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2009| January-February | Volume 55 | Issue 1
May 15, 2009
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Applications of Fractional Fourier Transform in Sonar Signal Processing
Roshen Jacob, Tessamma Thomas, A Unnikrishnan
January-February 2009, 55(1):16-27
Underwater scenario with all its complexities has been always very challenging for sonar signal processing. The reverberation and the fast-fading nature of the channel make it necessary to use chirp waveforms for sonar transmissions. The conventional techniques based on Fourier transforms often fail to fully address the issues like Doppler estimation with chirp waveforms and low signal-to-noise ratio detection due to the vagaries of the medium. Alternately, the fractional Fourier transform (henceforth shortened as FrFT) can be used in sonar signal processing for improved chirp-detection performance. However, this useful signal-processing tool is largely unknown to the sonar signal processing community. This paper demonstrates the application of FrFT in active and intercept sonar signal processing. The motivation to adopt the proposed method is the ability of FrFT to process chirp signals better than the conventional Fourier transform. FrFT is a parameterized transform with parameter a, related to the chirp rate. Many active sonar systems choose to transmit chirp signals for better detection in the presence of reverberation. FrFT if used instead of FFT in the correlation receiver has great potential as it takes advantage of the knowledge of transmitted waveform and can be therefore implemented for the optimum order. In the simulations, performance of matched filtering with FrFT has been compared with performance using conventional FFT. In the case of intercept sonar, FrFT can be used to estimate the parameters of chirps from a multi-component signal. This paper presents a novel parameter-estimation procedure by which chirp parameters are calculated from the two primary estimates, namely, optimum order and FrFT peak position. Simulation results clearly demonstrate the potential advantages of the proposed methods.
A Comparative Analysis of De-Noising Algorithms for Fetal Phonocardiographic Signals
Vijay S Chourasia, AK Mittra
January-February 2009, 55(1):10-15
This paper is aimed at the selection of de-noising algorithm for de-noising of the fetal phonocardiographic (fPCG) signals. Fourier-based analyzing tools have some limitations concerning frequency and time resolutions. Although wavelet transform (WT) overcomes these limitations, it requires selection of appropriate de-noising algorithm. The universal threshold, minimax threshold and rigorous SURE (Stein's Unbiased Risk Estimate) threshold algorithms along with soft or hard thresholding rule have been compared for de-noising of these signals. The mean-squared error (MSE) is used to evaluate the performance of these algorithms. The results show that, the rigorous SURE threshold algorithm with soft thresholding rule has a better performance for the analysis of fPCG signals when using the fourth-order Coiflets wavelet. The proposed approach is simple and proves to be effective when applied for the selection of de-noising algorithm for the fPCG signals. These de-noised signals can be used for the accurate determination of fetal heart rate (FHR) and further diagnostic applications pertaining to the fetus.
Mitigation of UWB Signals Spectral Leakage to the GPS L1 Band via Filtering After Clipping in the UWB Transmitter
K Deergha Rao, TSN Murthy
January-February 2009, 55(1):4-9
Ultra-wideband (UWB) has recently attracted much attention as an indoor short-range high-speed wireless communication. However, the high peak-to-average power ratio (PAPR) limits its capacity due to distortion caused by nonlinear components such as high-power amplifiers. Hence it is necessary to reduce the PAPR of UWB signals. Deliberate clipping is a simple technique for PAPR reduction. But PAPR reduction of UWB signals by clipping may cause spectral leakage. The spectral power leakage to outside frequency bands causes interference with the other systems operating in the vicinity of UWB. Global Positioning System (GPS) has a pivotal role in so many critical systems upon which the public depends for its safety and well-being, and thus it is necessary to assess the interference to the GPS band due to UWB signals spectral leakage. Therefore, in this paper, the interference to the GPS caused by spectral leakage of clipped direct-sequence UWB (DS-UWB) signals and multiband orthogonal frequency division multiplexing UWB (MB-OFDM UWB) signals is assessed, and the effect of filtering after clipping on the spectral leakage is evaluated using power spectral density (PSD) and bit-error rate (BER) as performance measures.
Design and Development of Millimeter-Wave Micromachined Patch Antennas
Preeti Sharma, Shiban K Koul
January-February 2009, 55(1):40-50
In this paper, we report design, development and fabrication of high-performance Ka-band micromachined patch antennas using monolithic microwave integrated circuit (MMIC)-compatible process technology. The main emphasis of this paper is to use radio frequency (RF) sputtering as the potential metal-dielectric film deposition process for rapid prototyping of many antenna structures in the absence of access to a well-established MEMS foundry. The fabricated antennas exhibited 4%-5% of impedance bandwidth, which is much wider than the one fabricated on bulk high-index substrates.
Comparative Analysis of the Techniques for Estimation of GPS DOP over Indian Region
Quddusa Sultana, Dhiraj Sunehra, AD Sarma, PVD Somasekhar Rao
January-February 2009, 55(1):28-34
Estimation of Dilution of Precision (DOP) plays an important role in aviation, terrestrial and marine navigation applications. In this paper results due to four techniques to estimate DOP namely, Kihara's method, 'all-in-view' SVs, 'best-5' SVs and 'best-4' SVs are investigated. Experiments are performed using Novatel (DL-4plus) GPS receiver and the collected data is used for the analysis. Bancroft algorithm is used to find preliminary position of the receiver. Using this position of the receiver and satellite coordinates, DOP is estimated. Comparative analysis of the specified techniques is performed. For most of the time, DOP values due to 'all-in-view' SVs are found as the best.
Scanning the Issue
Shiban K Koul
January-February 2009, 55(1):3-3
Mean-Square Performance of Selective Partial Update Subband Adaptive Filters
Mohammad Shams Esfand Abadi
January-February 2009, 55(1):35-39
In this paper, we present a general formalism for the mean-square performance analysis of selective partial update subband adaptive filter (SPU-SAF) algorithms. This analysis is based on energy conservation arguments and does not need to assume a Gaussian or white distribution for the regressors. We demonstrate through simulations that the results are useful in predicting the performance of this family of adaptive filters.
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