Kyoto University has sent data at 14.6 Gbit/s from a car on a real road to a receiver 140 metres away using the 300 GHz band. It is a research trial at 20 km/h with a fixed antenna, but it moves terahertz radio out of the laboratory.
The receiver in Kyoto University’s latest radio experiment did not sit on a mast or a gantry. It sat inside a building overlooking the road, about 5.8 metres up, pointing out through the structure at a fixed angle two or four degrees below horizontal. It did not swivel to follow the car. According to the university’s announcement of 5 November, a test vehicle with a transmitter mounted 1.5 metres high was driven past at about 20 km/h, between roughly 10 and 340 metres away, while the team logged what got through.
At 140 metres, the link carried 14.6 gigabits per second in the 300 GHz band, the region of the spectrum usually called terahertz. That is the speed at which a vehicle could unload a high-definition video stream, a dense lidar point cloud or a fresh slice of 3D map in a fraction of a second while passing an intersection.
Why the uplink matters
Most mobile networks are built to send data down to users. Autonomous vehicles invert the problem. A modern test car generates many gigabytes an hour from cameras, radar and lidar, and the industry wants some of it shared with roadside units, other vehicles and cloud services, a family of uses known as V2X. Today’s 5G allocations cannot move that volume from a car in the few seconds it spends near a junction.
The 300 GHz band offers far wider channels. The Kyoto group, led by Professor Hiroshi Harada and Associate Professor Yusuke Koda of the Graduate School of Informatics, used a 7.8 GHz-wide signal, about 20 times the 400 MHz maximum channel bandwidth allocated to 5G in Japan. Their equipment, built with software-defined radio, follows the signal structure of the 5G standard but widens subcarrier spacing from 120 kHz to 960 kHz. It also estimates and corrects Doppler shift automatically; in February the team showed it working in a laboratory emulation of motion at 1,000 km/h.
What was measured, and what was not
The detail in the release is careful, and the claims should be read that way. With a narrower 100 MHz channel at 176 Mbit/s, the team found a continuous coverage zone of about 120 metres, from 50 to 170 metres from the receiver, using a block error rate of 0.1 or less as the pass mark. With the full 7.8 GHz channel it achieved 14.6 Gbit/s at 140 metres and confirmed communication at several other points inside that zone. As the Japanese research summary service LC Signal points out, the results do not show 14.6 Gbit/s sustained across the whole 120 metres.
The resulting design principle is pragmatic: use a modest channel to keep a car connected across a wider area, and switch to the very wide channel for bursts of bulk upload where the link is strong. Both antennas were high-gain Cassegrain dishes of 43 dBi, which illustrates the central difficulty of terahertz radio. Signals at these frequencies are absorbed by air and blocked by almost anything, so they must be focused into narrow beams. A production system would need beams that track vehicles automatically, and the trial did not test that.
Who stands to gain
Japan has made terahertz spectrum a national bet for 6G, and a field result from a university is the kind of evidence that informs spectrum policy at the International Telecommunication Union. Makers of terahertz front-end chips and antennas, including Japanese electronics groups and indium phosphide and silicon-germanium specialists, would benefit if roadside terahertz units became a real product category. Car makers developing data-hungry driver assistance systems would gain an alternative to costly cellular data or to storing data until a vehicle returns to a depot.
The losers are less obvious. Millimetre-wave 5G infrastructure suppliers have pitched their own bands for V2X; a credible terahertz option could split that market. Roadside infrastructure is also expensive, and city authorities would need persuading to fit receivers at junctions, which could slow adoption regardless of the radio’s performance.
The road ahead
The team says the next steps are wider coverage on real roads and stabilising links as driving conditions vary. Twenty kilometres an hour on a single stretch of road, with fixed antennas, is a long way from a motorway in rain. No commercial partner or funding figure was given in the announcement. But the experiment shifts the question from whether terahertz links can survive motion at all to how they should be engineered for streets, and that is a meaningful step for a band that has spent most of its life on laboratory benches.