[Gibbon1]

Any receiver design, bandwidth and modulation technology will have an ultimate sensitivity. Far as I understand this is due to both noise created by the circuit itself and the thermal noise over the band.

You can't get better than that.

Then you add interference which raises your noise floor both statically and dynamically. Unlicensed bands tend to be polluted with short coherent pulses of RF.

One issue with interference. While attenuation is symmetrical between two transceivers, interference is utterly not symmetric.