202 research outputs found
Experimental Evaluation of Air-to-Ground VHF Band Communication for UAV Relays
Unmanned Aerial Vehicles (UAVs) are a disruptive technology that is
transforming a range of industries. Because they operate in the sky, UAVs are
able to take advantage of strong Line-of-Sight (LoS) channels for radio
propagation, allowing them to communicate over much larger distances than
equivalent hardware located at ground level. This has attracted the attention
of organisations such as the Irish Defence Forces (DF), with whom we are
developing a UAV-based radio relay system as part of the MISTRAL project. This
relay system will support digital Very High Frequency (VHF) band communication
between ground personnel, while they are deployed on missions. In this paper we
report on the initial set of experimental measurements which were carried out
to verify the feasibility of VHF signal relaying via UAV. In our experiments, a
UAV carrying a lightweight Software-Defined Radio (SDR) receiver is positioned
at a height of 500 meters above ground, while two 5W transmitters travel in
vehicles on the ground. The SDR receiver measures the received signal power,
while the Global Positioning System (GPS) coordinates of the vehicles are
logged. This is combined to measure the signal pathloss over distance. Our
results show that the signal is received successfully at distances of over 50
kilometers away. While the signals still appear to suffer from a degree of
obstacle blockage and multipath effects, these communication ranges are a
substantial improvement over the ground communication baseline, and validate
the use of UAVs to support wide area emergency communication.Comment: Pre-print of paper presented at the Workshop on Integrating UAVs into
5G and Beyond at IEEE International Conference on Communications 202
Millimeter Wave Channel Modeling via Generative Neural Networks
Statistical channel models are instrumental to design and evaluate wireless
communication systems. In the millimeter wave bands, such models become acutely
challenging; they must capture the delay, directions, and path gains, for each
link and with high resolution. This paper presents a general modeling
methodology based on training generative neural networks from data. The
proposed generative model consists of a two-stage structure that first predicts
the state of each link (line-of-sight, non-line-of-sight, or outage), and
subsequently feeds this state into a conditional variational autoencoder that
generates the path losses, delays, and angles of arrival and departure for all
its propagation paths. Importantly, minimal prior assumptions are made,
enabling the model to capture complex relationships within the data. The
methodology is demonstrated for 28GHz air-to-ground channels in an urban
environment, with training datasets produced by means of ray tracing.Comment: Submitted to IEEE GLOBECOM 2020 Workshop on Wireless Propagation
Channels for 5G and B5
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