Optical spatial modulation using colour LEDs

Spatial Modulation (SM) is a combined multiple-input-multiple-output (MIMO) and digital modulation technique. Like in any MIMO scheme, the performance of SM is related to the differentiability, i.e. the correlation, of the multiple channels. In this paper, we analyse the performance of optical SM for a wireless indoor environment. It is shown that the use of colour light-emitting diodes (LEDs) can improve the performance of SM by more than 10 dB. This is due to the fact that the responsivity of photo-diodes is a function of the optical wavelength. As a consequence, using LEDs with different colours induces specific optical power levels at the receiver. These distinctive power levels directly affect the channel characteristic since they reduce the channel correlation. Moreover, we analyse the computational complexity of optical SM and compare it to the complexity of other common MIMO techniques. It is found that SM requires a much lower computational complexity compared to Repetition Coding (RC) and Spatial Multiplexing (SMP).