8 phase shift keying is a complex form of digital modulation by altering a sine wave and a cosine wave: shifting their phase.
The best explanations I have found so far can be found at
http://en.wikipedia.org/wiki/Phase-shift_keying
and
http://www.sss-mag.com/pdf/1modulation.pdf
But they all explain the more simpler forms of phase shift keying:
Binary Phase Shift Keying (BPSK) and
Quadrature Phase Shift Keying (QPSK)
and they don't say much about 8PSK unfortunately.
However this might still give you an idea.
Good luck, I will keep searching myself.
Karen von Hünerbein