Channel Estimation, Equalization, Precoding, and Tracking

Abstract We present an overview/review of various approaches to channel estimation and equalization for wireless mobile systems with a brief discussion of channel precoding techniques. Since approaches to channel estimation depend upon the underlying channel model, we also review various approaches to channel modeling. First we present the relevant channel models including time-invariant and time-variant (doubly-selective) models where emphasis is on basis expansion modeling. Channel modeling is followed by a discussion of various approaches to channel estimation including training-based approaches, blind approaches, semi-blind approaches and hidden pilot (superimposed training) based approaches. Channel estimation approaches were followed by a discussion of channel equalization approaches including turbo-equalization for time-varying channels. A brief discussion of precoding was presented where the channel state information is available at the transmitter. We conclude with a discussion of channel tracking and combined data detection and channel tracking for time-varying channels. Channel tracking can be at block level suitable for block transmissions, or symbol-by-symbol level suitable for serial transmissions. Some of the approaches were illustrated via simulations.