Optimizing the transmit power for slow fading channels

We consider the design of power-adaptive systems for minimizing the average bit-error rate over flat fading channels. Channel state information, obtai ned through estimation at the receiver, is sent to the transmitter over a f eedback channel, where it is used to optimally adapt the transmit power. We consider finite-state optimal policies to reflect the limitations of the f eedback channel. We develop an iterative algorithm that determines the opti mal finite-state power control policy given the probability density functio n (pdf) of the fading. Next, we present a discretized formulation of the pr oblem and obtain a suboptimal solution via standard dynamic programming tec hniques. The discretization of the problem enables us to obtain a suboptima l policy for arbitrary fading channels for which the analytic expression of the fading probability density function is not available. Simulation resul ts are used to draw conclusions regarding the effects of limited feedback c hannel capacity, delay and number of states on the bit-error-rate performan ce of the proposed policies under slow and moderate fading conditions.