37 DQPSK signal constellation diagram.
FIGURE 2.38 Receiver block diagram emphasizing differential decoding operations.
FIGURE 2.39 Receiver block diagram emphasizing differential detection operations.
Based on the differential encoding equation, we were able to intuitively provide/solve the equation
to be used in the receiver. A more detailed derivation will be supplied in Chap. 4, where we discuss
detection techniques.
It must be mentioned that when differential detection is used, a single error will propagate into two
errors since the error will be used as a phase reference for the next symbol. With this in mind, we notice
that a receiver would require approximately 2.5 dB more Eb/No for differential detection when compared
to coherent detection operating in an AWGN channel and maintaining an average BER 1E-3.
Lastly, we have managed to give the receiver an option to use either coherent detection or differential
detection, thus having the possibility of deploying a simple implementation, if so desired.
However, we still have a spectral regrowth issue to address, particularly if the transmit PA is operating
close to the 1 dB compression point, in other words, in the nonlinear region.
2.2.5 /4-Shifted Differential QPSK (/4-DQPSK)
A solution to offer options for the receiver detection and implementation architectures, while avoiding
the origin, is /4-DQPSK.
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