WBUT Exam Papers EC Advanced Communication Systems B Tech 8th Sem April 2009

WBUT  Exam Papers EC 

           Advanced Communication Systems B Tech  8th Sem April 2009

[ Full Marks : 70

 GROUP – A ( Multiple Choice Type Questions )

Choose the correct alternatives for any ten of the following :

i)           A ray of light is passing from a silica glass of refractive index 1-48 to another silica of refractive index 1-46. What range of angles ( measured with respect to the interface , for which this ray will undergo total interna! reflection ?

b)            81” – 90°

d) 180° – 360“

ii)          Lighi. is guided within the core of a step-index-fibre by

a)         refraction at the core-air interface

b)          total internal reflection at the core-cladding interface

c)          total internal reflection at the outer surface of the cladding

d)         change in the speed of light within the core.   j

iii)        A SiF has a core with a refractive index of 1 50 and a cladding with a refracting index of I-46. Its numerical aperture is


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iv) Amplified output is given by the detector

b) p-f-i i photodiode d) photovoltaic diode.

a] p- a photodiode c) avalanche photodiode

t he interlace between BSC and MSC is


b) Abis interface d) SS7.

a! Radio air interface c) . A-interface


vi) in the c-band transponders the uplink frequency is about

b) 6 GHz d) 1-‘! GHz.

4 GHz

■) 11 GHz

vii) ‘B’i’S’ stands for

a) Base Transmission Station b) Base Transceiver Station e) Base Transmission Station d) Base Terminal Swtch.


viii) One of the following laws governs the movement of artificial satellites in earth orbits is

Newtonian laws of mechanics b) Laws of quantum mechanics c) Galilean laws                                           d) Kepler’s laws.

ix) Which type of modulation technique is used in GSM ?




a) PSK c) MSK

b) AiiK d) GMSK.




x) Most common form of modulation used in cellular communication is





b) FM d) NBFM,



6825 ( 21 /O’.


xi)         iylodal dispersion occurs in


b) Multimode fibres

a) GI fibre3


d) None of these.



xii)        Rake receiver is used by

a)          FDMA c) TDMA

Aiii) UMTS stands for

a)   Universal Mobile Telecommunication System

b)  Universal Mobile Telecommunication Standard

c)          Universal Mobile Telephone System

d)         Unified Mobile Transfer System.

xiv)      GSM up-linl frequency band is

a)          824 – 849 MHz c) 395 – 915 MHz

xv)        ERLANG is used to express

a)          Noise

c)          Traffic intensity

PiPS’JlZiliTGROUP -B ( Short Answer Type Questions )

Answer any three of the following.     3×5 = IE

Define litre acceptance angle and numerical aperture of a fibre. How u ? t’ .ey related ? if numerical aperture of gin optical fibre is 0-3, what will be its ac;ejtui.ee angle ? What is the maximum value of V-number for an SMF ?                                           2 + ! ; 1 + 1

What do you u.ean by drive circuit of an optical source ? Draw suitable drive circuits for analog modulation of LED. Why the LASER is more suitable in long heal ii al communication ?           ± -i i. -i- 2

What are the drawbacks of APD over p-i-n detector ? GaAs has a band gap ener. > of 1 43 eV at 300K. Determine the wavelength above which an intrinsic photodetector fabricated irom this material will cease to operate.’What is dark current ? ^2 -i 1

Draw dte simplest block diagram of a Ku band satellite transponder aau e;q la a t ;a function oi each block.                        2 -> 3

What do you mean by Frequency reuse ? How is it implemented ? Explain the importance of frequency reuse in mobile communication.   2 + 3

GROUP -C ( Long Answer Type Questions )

Answer any three of the following.    3 x i5 = h 5

aj Draw and explain the schematic diagram of an Optical Communication S. ,a .i .

b)         Explain why the performance of multimode grade index fibre is improved tvc:*. multimode step Index fibre ?

c)          The refractive index of the core of Step index fibre is ! 4£ and relative raa„..\ .. index difference between core and cladding of the fibre is 2% ; then esiu…it!

i)         ‘ Numerical Aperture

ii)         Acceptance angle in air

iii)   The critical angle at the core cladding interface within the fibre ? 4 ,• £.• 6

3. a) Discuss Lhe direct and indirect band gap semiconductor ?

b)          Explain .a>- working principle of p-rtJunction photodiode and p-i-n photodiod

c)          With derivation, px ove that the optical emitted rom LSD F = Plut fn ( n + i ) 2.                                         4 + 5

  1. aj What is adjacent and co-channel interference ?

b)          Derive an expression relating signal to noise ratio arid frequency reuse ratio therefore calculate the value of frequency reuse ratio and cluster size for AMPS.analogy FM system. Consider path loss exponent k » 4. 5 + 6 + 2

  1. a)  Draw mid explain GSM architecture.

b)         Discuss GPRS location management procedure.

c J        Explain how data transfer through GPRS network and routing occurs. 4 5 i l. Wale short notes on any three of the following :            3

a)          Dual reilector cassegrain antenna

b)          Temperature stabilisation of LASER diode

e)         3 G over 2 G wireless network

d)          Optica! power budgeting

ej    Cordless telephone system.

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