IEEE TRANSACTIONS ON INFORMATION THEORY 1 Communication Over Fading Channelswith Delay

We consider a user communicating over a fading channel with perfect channel state information. Data is assumed to arrive from some higher layer application and is stored in a buuer until it is transmitted. We study adapting the user's transmission rate and power based on the channel state information as well as the buuer occupancy; the objectives are to regulate both the long-term average transmission power and the average buuer delay incurred by the traac. Two models for this situation are discussed; one corresponding to xed-length/variable-rate codewords and one corresponding to variable-length codewords. The trade-oo between the average delay and the average transmission power required for reliable communication is analyzed. A dynamic programming formulation is given to nd all Pareto optimal power/delay operating points. We then quantify the behavior of this trade-oo in the regime of asymptotically large delay. In this regime we characterize simple buuer control policies which exhibit optimal characteristics. Connections to the delay-limited capacity and the expected capacity of fading channels are also discussed.