This preview shows pages 1–2. Sign up to view the full content.
ECE 402: Communications Engineering
Homework 8 Solutions (Fall 2009)
1. The carrier frequency should be located in the center of the band at
f
0
= (820 + 920)
/
2 = 870 kHz.
If the rolloﬀ is
r
= 0
.
5, the PSK signal bandwidth is
W
= 2(1 +
r
)
W
N
= 1
.
5
f
b
. For a channel
bandwidth of 100 kHz, the symbol rate that uses the entire band is
f
b
= 66
.
6 kbaud. The data rate is
R
=
kf
b
where
k
is the number of bits/pulse. Since we require
R
= 200 kb/s, the signal constellation
should have
k
= (
R/f
b
) = 3 bits/pulse, or
M
= 2
k
= 8 points. Thus, we should use 8PSK.
2.
(a)
From the ﬁgure
Z
(
f
) =
H
c
(
f
)
X
(
f
). Since
z
(
t
) =
x
(
t
+
T/
4) +
x
(
t

T/
4), we have
Z
(
f
) =
F
[
x
(
t
+
T/
4) +
x
(
t

T/
4)] = (
e
2
πjfT/
4
+
e

2
πjfT/
4
)
X
(
f
) = 2cos(
πfT/
2)
X
(
f
)
,
so
H
c
(
f
) =
Z
(
f
)
/X
(
f
) = 2cos(
πfT/
2).
(b)
From
G
(
f
) =
F
[sinc(2
t/T
)] = (
T/
2)Π(
Tf/
2), the system pulse is
P
(
f
) =
G
(
f
)
H
c
(
f
)
H
r
(
f
) = (
T/
2)Π(
Tf/
2)
·
2cos(
πfT/
2)
·
cos(
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
This is the end of the preview. Sign up
to
access the rest of the document.
This note was uploaded on 01/28/2012 for the course ECE 402 taught by Professor Townsend during the Fall '08 term at N.C. State.
 Fall '08
 Townsend
 Frequency

Click to edit the document details