[Mich VHF UHF Society] Fwd: Amazing: Did you know 70 GHz can travel several kilometers?

Wed Nov 23 10:38:40 CST 2016

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From: KENT BRITAIN <wa5vjb at flash.net>
Date: Wed, Nov 23, 2016 at 7:59 AM
Subject: Amazing: Did you know 70 GHz can travel several kilometers?


*Yea, no hams in this group!!!*


Millimeter Waves Travel More Than 10 Kilometers in Rural Virginia 5G
Experiment
By Amy Nordrum <http://spectrum.ieee.org/author/nordrum-amy>
Posted 7 Nov 2016 | 16:37 GMT
[image: NYU students Yunchou Xing and George MacCartney, pictured outside
of a van in a rural Virginia field on a clear summer day, adjust the horn
antenna of their receiver to find the strongest signal during a millimeter
wave measurement campaign in August.]Photo: Hangsong YanYunchou Xing (left)
and George MacCartney (right) adjust the horn antenna of their receiver to
find the strongest signal during a millimeter wave measurement campaign in
August. They are within line of sight of a transmitter stationed 4.3
kilometers away at the home of their NYU professor, Ted Rappaport.
A key 5G technology got an important test over the summer in an unlikely
place. In August, a group of students from New York University packed up a
van full of radio equipment and drove for ten hours to the rural town of
Riner in southwest Virginia. Once there, they erected a transmitter on the
front porch of the mountain home of their professor, Ted Rappaport
<http://wireless.engineering.nyu.edu/tedrappaport/>, and pointed it out
over patches of forest toward a blue-green horizon.
Then, the students spent two long days driving their van up and down local
roads to find 36 suitable test locations in the surrounding hills. An ideal
pull-off would have ample parking space on a public lot, something not
always easily available on rural backroads. At each location, they set up
their receiver and searched the mountain air for millimeter waves emanating
from the equipment stacked on the front porch.
To their delight, the group found that the waves could travel more than 10
kilometers in this rural setting, even when a hill or knot of trees was
blocking their most direct route to the receiver. The team detected
millimeter waves at distances up to 10.8 kilometers at 14 spots that were
within line of sight of the transmitter, and recorded them up to 10.6
kilometers away at 17 places where their receiver was shielded behind a
hill or leafy grove. They achieved all this while broadcasting at 73
Gigahertz (GHz) with minimal power—less than 1 watt.
[image: NYU students George MacCartney (left) and Jeton Koka (right) lean
over the backseat of a van to observe the signal strength from their
receiver on a Keysight E4407B spectrum analyzer, resting on a van seat,
before recording a measurement.]Photo: Hangsong YanGeorge MacCartney
(left) and Jeton Koka (right) observe the signal strength from their
receiver on a Keysight E4407B spectrum analyzer before recording a
measurement.
"I was surprised we exceeded 10 kilometers with a few tens of milliwatts,”
Rappaport says. “I expected we'd be able to go a few kilometers in
non-line-of-sight but we were able to go beyond ten."
The 73 GHz frequency band is much higher than the sub-6 GHz frequencies
that have traditionally been used for cellular signals. In June, the
Federal Communications Commission opened 11 GHz of spectrum
<https://apps.fcc.gov/edocs_public/attachmatch/DOC-339990A1.pdf> in the
millimeter wave range (which spans 30 to 300 GHz) to carriers developing 5G
technologies that will provide more bandwidth for more customers.
Rappaport says their results show that millimeter waves could potentially
be used in rural macrocells, or for large cellular base stations. Until
now, millimeter waves have delivered broadband
<http://wireless.fcc.gov/services/index.htm?job=service_home&id=lmds> Internet
through fixed wireless, in which information travels between two stationary
points, but they have never been used for cellular.
Robert Heath <http://www.profheath.org/>, a wireless expert at the
University of Texas at Austin, says the NYU group’s work adds another
dimension to 5G development. “I think it's valuable in the sense that a lot
of people in 5G are not thinking about the extended ranges in rural areas,
they're thinking that range is, incorrectly, limited at high carrier
frequencies,” Heath says.
In the past, Rappaport’s group has shown
<http://ieeexplore.ieee.org/ielx7/25/7469422/07434656.pdf?tp=&arnumber=7434656&isnumber=7469422>
that
a receiver positioned at street level can reliably pick up millimeter waves
broadcast at 28 GHz and 73 GHz at a distance of up to 200 meters in New
York City using less than 1 watt of transmitter power—even if the path to
the transmitter is blocked by a towering row of buildings.
Before those results, many had thought it wasn’t possible to use millimeter
waves for cellular networks in cities or in rural regions because the waves
were too easily absorbed by molecules in the air and couldn’t penetrate
windows or buildings. But Rappaport’s work showed that the tendency of
these signals to reflect off of urban surfaces including streets and
building facades was reliable enough to provide consistent network coverage
at street level—outside, at least.
Whether or not their newest study will mean the same for millimeter waves
in rural areas remains to be seen. Rappaport says the NYU team is one of
the first to explore this potential for rural cellular, and he feels
strongly that it could soon be incorporated into commercial systems for a
variety of purposes including wide-band backhaul and as a replacement for
fiber.
"The community has always been mistaken, thinking that millimeter waves
don't go as far in clear weather and free space—they travel just as far as
today’s lower frequencies if antennas have the same physical size,”
Rappaport says. "I think it's definitely viable for mobile.”
Others aren’t convinced. Gabriel Rebeiz
<http://jacobsschool.ucsd.edu/faculty/faculty_bios/index.sfe?fmp_recid=238>,
a professor of electrical and computer engineering who leads wireless
research at the University of California, San Diego, points out that the
NYU group ran their tests on two clear days. Rain can degrade 73-GHz signals at
a rate of 20 decibels per kilometer, which is equivalent to reducing signal
strength 100-fold for every kilometer traveled.
[image: A view looking out from Ted Rappaport's front porch in rural
Virginia, with patches of forest and a blue-green horizon.]Photo: Ted
RappaportThe view from the front porch of Ted Rappaport's home in Riner,
Virginia.
“Rain at 73 GHz has significant, significant, unbelievable attenuation
properties,” he says. “At these distances, the second it starts raining—I
mean, misting, if it just mists—you lose your signal.”
Rebeiz says signals would hold up better at 28 GHz, only degrading 6 to
10-fold over a range of 10 kilometers. Millimeter waves will ultimately be
more useful in cities, he says,  but he doubts they will ever make sense
for rural cellular networks: “It’s not going to happen. Period.”
George R. MacCartney Jr., <http://gmacc.me/> a fourth-year Ph.D student in
wireless engineering at NYU, thinks millimeter waves could perhaps be used
to serve rural cellular networks in five or 10 years, once the technology
has matured. One challenge is that future antennas must aim a signal with
some precision to make sure it arrives at the user. That’s because millimeter
waves reflect off of objects, and can take multiple paths from transmitter
to receiver. But as for millimeter waves making their rural cellular debut
in the next few years—“I'd say I'm a little skeptical just because you'd
have to have a lot of small antenna elements and you'd have to do a lot of
beamforming and beam steering,” he says.
By collecting rural measurements for millimeter waves, the NYU experiment
was designed to evaluate a propagation model that the standards group
called the 3rd Generation Partnership Project <http://www.3gpp.org/> (3GPP)
has put forth for simulating millimeter waves in rural areas. That model,
known as 3GPP TR 38.900 Release 14, tries to figure out the strength of a
millimeter wave signal once it’s emitted from a rural base station
according to factors such as height of the cell tower, height of the
average user, height of any buildings in the area, street width, and the
frequency used to broadcast it.
The NYU group suggests that because this model was “hastily adopted” from
an earlier one used for lower frequencies, it’s ill-suited to accurately
predict how higher frequencies behave. Therefore, according Rappaport’s
team, the model will likely predict greater losses at longer distances than
actually occur. Rappaport prefers what’s called a close-in (CI) free-space
reference distance model, which better fits his measurements. A
representative of 3GPP was not available for comment.
In October, Rappaport presented the group's work at the Association of
Computing Machinery’s MobiCom conference
<https://www.sigmobile.org/mobicom/2016/> and their latest study will be
published in the proceedings. In the meantime, it is posted to arXiv
<https://arxiv.org/pdf/1608.05384v2.pdf>.
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