AMIETE – ET (OLD SCHEME)

 

Code: AE22                                            Subject: SATELLITE & SPACE COMMUNICATION

Flowchart: Alternate Process: JUNE 2010Time: 3 Hours                                                                                                     Max. Marks: 100

 

 

NOTE: There are 9 Questions in all.

·      Question 1 is compulsory and carries 20 marks. Answer to Q.1 must be written in the space provided for it in the answer book supplied and nowhere else.

·      Out of the remaining EIGHT Questions answer any FIVE Questions. Each question carries 16 marks.

·      Any required data not explicitly given, may be suitably assumed and stated.

 

 

Q.1       Choose the correct or the best alternative in the following:                                  (210)

       

a.       Typical path length from an Earth Station to a GEO satellite is ________.

 

                  (A) 35,786 km                                     (B) 38,500 km

                  (C) 28,700 km                                     (D) 25,000 km

 

             b. The Equation describing the orbit of a satellite is _________.

 

                  (A)                  (B)

                  (C)                  (D)

 

             c.  The equivalent noise temperature (Te), absolute temperature (To) & noise figure (F) are related by the expression ____________.

 

                  (A) Te = To (F+1)                                (B) Te = F (To –1)                                                            

                  (C) Te = To (1– F)                               (D) Te = To (F–1)

 

d.      VSAT networks take advantage of the wide area broadcast capabilities of

                                                                      ___________ satellites.

            

                  (A) LEO                                              (B) MEO

                  (C) GEO                                              (D) All of above

 

             e.  Signal scintillations in satellite communication systems are caused by _________.

 

                                                                              (A) Rain and ice crystals.                                      

                  (B) Atmospheric gasses

                                                                              (C) Tropospheric and ionospheric refractivity fluctuations

                  (D) Earth’s surface and objects on the surface.

 

             f.   FDMA can be used with __________.

 

                  (A) digital signals only                           (B) analog and digital signals

                  (C) analog signals only                          (D) is not used these days

 

             g.  For an equatorial orbit, any movement of the satellite about the roll axis, results in __________movement of the antenna footprint.  

 

                  (A) north and south                              (B) east and west

                  (C) rotational                                        (D) unpredicted movement

            

             h.  Carson’s rule states that the bandwidth required to transmit an FM signal is given by ____________.

 

                  (A) B= 2(Δfpk + fmax) Hz                       (B) B= 2fmax Hz                                                                 

                  (C) B= 2(Δfpk - fmax) Hz                       (D) B= 2 Δfpk Hz                                                

 

             i.   Process of combining a number of signals into a single signal is known as______.

 

                  (A) demultiplexing                                (B) multiplexing

                  (C) multiple access                               (D) none of above

 

             j.   In the case of digital transmission, degradation in the quality of the information over a satellite communication link, is measured in terms of __________.

 

                  (A)  S/N ratio                                       (B) C/N ratio

                  (C) bit error rate                                   (D) none of these

 

 

 

Answer any FIVE Questions out of EIGHT Questions.

Each question carries 16 marks.

 

            

  Q.2     a.   State Kepler’s three laws of planetary motion. What do the terms perigee and apogee mean when used to describe the orbit of a satellite around the earth?                                                                 (10)

      

             b.   The apogee and perigee of an elliptical satellite orbit are 3000 km and 200 km, respectively. Determine the eccentricity, semi-major axis and semi-minor axis of the orbit.                                             6)        

       

  Q.3     a.   Write short notes on rain attenuation and explain how the total attenuation is determined.                 (6) 

 

             b.   The best frequency range for systems serving fixed earth stations is about 1 to 10 GHz. What determines the upper limit of 10 GHz?                         (4)

 

             c.   A geostationary satellite is located at a distance of 3000 km with an operating frequency 14.25 GHz. The gain of the transmitting and receiving antennas are 15 and 20, simultaneously. If the transmitter power is 200 kW, calculate the power received by the receiving antenna.                                 (6)

       


 

  Q.4     a.   Answer the following questions in brief:

 

(i)   Why is satellite link design necessary? What information does it                 provide us?

 (ii)   What do you understand by the term ‘Effective isotropic radiated              power (EIRP)’ of the transmitter?

(iii)   What effect does increase of the G/T ratio have on the C/N                                             ratio?                                                                                                 (6)

 

             b.   Write a technical note on system noise temperature and bring out its relationship to C/N ratio.                                                                    (10)

                                                                             

Q.5       a.   What is SCPC technique and how is it different from FM-FDM as far as bandwidth is concerned?                                                            (8)

       

b.   What is T1 24-channel frame? Explain its operation.                                          (8)

                                                                                                                                                               

Q.6      a.        (i)   Explain what is meant by ‘satellite attitude’ and which are the                                                      three axes which define its attitude?

(ii)  Why is attitude control necessary?

                       (iii) Differentiate between ‘attitude control’ and ‘station                                    keeping.’                              (6)                                                                                                       

 

             b.   Draw a neat diagram showing the roll, pitch and yaw axes for a geostationary orbit.                        (4)

 

             c.   Differentiate among FDMA, TDMA and CDMA.                                              (6)

 

  Q.7     a.   What is meant by burst time plan? Explain TDMA burst structure in details.                        (10)

 

             b.   What is satellite switched TDMA and why is it used?                                          (6)

 

  Q.8     a.   What is ‘Forward Error Correction (FEC)’ and why would it normally be used on satellite circuits?                                                                       (6)

 

             b.   Write short notes on the following:

(i)                  Block codes.

                          (ii)     Convolution codes.                                                                       (25)                                                                                                                                                                                      (2´5)                                                           (6)

 

  Q.9     a.   Draw neat labeled block diagrams showing two way implementation of a VSAT network (viewed from the satellite’s perspective) and using:

(i)      Star topology (ii) Mesh topology                                                 (25)

 

             b.           (i)     What does the acronym VSAT stand for?

                          (ii)     What is the underlying concept behind VSAT systems?

                          (iii)  Why are VSAT systems designed around the use of leased           transponders and not dedicated transponders?                                      (32)