TABLE OF CONTENTS We wish to transmit messages from point A to point B through space (transmission channel), or from point A to point A through time (recording channel). Any transmission of information is a voluntary energy modulation. The channel which allows the transmission is traversed by random energy impulses. This parasitic energy produces transmission errors: noise. In a binary transmission, 1 is transformed into 0, and conversely. When we have difficulties transmitting a word or a message because of the noise, we naturally tend to repeat the word or the message. It is then said that we add redundancy to the information. Now, let us consider that the message to be transmitted is coded into binary, i.e. it consists of a sequence of 1 and 0.
One of the first problems that had to be dealt with during World War II was how to contact the American spies in hostile German territory. The spies could not ask for retransmission for fear of being discovered. If the message was short it was completely destroyed by jamming if the jamming affected it. If the message was reinforced with redundancy, there was more chance than it would be affected, but it was less susceptible. The question that would then arise was the following: was a lot or little redundancy necessary for the security of these transmissions?
The answer was provided by C. Shannon (1948). He created the information theory, which led him to...
