Tewfik Mani - Academia.edu (original) (raw)

Papers by Tewfik Mani

[Proceedings] ICASSP-92: 1992 IEEE International Conference on Acoustics, Speech, and Signal Processing, 1992

A class of data transformation matrices is introduced for the estimation of angles of arrivals of... more A class of data transformation matrices is introduced for the estimation of angles of arrivals of multiple wideband sources. The proposed transformation matrices are unitary and minimize the average of the squared norm of the focusing error over the angles of interest without prior knowledge of source locations. They can also be used with the multigroup sources and lead to

10th IEEE Symposium on Computers and Communications (ISCC'05), 2005

Notice of Violation of IEEE Publication Principles&quot;Resource Management and Quality A... more Notice of Violation of IEEE Publication Principles&quot;Resource Management and Quality Adaptation in Distributed Multimedia Networks&quot; by Abed Elhamid Lawabni and Ahmed H. Tewfik,in Proceedings of the 10th IEEE Symposium on Computers and Communications (ISCC 2005), pp 604-610.After careful and considered review of the content and authorship of this paper by a duly constituted expert committee, this paper has been found to be in violation of IEEE&#x27;s Publication Principles. This paper is a duplication of the original text from the papers cited below. The original text was copied without attribution (including appropriate references to the original author(s) and/or paper titles) and without permission. The misconduct was committed specifically by Abed Elhamid Lawabni, and his actions were done without the knowledge or approval of his coauthor.It should be noted that the above paper copied without credit from the following:&quot;Heuristic Solutions for the Multiple-Choice Multi-Dimension Knapsack Problem&quot;by M. M. Akbar, E. G. Manning, G. C. Shoja, and S. Khan,in the International Conference on Computational Science, May 2001.&quot;Distributed Utility Model Applied to Optimal Admission Control and QoS Adaptation in Multimedia Systems and Enterprise&quot;by Md Mostofa Akbarin his Ph.D. dissertation at the Department of Computer Science, University of Victoria, Sept. 2002&quot;Solving the Multidimensional Multiple Choice Knapsack Problem by Constructing Convex Hulls&quot;by Md Mostofa Akbar, M. Sohel Rahman, M. Kaykobad, E. G. Manning, and G. C. Shojain Computers and Operations Research, Vol 33, pp 1259-1273&quot;Building an Adaptive Multimedia System Using the Utility Model&quot;by Lei Chen, Shahadat Khan, Kin F. Li, and Eric G. Manningin Parallel and Distributed Processing, Lecture Notes in Computer Science 1586, Springer Verlag, pp 289-298&quot;The Utility Model for Adaptive Multimedia Systems&quot;by Sha- - hadat Khan, Kin F. Li, and Eric G. Manningin the International Conference on Multimedia Modeling, Singapore, Nov. 1997&quot;Quality Adaptation in a Multisession Multimedia System: Model, Algorithms and Architecture&quot;by Shahadat Khanin his Ph.D. dissertation at the Department of Computer Science, University of Victoria, May 1998&quot;Solving the Knapsack Problem for Adaptive Multimedia Systems&quot;by S. Khan, K. F. Li, E. G. Manning, M. M. Akbar in Studia Informatica, 2002In this paper, the problem of allocating multiple finite resources to satisfy the quality of service (QoS) needs of multiple applications along multiple QoS dimensions is presented. A mathematical model that captures the dynamics of such adaptive problem is presented. This model formulates the problem as multiple-choice multidimensional 0-1 knapsack problem (MMKP), an NP-hard optimization problem. A heuristic algorithm is then proposed to solve the MMKP. Experimental results demonstrate that our proposed algorithm finds 96% optimal solutions on average, and outperforms other heuristic algorithms for MMKP. Furthermore, the time required is on average 50% to 70% less than that required by other benchmark heuristics. These two properties make this heuristic a strong candidate for use in real-time applications.

2001 IEEE Fourth Workshop on Multimedia Signal Processing (Cat. No.01TH8564)

This work considers a fundamental problem of image transmission over error-prone channels. The im... more This work considers a fundamental problem of image transmission over error-prone channels. The impairments that we target are long burst errors and transient channel failures, as would occur in the wireless network because of an obstruction in the transmission path, or severe traffic congestion in a packet network such as the Internet. These impairments cause many packets to be dropped.

SPIE Proceedings, 1998

In this paper we consider a discretized version of the problem of optimal beam-forming, or radar ... more In this paper we consider a discretized version of the problem of optimal beam-forming, or radar transmit and receive pattern design, for stationary radar target localization in the presence of white Gaussian noise. We assume that the target is equally likely to be in one of N discrete cells and the number of allowed observations L is strictly less than

Signal Processing, 1987

In this paper, we present a high resolution spectral estimation method for 2-D isotropic ranoom f... more In this paper, we present a high resolution spectral estimation method for 2-D isotropic ranoom fields with covariance functions equal to weighted sums of cylindrical harmonics. Such fields are often used to model some types of background noises in geophysics and in ocean acoustics. The approach that we present differs from previous 2-D spectral estimation techniques by the fact that we take maximal advantage of the symmetries implied by both the isotropy and the special covariance structure of these fields. Note that isotropy is the natural generalization to several dimensions of the I-D notion of stationarity. Our approach is similar in spirit to I-D harmonic retrieval techniques, such as the MUSIC method, which rely on an eigenanalysis of the covariance matrix. In the 2-D isotropic context, we begin with a Fourier series representation of an isotropic field with respect to the angle 0 in a polar coordinate representation of the underlying 2-D space. We then obtain a spectral estimate by performing an eigenanalysis of the covariance matrix of samples of the zeroth-order Fourier coefficient process in order to extract the cylindrical harmonics. We also discuss the estimation of this covariance matrix and present examples to illustrate the high resolution and robustness properties of our procedure. Zusammenfassung. Es werden einige neue Abtasttheoreme fiir isotrope Zufallsfelder und die zugeh/~rigen Fourierprozesse entwickelt. Aufgrund dieser Theoreme wird ein Algorithmus vorgestellt, mit dem sich die zylindrischen Harmonischen eines isotropen Zufallsfeldes aus Werten der zugehSrigen Kovarianzfunktion gewinnen iassen. Der vorgeschlagene Algorithmus nutzt die Eigenwertstruktur der Kovarianzmatrix des normalisierten Fourier-Koeffizientenprozesses nuUten Grades; dieser Proze6 erweist sich als robust. R6sum6, Cet article propose une m6thode d'estimation spectrale ~ grande resolution pour les champs isotropes al6atoires 2-D dont la fonction de covarianc¢ est 6gale A une somme d'harmoniques cylindriques. Ces champs sont utilis6s souvent pour mod61iser divers types de bruits ambiants en g6ophysique et acoustique marine. La diff6rence principale entre l'approche que nous proposons et les autres m6thodes d'estimation spectrale 2-D est que nous utilisons de mani6re syst6matique l'isotropie et la structure des fonctions de covariance des champs que nous consid6rons. La propri6t6 d'isotropie est la generalisation naturelle/l plusieurs dimensions de la notion de stationarit6 pour les processus ~ une dimension. Notre approche est proche des m6thodes d'analyse harmonique l-D, teiles que la m6thode MUSIC, qui utilisent une d6composition de la matrice de covariance sous forme de valeurs et vecteurs propres. Pour la cas 2-D, nous utilisons une repr6sentation du champs isotrope en s6rie de Fourier par rapport ~ rangle 0 en coordonn6es polaires. Nouse obtenons une estim6e spectrale en d6composant la matrice de covariance du coefficient de Fourier d'ordre z6ro sous forme de valeurs et vecteurs propres, de mani~re d6terminer les harmoniques cylindriques. Nous d6crivons l'estimation de la matrice de covariance du coefficient de Fourier d'ordre z6ro, et nous pr6sentons plusieurs exemples qui illustrent la haute r6solution et la robustesse de notre approche.

IEEE Transactions on Wireless Communications, 2008

In this paper we study the performance of IEEE 802.11e enhanced distributed channel access (EDCA)... more In this paper we study the performance of IEEE 802.11e enhanced distributed channel access (EDCA) priority schemes under finite load and error-prone channel. We introduce a multi-dimensional Markov Chain model that includes all the mandatory differentiation mechanisms of the standard: QoS parameters, CWMIN, CWMAX arbitration inter-frame space (AIFS), and the virtual collision handler. The model faithfully represents the functionality of

IEEE Transactions on Vehicular Technology, 2009

In this paper, we describe a novel approach for reducing the power consumption and complexity of ... more In this paper, we describe a novel approach for reducing the power consumption and complexity of a multiband orthogonal frequency-division multiplexing (MB-OFDM) ultrawideband (UWB) system by applying ideas from pulsed UWB systems. The approach is quite general and applicable to many other systems. Unlike the MB-OFDM system, the enhancement that we propose uses pulses with duty cycles of less than 1 as the amplitude shaping pulse of orthogonal frequency-division multiplexing (OFDM) modulation. Pulsating OFDM symbols spread the spectrum of the modulated signals in the frequency domain, leading to a spreading gain that is equal to the inverse of the duty cycle of the pulsed subcarriers. We study the spectral characteristics of pulsed OFDM and the added degrees of diversity that it provides. We show that pulsed-OFDM signals can easily be generated by either upsampling an equivalent OFDM baseband signal with a reduced number of carriers or by replacing the digital-to-analog converter (DAC) of a normal MB-OFDM transmitter with a lowduty-cycle DAC. We establish that a pulsed-OFDM receiver can fully exploit the added diversity without using Rake receivers. It is shown that, while pulsed OFDM has superior or comparable performance to MB-OFDM in multipath fading channels, it also has intrinsic low-complexity and power consumption advantages compared with MB-OFDM. To establish this fact, we describe an example design for the IEEE 802.15.3a Standard and present full simulation results for the UWB indoor propagation channels provided by the IEEE 802.15.3a Standard activity committee. Index Terms-Multiband orthogonal frequency-division multiplexing (MB-OFDM), orthogonal frequency-division multiplexing (OFDM), pulsed OFDM, ultrawideband (UWB). I. INTRODUCTION U LTRAWIDEBAND (UWB) communication systems use signals with a bandwidth that is larger than 25% of the center frequency or more than 500 MHz. UWB communication systems offer several potential advantages, including robustness to multipath interference and inherent support for locationaware networking and multiuser access [1], [2]. UWB is the underlying technology behind several emerging military sensor and communication networks. Furthermore, the vast majority of

IEEE Transactions on Signal Processing, 2002

Signal decompositions with overcomplete dictionaries are not unique. In this paper, we present tw... more Signal decompositions with overcomplete dictionaries are not unique. In this paper, we present two new approaches for identifying the sparsest representation of a given signal in terms of a given overcomplete dictionary. The first approach is an algebraic approach that attempts to solve the problem by generating other vectors that span the space of minimum dimension that includes the signal. Unlike other current techniques, including our proposed iterative technique, this algebraic approach is guaranteed to find the sparsest representation of the signal under certain conditions. For example, we can always find the exact solution if the size of the dictionary is close to the size of the space or when the dictionary can be represented by a Vandermonde matrix. Although our technique can work for high signal-to-noise cases, the exact solution is only guaranteed in noise-free cases. Our second approach is iterative and can be applied in cases where the algebraic approach cannot be used. This technique is guaranteed to achieve at least a local minimum of the error function representing the difference between the signal and its sparse representation.

IEEE Transactions on Multimedia, 2003

... in Mobile Terminals With a Guaranteed QoS Tse-Hua Lan, Member, IEEE, and Ahmed H. Tewfik, Fel... more ... in Mobile Terminals With a Guaranteed QoS Tse-Hua Lan, Member, IEEE, and Ahmed H. Tewfik, Fellow, IEEE ... The primary goal of the aforementioned methods is to keep the raw information bit error rate (BER) to a certain level. ...

Discrete & Continuous Dynamical Systems - A, 2005

Computers in Biology and Medicine, 2007

We introduce a new adaptive time-frequency plane feature extraction strategy for the segmentation... more We introduce a new adaptive time-frequency plane feature extraction strategy for the segmentation and classification of electroencephalogram (EEG) corresponding to left and right hand motor imagery of a brain-computer interface task. The proposed algorithm adaptively segments the time axis by dividing the EEG data into non-uniform time segments over a dyadic tree. This is followed by grouping the expansion coefficients in the frequency axis in each segment. The most discriminative features are selected from the segmented time-frequency plane and fed to a linear discriminant for classification. The proposed algorithm achieved an average classification accuracy of 84.3% on six subjects by selecting the most discriminant subspaces for each one. For comparison, classification results based on an autoregressive model are also presented where the mean accuracy of the same subjects turned out to be 79.5%. Interestingly the subjects and two hemispheres of each subject are represented by distinct segmentations and features. This indicates that the proposed method can handle inter-subject variability when constructing brain-computer interfaces.

Bulletin of Mathematical Biology, 2004

IEEE Communications Letters, 2003