An Enhanced Double Sided Pulse Interval Modulation (EDS-PIM) Based SIM-OFDM for Light Fidelity (LiFi) Networks

Subcarrier Index Modulated Optical Orthogonal Frequency Division Multiplexing (SIM-OFDM) has recently seen a lot of research interest in Light Fidelity (LiFi) networks. It has great potential due to its superior error performance over single-carrier approaches in a diffused indoor channel, and better power efficiency due to subcarrier indexing. However, due to a fixed sub-block size, the technique’s full potential has not been realized, since it causes unnecessary bandwidth wastage. A variant of SIM-OFDM called Double-Sided Pulse Interval Modulated SIM-OFDM (DS-PIM-SIM-OFDM) has recently been proposed. It allows the use of variable sub-block size, thereby enabling a dynamic subcarrier assignment and preventing subcarrier wastage. However, the technique has poorer Spectral Efficiency (S.E) for a large number of active subcarriers. This letter proposes an enhancement to the DS-PIM-SIM-OFDM. The proposed enhancement overcomes this weakness and considerably improves the spectral efficiency of DS-PIM-SIM-OFDM for a large number of active subcarriers. For a 3-bit index word, 3 active subcarriers, and a 16-QAM modulation, the proposed enhancement shows a 25% improvement in S.E.