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

翻译：本文提出了一种低复杂度IQ不平衡补偿架构，用于减轻同相（I）与正交（Q）支路不平衡的影响。该架构包含收发机IQ时偏估计方法及一种低复杂度多输入多输出均衡器结构。在IQ时偏估计之前，通过啁啾滤波在发射端对色散进行预补偿。接收端IQ时偏采用加德纳相位检测器进行估计，发射端时偏则通过寻找使均衡器误差最小的数值来确定。低复杂度MIMO均衡器由复数域MIMO和实数域判决导向最小均方MIMO构成，分别采用蝶形与非蝶形结构。复数域MIMO用于实现偏振解复用，实数域MIMO对两个偏振态分别进行均衡，并同步补偿发射端IQ不平衡。该架构首先以低复杂度补偿IQ时偏，其余非理想特性则由低复杂度MIMO均衡器进行补偿，从而能够以较低计算复杂度对受收发机IQ不平衡影响的信号实现均衡。通过36G波特双偏振正交幅度调制信号的100公里传输仿真与实验，结合离线数字信号处理验证表明：采用接收端IQ时偏估计时，实数乘法运算量较传统方案降低70%以上；配合低复杂度MIMO均衡器，实数乘法运算量较4x4 MIMO方案减少51%。