Wavelength widths of optical filters for optimum SINR in WDM-VLC systems

Wavelength division multiplexing (WDM) permits the light spectrum to be divided into several parallel channels, allowing the capacity of visible light communication (VLC) systems to be increased. However, the spectral overlap due to the emission spread of differently colored LEDs generates crosstalk interference that can degrade the WDM-VLC. In this context, the adequate design of optical filters (OFs) can mitigate this problem by limiting the spectral capture of the signals from the adjacent WDM channels. Thus, a specific WDM-VLC model is developed to analyze the effects of the width of OFs on the signal-interference-plus-noise ratio (SINR). After confirming the quasi-concavity of the SINR, the optimal widths of the OFs are determined by SINR maximization using iterative search algorithms considering fixed and mobile WDM-VLC systems. Considering mobile receiver operation, it was confirmed that the maximum SINR points shift, implying the variation in optimal OF width according to the optical powers captured, which vary according to the distance and orientation of the LEDs and/or receivers. Finally, a statistical approach is presented that allows the design of non-adaptive OFs.