EEE314: Data Communication And Computer Networks
Program:
BS Electrical (TE/CE) Engineering
Semester:
6th
Date:
25th April, 2009
Instructions for attempting paper
Mobile phones and digital diaries are not allowed in the examination hall.
Answer all questions.
Q No.1. [15 Marks]
The information in four analog signals is to be multiplexed and transmitted over a telephone
channel that has a 400 to 3100-Hz bandpass. Each of the analog baseband signals is bandlimited
to 500 Hz. Design a communication system (block diagram) that will allow the transmission of
these four sources over the telephone channel using
a) Frequency-division multiplexing with SSB (single sideband) subcarriers. Refer to fig 1.a
(5)
b) Time-division multiplexing using 6-bit PCM. What data rate must be supported in the
available bandwidth.
(5)
BW = 3100 – 400 = 2700 Hz
For 500 Hz bandlimited signals the sampling rate would be = 500 x 2
Data Rate for Each Signal = 1000 x 6 = 6000 bps
Net Data Rate for 4 sources = 6000 x 4 = 24 kbps
c) Why parallel transmission is not suitable for long distance communication? (2)
1. Cost
2. Skew
d) Why NRZ signaling is used in asynchronous communication? (2)
In asynchronous communication synchronization is achieved at every byte by start and
end bit so the most simple encoding scheme is used. There is no need to bear the overhead of
providing synchronization through encoding scheme. Synchronization through encoding scheme
comes at the cost of increased signal bandwidth
e) What is Dense-WDM? (1)
No fixed definition, carriers are closely spaced than WDM
2nd Sessional
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