Spatial Carrierless Amplitude and Phase Modulation Technique for Visible Light Communication Systems

Spatial carrierless amplitude and phase modulation (S-CAP) technique is developed in this paper as a physical layer solution to improve the spectral efficiency of the conventional CAP scheme while preserving its low-complexity transceiver design. The S-CAP technique is proposed and investigated for systems employing the visible light communication technology. An analytical expression for the joint detection of the spatial and signal bits for the user equipment experiencing line-of-sight propagation (LOS) is derived and validated via simulation. The effects of the multipath propagation and user mobility on the bit-error-rate (BER) performance of the proposed S-CAP are also investigated. It is found that the BER performance of the S-CAP in LOS is dictated by the minimum of the channel gains $h_\text {min}$ , the signal constellation points, and the channel gain dissimilarity, $\Delta |h|$ . The power factor imbalance (PFI) and multiple photodetectors (PDs) are then introduced to improve the performance and mitigate the channel impairments. The use of the PFI and PDs in LOS results in the signal-to-noise gain of 33.5 and 43 dB, respectively. The proposed scheme is thus a novel implementation of the CAP in a multiple-input–multiple-output system and demonstrates its potential as a suitable physical layer solution for the VLC technology.