Coding schemes in a communication system based on visible-light communication

White LEDS revolutionized the field of illumination technology mainly due to the energy saving effects. Besides lighting purposes LEDs can also be used in wireless communication systems when integrated in Visible Light Communication (VLC) systems. Indoor positioning for navigation in large buildings is currently under research in order to overcome the difficulties associated with the use of GPS in such environments. The motivation for this application is also supported by the possibility of taking advantage of an existing lighting and WiFi infrastructure. In this work it is proposed a bidirectional communication system between a static infrastructure and a mobile picking robot. The LED luminaires at the warehouse ceiling are used to lighten the warehouse space, and to transmit information for positioning and about available racks. The picking robots communicate with the ceiling luminaires to send information about the rack that is being removed and carried to the packaging station. Different codification schemes are proposed to establish both uplink and downlink communication between LED luminaires and mobile robots. Tri-chromatic white LEDs with the red and blue chips modulated at different frequencies and a pinpin photodetector with selective spectral sensitivity are used at the emitter and receiver modules.