Difference between absolute PSK and differential PSK?

Answer 1

In abs. PSK only instant phase for the incoming bits are considered.

For DPSK, the difference between previous phase and the present phase is considered.

Example: If BPSK is used, then for 0 if phase if pi and for 1 it is 0, then

for abs. BPSK the phase states for the bit stream 1010 will be 0,pi,0,pi

for DPSK, we assume initial phase is zero and a rule that , if incoming bit is zero, then phase difference is 0 and if it is 1 then, phase difference is pi.

So, phase difference will be--pi,0,pi,0

Instant phase will be, pi,pi,0,0....Easy!!

Answer 2

In absolute phase shift keying (PSK), the signal varies in phase relative to a reference phase, which remains constant for each symbol. In differential PSK, the phase difference between consecutive symbols is used to encode data, without referencing an absolute phase. This makes differential PSK more robust to phase shifts caused by factors such as variations in the transmission medium.