Reed's Talk. Reed is the radical mad scientist of open spectrum, who maintains that spectrum is not scarce, except due to a policy framework that is obsolete in the current technological reality. He's the appropriate opening keynoter for this conference.
Does spectrum have a "capacity?" This is the key question. If spectrum is limited, then there's a reason for apportioning it carefully. If it doesn't, then making spectrum scarce is scary First Amendment country.
The radio tradition developed from 1900-1950. In the beginning, all radios received all frequencies. Resonant systems allowed users to divide spectrum for different apps. Different frequencies had different properties -- low-frequency would go around the world, high frequency would bounce off the ionosphere. Increasing power lets you go farther.
Shannon invented information theory in the 50s, and invented the bit -- a measurement of info regardless of the form it takes.
C = W log (1+(P/N0W)), where C = Capacity in bits/sec; W = bandwidth in Hz, P = power in Watts and N0 = Noise power in Watts/Hz.
Channel capacity is roughly porportional to bandwidth and log of power. Capacity is analogous to bandwidth, but bandwidth is not the same as capacity.
This is only part of the story, though. The original theorem is a simple model consisting of a sender, a receiver and noise, with no consideration of geography and other transmitters (we treat other transmitters as noise).
Interference: this is the other key question. If interference exists, we need strong regulation to limit it. Read the rest