SoftBank Demonstrates Terahertz Communication for Vehicles with Cosecant Beam Antenna

Earlier this June, SoftBank achieved a significant milestone in Beyond 5G/6G innovation by successfully demonstrating terahertz (THz) outdoor coverage for connected cars using their proprietary Cosecant Beam Antenna technology. Traditionally, THz communication has been limited to Fixed Wireless Access (FWA) or Near Field Communication (NFC) due to its short-range characteristics. However, this ground-breaking field trial shows that THz frequencies can reliably support dynamic, mobile use cases like connected vehicles.

Terahertz frequencies can be a bit perplexing, spanning from 300 GHz to 3 THz. Interestingly, frequencies between 100 GHz and 300 GHz are now commonly referred to as sub-THz as we explained here. SoftBank's recent blog post clarifies that they consider the terahertz band to range from 100 GHz to 10 THz, offering a broader interpretation. Their detailed explainer provides insight into the technical nuances of this high-frequency spectrum.

A key enabler of this trial was SoftBank's innovative Cosecant Beam Antenna design. Quoting from their blog post: 

This technology, used in aviation radar, ensures that the received power at both the base station and the terminal remains constant regardless of the horizontal distance between the transmitting and receiving antennas, even with elevation differences. Specifically, by making the product of the antenna gains of the base station and the terminal proportional to the cosecant squared of the angle θ formed by the antennas, we can counteract the attenuation due to distance.

Traditionally, this characteristic could be achieved simply by making the antenna directional pattern a cosecant-squared beam. However, due to the short wavelength of the terahertz band, it is difficult to realize omnidirectional antennas. Therefore, we designed areas with cosecant-squared characteristics by configuring both the base station and terminal antennas with cosecant beam patterns.

As a result, we were able to maintain an antenna gain of approximately 20 dBi for both the base station and terminal, while achieving an almost constant received power from near the base station to the edge of the coverage area.

During the trial, SoftBank successfully demodulated broadcast signals over a horizontal distance of 10 to 140 meters from the base station. Although the test was constrained by road limitations, the consistently high power levels suggest ample margin for extending the communication range. This result hints at the potential for significantly longer-distance coverage in future deployments.

SoftBank's achievement marks a major step forward in demonstrating the viability of terahertz frequencies for real-world applications like connected cars. As research and development in Beyond 5G/6G continue to accelerate, we can expect to hear more exciting updates on the expansion of THz communication, paving the way for faster, more reliable, and ubiquitous connectivity.

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