563489578934

508
Upper channel
Receiver
r(t)=s(t)+n(t)
(
(
s 1 (t)
r(t)= or +n(t)
+
s 2 (t)
Low-pass filter
2 cos (
r 0 (t) Sample r 0 (t 0 )
1 t+¨c )
or
N
and
where p 0
n (f)= matched filter
hold
2 Lower channel
H(f)
Baseband
analog output
Threshold
device
(comparator)
~ m m ~
0
V T
r 0
Digital
output
2 cos ( 2 t+¨c )
(a) Receiver
Spectrum of s 2 (t)
Spectrum of n 2 (t)
Spectrum of s 1 (t)
2∆F
Spectrum of n 1 (t)
B
N 0 /2
R=
1
T
f 2 f c
f 1
(b) Power Spectra for Positive Frequencies
Figure 7–8
B p =2B
Coherent detection of an FSK signal.