Robust Frame and Frequency Synchronization Based on Alamouti Coding for RGI-CO-OFDM

TL;DR

This paper introduces a joint frame and frequency synchronization algorithm for RGI-CO-OFDM systems using Alamouti coding, leveraging Golay sequences for improved accuracy without extra overhead.

Contribution

It presents a novel synchronization method that uses existing training symbols and Alamouti coding, reducing overhead and enhancing robustness in high-speed optical systems.

Findings

Achieves accurate synchronization in RGI-CO-OFDM systems at 238.1 Gb/s.

Demonstrates robustness to linear fiber impairments.

Reduces training overhead by utilizing existing training symbols.

Abstract

We propose an algorithm for carrying out joint frame and frequency synchronization in reduced-guard-interval coherent optical orthogonal frequency division multiplexing (RGI-CO-OFDM) systems. The synchronization is achieved by using the same training symbols (TS) employed for training-aided channel estimation (TA-CE), thereby avoiding additional training overhead. The proposed algorithm is designed for polarization division multiplexing (PDM) RGI-CO-OFDM systems that use the Alamouti-type polarization-time coding for TA-CE. Due to their optimal TA-CE performance, Golay complementary sequences have been used as the TS in the proposed algorithm. The frame synchronization is accomplished by exploiting the cross-correlation between the received TS from the two orthogonal polarizations. The arrangement of the TS is also used to estimate the carrier frequency offset. Simulation results of a PDM RGI-CO-OFDM system operating at 238.1 Gb/s data rate (197.6-Gb/s after coding), with a total overhead of 9.2% (31.6% after coding), show that the proposed scheme has accurate synchronization, and is robust to linear fiber impairments.