Blind I/Q Imbalance Compensation for M-QAM Optical Coherent Systems Based on Pseudo-Rotation

This paper addresses the problem of Inphase/Quadrature (I/Q) imbalance sensitivity of communication systems when it occurs at both Transmitter (TX) and Receiver (RX) sides of an optical coherent system. A novel blind technique is proposed based on the pseudo-rotation of the M-QAM constellation. The pseudo-rotation based compensator is a generic approach, because it does not depend on the modulation order and the level of imbalance. To implement the proposed compensation in practical systems, two algorithms are proposed: Recursive Pseudo-Rotation (RPR) that achieves the performance of the ideal compensator and LRPR, a Low complexity version of RPR. Monte Carlo simulation results show that the proposed compensator outperforms state-of-the-art algorithms for an Additive White Gaussian Noise (AWGN) and the complexity/performance trade-off is also discussed. The efficiency of the proposed method is experimentally validated with a 10 Gbaud QPSK optical system showing its operation in the presence of Inter-Symbol Interference (ISI).