Exploring the Potential of Utilizing Nonline-of-Sight Channels for Networking in Visible Light Communication

Visible light communication (VLC), as one of the key technologies for new spectrum communication in 6G, has drawn much attention from both academia and industry. The femtocell-like deployment of VLC in indoor environments gives rise to the concept of optical attocells, where each light-emitting diode (LED) serves as an optical access point (AP), enabling illumination and communication simultaneously. However, the majority of existing optical attocell networks rely on wired backbone links (e.g., Ethernet or power-line connections) for inter-attocell connectivity, and this dependency renders the overall network vulnerable to backbone link failures. To this end, we introduce a novel network architecture that exploits the inherent non-line-of-sight (NLOS) optical channels between adjacent attocells to enable inter-attocell communication, enhancing network resilience and flexibility. In particular, we design a chirp signal based on chirp spread spectrum (CSS) modulation tailored for intensity-modulated VLC to improve the noise resilience in NLOS channels for reliable communication under low signalto-noise ratio (SNR) conditions. Moreover, we propose a twostage window alignment approach that integrates coarse-grained with fine-grained alignment to achieve precise synchronization while reducing real-time decoding latency. Finally, we build two prototypes of NLOS optical attocells based on different hardware platforms and conduct extensive field experiments using three modulation schemes, i.e., on-off keying (OOK), frequency-shift keying (FSK), and CSS, to evaluate their performance under variable parameters. Experimental results indicate that the CSS modulation scheme demonstrates superior robustness than the other two schemes, achieving bit error rates (BER) of 3.1×10-5 and 8.3×10-5 and packet reception rates (PRR) of 98.53% and 99.71% on two platforms, respectively, at a horizontal distance of 8 m between adjacent optical devices.