Over-the-Air Calibration via Two-Way Signaling for Millimeter Wave Systems.

Millimeter wave (and beyond) systems rely on beamforming at the analog/radio frequency (RF) level to enhance the link margin deteriorated by increased path, propagation and blockage losses. Beam correspondence is a key property of such systems that reduces latencies, power consumption and thermal overheads by enabling uplink beamforming via signal measurements and beam learning on the downlink. Beam correspondence is realized in practice via calibration procedures, which are assumed to be performed in a factory or premission mode operation. However, as system parameters evolve, such as with an increase in operating/supported bandwidths, operating temperature levels and range of gain values supported at the RF level, it cannot be assumed that calibration has been accurately performed at all operating points. In these scenarios, this work proposes an over-the-air (OTA) calibration procedure based on two-way signaling. The mainstay of the proposal is communications that samples the receive and transmit parts of the RF circuitries at a device and uses this information to derive the calibration adjustment parameters. The proposal is generalized to address the case of multi-antenna arrays (at both ends of the link), availability of phase or signal strength-only measurements at a device, and two sided vs. one sided calibration.