How do you perform a communication link budget analysis?

Link budget balances transmitter power against losses to achieve required signal-to-noise ratio at receiver. Components: Transmitter EIRP = Pt + Gt - Lt (power, antenna gain, losses in dB); Free space loss = 20*log(4*pi*d/lambda) (huge for interplanetary); Atmospheric/rain attenuation; Receiver G/T = Gr - Ts (antenna gain to system noise temperature ratio); and Received Eb/No = EIRP - FSL - attenuation + G/T - k - R (where k is Boltzmann constant, R is data rate). Link closes when Eb/No exceeds requirement (depends on modulation, coding, BER). Margin accounts for pointing loss, implementation, and aging. Analysis cases: Nominal and worst-case (maximum range, minimum power, degraded pointing). Trade-offs: Increase power, larger antennas, reduce data rate, better coding. Design iterate until margin is positive with acceptable equipment sizing.