Multilayered optical OFDM for high spectral efficiency in visible light communication system

This paper presents two new schemes for improving the spectral efficiency of an optical orthogonal frequency-division multiplexing-based visible light communication (OFDM-VLC) system. The proposed schemes employed the generalized spatial modulation (GenSM) along with multi-input multi-output (MIMO) techniques as well as modified the coded modulation optical OFDM (CMO-OFDM) approach to attain more bandwidth utilization and higher spectral efficiency. The proposed multilayered/enhanced CMO-OFDM (LeCMO-OFDM) systems ensure the real-valued optical OFDM signals without using Hermitian symmetry and utilize the redundant codes existed in CMO-OFDM for further improvements in system's spectral efficiency while ensuring acceptable bit error rate (BER) performance. LeCMO-OFDM scheme transmits multilayer optical signals after converting them to unipolar form either by using DC bias (DC-LeCMO-OFDM) or by separating them through employing the GenSM with no DC bias (NDC-LeCMO-OFDM). We present analytical and simulation results to evaluate the effectiveness of the proposed systems and demonstrate the additional capacity gain in terms of spectral efficiency. In addition, the impact of the spacing distance between the light emitting diodes has been addressed. Detailed performance comparison in terms of spectral efficiency and BER between the proposed techniques and other recent works is provided for validation purpose. Finally, results show that our schemes can achieve better spectral and power efficiencies performance with acceptable BER performance when compared with the related methods.