Iterative Channel Estimation, Equalization, and Decoding for Pilot-Symbol Assisted Modulation Over Frequency Selective Fast Fading Channels

A pilot-based channel estimation scheme is proposed for frequency selective Rayleigh fading channels which work in conjunction with the existing paradigm of turbo equalization. The iterative nature of the channel estimation technique provides substantial gain over noniterative methods and makes it a suitable choice for iterative equalization and decoding. The channel estimator has low complexity, is decoupled from the equalizer soft-input soft-output module, and is capable of tracking significant channel variations within a codeword. The scheme is compatible with quadratic-amplitude modulation and with both parallel concatenated convolutional and low-density parity checks coding. The proposed scheme provides an attractive low-complexity alternative to iterative receivers based on state-space models for channel parameter evolution. The use of pilot symbols is demonstrated to aid the equalizer both directly through channel estimation and indirectly through pilot message insertion.