Link Margin
Definition
Link margin is the excess of received signal quality over the minimum quality required to maintain the link at the target service level.
Key Points
- It measures how much reserve a link has above threshold.
- It absorbs fading, interference, and implementation loss.
- It is a core input to availability engineering.
- It is especially important in satellite and long-haul transport.
- It determines how much service degradation the link can tolerate.
Concept
Link margin is the safety buffer of the physical layer. A design with little margin may work in ideal conditions but fail when rain, interference, or pointing error arrives. Engineers therefore treat margin as the difference between a lab demonstration and a field-ready service.
Explainer
In satellite and wide-area transport, margin determines whether the service survives real-world variation. Weather, alignment drift, and interference all consume the reserve. If the margin is too thin, the service may oscillate between usable and unusable even though no hard fault is present.