The terahertz (THz) spectrum, ranging from 300 GHz to 3 THz, has been identified as a potential candidate for 6G technology due to its large bandwidth. This spectrum is expected to usher in an era of mobile data rates reaching 100 Gbps and enable advanced services. Similar to millimeter-wave (mmWave) technology, the THz spectrum has limited propagation capabilities, which could confine its usefulness to static applications like fixed-wireless access (FWA) and near-field communications (NFC).
However, a recent outdoor trial conducted by Softbank demonstrated the possibility of using the THz spectrum for mobility services, specifically connected cars. By employing a 300-GHz spectrum, Softbank was able to maintain a stable connection between a transmitter installed on a pedestrian bridge above a road and a receiver installed on a car traveling at various speeds, up to 30 km/hr. Although the road stretch was only 140 meters long, the signal strength was sufficiently strong at that distance, indicating the potential for even longer-distance coverage.
Softbank explained that the key to making it work is a beamforming technique known as the cosecant squared beam pattern. This technique allows for maintaining high antenna gain and stable power levels at both the transmitter and receiver. It is commonly used in aviation radar to achieve a uniform signal strength when tracking moving objects. Softbank mentioned that cosecant antennas would be too large for practical use at lower frequency bands with longer wavelengths.
However, the shorter wavelengths of the THz spectrum, less than a millimeter towards the upper end, enable smaller antenna sizes.
Softbank stated its commitment to continue testing various use cases and accelerating research and development towards the practical application of terahertz wireless technology. This initiative aligns with the goal of realizing ultra-high-speed wireless communication for the Beyond 5G/6G era and contributing to the growth of the telecommunications industry.
While it may take some time before we see widespread adoption of connected vehicle-to-everything (V2X) technology with THz connectivity, this progress demonstrates that with sufficient ingenuity, no frequencies are beyond the reach of cellular technology.