Enhanced Subband Index Carrierless Amplitude and Phase Modulation in Visible Light Communications

An enhanced subband index carrierless amplitude and phase modulation (eSI-CAP) scheme is developed to improve the spectral efficiency of the multiband CAP (m-CAP) in visible light communication (VLC) systems. Using indexing technique and a dual distinguishable constellations, the eSI-CAP carries information bits by modulating symbols on the subbands of m-CAP. It also encodes additional information bits on the selection of the subband indices that is modulated with the dual constellation symbols. The performance advantage of eSI-CAP is demonstrated through theoretical analysis, computer simulations and VLC experimental validations. In addition, a novel maximum likelihood detector is developed for eSI-CAP with the same order of complexity as the conventional m-CAP detector. On comparison with m-CAP, eSICAP requires lower signal-to-noise ratio (SNR) per bit (γ_b) to reach a fixed data rate (R_b). Alternatively, when the γ_b is fixed, it achieves a higher R_b for a target BER. The results show that eSI-CAP is very attractive for VLC systems due to its flexible configuration and its improvement of the power efficiency of the conventional m-CAP modulation scheme.