A wirelessly powered transceiver for non-line-of-sight 5G

Scientists at the Tokyo Institute of Technology have designed a 256-element wirelessly powered transceiver array for non-line-of-sight 5G communication, featuring efficient wireless power transmission and high-power conversion efficiency.

Millimetre-wave (mmWave) 5G communication, which uses extremely high-frequency radio signals (24–100 GHz), is a promising technology for next-generation wireless communication that exhibits high speed, low latency and large network capacity. However, current 5G networks face two key challenges: low signal-to-noise ratio (SNR) and link blockage, which refers to the disruption in signal between transmitter and receiver due to obstacles such as buildings.

Beamforming is a key technique for long-distance communication using millimetre waves which improves SNR. This technique uses an array of sensors to focus radio signals into a narrow beam in a specific direction, akin to focusing a flashlight beam on a single point. However, it is limited to line-of-sight communication, where transmitters and receivers must be in a straight line, and the received signal can become degraded due to obstacles. Furthermore, concrete and modern glass materials can cause high propagation losses.

Addressing the need for a non-line-of-sight (NLoS) relay system to extend 5G network coverage, especially indoors, Tokyo Tech researchers led by Associate Professor Atsushi Shirane designed a novel wirelessly powered relay transceiver for 28 GHz mmWave 5G communication. Their work was featured in the Proceedings of the 2024 IEEE MTT-S International Microwave Symposium.

“Previously, for NLoS communication, two types of 5G relays have been explored: an active type and a wireless-powered type,” Shirane explained. “While the active relay can maintain a good SNR even with few rectifier arrays, it has high power consumption. The wirelessly powered type does not require a dedicated power supply but needs many rectifier arrays to maintain SNR due to low conversion gain and uses CMOS diodes with lower than 10% power conversion efficiency. Our design addresses their issues while using commercially available semiconductor integrated circuits (ICs).”

The proposed transceiver consists of 256 rectifier arrays with 24 GHz wireless power transfer (WPT). These arrays consist of discrete ICs, including gallium arsenide diodes, and baluns, which interface between balanced and unbalanced signal lines, DPDT switches and digital ICs. Notably, the transceiver is capable of simultaneous data and power transmission, converting 24 GHz WPT signal to direct current (DC) and facilitating 28 GHz bi-directional transmission and reception at the same time. The 24 GHz signal is received at each rectifier individually, while the 28 GHz signal is transmitted and received using beamforming. Both signals can be received from the same or different directions and the 28 GHz signal can be transmitted either with retro-reflecting with the 24 GHz pilot signal or in any direction.

Testing revealed that the transceiver can achieve a power conversion efficiency of 54% and a conversion gain of -19 decibels — higher than conventional transceivers, while maintaining SNR over long distances. Additionally, it achieves about 56 mW of power generation which can be increased even further by increasing the number of arrays. This can also improve the resolution of the transmission and reception beams.

According to Shirane, “The proposed transceiver can contribute to the deployment of the mmWave 5G network even to places where the link is blocked, improving installation flexibility and coverage area.” It could therefore make high-speed, low-latency communication far more accessible.