Making full use of outdated channel estimates for block by block adaptive modulations

This paper explores the potential to use accurate but outdated channel estimates for adaptive modulation. The work is novel in that the research is conditioned on block by block adaptation. First, we define a new quantity, the Tolerable Average Use Delay (TAUD), which can indicate the ability of an adaptation scheme to tolerate the delay of channel estimation results. We find that for the variable-power schemes, TAUD is a constant and dependent on the target Bit Error Rate (BER), average power and Doppler frequency; while for the constant-power schemes, it depends on the adaptation block length as well. At last, we investigate the relation between the delay tolerating performance and the spectral efficiency and give the system design criterion. The delay tolerating performance is improved at the price of lower data rate.