Science and Development Network (SciDev.Net)
For each communication link, the channel encoder or decoder and modulator or demodulator can be optimized for the specific channel characteristics. Since the bits being transported are regenerated at each link, there is no noise accumulation. The preceding framework is based on a separation of source coding and channel coding. Not only does this separation principle yield practical advantages, but the authors are also reassured by the source - channel separation theorem of information theory, that it is theoretically optimal for point-to-point links (under mild conditions). While the separation approach is critical to obtaining the economies of scale driving the growth of digital communication systems, they note in passing that joint source and channel coding can yield superior performance.