Multicarrier CDMA using wavelets in multipath fading channel

Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to [email protected], referencing the URI of the item.Includes bibliographical references.Issued also on microfiche from Lange Micrographics.A new multicarrier direct sequence spread spectrum code division multiple access (DS-SS-CDMA) is proposed. Due to the wide bandwidth characteristic of the DS-SS-CDMA signal, it is considered to undergo the frequency selective fading, which causes severe degradation of the system. Applying frequency diversity to the system by subdividing the transmitting bandwidth into several narrow bandwidths, each narrow band may be subjected to a flat fading which can improve the performance of the system. This new scheme employs wavelets as orthogonal carriers to implement the frequency diversity of the system. By computer simulations, the performance of this new system is evaluated. Compared to the performance of the conventional CDMA which uses match filter receiver, the result shows that the new system outperforms the conventional CDMA system

Imaging through random multiple scattering media using integration of propagation and array signal processing

Imaging of objects through complex environment is important in several applications, including imaging of hidden objects in obscuring media such as atmospheric and ocean turbulence, rough ocean surfaces, rain, fog, snow, and biological tissues. These media are often randomly varying in space and time, and statistical treatments are necessary to obtain images with useful spatial and temporal resolutions. In recent years, there has been increasing interest in using signal processing and correlation techniques to improve resolutions and to distinguish images from clutter. This paper presents several imaging techniques for objects in the presence of random media. Time-reversal MUSIC (multiple signal classification) imaging has excellent resolution when multiple scattering is small or moderate. Modified beamformer imaging has moderately high resolution even at large multiple scattering. We also include time reversal (TR) and synthetic aperture radar (SAR) imaging for comparison. The technique involves stochastic Green's function and mutual coherence function (MCF), eigenvectors of time-reversal matrix and pseudo spectrum. Numerical examples are given to show the effectiveness of these imaging techniques