The decision you should be able to make
Select a reliability strategy based on modelled mechanisms rather than a folklore margin number.
Core engineering
Fade margin is the difference between nominal received level and the threshold for a stated performance mode. Availability prediction also needs path length, frequency, terrain, climate, antenna heights, multipath and rain mechanisms where applicable.
Annual and worst-month statistics are not interchangeable. Define the percentage, observation period and event that counts as unavailable.
Equipment failure, power loss and backhaul failure need separate availability budgets; extra RF margin does not repair them.
Equipment and field checks
- Use a current propagation implementation and retain its input file or report.
- Consider adaptive modulation: availability at a low-rate mode can differ from availability at committed capacity.
- Use diversity, route change, higher mounts or a lower service target when the model shows margin alone is inefficient.
Do not progress until
Predicted availability is attached to a defined mode, traffic requirement, time statistic and propagation method.
Limits and cautions
- A round-number fade-margin target may be useful for early screening but is not an availability calculation.
Primary sources
Sources were checked for this technical review. Recheck regulator and equipment requirements at the point of design or installation.