Telecommunications is the communication of information over a distance.
Etymology: The term comes from a contraction of the Greek tele, meaning 'far', and communications, meaning "n : the discipline that studies the principles of transmiting information and the methods by which it is delivered (as print or radio or television etc.)"
The term is most used to refer to communication using some type of signalling, such as the aldis lamp or the transmission and reception of electromagnetic energy. This covers many media and technologies including radio, fiber optics, telegraphy, television, telephone, data communication and computer networking, although other types of signalling are also included (see Telecommunications History and especially Early Telecommunications).
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The basic elements of a simple telecommunications system are:
a.) a transmitter that operates upon the information to be communicated in such a way that some type of signal suitable for transmission is produced (this includes any encoding, compression, and error correcting operations, modulation processes if some type of carrier is to be used, or virtually any other operation that is to be performed upon the information in order to prepare it for transmission in the form of a signal)
b.) a signal that is transmitted by the transmitter
c.) a transmission medium, which constitutes a communications channel over which the signal is transmitted
d.) a receiver (such as a radio receiver) that receives and converts the signal back into usable/readable information. Conversion is usually accomplished by reversing the transmission operations performed by the transmitter upon the information (e.g., the receiver decodes, decompresses, compares error correction codes, demodulates the signal to separate it from any carrier that was used, etc. and generally performs these operations in the exact reverse order in which they were performed by the transmitter)
Note: The transmission medium and the communications channel may also be considered to exist separately - i.e., the communications channel may be considered to consist of some limitation imposed upon the transmission medium, either by the physical nature of the transmission medium with respect to the type of signal energy that will be used to transmit the information over it (for example transmission lines, which have a finite bandwidth, create a 'channel' for electromagnetic energy because of this frequency limitation), or by some process designed explicitly for that purpose (such as multiplexing). However, this distinction is not always made (since virtually any practical transmission medium has some form of physical limitation associated with it), and the transmission medium 'connecting' the transmitter to the receiver is itself considered to be a communications channel (which, of course, may be further subdivided into other 'channels' by multiplexing).
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 may therefore require a decoding mechanism to recover the message from the received signal. This mechanism can be designed to tolerate a significant degree of signal degradation. Sometimes, the final "receiver" is the human eye, ear (or other sensory organ) and the recovery of the message is done by the brain.
Telecommunication can be point-to-point, point-to-multipoint or broadcasting, which is a particular form of point-to-multipoint that goes only from the transmitter to the receivers.
One of the roles of the telecommunications engineer is to analyse the physical properties of the line or transmission medium, and the statistical properties of the message (see Information theory) in order to design the most effective encoding and decoding mechanisms.
When systems are designed to communicate through human sensory organs (mainly those for vision and hearing), physiological and psychological characteristics of human perception must be taken into account. Certain types of defect, while objectively measurable, are not readily apparent to human perception while others are disproportionately apparent. The cost of a system can therefore be reduced by choosing to omit certain information. There is clearly a tradeoff between reduced cost and user demand for higher quality, and this is an important economic consideration for those who plan systems.
The field of telecommunications is no doubt one of the most exciting occupational fields that modern society has to offer. New technology is constantly being developed and finds its applications in the technical systems that make up a telecommunications network. This creates opportunities for developing existing services further, and introducing completely new ones.
Map showing undersea telegraph cables 1891
Examples of human (tele)communications
In a simplistic example, consider a normal conversation between two people. The message is the sentence that the speaker decides to communicate to the listener. The transmitter consists of the language areas in the brain, the motor cortex, the vocal cords, the larynx, and the mouth that produce those sounds, called speech. The signal consists of the sound waves (pressure fluctuations in air particles) that can be identified as speech when properly decoded. The communications channel consists of the air (transmission medium) carrying those sound waves, and the limitations of the 'channel' include all of the acoustic properties of the surrounding space: echoes, ambient noise, reverberation. Between the speaker and the listener, there might be other devices that do or do not introduce their own distortions of the original vocal signal (for example a telephone, a HAM radio, an IP phone, etc.), although for the sake of the example, each of these would technically be considered to be a separate telecommunication system. The receiver is the listener's ear and auditory system, the auditory nerve, and the language areas in the listener's brain that will "decode" the signal into information and filter out background noise, echos, and any other interference or distortions introduced by the physical properties of the channel.
Another important aspect of the channel is called the bandwidth. A low-bandwidth channel, such as a telephone, cannot carry all of the audio information that is transmitted in normal conversation, causing distortion and irregularities in the speaker's voice, as compared to normal, in-person speech.
History of Telecommunication
The history of telecommunication predates what is commonly thought of as modern ideas and the systems currently in place today. While the Internet is a major form of telecommunication in today's world its concept is far from new.
The first telegraphs were optical telegraphs, including the use of smoke signals and beacons. These have existed since ancient times. A semaphore network invented by Claude Chappe operated in France from 1792 and remained in operation until 1846. It helped Napoleon enough that it was widely imitated in Europe and the United States. The last (Swedish) commercial semaphore link left operation in 1880.
Electromagnetic and electrical
The first electromagnetic telegraph was created by Baron Schilling in 1832. The first commercial electrical telegraph was constructed by Sir Charles Wheatstone and Sir William Fothergill Cooke and entered use on the Great Western Railway. It ran for 13 miles from Paddington station to West Drayton and came into operation on 9 April 1839. It was patented in the United Kingdom in 1837.
An electrical telegraph was independently developed and patented in the United States in 1837 by Samuel Morse. He developed the Morse code signalling alphabet with his assistant, Alfred Vail. The Morse/Vail telegraph was quickly deployed in the following two decades.
The first transatlantic telegraph cable was successfully completed on 27 July 1866, allowing transatlantic telegraph communications for the first time. Earlier submarine cable transatlantic cables installed in 1857 and 1858 only operated for a few days or weeks before they failed. The study of underwater telegraph cables accelerated interest in mathematical analysis of these transmission lines.
Early wireless communication
As far back as Faraday and Hertz in the early 1800s, it was clear to most scientists that wireless communication was possible, and many people worked on developing many devices and improvements. In 1832, James Bowman Lindsay gave a classroom demonstration of wireless telegraphy to his students. By 1854 he was able to demonstrate transmission across the Firth of Tay from Dundee to Woodhaven (now part of Newport-on-Tay), a distance of two miles.
Patents for wireless telegraphy devices started appearing in the 1860s but it was not until 1893 that Nikola Tesla made the first public demonstration of such a system. Addressing the Franklin Institute in Philadelphia and the National Electric Light Association, he described and demonstrated in detail the principles of wireless telegraphy. The apparatus that he used contained all the elements that were incorporated into radio systems before the development of the vacuum tube.
The later derived system (which used several patents of Tesla's) that achieved widespread use was demonstrated by Guglielmo Marconi in 1896. Marconi and Braun shared the 1909 Nobel Prize in physics for "contributions to the development of wireless telegraphy".
A few decades later, the term radio became more popular. Early radio could not transfer sounds, only Morse code in the tones made by rotary spark gaps. Canadian-American scientist Reginald Aubrey Fessenden was the first to wirelessly transmit a human voice (his own) in 1900.
After the public demonstrations of radio communication that Tesla made in 1893, the principle of radio communication – sending signals through space to receivers – was publicised widely. The Telsa apparatus contained all the elements of radio systems used before the development of the vacuum tube.
On 19 August 1894, British physicist Sir Oliver Lodge demonstrated the reception of Morse code signalling using radio waves using a detecting device called a coherer, a tube filled with iron filings which had been invented by Temistocle Calzecchi-Onesti at Fermo in Italy in 1884.
The first benefit to come from radio telegraphy was the ability to establish communication between coast radio stations and ships at sea. Wireless telegraphy using spark gap transmitters quickly became universal on large ships after the sinking of the RMS Titanic in 1912. The International Convention for the Safety of Life at Sea was convened in 1913 and produced a treaty requiring shipboard radio stations be manned 24 hours a day.
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