Shannon Theorem

nsaspook

Joined Aug 27, 2009
13,544
Lets look at what QAM16 looks like using a Constellation diagram of the carrier when changing two properties of the wave.

Now PSK4 gray code changing one property of the carrier wave.


The channel capacity for different modulation types using the same bandwidth:

The 16 PSK and 16 QAM have different channel capacity slopes because QAM is slicing two properties instead of one.

The Shannon Information Theorem shows us the possible channel capacity in bits per modulation symbol increases as the SNr increases with a fixed bandwidth.

As we increase the number of possible carrier wave combinations per symbol the energy in each symbol slice of a wave property decreases in respect to the total energy of the carrier wave bandwidth so each individual slice must have a energy level sufficiently above the noise level for it to be detected as a discrete symbol from any other symbol of that wave property.

A great man:
http://en.wikipedia.org/wiki/Claude_Elwood_Shannon
 
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