mohatta2015.pdf

10 INTRODUCTION
phases (phase modulation) and/or different amplitudes (amplitude modulation).
For good receiver performance, we would like these symbol values to be as different
from one another as possible for a given average symbol power. Note that with
M possible symbol values, we can transmit log 2 (M) bits (e.g., 3 bits have M = 8
possible combinations)
Modulation is typically Gray-mapped Quadrature Amplitude Modulation (QAM),
such as Quadrature Phase Shift Keying (QPSK) (illustrated in Fig. 1.7) and 16-
QAM (illustrated in Fig. 1.9). These can be viewed as Binary Phase Shift Keying
(BPSK) and 4-ary Amplitude Shift Keying (4-ASK) on the in-phase (I) and
quadrature (Q) axes. The 4-ASK constellation, illustrated in Fig. 1.10, conveys
two modem bits: a most significant bit (MSB) and a least significant bit (LSB).
The MSB has better distance properties, giving it a lower error rate than the LSB.
Figure 1.9
Ki-QAM.
As for pulse shaping, root-Nyquist pulse shapes are typically used, which have
the property that their sampled autocorrelation function is given by
/
oc
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p(t + mT)p*{t) dt =