent amplitude modulation, is studied in 10 children in various depths of Desflurane anesthesia. Two parameters are defined to quantify the modulation: strength of modulation (SOM) and phase of modulation (POM). SOM indicates to what extent delta and alpha activities are related to each other, and POM is the delta phase in which the alpha amplitude is maximal. These parameters are analyzed in different DOA for various formations of delta... 

    Detection of a band-limited signal using an orthonormal, fully-decimated filter-bank

    , Article Scientia Iranica ; Volume 14, Issue 6 , 2007 , Pages 555-565 ; 10263098 (ISSN) Derakhtian, M ; Tadaion, A. A ; Nayebi, M. M ; Aref, M. R ; Sharif University of Technology
    Sharif University of Technology  2007
    In this paper, two methods are proposed for the detection of a band-limited signal in unknown variance white Gaussian noise. The complex amplitude and the frequency of the signal and the noise variance are assumed as unknown parameters. Using wavelet concepts, an orthonormal, fully-decimated filter-bank is employed to decompose the signal into its subband components. It is shown that, in this process, the noise is also decomposed into orthonormal zero-mean components. In the output, if a band-limited target signal is present, the respective single subband component (or two components in marginal cases) containing the target signal presents a non-zero mean. The presence of a non-zero mean... 

    Adapting power for BER improvement in wireless channels

    , Article 8th ACM Symposium on Modeling, Analysis and Simulation of Wireless and Mobile Systems, Montreal, Que., 10 October 2005 through 13 October 2005 ; Volume 2006 , 2006 , Pages 278-281 ; 1595931880 (ISBN); 9781595931887 (ISBN) MohammadNia Avval, M ; Pakravan, M. R ; Hossein Khalaj, B ; Sharif University of Technology
    Adaptive transmission is an effective way to improve the performance of communication links in time-varying channel environments. Former works use this technique to maximize the throughput; but we exploit it to minimize BER in a system with diversity reception. We do so by adapting power in response to the channel variations. We use analytical methods to derive our results. These expressions can be used for any type of channel fading and any modulation scheme. We then apply this method to a special case of 4-QAM over Rayleigh channel with MRC reception. Copyright 2005 ACM