How to calibrate massive MIMO?

Time-division duplexing (TDD) systems enjoy one superior characteristic referred to as channel reciprocity. However, due to different radio frequency branches for transmitting and receiving, calibrating the antenna array at the base station (BS) is necessary to effect this reciprocity between the end-to-end downlink (DL) and uplink (UL) channels. As the array size gets large in massive multi-input multi-output (MIMO) antenna systems, this procedure becomes extremely challenging if we simply rely on the existing antenna calibration approaches including “Self-Calibration” and “Over-the-Air Calibration (OTA)”. To release all the potentials of massive MIMO, this paper relies on compressive sensing theory and develops an efficient and robust way to calibrate the massive antenna array while only requiring a limited amount of channel state information (CSI) feedback. This work is the prerequisite for actual deployment of massive MIMO technique and allows us to take full advantage of the channel reciprocity in massive MIMO under TDD operation.