Optical Receiver Adaptive Equalizer Symbol Offset Minimization
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Solution Overview
Problem
Adaptive equalizers in digital coherent receivers face challenges in maintaining signal quality due to differential group delay (DGD) and polarization changes, leading to undesirable converging states that degrade bit error rate (BER), and increasing the number of taps is limited by circuit scale.
Innovation Solution
An optical transceiver is designed with a symbol offset determination part that repeatedly adjusts the initial reference index for tap coefficients to minimize symbol offset between polarized waves, optimizing the converging state of the adaptive equalizer without increasing the number of taps, thereby stabilizing the system and improving DGD tolerance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the number of taps of the finite impulse response (FIR) filter is increased to improve the DGD tolerance of an adaptive equalizer, then the DGD tolerance is improved, but the circuit scale increases beyond practical limits
Solution Approach 1:
The patent changes the parameter of the initial reference index for tap coefficients to optimize the converging state of the adaptive equalizer. By adjusting this index parameter, the system achieves better DGD tolerance without increasing the number of taps, thus avoiding circuit scale expansion while improving reliability
Solution Approach 2:
The patent applies preliminary action by optimizing the initial reference index before the adaptive equalizer starts processing signals. This preliminary optimization ensures the equalizer converges to a desirable state from the beginning, preventing signal quality degradation without requiring additional circuit resources
2Measurement precision
If BER monitoring is used to determine the suitability of the converging state of an adaptive equalizer, then the converging state can be accurately evaluated, but the system startup time increases
Solution Approach 1:
The patent introduces an intermediary approach by using symbol offset as an intermediate indicator to evaluate the converging state. This intermediate metric provides timely feedback during startup without requiring complete BER monitoring, thus maintaining evaluation accuracy while reducing startup time loss
Solution Approach 2:
The patent substitutes the mechanical BER monitoring process with a faster symbolic evaluation method. By replacing the time-consuming BER measurement with quicker symbol-level assessments, the system achieves accurate converging state evaluation without the time penalty of full BER monitoring
3Ease of operation
If the adaptive equalizer operates with a fixed initial reference index, then the circuit operation is simple, but the converging state may be undesirable causing signal quality degradation
Solution Approach 1:
The patent applies dynamics by making the initial reference index adjustable rather than fixed. This dynamic parameter can be optimized based on operating conditions to ensure desirable converging states, maintaining signal quality while keeping the circuit operation relatively simple through controlled adaptability
Data Source
AI summary
An optical transceiver converts a received optical signal to an electric signal and converts the electric signal to a digital signal, and has an adaptive equalizer to adaptively equalize the digital signal, a synchronization part to synchronize a first polarized wave and a second polarized wave contained in the adaptively equalized digital signal and having polarization axes perpendicular to each other, and a symbol offset determination part to determine an amount of symbol offset between the first polarized wave and the second polarized wave based upon symbol synchronization information of the first polarized wave and the second polarized wave supplied from the synchronization part, the symbol offset determination part being configured to repeat determination of the amount of symbol offset and restart the adaptive equalizer until the symbol offset is minimized.