I was reading MATLAB's documentation on
dpskmod. They gave an example of an $\pi/8$-DQPSK. I felt that this is strange as I have seen $\pi/4$-DQSPK and $\pi/8$-D8PSK, but I have not seen $\pi/8$-DQPSK.
Attached is a screenshot of the documentation showing $\pi/8$-DQPSK with 16 clusters in the constellation:
My question is: Is $\pi/8$-DQPSK actually used in industry or is this just a demonstration of the flexibility of MATLAB's functions?