arun batra - Academia.edu (original) (raw)

Papers by arun batra

Research paper thumbnail of Immunological Alterations in Alzheimer’s Disease

Research paper thumbnail of Is There an Immunopathology of the Serotonergic Synapse in Mental Disorder

Research paper thumbnail of Conduction studies on Ta2O5 layer under different metallic electrodes1

Electrochimica Acta, 1972

Rectification studies on Ta,O, anodic oxide layers with vacuum-deposited Au, Ag, Pb, Bi, Sb conta... more Rectification studies on Ta,O, anodic oxide layers with vacuum-deposited Au, Ag, Pb, Bi, Sb contacts have been made. No correlation between critical voltage and work function for metal electrodes was found. Non-uniform and unpredictable behaviour of Ta,O, fdrns under different metals have indicated the dominant dependence of conduction on the flaw density in the oxide film. R&sum&Etude de la rectification par des couches anodiques d'oxyde Ta,O,, en contact avec Au, Ag, Pb, Bi, Sb d6po& sous vide. 11 n'y a pas de relation entre le potentiel critique et le travail d'extraction dans les Electrodes m&alliques. Le comportement non uniforme et imprkvisible des Clms de Ta,O, sous da&rents m&aux dbnote l'influence pr6pondCrante de la densites des d6fauts sur la conduction du film d'oxyde. zusammenfassung-An anodischen TalOl-Schichten. welche mit-aus dem Vakuum abgeschiedenem-Au, Ag, Pb, Bi oder Sb kontaktiert waren, wurden Gleichrichtungsuntersuchungen durch-g&t. Man fand keine Korrelation zwischen der kritischen Spannung und der Austrittsarbeit fiir die metallische Elektroden. Das nicht einheitliche und nicht vorhenusagende Verhalten von Ta,O,-Schichten unter den verschiedenen Metallen zeigt die dominierdende AbhLingigkeit der Leitung von der Dichte der Fehlstellen in der Oxidschicht.

Research paper thumbnail of Narrowband interference mitigation in BICM OFDM systems

The performance of an orthogonal frequency division multiplexing (OFDM) system is degraded in the... more The performance of an orthogonal frequency division multiplexing (OFDM) system is degraded in the presence of narrowband interference (NBI). This degradation arises from spectral leakage of the interference power during demodulation, corrupting many subcarriers. The predictionerror filter (PEF) is introduced as a means for mitigating the NBI in the time-domain prior to demodulation. In the uncoded case, the PEF is shown to mitigate the interference, however, the performance is limited by an irreducible error floor due to the data subcarriers that are notched out. In the coded case, the coding provides a way for recovering the removed subcarriers. The PEF is compared with Bayesian erasure insertion over a range of SIRs and it is seen that the PEF performs best for all SIRs. The PEF acts an erasure insertion mechanism by inserting erasures via a notch around the tones closest to the interference, while leaving the surrounding tones unaffected.

Research paper thumbnail of A Two-Stage Approach for Improving the Convergence of Least-Mean-Square Adaptive Decision-Feedback Equalizers in the Presence of Severe Narrowband Interference

Eurasip Journal on Advances in Signal Processing, 2008

It has previously been shown that a least-mean-square (LMS) decision-feedback filter can mitigate... more It has previously been shown that a least-mean-square (LMS) decision-feedback filter can mitigate the effect of narrowband interference (L.-M. ). An adaptive implementation of the filter was shown to converge relatively quickly for mild interference. It is shown here, however, that in the case of severe narrowband interference, the LMS decision-feedback equalizer (DFE) requires a very large number of training symbols for convergence, making it unsuitable for some types of communication systems. This paper investigates the introduction of an LMS prediction-error filter (PEF) as a prefilter to the equalizer and demonstrates that it reduces the convergence time of the two-stage system by as much as two orders of magnitude. It is also shown that the steady-state bit-error rate (BER) performance of the proposed system is still approximately equal to that attained in steady-state by the LMS DFE-only. Finally, it is shown that the two-stage system can be implemented without the use of training symbols. This two-stage structure lowers the complexity of the overall system by reducing the number of filter taps that need to be adapted, while incurring a slight loss in the steady-state BER.

Research paper thumbnail of MITIGATION OF NARROWBAND INTERFERENCE USING ADAPTIVE EQUALIZERS

It has previously been shown that a decision-feedback filter can mitigate the effect of narrowban... more It has previously been shown that a decision-feedback filter can mitigate the effect of narrowband interference. An adaptive implementation of the filter was seen to converge relatively quickly for mild interference. It is shown here, however, that in the case of severe narrowband interference, the decision-feedback equalizer (DFE) requires a convergence time that makes it unsuitable for some types of communication systems. The introduction of a linear predictor, as a prefilter to this equalizer, greatly reduces the total convergence time. There is a trade-off, however, between convergence time and steady-state performance, and that is evaluated in this paper.

Research paper thumbnail of Mitigation of unknown narrowband interference using instantaneous error updates

Nonlinear effects of the Normalized Least Mean Square (NLMS) algorithm are studied in the presenc... more Nonlinear effects of the Normalized Least Mean Square (NLMS) algorithm are studied in the presence of multipath and severe narrowband interference, for applications where there is no direct reference for the interfering signal. The nonlinear characteristics of the adaptive equalizer are used to generate a reference signal for the interference from the instantaneous error signal. The adaptive coefficients are optimized such that the width of the notch is minimized in order to reduce signal distortion. The bit error rate improvement is quantified as a function of input SINR, multipath characteristics, and NLMS filter parameters.

Research paper thumbnail of Interference Rejection and Management

In this chapter, we consider interference suppression in several different wireless communication... more In this chapter, we consider interference suppression in several different wireless communication systems. The first topic treated is self-interference encountered among cooperating systems, for example, the self-interference that is encountered in cognitive radio systems and ultra-wideband (UWB) communication systems. Both single-carrier, direct sequence signals and multicarrier signals are considered, and the effects of the interference on the performance of a direct sequence UWB system that employs channel state estimation in the presence of the interference is evaluated.

Research paper thumbnail of Initialization Techniques for Improved Convergence of LMS DFEs in Strong Interference Environments

The least-mean square (LMS) decision-feedback equalizer (DFE) was previously shown [1], [2] to po... more The least-mean square (LMS) decision-feedback equalizer (DFE) was previously shown [1], [2] to possess an extended convergence time in an interference limited environment. In [1] it was shown that the convergence time can be significantly reduced by using the received samples and the training data to initialize (data-aided initialization) the LMS weights with an estimate for the Wiener weights. In this paper, two dataaided initialization techniques for equalization in the presence of severe narrowband interference are discussed and compared. The estimate of the Wiener filter is obtained from data-based averages of the autocorrelation matrix and the cross-correlation vector.

Research paper thumbnail of Narrowband interference mitigation in OFDM systems

Orthogonal frequency division multiplexing (OFDM) is noted for its resistance to narrowband inter... more Orthogonal frequency division multiplexing (OFDM) is noted for its resistance to narrowband interference when equipped with forward error correction. This technique along with erasure insertion is adequate when the the signal-to-interference ratio (SIR) is moderate, around 0 dB, however, when the interference is severe, i.e. SIR = -20 dB, a non-orthogonal interference corrupts a large number of the data subcarriers due to spectral leakage. This situation requires a large number of erasures that compromise the code's error correction capability. The prediction-error lter (PEF) is proposed as an erasure insertion mechanism that localizes the erasures to the tones surrounding the interference, while not affecting the remaining tones. The simulation results indicate excellent performance, for the bit-interleaved coded modulated (BICM) OFDM system using the PEF and BPSK modulation when the SIR = -20 dB in a frequencyselective fading channel.

Research paper thumbnail of Petrous apex arachnoid cyst extending into Meckel's cave

Australasian Radiology, 2002

A rare case of arachnoid cyst involving the petrous apex with an unusual clinical presentation ha... more A rare case of arachnoid cyst involving the petrous apex with an unusual clinical presentation has been described with special emphasis in the imaging features and importance of accurate presurgical diagnosis. Differentiation from the other benign lesions involving the petrous apex and the role of newer MR techniques in the diagnosis of these lesions has been highlighted.

Research paper thumbnail of Perfusion Magnetic Resonance Imaging in Intracerebral Parenchymal Tuberculosis: Preliminary Findings

Journal of Computer Assisted Tomography, 2003

To study the vascular perfusion patterns of focal intracerebral tubercular lesions using echoplan... more To study the vascular perfusion patterns of focal intracerebral tubercular lesions using echoplanar magnetic resonance (MR) imaging-derived relative cerebral blood volume (rCBV) maps. Seventeen focal tubercular lesions were evaluated with conventional and perfusion-weighted MR imaging on a 1.5-T MR system. The rCBVs of the center, peripheral wall, and perilesional white matter were calculated from the perfusion MR-derived data. Perfusion MR imaging findings as depicted on the rCBV maps were qualitatively compared with those of conventional MR findings. Eleven of the 17 lesions demonstrated vascularity greater than that of the contralateral white matter on rCBV maps. The mean of the measured rCBV values of the peripheral wall and center of the lesions was 2.5 +/- 1.42 and 0.33 +/- 0.3 (mean +/- SD), respectively. Most of the hypervascular lesions (8) revealed a concentric peripheral wall having alternating hypointense and hyperintense signal intensity rims surrounding a variable intensity center on T2-weighted images. All the lesions having a nodular enhancing pattern (4) were hypervascular. Focal cerebral tubercular lesions can have variable vascularity as shown on perfusion MR-derived rCBV maps. It may be difficult to differentiate hypervascular lesions from cerebral tumors in some patients based on perfusion MR imaging alone.

Research paper thumbnail of Immunological Alterations in Alzheimer’s Disease

Research paper thumbnail of Is There an Immunopathology of the Serotonergic Synapse in Mental Disorder

Research paper thumbnail of Conduction studies on Ta2O5 layer under different metallic electrodes1

Electrochimica Acta, 1972

Rectification studies on Ta,O, anodic oxide layers with vacuum-deposited Au, Ag, Pb, Bi, Sb conta... more Rectification studies on Ta,O, anodic oxide layers with vacuum-deposited Au, Ag, Pb, Bi, Sb contacts have been made. No correlation between critical voltage and work function for metal electrodes was found. Non-uniform and unpredictable behaviour of Ta,O, fdrns under different metals have indicated the dominant dependence of conduction on the flaw density in the oxide film. R&sum&Etude de la rectification par des couches anodiques d'oxyde Ta,O,, en contact avec Au, Ag, Pb, Bi, Sb d6po& sous vide. 11 n'y a pas de relation entre le potentiel critique et le travail d'extraction dans les Electrodes m&alliques. Le comportement non uniforme et imprkvisible des Clms de Ta,O, sous da&rents m&aux dbnote l'influence pr6pondCrante de la densites des d6fauts sur la conduction du film d'oxyde. zusammenfassung-An anodischen TalOl-Schichten. welche mit-aus dem Vakuum abgeschiedenem-Au, Ag, Pb, Bi oder Sb kontaktiert waren, wurden Gleichrichtungsuntersuchungen durch-g&t. Man fand keine Korrelation zwischen der kritischen Spannung und der Austrittsarbeit fiir die metallische Elektroden. Das nicht einheitliche und nicht vorhenusagende Verhalten von Ta,O,-Schichten unter den verschiedenen Metallen zeigt die dominierdende AbhLingigkeit der Leitung von der Dichte der Fehlstellen in der Oxidschicht.

Research paper thumbnail of Narrowband interference mitigation in BICM OFDM systems

The performance of an orthogonal frequency division multiplexing (OFDM) system is degraded in the... more The performance of an orthogonal frequency division multiplexing (OFDM) system is degraded in the presence of narrowband interference (NBI). This degradation arises from spectral leakage of the interference power during demodulation, corrupting many subcarriers. The predictionerror filter (PEF) is introduced as a means for mitigating the NBI in the time-domain prior to demodulation. In the uncoded case, the PEF is shown to mitigate the interference, however, the performance is limited by an irreducible error floor due to the data subcarriers that are notched out. In the coded case, the coding provides a way for recovering the removed subcarriers. The PEF is compared with Bayesian erasure insertion over a range of SIRs and it is seen that the PEF performs best for all SIRs. The PEF acts an erasure insertion mechanism by inserting erasures via a notch around the tones closest to the interference, while leaving the surrounding tones unaffected.

Research paper thumbnail of A Two-Stage Approach for Improving the Convergence of Least-Mean-Square Adaptive Decision-Feedback Equalizers in the Presence of Severe Narrowband Interference

Eurasip Journal on Advances in Signal Processing, 2008

It has previously been shown that a least-mean-square (LMS) decision-feedback filter can mitigate... more It has previously been shown that a least-mean-square (LMS) decision-feedback filter can mitigate the effect of narrowband interference (L.-M. ). An adaptive implementation of the filter was shown to converge relatively quickly for mild interference. It is shown here, however, that in the case of severe narrowband interference, the LMS decision-feedback equalizer (DFE) requires a very large number of training symbols for convergence, making it unsuitable for some types of communication systems. This paper investigates the introduction of an LMS prediction-error filter (PEF) as a prefilter to the equalizer and demonstrates that it reduces the convergence time of the two-stage system by as much as two orders of magnitude. It is also shown that the steady-state bit-error rate (BER) performance of the proposed system is still approximately equal to that attained in steady-state by the LMS DFE-only. Finally, it is shown that the two-stage system can be implemented without the use of training symbols. This two-stage structure lowers the complexity of the overall system by reducing the number of filter taps that need to be adapted, while incurring a slight loss in the steady-state BER.

Research paper thumbnail of MITIGATION OF NARROWBAND INTERFERENCE USING ADAPTIVE EQUALIZERS

It has previously been shown that a decision-feedback filter can mitigate the effect of narrowban... more It has previously been shown that a decision-feedback filter can mitigate the effect of narrowband interference. An adaptive implementation of the filter was seen to converge relatively quickly for mild interference. It is shown here, however, that in the case of severe narrowband interference, the decision-feedback equalizer (DFE) requires a convergence time that makes it unsuitable for some types of communication systems. The introduction of a linear predictor, as a prefilter to this equalizer, greatly reduces the total convergence time. There is a trade-off, however, between convergence time and steady-state performance, and that is evaluated in this paper.

Research paper thumbnail of Mitigation of unknown narrowband interference using instantaneous error updates

Nonlinear effects of the Normalized Least Mean Square (NLMS) algorithm are studied in the presenc... more Nonlinear effects of the Normalized Least Mean Square (NLMS) algorithm are studied in the presence of multipath and severe narrowband interference, for applications where there is no direct reference for the interfering signal. The nonlinear characteristics of the adaptive equalizer are used to generate a reference signal for the interference from the instantaneous error signal. The adaptive coefficients are optimized such that the width of the notch is minimized in order to reduce signal distortion. The bit error rate improvement is quantified as a function of input SINR, multipath characteristics, and NLMS filter parameters.

Research paper thumbnail of Interference Rejection and Management

In this chapter, we consider interference suppression in several different wireless communication... more In this chapter, we consider interference suppression in several different wireless communication systems. The first topic treated is self-interference encountered among cooperating systems, for example, the self-interference that is encountered in cognitive radio systems and ultra-wideband (UWB) communication systems. Both single-carrier, direct sequence signals and multicarrier signals are considered, and the effects of the interference on the performance of a direct sequence UWB system that employs channel state estimation in the presence of the interference is evaluated.

Research paper thumbnail of Initialization Techniques for Improved Convergence of LMS DFEs in Strong Interference Environments

The least-mean square (LMS) decision-feedback equalizer (DFE) was previously shown [1], [2] to po... more The least-mean square (LMS) decision-feedback equalizer (DFE) was previously shown [1], [2] to possess an extended convergence time in an interference limited environment. In [1] it was shown that the convergence time can be significantly reduced by using the received samples and the training data to initialize (data-aided initialization) the LMS weights with an estimate for the Wiener weights. In this paper, two dataaided initialization techniques for equalization in the presence of severe narrowband interference are discussed and compared. The estimate of the Wiener filter is obtained from data-based averages of the autocorrelation matrix and the cross-correlation vector.

Research paper thumbnail of Narrowband interference mitigation in OFDM systems

Orthogonal frequency division multiplexing (OFDM) is noted for its resistance to narrowband inter... more Orthogonal frequency division multiplexing (OFDM) is noted for its resistance to narrowband interference when equipped with forward error correction. This technique along with erasure insertion is adequate when the the signal-to-interference ratio (SIR) is moderate, around 0 dB, however, when the interference is severe, i.e. SIR = -20 dB, a non-orthogonal interference corrupts a large number of the data subcarriers due to spectral leakage. This situation requires a large number of erasures that compromise the code's error correction capability. The prediction-error lter (PEF) is proposed as an erasure insertion mechanism that localizes the erasures to the tones surrounding the interference, while not affecting the remaining tones. The simulation results indicate excellent performance, for the bit-interleaved coded modulated (BICM) OFDM system using the PEF and BPSK modulation when the SIR = -20 dB in a frequencyselective fading channel.

Research paper thumbnail of Petrous apex arachnoid cyst extending into Meckel's cave

Australasian Radiology, 2002

A rare case of arachnoid cyst involving the petrous apex with an unusual clinical presentation ha... more A rare case of arachnoid cyst involving the petrous apex with an unusual clinical presentation has been described with special emphasis in the imaging features and importance of accurate presurgical diagnosis. Differentiation from the other benign lesions involving the petrous apex and the role of newer MR techniques in the diagnosis of these lesions has been highlighted.

Research paper thumbnail of Perfusion Magnetic Resonance Imaging in Intracerebral Parenchymal Tuberculosis: Preliminary Findings

Journal of Computer Assisted Tomography, 2003

To study the vascular perfusion patterns of focal intracerebral tubercular lesions using echoplan... more To study the vascular perfusion patterns of focal intracerebral tubercular lesions using echoplanar magnetic resonance (MR) imaging-derived relative cerebral blood volume (rCBV) maps. Seventeen focal tubercular lesions were evaluated with conventional and perfusion-weighted MR imaging on a 1.5-T MR system. The rCBVs of the center, peripheral wall, and perilesional white matter were calculated from the perfusion MR-derived data. Perfusion MR imaging findings as depicted on the rCBV maps were qualitatively compared with those of conventional MR findings. Eleven of the 17 lesions demonstrated vascularity greater than that of the contralateral white matter on rCBV maps. The mean of the measured rCBV values of the peripheral wall and center of the lesions was 2.5 +/- 1.42 and 0.33 +/- 0.3 (mean +/- SD), respectively. Most of the hypervascular lesions (8) revealed a concentric peripheral wall having alternating hypointense and hyperintense signal intensity rims surrounding a variable intensity center on T2-weighted images. All the lesions having a nodular enhancing pattern (4) were hypervascular. Focal cerebral tubercular lesions can have variable vascularity as shown on perfusion MR-derived rCBV maps. It may be difficult to differentiate hypervascular lesions from cerebral tumors in some patients based on perfusion MR imaging alone.