8×8 MIMO Equalizer for Coherent Receiver I/Q Skew Compensation
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Solution Overview
Problem
Existing optical communication systems face performance limitations and high complexity due to transmitter I/Q skew and quadrature error in subcarrier multiplexing schemes, leading to signal degradation and increased channel noise.
Innovation Solution
A reduced complexity 8×8 adaptive equalizer is developed to compensate for transmitter I/Q imbalance and skew, featuring a digital signal processor with a chromatic dispersion/polarization-mode dispersion equalizer, carrier recovery, cycle slip correction, and timing synchronization modules, with each output connected to three inputs, reducing complexity by approximately four times while maintaining receiver performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional equalizers are used to compensate transmitter I/Q skew and quadrature error, then receiver performance can be maintained, but device complexity increases significantly
Solution Approach 1:
The equalizer is segmented into specialized modules: chromatic dispersion/PMD equalizer, carrier recovery module, cycle slip correction module, timing synchronization module, and reduced complexity 8×8 MIMO equalizer. Each module handles specific impairment compensation tasks, reducing overall system complexity while maintaining performance.
Solution Approach 2:
The patent changes the structural parameters of the equalizer by configuring each of the 8 outputs to be electrically coupled to only 3 of the 8 inputs (instead of all 8 inputs), reducing the number of digital filters from 64 to 24. This parameter change maintains compensation effectiveness while reducing complexity by approximately 4 times.
2Reliability
If phase and gain imbalance of the modulator is completely compensated at the receiver, then signal quality improves, but channel noise is amplified
Solution Approach 1:
The patent applies partial compensation rather than complete compensation for phase and gain imbalance. The reduced complexity 8×8 MIMO equalizer provides sufficient impairment compensation without fully correcting all imbalance parameters, thereby avoiding excessive noise amplification while maintaining acceptable signal quality.
Data Source
AI summary
A method and structure for compensation techniques in coherent optical receivers. The present invention provides a coherent optical receiver with an improved 8×8 adaptive MIMO (Multiple Input, Multiple Output) equalizer configured within a digital signal processor (DSP) to compensate the effects of transmitter I/Q skew in subcarrier multiplexing (SCM) schemes. The 8×8 MIMO equalizer can be configured such that each of the 8 outputs is electrically coupled to 3 of 8 inputs, wherein each of the input-output couplings is configured as a filter. The method includes compensating for impairments to the digital conversion of an optical input signal via the 8×8 MIMO equalizer following other signal processing steps, such as chromatic dispersion (CD)/polarization-mode dispersion (PMD) compensation, carrier recovery, timing synchronization, and cycle slip correction.