SDPSK module for gnuradio

[thunder87l]

I was told to write one as a practice task. Can anyone please tell me how it works? What is the difference between it and DBPSK? I was told to use DBPSK as a basis, and modify it to SDPSK. So there must be something in common?

Wiki is no good, google also doesn't help much. Any advice where to search info?