Adaptive coded-modulation in multipath fading channels

We have seen an explosive expansion and growth in wireless communications and a vision of communicating; any-where any-time is becoming reality. Future mobile radio systems are projected to support a data rate of up to a few Mbps. Considering current digital mobile radio systems are being operated at a spectral efficiency less than 1 bit/sec/Hz, the spectral efficiency of future wireless systems must be increased substantially to maximize the utilization of scarce radio spectrum and to make such high data rate services economically feasible. Adaptive coded modulation (ACM) is a promising way to provide a substantial improvement in spectral efficiency for slow fading channels. The basic idea is to adapt system functionality such as modulation, coding, information rate, and transmission power to varying channel conditions. In this work the potential of adaptive coded modulation was investigated using cut-off rate analysis in multipath fading channels. It was shown that the adaptive coded modulation can provide several folds of increase in spectral efficiency compared to a fixed modulation system employing QPSK when the channel varies slowly.