Wireless transmissions can take many routes to the intended receiver. The color lines are reconstructions of measured signal paths from millimeter waves between a transmitter (not visible) and a receiver (lower middle) in the NIST industrial control room. Each path is accurately characterized in terms of length and angle to the receiver. All these pathways are secondary, which means reflected or diffracted signals.



Settling a key dispute in wireless communications, researchers at the National Institute of Standards and Technology (NIST) found that transmission performance was consistent across different bands of the millimeter-wave spectrum (mmWave) targeting high-speed, data-rich 5G systems.

Wireless systems switch to the mmWave spectrum at 10-100 GHz (GHz), above overcrowded cell frequencies, as well as early 5G systems around 3 GHz. System operators tend to prefer lower bands of the new mmWave spectrum. One reason is that they are influenced by a formula that says more signals are lost at higher frequencies due to shorter wavelengths, resulting in less useful antenna area. But so far, measurements of this effect by many organizations disagree on whether this is true.

NIST researchers have developed a new method for measuring frequency effects, using the 26.5-40 GHz band as a target example. After extensive laboratory research and two real-world environments, the NIST results confirmed that the main signal pathway – above a clear “line of sight” between transmitter and receiver – does not vary according to the frequency commonly accepted for traditional wireless systems, but has not yet been proven. for the mmWave spectrum. The results are described in a new paper.

The team also found that signal losses in secondary roads – where transmissions are reflected, bent or scattered in clusters of reflections – can vary somewhat depending on the frequency, depending on the type of road. Reflective paths, which are second in strength and critical for maintaining connectivity, have lost little signal strength at higher frequencies. Weaker curved and diffuse paths lost a little more. Until now, the effects of frequency on this so-called multipath were unknown.

“This work can help to downplay many misconceptions about the spread of higher frequencies in 5G and 6G,” said NIST electrical engineer Camilo Gentile. “In short, while productivity will be worse at higher frequencies, the decline in productivity is gradual. So we expect the implementation of 5G and possibly 6G to be successful.

The NIST method emphasizes innovative measurement procedures and improved calibration of equipment to ensure that only the transmission channel is measured. The researchers used the NIST SAMURAI channel uncertainty (Synthesis in the measurement of synthetic aperture for angle of incidence), which supports the design and retesting of 5G mmWave devices with unprecedented accuracy in a wide range of frequencies and signal scenarios. The NIST system is unique in that the antenna beams can be directed in any direction for accurate arrival angle estimates.

NIST’s main innovations in the new study, as discussed in the paper, were calibration procedures to remove the effects of channel siren equipment from measurements, extending an existing algorithm to determine from a single measurement how individual pathways vary according to frequency, and research. in an industrial control center and a conference hall for classification of the types of included roads and determination of any frequency effects.

Reports: D. Guven, B. Jamroz, J. Chuang, K. Gentile, R. Khoransky, K. Remley, D. Williams, J. Quimby, A. Weiss, and R. Leonhard. Methodology for measuring the frequency dependence of multi-path channels in the spectrum of millimeter waves. IEEE Open Journal of Antennas and Propagation. Published online April 19, 2022 DOI: 10.1109 / OJAP.2022.3168401


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