Higher Order Colour Shift Keying Modulation Formats for Visible Light Communications

This work presents the higher order modulation schemes for the standardised trichromatic light-emitting diode (TLED) and recently developed quad-chromatic LED (QLED) based colour shift keying (CSK), and investigates their performance over diffuse optical wireless channels with colour cross-talk, insertion losses and additive white Gaussian noise (AWGN). The performance analysis shows that the uncoded and unequalised QLED CSK can provide up to 288 Mbit/s data links, using standard compliant optical clock rate, through the use of a 4096 level modulation scheme, which is the highest number of levels so far been developed for a CSK scheme. Additionally, the results show that QLED scheme has better spectral and power efficiencies than the TLED scheme as the 256-CSK of QLED requires 4.5 dB less optical power than the 64-CSK of TLED when the normalised delay spread is increased to 0.25. The performance of both the CSK schemes is also examined without the use of colour calibration, which reveals that 4-CSK of QLED scheme can operate without the receiver having any knowledge of the colour cross- talk, which makes this modulation format an ideal signalling channel for the estimation of colour cross-talk and impulse response of optical channel. The analytical approximations, for the bit error performance of all the modulation orders, with AWGN are also presented.