How do you calculate a wireless link budget?

A link budget calculates the received signal power considering all gains and losses: Prx = Ptx + Gtx - Ltx - FSPL - Lmisc + Grx - Lrx, where Ptx is transmit power (dBm), Gtx/Grx are antenna gains (dBi), Ltx/Lrx are cable/connector losses (dB), FSPL is free space path loss, and Lmisc includes fading margins, body loss, and environmental factors. The link margin = Prx - Sensitivity. For reliable communication, the margin should be 10-20 dB to account for fading. Example: 20 dBm Tx + 3 dBi Tx antenna - 2 dB cable loss - 100 dB FSPL + 6 dBi Rx antenna - 1 dB Rx loss = -74 dBm received power.