2.33, using an SRC with a roll-off factor 0.3.
The OQPSK eye diagram at the output of the SRC filter with a roll-off factor 0.3 is provided
in Fig. 2.34. It is a great opportunity to briefly discuss the OQPSK eye diagram using this SRC filter.
The RC filter has been slit up into two SRC filters, one at the transmitter and the other at the receiver.
The signal at the output of the receiver SRC is ISI free; however, the transmitter SRC filter output signal
contains ISI. It is this ISI that is present in the OQPSK eye diagram.
The receiver block diagram for OQPSK is very similar to that presented earlier for QPSK, with
the exception that the signals entering the decision devices must be delayed according to the time offsets
OQPSK NLA Output Constellation
??“2
??“1.5
??“1
??“0.5
0
0.5
1
1.5
2
??“2 ??“1.5 ??“1 ??“0.5 0 0.5 1 1.5 2
I-Channel
Q-Channel
FIGURE 2.33 OQPSK signal constellation at the output of a nonlinear PA.
72 CHAPTER TWO
OQPSK Eye Diagram
??“2
??“1.5
??“1
??“0.5
0
0.5
1
1.5
2
0 8 12 16
Normalized Symbol Time (Ts/8)
Eye Value
4
FIGURE 2.35 OQPSK receiver block diagram.
inserted in the transmitter. In the OQPSK modulator shown in Fig. 2.30, we inserted a bit time delay
into the Q-channel.
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