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Showing papers on "Fading distribution published in 1971"


Journal ArticleDOI
M. Gans1
TL;DR: In a fading channel, maximal ratio diversity combilling improves the average signal-to-noise ratio over that of a single branch in proportion to the number of diversity branches combined, however, its main advantage is the reduction of the probability of deep fades.
Abstract: In a fading channel, maximal ratio diversity combilling improves the average signal-to-noise ratio over thatof a single branch in proportion to the number of diversity branches combined. However, its main advantage is the reduction of the probability of deep fades. The effect of Gaussian errors in the combiner weighting factors on the probability distribution of the output signal-to-noise ratio is computed. The limits on allowable error for a specified probability of fades below any given level are indicated. The results are applied to a mobile radio example in which the weighting factor is determined from a pilot transmitted along with the signal. To keep the pilot from overlapping the signal, they are separated either in frequency or in time. In this case the Gaussian error is due to decorrelation of the pilot from the signal either because their frequency separation or their time separation is too large.

252 citations


Patent
W Lee1
02 Dec 1971
TL;DR: In this article, a nondiversity radio system provides compensation for multipath fading by means of continuous amplitude feedback, which is especially well suited for mobile radio telephone applications since fading can be eliminated at a relatively simple, single branch mobile station.
Abstract: A nondiversity radio system provides compensation for multipath fading by means of continuous amplitude feedback. Intelligence is transmitted from one station by means of frequency modulation, while amplitude modulation is caused by the fading en route. At the other station the received amplitude envelope is fed back as part of a frequency modulated, return intelligence signal. The feedback envelope is used at the first station to amplitude modulate the subsequent transmission to precompensate for the anticipated fade and produce fade-free reception at the other station. The system is especially well suited for mobile radio telephone applications since fading can be eliminated at a relatively simple, single branch mobile station.

33 citations


Journal ArticleDOI
TL;DR: In this article, the response of an FM discriminator to a fading signal is derived, taking into account the below-threshold noise and the effect of various diversity techniques, including maximal-ratio combining, selection diversity, and equal gain combining.
Abstract: The response of an FM discriminator to a fading signal is derived, taking into account the below-threshold noise and the effect of various diversity techniques. The effect of muting the discriminator output at low signal levels is considered and shown to achieve only marginal improvement. The diversity techniques considered are maximal-ratio combining, selection diversity, and equalgain combining. Only predetection combining is considered for the maximal-ratio and equal-gain techniques. The average SNR at the discriminator output is derived for each form of diversity, assuming that each diversity branch is independent of the others and subject to fading with a Rayleigh envelope distribution. Curves of average SNR plotted against the mean CNR in one branch are presented for various numbers of diversity branches and ratios of IF bandwidth and baseband bandwidth. The curves presented are for maximal-ratio combining only, but it is shown that the results for selection diversity and equal-gain combining may be obtained from these curves by simply applying a correction to the mean CNR. The theoretical results are supported by experimental measurements that show very close agreement with theory.

28 citations


Journal ArticleDOI
TL;DR: It is shown here that the use of diversity in a mobile radio system also will result in better utilization of the frequency spectrum, and that a diversity system utilizes the frequency Spectrum more efficiently than an equivalent nondiversity system.
Abstract: Diversity is often used in radio systems to alleviate the problem of fading. It is shown here that the use of diversity in a mobile radio system also will result in better utilization of the frequency spectrum. In a system which reuses channels in physically separated areas, probability distributions of signal-to-cochannel interference ratios in 1-, 2-, and 4-branch diversity systems are developed by Monte Carlo methods. We consider two cases: first, we assume signal strength to be Rayleigh distributed, which is a valid model for reception within a small localized area; second, we take shadow losses into account by assuming a more realistic long-term fading model. The effect of using diversity in a mobile radio system is considerable with either model. Assuming a hexagonal cell pattern of frequency reuse, it is shown that frequencies may be reassigned more often in a diversity system than in a system which does not use diversity. The conclusion, therefore, is that a diversity system utilizes the frequency spectrum more efficiently than an equivalent nondiversity system.

10 citations


Journal ArticleDOI
TL;DR: In this article, the probability of error of a wide-band FSK receiver when multipath reflections off the planetary surface cause signal fading was investigated for both low and high fading bandwidths and for small or large reflected path delays.
Abstract: Calculations are made for the probability of error of a wide-band FSK receiver of the type used in space telemetry when multipath reflections off the planetary surface cause signal fading. The error probability is found for both low and high fading bandwidths and for small or large reflected path delays.

10 citations