Scientists from the Tokyo Institute of Technology report that a recently developed wirelessly powered 5G relay could accelerate the development of smart factories. By adopting a lower operating frequency for wireless power, the proposed relay design solves many of the current limitations, including range and efficiency, resulting in more versatile and widespread deployment of sensors and transceivers in industrial environments.
One of the hallmarks of the Information Age is the transformation of industry toward a hyper-flow of information. This is easily seen in high-tech factories and warehouses, where robots, production machines and self-driving cars are equipped with wireless sensors and transceivers. In many cases, 5G networks are being used to coordinate the operations and communications between these devices.
To avoid relying on cumbersome wired power sources, sensors and transceivers can be remotely powered via wireless power transfer (WPT). However, one of the problems with traditional WPT designs is that they operate at 24 GHz. At such a high frequency, the transmission beam needs to be very narrow to avoid energy loss. Furthermore, power can only be transmitted when there is a clear line of sight between the WPT system and the target device. As 5G relays are often used to extend the range of 5G base stations, WPT needs to reach even farther, which is another challenge for 24 GHz systems.
To address the limitations of WPT, a research team at the Tokyo Institute of Technology has devised a clever solution. In recent work presented at the 2024 IEEE Symposium on VLSI Technology & Circuits, they developed a new 5G relay that can provide wireless power at a low frequency of 5.7 GHz (see Figure 1). “By using 5.7 GHz as the WPT frequency, we can cover a wider range than conventional 24 GHz WPT systems, allowing a wider range of devices to operate simultaneously,” explains lead author and Associate Professor Atsushi Shirane.
Figure 1. Proposed WPT 5G Relay
The key innovation in this design is the use of a 5.7 GHz Wireless Power Transfer (WPT) signal as both a means to generate DC power using a rectifier, and as an oscillator for the mixing and isolation circuit. By down-converting it to a lower frequency by mixing, and then amplifying the input signal, the circuit achieves higher efficiency and gain.
The proposed wirelessly powered relay is intended to act as a relay receiver and transmitter for 5G signals originating from a 5G base station or wireless device. The key innovation of this system is the use of a rectifier-type mixer that performs four functions:NumberIt also generates DC power at the same time as performing sub-harmonic mixing.
Specifically, the mixer uses the received 5.7 GHz WPT signal as a local signal, which, in combination with a multiplier circuit, a phase shifter, and a power combiner, “downconverts” the received 28 GHz signal to a 5.2 GHz signal, which is then internally amplified and upconverted to 28 GHz through the reverse process before being retransmitted to its intended destination.
To drive these internal amplifiers, the proposed system first rectifies the 5.7 GHz WPT signal to generate DC power, which is managed by a dedicated power management unit. This ingenious approach has several advantages, as highlighted by Shirane: “The path loss of the 5.7 GHz WPT signal is less than that of the 24 GHz signal, so you can get more power out of the rectifier. Furthermore, the 5.7 GHz rectifier has less loss than the 24 GHz rectifier and can operate with higher power conversion efficiency.” Finally, the proposed circuit design allows you to choose the transistor size, bias voltage, matching, filter cutoff frequency, and load to maximize the conversion efficiency and conversion gain simultaneously.
The research team demonstrated the functionality of the proposed relay through several experiments (see Figure 2). It occupies only a 1.5 mm x 0.77 mm chip using standard CMOS technology and can output a high power of 6.45 mW at an input power of 10.7 dBm with a single chip. Notably, higher output power can be achieved by combining multiple chips. Considering its many advantages, the proposed 5.7 GHz WPT system could make a significant contribution to the development of smart factories.
