Analysis of Non-Hermitian symmetry (NHS) IFFT/FFT size efficient OFDM for multiple-client non-orthogonal multiple access (NOMA) visible light communication (VLC) system

Abstract

Orthogonal-frequency-division-multiplexing (OFDM) format is widely deployed in visible-light-communication (VLC) systems due to its high spectral efficiency. To produce real-valued OFDM signal for VLC, Hermitian-symmetry (HS) is needed during the inverse-fast-Fourier-transform (IFFT) encoding process. However the HS requirement doubles the IFFT/FFT size and increase the encoding complexity. Non-Hermitian symmetry (NHS)-OFDM schemes are proposed, but they have different limitations. In this work, we propose and investigate a non-orthogonal multiple access (NOMA) VLC network serving 2, 3 or 4 clients simultaneously using NHS-OFDM IFFT/FFT size efficient (SE) OFDM format. Numerical analysis of signal amplitude effect to the bit-error-ratio (BER) performance for different users are performed, showing that the BER < 7% forward-error-correction (FEC) limit can be achieved as long as the required signal amplitude ratio of each user is fulfilled. We also compare the proposed system with a typical example of HS-OFDM modulation, i.e. direct-current optical (DCO)-OFDM NOMA-VLC system.