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

520 PERFORMANCE ANALYSIS OF DIGITAL COMMUNICATION SYSTEMS
and
(10.38)
This shows that the performance of any orthogonal binary signaling is inferior to that of polar
signaling by 3 dB. This naturally includes on-off signaling.
10.3 COHERENT RECEIVERS FOR DIGITAL
CARRIER MODULATIONS
We introduced amplitude shift keying (ASK), frequency shift keying (FSK), and phase shift
keying (PSK) in Section 7.9. Figure 10.8 uses a rectangular baseband pulse to show the three
binary schemes. The baseband pulse may be specifically shaped (e.g., a raised cosine) to
eliminate intersymbol interference and to stay within a finite bandwidth.
BPSK
In particular, the binary PSK (BPSK) modulation transmits binary symbols via
1 : ,,/ip' (t) COS Wet
0 : -,,/ip'(t) cos Wet
Here p' (t) denotes the baseband pulse shape. When p(t) = ,,/ip' (t) cos wet, this has exactly
the same signaling form as the baseband polar signaling. Thus, the optimum binary receiver
also takes the form of Fig. 10.5a. As a result, for equally likely binary data, the optimum
threshold a 0 = 0 and the minimum probability of detection error is identically
(10.39)
Figure 10.8
Digital
modulated
waveforms.
Baseband
I
ASK
I
I
1 0 1
I
I
I
(a)
O /\ 0 0 A O O A : A fl A :
0 0
t ----+-
t ----+-
t ----+-
t ----+-
(d)