A soft-demapper for coded MIMO-OFDM system

There has been increased demand for throughput in wireless communication systems in the past few decades. Orthogonal frequency division multiplexing (OFDM) combined with multiple input multiple output (MIMO) technology has been employed in many wireless standards including wireless LAN to achieve large throughput. To detect the streams of data symbols, various MIMO decoding schemes such as maximum likelihood (ML), zero forcing (ZF) and minimum mean squared error (MMSE) have been developed. These schemes provide hard data bits that have to be passed through a forward error correction (FEC) decoder. The performance of FEC decoder is improved by the use of soft information for each input bit. Therefore, it is desirable to employ a practical soft MIMO demapper at the receiver to provide the soft information in the form of log likelihood ratios (LLR´s) for each data bit that is passed through the FEC decoder. In This paper, we propose a soft MIMO demapper based on ZF and MMSE equalizers. We compare the performance and the complexity of the proposed method with that of existing methods using simulations. It is evident from the simulation results that the proposed method is suitable for the practical implementation in a wireless communication system such as wireless LAN.