Abstract: To solve the problem that the transmission rate of conventional asymmetrically clipped optical OFDM system with index modulation (OFDM) is not ideal, an asymmetrically clipped optical OFDM with enhanced index modulation system is proposed by selecting the active carrier twice to increase the index information carried by the active subcarrier and transmitting different modulation symbols on the active subcarrier. Meanwhile, the subcarrier selection algorithm is proposed to improve the bit error rate of the system. In particular, the modulation mapping principle of the proposed system is introduced in detail. Then, its theoretical bit error rate is derived by using the joint bound technique. Finally, the proposed system is compared with the conventional systems. The simulation results show that the proposed system not only increases the transmission rate but also improves the bit error rate. Specifically, when the turbulence is strong and the bit error rate is 1×10^-3, the transmission rate of (8,3,3) the proposed system is 1.25 times higher than that of(8,6) conventional system, meanwhile the signal to noise ratio is improved by about 1.4 dB.

Key words: wireless optical communication, orthogonal frequency division multiplexing, index modulation.