Multi-User Communications in Non-Gaussian Channels

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This project will investigate the problem of multiple-access communications through non-Gaussian channels via spread-spectrum modulation. It is motivated in large part by the fact that modern urban radio networks must operate in complex and variable noise environments that are often dominated by impulsive, non- Gaussian man-made and natural noise sources. Non-Gaussian disturbances are now known to be present in many situations, and they can greatly reduce the performance of conventional digital communication systems. The overall purpose of this research is to develop new design methods suitable for multiuser systems operating in such non-Gaussian channels. The study can be divided into two principal tasks to be considered. There are the development of time and phase synchronizers; and the design of "optimum" nonlinear, coherent, spread-spectrum receivers in non-Gaussian noise. In many applications, in the presence of non-Gaussian noise sources, the impulsive and transient characterisitics of noise suggest that a nonlinearity in the receiver structure can significantly reduce the effective noise power by reducing the large voltage deviation caused by noise impulses. Thus it is proposed to design and analyze the performance of optimum memoryless nonlinearities for synchronization and correlation reception. Possibilities of introducing memory in the structure of receivers will also be explored. It is anticipated that the results of this study will find widespread application in urban and military mobile radio networking and low frequency communications.