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Analog And Digital Communication Systems Question Paper
Analog And Digital Communication Systems
Course:Bachelor Of Telecommunication And Information Engineering ()
Institution: Kabarak University question papers
Exam Year:2012
KABARAK
UNIVERSITY
UNIVERSITY EXAMINATIONS
2011/2012 ACADEMIC YEAR
FOR THE DEGREE OF BACHELOR OF TELECOMMUNICATION
TLCM 311: ANALOG AND DIGITAL COMMUNICATION SYSTEMS
DAY: MONDAY
DATE: 30/07/2012
TIME: 2.00 – 5.00 P.M.
STREAM: Y3S1
INSTRUCTIONS:
1. Answer ALL questions in PART ONE and any THREE questions in PART TWO
2. Any extra questions answered will not be marked
• Boltzman’s constant = 1.38 x 10-23 J/K
• Room temperature = 290K
2
- A T
1
b
• Probability of error for DPSK is given by
?
2
Pe =
e
2
?
2
?
? A Tb ?
• Probability of error for coherent ASK is given by Pe = Q?
?
?
?
4
?
2
- A
1 8N
• Probability of error of non coherent ASK is given by
0
Pe =
e
2
?
2
?
? A T
p
b
?
• Probability of error for QPSK is given by Pe = 2
2
?
Q
sin
?
?
?
4 ?
Page 1 of 6
PART ONE
Question One (40 marks)
a.
Define
i.
A deterministic signal.
ii.
A linear system.
iii.
The noise figure of a two port device.
(6 marks)
b.
Prove that the noise figure of a device consisting entirely of restive elements at thermal
equilibrium is equal to the loss of the device.
(6 marks)
c.
A filter has a gain of 40dB and an equivalent noise bandwidth of 20GHz. When noise
with a power of 0.7microwatts is applied at the input of the filter, the output noise power
is 0.012W. Calculate
i.
The internal noise power generated in the filter.
(3 marks)
ii.
The noise figure of the filter in decibels.
(4 marks)
d.
Describe
i.
The function of a clock recovery network in a binary PAM system. (3 marks)
ii.
Inter symbol interference (ISI) and how it can be eliminated. (3 marks)
e.
Give two advantages of alternate mark inversion as compared to Manchester code.
(4 marks)
f.
Ten analog signals each with a bandwidth of 4500Hz are frequency division multiplexed
using a guard band of 900Hz. The multiplexer uses lower sideband, vestigial sideband
modulation. The bandwidth of the partial sideband that is transmitted is 400Hz. The
carrier frequency used to modulate the first signal is 15 KHz. (Note: The carrier
frequencies used to modulate the other signals is more than not less than 15 KHz.).
Calculate
i.
The bandwidth of the multiplexed signal.
(3 marks)
ii.
The minimum and maximum frequency of the multiplexed signal. (3 marks)
g.
A Gaussian transmission channel has a bandwidth of 7.8 KHz and a noise power spectral
density of 10-11W/Hz. If the capacity of the channel is 150Kbps, calculate
i.
The signal to noise ratio at the output of the channel.
(2 marks)
ii.
The signal power at the output of the channel.
(3 marks)
Page 2 of 6
PART TWO
Question Two (20 marks)
a.
A sinusoidal message signal given by A cos? t is used to amplitude modulate a carrier
m
m
given by A cos? t
Prove that the modulation index is A .
(3 marks)
c
c
.
m
b.
With regard to amplitude modulation, describe what is meant by the threshold effect.
(2 marks)
c.
Which linear modulation technique is most suitable for transmitting analog voice?
Give three reasons explaining your answer.
(4 marks)
d.
An analog message signal with a bandwidth of 6 KHz and an average power of 30W
is transmitted using double sideband (DSB) modulation over a Gaussian channel with
a noise power spectral density of 10-10W/Hz and a loss of 40dB. The carrier signal is
of the form15 cos? t . Calculate the signal to noise ratio (in decibels) at the output
c
of the channel.
(6 marks)
e.
An analog signal with a bandwidth of 8500Hz is transmitted using frequency modulation.
The frequency of the carrier signal is 105MHz and the maximum frequency deviation
is 24 KHz.
i.
Give one advantage of transmitting the signal using frequency modulation as compared to
suppressed sideband modulation.
(2 marks)
ii.
Calculate the bandwidth of the FM signal.
(3 marks)
Question Three (20 marks)
a.
Give one advantage and disadvantage of DPSK as compared to non coherent PSK.
(3 marks)
b.
Briefly describe quadrature amplitude modulation.
(3 marks)
c.
Binary data is transmitted over a Gaussian channel using non coherent ASK. The
bandwidth of the medium is 24KHZ, the loss is 60dB and noise power spectral density is
10-12W/Hz. Assuming that rectangular pulses are used to generate the ASK signal,
Calculate
i.
The maximum signaling rate.
(2 marks)
ii.
The signal power required at the input of the channel to achieve a probability of error
of 2.62x10-6
(6 marks)
Page 3 of 6
d.
Binary data with a bit rate of 89Mbps is transmitted over a Gaussian channel using
coherent QPSK. The noise power spectral density of the channel is 10-11W/Hz and the loss
is 30dB. The carrier used is of the form 20 cos? t V. Assuming that shaped pulses are
c
used to generate the QPSK signal, calculate the probability of error.
(6 marks)
Question Four (20 marks)
a.
Describe a systematic linear block code.
(3 marks)
b.
The parity check matrix of a (6,3) block code is given below.
Determine the minimum distance of the code.
(10 marks)
c.
What is the main advantage of cyclic codes compared to other classes of linear
block codes.
(2 marks)
d.
Describe why convolution codes are not suitable for use with error control with
retransmission.
(3 marks)
e.
Describe how errors are detected using cyclic codes.
(2 marks)
Question Five (20 marks)
a.
Why is delta modulation more suitable for use in digitizing a video signal than pulse code
modulation?
(3 marks)
b.
An analog signal, with a bandwidth of 9.2 KHz, is digitized using pulse code modulation.
The uniform quantization process has a signal to quantization noise ratio of 52dB.
i.
Define the quantization noise power.
(2 marks)
ii.
Calculate the minimum bandwidth required to transmit the digital signal using M-ARY
pulse amplitude modulation with M = 16.
(5 marks)
iii.
Give two disadvantages of transmitting the digital signal using M-ARY pulse amplitude
modulation.
(3 marks)
Page 4 of 6
c.
Define the information content of a symbol produced by a discrete information source.
(2 marks)
d.
A discrete information source emits one of 10 independent symbols every 2 milliseconds.
The probabilities of the symbols being emitted are given below
1/46, 3/46, 9/46, 1/23, 5/46, 2/23, 1/46, 4/23, 7/46 and 3/23
Calculate the information rate of the information source.
(5 marks)
Page 5 of 6
Page 6 of 6
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