Joint angle-diversity SDMA, OFDMA, and strict FFR framework for dense LiFi attocell networks

Dense deployment of LiFi and visible light communication attocells increases sensitivity to inter-cell interference, requiring coordinated interference and resource management. Angle-diversity transmitters (ADTs) for space-division multiple access (SDMA), OFDMA allocation, and fractional frequency reuse (FFR) have been studied separately under inconsistent assumptions, making it difficult to separate reuse-driven from activity- and resource-sharing effects. This work presents a protocol-level framework that unifies ADT-enabled SDMA, OFDMA, and strict FFR within an intensity-modulation direct-detection DCO-OFDM model. Each macrocell is served by a co-located multi-beam ADT defining beam-based microcells; users are classified as center or edge, and protected edge sub-bands are assigned using adjacency-aware graph coloring. Full-load and random-one-per-region regimes are evaluated in 10,000-trial Monte Carlo simulations with sensitivity sweeps over center-edge partitioning and user density. Both regimes achieve a mean SINR of about 28 dB, with no outage observed at 10 or 20 dB in the finite LOS sample. A dynamic extension incorporating mobility, receiver-orientation variation, a parametric first-order NLOS stress model, and variable multi-user OFDMA admission shows that OMN-PF improves edge-frame service success over conventional PF, while OMN-PF-A further improves high-threshold edge reliability with similar scheduled spectral efficiency. The framework provides a reproducible benchmark for dense LiFi resource management.