In a wireless communication system, the link margin (LKM) is a critical parameter that measures the reliability and robustness of the communication link. It is expressed in decibels (dB) and represents the difference between the minimum expected power received at the receiver's end and the receiver's sensitivity. The receiver's sensitivity is the minimum received power level at which the receiver can correctly decode the signal and function properly.

Link Margin (LKM)

Definition

Link Margin (LKM)=Preceived​−Psensitivity Where It is typical to design a system with at least a few dB of link margin, to allow for attenuation that is not modeled elsewhere. For example, a satellite communications system operating in the tens of gigahertz might require additional link margin (vs. the link budget assuming lossless propagation), in order to ensure that it still works with the extra losses due to rain fade or other external factors. A system with a negative link margin cannot transfer data, so one or more of the following are needed: more transmitter power; more antenna gain at the receiver or transmitter; less propagation loss (e.g., better antenna locations and/or shorter paths); lower receiver noise figure; improved error correction coding (FEC); reduced interference; or a lower data rate.

Importance of Link Margin