Preamble Design for Joint Frame Synchronization, Frequency Offset Estimation, and Channel Estimation in Upstream Burst-mode Detection of Coherent PONs

TL;DR

This paper introduces a novel preamble design for upstream burst-mode coherent PONs that enables joint frame synchronization, frequency offset, and channel estimation, significantly reducing preamble length and accelerating DSP convergence.

Contribution

It proposes a constant amplitude zero auto-correlation sequence-based preamble for comprehensive linear channel effect estimation and joint DSP function execution in coherent PONs.

Findings

Preamble length of 272 symbols is effective in a 15 Gbaud system.

Experimental results show improved convergence speed.

The design facilitates accurate channel estimation and synchronization.

Abstract

Coherent optics has demonstrated significant potential as a viable solution for achieving 100 Gb/s and higher speeds in single-wavelength passive optical networks (PON). However, upstream burst-mode coherent detection is a major challenge when adopting coherent optics in access networks. To accelerate digital signal processing (DSP) convergence with a minimal preamble length, we propose a novel burst-mode preamble design based on a constant amplitude zero auto-correlation sequence. This design facilitates comprehensive estimation of linear channel effects in the frequency domain, including polarization state rotation, differential group delay, chromatic dispersion, and polarization-dependent loss, providing overall system response information for channel equalization pre-convergence. Additionally, this preamble utilizes the same training unit to jointly achieve three key DSP functions: frame synchronization, frequency offset estimation, and channel estimation. This integration contributes to a significant reduction in the preamble length. The feasibility of the proposed preamble with a length of 272 symbols and corresponding DSP was experimentally verified in a 15 Gbaud coherent system using dual-polarization 16 quadrature amplitude modulation. The experimental results based on this scheme showed a superior performance of the convergence acceleration.