3.1 Information Theory and Channel Capacity

A fundamental aspect of communications theory is to consider a source of information symbols and discuss how we can represent these symbols as signals for reliable communication over a channel, while keeping physical limitations in mind. Information theory abstracts the signaling part (covered in Chapter 2) and focuses on the message information aspect. Information theory quantifies three basic concepts: the source information, the capacity of the channel to carry this information, and the coding (message representation) utilized in the channel. Information theory mathematically represents these three concepts for optimization of the information communication. If we have a source emitting symbols with an information rate that does not exceed the channel capacity, then there exists a coding technique that makes it possible to transmit the source information symbols over the channel with a small symbol error probability in the presence of channel noise. It will become more apparent that coding, here, means source coding, channel coding, and symbol to signal representation.

Let us refer back to Figure 2.1 which represents a generic channel model with the modulation of digital signals. Figure 2.1 is abstracted in Figure 3.1, as the noisy channel block. As mentioned above, channel encoding offers the means to communicate the source symbols to the destination almost error free. Source and channel coding are related in the sense that channel ...

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