1. bitwali.com 1 WIRELESS COMMUNICATION LEC 13-14

2. bitwali.com 2 Basics: How do Satellites Work When two Stations on Earth want to communicate through radio broadcast but are too far away to use conventional means. When two Stations on Earth want to communicate through radio broadcast but are too far away to use conventional means. The two stations can use a satellite as a relay ( ریلے کرنا۔ دوسرے اسٹیشن کے پروگرام نشر کرنا ) station for their communication The two stations can use a satellite as a relay ( ریلے کرنا۔ دوسرے اسٹیشن کے پروگرام نشر کرنا ) station for their communication One Earth Station sends a transmission to the satellite. This is called a Uplink. (the link from ground station to satellite) One Earth Station sends a transmission to the satellite. This is called a Uplink. (the link from ground station to satellite) The satellite Transponder converts the signal and sends it down to the second earth station. This is called a Downlink( the link from satellite to one or more ground stations or receivers) The satellite Transponder converts the signal and sends it down to the second earth station. This is called a Downlink( the link from satellite to one or more ground stations or receivers) Some companies sell uplink and downlink services to Some companies sell uplink and downlink services to television stations, corporations, and to other telecommunication carriers.television stations, corporations, and to other telecommunication carriers. A company can specialize in providing uplinks, downlinks, or both.A company can specialize in providing uplinks, downlinks, or both.

3. bitwali.com 3 Motivation to use Satellites

4. bitwali.com 4 Communication Satellite A Communication Satellite can be looked upon as ( خیال کرنا ) a large microwave repeater. A Communication Satellite can be looked upon as ( خیال کرنا ) a large microwave repeater. It contains several transponders which listens to some portion of spectrum, amplifies the incoming signal and broadcasts it in another frequency to avoid interference with incoming signals. It contains several transponders which listens to some portion of spectrum, amplifies the incoming signal and broadcasts it in another frequency to avoid interference with incoming signals.

5. bitwali.com 5 Satellite Uplink and Downlink

6. bitwali.com 6 Satellite Missions Source: Union of Concerned Scientists [www.ucsusa.org]

7. bitwali.com 7 Satellite Signals Used to transmit signals and data over long distances Used to transmit signals and data over long distances Weather forecastingWeather forecasting Television broadcastingTelevision broadcasting Internet communicationInternet communication Global Positioning SystemsGlobal Positioning Systems

8. bitwali.com 8 Satellite Transmission Bands Frequency BandDownlinkUplink C 3,700-4,200 MHz5,925-6,425 MHz Ku 11.7-12.2 GHz14.0-14.5 GHz Ka 17.7-21.2 GHz27.5-31.0 GHz The C band is the most frequently used. The Ka and Ku bands are reserved exclusively for satellite communication but are subject to rain attenuation

9. bitwali.com 9 Communications System Successive satellites have become larger, heavier and more costly but the rate at which the traffic capacity has increased has been much greater with each succeeding generation of satellite. Successive satellites have become larger, heavier and more costly but the rate at which the traffic capacity has increased has been much greater with each succeeding generation of satellite. The designer of a satellite communication system is not free to select any frequency and BW. The frequency and BW regulations are administered by regulatory agencies such as FCC in the United States. The bands currently used for majority of services are 4-6 GHz and 11-14 GHz with 20-30 GHz coming into service. The designer of a satellite communication system is not free to select any frequency and BW. The frequency and BW regulations are administered by regulatory agencies such as FCC in the United States. The bands currently used for majority of services are 4-6 GHz and 11-14 GHz with 20-30 GHz coming into service.

10. bitwali.com 10 Coverage of a Satellite

11. bitwali.com 11 Circular Orbit Circular Orbit  Centre at earth centre. This is the only orbit that can provide full global coverage by one satellite. In communications where the instantaneous transfer of information is required, full global coverage could be achieved with a series of satellites, separated in time and angle.  Elliptically Inclined Orbit An orbit of this type has unique properties that have been successfully used by some communications satellite systems, For this system, the elliptical orbit has an angle of inclination of 63° and a 12-hour orbit period. By using three satellites, suitably phased, continuous coverage of the polar region can be provided that would not be covered by other orbits.( mostly 0<i<90) Circular Equatorial orbit (Geostationary) Circular Equatorial orbit (Geostationary) A satellite in a circular orbit at 35,800 km has a period of 24 hours, and consequently appears stationary over a fixed point on the Earth's surface. A satellite in a circular orbit at 35,800 km has a period of 24 hours, and consequently appears stationary over a fixed point on the Earth's surface. Polar Orbit Polar Orbit A polar orbit is one in which satellite passes above both poles of the body. (i=90)

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13. bitwali.com 13 Source: Union of Concerned Scientists [www.ucsusa.org] Satellite Orbits

14. bitwali.com 14 Why Satellites remain in Orbits

15. bitwali.com 15 Space Segment Satellite Launching Phase Satellite Launching Phase Transfer Orbit Phase Transfer Orbit Phase Deployment Deployment Operation Operation Retirement Phase Retirement Phase

16. bitwali.com 16 Satellite System Elements

17. bitwali.com 17 Ground Segment Collection of facilities, Users and Applications Collection of facilities, Users and Applications Earth Station = Satellite Communication Station Earth Station = Satellite Communication Station (Fixed or Mobile)

18. bitwali.com 18 Transponders Communication equipment in satellites composed of one or more antennas which receive and transmit over wide bandwidths at microwave frequencies and a set of receivers and transmitters that amplify and retransmit the incoming signals The receiver transmitter units are Transponders Communication equipment in satellites composed of one or more antennas which receive and transmit over wide bandwidths at microwave frequencies and a set of receivers and transmitters that amplify and retransmit the incoming signals The receiver transmitter units are Transponders Signals transmitted by an earth station are received at the satellite by either a zone beam or a spot beam antenna. Zone beams can receive from transmitters anywhere within the coverage zone, whereas spot beams have limited coverage Signals transmitted by an earth station are received at the satellite by either a zone beam or a spot beam antenna. Zone beams can receive from transmitters anywhere within the coverage zone, whereas spot beams have limited coverage

19. bitwali.com 19 Frequency Bands Allocated to the FSS Different Frequency bands are allocated to different services at World Radio-communication Conferences (WRCs). Different Frequency bands are allocated to different services at World Radio-communication Conferences (WRCs). Allocations are set out in Article S5 of the ITU Radio Regulations. Allocations are set out in Article S5 of the ITU Radio Regulations. It is important to note that (with a few exceptions) bands are generally allocated to more than one radio services. It is important to note that (with a few exceptions) bands are generally allocated to more than one radio services. CONSTRAINTS CONSTRAINTS Bands have traditionally been divided into “commercial" and "government/military" bands, although this is not reflected in the Radio Regulations and is becoming less clear-cut as "commercial" operators move to utilize "government" bands.Bands have traditionally been divided into “commercial" and "government/military" bands, although this is not reflected in the Radio Regulations and is becoming less clear-cut as "commercial" operators move to utilize "government" bands.

20. bitwali.com 20 Advantages of Satellite Communication Can reach over large geographical area Can reach over large geographical area Easy to install new circuits Easy to install new circuits Circuit costs independent of distance Circuit costs independent of distance Broadcast possibilities Broadcast possibilities Temporary applications (restoration) Temporary applications (restoration) Mobile applications Mobile applications Terrestrial ( زمینی ۔ زمین سے متعلق ۔ زمین پر موجود ) network "by- passs" Terrestrial ( زمینی ۔ زمین سے متعلق ۔ زمین پر موجود ) network "by- passs" Provision ( مہیا کرنا ) of service to remote or underdeveloped areas Provision ( مہیا کرنا ) of service to remote or underdeveloped areas User has control over own network User has control over own network

21. bitwali.com 21 Disadvantages of Satellite Communication Large up front capital costs (space segment and launch) Large up front capital costs (space segment and launch) Interference and propagation delay Interference and propagation delay Congestion of frequencies and orbits Congestion of frequencies and orbits

22. bitwali.com 22 When to use Satellites When the unique features of satellite communications make it attractive When the unique features of satellite communications make it attractive When the costs of communication are lower than terrestrial ( زمینی ۔ زمین سے متعلق ۔ زمین پر موجود ) routing When the costs of communication are lower than terrestrial ( زمینی ۔ زمین سے متعلق ۔ زمین پر موجود ) routing When it is the only solution When it is the only solution Examples: Examples: Communications to ships and aircraft (especially safety communications)Communications to ships and aircraft (especially safety communications) TV services - contribution links, direct to cable head, direct to homeTV services - contribution links, direct to cable head, direct to home Data services - private networksData services - private networks Overload trafficOverload traffic Delaying terrestrial investmentsDelaying terrestrial investments 1 for N diversity1 for N diversity Special eventsSpecial events

23. bitwali.com 23 When to use Terrestrial (زمینی ۔ زمین سے متعلق ۔ زمین پر موجود) PSTN - satellite is becoming increasingly uneconomic for most trunk telephony routes PSTN - satellite is becoming increasingly uneconomic for most trunk telephony routes but, there are still good reasons to use satellites for telephony such as: very long distance traffic and remote locations. Land mobile/personal communications - in urban areas of developed countries new terrestrial infrastructure is likely to dominate (e.g. GSM, etc.) Land mobile/personal communications - in urban areas of developed countries new terrestrial infrastructure is likely to dominate (e.g. GSM, etc.) but, satellite can provide fill-in as terrestrial networks are implemented, also provide similar services in rural areas and underdeveloped countries but, satellite can provide fill-in as terrestrial networks are implemented, also provide similar services in rural areas and underdeveloped countries

24. bitwali.com 24 Basics: Factors in satellite communication (cont.) Other impairments( نقائص ) to satellite communication: Other impairments( نقائص ) to satellite communication:  The distance between an earth station and a satellite (free space loss).  Satellite Footprint: The satellite transmission’s strength is strongest in the center of the transmission, and decreases farther from the center as free space loss increases.  Atmospheric Attenuation caused by air and water can impair the transmission. It is particularly bad during rain and fog.

25. bitwali.com 25 Atmospheric Losses Different types of atmospheric losses can disturb radio wave transmission in satellite systems: Different types of atmospheric losses can disturb radio wave transmission in satellite systems: Atmospheric absorptionAtmospheric absorption Atmospheric attenuationAtmospheric attenuation Traveling ionospheric disturbancesTraveling ionospheric disturbances

26. bitwali.com 26 Atmospheric Absorption Energy absorption by atmospheric gases, which varies with the frequency of the radio waves. Energy absorption by atmospheric gases, which varies with the frequency of the radio waves.

27. bitwali.com 27 Atmospheric Attenuation Rain is the main cause of atmospheric attenuation (hail, ice and snow have little effect on attenuation because of their low water content). Rain is the main cause of atmospheric attenuation (hail, ice and snow have little effect on attenuation because of their low water content).

28. bitwali.com 28 Traveling Ionospheric Disturbances Traveling ionospheric disturbances are clouds of electrons in the ionosphere that provoke ( اکسانا ) radio signal fluctuations which can only be determined on a statistical basis. Traveling ionospheric disturbances are clouds of electrons in the ionosphere that provoke ( اکسانا ) radio signal fluctuations which can only be determined on a statistical basis.

29. bitwali.com 2929 Types of Waves Transmitter Receiver Earth Sky wave Space wave Ground wave Troposphere ( 0 - 12 km) Stratosphere ( 12 - 50 km) Mesosphere ( 50 - 80 km) Ionosphere ( 80 - 720 km)

30. bitwali.com 3030 Radio Frequency Bands Classification BandInitialsFrequency RangeCharacteristics Extremely lowELF< 300 Hz Ground wave Infra lowILF300 Hz - 3 kHz Very lowVLF3 kHz - 30 kHz LowLF30 kHz - 300 kHz MediumMF300 kHz - 3 MHzGround/Sky wave HighHF3 MHz - 30 MHzSky wave Very highVHF30 MHz - 300 MHz Space wave Ultra highUHF300 MHz - 3 GHz Super highSHF3 GHz - 30 GHz Extremely highEHF30 GHz - 300 GHz Tremendously highTHF300 GHz - 3000 GHz

31. bitwali.com 3131 Propagation ( پھیلانا ٬ افزایش کرنا ٬ مشتہر کرنا, ) Mechanisms Reflection Reflection Propagation wave impinges ( اوپر گرنا۔ ٹکرانا۔ لگنا۔ تصادم ہونا ) on an object which is large as compared to wavelengthPropagation wave impinges ( اوپر گرنا۔ ٹکرانا۔ لگنا۔ تصادم ہونا ) on an object which is large as compared to wavelength - e.g., the surface of the Earth, buildings, walls, etc. - e.g., the surface of the Earth, buildings, walls, etc. Diffraction Diffraction Radio path between transmitter and receiver obstructed ( رکاوٹ ڈالنا ) by surface with sharp irregular edgesRadio path between transmitter and receiver obstructed ( رکاوٹ ڈالنا ) by surface with sharp irregular edges Waves bend around the obstacle, even when LOS (line of sight) does not existWaves bend around the obstacle, even when LOS (line of sight) does not exist Scattering Scattering Objects smaller than the wavelength of the propagation waveObjects smaller than the wavelength of the propagation wave - e.g. foliage, street signs, lamp posts - e.g. foliage, street signs, lamp posts

32. bitwali.com 3232 Radio Propagation Effects Transmitter d Receiver hbhb hmhm Diffracted Signal Reflected Signal Direct Signal Building

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34. bitwali.com 34 Propagation Modes Ground-wave propagation Ground-wave propagation Sky-wave propagation Sky-wave propagation Line-of-sight propagation Line-of-sight propagation

35. bitwali.com 35 Ground Wave Propagation

36. bitwali.com 36 Ground Wave Propagation Follows contour of the earth Follows contour of the earth Can Propagate considerable distances Can Propagate considerable distances Frequencies up to 2 MHz Frequencies up to 2 MHz Example Example AM radioAM radio

37. bitwali.com 37 Sky Wave Propagation

38. bitwali.com 38 Sky Wave Propagation Signal reflected from ionized layer of atmosphere back down to earth Signal reflected from ionized layer of atmosphere back down to earth Signal can travel a number of hops, back and forth between ionosphere and earth’s surface Signal can travel a number of hops, back and forth between ionosphere and earth’s surface Reflection effect caused by refraction Reflection effect caused by refraction

39. bitwali.com 39 Line-of-Sight Propagation

40. bitwali.com 40 Line-of-Sight Propagation Transmitting and receiving antennas must be within line of sight Transmitting and receiving antennas must be within line of sight Satellite communication – signal above 30 MHz not reflected by ionosphereSatellite communication – signal above 30 MHz not reflected by ionosphere Ground communication – antennas within effective line of site due to refractionGround communication – antennas within effective line of site due to refraction Refraction – bending of microwaves by the atmosphere Refraction – bending of microwaves by the atmosphere Velocity of electromagnetic wave is a function of the density of the mediumVelocity of electromagnetic wave is a function of the density of the medium When wave changes medium, speed changesWhen wave changes medium, speed changes Wave bends at the boundary between mediumsWave bends at the boundary between mediums