In this study, a technique was developed to compensate for nonlinear distortion through cancelling subcarrier-to-subcarrier intermixing interference (SSII) in an electroabsorption modulator (EAM)-based orthogonal frequency-division multiplexing (OFDM) transmission system. The nonlinear distortion to be compensated for is induced by both EAM nonlinearity and fiber dispersion. Because an OFDM sig...

To ensure that linearity is maintained to a high degree, it is necessary to examine the nature of amplifier distortion. Audio amplifier distortion is of concern for many years. The conventional feedback techniques used at audio frequencies are not applicable to many RF amplifiers due to following problems: 1. Stability at high bandwidth; 2. Cost for high gains in RF stages. Memory less or Insta...

This paper introduces a novel robust watermarking scheme for digital images, which is robust against common signal processing and geometric distortion attacks. In order to be resistant to geometric distortion attacks, the matched feature points determined by the scale-invariance feature transform (SIFT) are used for image restoration to reduce the synchronization errors caused by geometric dist...

s: English and German provided Tables: None Figures: 15 Galley proofs: Please send galley proofs to J. K. Su at the MIT Lincoln Laboratory address given above. Telephone: +1-781-981-4188, fax: +1-781-981-7271, email: [email protected]. Abstract Using a theoretical approach based on random processes, signal processing, and information theory, we study the performance of digital watermarks subjected ...

Copyright notification and enforcement, authentication, covert communication, and hybrid transmission are examples of emerging multimedia applications for digital watermarking methods, methods for embedding one signal (e.g., the digital watermark) within another “host” signal to form a third, “composite” signal. The embedding is designed to achieve efficient trade-offs among the three conflicti...

The imaging depth of two-photon excitation fluorescence microscopy is partly limited by the inhomogeneity of the refractive index in biological specimens. This inhomogeneity results in a distortion of the wavefront of the excitation light. This wavefront distortion results in image resolution degradation and lower signal level. Using an adaptive optics system consisting of a Shack-Hartmann wave...

The detailed analysis of measured interferograms generally requires phase correction. Phase-shift correction methods are commonly used and well documented for conventional Fourier-transform spectroscopy. However, measured interferograms can show additional phase errors, depending on the optical path difference and signal frequency, which we call phase distortion. In spatial heterodyne spectrosc...

Vector Quantization (VQ) has been extensively used in speech vocoders. Phase information is often ignored or coarsely represented in parametric coders because of the difficulties facing phase quantization. This paper introduces a novel distortion measure for the low-band speech signal that takes phase information into consideration, with no increase in the bit-rate. This measure has been used i...

A novel subspace approach for speech enhancement using a subband whitening filter is proposed. Previous subspace approaches for enhancement either assumed white noise or used a fullband pre-whitening filter before enhancement for colored noise. The previous approaches were successful only in reducing the upper bound of the signal distortion while reducing noise. However, the proposed method min...

As an extension of previous work on computer-generated phantoms, more accurate, realistic phantoms are generated by integrating image distortion and signal loss caused by susceptibility variations. With the addition of real motions and activations determined from actual functional MRI studies, these phantoms can be used by the fMRI community to assess with higher fidelity pre-processing algorit...