ABSTRACT

            Stratellites (the term comes from combining the words stratosphere and satellite) are high-altitude, unmanned airships designed to operate continuously for weeks, months, or even years at a time. Their main purpose is to hover over one geographical location and function as a relay and/or transmission source for radio signals, including as broadband, mobile phone, and digital television transmissions. The idea is currently being developed by the company Sanswire and others. A stratellite would hover about 20 kilometers up, above the jet stream and most weather, and could service an area about 320 kilometers in diameter, or about 480,000 square kilometers. Lag times would be many times less than that for orbiting satellites carrying the same type of signals, but would cover a larger area than traditional transmission towers.

Abstract-

An adaptive decisioxi feedback equalizer to detect digital information transmitted by pulse-amplitude modulation (PAM) through a noisy dispersion linear channel is described, and its performance through several channels is evaluated by means of analysis, computer simulation, and hardware simulation. For the channels considered, the performance of both the fixed and the adaptive decision feedback equalizers are found to be notably better than that obtained with a similar linear equalizer. The fixed equalizer, which may be used when the channel characteristics are known, exhibits performance which is close to that of the optimum, but impractical, Bayesian receiver and is considerably superior to that of the linear equalizer. The adaptive decision feedback equalizer, which is used when the channel impulse response is unknown or time varying, has a better transient and steady-state performance than the adaptive linear equalizer. The sensitivity of the receiver structure to adjustment and quantization errors is not pronounced.

ABSTRACT:

This paper presents a theoretical analysis of the performance of an orthogonal multiplexing data transmission scheme (parallel transmission scheme) subject to a number of degrading factors normally encountered by a practical operating system. The factors considered jointly are sampling time error, carrier phase offset, and non ideal phase characteristics of transmitting and receiving filters. Performance is measured by the familiar criterion of eye opening of the received data signal. A closed-form expression for the eye opening is obtained. It is shown that the lengthy nonlinear functions in the solution can be closely approximated by
simple piecewise linear functions for parameter values of interest. The optimum settings of the sampling time and the arrier phase are determined for given filter phase distortion. Also, considering all factors, simple formulas are developed for computing inter channel interference, intersymbol interference, and the resulting eye opening. Simple relationships between the eye opening and filter phase distortion are explored, and a concept of parametric is introduced to aid in filter design. An illustrative example is considered which shows that the impairment of the system performance is not excessive for a reasonable range of system design parameters.