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:
- 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 |