Ground Segment and Earth Station Engineering for Satellite Communications - Coursework Example

Satellite Communication During the of this training I got to know many aspects of satellite communication and how crucial this communication has become for the interaction of the civilized society. Satellite communication can be stated to be the outcome of the civil society’s desire to have a global village. How this would be done was indicated by Sir, Arthur C Clarke in an article in 1945, when he foresaw that from communication point of view, entire earth could be covered using just three satellites, provided these satellite are placed in the ‘Geostationary orbit’ at three different locations in a manner that the three points make an equilateral triangle. Satellite communication is a form of wireless media in which the free space is used for communication. One important advantage of such media is that a large geographical area can be covered without actually carrying out the physical wired networking. Such a communication with the help of satellites is possible when the signal is sent from ground stations to the satellites placed in geostationary orbits, which in turn sends the signal back to another ground station/s located in different city, country or region depending upon the placement and alignment of the satellite. The ground based infrastructure plays a crucial role in this transmission process. The earth station closely monitors the movement of the satellite and keeps sending the signals to it. The signal are received by the transponder and then sent back. A number of commercial and domestic applications are now dependant on the satellite communication. With emerging technologies, standards, and protocols the usage of satellite communication in transmission, broadcasting and internet is also becoming cost effective. During this training I learned about the fundamentals of ground segment and earth station and how the satellite communication has evolved over the years from being a commercial facility with huge dish 30 m diameter antennas to small sized rooftop 0.6 m dish antenna for receiving DTH broadcasts. This has effectively made it possible even for the ordinary consumers to make use of satellite communication. In fact the range of advantages that satellite communication could bring in includes; Provisioning of multi-access two way communication between any two points on the earth. The cost of transmission is not dependent on the distance covered. The cost in turn depends upon the time period during which the communication takes place. Satellites are capable of handling very large bandwidth, thus a large number of consumers can be benefitted from the use of a single satellite. Satellites can provide communication and broadcast coverage even to places like valleys, dense forests, mountains and difficult terrains where it is not possible to erect communication towers or dig channels for communication lines. All this can be provided at practically no extra costs. What we require is a receiving dish antenna with other gadgets used at other similar places. Satellites can provided uniform signals without any discrimination for urban or rural areas unlike the terrestrial transmission networks where the emphasis happens to be more towards coverage of urban population. With the emergence of smaller satellite uplink gadgets like SNG and DSNG setting up of an uplink and downlink earth station has become quite handy. In fact, the DSNG (Digital Satellite News Gathering) equipment has become an integral part of the broadcasting set up all over the world. The basic components of a satellite communication system include; i. Ground Segment ii. Space Segment The Ground Segment: The ground segment or earth station is responsible for receiving the communication and broadcast signals from the satellite and then passing them on to the consumers using cables or terrestrial transmission system. These earth stations can be distinguished by the size of the earth station which varies according to the volume of the communication or broadcast traffic. Some of these earth stations can be used for twin roles i.e. for sending the signal to the satellite as well as for receiving the signal from the satellite. The earth stations are in general fixed at different places on earth surface, but we do have mobile earth stations as well, where we use mobile vehicles with mounted dish antennas moving from one place to another in case of requirements. Space Segment: The space segment comprises of a satellite orbiting around the earth in geostationary orbits. Orbit is the trajectory or path followed by the satellite while travelling around the earth. These satellites are able to stick to their orbit path making fullest use of the gravitational pull of the earth and the centrifugal force associated with the curvature of the satellite trajectory. The orbit path can also take different shapes depending upon the adjustments done by the ground stations; Elliptical orbits: An orbit of elliptical shape is formed when the angle of orbit is 640 with respect to the equatorial plane. Such an orbit helps the coverage of regions of high latitude for a large part of the orbit period when it passes through the apogee. Circular Inclined Orbits: When the altitude of the satellite is constant above the earth surface, a circular orbit is formed with the movement of the satellite. Circular Orbit: Such an orbit is also known as equatorial orbits and it is possible when no inclination is provided to the orbit. In general the factors which need to be considered for deciding the nature of the orbit vary with the nature of the mission, technology used, levels of interference etc. Some of the factors which prove crucial in deciding the selection of the orbit can be summarised as; The performance of the launchers Levels of interference prevailing within the area Period of transmission required The extent and latitude of the region to be covered by the transmission The elevation angle of the earth station Key terms associated with satellite communication are: Satellite Transponder: It is the key component of the satellite which helps in the process of transmission. The transponder is responsible for converting the frequencies, providing the signal some selective gains and subsequently sending it back to the desired earth station at a lower frequency. It is worth noting that the uplink frequency happens to be higher than the downlink frequency because in its journey upward the signal has to come across the resistance from ionospheric layers and secondly, there has to be a difference in uplink and downlink frequencies to avoid interference between the signals. TDMA: Time Division Multiple Access is the method that is used for enabling the earth stations or VSAT terminals to transmit on a single frequency. The signals are distinguished in time domain instead. The intermittent transmission in time domain are arranged in such a manner that no interferences or overlapping is there while the signals reach the satellite or when the satellite send the signals back the earth stations. This in effect means that a single carrier frequency is accessed by multiple users. FDMA: In contrast to TDMA Frequency Division Multiple Access allows users to communicate at a single time while the signals are differentiated in frequency domain. In this case the frequency band is divided into multiple channels and each channel is allotted to individual users, who can use it to communicate without the other users interfering in each other’s communication. Convergence and Telecommunication Telecommunication services delivered by satellite are playing an ever-increasing role in our lives today. Such services include Direct-to-Home (DTH), access to the Internet, VSAT services for business, mobile satellite communication (such as Inmarsat type services to ships or aeroplanes), hand-held satellite phones and global positioning system (GPS) for location determination. With the advent of compressed digital technique, the economics of delivering all such services has improved, giving an impetus to more such launches. In digital technique what really matters is 1’s and 0’s. So, for the satellite it is immaterial whether the data is a radio broadcast, some computed solution, TV signals or a phone call. This is where technology convergence and multimedia broadcasting come into play, and we start talking in terms of Value Added Services (VAS) like; High speed internet/E-mail services Video – on – demand Data communication for business in the form of: Video Conferencing, E-commerce, Telephony, Distance learning etc. Multimedia services Broadcast Information Services Security services Some of the application areas which form core components of satellite transmission are; VSAT services: Very Small Aperture Terminal i.e. VSAT services started the era of collaboration between the business houses and the telecom operators. Such services use comparatively smaller sized dish antennas (about 3-4 meters in size). These services allowed the business houses to erect a small earth station within their premises, erect a VSAT antenna and then use the services of VSAT for transmitting their own sets of documents and other communication over a broad range of dedicated communication lines. This allowed the usage of satellite communication in a cost effective manner. At the same time the telecom operators and service providers too gained dedicated customer base which in turn encouraged them to come out with further innovation. DVB: Digital Video Broadcasting is the latest contribution of satellite communication to the field of television signal transmission. DVB helps in delivering the video signals from a television station direct to the home of the consumer. The quality of DV broadcasts happen to be far better than the terrestrial broadcasts and cable TV signals. IPTV: Internet Protocol Television carries forward the convergence era by a few miles more. With this technique we can get television signals using the normal telecommunication broadband line, which we have been using for telephone services or internet services till now. IPTV is the form of television transmission which takes cue from internet protocol. IPTV is stated to be a cornerstone towards interactive television transmissions. As of now only the studio audience can take part in the TV shows, but IPTV has the potential to change all this. Now we too can be a part of any live television programme while sitting at home, without any need to go all over to the studio. With this technique television signals can be viewed without any glitches on our mobile, PDA, laptop and of course on the normal television receiving set. What is quite interesting is that if we wish not to miss our favourite programme then we can get the programme recorded while out of home, with a message from our mobile. Subsequently when we time, we can easily watch the show at our convenience. DAB: Digital Audio Broadcasts are the radio counterparts of the DVB. In this technique we get superb quality music and other radio programmes on our radio sets, mobile phone etc. from literally anywhere around the world, because we are not dependant on any radio channel in our surrounding areas. We can have the audio signals directly from the satellite itself. Read More