Error-correcting coding for CDMA systems

The preselected title of this paper highlights the misconception that most engineers, sometimes even communication specialists, still harbor concerning the central role of channel coding in communication system performance. More properly descriptive terms are "error-preventing", "error-protecting", or the more common "error control." The reason is that in modern communication systems, designed according to the norms of information theory, coding is an integral part of the modulation process and the optimum modulator and demodulator combine the coding and modulation, as well as the decoding and demodulation, processes into one function at both the transmitter and the receiver. This viewpoint has become commonplace for modulation systems which operate in additive Gaussian noise, with relatively high signal-to-noise ratios, at bit rates considerably greater than their transmission bandwidth. For such systems and channels, the evolution and general acceptance of trellis coded modulation (TCM) has demonstrated how modulation and channel coding can be integrated to provide superior performance.<>