A new iterative channel estimator for the log-MAP & max-log-MAP turbo decoder in Rayleigh fading channel

Abstract

A new iterative channel estimator for turbo decoding over flat fading channel is studied using the optimum log-MAP turbo decoder and the reduced-complexity sub-optimum max-log-MAP turbo decoder. Initially, pilot symbols are used to estimate the complex channel gain and noise variance. After each decoding iteration, only the detected message bits are fed back to the channel estimator to improve the channel estimates. The moving average filter, the FIR filter and the FFT filter are studied and compared to the optimum Wiener filter. It is shown that under very slow fading rate of f/sub d/T/sub s/ = 0.005, the various filters perform closely to one another. Under a faster fading rate of f/sub d/T/sub s/ = 0.02, the FFT filter and FIR filter respectively achieved performance within about 1/2 dB and 1 dB of that achieved by the optimum Wiener filter for a BER of 3 /spl times/ 10/sup -4/. When the max-log-MAP turbo decoder is used, performance degrades by up to about 0.5 dB for the same BER compared to the case of using the log-MAP turbo decoder.