Near Vertical Incidence Skywave field strength time variability characterization in the Medium Wave band

Emerging radio broadcasting digital systems in the Medium Wave (MW) band require accurate field strength prediction models for network planning. Near Vertical Incidence Sky-wave (NVIS) propagation provides wide coverage areas with only one transmitter but extremely high time variability. This time variability is statistically characterized for the first time in this paper, by means of the Maximum Likelihood Estimator that has been applied to data recorded during an extensive measurement campaign in static reception. The difference between the median value and the 1%-of-the-time lowest value has also been calculated. Statistics show a Log Normal behavior and that almost 10 dB should be added to the predicted median value in order to ensure the coverage during 99% of the time.