Multiple-subcarrier optical communication systems with subcarrier signal-point sequence

We propose a multiple-subcarrier (MS) optical communication system with subcarrier signal-point sequence (SSPS). We use the SSPSs having a large minimum value and large Euclidean distances, so that the required dc bias is minimized and the error-rate performance is improved. Note that in the proposed system, the signal points having the larger minimum value are selected, while the signal points having a lower peak-to-mean-envelope-power ratio (PMEPR) are selected in orthogonal frequency-division multiplexing (OFDM) systems. Therefore, the SSPSs good for OFDM with phase shifting by pi rad are not necessarily effective for MS optical communication systems. The main contributions of our paper are: 1) we derive transmit sequences having a large minimum value and large Euclidean distances by using 8-phase-shift keying and (8+1)-amplitude phase-shift keying; and 2) since designing optimal sequences would be prohibitively complex, we introduce a reasonable procedure for suboptimal sequence design, obtaining good results. We show that the normalized power requirements and normalized bandwidth requirements of the MS systems with SSPS are smaller than those of the conventional MS systems.