Discrete-Circulant-Transform Spread OFDM for Bandwidth-Limited VLC Systems

We propose and investigate discrete-circulant transform spread orthogonal frequency division multiplexing (DCrT-S-OFDM) for bandwidth-limited optical systems. We derive the conditions for optimal designs of DCrT-S-OFDM in the noise limited scenarios and verify its bit error rate advantage over conventional OFDM. We also analytically investigate the performance of DCrT-S-OFDM under the effect of inter-symbol interference (ISI) and inter-carrier interference (ICI), and prove its performance advantage over discrete-Fourier-transform spread OFDM (DFT-S-OFDM). Based on the developed theory, we propose several novel designs of DCrT-S-OFDM to achieve optimal or near-optimal performance. Extensive simulations have been performed in a visible light communication (VLC) system to validate the findings. The results agree with the theory and verify the performance advantage of DCrT-S-OFDM over other schemes. Finally, a ~650-Mbit/s VLC system with ~70-MHz 3-dB system bandwidth was experimentally demonstrated. The results also confirm that DCrT-S-OFDM outperforms conventional OFDM and DFT-S-OFDM, making the proposed DCrT-S-OFDM a promising solution for optical systems using low-bandwidth devices to achieve high data rates.