Pilot-based estimation of time-varying multipath channels

Reliable coherent communication over multipath wireless channels requires accurate estimation of time-varying channel parameters. For coherent estimation, a key channel characteristic is the coherence time that approximately corresponds to the interval over which the channel parameters remain strongly correlated. We address linear MMSE estimation of code division multiple access (CDMA) multipath channels based on a pilot transmission. We derive a simple characterization of the estimator in terms of a bank of filters. We show that the estimator performance is primarily governed by an effective SNR that is proportional to the coherence time. We also propose two suboptimal estimators that are easy to implement and demonstrate that they deliver near-optimal performance if properly designed.