Flexible PON With 25G Miller Coding for Legacy ONU Compatibility
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Solution Overview
Problem
Existing passive optical networks (PON) with a fixed 50G NRZ modulation rate face compatibility issues with older ONUs due to aging receiver components and marginal link conditions, leading to high bit error rates and operational limitations.
Innovation Solution
A flexible PON system that supports both 50G NRZ and 25G Miller-encoded data streams using the same front-end receiver configuration, allowing legacy ONUs to recover both by employing a 50 Gbaud clock rate, with 25G Miller data requiring a clock running at twice its rate for recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If fixed 50G NRZ modulation is used in downstream transmission, then transmission rate is improved, but compatibility with older ONUs deteriorates
Solution Approach 1:
The system dynamically switches between 50G NRZ and 25G Miller modulation schemes based on ONU capabilities and link conditions. The OLT can adaptively select the appropriate modulation format for each ONU, allowing the network to optimize transmission rate while maintaining compatibility with legacy equipment.
Solution Approach 2:
The patent changes the modulation parameter from fixed 50G NRZ to a variable scheme that includes 25G Miller modulation. By altering the modulation format and rate parameters, the system accommodates both modern high-speed requirements and legacy ONU constraints, resolving the contradiction between transmission rate and compatibility.
2Productivity
If 50G NRZ transmission is implemented, then data rate is improved, but receiver performance under aging and marginal conditions deteriorates
Solution Approach 1:
Instead of always using the maximum 50G NRZ rate, the system applies partial action by selectively using 25G Miller modulation for links that are aging or operating under marginal conditions. This reduces the data rate slightly but significantly improves reliability and extends the operational life of existing infrastructure.
Solution Approach 2:
The system prepares for future degradation by having 25G Miller modulation ready as a fallback option. When link conditions deteriorate or ONUs age, the network can switch to the more robust 25G Miller scheme beforehand, cushioning against performance degradation and maintaining reliable operation.
3Device complexity
If single 50G NRZ stream is transmitted, then system simplicity is maintained, but flexibility for different data rates deteriorates
Solution Approach 1:
The OLT is designed with multi-functionality to support both 50G NRZ and 25G Miller modulation schemes using the same physical infrastructure. This universal design allows a single system to serve multiple purposes - high-speed transmission for modern ONUs and reliable transmission for legacy ONUs - without requiring separate dedicated systems.
Solution Approach 2:
The downstream transmission is segmented into different modulation streams - 50G NRZ for capable ONUs and 25G Miller for legacy or marginal links. The OLT can segment the data flow and apply appropriate modulation schemes to different portions, providing flexibility while maintaining overall system simplicity through a unified architecture.
Data Source
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AI summary
Apparatus and method are disclosed that utilize a particular delay modulation technique (i.e., Miller coding) to encode 25 Gb/s data for inclusion with the 50 Gb/s NRZ data in a downstream broadcast transmission from an optical line terminal (OLT) to a plurality of optical network units (ONUs) through an optical distribution network (ODN). The specific Miller coding technique allows for a secondary data stream, operating at half the rate of the NRZ data) to supplement the primary 50 Gb/s NRZ transmission, since both signals are recovered using the same clocking circuitry at the ONU.