Calculate signal-to-noise ratio from signal and noise power values in dB and linear scales.
It depends on the application. For Wi-Fi: >40 dB is excellent, 25-40 dB is good, <15 dB is poor. For audio recording: >60 dB is professional quality. For digital TV: >25 dB for reliable reception.
Noise floor is the minimum signal level that can be detected above background noise. It's measured in dBm (decibels relative to 1 milliwatt). Lower noise floor means better sensitivity — a -90 dBm floor is better than -70 dBm.