In this paper, we investigate an efficient user selection and sub-band allocation algorithm in which each user transmits two-step partial CQI to reduce the amount of feedback in multi-user downlink OFDMA systems. Simulation results show that we can greatly reduce the feedback rate at the expense of negligible performance degradation compared to the full CQI feedback schemes or that we can greatly improve the performance with slightly reduced feedback rate compared to conventional partial CQI feedback schemes.

In previous literature on adaptive transmission in multiuser OFDMA systems, only uncoded case or capacity (coded with infinite length of codeword) has been considered. In this paper, an adaptive transmission algorithm for coded OFDMA systems with practical codeword lengths is investigated. Also, in order to keep the feedback overhead within a practical range, a two-step partial CQI scheme is adopted, which has both better performance and reduced feedback overhead compared to conventional partial CQI schemes. By allowing a long codeword block across all allocated sub-bands with appropriate power and modulation order allocation rather than using short codeword blocks to each sub-band, high coding gain can be obtained, which leads to performance improvement.