Optimal turbo decoding metric generation in a pilot assisted coherent wireless communication system

摘要

In this paper, we derive the exact expressions of the log-likelihood ratio (LLR) values generated from coherent demodulation using the channel coefficient estimated based on the pilot signal. These results are obtained based on the analytical results given in Ling (1999). It is shown that for Rayleigh fading channels, the LLR values for turbo decoding are the scaled dot products of the channel estimate and the sample of the coded bits. Examples of the computation of the LLR values are given. Considerations and principles for practical implementations are discussed. Simulation results are provided to demonstrate the importance of choosing the proper scaling factor in achieving optimal decoding performance.