18 Phase imbalance model for the quadrature modulator.
MODULATION THEORY 63
BPSK
QPSK
DQPSK O-QPSK
??/4-DQPSK MSK
FQPSK
FSK
GMSK
16-PSK 16-QAM VR-PSK
Advanced Modulation Schemes
??/4-FQPSK
M-ary FSK
64-QAM
FIGURE 2.19 Modulation scheme migration path.
Returning to the available options, one can choose the OQPSK path where the immediate attention
is focused on lowering spectral regrowth. This path can continue with FQPSK, which further
modifies the phase trajectories to have a behavior closer to our desired case.
FSK is clearly a modulation choice, and we have decided to insert this next to OQPSK since MSK can
be viewed as an extension of OQPSK. In order to focus on transmit emissions, GMSK is also included.
When spectral efficiency is not an immediate concern, M-ary FSK modulation can surely be used.
All of these modulation schemes eventually encounter the advanced modulation scheme block containing
16-QAM, 64-QAM, and Variable Rate??“PSK (see Fig. 2.19). In classical wireline communications,
these modulation schemes are in no way viewed as advanced. However, in the wireless medium,
higher-order modulation schemes impose many interesting and technically difficult hurdles [22].
2.2.1 Binary Phase Shift Keying (BPSK)
In this section, we will present the BPSK modulation scheme.
Pages:
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128