Adaptive Incremental Redundancy for HARQ Transmission with Outdated CSI

We analyze the throughout achievable in transmission over block-fading channels when the instantaneous channel state information (CSI) is not available at the transmitter. Assuming operation with incremental redundancy hybrid ARQ (HARQ), we propose to adapt the transmissions rates using the outdated CSI, i.e., the one experienced by the receiver in the past transmissions that resulted in a packet decoding failure. We show that, even if the CSI is fully outdated, i.e., in independently block-fading channel, the adaptation provides notable gains over a non-adaptive HARQ and for high SNR, a few transmissions are necessary to approach closely the ergodic capacity.