A Soft De-Mapping Algorithm Combined with Zero Forcing Equalization for M-QAM-OFDM Signal

Zero forcing equalization is a low complexity method widely used in orthogonal frequency division multiplexing (OFDM) system, and M-ary quadrature amplitude modulation (M-QAM) is the most common subcarrier constellation mapping scheme. This paper presents an M-QAM soft de-mapping algorithm combined with zero forcing equalization for OFDM signal. The algorithms for three different QAM mapping schemes of 4-QAM, 16-QAM and 64-QAM are derived by formula derivation, which are friendly for hardware implementation. To verify the validity of our proposed algorithm, we conduct comparative testing with the classic exact log-likelihood ratio (LLR) approach under the additive white Gaussian noise (AWGN) channel. The simulation results demonstrate that the proposed algorithm has almost no system performance loss.