Signaling-Embedded Preamble Design for Flexible Optical Transport Networks

Coherent optical orthogonal frequency division multiplexing (CO-OFDM) is a promising technique for future elastic optical transport networks. In CO- OFDM systems, the preamble is usually used for timing and frequency synchronization, and dedicated pilots are adopted to carry signaling for flexible system configurations. In this paper, we propose a judicious signaling-embedded preamble design to simultaneously achieve the exact timing synchronization based on the ideal Delta-like timing metric, the accurate frequency synchronization with sufficient estimation range, as well as reliable signaling transmission. This is achieved by designing the preamble in the frequency, i.e., two identical training sequences with a specific distance occupy the even subcarriers of the preamble, whereby the system signaling is carried by the combination of different training sequences and different distances between two sequences. Such frequency-domain design would result in the time-domain preamble having conjugate symmetric property and two repetitive parts. The former property is used to produce the ideal Delta-like correlation function for exact timing synchronization, while the latter one is used for accurate frequency synchronization. Simulation results also show that the improved signaling detection performance can be achieved.