Adaptive Subcarrier Allocation with Imperfect Channel Knowledge Versus Diversity Techniques in a Multi-User OFDM-System

In this paper, the performance of an adaptive multi-user OFDM system with imperfect channel knowledge at the transmitter is investigated, where the ergodic capacity is taken as performance criterion. This performance is then compared to the performance achievable with the use of diversity, where no channel knowledge at the transmitter is required. For that reason, different models of imperfect channel knowledge are introduced: noisy, outdated and quantised channel knowledge, where we provide an analytical derivation of the ergodic capacity for the combinations of the different models. By means of the ergodic capacity it is shown to which grade of channel knowledge imperfectness the use of adaptive subcarrier allocation with imperfect channel knowledge is still better than the use of diversity.