Digital Signal Processing Reference
In-Depth Information
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Fig. 6.25
QPSK waveform for binary data 10110001
T
B
Decision
Device
∫
0
Parallel to
Serial
Converter
ϕ
QPSK
(
t
)
Threshold
A
c
cos
ω
c
t
d
(
t
)
π
2
T
B
−
A
c
sinω
c
t
Decision
Device
∫
0
Fig. 6.26
QPSK coherent demodulator
6.6.4 Offset QPSK (OQPSK)
Offset QPSK modulation [
7
] is a specially designed QPSK to avoid out-of-band
interference. The difference between QPSK and OQPSK is only in the
alignment
of the two baseband signals. As shown in Fig.
6.27
, the duration of each original
pulse is T. Hence, when we consider di-bit (in the partitioned space), the duration
of each pulse becomes 2T. In standard QPSK, the odd and even pulse stream are
both transmitted at a rate of 1/2T bit/s and are synchronously aligned, such that their
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