B. P. Lathi, Zhi Ding - Modern Digital and Analog Communication Systems-Oxford University Press (2009)

588 PERFORMANCE ANALYSIS OF DIGITAL COMMUNICATION SYSTEMS
Figure 10.40
Error probability
of noncoherent
MFSK.
10-I r···~--,-----,------,----,----,--
10-3
peM
10- 5
10-6
0 2 4 6 8 10 12 14
Ei)N, dB _..
Figure 10.41
Differential PSK
detection.
H(f)
f
t = Tb
Threshold
r device Decision
Delay
Tb
of two pulses (p, p) or (-p, -p) over 2T b seconds (no transition). Similarly, a binary O is
transmitted by a sequence of two pulses (p, -p) or (-p, p) over 2T b seconds (transition).
Either of the pulse sequences used for binary 1 is orthogonal to either of the pulse sequences
used for binary 0. Because no local carrier is generated for demodulation, the detection is
noncoherent, with an effective pulse energy equal to 2E p
(twice the energy of pulse p). The
actual energy transmitted per digit is only E p
, however, the same as in noncoherent FSK.
Consequently, the performance of DPSK is 3 dB superior to that of noncoherent FSK. Hence
from Eq. (10.145), we can write P b for DPSK as
(10.147)
This error probability (Fig. 10.42) is superior to that of noncoherent FSK by 3 dB and is
essentially similar to coherent PSK for E b /N » 1 [Eq. (10.39)). This is as expected, because