CHANNEL
| Collection | International Encyclopedia of Systems and Cybernetics |
|---|---|
| Year | 2004 |
| Vol. (num.) | 2(1) |
| ID | ◀ 402 ▶ |
| Object type | General information |
- “The instruments (objects, events, and their properties) that produce transmission” (R. ACKOFF & F. EMERY, 1972, p.190).
- “That part of a communication system along which messages are conveyed, or its mathematical representation” (G. PASK, 1961, p.114).
R. ACKOFF and F. EMERY give the following examples: “In sending a letter, the postal service is the channel, in telephone communication it is the telephone system, and in speech it is the atmosphere” (Ibid).
There are numerous different types of channels. Some examples are:
- a telephone wire
- electro magnetic waves of well defined frequency
- atmosphere as transmitter of sounds
- the operating system within a computer
- defined paths within the nervous system
To be transmissible through a specific channel, information must be translated into the kind of signals proper to the channel. This is done by a sender using a code.
The physical code to be used should not be confused with the code expressing meanings. Generally, both are needed.
A physical channel has a specific capacity to convey so many signals per time-unit, as a maximum. The main concern of an engineer is the choice of the best possible type of channel corresponding to some class of signals to be transmitted; the protection of this channel against outside perturbations (noise) and, if this is not absolutely possible, calculating the number of repetitions of the signals (redundancy) needed to maintain intelligibility.
Of course, this complex process of communication is used to transmit information, but this should be understood in a quantitative sense. For example, a channel may be able to carry so many bits per second, when in optimal condition, i.e. noiseless. This is however never possible in any real channel. And, taking noise into account, the transmitter should allow for so many bits of redundancy per second. It is in this sense that information can be quantified.