# Shannon Theorem

Joined Nov 24, 2013
38
Please tell me difference between M-QAM and M-PSK. And also tell about Shannon Theorem.
Thanks

#### nsaspook

Joined Aug 27, 2009
13,543

#### Veracohr

Joined Jan 3, 2011
772
Please tell me difference between M-QAM and M-PSK.

Joined Nov 24, 2013
38
QAM stands for Qudrature Amplitude Modulation and PSK Stands for Phase Shift Modulation. M is number li 2,4,8,16,32,64...............

#### nsaspook

Joined Aug 27, 2009
13,543
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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#### Veracohr

Joined Jan 3, 2011
772
QAM stands for Qudrature Amplitude Modulation and PSK Stands for Phase Shift Modulation. M is number li 2,4,8,16,32,64...............