Wi-Fi From Your Local Lamppost

As Wi-Fi is deployed in cities and at greater frequencies, it may rely on an abundant urban resource: streetlight poles.

To guarantee these networks work well, scientists at the National Institute of Standards and Technology (NIST) have created and validated a unique model that will allow wireless communications companies to analyze how high to attach Wi-Fi tools to light poles.

The NIST team discovered that the ideal elevation depends on transmission frequency and antenna design. Securing equipment at lower elevations of about 4 meters is far better for conventional wireless systems with omnidirectional antennas. In comparison, higher locations 6 or 9 meters up are better for the newest systems like 5G, utilizing greater millimeter-wave frequencies and narrow-beam antennas.

An international team, the Telecom Infra Project, is endorsing the concept of providing Wi-Fi over the unlicensed 60 GHz frequency band by installing access points on light poles. One obstacle is that signals in this band, which are greater than conventional cellphone frequencies, are scarce and tend to scatter off rough surfaces.

Previously, measurements of 60 GHz urban channels have generated limited data. NIST developed a channel system for tracking transmissions that recognize these signals’ sparse, dispersing attributes and uses a novel algorithm for evaluating the measured paths that extend past the typical specifications of signal lag and angles to include receiver locations. The model’s predicted precision approaches that of more complicated systems.

A Field tested technology 

NIST scientists traveled to downtown Boulder, Colorado, to test their model against real network measurements. The measurements were recorded at 4, 6, and 9-meter antenna elevations to examine the tradeoffs. The model matched real-world measurements quite well.

Derek Caudill, an electronics engineer involved in the NIST project, stated that they validated their developed model and supported it with measurements from a downtown area. He further added that their work demonstrated the ability of cell providers to consider the pros and cons of 60 GHz access points and signals on light poles in urban settings using their model.

To conduct the study, the team used NIST’s custom-made equipment, called a channel sounder, which consists of a fixed transmitter installed on a pole and a mobile receiver mounted on top of a van. The sounder is equipped with a range of electronically switched antennas with defined 3D radiation patterns. It can accurately measure various radio channel characteristics, including the time dynamics of a millimeter-wave channel, i.e., how the properties of the waves change over time as the receiver moves.

The scientists’ reasoning

The scientists were particularly curious about data on how signals spread throughout physical space. Large spreads are generally bad as they show several received signals and more disturbance. It is typically better to have one clear route for communication.

“Our data show that those spreads are wider at higher heights,” NIST engineer Jelena Senic pointed out. “This means that with fewer obstructions between transmitter and receiver, the power is more distributed in space.”

Traditional wireless systems with omnidirectional antennas require smaller spreads to prevent interference, which means that Wi-Fi equipment must be installed at lower elevations on lampposts. However, the upcoming generation of wireless systems will operate at millimeter-wave frequencies and utilize highly directional antennas with very narrow beams, known as pencil beams.

According to Senic, in this configuration, the transmitter and receiver will steer their narrow beams to find the best link, i.e., the propagation path with maximum power. In this scenario, a higher angular spread is preferred as it provides diversity in space, enabling transceivers to steer beams in more directions to find the best possible link.

NIST scientists went a step further and recorded the measurement data on the NIST campus confirming that they could apply the new design to varying environments. Outcomes on campus approached downtown, validating that the model can be generalized to various environments and use cases. The research appears in IEEE Antennas and Wireless Propagation Letters.

Read the original article on Tech Xplore.

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