Echo Cancellation in Coherent Optical Networks
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Solution Overview
Problem
Coherent optical systems face challenges in accurately detecting primary signals due to echo interference caused by reflections, which are exacerbated by weak received signals and faulty connections, hindering the adoption of full-duplex coherent optics in access networks.
Innovation Solution
An echo cancellation method and system that involves extracting phase-distortion estimates, reconstructing echo signals, generating clean signals, and producing primary signals by mapping clean-phase estimates to constellation symbols, utilizing a decision decoder, subtractor circuits, modulus equalizers, phase-distortion estimators, phase retrievers, and adaptive filters to mitigate echo interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If coherent detection is used to improve receiver sensitivity, then detection precision is improved, but echo interference from reflections increases
Solution Approach 1:
The patent extracts the echo signal from the received signal by separately detecting the direct signal and echo signal components. The echo cancellation unit removes the echo component by subtracting it from the received signal, thereby eliminating the harmful echo interference while preserving the improved receiver sensitivity provided by coherent detection.
Solution Approach 2:
The patent introduces an intermediary echo cancellation unit that processes the received signal to separate and remove echo components. This intermediary processing stage acts as a mediator between the coherent detection process and the final signal decision, eliminating echo interference without compromising the sensitivity benefits of coherent detection.
2Productivity
If full duplex coherent optics is implemented to double fiber capacity, then productivity is improved, but echo interference from bidirectional transmission increases
Solution Approach 1:
The patent extracts and separately processes the echo signal component that arises from bidirectional transmission. By identifying and removing the echo component through the echo cancellation unit, the system enables full duplex coherent optics operation to double fiber capacity while eliminating the echo interference inherent in bidirectional transmission.
Solution Approach 2:
The patent implements a feedback mechanism where the detected echo signal is fed back to the echo cancellation unit for continuous suppression. This feedback loop allows the system to maintain full duplex coherent optics operation for doubled fiber capacity while dynamically compensating for echo interference from bidirectional transmission.
3Reliability
If angle-polished connectors are used to reduce reflections, then reliability is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent introduces an intermediary echo cancellation processing stage that compensates for reflections from standard connectors. This intermediary processing approach achieves reliable reflection reduction without requiring high-precision angle-polished connectors, thereby reducing manufacturing precision requirements while maintaining system reliability.
4Measurement precision
If echo cancellation processing is added to mitigate reflections, then signal quality is improved, but device complexity increases
Solution Approach 1:
The patent segments the received signal processing into distinct functional units: coherent detection unit, echo cancellation unit, and signal decision unit. This segmentation allows echo cancellation to be implemented as a modular add-on to coherent detection, improving signal quality while managing device complexity through structured, incremental processing stages.
Solution Approach 2:
The patent performs preliminary echo cancellation processing on the received signal before final signal decision. By removing echo interference in advance through the echo cancellation unit, the system improves signal quality for subsequent processing while managing complexity through preliminary rather than continuous complex processing.
Data Source
AI summary
An echo cancellation method includes steps of (a) extracting phase-distortion estimates, (b) reconstructing an echo signal, (c) generating a clean signal, and (d) producing a primary signal. Step (a) includes extracting, from a first phase signal, a plurality of phase-distortion estimates, the first phase signal having been estimated from an echo-corrupted signal received at a first coherent transceiver of a coherent optical network. Step (b) includes reconstructing an echo signal from the plurality of phase-distortion estimates and a transmitted signal transmitted by the first coherent transceiver. Step (c) includes generating a clean signal as a difference between the reconstructed echo signal and the first phase signal. Step (d) includes producing a primary signal by mapping each of a plurality of clean-phase estimates of the clean signal to one of a plurality of constellation symbols associated with a modulation scheme of the primary signal.