Showing papers on "Channel state information published in 1968"

A Survey of Microwave Fading Mechanisms Remedies and Applications

Abstract: After a brief description of the significance of the radio refractive index and its variation in the lower troposphere, a catalog of fading mechanisms is presented. Attention is directed to the supporting refractive index structure, the characteristics of the fading signal, and the available remedies. The phenomena of multipath fading are described, and the theoretical amplitude distributions are presented. Diversity reception (frequency or space) is outlined for reducing the fading due to multipath. Specific expressions are given for determining the frequency or space separations. Successful remedies for microwave fading that are keyed to specific fading mechanisms also constitute a means of measuring the characteristics of the prevailing meteorological conditions. Specific expressions are given to accomplish this for the multipath and diffraction fading mechanisms.

Space DIversity on Line-of-Sight Microwave Systems

Abstract: Deep fading on line-of-sight microwave paths is usually a result of multipath interference phenomena. Frequency diversity has been the most common method of protecting against such fading. In the past few years, vertical space diversity has also come into use. This paper discusses its characteristics, methods of determining spacings, and describes some results achieved. It is concluded that vertical space diversity provides a very effective tool for combating multipath fading on line-of-sight paths, regardless of the source of the fading.

Performance of Analog Demodulators in a Fading Environment

Abstract: Various structures have recently been obtained for optimally demodulating analog signals transmitted over a noisy, randomly fading channel. Their performance, in a least mean-signal error sense, is evaluated in this paper. In the case of the optimum linear filter for AM (or equivalent baseband) signals, as the carrier-to-noise ratio increases indefinitely, an irreducible error is found. The Cramer-Rao (lower) bound on the error is found and indicates, however, that the fading error can be reduced to zero by use of a nonlinear receiver. An analysis of the maximum a posteriori receiver, utilizing estimates of the channel fading characteristics, does in fact indicate that for this nonlinear receiver, the fading error can be made to approach zero. Similar considerations are found to apply in the case of PM signals.

A Performance Monitoring Scheme for FSK Transmission over Fading Channels

Abstract: A scheme for monitoring performance of a frequency-shift-keyed (FSK) transmission over a selectively fading channel with a nonfading component is treated. The design of the monitoring scheme is based heavily on the assumption that the received signal and additive noise are Gaussian. The monitoring requires no special test signal. An asymptotically unbiased estimate of error probability is obtained in terms of four measurements of the received signal. The measurement time required for a reliable estimate of error probability is determined.

On the Error Probablity of Binary Signals Passed Through the Rican Fading Channel

Abstract: The expression for the error probability of reception of binary signals in a Rician channel has been stated. In general, the expression is difficult to compute. That is why only two opposite cases were computed (no fluctuations in any branches, and the case when the specular component was absent). This paper considers the case of dependent and nondependent fluctuations, and an exact estimation of the channel parameters is presumed. Also fluctuations of energy in the specular branches are taken into account.

Adaptive receiver techniques for digital communication through selective fading channels.

Abstract: Sunde model of troposcatter channel as transmission medium in computer simulation of adaptive digital communication scheme for selective fading channels