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Sample Question Paper for 9210-214
Level 7 Post Graduate Diploma in Engineering
Telecommunication systems engineering
Duration: three hours
You should have the
following for this examination
• one answer book
• non-programmable calculator
• pen, pencil, ruler
General instructions
• This paper consists of eight questions.
• Answer any five questions.
• A non-programmable electronic calculator may be used but candidates must
show sufficient steps to justify their answers.
• Drawings should be clear, in good proportion and in pencil. Do not use red ink.
• All questions carry equal marks. The maximum marks for each section within
a question are shown.
1
a)
b)
c)
d)
2
a)
b)
c)
d)
Describe a basic voice communication system including its main building blocks.
Voice communication is merging with data/video communication. Explain the
concept of ‘Tri-service’ in next generation networks with examples of services
and user experiences this enables.
Compare and contrast twin pair and mobile access techniques used in
telephone networks.
Transcoding means code conversion to suit the transmission media. The following
bit patterns are to be transmitted in HDB3 NRZ transcoding. Draw the wave forms
for each of the following data patterns.
i)
110 0 0 0 1 1 0 1 1
ii) 1 0 1 0 0 0 0 0 1 1 0 0 0 0 1 1 0 0 0 0
iii) 1 0 1 0 0 0 0 1 0 0 0 0 1 1 0 0 0 0 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 0 1
Higher order multiplexing is now prevalent in transmission networks. Explain the
basic differences between Plesiochronous Digital Hierarchy (PDH) and
Synchronous Digital Hierarchy (SDH) transmission systems?
i)
Show how the European Conference of Postal and Telecommunications
Administrations (CEPT) and North American PDH systems are connected
to form a Synchronous Transport Module-1(STM1) level. Clearly indicate the
matching at each level of PDH system STM sub containers.
ii) Table Q2 shows the Synchronous Optical Networking (SONET) data rate.
List the corresponding Synchronous Digital Hierarchy (SDH) equivalent for
each SONET level showing its interoperability.
Explain why an 8Mb/s CEPT system cannot be connected to an STM1.
Estimate the number of voice channels and the channel utilisation efficiency
which can be accommodated by an STM-16 signal. Assume that the STM frame
is filled with ITU-T primary multiplex group signals.
(Hint: STS payload has 86 columns and a primary multiplex occupies 4 columns)
SONET Level
Line rate (Mb/s)
OC-1
51.84
OC-3
155.52
OC-12
622.08
OC-24
1244.16
OC-48
2488.32
OC-96
4976.64
OC-192
9953.28
OC-768
39813.12
Table Q2
2
SDH Equivalent
(6 marks)
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3
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4
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5
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b)
c)
Explain the meaning of the functions station keeping and attitude control as
applied in satellite communication systems and the need for each.
Name two techniques used for attitude control.
Describe four reasons for the importance of attitude control of a satellite for its users.
An earth station located at 80° 40’ 00” East longitude and 7° 25’ 00” North latitude,
should uplink a digital video carrier to Intelsat APR-1 multimedia satellite parked
in Geostationary Earth Orbit (GEO) at 83° East position. The digital video signal
having 34 Mbps transmission rate is QPSK modulated and uplinked with an
Equivalent Isotropically Radiated Power (EIRP) of 85 dBW to the transponder
labelled L7 operating at 6230/3485 MHz. This transponder has a saturation flux
density of –70 dBW/m2 at its input and a G/T of –7 dB/K. Additional uplink
transmission loss is 0.5 dB. Estimate the following;
i)
Uplink path distance.
ii) Elevation angle.
iii) Time delay.
iv) Input back-off of the satellite transponder.
v) Bit energy to noise power density ratio for the uplink.
[Radius of earth = 6378.2 km, Radius of GEO = 42164.2 km]
State three mechanisms of loss in optical fibres.
Fibre dispersion is a key issue in optical transmission system. Explain the fibre
dispersion effect in relation to source wavelength and line coding (Non return
to zero and return to zero).
i)
Sketch both the silica fibre attenuation (dB/km) and dispersion (D in ps/nm/km)
characteristics identifying the important wavelength regions.
ii) State the factors that have led to the 1550 nm region being the window of
choice for current Dense Wavelength Division Multiplexing (DWDM) systems.
Suppose you are asked to design a 1550 nm laser for a 100 km DWDM fibre-optic
link with a data rate of 10 Gb/s per channel. If the fibre dispersion is D = 17 ps/(nm
km), what is the maximum allowable spectral linewidth of this laser?
If the channel spacing is 25 GHz, is this laser usable in the above mentioned
DWDM system?
[Velocity of the light in vacuum (c) = 3.0 x 108 ms–1]
Describe the use of Private Mobile Radio (PMR) in relation to frequency allocation,
bandwidth, and modulation techniques.
i)
What is the coherence bandwidth of a fading channel?
ii) Write the relationship between the coherence bandwidth and the delay
spread of the channel.
Describe the following terms:
i)
Slow fading.
ii) Fast fading.
iii) Frequency selective fading.
3
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See next page
6
a)
i)
ii)
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7
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8
a)
b)
In relation to the commonly adopted geometry for cellular systems, show
––
d
that = √3n, where r is the cell radius, n is the number of cells in the
r
cluster and d is the frequency reuse distance.
(Hint: consider a seven cell cluster arrangement)
State the formula using r and d for the C/I ratio for an n-cell cluster assuming
a 4th power propagation law.
A mobile phone operator needs to provide the service to a rural area.
The system is operating on GSM 900. The cluster size designed has 7 cells
with a cell radius of 5 km. Calculate the C/I ratio close to the edge of the cell.
Describe the operating principle of Code Division Multiple Access (CDMA)
as a wireless access system.
State five benefits of CDMA over Time Division Multiple Access (TDMA) or
Frequency Division Multiple Access (FDMA).
Describe fixed and wireless access in telecommunication networks giving examples.
Write short notes on Frequency Division Duplex (FDD) and Time Division Duplex
(TDD) access systems giving examples.
Duplexing schemes may be compared in terms of factors such as duplex
separation method, dynamic bandwidth allocation capability, cost and latency.
Compare and contrast FDD and TDD in terms of the above and identify the better
method with respect to each factor.
State three major differences between mobile access and fixed wireless access.
Describe the following modes of operation relating to wireless access systems
using sketches.
i)
Infrastructure network mode.
ii) Ad-hoc network mode.
iii) Hybrid network mode.
i)
Describe briefly, ‘Ethernet’ and ‘Token Ring’ concepts with respect to the
protocols used, speed of operation and different transmission media.
ii) A 10 Mbit/s token ring has 50 stations, each having a latency of 2 bits.
The total length of the ring is 4 km, and the propagation delay of the cable
is 6 µs/km. Determine the maximum waiting time when the ring is empty,
and when all stations are transmitting. The full frame length is 64 bytes.
4
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