Trace-orthogonal PPM-space time block coding under rate constraints for visible light communication

Visible light communications (VLC) represents a new frontier of communications allowing high data-rate Internet access, specially in indoor environments, where the use of light emitting diodes (LEDs) is growing as a viable alternative to traditional illumination. As a result, LED output intensity can be varied faster than human eye can perceive, thus guaranteeing simultaneous wireless communications and illumination. One of the key challenges is the limited modulation bandwidth of sources that is typically around several MHz. The use of multiple input and multiple output (MIMO) techniques in optical wireless system helps to increase the capacity of the system and thus improve the system performance. In this paper, we investigate the use of an optical MIMO technique jointly with pulse position modulation (PPM) in order to improve the data rates without reducing the reliability of the link. PPM is known to be signal-to-noise ratio efficient modulation format, while it is bandwidth inefficient so the use of MIMO can compensate that drawback with reasonable complexity. Furthermore, an offline tool for VLC system planning, including error probability and transmission rate, has been proposed in order to solve the tradeoff between transmission rate and error rate. Finally, several numerical results and performance comparisons are reported.