2.98. This signal is sometimes called
the square QAM constellation. The dashed lines were inserted to represent the decision boundaries.
I-Channel
Q-Channel
n is the noise
immunity
vector. n
FIGURE 2.98 Unfiltered 16-QAM constellation block diagram.
Next the BER performance results for M-ary QAM is presented in Fig. 2.99, with modulation levels
of M 4, 16, 32, and 64.
Next we assume the transmit filters used an RC filter with 0.3 and plot the signal constellation
in Fig. 2.100. The diagram clearly shows the transmit waveform is a nonconstant envelope signal.
108 CHAPTER TWO
Coherent Detection of M-ary QAM
0 2 4 6 8 10 12 14 16 18 20
Eb/No (dB)
Pb(4-QAM)
Pb(16-QAM)
Pb(32-QAM)
Pb(64-QAM)
1.0E??’5
1.0E??’4
1.0E??’3
1.0E??’2
1.0E??’1
1.0E+0
Probability of Bit Error (Pb)
FIGURE 2.99 BER curves for QAM modulation signals.
16-QAM Constellaion Diagram
??“8
??“6
??“4
??“2
0
2
4
6
8
??“8 ??“6 ??“4 ??“2 0 2 4 6 8
I-Channel
Q-Channel
FIGURE 2.100 16-QAM signal constellation diagram using RC with 0.3.
The eye diagram of the corresponding signal constellation is given in Fig. 2.101. Since an RC
filter was used, there is no ISI present in the signal. The 16-QAM modulation has 4 levels on the
I-Channel and 4 levels on the Q-Channel, as visible.
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