What is link margin?

Link margin represents the safety buffer or 'cushion' in a radio link. Once you calculate your link budget to find the expected received power, you compare it to the absolute minimum signal level the receiver needs to successfully decipher the data (its sensitivity). The difference between the power you actually receive and the bare minimum required by the receiver is the link margin. For example, if your receiver requires -100 dBm to work, and your received signal is -90 dBm, you have a link margin of 10 dB. Options that simply subtract receiver sensitivity from transmit power are incorrect because they completely ignore all path losses and antenna gains that happen between the two radios.