Kyoto, Japan -- The fifth-generation mobile communication system, also known as 5G, is expected to evolve as a critical infrastructure supporting individual users, industrial applications, and social systems. This requires access to broader frequency resources, but concerns have emerged regarding future congestion even in the existing frequency bands, creating a strong need to explore new spectrum resources and progress to 6G.
A promising candidate to address this challenge is terahertz waves, THz, which operate at frequencies approximately ten times higher than those of millimeter waves, commonly used in 5G. However, many of the experimental demonstrations of THz-band communications have been limited to the transmission of modulation waveforms that do not comply with 5G standards.
Furthermore, to develop 6G, an important research challenge is to transmit wideband signals on the order of several gigahertz -- exceeding the 400 MHz maximum per-channel bandwidth currently used in 5G -- in the THz band while maintaining compliance with 5G standardized transmission schemes.
To meet these requirements, a team of researchers at Kyoto University, led by Hiroshi Harada and Yusuke Koda, realized the necessity of modifying various parameters employed in 5G in order to ensure stable receiver operation, even in the THz-band and in high-mobility environments. So they took on the task of developing a wireless transmission testbed capable of verifying such configurations.
Using software-defined radio technology, the team developed a wireless transmission testbed that transmits ultra-wideband signals -- approximately 20 times wider than the channel bandwidth currently allocated for 5G in Japan -- over the THz band. They also ensured the testbed is compliant with existing 5G standardized communication specifications.
Using this lab environment, the research team performed high-mobility emulation corresponding to speeds of up to approximately 1,000 km/h, as well as transmission performance evaluations. The block error rate, or BLER, was measured and evaluated as a key performance metric, and when proper synchronization could not be achieved, the corresponding transmission block was treated as an error.
When the assumed mobility speed was varied up to approximately 1,000 km/h, conventional signal processing methods originally developed for lower-frequency bands failed to achieve the required BLER threshold of 10% in the speed range of approximately 700-1,000 km/h. In contrast, by applying the newly developed signal processing method, the required BLER performance was satisfied across all evaluated mobility conditions. These results indicate that, from the perspective of robustness against carrier frequency offset, stable signal transmission can be achieved even in environments corresponding to mobility speeds of up to 1,000 km/h.
This achievement enables the development and proof-of-concept experiments of communication systems for a wide range of mobility scenarios, from fixed wireless systems to terrestrial mobile communications and non-terrestrial networks. The results are expected to further accelerate research and development of THz-based ultra-high-speed wireless communication systems in the move toward 6G.
