Coherent Detection of Turbo-Coded OFDM Signals Transmitted through Frequency Selective Rayleigh Fading Channels with Receiver Diversity and Increased Throughput

摘要

In this work, we discuss techniques for coherently detecting turbo codedorthogonal frequency division multiplexed (OFDM) signals, transmitted throughfrequency selective Rayleigh (the magnitude of each channel tap is Rayleighdistributed) fading channels having a uniform power delay profile. The channeloutput is further distorted by a carrier frequency and phase offset, besidesadditive white Gaussian noise (AWGN). A new frame structure for OFDM,consisting of a known preamble, cyclic prefix, data and known postamble isproposed, which has a higher throughput compared to the earlier work. A robustturbo decoder is proposed, which functions effectively over a wide range ofsignal-to-noise ratio (SNR). The key contribution to the good performance ofthe practical coherent receiver is due to the use of a long preamble (512 QPSKsymbols), which is perhaps not specified in any of the current wirelesscommunication standards. We have also shown from computer simulations that, itis possible to obtain even better BER performance, using a better code. Asimple and approximate Cramer-Rao bound on the variance of the frequency offsetestimation error for coherent detection, is derived. The proposed algorithmsare well suited for implementation on a DSP-platform.