Feedback Adjustable Constellation De-mapper for Optical Coherent Systems
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Solution Overview
Problem
In optical coherent communications systems, Carrier Frequency Offset (CFO) causes de-mapper mismatch due to symbol rotation, leading to incorrect binary data output, especially when blind CFO estimation algorithms fail to accurately compensate for large CFO values.
Innovation Solution
A feedback de-mapper adjustment module that uses average Error Vector Magnitude (EVM) and Bit Error Ratio (BER) monitoring to detect mismatches and rotate the constellation de-mapper, ensuring correct signal interpretation by comparing these metrics to a predefined table and adjusting the de-mapper accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If blind CFO estimation algorithms are used to compensate for carrier frequency offset, then bandwidth efficiency is preserved and transmitter architecture is simplified, but de-mapper mismatch occurs when CFO exceeds a certain threshold
Solution Approach 1:
The patent implements a feedback mechanism where the de-mapper outputs bit error ratios (BER) that are fed back to a controller. The controller uses this BER feedback to detect when CFO-induced rotation causes de-mapper mismatch and automatically adjusts the de-mapper configuration or triggers re-estimation of CFO, thereby maintaining reliability while preserving the bandwidth efficiency of blind estimation.
Solution Approach 2:
The patent makes the de-mapper dynamic by allowing it to change its configuration based on real-time conditions. The controller adjusts the de-mapper's operating parameters or triggers re-synchronization when CFO exceeds thresholds, enabling the system to adapt to varying CFO conditions without sacrificing the simplicity of blind estimation architecture.
2Manufacturing precision
If constellation de-mapper is designed after back-to-back calibration at transmitter, then correct binary data output is guaranteed under normal conditions, but de-mapper mismatch occurs when CFO causes symbols to shift
Solution Approach 1:
The patent performs preliminary calibration at the transmitter to establish the correct de-mapper configuration for normal conditions. However, it also pre-establishes fallback mechanisms and monitoring thresholds that activate when CFO causes symbol shifts, ensuring that the system can recover from calibration drift without losing data correctness.
Solution Approach 2:
The system continuously monitors bit error ratios and uses this feedback to detect when CFO-induced rotation causes de-mapper mismatch. When mismatch is detected, the controller automatically triggers correction actions such as re-estimating CFO or adjusting de-mapper parameters, thereby maintaining data correctness despite CFO variations that would otherwise cause symbol shifts.
3Device complexity
If blind CFO estimation is used to avoid transmitter calibration complexity, then system complexity is reduced, but accuracy of symbol detection deteriorates under large CFO values
Solution Approach 1:
The patent uses feedback from bit error ratio monitoring to detect when blind CFO estimation becomes inaccurate under large CFO conditions. The controller receives this feedback and triggers corrective actions such as switching to alternative estimation methods or re-synchronizing the de-mapper, thereby maintaining measurement precision while preserving the simplicity of the blind estimation architecture under normal conditions.
Data Source
AI summary
A system and method to adjust the symbol constellation used to de-map a signal in an optical coherent communications system. A feedback de-mapper adjustment module is configured to compare average Error Vector Magnitude and Bit Error Ratio to a pre-defined table to determine when a constellation de-mapper mismatch occurs. The feedback de-mapper adjustment module then rotates the de-mapper constellation in order to compensate for phase drift.