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

TL;DR

This paper presents a new coherent detection method for turbo-coded OFDM signals over Rayleigh fading channels, introducing a high-throughput frame structure, a robust turbo decoder, and effective frequency offset estimation, suitable for DSP implementation.

Contribution

It proposes a novel frame structure with a long preamble, a robust turbo decoder, and a frequency offset estimation bound, enhancing detection performance in challenging wireless channels.

Findings

Improved BER performance with longer preamble and better coding.

Effective detection over Rayleigh fading channels with frequency offset.

Feasible implementation on DSP platforms.

Abstract

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.