oqpsk
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Digital Modulation schemes
OQPSK Offset Quadrature Phase-shift keying
Shahid Beheshti Univ. of Tehran
Faculty of electrical and computer engineering
Department of Electrical Engineering
Instructor: M. Naslcheraghi
Assistant Professor: Dr. Sadough
October 2014
Contents
1. Drawback of QPSK Modulation
2. OQPSK Modulation
Digital Modulation Schemes (OQPSK) 1 / 7
Drawback of QPSK Modulation
Transmitting binary sequence
11000111
11 , 00 , 01 , 11
Digital Modulation Schemes (OQPSK) 2 / 7
split
in-phase (I) component
of the signal
the quadrature (Q)
component of the signal
Signal Duration = 2Tb
Drawback of QPSK Modulation
Digital Modulation Schemes (OQPSK) 3 / 7
In-phase components for QPSKquadrature components for QPSK
11 , 00 , 01 , 11
1 , 0 , 0 , 11 , 0 , 1 , 1
Note that changes can occur only at
even multiples of Tb
both I and Q components
change simultaneouslyresulting in a
change of 180◦in the phase !
Drawback of QPSK Modulation (Application)
180◦ phase changes cause abrupt changes in the signal,
resulting in large spectral side lobes.
Digital Modulation Schemes (OQPSK) 4 / 7
In high amplifiers and for certain satellite applications,
OQPSK offers better performance
Solution (QPSK modified to became OQPSK)
Digital Modulation Schemes (OQPSK) 5 / 7
misaligned by Tb
The OQPSK signal can be written as:
Solution (QPSK modified to became OQPSK)
Company nameDigital Modulation Schemes (OQPSK) 6 / 7
A possible mapping for QPSK signal.Possible phase transitions in QPSK signaling.
Phase transition diagram for OQPSK signaling.
Results:
1. prevents both components changing at the
same time
2. In constellation-speak, if the signal wave in the
right upper quadrant, the next signal can only
go to either the lower right quadrant or to upper left
quadrant but not across.
But in QPSK all transitions can occur.
Solution (QPSK modified to became OQPSK)
Company nameDigital Modulation Schemes (OQPSK) 7 / 7
The absence of 180◦ phase jump is, however, offset by more
frequent ±90◦ phase shifts
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Reference:
Digital Communicationm, John G. Proakis , Masoud Salehi
Direct Download link: www.Teleinfra.net/OQPSK.pptx
www.Teleinfra.net/OQPSK.pdf
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