Wirelessly powered relay brings 5G tech to smart factories

Factories and warehouses are increasingly relying on sensors and transceivers, installing them 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 wired power sources, sensors and transceivers can be energised remotely via wireless power transfer (WPT). However, one problem with WPT designs is that they operate at 24 GHz; at such high frequencies, transmission beams must be 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 can extend the range of 5G base stations, WPT needs to reach even further, presenting another challenge for 24 GHz systems.

To address the limitations of WPT, researchers from the Tokyo Institute of Technology have developed a novel 5G relay that can be powered wirelessly at a lower frequency of 5.7 GHz. Associate Professor Atsushi Shirane said using 5.7 GHz as the WPT frequency allowed the researchers to gain wider coverage than conventional 24 GHz WPT systems, enabling a range of devices to operate simultaneously.

The proposed wirelessly powered relay acts as an intermediary receiver and transmitter of 5G signals, which can originate from a 5G base station or wireless devices. The key innovation of this system is the use of a rectifier-type mixer, which performs 4th-order subharmonic mixing while generating DC power. The mixer uses the received 5.7 GHz WPT signal as a 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 system first rectifies the 5.7 GHz WPT signal to produce DC power, which is managed by a dedicated power management unit. “Since the 5.7 GHz WPT signal has less path loss than the 24 GHz signal, more power can be obtained from a rectifier. In addition, the 5.7 GHz rectifier has a lower loss than 24 GHz rectifiers and can operate at a higher power conversion efficiency,” Shirane said.

This proposed circuit design allowed for selecting the transistor size, bias voltage, matching, cut-off frequency of the filter and load to maximise conversion efficiency and conversion gain simultaneously. The researchers showcased the capabilities of the proposed relay. Occupying a 1.5 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. Multiple chips could also be combined to achieve a higher power output. Considering its advances, the proposed 5.7 GHz WPT system could contribute to the development of smart factories.

Image credit: iStock.com/Traitov