The information produced by most sources of information is not in a suitable form for transmission via a channel, so that some type of coding procedure is necessary. The channel may be analogue or digital, and will have various characteristics such as bandwidth, transmitted power, error rate etc. Two important requirements of the system may be firstly that the information be transmitted as rapidly as possible and secondly that it be transmitted with as few errors as possible. These two requirements cannot easily be attained together; in order to increase the speed the redundancy of the code used has to be low, whereas to reduce the error rate the redundancy has to be high. However, we will see that Information Theory offers a surprising compromise, whereby under certain conditions both can be achieved together. The two requirements are often referred to as source coding and channel coding respectively.
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