A Time-alignment Algorithm of Multiple Power Delay Profiles Measured by Antenna Rotations Towards Flexible mmWave Channel Measurements

Towards flexible channel measurements of millimeter wave (mmWave) communications, this paper proposes a time-alignment algorithm of multiple power delay profiles (PDPs) separately measured with different antenna rotation angles. To characterize mmWave channels, capturing both delay time and angular property of multi-path components is necessary, which requires multiple PDP measurements with antenna rotations and alignment of the delay time with respect to a standard time, e.g., time of departure or the arrival time of a line-of-sight ray. While this alignment conventionally requires hardware synchronization between the transmitter and the receiver, this study turns this synchronization into the softwarelized post-processing to eliminate any nuisances incurred by the hardware synchronizations during measurements. To this end, we propose a time of arrival (ToA) estimation method of a maximum power peak in PDPs unsynchronized among different antenna rotation angles, which can be performed without any hardware synchronizations. The core idea is to align the time of the PDPs so that the powers between adjacent antenna rotation angles are highly correlated to each other because the ground-truth time-aligned PDP should possess such higher correlations. This paper formulates this problem as maximum-likelihood estimations; thereby deriving the algorithm to reach this objective. The experimental results based on real measurements demonstrate the feasibility of the time-alignment of the unsynchronized PDPs by comparing to the results by raytracing simulation.