Page 75 - Complete Wireless Design

Modulation

74 Chapter Two

TABLE 2.2 Maximum Bits/Symbol for
Common Modulation Schemes
Modulation Bits/symbol

MSK 1
BPSK 1
QPSK 2
QAM-16 4
QAM-32 5
QAM-64 6
QAM-256 8

TABLE 2.3 SNR for Various Modulation Formats
Signal-to-noise ratio, dB
BER QPSK QAM-16 QAM-32 QAM-64 QAM-128 QAM-256

10 4 8 13 15 17 19 21.5
5
10 10 14 16 18 20.5 23
10 5 11 15 17 19 21.5 24
7
10 12 15.75 18 20 22.5 25
10 8 12.5 16.25 18.5 21 23.5 25.75
9
10 13 16.5 19 21.5 24 26.25
10 10 13.25 16.75 19.25 21.25 24.25 26.5

TABLE 2.4 Common Modulation Schemes and Their Properties

type Bits/symbol (h) States Amplitudes Phases
BPSK 1 2 1 2
QPSK 2 4 1 4
PSK-8 3 8 1 8
QAM-16 4 16 3 12
QAM-32 5 32 5 28
QAM-64 6 64 9 52

Adaptive equalization will correct certain signal impairments in real time,
such as group delay variations (GDV), amplitude tilt, ripple, and notches.
Adaptive equalization, however, will not improve impairments created by a
nonlinear amplifier, noise, or interference, but it will mitigate the sometimes
massive multipath effects that would normally render a digitally modulated
signal unreadable because of the high BER caused by the resultant amplitude
variations.
Adaptive equalization basically uses a dynamically varying adaptive filter
that corrects the received signal in amplitude, phase, and delay, making high-
density modulations possible. Virtually all terrestrial microwave communica-
tion systems employ some form of adaptive equalization, located right after
the receiver’s demodulator.

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