Channel estimation and prediction for adaptive OFDMA/TDMA uplinks, based on overlapping pilots

In adaptive wireless packet transmission for multiple users, resources are allocated based on measurement and feedback of the channel qualities. Uplink channels of adaptive OFDM systems that use FDD have to be estimated and predicted based on uplink pilots transmitted by all active users. To prevent a prohibitive pilot overhead, the use of overlapping (simultaneously transmitted) pilots is considered. Kalman estimators and predictors can efficiently utilize the channel correlation in time and frequency to obtain estimates. The estimates have higher error than in the downlink case where overlapping pilots are not needed. However, the estimation and prediction MSE increases rather slowly with the number of simultaneous users. The results indicate that the accuracy is adequate for control of an adaptive transmission loop.