PON Downstream Interleaving for 25G Protection Mode Sensitivity
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Solution Overview
Problem
Current passive optical networks (PON) systems face challenges in maintaining operation when an Optical Network Unit (ONU) is pushed beyond sensitivity due to factors like fiber issues or heating, leading to service outages, as they are not compatible with reduced rate protection modes like 25G signals within the 50G PON standard.
Innovation Solution
Generating low-rate NRZ and Miller signals that are compliant with the G.9804 standard by creating an interleaved bitstream with redundant bits, which reduces inter-symbol interference and allows for seamless operation at reduced rates while maintaining compatibility with the 50G standard, thereby enabling improved sensitivity and compatibility with legacy ONUs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If 50G NRZ signals are used for high-speed downstream transmission, then transmission rate is improved, but sensitivity deteriorates making the system vulnerable to fiber issues and heating
Solution Approach 1:
The system dynamically switches between 50G NRZ and 25G protected modes based on channel conditions. When fiber issues or heating occur, the ONU can transition to the protected 25G mode, which uses different encoding (Miller or NRZ with repetition) that is more robust to degradation, thus maintaining reliability while preserving the ability to operate at high speed when conditions are good
Solution Approach 2:
The invention changes the signaling parameters by introducing a protected mode at 25G with alternative encoding schemes. The 25G Miller encoding changes the transition patterns to avoid worst-case ISI scenarios, and 25G NRZ with bit repetition changes the temporal structure of the signal, both improving sensitivity under degraded conditions while maintaining compatibility with the 50G PON infrastructure
2Reliability
If 25G Miller encoding is used for protection mode, then sensitivity is improved, but compatibility with G.9804 standard deteriorates due to non-systematic encoding
Solution Approach 1:
The invention introduces an intermediary mapping layer between the 25G encoded bits and the 50G PON frame structure. The 25G Miller or NRZ-encoded data is mapped to subsets of the 50G downstream frames, with idle codewords in the 50G structure carrying the protected 25G data. This intermediary mapping allows the non-standard 25G protected mode to coexist with the G.9804 50G standard without requiring modifications to the core standard
3Reliability
If 25G NRZ with bit repetition is used for protection mode, then sensitivity is improved, but compatibility with G.9804 standard deteriorates due to scrambling incompatibility
Solution Approach 1:
The invention uses an intermediary mapping approach where 25G NRZ-encoded bits (with repetition) are assigned to specific positions in the 50G downstream frame structure. The encoding is applied before mapping, and the resulting protected data stream is integrated into the 50G frame format. This allows the 25G protected mode to benefit from bit repetition for improved sensitivity while maintaining compatibility with the G.9804 standard through proper frame structure integration
Data Source
AI summary
An apparatus configured to perform obtaining a stream of codewords, including a first type codeword and a second type codeword, wherein, the first type codeword is an idle codeword, and the second type codeword includes data intended for at least one of the ONUs; obtaining, an interleaved bitstream from the stream of codewords based on an interleaving scheme, wherein, in the interleaved bitstream, bits at positions corresponding the first type codeword include redundant bits, and bits at positions corresponding to the second type codeword include information bits; determining values for one or more redundant bits placed between two adjacent information bits in the interleaved bitstream based on the values of either or both of the two adjacent information bits; and transmitting the interleaved bitstream to one or more of the ONUs.