Unique Word DMT Schemes for Optical Systems With Intensity Modulation and Direct Detection

Discrete multitone transmission (DMT) schemes, such as asymmetrically clipped DMT and DC-biased DMT, are popular multicarrier transmission schemes for dispersive optical channels employing intensity modulation and direct detection. These transmission schemes utilize a cyclic prefix (CP) to have a simple frequency domain equalization at the receiver. In this paper, we propose two novel DMT signaling schemes for such optical systems, where the guard interval is built of a unique word (UW), i.e., a deterministic data-independent sequence. This approach becomes possible since redundancy is added in the frequency domain and the UW is a part of the discrete Fourier transform interval. The results show that the proposed UW-DMT schemes outperform the conventional CP-DMT schemes in dispersive optical channels. Furthermore, the UW can be additionally used for other purposes, such as synchronization and channel estimation.