Most of the existing scheduling algorithms in OFDMA and TDMA systems assume the availability of perfect channel quality indicator (CQI) at the transmitter. Unfortunately, this is unrealistic since the receiver (e.g. mobile users) estimates the CQI at time t - ¿ and feed back this CQI estimate to the transmitter (e.g. base station). The scheduler uses then this outdated CQI at time t to make the allocation. In this paper, we analyze the impact of outdated CQI on the performance of MPF (multi carrier proportional fair) scheduler in the context of downlink OFDMA system. We propose thus improvement of this algorithm in order to reduce the impact of outdated CQI. The idea consists in analyzing the probability distribution function (pdf) of the CQI with respect to an estimated CQI and using this pdf in the scheduling rule. The improvement method proposed in this paper can be applied to other scheduling rules. Simulation results show improvement of the system performance.