Coherent Optical Receiver Adaptive Equalization
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Solution Overview
Problem
Conventional optical communication systems face performance limitations and high power consumption due to misalignment of data channels caused by delay, which degrades data recovery in receivers.
Innovation Solution
A coherent optical receiver device employing a constrained frequency-domain block least means square (CFBLMS) algorithm for chromatic dispersion and polarization mode dispersion equalization, reducing implementation complexity and achieving better performance by filtering in the frequency domain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional equalization methods are used to compensate for chromatic dispersion and polarization mode dispersion, then data recovery performance is maintained, but device complexity and power consumption increase
Solution Approach 1:
The equalization process is segmented into two independent stages: a frequency-domain equalizer for chromatic dispersion compensation and a time-domain equalizer for polarization mode dispersion compensation. This segmentation allows each stage to be optimized separately, reducing overall implementation complexity while maintaining data recovery performance.
Solution Approach 2:
The patent transitions from purely time-domain equalization to frequency-domain equalization by incorporating an FFT (Fast Fourier Transform) module. This dimensional change enables chromatic dispersion compensation through frequency-domain filtering, which is more computationally efficient than conventional time-domain methods.
2Reliability
If conventional equalization algorithms are implemented, then dispersion compensation is achieved, but power consumption increases
Solution Approach 1:
By segmenting the equalization into frequency-domain and time-domain stages, the patent reduces the computational burden on the receiver. The frequency-domain equalizer uses efficient FFT-based processing for chromatic dispersion compensation, while the time-domain equalizer handles polarization mode dispersion with reduced complexity, thereby lowering overall power consumption.
Solution Approach 2:
The patent changes the processing domain from time-domain to frequency-domain for chromatic dispersion compensation. This parameter change enables the use of more efficient algorithms that consume less power while achieving the same compensation effect, as frequency-domain processing can leverage the spectral properties of the channel more effectively.
3Measurement precision
If delay compensation is applied to align data channels, then timing alignment is improved, but implementation complexity increases
Solution Approach 1:
The timing alignment function is segmented and integrated into the frequency-domain equalization process. By compensating for delay in the frequency domain rather than attempting precise time-domain alignment, the patent achieves timing synchronization with reduced implementation complexity, as the FFT-based approach naturally handles timing variations.
Data Source
AI summary
A method and structure for equalization in coherent optical receivers. Block-based LMS (BLMS) algorithm is one of the many efficient adaptive equalization algorithms used to (i) increase convergence speed and (ii) reduce implementation complexity. Since the computation of the equalizer output and the gradient of the error are obtained using a linear convolution, BLMS can be efficiently implemented in the frequency domain with the constrained frequency-domain BLMS (FBLMS) adaptive algorithm. The present invention introduces a novel reduced complexity constrained FBLMS algorithm. This new approach replaces the two discrete Fourier transform (DFT) stages required to evaluate the DFT of the gradient error, by a simple frequency domain filtering. Implementation complexity can be drastically reduced in comparison to the standard constrained FBLMS. Furthermore, the new approach achieves better performance than that obtained with the unconstrained FBLMS in ultra-high speed coherent optical receivers.