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JNTU B.Tech IV SATELLITE COMMUNICATIONS Previous Question Paper (July - 2021 - R15)
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A satellite is in an elliptical orbit with a perigee of 1200 km and an apogee of 4000 km. Using the mean earth radius of 6378.16 km, find the period of the orbit and the eccentricity of the orbit.
Answer
Given: Perigee height hp = 1200 km, Apogee height ha = 4000 km, Earth radius Re = 6378.16 km. The distances from the center of the Earth are rp = Re + hp = 7578.16 km and ra = Re + ha = 10378.16 km. The semi-major axis a = (rp + ra) / 2 = 8978.16 km. The eccentricity e = (ra - rp) / (ra + rp) = 2800 / 17956.32 ≈ 0.1559. The orbital period T = 2π * sqrt(a3 / μ), where μ = 3.986004418 * 105 km3/s2. Calculating a3 = 7.237 * 1011 km3, T = 2π * sqrt(7.237 * 1011 / 3.986 * 105) ≈ 8472 seconds, which is approximately 141.2 minutes.
Two different geostationary satellites in INSAT series are located at 64°E and 84°E. Determine the line of distance between the two satellites orbiting the earth at a height of about 34000 km above the surface of the earth. Assume radius of the earth to be 6370 km.
Answer
Given: Satellite heights h = 34000 km, Earth radius Re = 6370 km. The orbital radius r = Re + h = 40370 km. The satellites are at longitudes θ1 = 64°E and θ2 = 84°E, so the angular separation Δθ = 20°. In a geostationary orbit, the satellites lie in the equatorial plane. The distance d between two points on a circle of radius r separated by an angle Δθ is given by the chord length formula: d = 2 * r * sin(Δθ / 2). Substituting the values: d = 2 * 40370 * sin(20° / 2) = 80740 * sin(10°) ≈ 80740 * 0.1736 ≈ 14016.46 km.
Explain the relation between transmitted power and received power. Also show in detail how the difference between these two powers is accounted for.
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Low earth orbit satellites use mainly L band, with ranges varying from 1200 km to 2,700 km. Calculate the maximum and minimum path loss from earth to a satellite, in dB, for the uplink frequency of 1.8 GHz, and the downlink frequency of 1.7 GHz.
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Ionospheric scintillation effects are variable in both time and location. What causes the time variability and Over what periodic interval of time worst effects are expected to be observed repeating on a given satellite link? Also Within what latitude range on the earth’s surface are these effects the worst for geostationary satellite links?
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With a neat diagram discuss the three CDMA techniques. Also list out the advantages of each of these techniques.
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Calculate the timing measurement if C/N = -18.4, Gp=1034, losses = 1.4dB, power ratio is 10. Given the theoretical noise bandwidth of the correlator is 2MHz.
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Find the maximum Doppler shift of the L1 signal frequency for a GPS satellite at an altitude of 30,600 km when the satellite has an elevation angle of 30°.
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If a slotted ALOHA protocol is used to share a 53kbps satellite channel and the frames are 800 bits long. Find the maximum throughput of the system in frames/second.
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How is a message transmitted in FDMA? Discuss.
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A satellite is orbiting the equatorial plane with a period from perigee to perigee of 12h. If equatorial radius of the earth is 6738.2424km and eccentricity is 0.001, calculate the semi major axis.
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Design a transmitting earth station to provide a clear air C/N of 24 dB in a C-band transponder at a frequency of 5.236 GHz. Use an uplink antenna with a diameter of 8 m and an aperture efficiency of 64%, and find the uplink transmitter power required to achieve the required C/N. The uplink station is located on the 3 dB contour of the satellite footprint. Allow 0.4 dB for clear air atmospheric attenuation and other losses.
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Explain the Satellite switched TDMA and CDMA.
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“The problem of uplink attenuation in rain is most severe for 30/20 GHz uplinks with small margins.” How can we overcome this problem?
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Derive the equation for expected delay of a packet in M/G/1 queuing systems.
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A satellite downlink at 10GHZ operates with a transmit power of 8w and an antenna gain of 34.2db. Calculate the EIRP in Dbw.
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