OFDMA uplink channel predicion to enable frequency-adaptive multiuser scheduling

Frequency-adaptive multiuser scheduling utilizes the frequency-selective small-scale fading to allocate sub-carriers 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 of Kalman predictors used for uplink prediction, in the context of the EU WINNER project baseline design system. The paper investigates how the performance depends on the type of pilots that are transmitted from each terminal. The conclusion is that for frequency-selective channels, the use of overlapping pilots outperforms schemes where each user places pilots on exclusive time-frequency symbols. Another conclusion is that cycling the pilot patterns in time improves the performance. Channel prediction in an environment with flat Doppler spectrum is also evaluated. The resulting performance is adequate for use at vehicular velocities at 3-5 GHz carriers.