Mobile Satellite Telephony System Research Assignment (Research Paper Sample)

Mobile Satellite Telephony System
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Mobile Satellite Telephony System
Introduction
A satellite refers to any object which moves around a planet in a curved path referred to as an orbit. Planets can either be natural or artificial (man-made). An example of a natural satellite to the earth is the Moon while there are several artificial satellites revolving round the earth. The satellites move freely around their respective planets a motion which is explained using Newton’s theories and equations which relate the force acting between the two objects (i.e. the planet and the satellite) to their respective gravitational forces, their masses and the radius between their centers. It is because of the attraction force between the two objects that keeps the satellite in circular motion around the planet (Maini & Agrawal, n.d.).
Several different man-made satellites move around the earth at different distances from the earth to perform different functions. Their movements are controlled and monitored depending in the various functions they are used for. Some satellites move around a single spot over the Earth’s surface while others travel over the Earth covering several kilometers of its surface. Among other functions satellites are used to track hurricanes or predict weather by meteorologists, take pictures of planets used by scientists for study, while some are used for communication purposes (Maini & Agrawal, n.d.).
Satellites used for communication help in beaming phone and Television signals around the world. These satellites have developed over the centuries and have been categorized into different groups depending on the frequencies they use example is spectrum utilized, or depending on Multiple Access Methods an example is TDMA, FDMA, or CDMA, or depending on the Earth’s orbits in which the satellites lie. The Earth’s orbits are Low Earth Orbit (LEO), Medium Earth Orbit (MEO), Highly Eliptical Orbit (HEO), and Geosynchronous Earth orbit (GEO) (Maini & Agrawal, n.d.).
Low Earth Orbit (LEO) satellites
LEO satellites revolve above the Earth at a height of about 500 to 1500. These satellites experience shorter periods of 95 to 120 minutes. The system is made up of several satellites to ensure global coverage. The use of LEO satellites has several advantages because of its low altitude, the delay time of the packets delivered is low, at approximately 10 ms hence provides faster communication. The low altitude also ensures low signal strength loss hence use of low power transmitters which are cheaper and less bulky. Because of the smaller footprints it has better frequency reuse and they high numbers of LEO satellites used provide a better global coverage including the Polar regions. Disadvantages experienced by LEO satellite systems is that for better communication and global coverage, many satellites must be used because of the smaller footprints. Also the system set up is complex and expensive because of the moving satellites and more switching required for long distance communications. In addition, gateway cost is very expensive compared to other satellites (Dev & Dev, 2017).
Medium Earth Orbit (MEO) satellites
These satellites are found at an altitude between 5000 km and 12000 above the Earth’s surface and is between the LEO and GEO satellites. It has an orbital period of approximately 6 hours. MEO satellites have higher features compared to LEO satellites while has lower features compared to Geo satellites. Compared to LEO satellites, its construction requires few satellites for global coverage which is an advantage over LEO satellites. It requires high signal power because of its higher altitude compared to LEO which is a disadvantage. It is used in ICO communication systems, GALILEO, and GPS systems. The gateway cost for these satellites is expensive compared to GEO satellites but cheaper than LEO satellites (Dev & Dev, 2017).
Highly Elliptical Orbit (HEO) satellites
These satellites revolve around the earth on elliptic orbits with low-altitude, perigee being approximately 1000 km and high-altitude, the apogee being approximately 36000 km above Earth’s surface. The elliptical orbits have an advantage of providing good coverage of the Earth surface including the Polar Regions. HEO satellites gives more options for an area coverage compared to other circular orbits. But with this, a disadvantage of HEO is because of different travelling speeds and shape of their orbits, they take longer times on some areas and shorter time on other areas ("GEO vs MEO vs LEO vs Molniya satellite | difference between GEO,MEO,LEO,Molniya satellites", 2017).
Geosynchronous Earth orbit (GEO) satellites
These are satellites position at the highest altitude of approximately 35786 km above the Earth’s surface. For complete global coverage, only three satellites are required. The satellites have an orbital period of 24 hours and a long satellite life. Advantages of these satellites is that only three satellites are required for complete global coverage and therefore no handover is necessary. Disadvantages posed by using GEO satellites is a high time delay of at least 120 milliseconds for one-way transmission taking place between the ground and the satellite. This is caused by their high distance of approximately 36,000 km above the Earth’s surface. In addition to this high time delay, the high height leads to high signal losses. To overcome the losses, large antennas and more powerful transmitters are required for user terminals on Earth. This is disadvantageous because smaller devices of GEO communications become impractical because of the large terminals required for the receivers and also, the large terminal constructions are quite bulky and expensive to build. Since the satellites are relatively fixed in their positions above the equator, they have bad elevations in areas whose latitude is above 60o. They also poorly serve the Polar regions. The gateway cost for these satellites is cheap to set up. Because of these characteristics it is suitable for use in broadcast services ("GEO vs MEO vs LEO vs Molniya satellite | difference between GEO,MEO,LEO,Molniya satellites", 2017).
Iridium
Iridium satellite telephony idea started as early as 1985 and was built by Motorola. It was aimed at wirelessly supporting global messaging, voice and paging services to users on land, sea or in air by the use of portable cellular radiotelephones. The name iridium was coined from the 77th element in the periodic table which is, Iridium element because t...