“Availability of the wireless link is the long-term average time when the link performs its intended function”.
In our context:
Availability is usually expressed as a percentage and defines the time a system, link or terminal is meeting its operational requirements, i.e. data is being transmitted through the link at a projected Capacity.
Unavailability is described as “a state of nonservice that occurs due to failure caused by signal drops or other outage”. Signal drops are a result of fading, multipath propagation, precipitation attenuation and other atmospheric issues. Together with noise issues this results in degraded BER (Bit Error Rate).
Classification of Availability issues:
Link: Outage or lower Capacity due to signal drops
Equipment: Hardware failures and Repair Time (expressed by MTBF + MTTR)
External threats: Human error, superior power, noise from other sources, etc.
These can’t be calculated in advance and thus Availability calculations do not consider them