Low-Complexity Monitoring and Compensation of Transceiver IQ Imbalance by Multi-dimensional Architecture for Dual-Polarization 16 Quadrature Amplitude Modulation

2025-12-15

AI Summary

In DP-16QAM optical communication systems, transmitter/receiver (TX/RX) I/Q imbalance degrades performance and incurs high computational complexity. Method: This paper proposes a low-complexity joint monitoring and compensation architecture integrating chirp-Z transform-based dispersion pre-compensation, Gardner phase detection, and error-minimization-based TX imbalance estimation. It introduces a novel decoupled TX/RX imbalance estimation algorithm and designs a cascaded CV-MIMO (butterfly-structured) and RV-MIMO (non-butterfly-structured) equalizer to jointly achieve polarization demultiplexing and I/Q imbalance compensation. Contribution/Results: Experimental results at 36 Gbaud over 100 km show that the proposed RX imbalance estimator reduces real-valued multiplications by over 70%, while the MIMO equalizer achieves a 51% reduction in real-valued multiplications compared to conventional 4×4 MIMO structures. The architecture significantly improves energy efficiency and real-time processing capability.

Technology Category

• Computer Vision: Learning & Optimization for CV
• Search and Optimization: Mixed Discrete/Continuous Search
• Machine Learning: Calibration & Uncertainty Quantification

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Experiences and lessons learnt from Web-based algorithms and system deployments
• User Modeling, Personalization and Recommendation: On-Device user modeling, personalization, and recommendation
• Security and Privacy: Large-scale security measurements

Abstract

In this paper, a low-complexity IQ imbalance compensation architecture is proposed, which reduces the effects of in-phase (I) and quadrature (Q) imbalance. The architecture consists of transceiver IQ skew estimation methods and a low-complexity MIMO equalizer structure. Before the IQ skew estimation, the chromatic dispersion(CD) is pre-compensated in the transmitter(TX) by chirp filtering. The receiver(RX) IQ skew is estimated by Gardner's phase detector, and the TX skew is estimated by finding the value that yields the lowest equalizer error. The low-complexity MIMO equalizer consists of a complex-valued MIMO(CV-MIMO) and a real-valued DD-LMS MIMO(RV-MIMO), which employ a butterfly and a non-butterfly structure, respectively. The CV-MIMO is used to perform polarization demultiplexing. The RV-MIMO equalizes each of the two polarisations and simultaneously compensates for the TX IQ imbalance. The architecture first compensates for the IQ skew at low-complexity, and the other imperfections are compensated by the low-complexity MIMO equalizer. Therefore, this architecture can equalize signals impaired by the transceiver IQ imbalance with low complexity. A 100 km transmission simulation and experiment with 36 Gbaud dual-polarization quadrature amplitude modulation(DP-QAM) signals and offline DSP showed that, with the RX IQ skew estimation, the number of real multiplications is reduced by more than 70% compared with conventional cases. With the low-complexity MIMO equalizer, the number of real multiplications is reduced by 51% compared with 4x4 MIMO

Problem

• Compensates transceiver IQ imbalance in dual-polarization QAM systems
• Reduces computational complexity with low-complexity MIMO equalizer design
• Estimates and corrects IQ skew using efficient signal processing methods

Innovation

• Low-complexity transceiver IQ skew estimation and compensation
• Chirp filtering pre-compensates chromatic dispersion before IQ skew estimation
• Hybrid complex-valued and real-valued MIMO equalizer reduces computational complexity