Fade and Interfade Duration Characteristics in a Slant-Path Ka-Band Link

Satellite-to-earth links are subject to several propagation effects in the troposphere, being rain attenuation the impairment that can cause the deepest fades. In this paper, the duration of both fades and the intervals between consecutive fades (interfade intervals) are characterized on the basis of the results of a long-term slant-path Ka-band propagation experiment carried out in Madrid, Spain. The experimental and statistical results included in this paper correspond to seven complete years of measurements, a period large enough to characterize not only the average-year statistics of fade dynamics but also their variability, which is assessed on the basis of annual statistics of durations. The obtained average-year statistics of fade durations are in many cases close to the predictions made by the International Telecommunication Union-Radiocommunications and Communications Research Center Canada models, although the predictions could be improved with a better selection of the parameters of the distributions used in the models. Interfade duration statistics are also presented and related to recent modeling efforts. The interannual variability of statistics, such as the relative number of fades, is quantified and found to be low, except for the higher attenuation thresholds or the highest durations considered in this paper.

I. Introduction

Satellite communication systems are increasingly using the Ka-band (30/20 GHz) to deliver broadband services through very small aperture terminal networks, using either traditional fixed satellite service or innovative high throughput satellite [1] configurations. Despite the attractiveness of using the Ka-band, the limitation caused by atmospheric impairments observed at these frequencies is well known, in particular those caused by precipitation. In order to counteract these propagation effects, Ka-band satellite systems make use of fade mitigation techniques that can improve their performance. Such techniques consist in adapting in real time some parameters of the satellite link, such as transmission power, modulation and coding, among others. Thus, the control loop must adapt itself to the dynamic behavior of the propagation channel. With the purpose of implementing these techniques, the characterization of the variability of fade dynamics is more important than in the past. For example, identifying the fade duration parameters that are more prone to suffer higher interannual variability could help to better design fade mitigation techniques, minimizing the effects of outages and improving their capacity of adaptation to different conditions.