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 (VLC) technology. An analytical expression for the joint detection of the spatial and signal bits for the user equipment (UE) experiencing line-of-sight propagation (LOS) is derived and validated via simulation. The effect of 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 S-CAP in LOS is dictated by the minimum of the channel gains h min, the signal constellation points (SCP) and the channel gain dissimilarity, ∆|h. The power factor imbalance (PFI) and multiple photodetectors (PDs) are then introduced to improve performance and mitigate channel impairments. The use of PFI and PDs in LOS result in signal-to-noise (SNR) gain of 33.5dB and 43dB, respectively. The proposed scheme is thus a novel implementation of CAP in a multiple-input multiple-output (MIMO) system and demonstrates its potential as a suitable physical layer solution for VLC technology.