EPON Frame Delimiter Detection Using Hamming Distance Scanning
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Solution Overview
Problem
In Ethernet Passive Optical Networks (EPON) with Forward Error Correction (FEC), the current delimiters used to separate Ethernet frames from FEC parity bits are prone to misidentification due to high auto-correlation, leading to potential frame errors, especially as the network size increases and signal-to-noise ratio decreases.
Innovation Solution
An enhanced delineator window is implemented to scan through a longer bit stream, identifying the best match to the TFEC_E sequence with the shortest Hamming distance, reducing the likelihood of premature misidentification by selecting the frame bits with the shortest Hamming distance as the delimiter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional delimiters (TFEC) are used to separate Ethernet frames from FEC parity bits, then the delimiter structure is simple and backward-compatible with non-FEC equipment, but the high auto-correlation of the delimiter sequence causes misidentification in noisy conditions
Solution Approach 1:
The patent introduces an intermediary verification process between the delimiter detection and frame processing stages. A verification module checks the detected delimiter by examining subsequent bits to confirm whether they match the expected TFEC sequence pattern, thereby mediating the harmful effect of auto-correlation-induced misidentification
Solution Approach 2:
The patent implements feedback by using the detected delimiter position to guide subsequent verification checks. When a potential delimiter is detected, the system feeds back to verify the following bits match the expected TFEC pattern, and adjusts the detection strategy based on verification results to prevent misidentification
2Productivity
If the network size increases in passive optical transmission, then the network capacity and coverage are improved, but the signal-to-noise ratio decreases leading to more frequent bit errors
Solution Approach 1:
The patent applies preliminary action by implementing Forward Error Correction (FEC) encoding at the transmitter before data transmission. The FEC code adds redundant parity bits to the Ethernet frame, enabling the receiver to detect and correct bit errors that occur during transmission over extended distances, thereby maintaining reliability as network size increases
Solution Approach 2:
The patent uses beforehand cushioning by incorporating FEC parity bits in advance to cushion against the accumulation of bit errors that occur during long-distance passive optical transmission. This protective measure is built into the frame structure before transmission, allowing error correction without requiring retransmission
3Adaptability or versatility
If FEC parity bits are aggregated and appended to conventional Ethernet frames, then backward compatibility with non-FEC equipment is maintained, but the frame structure becomes more complex
Solution Approach 1:
The patent applies universality by designing the TFEC delimiter to serve multiple functions: it acts as both the end-of-frame delimiter for FEC-capable equipment and as a separator between the Ethernet frame and FEC parity bits. This multi-functional design maintains backward compatibility while supporting FEC, without requiring fundamentally different frame structures for different equipment types
Data Source
AI summary
Embodiments of the present invention provide a system that identifies an even delimiter in a forward error correction (FEC)-coded Ethernet frame. The system receives an FEC-coded Ethernet frame that includes the even delimiter, which is a predetermined sequence that separates a conventional Ethernet frame and FEC parity bits in the FEC-coded Ethernet frame. Next, the system scans a bit stream of the FEC-coded Ethernet frame. Then, the system determines a first Hamming distance between a first consecutive set of frame bits in the bit stream and the even delimiter. The system also determines a second Hamming distance between a second consecutive set of frame bits in the bit stream and the even delimiter. Both the first and second Hamming distances are shorter than a predefined value. The system subsequently selects one of the first and second sets of frame bits having the shorter Hamming distance as the even delimiter.