Soft-decision decoder employing eigenvalue of channel matrix in MIMO systems

This paper proposes a new soft-decision decoder employing the eigenvalue of the channel matrix as a weighting factor for conventional codes in MIMO (multi-input multi-output) systems. As is generally known, sufficient coding gain in a soft-decision decoder can only be obtained by employing the square Euclidean distance as a branch metric under AWGN (additive white Gaussian noise) channels. On the other hand, this gain cannot be obtained by simply doing the same under Rayleigh fading channels. This paper studies a suitable weighting factor for obtaining the coding gain in soft-decision decoders under Rayleigh fading channels in MIMO systems. First, we propose that the minimum eigenvalue power of the channel matrix indicates an effective carrier power in MIMO systems. Next, we propose the effective carrier power as a weighting factor for soft-decision decoders. We then calculate BER performance. According to the results, the proposed decoder gives a margin of about 5 dB at BER=10^-4 compared to a conventional decoder employing received power as a weighting factor. The results also demonstrate that the proposed weighting factor can enhance the ability of soft-decision decoders under frequency non-selective Rayleigh fading channels in MIMO systems.