
cumbersome demodulation scheme is to use m/2 ODIs with the following different
phase offsets (between the two arms of each ODI).
D
ODI
ðnÞ=
1 2 n 1ðÞ½p
m
; n = 1; 2;:::;m=2:
(4.21)
For example, the demodulation of an 8-ary DPSK signal thus requires four
ODIs with phase offsets of /8, –/8, –3/8, and –5/8 between the interfering
arms. Following the demodulation, m/2 pairs of balanced detectors are needed to
obtain m/2 decision variables, u[D
ODI
(n)], where n = 1, 2,..., m/2. Generalizing
the analysis on 8-ary DPSK to m-ary DPSK, we can recover the log
2
(m) data
tributaries of an m-ary DPSK signal by [36]
c
1
=c
I
¼ u
p
m
>0
hi
; c
2
¼c
Q
¼ u
p
m
p
2
>0
hi
;
c
3
¼ u