Psync Field FEC Status Indication in TWDM-PON Downstream Frames
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Solution Overview
Problem
The bit error rate after error correction in the frame header of downstream data frames in TWDM-PON systems does not meet the requirements, leading to inconsistent processing between the OLT and ONU, affecting normal payload data reception.
Innovation Solution
A downstream data frame transmission method that uses an 8-byte physical synchronization sequence (Psync) field to indicate the FEC status, allowing for fuzzy matching and optimal error correction performance, and optionally includes a reserved field to increase the length and reliability of the FEC indication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If BCH(63,12,1) error correction code is used to protect the frame header, then the error correction capability is improved, but the bit error rate after correction is still 1e-6 which cannot meet the requirement of the FEC indication field
Solution Approach 1:
The frame header is segmented into multiple fields, with the Psync field specifically dedicated to FEC status indication. This segmentation allows the Psync field to be protected with stronger error correction (RS code) while other header fields use BCH code, resolving the contradiction between overall error correction capability and the specific bit error rate requirement for FEC indication.
Solution Approach 2:
Different error correction schemes are applied to different parts of the frame header. The Psync field uses RS(248,216) coding for higher reliability to meet the 1e-6 bit error rate requirement, while other header fields use BCH(63,12,1) coding. This local differentiation of quality resolves the contradiction by providing enhanced protection only where needed.
2Reliability
If the Psync field is used to indicate FEC status, then the FEC indication reliability is improved, but the field length and frame structure complexity increase
Solution Approach 1:
The Psync field serves multiple functions: it acts as a physical synchronization sequence for frame identification, carries FEC status indication, and enables ONU synchronization state determination. By making this field multi-functional, the patent avoids adding separate fields for each function, thereby reducing overall frame structure complexity while improving FEC indication reliability.
Data Source
AI summary
A downstream data frame transmitting method includes: generating, by an optical line terminal (OLT), a downstream data frame, where the downstream data frame includes a frame header and a payload, the frame header includes a physical synchronization sequence (Psync) field, and the Psync field is used to identify the downstream data frame, where when a value of the Psync field is a first value, the Psync field is further used to indicate that payload data is protected by forward error correction (FEC); or when a value of the Psync field is a second value, the Psync field is further used to indicate that payload data is not protected by FEC; and sending, by the OLT, the downstream data frame. Embodiments of the present invention can reduce a bit error rate of a FEC indication status and improve reliability of the FEC indication status.