Non-terrestrial Networks and Aerial Communications

Non-terrestrial networks (NTNs), attracting great attention lately, are expected to provide seamless connectivity and ubiquitous coverage for high data rate applications with their integration of space-air-ground networks. This includes both high- and low-altitude aerial platforms, which have unique features in terms of positioning flexibility and require proper designs for efficient and reliable wireless communications. Unmanned aerial vehicles (UAVs), an example of low-altitude platforms, can significantly improve connectivity and have wide range of civilian and military applications.

There have been many research problems to be investigated in airborne wireless communication systems considering different perspectives, such as

a) Detection/tracking/neutralization of malicious UAVs

UAVs' prevalence raised security concerns if they are controlled to breach into highly restricted areas such as oil and gas facilities. We have adopted low-cost passive RF-based sensing of unauthorized drones with well-distributed sensors considering realistic fading channel model in an urban environment. We derived closed-form expressions for the probability of detection, which are corroborated with extensive Monte-Carlo simulations demonstrating the performance of the proposed low-complexity detector.

b) Ultra-reliable uplink communication schemes in airborne networks

We proposed ultra-reliable uplink (UL) communication schemes for airborne networks. Particularly, a device-centric scheme in which the UAV travels to the scheduled device(s) for UL transmissions. The performance is benchmarked against a stationary UAV-centric uplink scheme, where the UAV is hovering at a static location. Utilizing stochastic geometry and queueing theory, novel spatiotemporal mathematical models are developed accounting for the UAV spatial densities, mobility, altitude, antenna directivity, ground-to-air channel, and temporal traffic, among other factors.

c) Multi-hop UAVs using FSO communications under harsh conditions

We investigated the performance of multi-hop hovering UAVs using free space optical communications with decode-and-forward relaying. We consider the atmospheric attenuation due to the sandstorm and relative humidity, in addition to the atmospheric turbulence, angle-of-arrival fluctuations, and pointing errors. We obtain the outage probability and ergodic capacity considering atmospheric attenuation conditions, and the impact of transmitted power, field of view and optical beamwidth.

Wireless Geophone Networks

Oil and gas industries have been directing their interest and resources towards monitoring and exploring the Earth’s subsurface and its underlying stratigraphy/structure. They have increased their investments in seismic exploration to discover new hydrocarbon reservoirs in pursuit of efficient production. The tendency towards wireless seismic acquisition has motivated many researchers and companies to investigate Wireless Geophone Networks (WGNs) as a transition from traditional cable-based seismic acquisition systems in exploration. During these surveys, geophones are placed at the surface -typically in an array configuration- to cover the area under exploration, then they detect reflected waves, e.g. P- and S-waves, surface waves, after a seismic sweep by truck-mounted vibrators on ground. Upon proper processing of the collected seismic data from all geophones, high quality seismic images/maps of the subsurface can be obtained. We have investigated and proposed novel WGN architectures for high-density seismic acquisition with high-speed and efficient power consumption in collecting seismic data.

Underwater Wireless Communications

Underwater wireless communication has recently attracted attention for many applications including oceanographic data collection, pollution monitoring, seismic activities measurement, exploration of natural resources among others. Orthogonal frequency division multiplexing (OFDM) combined with multi-relay cooperative transmission provides additional spatial diversity compared to conventional non-cooperative underwater acoustic (UWA) systems. We have analyzed the Intercarrier interference (ICI) due to non-uniform Doppler distortion, proposing different receiver structures, and deriving expressions for ICI matrices. We have also investigated the outage performance for a cooperative OFDM UWA communication system, both amplify-and-forward (AF) and decode-and-forward (DF) relaying schemes. Analytical expressions as bounds on outage probability and outage capacity were derived. Monte-Carlo simulations corroborate the enhanced performance of cooperative OFDM UWA communication systems.