  Visible light communications (VLC) is gaining interest as one of the enablers
of short-distance, high-data-rate applications, in future beyond 5G networks.
Moreover, non-orthogonal multiple-access (NOMA)-enabled schemes have recently
emerged as a promising multiple-access scheme for these networks that would
allow realization of the target spectral efficiency and user fairness
requirements. The integration of NOMA in the widely adopted orthogonal
frequency-division multiplexing (OFDM)-based VLC networks would require an
optimal resource allocation for the pair or the cluster of users sharing the
same subcarrier(s). In this paper, the max-min rate of a multi-cell indoor
centralized VLC network is maximized through optimizing user pairing,
subcarrier allocation, and power allocation. The joint complex optimization
problem is tackled using a low-complexity solution. At first, the user pairing
is assumed to follow the divide-and-next-largest-difference user-pairing
algorithm (D-NLUPA) that can ensure fairness among the different clusters.
Then, subcarrier allocation and power allocation are solved iteratively through
both the Simulated Annealing (SA) meta-heuristic algorithm and the bisection
method. The obtained results quantify the achievable max-min user rates for the
different relevant variants of NOMA-enabled schemes and shed new light on both
the performance and design of multi-user multi-carrier NOMA-enabled centralized
VLC networks.
