Multi-LED Transmission Schemes using OTFS Modulation in Visible Light Communication

Orthogonal time frequency space (OTFS) modulation is a recently introduced modulation which has been shown to perform better than OFDM in RF wireless communications. In this paper, we investigate OTFS in multi-LED indoor visible light wireless communications. We propose two multi-LED OTFS schemes, namely, quadrature spatial modulation OTFS (QSMOTFS) scheme and dual mode index modulation OTFS (DMIMOTFS) scheme. The proposed schemes use dual-LED complex modulation as the basic building block and offer enhanced rates compared to conventional index modulation schemes. The schemes also have the advantage of not requiring Hermitian symmetry and DC bias operations to obtain real, positive-valued signals suited for intensity modulation of LEDs. We obtain upper bounds on the bit error rate performance of the proposed schemes, which are tight at high signal-to-noise ratios. The proposed OTFS schemes are shown to perform better than their OFDM counterparts known in the literature. In addition, the spatial distribution of the performance gap between OTFS and OFDM across the room is captured using the ratio of the minimum distance of normalized received signal sets of the considered schemes as a metric.