Convergence of Technologies for 5G and Beyond: Drone Base Stations, Millimeter Wave Communications and Wireless Energy Transfer

The possibilities behind 5G and the issues surrounding it
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"Vehicular networks, autonomous driving, robotics, healthcare, and virtual and augmented reality are other examples where the need is greatly increasing." -Dr. M Cenk Gursoy, Syracuse University

In recent years, there has been exponential growth in mobile data traffic and in the number of wireless devices. According to the Cisco Visual Networking Index (VNI) Global Mobile Data Traffic Forecast Update, mobile data traffic has grown 17-fold over the past 5 years. The number of global mobile devices and connections in 2017 grew to 8.6 billion in total. It is expected that this growth will continue into the future. In particular, global mobile data traffic is predicted to reach 77.5 exabytes per month by 2022. This demand is directly tied to the increasing use of smartphones, portable devices, data-hungry multimedia applications, and new technologies and designs. This has prompted the international demand by world leaders for fifth generation (5G) cellular networks. Success in this endeavor should include the use of drones as base stations, operating at millimeter wave frequencies, alongside wireless energy transfer.

Indeed, the deployment of unmanned aerial vehicle (UAV) base stations, also known as drone base stations, has started to become a reality. In particular, the use of low-altitude drones has become popular, as there is an advantage to having better link quality in shorter-distance line-of-sight channels with ground users. As a result of the relative flexibility in drone deployments, drone base stations have the potential to be employed in a variety of scenarios. We see this with public safety communications, data collection in (IoT) applications, as well as in disaster or emergency scenarios. Temporary events like this, require substantial network resources to sustain and provide wireless connectivity rapidly.

With these motivations, there has been a steadily growing interest in UAV communications and drone networks in both academia and industry. In particular, researchers at universities are currently investigating accurate models for air-to-ground links between the drones and ground users. They are consistently performing coverage analysis, studying 3-D drone placements, as well as efficient trajectory designs. Deployments of actual drone base stations have also been demonstrated recently. According to the FCC Communications Status Report, in areas impacted by Hurricane Maria, roughly 90 percent of cell-sites were out of service in Puerto Rico and 66 percent of the cell-sites were out of service in the U.S. Virgin Islands. This staggering loss of connectivity can have significant detrimental impact on emergency response and disaster recovery efforts. As one remedy for this, AT&T deployed for the first time, its Flying COW (Cell on Wings) drone to establish LTE cell-sites and restore connectivity in parts of Puerto Rico.

Another key 5G technology is millimeter wave communications. The limited available spectrum in the prime portion of the radio frequency spectrum, (below 6GHz) does not seem capable of meeting demand. The rapid increase in the bandwidth-intensive mobile multimedia data traffic is the result of tactile internet, IoT and other wireless applications in industrial automation. Vehicular networks, autonomous driving, robotics, healthcare, and virtual and augmented reality are other examples where the need is greatly increasing. Huge congestion is motivating the move to new frequency bands. Therefore, the use of large-bandwidth millimeter wave frequency bands, (between 30 and 300 GHz) becomes a good candidate for next-generation 5G wireless networks. Operating at millimeter wave frequencies is also attractive for drone communications, because drones can establish line-of-sight connections with the ground users by adjusting their locations and supporting directional transmissions at very high rates (e.g., to support 4K video traffic) by utilizing the large bandwidths.

The explosive growth in mobile data traffic needs support by wireless systems equipped with limited energy resources and energy-efficient operations. For instance, in mobile applications, a battery is commonly the only source of energy. In the multitude of scenarios where wireless networks are deployed in hard-to-reach places, conventional battery charging becomes infeasible. Mobile users may also choose to avoid the disruption of battery replacement or recharging if there are other means to providing continuous power supply. These considerations have led to increased interest in energy-harvesting wireless communications. In particular, radio frequency energy harvesting from ambient electromagnetic signals, or dedicated energy beamforming sources via wireless power transfer, have each become viable approaches. Such technology holds the promise to enable drones that are equipped with wireless power transmitters which energize sensors on the ground and collect data.

The ambitious design goals for 5G-and-beyond wireless networks involve billions of users and devices. These networks need to operate seamlessly in an energy-efficient manner and support extremely high data rates. The convergence of key technological advances is vital to success in this endeavor, and there are many tangible benefits to this success. Improved public safety, efficient emergency communications, the emergence of IoT, tactile internet, industrial automation, and autonomous vehicle applications, are examples which are poised to transform our lives and have significant impact on society.

Dr. M. Cenk Gursoy is a Professor in the Department of Electrical Engineering and Computer Science at Syracuse University