Time and space coherence of ionospheric channels in median latitude

The ionospheric time coherence has been studied for a long time. The space coherence has to be defined for new systems. This article describes the comparison of the propagation of two near ionospheric links in an experiment made with a coded transmitter and two receivers separated by only a few kilometers. The distance between the two half way points was always lower than 40 kilometers. Two transmission ranges were operated: one short and a median one. Studies have been made based on impulse responses and scattering functions of the ionospheric channel. A measurement procedure was used to quantize the correlation between these functions, and the correlation between the different modes. These correlations are given values by the computation of correlation coefficients. Two correlations classes were studied. First, the correlation between the different delay Doppler components of the scattering function were studied. Second we researched correlations between space frequency components of the different modes of propagation existing in a channel. The obtained results constitute a database that can be used in various system studies in which the space and time coherence is used. Instabilities of the channel, due to the environment and ionospheric disturbances, show the constraints that the environment imposes on systems. Results are used to analyse transmission methods using the spatial dimension to improve the reliability of telecommunications