Index modulation-aided ACO-OFDM differential chaos shift keying system for optical wireless communications

In this paper, we introduce differential chaos shift keying (DCSK) into asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) and propose the index modulation-aided ACO-OFDM differential chaos shift keying (IM-ACO-OFDM-DCSK) system. Our aim is to eliminate the need for channel state information (CSI) estimation in the index modulation-aided OFDM (IM-OFDM) system for optical wireless communication (OWC). In our design, we transmit the DCSK or its orthogonal signal as the information-bearing signals on non-indexed and indexed subcarriers, respectively. This scheme allows each subcarrier to convey constellation symbols, thereby addressing the resource wastage problem and enhancing the transmission rate. We derive the theoretical bit error rate (BER) expressions over the exponential Weibull channel and analyze the spectral efficiency, energy efficiency, and complexity. Monte Carlo simulations validate the theoretical analysis. The results show that the proposed scheme completely avoids complex channel estimation procedures and improves the transmission rate and energy efficiency, albeit at a higher complexity cost compared to ACO-OFDM-DCSK.