Digital Modulation Techniques in Mobile Communications

π/4-QPSKDual constellation diagram for π/4-QPSK. Thisshows the two separate constellations withidentical Gray coding but rotated by 45° withrespect to each other.This final variant of QPSK uses two identicalconstellations which are rotated by 45° (π / 4radians, hence the name) with respect to oneanother. Usually, either the even or odd databits are used to select points from one of theconstellations and the other bits select pointsfrom the other constellation. This also reducesthe phase-shifts from a maximum of 180°, butonly to a maximum of 135° and so theamplitude fluctuations of π / 4–QPSK arebetween OQPSK and non-offset QPSK.Fahredd'n Sadikoglu 25