Features – Evaluate Multipath
To estimate the probability of multipath fading, the frequency, path length, climatic and environmental conditions are used to calculate the Multipath Occurrence Factor and equipment data, and diversity configuration are then used to calculate the prediction for each terminal.
Multipath Occurrence Factor may be calculated from three propagation models: the Barnett-Vigants model (from Bell Labs publications, then generalised in ITU-R Rep. 338-5) and two ITU-R models (Rec. P.530-7, 1997, and Rec. P.530-12, 2007). The most recent ITU-R model reads refractivity data (Rec. P.453) from the ITU-R database file, and is installed with the program.
Once the Multipath Occurrence Factor is known, the time percentages corresponding to given multipath fading levels are computed. The results are shown on a diagram, dealing with single and diversity reception (if configured). From those diagrams, the multipath outage prediction for narrow-band signals can be derived, on the basis of the flat fade margin available at each terminal site.
If wide-band signals are transmitted, the ITU-R (Rec.530) model is used, by applying the signature data, typical of the installed radio equipment and recorded in the Equipment database. Alternatively, the Dispersive Fade Margin model can be used. If signature data and Dispersive Fade Margin are not available, only the narrow-band multipath model can be used). It is important to enter DFM and Signature data if available into the equipment database as this information is representative of the performance and ability of the radio to equalize the distorted signal. More expensive radios tend to have better performance due to enhanced electronics to deal with distortion.
In drawing the Outage diagram, options are available to compare the outage time with/without multipath selectivity, diversity, and interference (when applicable).