Noise-immune reception regions for selective excitation of characteristic waves in an ionospheric communication link are investigated. It is shown that for ionospheric paths to 16 $Z_m$. long, the area of noise-immune reception is about $S\sim\:$50 Z$_m^2$ (at the ionospheric layer half-depth $Z_m=\:$100 km, $S\sim\:$500,000 sq. km). The area $S$ for different azimuthal angles and different radio path lengths is evaluated. It is shown that vertical wave incidence creates especially favorable conditions for implementing regional ionospheric radio communication networks with single-path propagation of radio waves and, consequently, highly reliable data transmission.
Department of Radiophysics, Faculty of Physics, Moscow State University, Leninskie Gory, Moscow, 119992, Russia