  Orthogonal frequency division multiplexing (OFDM) based non-orthogonal
multiple access (NOMA) has increased complexity and reduced spectral efficiency
in visible light communications (VLC) NOMA compared to radiofrequency NOMA due
to non-negative real value constraints on transmit symbols. To address this
issue, we propose a generalized non-OFDM based scheme for two scenarios of
indoor VLC; i) Multiple access channel (MAC), ii) Broadcast channel (BC). We
evaluate the performance of the proposed scheme for MAC using successive
interference cancellation (SIC) based decoding, joint maximum likelihood (JML)
decoding, and a combination of SIC and JML decoding. For BC, we evaluate the
performance using SIC based decoding. It is observed that, for MAC, the
proposed scheme with JML decoding performs better than the state-of-the-art
orthogonal multiple access both in terms of bit error rate (BER) and
computations. For BC, the proposed scheme is computationally efficient with
trade-off on BER.
