Unique Word DMT Schemes Using Real-Valued Constellations for IM/DD Optical Systems

Discrete multitone transmission (DMT) schemes employing real-valued constellations such as PAM (PAM-DMT) are popular multi-carrier transmission schemes for optical systems using intensity modulation and direct detection. PAM-DMT employs a data dependent cyclic prefix (CP) to maintain cyclicity. In this letter, we propose a novel DMT scheme using real-valued modulation formats where the usual CPs are replaced by a unique word (UW) that is a known deterministic sequence. This is achieved by designing a code generator matrix in the frequency domain that introduces correlation among the data symbols. The proposed PAM UW-DMT scheme shows a superior bit error ratio performance as compared with PAM CP-DMT. Moreover, the UW can be used for other purposes, such as synchronization and channel estimation.