Making Waves: How Waves in 5G Frequency Band Behave Inside High-Speed Rails
Researchers from Korea perform a comprehensive study of 5G millimeter wave propagation characteristics in a high-speed train environment.
Daejeon, July 2, 2021
Despite the potential applications of 5G technology in high-speed train (HST) communication, its study has been limited owing to difficulties in measuring 5G millimeter wave (mmWave) in such an environment. In a new study, researchers at ETRI, Korea conduct mmWave measurements in a realistic HST environment, considering the effects of railway structures and pathways on their propagation, paving the way for an innovative 5G-enabled railway system!
Globally, we’ve moved past 4G and into 5G networks. With this new wireless standard, we are on the verge of witnessing an altogether new kind of network that not only connects people through their smartphones but also connects people to objects, machines, and devices. In short, 5G connects everyone and everything.
One of the promising applications of 5G and beyond wireless communications is high-speed train (HST) communication that is expected to support not only control and safety applications but also several high-data rate applications such as HD video surveillance, on-board broadband internet access, live train departure video, mobile railway ticketing, and Internet of Things for railways.
To enable these facilities, millimeter wave (mmWave) frequency bands, corresponding to about 28 gigahertz (GHz) for 5G, needs to be utilized in an HST environment. However, studies on mmWave measurements in such environments has been limited due to practical difficulties. “Most HST propagation studies have focused on characteristics below 6 GHz and while a few deal with mmWave frequency bands, they do not sufficiently cover various HST environments, limiting the deployment of mmWave wireless systems,” explains Mr. Jae-Joon Park from Electronics and Telecommunications Research Institute (ETRI), Korea, who researches on modeling mmWave high-speed vehicular communication.
Addressing this issue in a recent study published in ETRI Journal, Mr. Park and his colleagues at ETRI have now performed field measurements in a realistic HST environment at the 28 GHz band, investigating the propagation characteristics and their evolution for different HST scenarios as well as the effects of railways structures unique to HSTs.
To conduct their measurements, the team used a channel sounder (a device that evaluates the radio environment for wireless communication) comprising, among other things, a transceiver (i.e. transmitter and receiver) module and a radio frequency module (RFM), and operating at a center frequency of 28 GHz. They installed the transmitter (TX) RFM and antenna next to a test track (for a test HST moving at 170 km/h) and the RFM and receiver (RX) antenna on the roof of the train carriage.
For HST measurement, the team considered two propagation scenarios: viaduct propagation and tunnel propagation, and quantified them in terms of path loss (transmitting power/receiving power), RMS delay spread (a parameter for characterizing the temporal spreading of signal), and Doppler shift (frequency shift due to receiver motion relative to transmitter). Additionally, they considered the effect of overhead line equipment (OLE) along the test track (supplying high-voltage electricity to the HST) on these characteristics.
The team found that OLEs had a considerable effect on RMS delay spread and Doppler shift, observing a value of 24.6 nanoseconds for the former in viaduct propagation and a frequency shift ranging from +3.3 kHz to -3.3 kHz for the latter. As for path loss, they found it to be nearly constant relative to distance for tunnel propagation while a bit higher than free-space loss for the viaduct.
“These measurement characteristics will be beneficial in 5G mobile communication systems,” comments an optimistic Mr. Park. “A potential direction for future research might be a comparison with simulations, which will enable verification of the observed impacts of HST environments,” he concludes.
Reference
Titles of original papers: Empirical Millimeter-wave Wideband Propagation Characteristics of High-speed Train Environments
Name of author: Jae-Joon Park, Juyul Lee, Kyung-Won Kim, Heon-Kook Kwon, and Myung-Don Kim
Affiliation: Telecommunications & Media Lab., Electronics and Telecommunications Research Institute (ETRI)
About Jae-Joon Park
Jae-Joon PARK has been with the Electronics and Telecommunications Institute (ETRI) in Daejeon, Korea, since 1999. In 1999, he received a MS degree in control and instrumentation from Chung-Ang University in Seoul, Korea. At present, he is a principal researcher at the Radio & Satellite Research Division at ETRI. He has contributed to ITU-R IMT-Advanced (4G) and IMT-2020 (5G) channel models for evaluating the candidate radio interface technologies, and his current research interests include channel measurements and modeling for millimeter-wave high-speed vehicular communications and future terahertz communication systems.
