Digital Signal Processing Reference
In-Depth Information
6.36.
Find and sketch the frequency spectrum of the flat-topped PAM signal resulting from
modulating the signal
p(t)
shown in Figure P6.33(b) with a signal
m(t) = 4 sinc(40pt).
6.37.
In early modems (e.g., those with 300 bits/second data rates), binary data (bits) were
sent over an analog channel by a modulation method known as Frequency Shift Key.
To send a digital 0, the signal
s
0
(t)
is sent where
s
0
(t) = Af
0
(t).
To send a digital 1, the signal
s
1
(t)
is sent where
s
1
(t) = Af
1
(t).
The basis functions
f
0
(t)
and
f
1
(t)
are orthonormal, meaning that
T
1
j = k
f
j
(t)f
k
(t)dt =
b
.
0
j Z k
L
0
The receiver works by determining a constant
r
i
, i = 0, 1
as
T
r
i
=
L
r(t)f
i
(t)dt
,
0
where
r(t)
is the received signal (see Figure P6.37).
0
(
t
)
r
0
Integrator (from 0 to
T
)
s
0
(
t
)
or
s
1
(
t
)
r
(
t
)
Communication
Channel
1
(
t
)
r
1
Integrator (from 0 to
T
)
Figure P6.37
Assume that the received signal is equal to the signal that is sent (i.e., you do not
have to consider noise in the communication channel).
r(t)
(a)
If
s
0
(t)
is sent for a 0, determine
r
0
and
r
1
.
(b)
If
s
1
(t)
is sent for a 1, determine
r
0
and
r
1
.
6.38.
In Binary Phase Shift Key, binary data (bits) are sent over an analog channel by the fol-
lowing method:
A signal
s(t) = (2a - 1)f(t)
is sent in which
a
is the binary bit being sent (0 or 1).
