In a wireless communication system, the link margin, measured in dB

DB

DB may refer to:In science and technology:*Decibel , a logarithmic unit of measurement in acoustics and electronics*Dubnium , a chemical element*DB connector, a size of D-subminiature electrical connector...

, is the difference between the receiver's sensitivity (i.e., the received power at which the receiver will stop working) and the actual received power. A 15 dB link margin means that the system could tolerate an additional 15 dB of attenuation between the transmitter and the receiver, and it would still just barely work.

It's typical to design a system with at least a few dB of link margin, to allow for attenuations that are not modeled elsewhere. For example, a satellite communications system operating in the tens of gigahertz might require additional link margin (vs. the link budget

Link budget

A link budget is the accounting of all of the gains and losses from the transmitter, through the medium to the receiver in a telecommunication system. It accounts for the attenuation of...

 assuming lossless propagation), in order to ensure that it still works with the extra losses due to rain fade

Rain fade

Rain fade refers primarily to the absorption of a microwave radio frequency signal by atmospheric rain, snow or ice, and losses are especially prevalent at frequencies above 11 GHz. It also refers to the degradation of a signal caused by the electromagnetic interference of the leading edge of a...

or other external factors.