Subcarrier-Index Modulation for Reed Solomon Encoded OFDM-Based Visible Light Communication

In this paper, we propose the subcarrier-index modulation with Reed Solomon encoded Optical Orthogonal Frequency Division Multiplexing with index modulation (IM-RS-OFDM) scheme for visible light communication (VLC). In this technique, the data is encoded using an RS codeword and then part of the redundancy introduced by the frame which exceeds the clipping range are punctured and their corresponding subcarriers are set as inactive, where the indices of these inactive subcarriers are used to transmit extra information bits. The puncturing of the redundancy aids in mitigating clipping noise generated due to the dynamic range constraints of the optical transmitter by shortening the number of active subcarriers, while the locations of the punctured subcarriers are exploited to convey more bits in order to compensate for the reduction in spectral efficiency caused by coding redundancy. In the proposed scheme, the bipolar transmitting signal is clipped and biased according to DC bias optical OFDM (DCO-OFDM) system, and a Log-Likelihood ratio (LLR) calculation based detector is used to find the indices of punctured symbols in the codeword. Our simulation results show that the new scheme offers a better bit error rate performance compared to the conventional coded OFDM-based visible light communication.