Nonlinear visible light communications broadcast channel precoding: A new solution for in-flight systems

In this paper, we consider a multiuser multiple-input-single-output (MU-MISO) downlink visible light communication (VLC) system deployed in airplane cabins, for serving high-speed Internet to the passengers through the reading lamps. The high number of closely spaced lamps (i.e., transmitters) suggests the use of a transmit precoding scheme to suppress the strong mutual light interference and enhance the performance of the system. Constraints are the complexity of the hardware and the integration into commercial devices (smartphones, tablets, etc.). Since nominal lighting is constrained by LEDs saturation, here we adapt the Tomlinson-Harashima precoding algorithm to the on-board VLC scenario and demonstrate its definite improvement on channel capacity with respect to the unprecoded case and also to the zero-forcing precoding one. The optimum directivity of the sources trades over performance and robustness against source-receiver misalignments (i.e., the passengers' mobility) by validating MISO channels for a number of receivers' positions around the best alignment one with a ray tracer specifically designed.