Scheduling for TWDM-EPON-Based Fronthaul Without a Dedicated Registration Wavelength

TL;DR

The paper addresses the challenge of periodic RU registration in EPON-based fronthaul without sacrificing spectral efficiency or violating eCPRI delay/jitter budgets. It introduces a traffic-redistribution framework for TWDM-EPON, hosting registration on one wavelength and dynamically reassigning ONUs to the other $W-1$ wavelengths, paired with a delay-bounded MIQP optimization to maximize the number of RUs $N$ under cycle-pattern constraints. The approach yields up to a 71% increase in supported RUs over the ITU-T dedicated-wavelength baseline, validated through MIQP feasibility solved with Gurobi and detailed parameter studies. This method significantly improves spectral efficiency and scalability for C-RAN fronthaul while maintaining stringent latency and jitter requirements.

Abstract

The adoption of Centralized Radio Access Network (C-RAN) architectures requires fronthaul systems capable of carrying large volumes of radio data while meeting stringent delay and jitter requirements. Ethernet Passive Optical Networks (EPONs) have emerged as a promising fronthaul solution due to their cost efficiency and compatibility with existing infrastructure. However, the traditional registration process for EPON systems halts the ongoing data transmissions during the registration period, thereby violating the enhanced Common Public Radio Interface (eCPRI) delay and jitter requirements. This limitation has been acknowledged by the ITU-T, which recommends the use of a dedicated wavelength channel for registration, leading to inefficient bandwidth utilization. In this paper, we propose a novel scheduling framework for a Time and Wavelength Division Multiplexed (TWDM) EPON-based fronthaul that enables periodic registration without wasting an additional wavelength channel. Performance evaluation demonstrates that the proposed method achieves up to a 71\% increase in the number of Radio Units (RUs) supported for a given number of wavelength channels, compared to a baseline scheme employing a dedicated registration wavelength.

Figures (9)

• Figure 1: X-haul architecture illustrating the connectivity among the Central Unit (CU), Distributed Unit (DU), and Radio Units (RUs).
• Figure 2: EPON-based fronthaul architecture illustrating the OLT, passive splitter, and multiple ONUs.
• Figure 3: Standard EPON Registration Process.
• Figure 4: Conventional EPON upstream scheduling, highlighting the periodic interruption due to the mandatory registration window.
• Figure 5: Proposed redistribution example for $N\!=\!4$ and $W\!=\!3$. During registration cycles, the remaining $W\!-1$ wavelengths support $N_r\!=\!6$ ONUs per wavelength (see Eq. \ref{['eq-nr-value']}) .