
4.4.3 Detection of m-ary DPSK
The DSCOR can be used to receive high spectral-efficiency m-ary DPSK signals
[17, 36]. As described previously, the log
2
(m) data tributaries of an m-ary DPSK
signal are usually obtained from m/2 decision variables associated with m/4 ODI
pairs having the following orthogonal phase offsets,
m
;
m
2
;
3
m
;
3
m
2
;:::;
ðm=21Þ
m
;
m
. With the assistance of DSP, we show below that the last (m/2–2)
decision variables can be derived by linear combinations of the first two decision
variables, u
I
and u
Q
. This dramatically reduces the optical complexity associated
with the detection of m-ary DPSK. The decision variables associ ...