| During the past decade 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 that current digital mobile radio systems are being operated at a spectral efficiency of 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 the higher data rate services economically feasible.; The 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 the system functionality such as modulation, coding, information rate, and transmission power to time varying channel conditions. In this work, the potential of adaptive coded-modulation was investigated using cut-off rate analysis in a unified way. The analysis included various effects of fading channels such as feedback delay and channel prediction error, starting from an ideal situation. It is shown that the adaptive coded-modulation can provide several folds of increase in spectral efficiency compared to a fixed modulation system employing QPSK when channel varies slowly. Also channel conditions for successful operation of the ACM systems are identified. |
