Electrical and Computer Engineering

An elegant method to design a Michelson interferometer based interleaver using a classic infinite impulse response (IIR) filter such as Butterworth, Chebyshev, and elliptic filters as a starting point are presented. The proposed design method allows engineers to design a Michelson interferometer based interleaver from specifications seamlessly. Simulation results are presented to demonstrate the validity of the proposed design method.

In this paper, a fifth-order Volterra kernel estimation algorithm, which is optimal in the least mean square error sense, for a bandpass nonlinear system is derived. The algorithm is based on some characteristics of i.i.d. circularly-symmetric zero-mean complex-valued Gaussian random variables. The proposed algorithm can be used to identify a nonlinear system under uniformly i.i.d. rectangular M-QAM input and under uniformly i.i.d. M-PSK input (4) with modest modification. The same approach has been used to derive an optimal Volterra kernel estimation algorithm up to the third order. However, in some cases, a thirdorder model is not of "high enough order" to capture the nonlinear system characteristics. A simulation example is given to show the necessity of deriving a fifth-order Volterra kernel estimation algorithm and to test for the correctness of the algorithms.

The authors proposed an in-phase/quadrature (I/Q) imbalance compensation technique for wideband digital receiver applications. An I/Q channel-based receiver can double the receiver working bandwidth. However, the amplitude/phase imbalance of an imperfect hybrid coupler can generate image signals thus reducing the receiver's instantaneous dynamic range. They developed a finite impulse response filter-based technique to mitigate deleterious effects because of the amplitude/phase imbalance. Both simulations and experiments were conducted to verify validity of the developed algorithm. The simulation and experiment results show that the proposed imbalance mitigation technique can reduce image signal powers by more than 24 dB or down to noise level. A receiver system level simulation is also conducted to demonstrate the practicality of the proposed imbalance mitigation method.

A main drawback of Coherent Optical Orthogonal Frequency Division Multiplexing (CO-OFDM) system is its sensitivity to fiber nonlinearity. Nonlinear electrical equalizer based on Volterra model has been demonstrated capable of compensating fiber nonlinear distortion in an OOK or PSK optical communication system. However, the implementation complexity of a Volterra model based electrical equalizer prohibits its deployment in a real-life CO-OFDM system. In this paper, we demonstrate that the number of kernels of a Volterra model based equalizer can be significantly reduced using the modified Gram-Schmidt method with reorthogonalization techniques. The resulting "sparse" Volterra model based electrical equalizer and the electrical equalizer based on the "full" Volterra model have comparable performance and can compensate intra-channel nonlinearity of a 16-QAM 100 Gbit/s CO-OFDM System.

Nonlinear distortion caused by fiber nonlinearity is a major performance-limiting factor in advanced optical communication systems. We proposed a nonlinear electrical equalization scheme based on the Wiener-Hammerstein model. Compared with other popular nonlinear compensation techniques such as the Volterra model, the Wiener-Hammerstein model approach has a simpler structure and requires less calculation. Simulation results are presented to demonstrate the capability of a Wiener-Hammerstein model based electrical equalizer used in a coherent optical orthogonal frequency division multiplexing system. It is shown that the Wiener-Hammerstein model based equalizer can significantly reduce nonlinear distortion and can deliver a performance comparable to the Volterra model based equalizer.

One of major issues of the advanced optical communication system is the signal distortion caused by fiber nonlinearity. Both predistorters and equalizers have been used for nonlinearity compensation and electrical compensation has become a popular choice among optical communication engineers in recent years. However, to the best of the authors' knowledge, no comparative study about electrical equalizers and predistorters has been conducted for optical communication systems. Using a coherent optical orthogonal frequency division multiplexing (CO-OFDM) system as a test system, we investigated the performance of electrical th-order inverse Volterra predistorters and equalizers. Our research results show that both the equalizer and the predistorter can compensate for the nonlinearity of the CO-OFDM system. The major difference between the predistorter and the equalizer is that the predistorter regulates the input power; therefore, the performance of the CO-OFDM system with a predistorter is independent over a wide range of the laser launch power. The results presented in this paper can lead to a better understanding of electrical equalization and predistortion techniques for optical communication systems.

Chromatic dispersion (CD) caused by an imperfect antireflection coating is a great concern for optical engineers, and different techniques have been proposed to reduce CD in optical devices. In this article, we investigate two popular CD reduction techniques used in birefringent interleaver manufacturing and their effects on performance improvement of optical communication systems. Our results show that some CD reduction scheme bringing about a smaller CD ripple amplitude does not necessarily guarantee better system performance. This result can be used as a guideline for optical engineers working on reducing CD caused by an imperfect antireflection coating.

We investigate the practical applicability of video photoplethysmography (VPPG) to extract heart rates of subjects using noncontact color video recordings of human faces collected under typical indoor laboratory conditions using commercial video cameras. Videos were processed following three previously described simple VPPG algorithms to produce a time-varying plethysmographic signal. These time signals were then analyzed using, to the best of our knowledge, a novel, lock-in algorithm that was developed to extract the pulsatile frequency component. A protocol to associate confidence estimates for the extracted heart rates for each video stream is presented. Results indicate that the difference between heart rates extracted using the lock-in technique and gold-standard measurements, for videos with high-confidence metrics, was less than 4 beats per minute. Constraints on video acquisition and processing, including natural subject motion and the total duration of video recorded required for evaluating these confidence metrics, are discussed.

A new method was proposed for chirp signal detection and estimation built on the frame-based fast Fourier transform (FFT). The proposed method uses the peak frequency difference between FFT frames to detect a chirp signal and estimate chirp rate. This approach differs from conventional methods and is easy to implement. It generates more accurate chirp rate estimation especially under a low signal-to-noise ratio. Simulation and experimental data are used to verify the proposed methods.

Prof. Bin Wang earned his Ph.D. from the Ohio State University in 2000. He joined the Wright State University in September 2000, where he is currently full professor of computer science and engineering. His research interests include optical networks, real-time computing, mobile and wireless networks, cognitive radio networks, trust and information security, and semantic web. He is a recipient of the US Department of Energy Career Award. His research has been supported by

as assistant professor from 2003 to 2005. He joined Wright State University in 2005 and currently serves as full professor. Dr. Wu is the author of national CDMA network management standard of China. He also co-authored one of the first books on multi-carrier transmission for wireless communication. He has published more than 100 papers in journals and conferences. He has served as Chair of Acoustic Communication Interest Group of IEEE Technical Committee on Multimedia Communications. His research has been supported by the

A design of sub-Nyquist uniform linear array receiver with different sampling rates is proposed, investigated, and reported in this paper. The proposed architecture increases functionality of conventional linear array receiver with modest modifications. Simulation results show that the proposed receiver is capable of determining angle of arrival (AOA) and signal frequencies of multiple continuous-wave/chirp signals over several Nyquist zones. INDEX TERMS Direction of arrival estimation, MUSIC, antenna arrays, signal sampling, sub-Nyquist.

In this article, a machine learning aided electronic warfare (EW) system is presented and the simulation results are discussed. The developed EW system uses an automatic decision tree generator to create engagement protocol and a fuzzy logic model to quantify threat levels. A long-short term memory (LSTM) neural network was also trained to predict the next signal set of multifunction radars. The simulation results demonstrate the effectiveness of the developed EW system's ability to engage multiple multifunction radars.

A wideband receiver is designed to detect signals over a broad bandwidth. To increase the receiver's capability of detecting multiple signals, it is a common practice to apply a window to reduce spectral leakage. The modified periodogram applies a window before auto-correlation and Blackman-Tucky method applies the window after auto-correlation. To the best of authors' knowledge, no one has compared the performance difference in the context of wideband receiver applications. This study finds that the modified periodogram can better enable a receiver to detect multiple signals with a significant power difference at the expense of reduced frequency resolution and sensitivity.

A multifunctional radar (MFR) with varying pulse sequences can change its signal characteristics and/or pattern, based on the presence of targets and to avoid being jammed. To take a countermeasure against an MFR, it is crucial for an electronic warfare (EW) system to be able to identify and separate a MFR's modes via analyzing intercepted radar signals, without a priori knowledge. In this article, two correlationbased methods, one taking the signal's order into account and another one ignoring the signal's order, are proposed and investigated for this task. The results demonstrate their great potential.

The effect of an imperfect antireflection ͑AR͒ coating on a birefringent interleaver ͑an important optical communication component͒ and on an optical communications system containing such a birefringent interleaver is investigated. We demonstrate how the imperfect AR coating on the rhomb surfaces affects the birefringent interleaver's intensity spectrum and generates undesirable chromatic dispersion ͑CD͒ ripples for an interleaver that should be dispersion-free by design. Our results show that a rhomb with a close-to-perfect AR surface coating ͑T = 99.8% ͒ can still generate a ±30-ps/ nm CD ripple, causing a nonnegligible power penalty in an optical communications system. We also demonstrate a simple and practical approach to reduce the CD ripple caused by the imperfect AR coating.

I am grateful to many individuals who have helped me over the course of my graduate school career. First, I would like to thank my advisor, Dr. Chi-Hao Cheng for his mentorship. Whether it was the late-night emails or driving back and forth to Dayton, his support was greatly appreciated, and his dedication to his students can never be questioned. Thank you to Dr. Dmitriy Garmatyuk and Dr. Vasu Chakravarthy for taking the time to serve on my thesis committee. I would also like to thank the rest of the faculty and staff of the Electrical and Computer Engineering department at Miami University for all of their support over the past 6 years. I would like to express my gratitude to my colleagues at the Air Force Research Laboratory, Sensors Directorate for their support and guidance, including Cliff Bullmaster, George Gonczy, Jim Stephens, Ed Huling and Jill Johnson. A special thanks goes to the Dayton Area Graduate Studies Institute (DAGSI) for funding my graduate study. Finally, I would like to thank my family (including my fiancée Becky Williams and her family) and friends for their love and support.

We propose a digital wideband receiver scheme covering multiple Nyquist zones by exploiting phase and magnitude mismatch in the conversion from real-valued signals to complex-valued signals. The digital wideband receiver is designed to detect uncooperative signals. The magnitude/phase mismatch due to an imperfect hybrid coupler is often considered undesirable and needs to be compensated. However, by exploiting the frequency-dependent magnitude/phase mismatch phenomenon, we can distinguish signals from different Nyquist zones. Simulation results demonstrate that, using carefully designed magnitude/phase mismatch, we can detect signals over multiple Nyquist zones. The proposed method can lead to a new wideband receiver design.

The Automatic Fingerprint Matching (AFM) uses similarity score between an input and a reference fingerprint images to match fingerprints and the similarity score can be determined with a Minutiae Extraction Algorithm (MEA), which extracts minutiae of input and reference fingerprints. The performance of MEA depends on the quality of input fingerprint images. In case of blurred input fingerprint images, it becomes difficult to obtain a legitimate similarity score used in the AFM process. Therefore, an image enhancement algorithm must be incorporated with MEA to improve the performance of AFM process. In this study, good quality input fingerprint images have been intentionally blurred. Different enhancement algorithms are used to enhance the quality of blurred input fingerprint images. The performance of enhancement algorithms is analyzed and evaluated using the similarity score of extracted minutiae. Experimental results show that Volterra filter significantly enhances the quality of blurred input fingerprint images than other linear filters such as Laplacian and Gabor filters considered in this study.