A Transmit Diversity Scheme for Multi-pulse Pulse Position Modulated Visible Light Communications

The increasing saturation of traditional radio frequencies, from the massive growth of mobile data and the internet of things, demands the exploration of new channels for wireless communications. Visible light has emerged as a promising technology capable of transmitting digital data over line-of-sight paths. Broad deployment of light-emitting diodes offers the potential to leverage existing lights for dual uses of illumination and communication. Communicating through visible light avoids both the growing congestion and costs associated with operating in the radio frequency band. This paper presents a transmit diversity technique for a visible light communications system with direct application to intelligent transportation systems and vehicle-to-vehicle communication. Building on previous multi-pulse pulse position modulation techniques, we introduce transmit diversity to reduce the overall system bit error rate and improve throughput while maintaining symbol self-synchronization. The use of select transmit symbols and a combiner scheme at the receiver counter errors from interference pulses in the optical channel. We develop the relationship between multi-pulse pulse position modulation symbol choices and error rates in a multiple-input multiple-output system compared to single-input single-output systems, and other modulation techniques through theoretical calculations and prove results through computer simulation and experiment.