The use of tethered unmanned aerial vehicles (TUAVs) has been modeled as a powerful new tool for improving cellular phone and Internet networks. When employed as flying base stations with a cable connection, multirotor drones could quickly ramp up coverage, increase the efficiency of urban networks, and provide much needed access in remote rural areas.
In 2017, after Hurricane Maria devastated Puerto Rico, the U.S. telecommunications company AT&T showed how drones (UAVs) fitted with cellular transceivers could quickly be deployed to replace inoperable base stations and restore mobile coverage. Mathematicians have been calculating the optimal positioning of such COWs (cells on wings) ever since.
Adding a cable for power and data has been an obvious development. TUAVs on the market today can stay aloft for a month or more — much longer than their untethered counterparts that must land to recharge every hour or so. With a fiber optic line running alongside their power connection, TUAVs can also “backhaul” their data to the core network with much greater efficiency. Their drawback is their restricted mobility, although the cable connecting currently available products can be as long as 150 meters.
Unlike free-flying UAVs, little theoretical work has been done on how best to position their tethered counterparts. Researchers used search optimization to locate every item in a set of possible locations, with each location corresponding to a value of coverage probability. Then they derived closed-form expressions for a suboptimal solution; faster arrived at but less accurate. Future modeling will likely use both methods, with the latter greatly reducing the size of the set searched through by the former.
The researchers found that with longer tethers, TUAVs will outperform free-flying UAVs in just about every scenario. Tomorrow’s 5G equipment is heavier and consumes more power than 4G today, so their advantage will become more apparent. Eventually, the researchers envisage TUAVs complementing fixed base stations in high-density urban networks.
Tethered to tall buildings, they would offload data during peak hours and shift their position around the clock to cover varying traffic distribution throughout the day. In the low-density countryside, high-flying TUAVs promise a more viable alternative to expensive, tall towers needed to provide coverage to large but sparsely populated regions.
While the researchers only looked into the optimal placing of one TUAV, they are now developing more complex models featuring two or more flying base stations.