Evaluation of simplified demapping algorithm for NUQAMs using urban MIMO channel response

We have been researching a transmission system that uses high-order carrier modulation with orthogonal frequency division multiplexing (OFDM) and dual-polarized multiple-input multiple-output (MIMO) for 8K Super Hi-Vision terrestrial broadcasting. We evaluated the transmission performance of non-uniform QAMs (NUQAMs) with a simplified demapping algorithm that approximates the log-likelihood ratio (LLR) as a simple distance from a boundary of only the in-phase or quadrature component. Simulations using the MIMO channel response captured in an urban area demonstrated that the higher-order NUQAMs mitigate the degradation caused by the LLR approximation compared with conventional QAMs. The results show that the degradation in the simplified demapping algorithm in the required CNR is approximately 0.4 dB and that the LLR approximation is applicable to transmission systems with high-order NUQAMs.