ISI channel equalizers based on the factor graphs for M-QAM signalling

In this work, we consider two methods especially for high order modulation types, namely the sum-product (SP) and linear minimum mean square error (LMMSE) algorithms, which were previously utilized to equalize the inter-symbol interference (ISI) channel. Techniques for reducing the computational complexity are proposed for the SP-based method. In addition, a new technique for the calculation of the extrinsic information is proposed, which significantly improves the performance in the LMMSE equalizer. The comparison of these proposed techniques is made through simulations carried out under the fading channel assumption.