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CS/ECE 438: Communication Networks for Computers
Spring 2010
Problem Set 2
Due: start of class, Wednesday, February 10
th
.
Direct Link Networks and Error Correction Codes
Assigned reading: Peterson and Davie: Chapter 2.1 – 2.4. All problems carry equal weight.
1.
Noisy Channel Data Rates
The decibel is a measure of the ratio between two signal levels: N
db
= 10 log
10
(P
2
/P
1
), where N
db
= the number of
decibels, P
1
= the input power level and P
2
= the output power level.
a.
A telephone line is known to have a loss of 20db. The input signal power is measured as 0.50 watt and
the output noise is measured as 8
watt. Using this information, calculate the output signaltonoise
ratio in dB.
b.
What is the capacity of this phone line with a frequency range of 100 Hz – 1000 Hz?
c.
If the attenuation rate of this phone line is 2db/km, and the minimum output signal is 0.00025 watt,
given the input signal from part a), how long can the phone line be before requiring a repeater?
2.
Encoding, Channel Capacity and Modulation
a.
Show the NRZ, Manchester, NRZI and 4B/5B encoding signals (the resulting NRZI signal for 4B/5B),
using a diagram similar to that in Figure 2.10, p. 82, P&D, for the data bit sequence 10111 10100
11011 10110. To be definite, suppose the NRZI signals begin at a low voltage.
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This note was uploaded on 07/10/2011 for the course CS 438 taught by Professor Luo during the Spring '08 term at University of Illinois, Urbana Champaign.
 Spring '08
 Luo

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