Constellation Design for Channel Precompensation in Multi-Wavelength Visible Light Communications

The predicted ubiquity of light-emitting diodes (LEDs) suggests great potential for dual-use systems with visible light communications (VLC) capabilities. One class of LEDs employs multiple emitters at different wavelengths, making them appropriate for applications requiring colored output and providing multiple channels for communication. We present a design framework for optimizing the signaling constellation of VLC systems employing an arbitrary number of such LEDs, each with an arbitrary number of emitters. In particular, by considering the design of constellation-symbol locations jointly across LED emitters, the framework provides for the precompensation of linear channel distortions arising from, for example, cross-channel leakage, noise correlation, or wavelength-dependent received-signal and/or noise power, as well as the incorporation of design constraints for color-shift keying, dimming, and/or perceived color. Simulation results demonstrate the design approach and the potential performance enhancement that can be achieved for particular system scenarios. Experimental measurements using a prototype VLC system confirm such performance enhancements, providing real-world evidence of the benefit of applying the proposed framework to VLC channel precompensation.