A Real-time Radio Frequency Mismatch Calibration Method for TDD massive MIMO Base Station

To realize efficient precoding, accurate channel state information (CSI) is essential. Although the wireless propagation channel is reciprocal, the mismatches of transceiver Radio Frequency (RF) circuits disable the reciprocity of the whole communication channel, which is the key condition for applying uplink channel estimation results to downlink precoding. Furthermore, the discrepancies between paths directly lead to inaccurate beam direction and large sidelobe level in massive multiple-input multiple-output (MIMO) beamforming system. Hence, to avoid RF gain mismatch leading to a severe performance degradation of the system, RF mismatch calibration is necessary. In this paper, we propose a real-time RF mismatch calibration method for TDD base station (BS) with the hybrid beamforming structure in hardware-based way for the first time, adopting channel estimation method. The analytical expressions for RF mismatch module of TDD hybrid beamforming system are derived at first. Then specific program designs are presented, which consists of two stages, digital beamforming chains calibration (DBCC) and analog beamforming transceivers calibration (ABTC). Simulations are provided to verify the effectiveness of our schemes.