High temporal-resolution channel characteristics at 40 GHz from a 30 km slant path radiowave propagation experiment

Propagation at millimetric frequencies (30-300 GHz) is highly dependent on tropospheric phenomena such as rain, clouds, fog, water vapour and atmospheric gases, all of which combine to cause signal absorption, dispersion and scattering. The need to accurately characterise the signal propagation channel in both time and frequency is essential not only for cost effective system design, but also to minimise interference and optimise globally deployable mobile links. Although models exist to predict (e,g, MAPEL, ITU) the long term attenuating characteristics of the tropospheric channel due to clouds, rain, water vapour and atmospheric there is limited information regarding characteristics of the channel. For example, MAPEL may predict a 1% (~7 hours) monthly signal-outage in June at a signal to noise threshold of 15 dB. To optimise and evaluate key system elements such as AGC loops, mobile antenna tracking loops, adaptive data-rate schemes, etc., it is important to know if the predicted 7 hour outage is distributed. For example, does it occur in a few long (e.g. 1 hour) periods, or in small (<1 min) segments; how long before such an event occurs again ? To obtain high (<l s) temporal-resolution channel data, a slant path experiment was designed to represent a short range air-ground link. Although the complete trial data-set comprises 28 days of data, this paper only presents an analysis of a small sub-set in order to provide illustrative channel characteristics