In communications systems, the altering of the characteristics of a signal to make the signal more suitable for an intended application, such as optimizing the signal for transmission, improving transmission quality and fidelity, modifying the signal spectrum, increasing the information content, providing error detection and/or correction, and providing data security. Note: A single coding scheme usually does not provide more than one or two specific capabilities. Different codes have different advantages and disadvantages. 2. In communications and computer systems, implementing rules that are used to map the elements of one set onto the elements of another set, usually on a one-to-one basis. 3. The digital encoding of an analog signal and, conversely, decoding to an analog signal.