Millimeter Wave RFID Aids Drone Navigation in Disaster Response

Published: December 7, 2023

NTT Group is testing RF transmission from chipless RFID tags to help drones identify specific locations on the ground and wind turbine inspections

Telecom company NTT Group has released a drone navigation solution that uses passive, millimeter wave RFID tags to help drones identify a location on the ground during adverse weather conditions or low visibility.

With the technology, drones can capture tag IDs to better identify their own location for applications such as disaster response or for researchers exploring remote territories. Additionally, NTT Group recently tested RF technology for drones inspecting offshore wind turbines.

NTT Group worked with the University of Tokyo to design its Millisign unmanned aerial vehicle communication system. By using RFID tags attached to the ground, the company wanted to see if UAVs could locate where they were in instances of rain, fog or other low visibility conditions.

Alternative to QR Codes for Drone-based Navigation

The solution consists of a radar transmitter mounted on the drones, and specially designed passive RFID tags. In fact, NTT built a tag design, as well as signal processing method, to provide the best reading performance in challenging conditions.

To help UAVs navigate their position, traditionally developers have used methods such as QR codes. The drones would scan a QR code attached to a specific location such as a landing point, says Tatsuya Iizuka, NTT research engineer.

That scan could then identify which tag the drone was in front of, and therefore where it was. Visual signs like these don’t work at night or in inclement weather, though. RFID, on the other hand, doesn’t require a line of sight.

Putting an electronics-based RFID tag, with a chip and antenna in a remote outdoor location, would be challenging. Therefore, the team devised a system with an RFID tag without the chip. Instead, the customized tag comes with a unique three-dimensional slant corner reflector structure. The spatial patterns on the RFID tag create its unique ID.

Transmitting Specifications

The UAV itself comes with a mounted millimeter-radar transmitter rather than a traditional RFID reader. The drone’s device transmits using a 79 GHz millimeter wave frequency, unlike other RFID systems— such as standard UHF RFID which uses about 900 MHz.

As the drone flies, the transmitter sends its signal. When it approaches the RFID tag, the tag receives that transmission and reflects its own unique response to the transmitter from wide viewing angles.

The UAV’s onboard processor analyzes the response to identify the tag, linked to a specific location. It then analyzes the signal strength to determine where the UAV is and where to land or conduct another action.

To ensure effective and reliable transmission, NTT with the university researchers built a signal processing pipeline that extracts information from the reflectors.

Advanced Landing Control

The team built a prototype with a commercial off-the-shelf millimeter wave radar device on the drone, such as the Texas Instruments IWR1443, 76 to 81 GHz wave module, says Iizuka.

“We conducted experiments and validated the wide read range using the reflective array,” he says.

Testing included the spatial position estimation, based on Eigenvalue analysis—a statistical method of analyzing interrelationship among a large set of variables. It uses clustering techniques to differentiate a tag from other objects in its vicinity in crowded environments, or spaces with obstacles like walls, vehicles or stairs.

The UAV was tested in a wide variety of conditions and sites, with a 292 millimeter-wide (11-inch) tag being read at a distance of 10 to 15 meters.

”Increasing the width of the tags, resulting in stronger reflections, would increase the reading range,” says Iizuka.

Putting The System to Test in Rain, Fog

The drone used the technology to identify a landing point in thick fog and in heavy rain. The system was also tested in multipath-rich locations where the tag was placed near stairs, and a parking lot-like environment where it was placed near a van and a wall.

The system was tested with different surface conditions as well: installed on grass, sand, in water and on metal.

Because some applications might benefit from more than one tag, they also tried the system with several tags at once. “We placed multiple tags in a one-meter square area and found little performance degradation up to three tags,” Iizuka says.

Researchers tested the read functionality at different UAV speed and found the results remained consistent. “We validated that the UAV speed did not affect the readout performance,” said the research engineer.

Rescue Missions in Disaster Scenarios

NTT expects the MilliSign technology to be used primarily for rescue missions in a disaster scenario, with company officials predicting autonomous and continuous operation of UAVs for disaster monitoring and relief transport would increase the productivity of rescue operations. Such situations might require UAVs to operate at night or in inclement weather, where conventional UAVs cannot operate due to poor visibility.

This is the first study to demonstrate that UAVs can be safely navigated in poor visibility conditions, and the system remains at the prototype stage.

Next, says Iizuka, “we need to work with partners such as drone companies to integrate the MilliSign technology into the flight control system, and to create fully autonomous drones that can operate in all day and all weather conditions.”

Detecting Wind Turbine Operation with Drones

NTT Group has completed other deployments using wireless communication between UAVs as well. It has built an RF transmission system to enable drone-based inspections of wind turbines while the turbines are in operation.

Traditionally, human engineers have had to visually inspect wind turbines for any tears or damage, a dangerous process as it takes place often while the turbines are moving and requires climbing to considerable heights.

With NTT’s solution, pairs of autonomous drones fly on opposite sides of turbines. They transmit and receive radio signals from each other as they circle the structure. As a UAV transmits the RF signal, the energy passes through the turbine to the opposite drone which has an RF receiver. The radio signals being transmitted are intentionally weak, to ensure users do not have to obtain a radio station license.

The turbine itself creates a Fresnel Zone —the space in which radio waves propagate.

Testing found that transmission and reception of radio signals was possible at an altitude of 30 meters. The next step for NTT Group is to further test the technology in the field.

Key Takeaways:
  • NTT prototypes a chipless RFID tag to be detected by drones during disaster response.
  • The company next will work with technology companies such as drone manufacturers to further test and commercialize the millimeter wave RFID system.