Scheduling in OFDMA Systems with Outdated Channel Knowledge

In wireless systems, most of nowadays scheduler assumes perfect knowledge of the channel quality indicator (CQI) at the transmitter. Unfortunately, this is never the case since the receiver (e.g. mobile users) estimates the CQI at time t-τ and feed back the estimate to the transmitter (e.g. base station). The transmitter uses then this outdated CQI at time t to allocate the radio resources to the users. This paper analyzes this issue at various mobile velocities and proposes improvement of scheduling that reduces the impact of outdated CQI. By using a channel prediction model, we determine the probability distribution function (pdf) of CQI conditioned on the outdated CQIs. We use then this (pdf) in the evaluation of the Block Error Rate (BLER) of the users´ transmission and we exploit the result in the development of a novel scheduling rule. Simulation results show improvement of the system performance without any fairness loss.