16 QAM

16-QUADRATURE AMPLITUDE MODULATION(16 QAM):

  • Both amplitude and phase gets modulated.
  • 4 bits encoded forming and producing 16 different outputa are possible.
  • N = 4, M = 2N = 24 = 16
  • Therefore 16 output phases will be produced.

16 QAM transmitter:

16 QAM

  • Each channel bit rate is fb/4.
  • The input bit is serially inputted and outputted simultanously as I,I’,Q,Q’ which are parallel to each other.
  • I,Q determines the parity whereas I’,Q’ determines the magnitude (logic= 0.821V, logic 0= 0.22V).
  • Two polarities and magnitudes are possible at 2 to 4 level convertor(±0.821 , ±0.22V).
  • The output of I-product modulator, ±0.821 sin wct, ±0.22 sin wc
  • The output of Q-product modulator, ±0.821 sin wct, ±0.22 sin wc
  • The linear summer produces 16 output conditions.

Algorithm:

  • I and Q represent the polarity.
  • Logic 1 = +ve
  • Logic 0 = -ve
  • I’ and Q’ represent the magnitude.
  • Logic 1 = 0.821V
  • Logic 0 = 0.22V
  I    I’ output
 0 0 -0.22V
0 1 -0.821V
1 0 +0.22V
1 1 +0.821V
  Q    Q’ output
 0 0 -0.22V
0 1 -0.821V
1 0 +0.22V
1 1 +0.821V

Truth table:

    I     I’     Q       Q’  
0 0 0 0 -0.22 sin wct – 0.22 cos wct
0 0 0 1 -0.22 sin wct – 0.821 cos wct
0 0 1 0 -0.22 sin wct + 0.22 cos wct
0 0 1 1 -0.22 sin wct + 0.821 cos wct
0 1 0 0 -0.821 sin wct – 0.22 cos wct
0 1 0 1 -0.821 sin wct – 0.821 cos wct
0 1 1 0 -0.821 sin wct + 0.22 cos wct
0 1 1 1 -0.821 sin wct + 0.821 cos wct
1 0 0 0 +0.22 sin wct – 0.22 cos wct
1 0 0 1 +0.22 sin wct – 0.821 cos wct
1 0 1 0 +0.22 sin wct + 0.22 cos wct
1 0 1 1 +0.22 sin wct + 0.821 cos wct
1 1 0 0 +0.821 sin wct – 0.22 cos wct
1 1 0 1 +0.821 sin wct – 0.821 cos wct
1 1 1 0 +0.821 sin wct + 0.22 cos wct
1 1 1 1 +0.821 sin wct + 0.821 cos wct
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