Bidirectional visible light communication

Visible light communication (VLC) is a data transmission technology that uses the LED lighting infrastructure to simultaneously illuminate and communicate. The ubiquitous existence of LED lamps opened a new opportunity for addressing VLC in many indoor communication scenarios. The motivation for the presented application is the efficient management of warehouses supported by autonomous navigation robots that grab goods and deliver them at the packaging station. This functionality demands bidirectional communication between infrastructures and vehicles. We propose links for infrastructure-to-vehicle (I2V), vehicle-to-infrastructure (V2I), and vehicle-to-vehicle (V2V) to perform indoors, bidirectional communication. A bidirectional communication system between a static infrastructure and a mobile robot (I2V) is proposed. The LED lamps of the warehouse illumination system are used to lighten the space and to transmit information on position and racks' contents. The mobile robots communicate with the infrastructure (V2I) to transmit information on the items that are being removed and carried to the packaging station. The communication among robots (V2V) provides information on the number of items intended to be collected when the vehicles are in the same lane. The proposed coding schemes are used as modulation for the ON-OFF keying method. Trichromatic white LEDs and a photodetector based on a-SiC:H/a-Si:H with selective spectral sensitivity are used at the emitter and receiver. Position information is provided by each LED lamp to the vehicle by adequate modulation of the RGB emitters. The decoding strategy is based on accurate calibration of the output signal. Different scenarios were designed and tested. Requirements related to synchronous transmission and flickering were addressed to enhance the system performance. The decoding task is discussed using a bit parity error control methodology to ensure simultaneous detection and correction of bit errors. The consequent increase of bit error rate in the VLC transmission is discussed in the I2V link.