PERTANIKA JOURNAL OF SCIENCE AND TECHNOLOGY

Layered Asymmetrically Clipped Optical Orthogonal Frequency Division Multiplexing (LACO-OFDM) is a promising multicarrier modulation scheme applied in Visible Light Communication (VLC) systems. The conventional LACO-OFDM with iterative receiver introduces high computational complexity and low noise resilience, particularly under high-order modulation and multi-layer configurations. A new enhancement of the demodulation technique based on approximate Log-Likelihood Ratio (approxLLR) with a single-FFT receiver was proposed to address this limitation. The approach enhances noise robustness by estimating bit-wise confidence levels via LLR approximation, while significantly reducing complexity by eliminating the need for pairwise FFT/IFFT operations and the layer-by-layer reconstruction of clipping distortion, which are typically required in conventional LACO-OFDM with iterative receiver demodulation schemes. A significant performance improvement at a target bit error rate (BER) of 10-4, effectively demonstrated with a 4 to 5 times enhancement over the conventional scheme under moderate modulation orders. This corresponds to BER reductions of approximately ~0.705, ~0.615, and ~0.591 orders of magnitude at SNR = 10 dB for 16-QAM, 32-QAM, and 64-QAM. For symbol detection on higher layers (layer≥2), 0.7, 0.3, and 0.1 were identified as optimal scale factors for 4-QAM, 16-QAM, and 64-QAM, respectively. The approxLLR SD approach preserves energy efficiency (EE) in the power analysis, despite only slightly increasing power even with a higher layer count configuration.