Statistical Analysis of the Level Crossings and Duration of Fades of the Signal from an Energy Density Mobile Radio Antenna

The study of signal fading appears to be very important to mobile radio systems. When a steady sine wave is sent out from a fixed station, the signal received by a mobile receiver in motion fluctuates, or, in radio jargon, fades. The received signal fluctuates more rapidly as both the frequency of the transmitted wave and the speed of the mobile radio increase. For a field received by a moving isotropic antenna, the maximum fading frequency /,,, as Ossanna 1 has pointed out, is f d = 27/X, where V is the speed of the mobile radio and X is the wavelength of the steady sine wave. For instance, at 836 MHz and a speed of 15 miles/hr, the signal fades at a rate of about 40 times every second and is a serious disturbance to the mobile radio communication. There have been many investigations of the fading problem. Aikens and Lacy" made a test using 450-MHz transmission to a mobile receiver 417 418 T H E BELL SYSTEM TECHNICAL J O U R N A L , FEBRUARY 1967 in an urban area. Bullington 3 investigated radio propagation variation at V H F and UHF. Young 4 pointed out that for the test samples of signal strength taken over a small area, the amplitude follows a Rayleigh distribution to a fair approximation. Also S. 0. Rice 5 pointed out that the fluctuations of a received radio signal have the same behavior as the envelope of a narrow-band Gaussian noise. Recently, Ossanna 1 measured the power spectra of a mobile radio fading signal. They all treated the signal as obtained from an isotropic antenna.