Flexible multi-access scheme for indoor VLC using multiband N-dimensional CAP and a wide field-of-view white laser transmitter.

Visible light communication (VLC) has emerged as a crucial technology for next-generation (6 G) communication, integrating illumination and data transmission. However, the modulation bandwidths of light-emitting diodes (LEDs) are relatively limited, which restricts communication capacity. In contrast, laser diodes (LDs) offer distinct advantages, including high luminous flux, compact size, and large modulation bandwidth. Notably, white LDs with a wide field-of-view (FOV) are particularly suitable for indoor VLC applications, as they can cover a broad range. To meet the diverse requirements of indoor access devices, we propose a multiband N-dimensional carrierless amplitude and phase (multiband N-D CAP) modulation technique. In multiband N-D CAP, N users are distributed across multiple sub-bands, where frequency division multiplexing is applied between sub-bands and code division multiplexing is adopted within each sub-band. This structure enables adaptable configurations of sub-band numbers, user counts, and data rates, providing superior flexibility and compatibility compared to traditional multiband CAP or N-D CAP techniques. In our VLC system with a wide FOV white laser transmitter, we tested four configurations for 12 users with different user distributions or data rates. Results show total data rates ranging from 3.45 Gbps to 2.75 Gbps at 1.0 m, and from 1.35 Gbps to 1.00 Gbps at 2.5 m, with an effective FOV angle of approximately 25°. These results underscore the potential of multiband N-D CAP modulation for flexible and efficient indoor VLC access.