In this paper we study an over-the-air (OTA) approach for digital pre-distortion (DPD) and reciprocity calibration in massive multiple-input-multiple-output systems. In particular, we consider a memory-less non-linearity model for the base station (BS) transmitters and propose a methodology to linearize the transmitters and perform the calibration by using mutual coupling OTA measurements between BS antennas. We show that by only using the OTA-based data, we can linearize the transmitters and design the calibration to compensate for both the non-linearity and non-reciprocity of BS transceivers effectively. This allows to alleviate the requirement to have dedicated hardware modules for transceiver characterization. Moreover, exploiting the results of the DPD linearization step, our calibration method may be formulated in terms of closed-form transformations, achieving a significant complexity reduction over state-of-the-art methods, which usually rely on costly iterative computations. Simulation results showcase the potential of our approach in terms of the calibration matrix estimation error and downlink data-rates when applying zero-forcing precoding after using our OTA-based DPD and calibration method.

翻译：本文研究了一种用于大规模多输入多输出系统的空中数字预失真与互易性校准方法。具体而言，我们采用无记忆非线性模型描述基站发射机，并提出一种利用基站天线间互耦空中测量实现发射机线性化及系统校准的方法。研究表明，仅基于空中测量数据即可实现发射机线性化，并通过校准设计有效补偿基站收发机的非线性与互易性偏差。该方法可降低对专用收发机特性表征硬件模块的依赖。此外，借助数字预失真线性化步骤的结果，我们的校准方法可通过闭式变换实现，相比通常依赖高成本迭代计算的现有技术方案，显著降低了计算复杂度。仿真结果表明，在应用基于空中的数字预失真与校准方法后，采用迫零预编码时，所提方案在校准矩阵估计误差与下行链路数据速率方面展现出显著优势。