Reviewed by Alex SmithMay 4 2022
As Wi-Fi becomes more widely available in cities, and possibly at higher frequencies, it may become reliant on a common urban resource: streetlight poles.
NIST communications researchers traveled to downtown Boulder, Colorado, to verify their channel model for evaluating high-frequency wireless network designs. Sung Yun Jun is checking the alignment of the transmitter, mounted 6 meters high on a mast, with the receiver antenna array on the roof of the blue van. Derek Caudill, barely visible inside the van, is preparing software programs to collect measurement data. Justin Sadinski, in a yellow vest, is checking equipment on the masts. Image Credit: National Institute of Standards and Technology.
Scientists at the National Institute of Standards and Technology (NIST) created and validated a unique model that will assist wireless communications providers in determining how high to connect Wi-Fi equipment to light poles to guarantee that these networks function properly.
In general, the NIST team found that the optimal height depends on transmission frequency and antenna design. Attaching equipment at lower heights of around 4 meters is better for traditional wireless systems with omnidirectional antennas, whereas higher locations 6 m or 9 m up are better for the latest systems such as 5G using higher, millimeter-wave frequencies and narrow-beam antennas.
An international group, the Telecom Infra Project, is promoting the idea of making Wi-Fi available over the unlicensed 60 gigahertz (GHz) frequency band by installing access points on light poles. A technical challenge is that signals in this band, which are higher than traditional cellphone frequencies, are sparse and tend to scatter off rough surfaces.
Measurements of 60 GHz urban channels have shown limited results until now. NIST created a channel model for monitoring transmissions that identifies the sparse, scattery nature of these signals and employs a unique technique for assessing the observed pathways that go beyond the typical signal delay and angle characteristics to add receiver locations. The accuracy of the model’s predictions is equivalent to that of more complex approaches.
Researchers from the National Institute of Standards and Technology (NIST) flew to downtown Boulder, Colorado, to verify their model against actual channel data. To study the trade-offs, measurements were taken at 4-, 6- and 9-meter antenna heights. The model closely matched real-world observations.
We verified the model we developed and used measurements from downtown to prove this point further. This work shows that by using our model, someone like a cell provider can account for various advantages and disadvantages of 60 GHz access points and signals on light poles in urban environments.
Derek Caudill, Electronics Engineer, National Institute of Standards and Technology
The team employed custom NIST equipment named a channel sounder, which consisted of a stationary transmitter installed on a pole and a mobile receiver mounted on the roof of a van. An array of electrically switched antennas with specified 3D radiation patterns is mounted on top of both the transmitter and receiver.
The sounder can directly measure numerous radio channel parameters and has the unique ability to measure the time dynamics of a millimeter-wave channel, which is how the parameters of the waves change over time as the receiver travels.
Data on how signals propagate throughout physical space caught the researchers’ interest. Large spreads are often seen as undesirable since they suggest many received signals and increased interference — in general, having a single clear path for communication.
Our data show that those spreads are wider at higher heights. This means that with fewer obstructions between transmitter and receiver, the power is more distributed in space.
Jelena Senic, Engineer, National Institute of Standards and Technology
Smaller spreads are preferred for traditional wireless systems with omnidirectional antennas to reduce interference, which implies Wi-Fi equipment should be positioned at lower heights on lampposts.
However, the next-generation wireless systems will operate at millimeter-wave frequencies and should employ highly directional antennas with very narrow beams, or pencil beams.
Jelena Senic, Engineer, National Institute of Standards and Technology
“With this configuration, transmitter and receiver will steer their narrow beams in order to find the best possible link; that is, the propagation path that has maximum power. In this case, a higher angular spread is preferable because it will provide diversity in space; that is, transceivers will have the ability to steer beams in more directions in order to find the best link,” Senic concluded.
NIST researchers took it a step further and captured measurement data on the NIST campus to ensure that the new model could be used in a variety of settings. The model’s results on campus were similar to those downtown, demonstrating that it can be applied to a variety of environments and use cases.
Journal Reference:
Jun, S. Y., et al. (2022) Quasi-Deterministic Channel Propagation Model for 60 GHz Urban WiFi Access from Light Poles. IEEE Antennas and Wireless Propagation Letters. doi.org/10.1109/LAWP.2022.3171503.