Fig. 1. Block diagram of diversity-combining DHT-based ACO-OFDM.

Fig. 2. (a) BPSK-modulated OFDM based on the 32-order DHT and (b) corresponding ACO-OFDM.

Fig. 3. Diversity-combining module, where sgn(·) represents the sign function.

Fig. 4. (a) Symbol on odd subcarrier; (b) symbol on even subcarrier; and (c) under the circumstances of no noise, the regenerated signal from the symbol on the even subcarrier indicated by the polarity of the symbol on the odd subcarrier.

Fig. 5. Eb/N0 gain versus α for diversity-combining technique in DHT-based ACO-OFDM with BPSK, 4-PAM, 8-PAM, and 16-PAM modulated.

Fig. 6. Comparison of BER performance between conventional DHT-based ACO-OFDM without diversity-combining module and optimal diversity-combining DHT-based ACO-OFDM with different given modulation formats, where original means conventional DHT-based ACO-OFDM without diversity-combining module.

Fig. 7. BER versus received power for diversity-combining DHT-based ACO-OFDM systems after BTB and 50 km SSMF transmission.