Flexible FEC Selection in Optical Network Units
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Solution Overview
Problem
Passive optical networks (PONs) face challenges in upstream FEC coding flexibility due to variable laser quality in optical network units (ONUs) and limitations from temperature variations and distance from the optical line terminal (OLT).
Innovation Solution
The implementation of messaging structures and protocols that allow for flexibility in upstream FEC coding, enabling ONUs to support multiple pre-defined FEC codes and adapt to changing channel characteristics, while maintaining overhead constraints within standard messaging systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single pre-defined FEC code is used in PON systems, then the system structure remains simple and standardized, but the system cannot adapt to variable ONU laser quality and channel conditions
Solution Approach 1:
The system dynamically selects FEC codes based on channel conditions. The OLT and ONU exchange capability information through PLOAM messages, and the OLT selects appropriate FEC codes (RS(255,239), RS(255,223), or RS(255,207)) based on measured channel quality and ONU laser characteristics, allowing the system to adapt from a static single-code approach to a dynamic multi-code selection approach.
Solution Approach 2:
The invention changes the FEC code parameters (code rate, generator polynomial) based on channel conditions. Different FEC codes with varying error correction capabilities are selected and configured through messaging protocols, allowing the system to adjust the degree of forward error correction applied according to the severity of channel impairments and laser quality variations.
2Reliability
If multiple FEC codes are supported to improve adaptability, then the system can handle variable laser quality and environmental conditions, but the messaging overhead and protocol complexity increase
Solution Approach 1:
The system implements partial FEC code diversity by supporting a limited set of three specific RS codes rather than an exhaustive list of all possible FEC codes. This partial implementation provides sufficient adaptability for different channel conditions while keeping the messaging overhead manageable, as only the necessary capability indication and selection messages are exchanged.
Solution Approach 2:
The OLT measures channel quality and provides feedback to the ONU through PLOAM messages, indicating which FEC code should be used. The ONU acknowledges its FEC capabilities and receives selection instructions, creating a closed-loop feedback system that optimizes BER performance while managing messaging overhead through efficient feedback mechanisms.
3Reliability
If FEC code selection is made flexible to accommodate temperature variations and distance effects, then communication reliability improves, but the overhead constraints of standard messaging systems are violated
Solution Approach 1:
The existing PLOAM message structures are extended to serve multiple functions: capability indication, FEC selection, and channel quality feedback. The same messaging infrastructure is used for both initial ONU registration and ongoing FEC code management, allowing flexible FEC selection without requiring separate dedicated protocol structures for each function.
Data Source
AI summary
An optical network unit (ONU) includes a transmitter and receiver to optically communicate with an optical line terminal (OLT) of a passive optical network. The ONU is configured to send an acknowledgment message to the OLT in response to a burst-profile message unicast by the OLT. The acknowledgement message indicates unsupported forward error correction (FEC) code in response to the burst-profile message identifying an FEC code for upstream transmission and the ONU not supporting the FEC code for upstream transmission to the OLT.