OTFS Modulation in Dual-LED Indoor Visible Light Communication Systems

In this paper, we investigate the use of a new modulation scheme recently introduced in the RF domain, called orthogonal time frequency space (OTFS) modulation, in an indoor visible light communication (VLC) setting. In particular, we consider VLC systems that employ dual-LED schemes for transmission. The following dual-LED schemes are considered: 1) non-DC biased (NDC) scheme, and 2) dual-LED complex modulation (DCM) scheme. The proposed NDC-OTFS scheme uses 2-dimension (2D) Hermitian symmetry operation to convert complex signals to positive, real-valued signals suitable for transmission in the optical domain, and the proposed DCMOTFS scheme achieves this by exploiting the polar representation of complex signals. We obtain analytical upper bounds on the bit error performance of the proposed NDC-OTFS and DCM-OTFS schemes, which are found to be tight at high signal-to-noise ratios (SNR). Our analytical and simulation results show that the proposed NDC-OTFS and DCM-OTFS schemes achieve better performance, respectively, compared to NDC-OFDM and DCM-OFDM schemes known in the VLC literature. Further, using the ratio of the minimum distance of different normalized received signal sets as a metric, we quantify the spatial distribution of the SNR gain of the proposed NDC-OTFS/DCM-OTFS schemes compared to NDC-OFDM/DCM-OFDM schemes.