Wireless transmissions can take many routes to the intended receiver. The colored lines are reconstructions of measured paths of millimeter-wave signals between a transmitter (not visible) and receiver (lower middle) in a NIST industrial control room. Each path is precisely characterized in terms of length and angle to the receiver. These paths are all secondary, meaning reflected or diffracted signals.
Credit: NIST
Settling a key dispute in the wireless communications field, researchers at the National Institute of Standards and Technology (NIST) found that transmission performance is consistent across different bands of the millimeter-wave (mmWave) spectrum targeted for high-speed, data-rich 5G systems.
Wireless systems are moving to the mmWave spectrum at 10-100 gigahertz (GHz), above crowded cellular 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 smaller wavelengths resulting in a smaller useful antenna area. But until now, measurements of this effect by many organizations have disagreed over whether this is true.
NIST researchers developed a new method to measure frequency effects, using the 26.5-40 GHz band as a target example. After extensive study in the laboratory and two real-world environments, NIST results confirmed that the main signal path — over a clear “line of sight” between transmitter and receiver — does not vary by frequency, a generally accepted thesis for traditional wireless systems but until now not proven for the mmWave spectrum. The results are described in a new paper.
The team also found that signal losses in secondary paths — where transmissions are reflected, bent or diffused into clusters of reflections ..
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