Adaptive Equalization With MLSE for Nyquist-Limit Optical Signals
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Solution Overview
Problem
Existing digital signal processing techniques face challenges in compensating for band-limited distortion near the Nyquist limit, leading to increased transmission penalties and spectral efficiency limitations, while also struggling with high computational complexity in multi-lane transmissions.
Innovation Solution
A digital signal processing apparatus employing an adaptive equalization filter with a decision feedback mechanism and a feedback loop containing a fixed filter for band limitation, combined with maximum likelihood sequence estimation, to optimize parameter settings and maintain inter-symbol interference, and utilizing a butterfly filter for polarization demultiplexing and distortion compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If adaptive equalization filter amplifies high-frequency signal components to compensate for band-limited distortion, then compensation for band-limited distortion is improved, but signal-to-noise ratio deteriorates
Solution Approach 1:
The patent introduces a feedback loop where the output of the adaptive equalization filter is fed back through a model of the frequency filter's transfer function. This feedback mechanism allows the system to learn and compensate for the band-limited distortion without simply amplifying noisy high-frequency components, as the feedback provides information about the actual distortion introduced by the frequency filter.
Solution Approach 2:
The patent uses an intermediate model of the frequency filter's transfer function as a mediator between the adaptive equalization filter and the input signal. This model allows the system to predict and compensate for band-limited distortion without directly manipulating the noisy high-frequency signal components, thereby avoiding noise amplification while still achieving distortion compensation.
2Reliability
If adaptive equalization filter compensates for band-limited distortion near Nyquist limit, then transmission quality is improved, but transmission penalty increases
Solution Approach 1:
The feedback loop using the frequency filter transfer function model enables the system to achieve effective distortion compensation without the need for excessive amplification of high-frequency components. This reduces the transmission penalty by avoiding noise amplification while still improving transmission quality through intelligent distortion compensation.
3Manufacturing precision
If adaptive equalization filter performs distortion compensation, then signal distortion is reduced, but computational complexity increases
Solution Approach 1:
The patent performs preliminary action by pre-modeling the frequency filter's transfer function and incorporating it into the feedback loop. This preliminary modeling allows the adaptive equalization filter to compensate for band-limited distortion more efficiently, reducing the computational complexity required for real-time distortion compensation while maintaining high accuracy.
Data Source
AI summary
A parameter of an adaptive filter is optimized so that inter-symbol interference having an amount corresponding to an inserted fixed filter remains. A digital signal processing apparatus which is included in an optical signal receiver and processes a digital signal converted from an optical signal is provided with: a linear adaptive filter which applies a dynamically controllable linear transfer function to the digital signal; a maximum likelihood sequence decoder which applies a transfer function of a transmission-path model to a plurality of signal sequence candidates to generate a plurality of reference signals, and decodes a reception signal using maximum likelihood sequence estimation which evaluates the differences between an output signal of the linear adaptive filter and the reference signals to estimate the most likely transmission time sequence; a signal regenerator which generates a signal corresponding to decoded data from the maximum likelihood sequence decoder; a feedback distortion adding filter which adds distortion that is equivalent to the transmission-path model used in the maximum likelihood sequence decoder to an output signal of the signal regenerator; and an adaptive equalization filter control block which updates a tap coefficient of the linear adaptive filter in accordance with an LMS algorithm using the difference between a target signal that is an output signal of the feedback distortion adding filter and the digital signal as an error signal.