A Bandwidth Efficient Pilot Symbol Technique for Coherent Detection of Turbo (Codes over Fading Channels*

A method is proposed to implement coherent detect ion of turbo coded binary phase shift keying (BPSK) signals transmitted over frequency-fiat Rayleigh fading channels. After turbo encoding, a subset of the parity symbols is punctured and replaced with known pilot symbols. Because the pilot symbols replace existing pamity symbols, no bandwidth expansion is required. However, there is a restriction on the set of possible pilot symbol spacings and interleaver sizes. At the receiver, estimi~tes of the complex channel gain and variance of the aciditive noise are first computed by filtering observations of the pilot symbols. As the turbo ciecoder performs its iterations, the channel estimates are refined by using information produced by the decoder. The performance oft he proposed technique is assessed lbycomputer simulation, and compared for two normalized fade rates with both perfect coherent detection (corresponding to perfect knowledge of the fading process and noise variance) and differential detection of differentially-encoded binary phase shift keying (DPSK).