Communication Networks (2
nd
Edition) Chapter 4 Solutions
Leon-Garcia/Widjaja 1
Solutions to Chapter 4
1. A television transmission channel occupies a bandwidth of 6 MHz.
Solutions follow questions:
a. How many two-way 30 kHz analog voice channels can be frequency-division multiplexed in a
single television channel?
6 × 10
6
/ 30 × 10
3
= 200 channels
b. How many two-way 200 kHz GSM channels can be frequency-division multiplexed in a
single television channel?
6 × 10
6
/ 200 × 10
3
= 30 channels
c. Discuss the tradeoffs involved in converting existing television channels to cellular telephony
channels?
The biggest advantage of using existing television channels to provide cellular telephony
channels is the very large bandwidth that they occupy. In theory, one could divide each television
channel into many cellular telephone channels, as shown in parts (a) and (b). The frequency
reuse aspect of cellular networks would multiply these channels many times. This would be at
the cost of television channels that cover a broad region and presumably provide service to a
large audience.
2. A cable sheath has an inner diameter of 2.5 cm.
Solutions follow questions:
a. Estimate the number of wires that can be contained in the cable if the wire has a diameter of 5
mm.
Ignoring empty space between the wires:
2
2
)
2
5
(
)
2
25
(
π
π
= 25 wires
b. Estimate the diameter of a cable that holds 2700 wire pairs.
Ignoring empty space between the wires:
2
2
)
2
5
(
)
2
(
π
π
d
= 2x2700 wires Æ d ≅ 368 mm
每一个抄通信网答案的学生都是头疼的天使----Laofuzi
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