Empirical Low-Altitude Air-to-Ground Spatial Channel Characterization for Cellular Networks Connectivity

Abstract

Cellular-connected unmanned aerial vehicles (UAVs) have recently attracted a surge of interest in both academia and industry. Understanding the air-to-ground (A2G) propagation channels is essential to enable reliable and/or highthroughput communications for UAVs and protect the ground user equipments (UEs). In this contribution, a recently conducted measurement campaign for the A2G channels is introduced. A uniform circular array (UCA) with 16 antenna elements was employed to collect the downlink signals of two different Long Term Evolution (LTE) networks, at the heights of 0-40 m in three different, namely rural, urban and industrial scenarios. The channel impulse responses (CIRs) have been extracted from the received data, and the spatial, including angular, parameters of the multipath components in individual channels were estimated according to a high-resolution-parameter-estimation (HRPE) principle. Based on the HRPE results, clusters of multipath components were further identified. Finally, comprehensive spatial channel characteristics were investigated in the composite and cluster levels at different heights in the three scenarios.Index terms-UAV, cellular networks, air-to-ground, spatial channels, angular characteristics, and clusters. I. INTRODUCTIONRecently, unmanned aerial vehicles (UAVs) have been shifting their use from purely military operations to a more generalpurpose scope with rapidly increasing popularity, due to the continuous reduction of cost, size, weight and consumption. A huge market is foreseen with many new civilian and commercial applications such as forest monitoring, goods delivery or search and rescue in hostile environments [1]-[3].Temporary network access provided by UAVs as movable aerial base stations (BSs) in emergency situations or saturated communication environments has become a key scenario addressed for

Air-to-Ground Channel Characterization for Low-Height UAVs in Realistic Network Deployments

“…Citation information: DOI 10.1109/TAP.2020.3016164, IEEE Transactions on Antennas and Propagation for the takeoff-and landing scenario, which considers heights between 30 m and 330 m. Link distance ranges from 500 m to 350 km. Based on a extensive measurement campaign using an UAV and a commercial LTE BS in suburban environments, the publications [24], [55], [56] were released. In [24], [55] a stochastic channel model was proposed, including characterizations of path loss, shadow fading, delay spread and Doppler frequency spread for horizontal and vertical flights at different heights and distances to the BS.…”

On the Scheduling and Power Control for Uplink Cellular-Connected UAV Communications

“…Many measurement-based investigations such as [21]- [25] have demonstrated that the A2G propagation channels at higher heights are nearly LoS. For example, 3GPP [21] suggests a LoS probability of 1 for rural area and moderately high UAV altitude larger than 40 m, which is also verified by the measurements in [25] for even lower heights. In [22], path loss exponents (PLEs) were found to be almost free-space values as 2.1 and 2 at 60 m and 120 m, respectively.…”

“…In [23], [24], the Rician K-factors of the A2G channels were found to be large for most cases at higher heights with mean value around 15 dB. Although in few cases, the K-factor could be smaller due to, e.g., the reflections from buildings [24], [25] in urban or industrial areas, spatial analysis in [25] for the A2G channels has shown that the additional cluster(s) are usually separable to the LoS cluster in the azimuth domain with angle differences larger than 60 • . This means that if a UAV is equipped with directional antennas, even the channel with several clusters can probably be simplified as a single-cluster channel with a high K-factor.…”

Air-to-Ground Channel Characterization for Low-Height UAVs in Realistic Network Deployments

“…Based on a extensive measurement campaign using an UAV and a commercial LTE BS in suburban environments, the publications [24], [55], [56] were released. In [24], [55] a stochastic channel model was proposed, including characterizations of path loss, shadow fading, delay spread and Doppler frequency spread for horizontal and vertical flights at different heights and distances to the BS.…”