How does TAP™ estimate microwave link reliability based on computed fade margin?

The reliability of a system based on the computed fade margin is calculated based on the following equation (from Lenkurt)

Undp = a x b x 2.5 x 10-6 x f x D3 x 10-F/10

where:

  • Undp is the non-diversity outage probability.
  • a is the terrain factor.
  • b is the climate factor.
  • f is the frequency in GHz.
  • D is the path length in miles.
  • F is the fade margin in dB.

For systems which include a space antenna, a fade margin is computed for each receive antenna (primary and diversity). The values will be different if the two receive systems have different antenna gains, transmission line lengths, or other losses. The higher value fade margin (“best case”) is used for this non- outage calculation. The other fade margin value is used to compute the diversity as described below.

The percent reliability is computed from the outage probability by:

%R = 100 x (1 - Undp)

Reference:

Engineering Considerations for Microwave Communications Systems, 1975, GTE Lenkurt Incorporated.