Measurement of the tropospheric scintillation decorrelation scale-length at millimetre wave frequencies

Millimetre wave propagation for both terrestrial and satellite communications is highly dependent on the dynamic nature of the atmospheric boundary layer. Small-scale changes in temperature, pressure and humidity may result in the formation of turbulence. Turbulence can affect radiowave propagation by either scattering a small part of the signal´s energy outside of the incident beam or by focusing and defocusing energy within the beam. In the former case, this redirected energy may be used to provide communications on over-the-horizon paths (typically at frequencies up to 5 GHz), or may indeed result in interference with other systems. In the latter case, turbulence may result in rapid amplitude fluctuations in signal strength scintillation. Systems that employ power control algorithms may be adversely affected by the rapid fluctuation of a scintillation event. Therefore, as the characteristics of the channel will ultimately determine the data throughput, a technique to mitigate scintillation could prove to be very useful. One such mitigation technique that could be used is spatial diversity. To achieve the diversity advantage requires the spatial coherence of events. This paper therefore investigates the spatial coherency of scintillation to determine the suitability of small-scale spatial diversity as a mitigation technique