OLT Downstream Bit Interleaving for ONU Sensitivity Protection
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Solution Overview
Problem
Current PON systems face challenges in maintaining operation when an ONU is pushed beyond sensitivity due to unforeseen circumstances, leading to service outages and the need for urgent repairs.
Innovation Solution
The solution involves generating low-rate NRZ and Miller signals that are compliant with the G.9804 standard, using an apparatus and method that include obtaining a stream of codewords, interleaving them to insert redundant bits, and transmitting the interleaved bitstream to ONUs, thereby reducing inter-symbol interference and improving sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If 50G NRZ signals are transmitted at high line rate, then downstream transmission speed is improved, but ONU sensitivity deteriorates making the system vulnerable to fiber pulls, bends, and connector issues
Solution Approach 1:
The system dynamically switches between 50G NRZ mode and 25G protected mode based on ONU sensitivity conditions. The OLT monitors ONU performance and activates the protection mode when sensitivity degradation is detected, allowing the system to adapt to changing channel conditions while maintaining service continuity
Solution Approach 2:
The invention changes the signal parameters by introducing a 25G protected mode with different modulation characteristics. The 25G signal uses different encoding (Miller or NRZ with specific patterns) that is more robust to channel impairments, effectively changing the transmission parameters to improve reliability when the original 50G parameters become problematic
2Reliability
If 25G Miller encoding is used for protection mode, then ONU sensitivity is improved, but compatibility with G.9804 standard and existing PSBd synchronization is worsened
Solution Approach 1:
The invention uses the existing 25G protection mode infrastructure as an intermediary between the 50G NRZ signal and the ONU receiver. This 25G mode acts as a mediator that provides the sensitivity improvement needed while maintaining compatibility with the G.9804 standard framework, avoiding the need for completely new synchronization mechanisms
Solution Approach 2:
The 25G protected mode is designed to serve multiple functions: it provides sensitivity improvement for degraded channels, maintains compatibility with G.9804 standard requirements, and works with existing ONU hardware. This multi-functionality allows a single solution to address both sensitivity and compatibility requirements
3Reliability
If 25G NRZ signaling is used for protection mode, then ONU sensitivity is improved, but inter-symbol interference impact on 50G NRZ equalization worsens
Solution Approach 1:
The downstream signal is segmented into separate 50G NRZ and 25G protected mode components that are transmitted in different time slots or frequency resources. This segmentation prevents the 25G signal from causing inter-symbol interference to the 50G equalization process, as they operate in separate domains
Solution Approach 2:
The invention extracts the protection functionality into a separate 25G signal path that is independent from the main 50G NRZ data stream. By taking out the protection mode as a separate entity with its own encoding and modulation, the system avoids the inter-symbol interference that would occur if 25G signaling were mixed with 50G NRZ in the same signal path
Data Source
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Figure 3a~3b
AI summary
The present invention discloses an apparatus for use by an OLT, communicatively connected to optical network units, ONUs, comprising means for performing: obtaining a stream of codewords, comprising a first type codeword and a second type codeword, wherein, the first type codeword is an idle codeword, and the second type codeword comprises 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 comprise redundant bits, and bits at positions corresponding to the second type codeword comprise 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, to reduce inter-symbol interference on either or both of the two adjacent information bits; transmitting the interleaved bitstream to one or more of the ONUs.