BROADBAND COMMUNICATION QUESTION BANK
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1. (a)
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What are the advantages of
optical fiber cables over the co-axial cables?
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(06)
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(b)
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Calculate NA, Acceptance
angle and Angle of fiber with core and cladding refractive index values as n1=1.5
and n2=1.45 respectively.
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(06)
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(c)
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Explain the “mode theory”
of optical fiber.
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(06)
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2. (a)
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What is meant by acceptance
angle and acceptance cone for optical fiber? Show and explain it’s
relationship to numerical aperture and refractive indices of core &
cladding.
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(06)
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(b)
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If a MMSI fiber of core radius
25 micrometer operating at 1300nm, has
core and cladding refractive index as 1.5 & 1.38 respectively;
Calculate Numerical aperture, Normalized frequency, Solid acceptance angle
and number of modes entering in the fiber
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(06)
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(c)
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If the mean optical power
in a 8 km long fiber at launching and output zone is 12 and 2 microwatt;
determine (1) overall signal attenuation in dB and (2) when length is 10 km
with the splices of 1dB attenuationeach at the interval of 1km.
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(06)
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3. (a)
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What is dispersion in
fiber? Explain intra-modal dispersion in details.
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(08)
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(b)
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A SMSIfiber with core and
cladding refractive indices as 1.447 and 1.442respectively is designed to
operate at wavelength 1.3 micrometer. When core diameter is 7.2 micrometer;
confirm that the fiber permits single mode transmission and estimate the
range of wavelengths over which this will occur.
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(08)
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4. (a)
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Explain the “linear
scattering losses” in fibers.
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(08)
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(b)
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A MMSIF has NA
as 0.3 and core refractive index as 1.45. The material dispersion parameter
as 250 ps/nm.km makes it totally dominating intra-modular dispersion
mechanism. Estimate (1) total pulse broadening/km when the fiber is used with
the LED source of RMS spectral width of 50 nm, and (2) corresponding
bandwidth-length product.
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(08)
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5. (a)
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Explain the three
transmissions windows of optical communication along with the attenuation
curves for SMF.
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(08)
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(b)
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Explain bending
losses in fiber.
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(08)
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6. (a)
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Explain material absorption
losses in silica fiber.
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(08)
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1. (a)
Compare the surface and Edge emitting LED and explain one of them in details.
[10]
(b)The radiative and non-radiative
recombination lifetime of the minority carriers in the active region of a
double heterojunction LED are 50 and 110 ns respectively. Determine the total
carrier recombination life time and the power internally generated within the
device when the peak emission is 0.87 µm at the derive current of 40mA. [08]
2. (a)
what do you understand by line coding?
Why is it needed? Explain NRZ and RZ code in details. [10]
(b)An InGaAsP
Surface ELED has an activation energy of 0.9 eV with a constant of
proportionality β0 = 1.85*107 h-1. Find out
the operating life time of the LED at constant junction temp. of 200C,
if assumed that the device is no longer useful when it’s optical output power
goes down to 0.65 of it’s original value. [08]
3.
(a)
Draw block schematic of the front end of an optical receiver showing and explaining
various noise sources at different locations/stages. [08]
(b)A given
silicon APD has quantum efficiency of 65% at a wavelength of 900 nm. Suppose
0.5 µW of optical power produces a multiplied photocurrent of 10µA; find the
avalanche gain.
[08]
4.(a)
What are the criteria for photo diodes to be used as detectors in optical fiber
communication? Draw the structure of APD and explain it’s working. Also list its
advantages and drawbacks. [08]
(b)A photo
diode used for an optical receiver has a quantum efficiency of 65% when
operating at 850 nm. The dark current is 3.5 nA and the load resistance is 5
k-ohm. If the incident optical power and post detection BW are 300 nW and 6.5
MHz; compare the shot noise generated in photodiode with the thermal noise in
the load resistor at room temperature. [08]
5.(a)
What are the key system requirements that are needed in analyzing a “point to
point” link? Explain the point to point link design with reference to the
choice of components and their associated characteristics. [08]
(b)
An analog optical fiber system employs an LED that
emits 3dB mean optical power into air. However, a coupling loss of 17.5 is
encountered when launching into a fiber cable. The fiber cable extended to 6 km
without repeator exhibit a loss of 5 dB/km. it is spliced every 1.5 km with an
average loss of 1.1dB/splice. In addition there is a connector loss at the
receiver of 0.8 dB. The receiver has a sensitivity of -54dBm at the operating
bandwidth of the system. Assuming there
is no dispersion-equalization penalty, perform an optical power budgeting for
the system and establish a safety margin. [08]
6. (a)
Explain basic elements of an analog link through block diagram, show major
noise contributors and discuss working of analog transmission system.
[08]
(b)
The
10 to 90% rise time for possible components to be used in D-IM analog optical
fiber link are specified as: LED source-9 ns/km, fiber cable- 9 ns/km
(intermodal) and 2 ns/km (intramodal), APD detector- 3 n sec. the desired link
length without repeator is 5 km and the required BW is 6 MHz. Determine the
combination for components give an adequate response. [08]
Unit
-V - Satellites
1.
With
the help of block diagram, explain typical tracking, telemetry system.
2.
With
the help of block diagram, explain typical command and monitoring system.
3.
Explain
the transponder arrangement and frequency plan (uplink and downlink) for any
satellite. Also draw block diagram of single conversion transponder for 6/4 GHz
band.
4.
What
are different types of antennas used in satellite systems, explain importance of
each.
5.
Explain
the term reliability in connection with satellite communication.
6.
Explain
satellite communication systems and their applications
7.
Write
a note on power subsystems.
8.
Write
note on Equipment lifetime and space qualification.
Unit VI – Introduction Satellite Link Design
1. Explain
basic transmission theory of satellite communication link design.
2. Derive
the equation of Gain as G = 4πηA/λ2
3. Derive
the equation of Gain as G = 4πηA/λ2
4. In
relation to satellite communication, define noise temperature and derive the
equation for carrier to noise ratio at the output of demodulator.
5. Explain
system noise temperature and G/T ratio.
6. Explain design parameters and features of uplink
systems.
7. Explain design parameters and features of downlink
systems.
8. Write
a short note on satellite systems using small earth stations