  In this work, we discuss techniques for coherently detecting turbo coded
orthogonal frequency division multiplexed (OFDM) signals, transmitted through
frequency selective Rayleigh (the magnitude of each channel tap is Rayleigh
distributed) fading channels having a uniform power delay profile. The channel
output is further distorted by a carrier frequency and phase offset, besides
additive white Gaussian noise (AWGN). A new frame structure for OFDM,
consisting of a known preamble, cyclic prefix, data and known postamble is
proposed, which has a higher throughput compared to the earlier work. A robust
turbo decoder is proposed, which functions effectively over a wide range of
signal-to-noise ratio (SNR). The key contribution to the good performance of
the practical coherent receiver is due to the use of a long preamble (512 QPSK
symbols), which is perhaps not specified in any of the current wireless
communication standards. We have also shown from computer simulations that, it
is possible to obtain even better BER performance, using a better code. A
simple and approximate Cramer-Rao bound on the variance of the frequency offset
estimation error for coherent detection, is derived. The proposed algorithms
are well suited for implementation on a DSP-platform.
