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Satellite Communication Random

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Published in: Civil | Networking
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The article contains solutions of some random questions on satellite communication

Kalyan K / Lucknow

7 years of teaching experience

Qualification: M.Tech - Pursuing

Teaches: Mathematics, Physics, Electrical, Electronics

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  4. D 51m 0 PDF Creator unre istered version sateliite e:alth station, usua]l" of satellite manage status of all sensors communication sys- satellite owner, or - contract. antennas may tr - htt www.sim o df.com 3.3 TELEMETRY, TRACKING, COMMAND, AND MONITORING Satellite Satellite TTC&M antenna 69 ceormed primarily b} earth station. *tellite and send sensors locatet -n the power currents in the is important and are fitted. in the communy i: 'tyr sighting devices . essential in case faulty unit mug or some otha keying (PSK) rate is normall" and thus main- I hmands of bits 01 b bin computer can of any system on the earth limits. Velociti In orbit from •hi{zng the satel- itter cama ngular mea,+ elements sequence oi again inn. and more 'f earth sta- establish& Telemetry receiver Data processor Receive antenna Tracking system Computer for attitude and orbital control Transmit antenna Tele- command transmitter Controller Ephemeris data FIGURE 3.8 Typical tracking, telemetry, command and monitoring system. by triangulation from the earth station by simultaneous range measurements. With pre- cision equipment at the earth stations, the position of the satellite can be determined within 10 m. Ranging tones are also used for range measurement, A carrier generated on board the satellite is modulated with a series of sine waves at increasing frequency, usually harmonically related. The phase of the sine wave modulation components is compared at an earth station, and the number of wavelengths of each frequency is calculated. Am- biguities in the numbers are resolved by reference to lower frequencies, and prior knowl- edge of the approximate range of the satellite. If sufficiently high frequencies are used, perhaps even the carrier frequency, range can be measured to millimeter accuracy. The technique is similar to that used in the terrestrial telurometer and in aircraft radar altimeters.
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  9. This PDF is Created by Simoo PDF Creator unregistered version - httD://www.simD0Ddf.com T kc SQLLUctZ LkutLd ' t V(ash ) 3q,15 = goo"M SCUULt1 Axes tDCo-E 0M (32 eq Pup
  10. This PDF is Created by Simpo PDF Creator unregistered version - http://www.simpopdf.com SECTION C Part a. 1. Tropospheric Scintillation 2. Cloud Attenuation and Scintillation 3. Ice Depolarization 4. Wet Surface Effects 5. Combined Effects In addition, extensive modeling updates and revisions have been developed for the traditional propagation factors such as 1. Rain Attenuation 2. Atmospheric Gaseous Attenuation 3. Ionospheric Scintillation 4. Frequency Scaling 5. Site Diversity. Detailed explanation of these effects is in-Timothy Pratt (Wiley & Sons Publication) Second Edition PAGE 298 to PAGE 316 Part b. 28 satellites inclined at 550 to the equator orbit the Earth every 11 hours and 58 minutes at a height of 20,180 km on 6 differentorbitalplanes. Each one of these satellites has up to four atomic clocks on board. Atomic clocks are currently the most precise instruments known, losing a maximum of one second make them even more accurate, they are regularly adjusted or synchronised from variouscontrolpointsonEarth.Eachsatellite transmitsitsexactpositionanditspreciseon boardclock time toEarthata frequencyof 1575.42MHz.Thesesignalsaretransmitted at the speed of light (300,000 km/s) and thereforerequireapprox.67.3mstoreacha position on the Earth's surface located directly below the satellite. The signals require a further 3.33 us for each excess kilometer of travel. If youwish to establish yourpositiononland(oratseaorintheair), all you require is an accurate clock. By comparing the arrival time of the satellite signal with the on board clock time the moment the signal was emitted, it is possibletodeterminethetransittimeofthat signal A positionhastobedeterminedinthree dimensionalspace,ratherthanonaplane. Asthedifference between a plane and three-dimensional space consists of an extra dimension (height Z), an additional third satellite must be available to determine the true position.
  11. This PDF three satellites are synchronised, the transit time in the case of all three measurements is inaccurate by the same amount.Mathematics is the only thing that can help us now.We are remindedwhen producing calculations thatifNvariablesareunknown,weneedNindependentequations. Ifthetimemeasurementisaccompaniedbyaconstantunknownerror,wewillhavefourunknownvariablesin 3- Dspace: • longitude(X) • latitude(Y) • height(Z) • timeerror(At) Itthereforefollowsthatinthree dimensional space four satellites are needed. GPS SV DATA TO SV DATA FROM SV DATA FROM SV CONTROL STATION RECEIVER GPS CONTROL Detailed explanation of these effects is in-Timothy Pratt (Wiley & Sons Publication) Second Edition PAGE 463 to PAGE 467
  12. This PDF is Created by Simpo PDF Creator unregistered version - http://www.simpopdf.com Part c. Analog Satellite Backhaul Cable or Fiber Cassette 17.3—17.8 GHz High Power Ampl ifier U pconvert Forward Error Correction and Modulate DBS Satellite Report Back 12.2—12.7 GHz Program Compress and Multiplex I-NB —Modem Outside O—Ax Cable 950—1450 MHz Inside Integrated Receiver Decoder Conditional Access IJnlink Facilitv Subscriber's Home The incoming source materials are input to video and audio compressors. The outputs of the video and audio compressors are Packetized Elementary Streams (PES), which are input to the multiplexer. A number of separate services are Time Division Multiplexed (TDM) into a single bitstream for each transponder. Chapter 7 discusses the formation, multiplexing, and transport of PESS in detail. As shown in Figure 3.1, other data can be multiplexed into the bitstream for each transponder. Program Guide information and Conditional Access entitlement messages are the most important sources in this category, but other functions, such as e-mail messages, also can be included. The Forward Error Correction (FEC) then is applied to the bitstream from the multiplexer. As discussed in detail in Chapter 5, a Reed-Solomon block code is applied first, followed by interleaving and a convolutional code. The final bitstream (information bits and FEC parity bits, sometimes called the chip stream) is input to the Quaternary (Quadrature) Phase Shift Keying (QPSK) modulator. In a digital communication system, digital modulation usually is employed, which means one of a finite set of waveforms is transmitted in a basic interval called the symbol time. In QPSK there are four possible waveforms, each of which represents two bits.
  13. This PDF is 17.3— 17.8 GHz In Band Pass Filter Band Pass Filter Local Oscillator 5.1 GHz High Power Amplifier 12.2- 12.7 GHz Out Detailed explanation of these effects is in-Timothy Pratt (Wiley & Sons Publication) Second Edition PAGE 441 to PAGE 447

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