Hybrid PN-ZP-DMT Scheme for Spectrum-Efficient Optical Communications and Its Application to SI-POF

In this paper, a novel discrete multi-tone (DMT) scheme is proposed for optical communications. Instead of the traditional cyclic prefix, a hybrid structure of pseudonoise (PN) sequence and zero-padding (ZP) sequence is proposed to serve as guard interval for the DMT transmission in order to achieve higher spectrum efficiency. The proposed PN-ZP-DMT scheme directly reuses PN sequence for channel estimation. The proposed PN-ZP-DMT scheme is then applied to plastic optical fiber (POF) transmission systems. Compared to the classical DMT block-based channel estimation and time-frequency pilot-based channel estimation, the PN sequence-based channel estimation improves both performance and spectrum efficiency in POF. The optimal selection of PN sequence length is investigated. Simulation results show that the PN sequence-based channel estimation can approach the optimal performance. Moreover, some practical features of PN-ZP-DMT transmission over POF such as system complexity and influence of time synchronization errors are studied. Finally, a PN-ZP-DMT transmission with 1.49-Gbps net rate is implemented in the low-cost 50 m step index-POF system which eventually proves the effectiveness of the proposal.