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Shannon's model of a communications system has several components: An information source creates a message. This message is “encoded” into a signal by a transmitter. The signal passes through a channel to a receiver, which recovers a message in the original alphabet and passes it on to a destination.
Sometimes, the signal sent by the transmitter will be distorted before it is received. We therefore envision a source of noise between the transmitter the receiver. The components of Shannon's model are shown to the left.
Bear in mind that the signal being transmitted need not be in the same language as the original message. For example, we often want to transmit English text across a channel as a sequence of bits. In this case, the original alphabet is the set of English letters, while the signal is written in the binary alphabet.
In this tutorial, we will typically use the binary language in our demonstrations. The popularity and simplicity of this language makes it an excellent example. In order to emphasize the fact that the message and the signal need not be in the same language, we will usually write the original message using the symbols A and B, while the signal will be written in 0's and 1's.
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