Radar-Assisted Channel Measurement System for Beyond 5G Wireless Communication in Sub-THz Band

Prof. Gye-Tae Gil’s research team at the KI IT Convergence Lab. developed a novel technique for estimating the path loss parameter of a wireless channel using a monostatic radar, and showed the feasibility of the technique through channel measurement campaign in a real indoor environment.

Due to the rapidly increasing wireless communication traffic and the depletion of the existing allocated frequency spectrums, wireless communication researchers are faced with the need to develop a new next-generation communication system that can provide ultrahigh data rates.

Among the frequency bands that can be used to solve such a problem, the millimeter-wave band from 30 GHz to 300 GHz and the sub-terahertz (sub-THz) band from 0.1 THz to 1 THz are attracting more attention because the radio frequency (RF) circuits for those bands can be designed and implemented with existing technologies.

In designing a new wireless communication system, the most important things to consider are the radio channel and the use cases of the system. In particular, to obtain a reliable link budget and signal strength prediction, a path loss model must be established at the beginning stage.

In the literature, there have been a few papers on path loss modeling based on channel measurement campaign of the sub-THz band mostly using vector network analyzer (VNA) based channel sounder, which can be categorized into D-band (110–170 GHz) and 300 GHz band measurements.

In the case of the existing channel measurement methods, however, expensive equipments, including a VNA, a signal generator, and an optical fiber extension cable, need to be in place to measure the path loss of one-way channels, which becomes an obstacle to exploring new frequency bands for which a transceiver module is not available or hard to implement.

In this research, a novel technique was developed that estimates the path loss parameters of a wireless channel using a monostatic radar. Specifically, a two-way path loss model for a scenario using monostatic radar for sub-THz band channel measurement was expressed as a function of the parameters of a one-way path loss model, and then two linear regression based maximum-likelihood estimation techniques were developed for estimating channel parameters of the one-way path loss model, one of which is the single reference distance based method and the other is the dual reference distance based method.

To verify the effectiveness of the proposed technique, a measurement system based on frequency modulated continuous wave (FMCW) radar with a 122 GHz frequency band was implemented, and then a channel measurement campaign was carried out in a real indoor environment of the KAIST Institute (KI) building.

This research was supported by IITP grant funded by the Korea government (MSIT): No.2018-0-00809, Development on the disruptive technologies for beyond 5G mobile communications employing new resources.

Prof. Gil said that the developed system with the azimuth/elevation scanning capability is under use for channel measurements in typical indoor environments to complete a geometry-based stochastic cluster channel model for ultra-massive MIMO (UM-MIMO) communications in sub-THz band.