Sub-Carrier Interleaving for Optical Forward Error Correction
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Solution Overview
Problem
In optical transmission systems using digital subcarriers, the signal-to-noise ratio (SNR) varies across subcarriers due to analog bandwidth constraints, leading to differing bit error rates (BER) and performance issues, as subcarriers closer to the carrier frequency tend to have better SNR than those at the outer edges.
Innovation Solution
Implementing multiple forward error correction (FEC) encoders to encode data streams and interleave information across multiple subcarriers, ensuring that both high and low SNR subcarriers carry information from each data stream, thereby distributing errors and improving overall error correction capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If data streams are assigned to corresponding subcarriers in conventional manner, then each subcarrier can be independently modulated and detected, but subcarriers at outer edges of spectrum suffer from poor SNR leading to high bit error rates
Solution Approach 1:
The data stream is segmented into multiple portions that are distributed across multiple subcarriers. Each FEC encoder processes a portion of the data and assigns it to a different subcarrier, ensuring that no single subcarrier carries the entire data stream. This segmentation allows the system to overcome the SNR variations of individual subcarriers.
Solution Approach 2:
Multiple FEC encoders are combined to process different portions of the same data stream simultaneously. The encoded portions from multiple encoders are then merged and transmitted over different subcarriers. At the receiver, the portions are recombined and decoded, effectively combining the error correction capabilities across all subcarriers including those with poor SNR.
2Reliability
If multiple FEC encoders are used to encode data streams and interleave information across multiple subcarriers, then error correction capability is improved, but system complexity increases
Solution Approach 1:
The data stream is divided into multiple portions that are processed by different FEC encoders. Each encoder handles a specific segment of the data, which reduces the computational burden on each individual encoder while collectively providing robust error correction across all subcarriers.
Solution Approach 2:
Multiple FEC encoders are deployed to perform the same error correction function on different portions of the data stream. This universal application of FEC across multiple encoders allows the system to achieve enhanced error correction capability without requiring fundamentally different or specialized components for each encoder.
Data Source
AI summary
Consistent with the present disclosure, multiple forward error correction (FEC) encoders are provided for encoding a respective one of a plurality of data streams. A mechanism is provided to mix or interleave portions of the encoded data such that each subcarrier carries information associated with each data stream, as opposed to each subcarrier carrying information associated with only a corresponding one of the data streams. As a result, both higher SNR and low SNR optical subcarriers carry such information, such that errors occurring during transmission are distributed and not concentrated or limited to information associated with a single data stream. Accordingly, at the receive end, each FEC decoder decodes information having a similar overall error rate. By balancing the error rates across each FEC encoder/decoder pair, the overall ability to correct errors improves compared to a system in which mixing or interleaving is not carried out.