Analysis of two-layered adaptive transmission systems

A major challenge for personal communication systems is to meet the growing demand for various services when the frequency resources are increasingly scarce. Given the time varying nature of the radio channel, an efficient resource utilization calls for channel-adaptive transmission schemes. This paper integrates the two concepts of channels with side information and broadcast channels and introduces a model for flat Rayleigh fading channels with perfect interleaving and a single bit channel state information at the receiver. A true-level modulation constellation is deployed to send information to a two-state channel, where the state of the channel is determined by monitoring the received signal to noise ratio. The limited adaptability of the system helps gear up to a higher data rate as channel conditions improve, without any adjustment at the transmitter. A two-stage receiver, driven by the channel state estimation device, demodulates at full rate only if the channel signal to noise ratio is above a pre-set threshold. The average mutual information of the model as well as the bit probability expressions are derived for a non-uniform 8 PSK signal set. It is shown that the achievable rate is higher than that obtained using a uniform QPSK with only a negligible loss in error rate.