Moreover, the in-band signal is distorted and can lead
to Bit Error Rate (BER) degradation, depending on the degree of nonlinearity [14].
Next we give an example of Quaternary Phase Shift Keying (QPSK), Offset QPSK (OQPSK), and
/4-Shifted Differential QPSK (/4-DPSK) modulation schemes.
The first transmit Power Spectral Density (PSD) plot in Fig. 2.11 compares the PA input and output
emissions for QPSK. The PA operating point used in these simulation results was intentionally
placed in the nonlinear region. The spectral regrowth phenomenon, as well as the significant signal
information present outside the main spectral lobe, are clearly visible.
The second transmit PSD plot in Fig. 2.12 compares the PA input and output emissions for OQPSK.
For the same PA nonlinear operating point, the spectral regrowth is slightly less than the previous plot.
The last transmit PSD plot compares the PA input and output emission for /4-QPSK. Similar
results to QPSK can be seen when comparing the PSD plot in Fig. 2.13 to the one presented earlier.
??“75
??“70
??“65
??“60
??“55
??“50
??“45
??“40
??“35
??“30
??“25
??“20
Magnitude (dB)
OQPSK NLA Output PSD
??“4 ??“3 ??“2 ??“1 0 1
Frequency (Hz)
2 3 4
PA
Input
PA
Output
FIGURE 2.
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