Space-Time Indexed Multiple-LED Complex Modulation Schemes for VLC Systems

Abstract

This paper proposes two index modulation schemes for multiple-input multiple-output (MIMO) visible light communication (VLC) systems, referred to as time index modulated DCM (TIM-DCM) and space-time index modulated DCM (STIM-DCM) schemes. The proposed schemes use dual-LED complex modulator (DCM) as a basic unit (termed as DCM block) to transmit complex modulation symbols. In TIM-DCM scheme, a time slot in given frame can be used or unused, and the pattern in which the slots are used for transmission also conveys information bits (referred to as slot index bits) besides the information bits conveyed through complex modulation symbols. In STIM-DCM scheme, in addition to the slot index bits and modulation bits, spatial index bits are conveyed by activating one among the available DCM blocks in every used time slot. Hence, the proposed schemes can achieve high rates. We study the bit error rate (BER) performance of the proposed schemes and compare with that of the state-of-art modulation schemes such as spatial modulation DCM (SM-DCM) scheme. Results show that the proposed schemes can achieve better BER performance. Also, results on the spatial distribution of best performing modulation scheme indicates that the proposed schemes are favorable for different receiver locations across the room.