Second part of question takes account of fact that frequency bands are almost never exclusive; sharing almost always necessary; therefore must recognise possibility of interference:
is strength of interfering signal sufficiently below that of wanted signal?
does this situation occur within required coverage area?
does interference exist for acceptable period of time? (e.g. 0.1% for 99.9% availability).
is the distortion or error rate acceptably low?
Ultimate question – is sharing possible?
None of these questions can be answered without considering the propagation of the signals concerned (wanted and interfering).
