Wireless systems are moving to the mm spectrum at 10-100 GHz, which puts them above the crowded cellular frequencies as well as early the 5G systems that work at around 3 GHz, according to the National Institute of Science and Technology (NIST). System operators seem to prefer the lower bands of the new mm spectrum because they believe more signals are lost at higher frequencies due to smaller wavelengths using less of an antenna’s surface. But until now, no one has been able to definitely prove whether this true or not.
To settle this dispute, researchers at the NIST found that transmission performance is consistent across different bands of the millimeter-wave spectrum targeted for high-speed 5G.
NIST researchers developed a way to measure frequency effects using the 26.5-40 GHz band as a target example. After extensive study in the laboratory and in the field, NIST confirmed that the main signal path over a clear line of sight between transmitter and receiver does not vary by frequency.
The team also found that signal losses in secondary paths where transmissions are reflected, bent or diffused into clusters of reflections can vary by frequency, depending on the type of path. Reflective paths, the second strongest and critical for maintaining connectivity, lost only a little signal strength at higher frequencies. The weaker bent and diffuse paths lost a bit more. Until now, the effects of frequency on this so-called multipath were unknown.
“This work may serve to debunk many misconceptions about propagation at higher frequencies in 5G and 6G,” NIST electrical engineer Camillo Gentile says. “In short, while performance will be worse at higher frequencies, the drop in performance is incremental. So, we do expect the deployment at 5G and eventually at 6G to be successful.”
The NIST method emphasizes innovative measurement procedures and enhanced equipment calibration to make sure only the transmission channel is measured. The researchers used NIST’s Synthetic Aperture Measurement Uncertainty for Angle of Incidence channel sounder for its repeatable and accurate testing of 5G mm devices across a wide range of signal frequencies and scenarios. The NIST sounder is unique in that its antenna beams can be steered in any direction for precise estimates of angle-of-arrival.
NIST’s main innovations in the new study were to calibrate procedures to remove the effects of equipment from the measurements, extend an existing algorithm to determine from a single measurement how individual paths vary by frequency, and to conduct studies in an industrial control center and a conference room to classify the types of paths involved and determine any frequency effects.