A bandwidth efficient pilot symbol technique for coherent detection of turbo codes over fading channels

A method is proposed to implement coherent detection of turbo coded binary phase shift keying (BPSK) signals transmitted over frequency-flat 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 parity 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, estimates of the complex channel gain and variance of the additive noise are first computed by filtering observations of the pilot symbols. As the turbo decoder performs its iterations, the channel estimates are refined by using information produced by the decoder. The performance of the proposed technique is assessed by computer 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).