Wirelessly powered relay enables 5G in smart factories

Scientists at the Tokyo Institute of Technology (Tokyo Tech) have developed a wirelessly powered 5G relay that could accelerate the development of smart factories by solving many of the current limitations, including range and efficiency. Their proposed relay design has been presented at the 2024 IEEE Symposium on VLSI Technology & Circuits.

In high-tech factories and warehouses, wireless sensors and transceivers are installed in robots, production machinery and automatic vehicles. In many cases, 5G networks are used to orchestrate operations and communications between these devices.

To avoid relying on cumbersome wired power sources, sensors and transceivers can be energised remotely via wireless power transfer (WPT). However, one problem with conventional WPT designs is that they operate at 24 GHz. At such high frequencies, transmission beams must be extremely narrow to avoid energy losses. Moreover, power can only be transmitted if there is a clear line of sight between the WPT system and the target device. Since 5G relays are often used to extend the range of 5G base stations, WPT needs to reach even further, which is yet another challenge for 24 GHz systems.

To address the limitations of WPT, Tokyo Tech researchers developed a novel 5G relay that can be powered wirelessly at a lower frequency of 5.7 GHz. Senior author Associate Professor Atsushi Shirane explained that, by using 5.7 GHz as the WPT frequency, the team can achieve wider coverage than conventional 24 GHz WPT systems, enabling a wider range of devices to operate simultaneously.

A key innovation in the team’s design is the use of the 5.7 GHz WPT signal as both a means of generating DC power using a rectifier and as an oscillator for the mixing and unmixing circuits. By amplifying the input signal after down conversion to a lower frequency via mixing, this circuit achieves higher efficiency and gain.

The proposed wirelessly powered relay is meant to act as an intermediary receiver and transmitter of 5G signals, which can originate from a 5G base station or wireless devices. A rectifier-type mixer performs fourth-order subharmonic mixing while also generating DC power.

Notably, the mixer uses the received 5.7 GHz WPT signal as a local signal. With this local signal, together with multiplying circuits, phase shifters and a power combiner, the mixer ‘down-converts’ a received 28 GHz signal into a 5.2 GHz signal. Then, this 5.2 GHz signal is internally amplified, up-converted to 28 GHz through the inverse process, and retransmitted to its intended destination.

To drive these internal amplifiers, the proposed system first rectifies the 5.7 GHz WPT signal to produce DC power, which is managed by a dedicated power management unit. This approach offers several advantages, according to Shirane.

“Since the 5.7 GHz WPT signal has less path loss than the 24 GHz signal, more power can be obtained from a rectifier,” Shirane said. “In addition, the 5.7 GHz rectifier has a lower loss than 24 GHz rectifiers and can operate at a higher power conversion efficiency.” Finally, the proposed circuit design allows for selecting the transistor size, bias voltage, matching, cutoff frequency of the filter, and load to maximise conversion efficiency and conversion gain simultaneously.

Through several experiments, the research team showcased the capabilities of their proposed relay. Occupying only a 1.5 x 0.77 mm chip using standard CMOS technology, a single chip can output a high power of 6.45 mW at an input power of 10.7 dBm. Notably, multiple chips could be combined to achieve a higher power output.

The proposed 5.7 GHz WPT system could thus greatly contribute to the development of smart factories, allowing for a more versatile and widespread arrangement of sensors and transceivers in industrial settings.

Image credit: iStock.com/Traitov