By: Dr. N. Ioannides (Feb. 2010)CT0004N - L.05 - Satellite Communications - pp 1/28 Satellite Communications Saroj Regmi Lecture 05 CT0004N Principles of Comms Systems

By: Dr. N. Ioannides (Feb. 2010)CT0004N - L.05 - Satellite Communications - pp 2/28 Introduction to Wireless Communications. Radio Wave Frequency Bands. Modes of Propagation of Signals. Mobile Radio Systems. Last Lecture: 04 Wireless Communications & Mobile Telephony

By: Dr. N. Ioannides (Feb. 2010)CT0004N - L.05 - Satellite Communications - pp 3/28 Today’s Lecture: 05 Satellite Communications Introduction to Satellites, Components of a Human-Made Satellite, Launching a Satellite, Orbital Altitudes, Satellites in Orbit, Satellite Systems, GSO, MEO and LEO Satellites, Satellite Payload.

By: Dr. N. Ioannides (Feb. 2010)CT0004N - L.05 - Satellite Communications - pp 4/28 Satellite Communications A satellite is an object that goes around, or orbits, a larger object, such as a planet.  While there are natural satellites, like the moon, hundreds of man-made satellites also orbit the Earth. Communications via satellite is a natural outgrowth of modern technology and of the continuing demand for greater capacity and higher quality in communications.  Satellite communications are reliable, survivable, secure, and a cost effective method of telecommunications. Today, there are more than 150 communications satellites in orbit, with over 100 in geosynchronous orbit.

By: Dr. N. Ioannides (Feb. 2010)CT0004N - L.05 - Satellite Communications - pp 5/28

By: Dr. N. Ioannides (Feb. 2010)CT0004N - L.05 - Satellite Communications - pp 6/ : Sputnik, the first artificial satellite placed in orbit by the Russians signalling the beginning of a new era Score, 1960 Echo and 1962 Telstar: Communications satellites launch by NASA orbiting the earth every 90 minutes providing communication to a specific region for a few minutes per orbit Syncom 2: The first communications satellite in geostationary or geosynchronous orbit was launched by NASA.  Syncom 2 could provide coverage 100% of the time, 24 hours a day to a fixed area.  Could view approximately 42% of the earth.  A system of three such satellites, with the ability to relay messages from one to the other could interconnect virtually all of the earth except the polar regions. Historical Developments

By: Dr. N. Ioannides (Feb. 2010)CT0004N - L.05 - Satellite Communications - pp 7/28 Components of a Human-Made Satellite System UPLINKDOWNLINK

By: Dr. N. Ioannides (Feb. 2010)CT0004N - L.05 - Satellite Communications - pp 8/28 Launching a Satellite A satellite must be launched at 27,500 kmph if its forward momentum is to balance the earth’s gravity thus causing it to circle the earth.  If launched at more than 38,000 kmph it will leave the gravitational pull of the Earth.  If launched at less that 27,000 kmph it will fall back to earth.

By: Dr. N. Ioannides (Feb. 2010)CT0004N - L.05 - Satellite Communications - pp 9/28 Communications antennae, radio receivers and transmitters enable the satellite to communicate with one or more ground stations, called command centres. Messages sent to the satellite from a ground station are uplinked; messages transmitted from the satellite to Earth are downlinked. Satellite Communication Capabilities

By: Dr. N. Ioannides (Feb. 2010)CT0004N - L.05 - Satellite Communications - pp 10/28 1 GHz10 GHz20 GHz30 GHz LSCKuKa FSS Uplinks FSS Downlinks Mobiles Rainfall Fading Negligible Rainfall Fading Significant Rainfall Fading Severe The most commonly used satellite frequency carrier bands are:  C band (4-8 GHz),  Ku band (10-18 GHz),  Ka band (18-31 GHz). Frequency Spectrum for Satellite

By: Dr. N. Ioannides (Feb. 2010)CT0004N - L.05 - Satellite Communications - pp 11/28 Many satellites are powered by rechargeable batteries. Solar panels recharge many satellite batteries. Other satellites have fuel cells that convert chemical energy to electrical energy, while a few rely on nuclear energy. Satellite Power Source

By: Dr. N. Ioannides (Feb. 2010)CT0004N - L.05 - Satellite Communications - pp 12/28 Small thrusters provide attitude, altitude, and propulsion control to modify and stabilize the satellite's position in space. Specialized systems such as sensors accomplish the tasks assigned to the satellite. Satellite Control System

By: Dr. N. Ioannides (Feb. 2010)CT0004N - L.05 - Satellite Communications - pp 13/28 Consist of Space Segments and Ground Segments.  The Space Segment is composed of satellites, classified as: Geostationary Orbit (GSO) satellites, Non-geostationary Orbit (NGSO) satellites, including Medium Earth Orbit (MEO) and Low Earth Orbit (LEO) satellite, according to the orbit altitude above the Earth's surface. Satellite System

By: Dr. N. Ioannides (Feb. 2010)CT0004N - L.05 - Satellite Communications - pp 14/28  The Ground Segment consists of: Gateway Stations (GSs):  Acting as network interfaces between various external networks and the satellite network.  Also perform protocol, address, and format conversions. A Network Control Center (NCC) and Operation Control Centers (OCCs):  Handle overall network resource management, satellite operation, and orbiting control. Satellite System (…2)

By: Dr. N. Ioannides (Feb. 2010)CT0004N - L.05 - Satellite Communications - pp 15/28 Satellites in Orbit (Space Segment)

By: Dr. N. Ioannides (Feb. 2010)CT0004N - L.05 - Satellite Communications - pp 16/28 LEO MEO GEO First Van Allen BeltSecond Van Allen Belt Orbital Altitudes

By: Dr. N. Ioannides (Feb. 2010)CT0004N - L.05 - Satellite Communications - pp 17/28 Circular Orbits Highly Elliptical Orbits (HEO) Polar Inclined Equatorial Polar Inclined Equatorial Satellite Orbits for Telecommunications Identify how satellites orbit the earth.

By: Dr. N. Ioannides (Feb. 2010)CT0004N - L.05 - Satellite Communications - pp 18/28 Global Hemispheric Regional or Zone Spot Satellite Footprints The footprint identifies the ground coverage of a satellites transmission.

By: Dr. N. Ioannides (Feb. 2010)CT0004N - L.05 - Satellite Communications - pp 19/28 The GSO satellite is 35,786 km above the equator, and its revolution around the Earth is synchronized with the Earth's rotation. It appears fixed to an observer on the Earth's surface, and may serve as a repeater in the sky. Its high altitude allows each GSO satellite to cover approximately one third of the Earth's surface, excluding the high latitude areas. The area of coverage of a satellite is called its footprint. Three GSO satellites are sufficient for global coverage. The majority of satellites in operation nowadays are placed in GSO. Geostationary Orbit (GSO) Satellites

By: Dr. N. Ioannides (Feb. 2010)CT0004N - L.05 - Satellite Communications - pp 20/28 The cost of launching GSO satellites is high:  Their high altitude and the inherent signal degradation calls for large antennas and large transmission power for both the GSO satellite and ground terminals. The most significant problem is the large propagation delay for GSO satellite links (typical round-trip delay is 250–280 ms, which is undesirable for real-time traffic). Geostationary Orbit (GSO) Satellites (…2)

By: Dr. N. Ioannides (Feb. 2010)CT0004N - L.05 - Satellite Communications - pp 21/28 Non-Geostationary Orbit (NGSO) Satellites NGSO Satellites are split into two different groups according to the orbit altitude above the Earth's surface:  Medium Earth Orbit (MEO) satellites.  Low Earth Orbit (LEO) satellites.

By: Dr. N. Ioannides (Feb. 2010)CT0004N - L.05 - Satellite Communications - pp 22/28 MEOs distance from the Earth's surface is from 3000 km up to the GSO orbit with a typical round-trip propagation delay of 110–130 ms. LEOs are located 200–3000 km above the Earth's surface.  For a LEO satellite the round-trip delay is 20–25 ms, which is comparable to that of a terrestrial link. LEO and MEO satellites are closer to the Earth's surface thus requiring much smaller antennae sizes and transmission power levels. MEO & LEO Satellites

By: Dr. N. Ioannides (Feb. 2010)CT0004N - L.05 - Satellite Communications - pp 23/28 Their footprints are much smaller than those of the GSO thus a constellation of a large number of satellites is necessary for global coverage.  The lower the orbit altitude, the greater the number of satellites required. Also, since satellites travel at high speeds relative to the Earth's surface, a user may need to be handed off from satellite to satellite as they pass rapidly overhead.  Therefore, steerable antennas are crucial to maintain continuous service. MEO & LEO Satellites (…2)

By: Dr. N. Ioannides (Feb. 2010)CT0004N - L.05 - Satellite Communications - pp 24/28 The satellite payload is responsible for the satellite communication functions.  Traditional satellites, especially GSOs, act as repeaters between two communication points on the ground, i.e. there is no onboard processing (OBP) making them simple and easy to implement.  Some satellite systems allow OBP, including demodulation and remodulation, decoding and recoding, transponder and beam switching, and routing to provide more efficient channel utilization.  OBP can support high-capacity intersatellite links (ISLs) connecting two satellites within line of sight. By using a sophisticated constellation with ISLs, connectivity in space without any terrestrial resource is possible. Satellite Payload

By: Dr. N. Ioannides (Feb. 2010)CT0004N - L.05 - Satellite Communications - pp 25/28 Too expensive! The satellite payload must be simple and robust since once the satellite is launched, it is very expensive and almost impossible to upgrade or repair due to the fact that the space environment, with radiation, rain, and space debris, is very harsh for satellites. Satellite Maintainability

By: Dr. N. Ioannides (Feb. 2010)CT0004N - L.05 - Satellite Communications - pp 26/28 Comparing GSO, MEO and LEO Satellites ParameterGSOMEOLEO Distance from Earth (km)36,000 3,000 – 36, – 3,000 Antenna SizeLargeMediumSmall Transmitter PowerLargeMediumSmall Round Trip Propagation Delay (ms) 250 – – – 25

By: Dr. N. Ioannides (Feb. 2010)CT0004N - L.05 - Satellite Communications - pp 27/28 Summary Introduction to Satellites, Components of a Human-Made Satellite, Launching a Satellite, Orbital Altitudes, Satellites in Orbit, Satellite Systems, GSO, MEO and LEO Satellites, Satellite Payload.

By: Dr. N. Ioannides (Feb. 2010)CT0004N - L.05 - Satellite Communications - pp 28/28 Tutorial Questions 1.Information is transmitted from the UK to the USA via a geostationary satellite. How long would it take for the signal to be received if the satellite is positioned above both ground stations at a distance of: a. 33,000 km, b. 38,000 km, c. 42,000 km, d. 55,000 km. 2.How long would it take a wave to propagate up to and down from a communications satellite if the satellite is positioned above the earth’s ground stations at a distance of: a. 30,000 km, b. 35,000 km, c. 40,000 km, d. 50,000 km. 3.What is the wavelength of a satellite microwave transmission if the uplink frequency is: a. 7 GHz b. 12 GHz, c. 14 GHz, d. 18 GHz, e. 30 GHz. 4.What is the wavelength of a satellite microwave transmission if the downlink frequency is: a. 9 GHz b. 15 GHz, c. 19 GHz, d. 25 GHz, e. 28 GHz. 5.What is the velocity of a satellite transmission if the satellite is: a. GSO, b. MEO, c. LEO