4 ms·
Maybe I am doing the math wrong, but I think the plot "Minor Violations of the Laws of Physics" has the Shannon Limit 2x smaller that what it should be. Accordi
by giovannibonetti 12y ago
Maybe I am doing the math wrong, but I think the plot "Minor Violations of the Laws of Physics" has the Shannon Limit 2x smaller that what it should be.
According to [1], for each 2x increase in SNR, the limit should increase in a full Bandwith.
However, when we compare the plotted values at 45db and 60db, we see that SNR increased 15db = 5 * 3db => 2^5.
That way, the limit should increase in 5 bandwidths.
But the plot increased from 300Mbps to 400Mbps => 100Mbps.
Hence the plot was made with a bandwith of 100/5 = 20Mhz, instead of the 40Mhz mentioned.
[1] http://en.wikipedia.org/wiki/Shannon%E2%80%93Hartley_theorem#Statement_of_the_theorem http://en.wikipedia.org/wiki/Shannon%E2%80%93Hartley_theorem...
- apenwarr 12y agoI'll be honest, I find this math very confusing (as I am self taught using flakey internet resources similar to the one we're discussing :)). But my understanding is that there is a 2x factor somewhere that affects Shannon limit calculations. I think it might relate to the "negative frequency" mirrored half of the fourier transform at baseband. Or maybe I'm just doing the math wrong. In any case, the underlying concept is correct: a 2x2 or 3x3 MIMO radio can exceed the Shannon limit calculated for a single channel.