Use of multiple light emitting diodes (LED) is an attractive way to increase
spectral efficiency in visible light communications (VLC). A non-DC-biased OFDM
(NDC OFDM) scheme that uses two LEDs has been proposed in the literature
recently. NDC OFDM has been shown to perform better than other OFDM schemes for
VLC like DC-biased OFDM (DCO OFDM) and asymmetrically clipped OFDM (ACO OFDM)
in multiple LEDs settings. In this paper, we propose an efficient multiple LED
OFDM scheme for VLC which uses {\em coded index modulation}. The proposed
scheme uses two transmitter blocks, each having a pair of LEDs. Within each
block, NDC OFDM signaling is done. The selection of which block is activated in
a signaling interval is decided by information bits (i.e., index bits). In
order to improve the reliability of the index bits at the receiver (which is
critical because of high channel correlation in multiple LEDs settings), we
propose to use coding on the index bits alone. We call the proposed scheme as
CI-NDC OFDM (coded index NDC OFDM) scheme. Simulation results show that, for
the same spectral efficiency, CI-NDC OFDM that uses LDPC coding on the index
bits performs better than NDC OFDM
