Layered Optical OFDM Schemes for IM/DD OWC Systems

Most conventional optical OFDM (O-OFDM) schemes suffer from low spectral efficiency due to the interference introduced by time-domain signal processing. In this paper, we propose a novel design principle for layered O-OFDM schemes for intensity modulation with direct detection (IM/DD) optical wireless communication (OWC) to fully exploit the spectral resources. All layered O-OFDM schemes are designed to meet the constraint that the interference introduced by time-domain signal processing at each layer is designed mutually orthogonal to the frequency-domain signals at the current and lower layers. To satisfy this constraint, we discuss two approaches for time-domain signal processing and corresponding spectrum resource allocation, and present the subsequent transceiver design for the proposed layered O-OFDM schemes. The proposed layered O-OFDM schemes exhibit high spectral efficiencies, and numerical results demonstrate their low bit error rates (BERs) and high power efficiencies. Furthermore, the high flexibility of these schemes guided by the proposed design principle enables them to meet a wide range of diverse communication requirements.