大规模天线耦合效应的节俭校准

Frugal calibration of mutual coupling in massive MIMO antenna array

在时分双工系统中,上行信道和下行信道的互易性因为存在天线射频元件增益失配而被破坏。同时,在大规模天线系统中,天线元素之间的距离变得很近,相邻天线间的互耦效应会对信道增益产生明显的影响。发送和接收情况下阵列的耦合效应一般是不对称的,同样会破坏上下行信道端对端互易性。为了用较少的通信资源恢复信道端对端的互易性,提出对发送和接收模式的射频增益失配和耦合效应失配的校准系数分开估计。特别的,依赖基站天线阵列的对称性和阵列内天线的导频交换补偿所有天线射频器件的发送和接收增益失配。与之前的校准工作不同,提出的校准方案可以同时估计出校准矩阵的对角线和非对角线元素。数值仿真结果证实了该设计的优越性能。

In a time-division duplexing（TDD）system,the reciprocity of uplink（UL）and downlink（DL）channel is ruined because of the mismatches of the antenna radio frequency（RF）electronics.Meanwhile,in massive multiple-input-multiple-output（MIMO）,the antenna elements are installed very compact to each other,and this leads the mutual coupling effects among the adjacent antennas become pronounced. Non-symmetry coupling matrices for transmission and reception also affect the endto-end UL/DL channel reciprocity. In order to recover the end-to-end channel reciprocity with little over-the-air（OTA）resources,the author propose to estimate the RF electronics gain mismatches and the coupling effect mismatches separately. Specifically,the author utilize the pilot exchanges among the BS antennas and the symmetry of the antenna array to recover the transmit and receive gains of each RF component. Unlike previous calibration works,this schemes can obtain the off-diagonal elements of the calibration matrix. These proposed methods are also confirmed with numerical simulations.