2 Brief history of satellite communication NameDate of launchnoteSPUTNIK IOctober 4, 1957the world's first orbital spacecraft. Nov 1957, Sputnik 2 and a dog escape earth and enter outerspaceSCOREDecember 18, 1958The first communication satellite which broadcasted a Christmas message for 12 days until the batteries failedEcho 1August 12, 1960a passive reflector satellite, the technology was soon abandonedApril 12, 1961First man in spaceTelstar1962First telecommunication satellite, first real-time activeIntelsatgeosynchronous earth orbit ,open to use by all nationsInmarsat1979used in international shippingACTS1993spot beams, on-board storage and processing, and all digital transmissionDirecTV1994begins Direct Broadcast to HomeIridiumMotorolawas supposed to provide mobile telephone serviceSpot beams subdivide a satellite's footprint which allows the satellite to use its portion of the spectrum more efficientlyOn-board storage and processing allows for inter-satellite communication and the caching of information until a spot beam finds its targetAll-digital transmission allows a satellite to incorporate error codes into its signal which helps to overcome rain fade.
3 SATELLITE NETWORKSA satellite network is a combination of nodes, some of which are satellites, that provides communication from one point on the Earth to another. A node in the network can be a satellite, an Earth station, or an end-user terminal or telephone.
5 Table 1 Satellite frequency bands Sky UK, Eutelsat 28A; Ku band
6 Example 16.1What is the period of the Moon, according to Kepler’s law?Here C is a constant approximately equal to 1/100. The period is in seconds and the distance in kilometers. The Moon is located approximately 384,000 km above the Earth. The radius of the Earth is 6378 km. Applying the formula, we get.
7 Example 16.2According to Kepler’s law, what is the period of a satellite that is located at an orbit approximately 35,786 km above the Earth?SolutionThis means that a satellite located at 35,786 km has a period of 24 h, which is the same as the rotation period of the Earth. A satellite like this is said to be stationary to the Earth. The orbit, as we will see, is called a geosynchronous orbit.
8 Medium Earth Orbit (MEO) Geosynchronous Orbit (GEO) Figure Satellite categoriesGEO: EXACTLY milesMEO: typically around 8000 milesHEO: var.LEO: typically between 500 and 1000 milesLow Earth Orbit (LEO)Medium Earth Orbit (MEO)Geosynchronous Orbit (GEO)
10 Geosynchronous Orbit (GEO) Satellite Systems Advantages:large area coverage, stay where they are at 35,786km (22,000miles) above the Earthsatellite rotation is synchronous to earththree satellites can cover the whole globelow system complexityDisadvantages:long propagation delay (~125 msec)high transmission power is required
12 Medium Earth Orbit (MEO) Satellite Systems Advantages:slightly longer propagation delays (~40 msec)slightly higher transmission power requiredmore expensive than LEOs but cheaper than GEOsDisadvantages:coverage spot greater than a LEO, but still less than a GEOstill the need to be in rotation to preserve their low altitude 6-8 hours to circle the earth.multiple MEO satellites are still needed to cover a region continuouslyhandovers and satellite tracking are still needed, hence, high complexity
13 Global Position System (GPS) Operated by the US Department of Defense.Orbiting at an altitude about 18,000kmConsists of 24 satellites in 6 orbits; 32 by Dec 2012At any time, about 9 (>4) satellites are visible from any point on EarthA GPS receiver has an almanac that tell the current position of each satellite
14 Figure TrilaterationIf we now our distance from three points, we know exactly where we are. (three circles meet at one signal point)
15 Application of GPS Military forces Navigation Clock synchronization, CDMA cellular system
16 Low Earth Orbit (LEO) Satellite Systems Advantages:short propagation delays (10-15 msec)low transmission power requiredlow price for satellite and equipmentDisadvantages:small coverage spotthey have to be in rotation to preserve their low altitude (90 mins period)a network of at least 6 LEO satellites is required to cover a region continuouslyhigh system complexity due the need for handovers and satellite tracking
17 Low Earth Orbit (LEO) Satellite Systems LEO satellites have polar orbitsAltitude is between kmRotation period of min.An LEO system has a cellular type of accessFootprint has a diameter of 8000 km.Delay < 20 ms, accept for telephonyWork together as a network, connected through intersatellite links (ISLs)
19 Three categories of LEO Little LEO, under 1GHz, for low date rate messageBig LEO: between 1-3 GHz, Globalstar and Iridium systemBroadband LEO provide communication similar to fibre optic network. Teledesic
20 Figure Iridium constellation The Iridium system has 66 (planning was 77) satellites in six LEO orbits, each at an altitude of 750 km.Iridium is designed to provide direct worldwide voice and data communication using handheld terminals, a service similar to cellular telephony but on a global scale ( including poles, oceans and airways).
22 Figure TeledesicInternet in the sky. Teledesic officially suspended its satellite construction work on October 1, 2002.Teledesic was a company founded in the 1990s to build a commercial broadband satellite constellation for Internet services. Using low-earth orbiting satellites small antennas could be used to provide uplinks of as much as 100 Mbit/second and downlinks of up to 720 Mbit/second. The original 1995 proposal was extremely ambitious, costing over US$9 billion originally planning 840 active satellites with in-orbit spares at an altitude of 700 km. In 1997 the scheme was scaled back to 288 active satellites at 1400 km and was later scaled back further in complexity and number of satellites as the projected market demand continued to decrease.The commercial failure of the similar Iridium and Globalstar ventures (composed of 66 and 48 operational satellites, respectively) and other systems, along with bankruptcy protection filings, were primary factors in halting the project, and Teledesic officially suspended its satellite construction work on October 1, 2002.Teledesic was notable for gaining early funding from Microsoft (investing US$30 million for an 8.5% stake), Craig McCaw, Bill Gates, Paul Allen and Saudi prince Alwaleed bin Talal, and for achieving allocation on the Ka-band frequency spectrum for non-geostationary services. Teledesic's merger with ICO Global Communications led to McCaw's companies taking control of ICO, which has successfully launched one test satellite.Teledesic has 288 satellites in 12 LEO orbits, each at an altitude of 1350 km.
24 Use Kepler’s formula to find the period and altitude for an Iridium satellite and Globalstar satellite.Iridium satellites are orbiting at 750 km above the earth surface. Globalstar satellites are orbiting at 1400 km above the earth surface. The radius of the earth 6378 km
25 Iridium satellites are orbiting at 750 km above the earth surface Iridium satellites are orbiting at 750 km above the earth surface. Considering theradius of the earth 6378 km, the radius of the orbit is then (750 km km) = 7128 km.Using the Kepler formula, we havePeriod = (1/100) (distance) 1.5 = (1/100) (7128)1.5 = 6017 s = 1.67 hours
26 Globalstar satellites are orbiting at 1400 km above the earth surface Globalstar satellites are orbiting at 1400 km above the earth surface. Consideringthe radius of the earth, the radius of the orbit is then (1400 km km) = 7778km.Using the Kepler formula, we havePeriod = (1/100) (distance) 1.5 = (1/100) (7778)1.5 = 6860 s = 1.9 hours
27 The space shutter is an example of a LEO satellite The space shutter is an example of a LEO satellite. Sometimes, it orbits at an altitude of 250 km.Using a mean earth radius of 6378km, calculate the period of the shuttle orbit.Determine the linear velocity of the shutter along this orbit.a = = 6628 kmT = 1/100 a1.5 = 5396 sec = 1.5 hoursb. The linear velocity is the circumference divided by the period(2πa)/T = (41645)/(5396) = 7.72 km/s