Propagation Measurements and Analyses at 28 GHz via an Autonomous Beam-Steering Platform

TL;DR

This paper presents an autonomous beam-steering platform for 28 GHz V2X propagation measurements, enabling continuous, accurate channel modeling in urban and suburban environments, revealing limitations of existing pathloss models.

Contribution

The paper introduces a novel autonomous antenna alignment system with high accuracy and real-time tracking, facilitating millimeter wave channel measurements in vehicular scenarios.

Findings

Existing 3GPP and ITU-R pathloss models are inaccurate for 28 GHz in foliage and suburban areas.

The system achieves 17 cm geo-positioning accuracy and 27.8 ms tracking response time.

Autonomous tracking enables continuous measurements critical for millimeter wave channel analysis.

Abstract

This paper details the design of an autonomous alignment and tracking platform to mechanically steer directional horn antennas in a sliding correlator channel sounder setup for 28 GHz V2X propagation modeling. A pan-and-tilt subsystem facilitates uninhibited rotational mobility along the yaw and pitch axes, driven by open-loop servo units and orchestrated via inertial motion controllers. A geo-positioning subsystem augmented in accuracy by real-time kinematics enables navigation events to be shared between a transmitter and receiver over an Apache Kafka messaging middleware framework with fault tolerance. Herein, our system demonstrates a 3D geo-positioning accuracy of 17 cm, an average principal axes positioning accuracy of 1.1 degrees, and an average tracking response time of 27.8 ms. Crucially, fully autonomous antenna alignment and tracking facilitates continuous series of measurements, a unique yet critical necessity for millimeter wave channel modeling in vehicular networks. The power-delay profiles, collected along routes spanning urban and suburban neighborhoods on the NSF POWDER testbed, are used in pathloss evaluations involving the 3GPP TR38.901 and ITU-R M.2135 standards. Empirically, we demonstrate that these models fail to accurately capture the 28 GHz pathloss behavior in urban foliage and suburban radio environments. In addition to RMS direction-spread analyses for angles-of-arrival via the SAGE algorithm, we perform signal decoherence studies wherein we derive exponential models for the spatial/angular autocorrelation coefficient under distance and alignment effects.