A novel semi-angle-based index modulation scheme for MIMO visible light communication

Visible light communication (VLC) with the use of multiple light-emitting diodes (LEDs) has recently offered extensive indoor coverage for both communication and illumination purposes. Meanwhile, index modulation refers to modulation techniques that use the indices of certain mediums to transmit additional information. The medium can be a time slot, frequency carrier, or especially antenna activation index. In this paper, we present the first attempt at semi-angle-based index modulation for a visible light communication (VLC) system by using LED with different semi-angle values. Instead of using identical semi-angle LEDs, multiple LEDs are divided into several clusters and all LEDs in each cluster have different semi-angle values. Moreover, at any time of transmission, only some clusters are active, and only a single LED of each active cluster is used to convey the pulse amplitude modulation (PAM) signal. We also proposed a minimum mean-squared error (MMSE) based maximum likelihood (ML) detector that performs ML detection on some candidates based on an initial MMSE solution. The simulation results show that the proposed scheme significantly improves the symbol error rate (SER) compared to conventional schemes. Finally, the proposed detector also proves to approach the ML detector performance while still maintaining acceptable complexity cost.