Fade Margin
The additional signal power, expressed in decibels, built into a link budget above the minimum demodulation threshold to maintain service during adverse propagation conditions.
Full Definition
Fade margin (also called link margin) is the decibel difference between the actual received signal level under nominal conditions and the minimum signal level required for reliable demodulation (the demodulator threshold or minimum Eb/N0). A positive fade margin indicates that the system has headroom to absorb rain fade, atmospheric losses, pointing errors, and component ageing before service is degraded. In satellite system design, fade margins are selected to meet a specified availability (for example, 99.9% of the year). Editors should note that 'fade margin' is two words and is not hyphenated as a noun; it is hyphenated only when used as a compound modifier ('a 6 dB fade-margin requirement').
Usage
Usage note: Two words as a noun; hyphenate only in attributive use ('fade-margin calculation'). 'Link margin' is an acceptable synonym but distinguish from 'power margin', which may refer to the satellite's onboard power budget rather than RF link performance.
In Context
- "A fade margin of 8 dB was specified to guarantee 99.95% annual availability at the Ka-band gateway." — System requirements document
- "The fade-margin values in Annex B are inconsistent with those in Section 5; reconcile before publication." — Review comment