Hybrid MIMO Equalizer for WDM Optical Transmission
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Solution Overview
Problem
Existing wavelength-division multiplexing optical transmission systems face challenges with signal spectrum narrowing and asymmetric band narrowing due to ROADM devices and analog front-end bandwidth limitations, leading to increased circuit size and degraded convergence performance of MIMO equalizers.
Innovation Solution
The implementation of a hybrid MIMO equalizer combining frequency-domain and time-domain MIMO equalizers, where the frequency-domain MIMO equalizer provides efficient circuit implementation for static band narrowing and the time-domain MIMO equalizer handles dynamic variations, effectively canceling crosstalk and minimizing circuit size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single MIMO equalizer is used to compensate for waveform distortion and cancel crosstalk, then the circuit size increases and convergence performance deteriorates due to the need for extremely steep filter characteristics
Solution Approach 1:
The patent divides the single MIMO equalizer into two separate functional blocks: a frequency-domain MIMO equalizer for crosstalk cancellation and a time-domain MIMO equalizer for waveform distortion compensation. This segmentation allows each block to have optimized, less steep filter characteristics, reducing the overall circuit size while maintaining both crosstalk cancellation and distortion compensation functions.
2Adaptability or versatility
If the signal band is narrowed by ROADM device characteristics, then the signal spectrum is cut off and transmission flexibility is reduced
Solution Approach 1:
The patent creates a digital copy of the ROADM device's band narrowing characteristics and reproduces this filtering effect in the digital signal processing domain. By measuring the actual spectrum characteristics after ROADM filtering and implementing an equivalent digital filter, the system compensates for the ROADM-induced spectrum narrowing, restoring the original signal spectrum and maintaining transmission flexibility.
3Productivity
If dense subcarrier spacing is used to increase frequency usage efficiency, then crosstalk between subcarriers increases
Solution Approach 1:
The patent introduces a frequency-domain MIMO equalizer as an intermediary processing block between the demultiplexer and the time-domain equalizer. This intermediate frequency-domain processing effectively separates overlapping subcarrier signals and cancels crosstalk before the signals undergo time-domain equalization, enabling dense subcarrier spacing to be used without suffering from excessive crosstalk.
Data Source
AI summary
To suppress the deterioration of the characteristics of a MIMO equalizer as well as minimizing an increase in circuit size in spite of the occurrence of signal spectrum narrowing and asymmetric spectrum degradation, a wavelength-division multiplexing optical transmission system (10) according to an embodiment includes a transmitter (1) that generates one channel signal by wavelength-division multiplexing a plurality of subcarrier signals so as to overlap each other and transmits the channel signal, and a receiver (2) that separates a received channel signal into subcarrier signals, and performs equalization using an MIMO equalizer (3) including a FDE-MIMO equalizer (4) and a TDE-MIMO equalizer (5) on each of the separated subcarrier signals.