Blind Calibration of Phase Drift in Millimeter-Wave Channel Sounders

Abstract

Millimeter-wave channel sounders are much more sensitive to phase drift than their microwave counterparts by virtue of shorter wavelength. This matters when coherently combining untethered channel measurementsscanned over multiple antennas either electronically or mechanically in seconds, minutes, or even hoursto obtain directional information. To eliminate phase drift, a synchronization cable between the transmitter and receiver is required, limiting deployment range and flexibility indoors, and precluding most outdoor and mobile scenarios. Instead, we propose a blind technique to calibrate for phase drift by postprocessing the channel measurements; the technique is referred to as blind because it requires no reference signal and, as such, works even in non-line-of-sight conditions when the (reference) direct path goes undetected. To substantiate the technique, it was tested on real measurements collected with our 60 GHz virtual phased-array channel sounder, as well as through simulation. The technique was demonstrated robust enough to deal with the most severe case of phase drift (uniformly distributed phase) and in non-line-of-sight conditions.

Adaptive Beamforming With Software-Defined-Radio Arrays

“…To mitigate some of these issues, variable loading has more recently been introduced; it improves robustness to steering vector errors while maintaining a desired SINR. While these techniques can provide robustness to certain mismatch issues, and usually at the expense of a higher noise, to the best of our knowledge, very limited work has been reported on robust approaches that account for signal corruptions arising from carrier frequency offsets [17], [23], [24]. Our studies in this section investigates new techniques that provide robustness without adding noise to the system, i.e., beamforming with maximum SINR.…”

“…A different category of beamformer mismatch is when the transmitter and receiver are not synchronized. Very limited work has been reported on robust approaches that account for signal corruptions arising from carrier frequency offsets [17], [23], [24]. However, in high-interference and high-multipath environments, typically measuring the carrier frequency offset is not feasible and robust solutions are needed.…”