Optimized channel capacity for DWT-OFDM based NOMA with adaptive power allocation in VLC system communication

The visible light communication (VLC) is considered one of the most promising alternatives for indoor communications due to its unlicensed spectrum and inherent security features. Since light-emitting diodes (LEDs) are limited in modulation bandwidth, orthogonal frequency division multiplexing (OFDM) has been widely adopted to support high data rates, while non-orthogonal multiple access (NOMA) enhances spectral efficiency in multi-user scenarios. This work integrates discrete wavelet transform-based OFDM (DWT-OFDM) with adaptive spatial modulation (ASM) to further improve overall system performance. Compared with conventional FFT-OFDM, DWT-OFDM offers higher spectral efficiency, stronger noise resilience, and lower error probability. Moreover, particle swarm optimization (PSO) is employed to maximize channel characteristics under both line-of-sight (LOS) and non-line-of-sight (NLOS) conditions. MATLAB simulations demonstrate that the proposed system achieves a BER of 3 × 10 −6 at an SNR of 18 dB, along with a PAPR reduction exceeding 5 dB compared to FFT-OFDM, confirming its efficiency and reliability for next-generation VLC networks.