Umapathi Reddy

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Ali Ahmed

University of Liverpool online programme with Laureate

Manuel David Masseno

Instituto Politécnico de Beja

Anirach Mingkhwan

King Mongkut's University of Technology North Bangkok

Armando Marques-Guedes

UNL - New University of Lisbon

Rogerio Bravo

Instituto Politécnico de Beja

Zdravka Krasteva

Sofia University "St. Kliment Ohridski"

Vania V Estrela

UFF - Universidade Federal Fluminense

Eoghan Casey

University of Lausanne

Omer Jasim

Ain Shams University

Hendra Grandis

Institut Teknologi Bandung

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Papers by Umapathi Reddy

Further results in spatial smoothing

by Umapathi Reddy and Maheswara Reddy

Signal Processing, 1996

... The source signal K. Maheswara Ready, VU Reddy Signal Processing 48 (1996) 217224 covariance ... more

Adaptive two-dimensional harmonic retrieval and its application to radar

Estimation of the frequency and the angle of arrival of point-source emitters is viewed as an app... more Estimation of the frequency and the angle of arrival of point-source emitters is viewed as an application of two-dimensional spectral analysis. In this paper, stochastic gradient and approximate least-square algorithms for adaptive two-dimensional harmonic retrieval are derived. These algorithms extend the results obtained by Reddy et al. (1982) to the two-dimensional case.

Performance Analysis of the Music Algorithm with Spatial Smoothing in the Presence of Coherent Sources

We study the effect of spatial smoothing on the performance of the MUSIC algorithm for directions... more We study the effect of spatial smoothing on the performance of the MUSIC algorithm for directions-of-arrival estimation of partially and fully coherent sources. We show that spatial smoothing improves the sensitivity of the invariant subspaces as a result of progressive decorrelation of the sources, and that the rate at which this happens depends upon the spacing and directions of the sources. This analysis explains the performance improvement observed with moving arrays in the presence of coherent sources. We also show that smoothing reduces the magnitude of the perturbations through subarray averaging, thereby further improving DOA estimation performance. Results of computer simulations are included to support our analysis.

A Subspace Approach To Determining Sensor Gain And Phase With Applications To Array Processing

Exact characterization of the array in terms of its geometry and the sensor gain and phase is imp... more Exact characterization of the array in terms of its geometry and the sensor gain and phase is important in beamforming and directions-of-arrival estimation problems. In practice the sensor gain and phase may not be known exactly due to drift in the sensor characteristics. We present a subspace approach which uses the received array signals to estimate the sensor gain and phase. We assume that the directions-of-arrival of some of the several sources that impinge on the array are known and show how this information can be used to determine sensor parameters. The resulting estimates can then be used to improve the robustness of array processing algorithms both for directions-of-arrival estimation and beamforming. Results of simulations carried out to verify the performance of this method are presented.

A hybrid energy detection approach to spectrum sensing

This paper introduces a hybrid energy detection approach to spectrum sensing in cognitive radio. ... more This paper introduces a hybrid energy detection approach to spectrum sensing in cognitive radio. Conventional energy detection technique (with N samples) is based on two hypotheses - i) where all N are signal samples corrupted by noise, ii) where all N are noise-only samples. Based on these two hypotheses a threshold is set for declaring a given N-sample signal as belonging to either of the two cases. This paper considers those cases which occur in practice - M samples out of N being signal corrupted with noise and the rest being noise-only, 0 ≤ M ≤ N, thus covering the conventional two hypotheses as well. The method described here, referred to as “hybrid energy detection”, proposes a combination of a 32-sample detector with a 16-sample detector which yields an improvement in performance in most such mixed signal-noise cases. The “hybrid energy detection” method requires certain thresholds to be set, in order to maximize the gain. We use simulated annealing to find those threshold v...

Signal design for a specified transmit beampattern, spatial ambiguity function for MIMO radar: A brief review of recent results

In phased-array radars, the transmitted waveforms from its different antenna elements are fully c... more In phased-array radars, the transmitted waveforms from its different antenna elements are fully correlated resulting in a focused beampattern. On the other hand, MIMO (multiple-input multiple-output) systems with transmit array containing colocated elements produce omni-directional beampattern with uncorrelated waveforms transmitted from its antennas. In some applications, it might be desirable to synthesize a beampattern that is between these two extremes so that wide focus areas can be formed without wasting power in the directions that are of no interest. In this paper, we present a brief review of recent results on the signal design. Specifically, we first introduce briefly the transmit beampattern and spatial ambiguity function, and then illustrate through examples how the zero-lag cross-correlation matrix of the transmitted signals, R, impacts the transmit beampattern. Next, we describe the beampattern/spatial ambiguity function design, through the design of R, as an optimizat...

Complex convolutions using rectangular transforms

Electronics Letters - ELECTRON LETT, 1978

Fig. 3 shows the C/V data obtained by this technique on a bulk single-crystal sample of InP replo... more

A double-talk detector for acoustic echo cancellation applications

Signal Processing, 2000

In acoustic echo cancellation applications, the presence of near-end speech causes divergence of ... more In acoustic echo cancellation applications, the presence of near-end speech causes divergence of the adaptive "lter which is used to model the echo path. A robust acoustic echo canceler is the one which is equipped with an algorithm that detects periods of double talk and puts the adaptive algorithm into a double-talk handling mode. This paper proposes a double-talk detector based on an angle measure between two vectors comprising samples of input signal to the near-end microphone and the estimated echo at the output of the adaptive "lter. Whenever the double talk is detected, the adaptive algorithm is frozen. The proposed detector has a quick reaction to the onset and cessation of the double talk and we illustrate this with a few simulations with pre-recorded speech segments. Performance of the subband adaptive 0165-1684/00/$ -see front matter

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Voice-band modem: A device to transmit data over telephone networks

Resonance, 2001

O v e r th e la st 4 0 y e a rs, th e re h a s b e e n c o n tin u o u s e v o lu tio n in th e d... more O v e r th e la st 4 0 y e a rs, th e re h a s b e e n c o n tin u o u s e v o lu tio n in th e d e sig n o f v o ic e -b a n d m o d e m s { sta rtin g a t a d a ta ra te o f 3 0 0 b its p e r se c o n d in th e la te 1 9 5 0 s, a ra te o f 3 3 ,6 0 0 b its p e r se co n d h a s b e e n a c h ie v e d in 1 9 9 5

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Voice-band modems: A device to transmit data over telephone networks

Resonance, 2001

Over the last 40 years, there has been continuous evolution in the design of voice-band modems-st... more Over the last 40 years, there has been continuous evolution in the design of voice-band modems-starting at a data rate of 300 bits per second in late 1950s, a rate of 33,600 bits per second has been achieved in 1995. Realising such high data rates over the voice band of 3400 Hz is a remarkable feat made possible by combining sophisticated techniques from three disciplines, communication theory, signal processing and information theory. In this article, we begin with a brief introduction of voice-band modems and then introduce the basic principles of data transmission.

Multichannel maximum-likelihood sequence estimation (MLSE) equalizer for GSM using a parametric channel model

IEEE Transactions on Communications, 1999

We propose a novel algorithm for the maximum-likelihood sequence estimation (MLSE) equalizer for ... more We propose a novel algorithm for the maximum-likelihood sequence estimation (MLSE) equalizer for the Global System for Mobile Communications (GSM) system. Specifically, we use a parametric model for the channel, along with a modified phase pulse-shaping function of Gaussian minimum shift keying (GMSK) modulation to obtain the modified Viterbi equalizer which we refer to as the parametric channel-Viterbi equalizer (PC-VE).

Combination of complex rectangular transforms and f.n.t. to implement fast convolution

Electron Lett, 1979

Abstract Recently, complex rectangular transforms (cxrts) have been derived which can be shown to... more

Method and system for V-BLAST detection with near maximum likelihood performance and low complexity

Application of modified least-squares algorithms to adaptive echo cancellation

ICASSP '83. IEEE International Conference on Acoustics, Speech, and Signal Processing, 1983

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Least squares type algorithm for adaptive implementation of Pisarenko's harmonic retrieval method

IEEE Transactions on Acoustics, Speech, and Signal Processing, 1982

versity of Tokyo, Tokyo. In 1968 he joined the Faculty of Engineering Science at Osaka 'Universit... more

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Optimized lattice-form adaptive line enhancer for a sinusoidal signal in broad-band noise

IEEE Transactions on Acoustics, Speech, and Signal Processing, 1981

A bstruct-An adaptive filter configuration, known as the adaptive line enhancer (ALE), has previo... more A bstruct-An adaptive filter configuration, known as the adaptive line enhancer (ALE), has previously been suggested by Widrow et al. for the detection of sinusoidal signals in wide-band noise. Some refinements of the ALE are suggested in this paper. First, for the special case of a single sinusoid, it is shown that there exists an optimum value of the so-called decorrelation parameter, which in earlier studies seems always to have been chosen equal to unity. Second, a lattice filter implementation of the general ALE is derived and turns out to be somewhat different from those suggested in the literature.

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Gauss-Newton based adaptive subspace estimation

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

ABSTRACT An adaptive approach for estimating all (or some) of the orthogonal eigenvectors of the ... more ABSTRACT An adaptive approach for estimating all (or some) of the orthogonal eigenvectors of the data covariance matrix (of a time series consisting of real narrowband signals in additive white noise) is presented. The inflation approach is used to estimate each of these vectors as minimum eigenvectors (eigenvectors corresponding to the minimum eigenvalue) of appropriately constructed symmetric positive definite matrices. This reformulation of the problem is made possible by the fact that the problem of estimating the minimum eigenvector of a symmetric positive definite matrix can be restated as the unconstrained minimization of an appropriately constructed nonlinear nonconvex cost function. The modular nature of the algorithm that results from this reformation makes the proposed approach highly parallel, resulting in a high-speed adaptive approach for subspace estimation.

A quasi-Newton adaptive algorithm for estimating generalized eigenvectors

Proceedings of 1994 28th Asilomar Conference on Signals, Systems and Computers, 1994

We first introduce a constrained minimization formulation for the generalized symmetric eigenvalu... more We first introduce a constrained minimization formulation for the generalized symmetric eigenvalue problem and then recast it into an unconstrained minimization problem by constructing an appropriate cost function. Minimizer of this cost function corresponds to the eigenvector corresponding to the minimum eigenvalue of the given symmetric matrix pencil and all minimizers are global minimizers. We also present an inflation technique for obtaining multiple generalized eigenvectors of thia pencil. Based on this asymptotic formulation, we derive a quasi-Newton adaptive algorithm for estimating these eigenvectors in the data case. This algorithm is highly modular and parallel with a computational complexity of O ( N z ) multiplications, N being the problem-size. Simulation results show fast convergence and good quality of the estimated eigenvectors.

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DISCRETE WAVELET PACKET BASED MULTITONE MODULATION FOR TRANSMITTING COMPLEX SYMBOLS

by Umapathi Reddy and Tushar K Adhikary

Multicarrier modulation (MCM) methods have been attract-ing considerable attention lately. In thi... more Multicarrier modulation (MCM) methods have been attract-ing considerable attention lately. In this paper, we address MCM techniques based on wavelet packets for QAM (quadra-ture amplitude modulation) and PM (phase modulation) sym-bol constellations. We rst discuss the design of complex wavelet packets, which serve as orthonormal carriers for MCM, and then describe a DWMT (discrete wavelet multitone) scheme for transmitting QAM and PM symbols. We consider both blind and non-blind schemes for retrieving the symbols at the receiver. Simulations have been carried out to study the performance with both the schemes.

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Techniques in optimum weighted smoothing

Further results in spatial smoothing

by Umapathi Reddy and Maheswara Reddy

Signal Processing, 1996

... The source signal K. Maheswara Ready, VU Reddy Signal Processing 48 (1996) 217224 covariance ... more

Adaptive two-dimensional harmonic retrieval and its application to radar

Performance Analysis of the Music Algorithm with Spatial Smoothing in the Presence of Coherent Sources

A Subspace Approach To Determining Sensor Gain And Phase With Applications To Array Processing

A hybrid energy detection approach to spectrum sensing

Signal design for a specified transmit beampattern, spatial ambiguity function for MIMO radar: A brief review of recent results

Complex convolutions using rectangular transforms

Electronics Letters - ELECTRON LETT, 1978

Fig. 3 shows the C/V data obtained by this technique on a bulk single-crystal sample of InP replo... more

A double-talk detector for acoustic echo cancellation applications

Signal Processing, 2000

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Voice-band modem: A device to transmit data over telephone networks

Resonance, 2001

Download

Voice-band modems: A device to transmit data over telephone networks

Resonance, 2001

Multichannel maximum-likelihood sequence estimation (MLSE) equalizer for GSM using a parametric channel model

IEEE Transactions on Communications, 1999

Combination of complex rectangular transforms and f.n.t. to implement fast convolution

Electron Lett, 1979

Abstract Recently, complex rectangular transforms (cxrts) have been derived which can be shown to... more

Method and system for V-BLAST detection with near maximum likelihood performance and low complexity

Application of modified least-squares algorithms to adaptive echo cancellation

ICASSP '83. IEEE International Conference on Acoustics, Speech, and Signal Processing, 1983

Download

Least squares type algorithm for adaptive implementation of Pisarenko's harmonic retrieval method

IEEE Transactions on Acoustics, Speech, and Signal Processing, 1982

versity of Tokyo, Tokyo. In 1968 he joined the Faculty of Engineering Science at Osaka 'Universit... more

Download

Optimized lattice-form adaptive line enhancer for a sinusoidal signal in broad-band noise

IEEE Transactions on Acoustics, Speech, and Signal Processing, 1981

Download

Gauss-Newton based adaptive subspace estimation

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

A quasi-Newton adaptive algorithm for estimating generalized eigenvectors

Proceedings of 1994 28th Asilomar Conference on Signals, Systems and Computers, 1994

Download

DISCRETE WAVELET PACKET BASED MULTITONE MODULATION FOR TRANSMITTING COMPLEX SYMBOLS

by Umapathi Reddy and Tushar K Adhikary

Download

Techniques in optimum weighted smoothing

Umapathi Reddy

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