Chapter 7

The Transmission of Information

In the previous chapter, although we spoke of the recipient of a message, implying

also the existence of a dispatcher, the actual process of communicating between

emitter and receiver remained rather shadowy. The purpose of this chapter is to

explicitly consider transmission or communication channels.

Information theory grew up within the context of the transmission of messages

and did not concern itself with the appraisal of the meaning of a message. Later,

Shannon (1951) (and others) went on to study the redundancy present in natural

languages, since if the redundancy is taken into account in coding, the message

can be compressed, and more information can be sent per unit time than would

otherwise be possible (although, as we have noted in the previous chapter, much

more compression may be achieved at the level of semantics or style).

Physically, channels can be extremely varied. The archetype used to be the cop-

per telephone wire; nowadays, it would be an optical fibre. Consider the receipt

of a weather forecast. A satellite orbiting Earth emits an image of a mid-Atlantic

cyclone or a remote weather station emits wind speed and temperature. Taking the

first case, photons first had to fall on a detector array, initiating the flow of electrons

along wires. These flows were converted into binary impulses (representing black or

white; i.e., light or dark on the image) preceded by the binary address of each pixel.

In turn, these electronic impulses were converted into electromagnetic radiation and

beamed towards Earth, where they were converted back into electrical pulses used

to drive a printer, which produced an image of the cyclone on paper. This picture

was viewed by the meteorologist, photons falling on his retina were converted into

an internal representation of the cyclone in the meteorologist’s brain, and after some

processing he composed a few sentences expounding the meaning of the informa-

tion and its likely effect; these sentences were then spoken, involving the passage

of neural impulses from brain to vocal chords; the sound emitted from his mouth

travelled through the air, actuating resistance, hence electronic current fluctuations

in a microphone, which travelled along a wire to be again converted into electromag-

netic radiation, broadcast, and picked up by a wireless receiver, converted back into

acoustic waves travelling through the air, picked up by the intricate mechanism of

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J. Ramsden, Bioinformatics, Computational Biology,

https://doi.org/10.1007/978-3-030-45607-8_7

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