An improved relative channel reciprocity calibration method in TDD massive MIMO systems

In this paper, we introduce an improved relative channel reciprocity calibration method in TDD massive multiple-input multiple-output (MIMO) systems. The improved calibration method divide the massive MIMO system into one Single-Input Single-Output (SISO) system and two Single-Input Multiple-Output (SIMO) systems instead of calibrating the massive MIMO directly. We select the channel with high channel gain to be the reference channel (the SISO system), the antennas of the SISO system are the reference antennas. At the same station the reference antenna and the other antennas consist the SIMO system. The three systems include all the receive circuitry and the transmit circuitry information of the massive MIMO system. We calibrate the three systems and acquire the calibration coefficients. Then we use the calibration coefficients of the three systems to calibrate the massive MIMO system. The proposed calibration method in this paper can reduce the amount of feedback and the computation complexity compared with calibrating the massive MIMO directly. What´s more, the improved calibration method outperforms the traditional calibration method under high-speed mobile environment.