Over the air calibration of massive MIMO TDD arrays for 5G applications

This paper address the problem on how to accurately calibrate Massive MIMO system using time-division duplexing (TDD). In practical MIMO array implementations the transmission and reception path are different and hence a calibration mechanism, linking optimum receive array coefficients to optimum transmit coefficients is needed. We propose an Over-the-Air OTA calibration technique based on post-processing of the measured transmit and receive beam. The method is described and uncertainties linked to the method are investigated. A demonstration measurement on a representative array is presented to illustrate the application of the calibration method to realistic MIMO systems.