Linear LLR approximation for LDPC decoding using a Gaussian approximation

In fading channels, the computation of Loglikelihood ratio (LLR) without channel state information (CSI) is complicated. The maximum capacity linear approximation (MCLA) has been proposed to reduce the computational complexity of LLR. However, the computation of LLR' probability density function (PDF) is still complicated due to numerical integrations. To overcome this shortage, we propose a simple Gaussian approximation to PDF of LLR. Using our proposed method, the computational complexity is significantly reduced and the BER performance is still very close to that of the MCLA in uncorrelated Rayleigh fading channels.