Satellite communications systems engineering: atmospheric effects, satellite link design, and Some Basic Communications Satellite System Definitions. 8. PDF | Al-Ahliyya Amman University Electronics and Communication Engineering. Satellite Communication Systems. Satellite Subsystem. Contents. Preface xi. CHAPTER 1. Fundamentals of Satellite Systems. 1. Basic Characteristics of Satellites. 1. Advantages of Satellite Communication.
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WCDMA, multi – carrier and OFDM systems. ❑Overview of satellite Communications; link calculations; Earth station and satellite antennas; Earth station. the significance of satellite communication and its role in present scenario. Prerequisites communication systems, in order draw benefit from this tutorial. Earth Station Antennas. ▫ Major Earth Stations Components. ▫ Satellite Communications Summary. ▫ Part 2 – Communication System Link.
Relay 1 was launched on December 13, , and it became the first satellite to transmit across the Pacific Ocean on November 22, Syncom 2 was the first communications satellite in a geosynchronous orbit. It revolved around the earth once per day at constant speed, but because it still had north-south motion, special equipment was needed to track it.
Its successor, Syncom 3 was the first geostationary communications satellite. Syncom 3 obtained a geosynchronous orbit, without a north-south motion, making it appear from the ground as a stationary object in the sky. Beginning with the Mars Exploration Rovers , landers on the surface of Mars have used orbiting spacecraft as communications satellites for relaying their data to Earth. The landers use UHF transmitters to send their data to the orbiters, which then relay the data to Earth using either X band or Ka band frequencies.
These higher frequencies, along with more powerful transmitters and larger antennas, permit the orbiters to send the data much faster than the landers could manage transmitting directly to Earth, which conserves valuable time on the NASA Deep Space Network.
This orbit has the special characteristic that the apparent position of the satellite in the sky when viewed by a ground observer does not change, the satellite appears to "stand still" in the sky. This is because the satellite's orbital period is the same as the rotation rate of the Earth. The advantage of this orbit is that ground antennas do not have to track the satellite across the sky, they can be fixed to point at the location in the sky the satellite appears.
As satellites in MEO and LEO orbit the Earth faster, they do not remain visible in the sky to a fixed point on Earth continually like a geostationary satellite, but appear to a ground observer to cross the sky and "set" when they go behind the Earth.
Therefore, to provide continuous communications capability with these lower orbits requires a larger number of satellites, so one will always be in the sky for transmission of communication signals. However, due to their relatively small distance to the Earth their signals are stronger.
In addition, satellites in low earth orbit change their position relative to the ground position quickly. So even for local applications, a large number of satellites are needed if the mission requires uninterrupted connectivity.
Low-Earth-orbiting satellites are less expensive to launch into orbit than geostationary satellites and, due to proximity to the ground, do not require as high signal strength Recall that signal strength falls off as the square of the distance from the source, so the effect is dramatic.
Thus there is a trade off between the number of satellites and their cost. In addition, there are important differences in the onboard and ground equipment needed to support the two types of missions. Main article: Satellite constellation A group of satellites working in concert is known as a satellite constellation.
Two such constellations, intended to provide satellite phone services, primarily to remote areas, are the Iridium and Globalstar systems. The Iridium system has 66 satellites. For large no of circuits Microwave communication equipment is put to use.
Earlier the equipment was large in size was using analogue technology.
In Radio the speech signals are converted to electromagnetic power. Power is transmitted in space towards the destination. Electromagnetic waves are intercepted by receiving Antenna signal power is collected at receive antenna. Omni directional — In this case radio power is transmitted uniformly in all the directions.
Such type of antenna are preferred where uniform coverage is desired such as in cellular systems. Highly Directional: Microwave, signals are transmitted in very narrow beam. Radio equipment required at the terminal: Base Band Processing equipment.
F modulation equipment, 3. Normally antenna are kept vertically hanging on the tower The Antennas are pointed towards the sector which these they 16 are supposed to cover.
Normally rooftops Should be preferred for tower construction. For providing Mobile Communication normally light weight towers mounted on the rooftops are used. It is free from Ionospheric disturbances and multi-path effects. Application of satellites for TV broadcasting,and teleconferencing, facsimile data and news dissemination is therefore, increasing rapidly.
Total VSATs including private.
Point to multipoint video service 2. It is interesting to remember here the FCC decision to favor the development of privately owned submarine cables.
Whereas a general consensus exists that satellites remain unbeatable for implementing aeronautical and maritime communication services and unidirectional systems such as data collection or broadcasting, the development of satellite systems for fixed-point communications is facing increasing difficulties. Optical fiber is a tough competitor for high-density routes, where the fiber filling coefficient may he very high and the average cost per circuit very low.
A satellite can compare much more favorably when the purpose of the system is to create an end-to-end connectivity, picking up the traffic directly at the user premises and completely bypassing all terrestrial means. This type of system is called user oriented and may prove attractive for implementing business services. Of course, the traffic capture capability of a user-oriented system will vary inversely to the ES dimensions, complexity, and cost. It is therefore of paramount importance to decrease the ES standard, thus paying the price of a much more complex satellite.
Because of these considerations, it is not difficult to understand why satellite systems complexity is quickly migrating from the ground segment to the space segment.
Major developments are expected in three areas: 1. Implementation of ISLs, at microwave or optical frequencies, which will allow unification of the present multiplicity of global, regional, and national systems so that a user may access a single satellite network by using a single earth antenna.
Development of increasingly complex satellite antennas, to achieve high directivity without loss of flexibility or reliability of the system. Development of processing repeaters, using onboard regeneration, coding-decoding, complex connection networks to achieve satisfactory connectivity among the various satellite antenna beams, and multicarrier demodulators to allow the coexistence of small-capacity carriers in the uplink with high-capacity carriers in the downlink.
More spectacular developments of the space segment may be expected in the distant future, when space transportation will become cheaper by at least one order of magnitude. An inexpensive way to put robots and men in space would allow a failed satellite to be repaired, with accompanying major impacts on reliability design, satellite development philosophy, space segment operational criteria, space segment cost.
A major decrease in space transportation cost could also make possible the development of personal communications by satellite, with an elimination of the present subdivision between fixed-point and mobile communications. In addition to technical developments already discussed, important changes could occur from an institutional viewpoint.
The satellite is an ideal deregulation tool, since it allows the creation, at reasonable cost, of a fully autonomous and fully connected network in a relatively short time. The attention of political powers has therefore become increasingly focused on satellite communications. After the formulation of the new FCC policy in favor of deregulation, the European Economic Communities EEC in an early version of their Green Book pushed for a deregulation of communication services in Europe, with an important role to be possibly assigned to satellite communications.
Despite the reaction of the European Post and Telecommunications PT Administrations, which recently caused some involution of the EEC policy, the possibilities offered by the modern space technology will continue de facto to push in the direction of a deregulation.
In the long term the presence of private operators even inside international organizations could become a real possibility. The Regulatory Bodies The International Telecommunication Union ITU is the most important regulatory body for communication systems in general and satellite communication systems in particular.
All countries take part in the work of ITU, with the aim of defining widely accepted standards, thus making it easy to implement an internationally compatible communication system. CCITT recommendations are designated by a capital letter followed by a number. The letter indicates a series of recommendations, all pertaining to the same subject; for instance, series 0 contains all recommendations for measuring instruments, series Q contains recommendations for signaling systems.
The International Radio Consultative Committee CCIR produces recommendations and reports and is responsible for the normalization of radio transmission systems. At present, the CCIR classifies communications systems in three categories: fixed-point, broadcasting, and mobile. The classification applies to both terrestrial and satellite systems. Assignment of frequency bands to the various types of terrestrial and space communications is decided in the World Administrative Radio Conferences WARCs.
Sometimes a frequency band may be assigned to terrestrial systems or to satellite systems on an exclusive basis, whereas at other times it may be assigned to both terrestrial and satellite systems.
In the second case technical coordination between terrestrial and satellite systems is needed. This applies to the coordination of terrestrial systems with satellite systems, and to the coordination of a new satellite system with existing ones or systems simply registered at the IFRB at the time the new system is submitted to the IFRB. The proliferation of satellite systems has led to the development of rigid plans for efficient use of the geostationary orbit and frequency resource.