SOFT-DEMAPPING OF QAM SIGNALS

摘要

This invention concerns soft-decision demapping of Quadrature Amplitude Modulation (QAM) signals to enable soft-decision channel decoding in a communications system. In a first aspect the invention is a method for performing the soft-decision demapping of Quadrature Amplitude Modulation (QAM) signals to enable soft-decision channel decoding in a communications system. The method comprises the steps of: Extracting baseband signals from both I-and-Q channels. Sampling the baseband signals to extract a stream of complex numbers. Converting the stream of complex numbers to frequency domain vectors with components for each subcarrier frequency. Approximating bit log- likelihood ratios for each symbol directly from the real and imaginary parts of the corresponding frequency vector, without equalisation by the estimated channel. And, soft-decoding of the channel codes using the approximated log-likelihood ratios. In other aspects the invention concerns a device for performing the method and software for performing the method.