Kalman Predictor Design for Frequency-Adaptive Scheduling of FDD OFDMA Uplinks

Frequency-adaptive multiuser scheduling in OFDM utilizes the frequency-selective small-scale fading to allocate subcarriers with advantageous signal-to-noise ratio to each user. Due to channel time-variability and delays of the transmission control loop, this will in general require channel prediction. FDD (Frequency Division Duplex) uplinks pose the most challenging prediction problem: All sub-bands that may potentially be allocated must here be predicted for all involved user terminals, based on pilots transmitted from all terminals. This poses challenges with respect to prediction accuracy, estimator complexity and pilot overhead. This paper explores the design, performance and complexity of Kalman predictors used for uplink prediction, in the context of the EU WINNER project baseline design system. One conclusion is that uplink prediction that is useful at vehicular velocities in 4G systems operating at 3-5 GHz is indeed feasible. However, the channel predictability depends crucially on the local fading environment, so predictors should be based on models of the Doppler spectrum for each terminal.