Link Budget - Received Power

Description

A link budget is accounting of all of the gains and losses from the transmitter, through the medium (free space, cable, waveguide, fiber, etc.) to the receiver in a telecommunication system. It accounts for the attenuation of the transmitted signal due to propagation, as well as the antenna gains, feedline and miscellaneous losses. Randomly varying channel gains such as fading are taken into account by adding some margin depending on the anticipated severity of its effects. The amount of margin required can be reduced by the use of mitigating techniques such as antenna diversity or frequency hopping.

A simple link budget equation looks like this:
Received Power (dBm) = Transmitted Power (dBm) + Gains (dB) − Losses (dB)

Note that decibels are logarithmic measurements, so adding decibels is equivalent to multiplying the actual numeric ratios.

A link budget equation including all these effects, expressed logarithmically, might look like shown here.

Related formulas

Variables

PRXreceived power (dBm) (dimensionless)
PTXtransmitter output powe (dBm) (dimensionless)
GTXtransmitter antenna gain (dB) (dimensionless)
LrTXtransmitter losses (coax, connectors...) (dB) (dimensionless)
LFSpath loss, usually free space loss (dB) (dimensionless)
LMmiscellaneous losses (fading margin, body loss, polarization mismatch, other losses...) (dB) (dimensionless)
GRXreceiver antenna gain (dBi) (dimensionless)
LRXreceiver losses (coax, connectors...) (dBi) (dimensionless)