Passive Optical Network Multimodulation for Legacy ONU Compatibility
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Solution Overview
Problem
Current passive optical networks (PONs) face challenges in upgrading downstream signals to higher bit rates without requiring upgrades or replacements of legacy Optical Network Units (ONUs) at subscriber premises, which is logistically difficult and expensive.
Innovation Solution
The implementation of a multimodulation capability in PONs, where a signal encoder generates a digital encoding signal for modulation with a number of constellation points greater than 2, and a modulator uses this signal to generate a modulated signal with adapted probability of transitions, allowing for backwards compatibility with legacy ONUs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a higher bit rate signal is provided on a new wavelength, then the downstream signal bit rate is improved, but legacy ONUs must be replaced or upgraded which increases device complexity and upgrade cost
Solution Approach 1:
The OLT is configured to transmit downstream signals using multiple modulation formats (NRZ and PAM4) on the same wavelength, enabling the system to serve both legacy ONUs (which can decode NRZ) and upgraded ONUs (which can decode PAM4) simultaneously. This multi-functionality eliminates the need for wavelength separation and ONU replacement.
Solution Approach 2:
The system changes the modulation format parameter from单一的NRZ to a combination of NRZ and PAM4 formats. By adjusting the modulation scheme rather than changing the wavelength or hardware, the OLT achieves higher bit rates while maintaining compatibility with existing ONUs.
2Productivity
If OLTs are upgraded to provide higher bit rate signal, then the downstream signal bit rate is improved, but backwards compatibility with legacy ONUs deteriorates
Solution Approach 1:
The downstream signal is segmented into multiple portions, each modulated with a different format (NRZ for legacy compatibility, PAM4 for higher bit rate). This segmentation allows the OLT to provide upgraded service to capable ONUs while maintaining support for legacy devices on the same network infrastructure.
Solution Approach 2:
The upgraded OLT is designed with multi-functionality to transmit both NRZ and PAM4 modulation formats simultaneously, enabling it to serve both legacy and upgraded ONUs without sacrificing backwards compatibility while achieving higher overall network bit rates.
3Productivity
If legacy ONUs are replaced or upgraded, then the downstream signal bit rate is improved, but logistical difficulty and upgrade cost increase
Solution Approach 1:
The OLT acts as an intermediary that performs the modulation format conversion and signal generation, eliminating the need for ONU replacement. The OLT's ability to transmit multiple modulation formats serves as the mediator that enables higher bit rates while keeping legacy ONUs in place.
Solution Approach 2:
Instead of changing physical hardware (ONUs), the system changes the signal parameter (modulation format) at the OLT. This parameter change approach achieves bit rate improvement without the logistical complexity and cost of field device replacements.
Data Source
AI summary
An optical line terminal (OLT) in flexible passive optical network (PON) transmits a downstream signal with two or more modulation formats, wherein at least one of the modulation formats is a modified PAMx modulation format and wherein x is greater than 2. The modified PAMx modulation encodes data bits such that the probability of at least one predetermined transition between amplitude levels is modified. Furthermore, an optical network unit (ONU) in the flexible PON is assigned to one of the plurality of modulation formats based on one or more parameters, such as configuration of the ONU and line conditions.