5)Ts b(n 2)p(t (n 1.5)Ts)
I(t) a(n)p(t nTs) a(n 1)p(t (n 1)Ts)
MODULATION THEORY 95
IJF-OQPSK IJF-QPSK Q
I
Q
I
FIGURE 2.77 IJF constellation diagram comparisons.
The IJF criteria discussed above can best be explained with the pictorial description in Fig. 2.78.
Next, an improved concept called FQPSK-KF was applied [43]. The previous approach was used
as a stepping stone to the following FQPSK-KF modulation scheme. Here the artificial crosscorrelation
property is inserted into the FQPSK-1 modulation scheme. A simplified block diagram
for this waveform generation is shown in Fig. 2.79.
FIGURE 2.78 Description of the IJF filter.
Zero
ISI
Zero
Jitter
The basic idea behind the cross-correlator block is to produce some desirable behavior of reducing
envelope variations. For example, let??™s consider
??? When the I- (or Q-) channel is zero, then the Q- (or I-) channel is at 1.
??? When the I (or Q) channel is nonzero, the Q- (or I-) channel is reduced to A, where the constraint
applies.
Let??™s now describe the cross-correlation used in [43] next. The output of the IJF filter will be controlled
by four transitions plus the two sinusoidal waveforms. Choice of the combinations depends on
the present symbol and the preceding symbols.
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