Scheduling and Power Allocation for Delay-Limited Multiuser Communications with Causal Channel Feedback

This paper studies the joint scheduling and power allocation problem for a block Rayleigh flat-fading channel in the downlink assuming that causal channel state information (CSI) is available at the transmitter. An outage rate probability constraint which requires a certain rate to be achieved with a specified probability in a preset number of blocks, is imposed to each user and is regarded as a delay constraint. Our aim is to determine, for each block, which user should gain access to the channel and how much power is transmitted, for minimizing the overall transmit power with individual users´ delay constraints, based on the causal CSI. The proposed approach is based on replacing the original probability constraints by upper bounds, and then convexizing the problem via relaxation. Results reveal that there is a significant performance gain between the methods with and without causal CSI at the transmitter.