Telecommunications

The term Telecommunications refers to the communication of information at a distance. This covers many technologies including radio, telegraphy, television, telephone, data communication and computer networking.

Explanation

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 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 (see psychoacoustics.)

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 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.

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 is 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 is the sound waves (pressure fluctuations in air particles) that can be identified as speech. The channel is the air carrying those sound waves, and all 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.) 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.

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.