We know that the signal attenuates out with distance and according to the channel transfer function or frequency response, the signal frequency components attenuate to different values based on frequency.
The effect of distance is widely acknowledged & used in practice as a path-loss model which is exponentially decreasing in distance but frequency component is relatively less discussed.
It is very embarrassing to find that the everyday used wireless channel's transfer function is not known to most of us!
I searched all over the web with all naive keywords but it seems the spectrum of the channel transfer function is not there anywhere not even in many text books!
On the similar lines, what is the typical conclusion about the spectrum? are high frequencies better for some reason, so that we always modulate to higher frequencies or it is just that we have available bands there?
After a fundamental clarification by user5108_Dan, It seems to be widely acknowledged that very-high-frequency communication is highly-challenging (I am not sure if is it just the dsp/hardware challenge!). See for eg, http://en.wikipedia.org/wiki/Extremely_high_frequency
I am thinking that the channel transfer function if exists, becomes crucial to know before we decide our band of transmission and transmit power.
OR, Is this freq. response completely application specific that it includes antenna characteristics and other hardware in the chain? Even in that case, it appears to me that it helps the designer in choosing the right hardware. is n't it?