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TelecommunicationTelecommunication is the technique of transmitting a message, from one point or place to another with the typical additional attribute of being bi-directional. In practice it also recognizes that something may be lost in the process; hence the term 'telecommunication' covers all forms of distance communications, including radio, telegraphy, television, telephony, data communication and computer networking.
The elements of a telecommunication system are a transmitter, a medium (line) and possibly a channel imposed upon the medium (see baseband and broadband as well as multiplexing), and a receiver. The transmitter is a device that transforms or encodes the message into a physical phenomenon; the signal. The transmission medium, by its physical nature, is likely to modify or degrade the signal on its path from the transmitter to the receiver. The receiver has a decoding mechanism capable of recovering the message within certain limits of signal degradation. In some cases, the final "receiver" is the human eye and/or ear (or in some extreme cases other sense organs) and the recovery of the message is done by the brain (see psychoacoustics.)
The art of the telecommunications engineer is to analyse the physical properties of the line or transmission medium, and the statistical properties of the message in order to design the most effective encoding and decoding mechanisms.
When systems are designed to communicate through human sense organs (mainly vision and hearing), physiological and psychological characteristics of human perception will be taken into account. This has important economic implications and engineers will research what defects may be tolerated in the signal yet not affect the viewing or hearing experience too badly.
The car passing by is an example of an important property of the channel called noise. Another important aspect of the channel is called the bandwidth, and you would become very aware of the effects of a limited bandwidth if you were now talking to your friend on a telephone or a walkie-talkie.
At the time of publication, telecommunication systems were predominantly based on analog electronic circuit design. The introduction of mass-produced digital integrated circuits has enabled telecom engineers to take full advantage of information theory. From the demands of telecom circuitry, a whole specialist area of integrated circuit design has emerged called digital signal processing.
Possible imperfections in a communication channel are: shot noise, thermal noise, latency, non-linear channel transfer function, sudden signal drops, bandwidth limitations, signal reflections (echos). More recent telecommunications systems take advantage of some of these imperfections to actually improve the quality of the channel.
Modern telecommunication systems make extensive use of time synchronization. There is a link between the development of telecommunications and very fine-grained (microsecond) time-keeping technology. Until the recent rise of the use of IP Telephony, most modern, wide-area telecommunications systems were synchronised to atomic clocks, or to secondary clocks synchronised to atomic time.
See modulation for examples of techniques for encoding information into analog signals.
Examples of telecommunications systems:
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