5G/IoT
Major Challenges Remain for 5G Deployment
By Pasternack
For most people, the most noticeable
difference from 4G to 5G will be a mas -
sive increase in downstream data rates
and reduced latency, and the most significant
benefits will be for gaming and
video streaming, the latter predicted
to produce four-fifths of all data traffic
by 2022. However, unlike its predecessors,
the fifth generation will empower
more than smartphones and tablets, but
fixed-wireless access (FWA) broadband
delivery, autonomous vehicles, the
“Factory of the Future”, connected
cities, and dozens of applications within
the broad umbrella of IoT. It’s a tall
order, and delivering on all this presents
enormous technological challenges, of
which three, millimeter-wave operation,
small cells, and artificial intelligence,
stand out.
For example, even though carrier
aggregation, more spectrally-efficient
modulation schemes, and spectrum
sharing will help, 5G along with Wi-
Fi and other services will ultimately
consume nearly all that remains of the
available spectrum below 6 GHz. After
that, there’s nowhere to go but up in
frequency, possibly even to 95 MHz,
for which even the FCC in the U.S. is
on board (Figure 1). In the spirit of Field
of Dreams, the commission is evaluating
the viability of allocating more
than 21 GHz of unlicensed spectrum
between 95 GHz and 3 THz. The hope
is that if spectrum is available “they
will come”. After making the announcement,
FCC Chairman Ajit Pai noted
the limitations of this new frontier
but touted the “mammoth swaths of
airwaves” available.
However, for anyone who’s developed
components and systems in this
region such a plan probably seems
comical at best and impossible at worst
considering its immense challenges.
That is, there are good reasons why,
except for microwave links, satellite
communications, and some military
systems, millimeter wavelengths have
remained uninhabited. But the commitment
by the wireless industry illustrates
just how much bandwidth the industry
believes it will need to handle the disparate
services that 5G will eventually
provide. Why else would this or any
other industry take it upon itself to operate
in a region of the spectrum
that is inherently inhospitable to
the transmission and reception of
electromagnetic energy?
Not only are these frequencies
limited to line-of-sight paths, lowpower
signals can traverse only a
Figure 1 – There is plenty of bandwidth in the
millimeter-wave region. Source: Qualcomm.
few hundred meters under ideal
conditions (which are rare), and
are attenuated by almost anything,
from precipitation to leaves. They
won’t penetrate common building
materials either, including the
low-emissivity glass used in new
construction and replacement
windows. “Low-e” glass works
fantastically for reducing UV rays
from the Sun, but it’s metal-oxide
coating is equally effective in
attenuating sometimes entirely blocking
millimeter-wave signals.
In addition to its propagation challenges,
Table 1 – The small cell hierarchy.
millimeter-wave operation requires
further development of semiconductor
technologies such as silicon-on-insulator
and silicon germanium, greater
integration with baseband components,
massive MIMO on a scale that befits its
name, and Active Electronically-steered
Array (AESA) antennas currently the
exclusive domain of next-generation
military radar systems.
Considering the challenges presented
by millimeter-wave operation,
it may seem odd that one of the first
applications of 5G will be at 24 and
28 GHz in the form of fixed wir eless
access (FWA). On one level, delivering
residential wireless broadband at these
frequencies makes sense, because it’s
a good “beta application” for millimeter
wave technology. It will allow carriers
to further develop millimeter-wave
wireless systems based on insights
from actual operation rather than trials
or simulations. It’s also a point-to-multipoint
application, so it won’t have to
serve mobile devices or deal with the
integrating these bands into smartphones
that are already cramped for
space.
THE SMALL CELL SCENARIO
One of the issues whose challenges
are often understated is just how much
infrastructure or “densification” will
be required to support 5G in the next
few years and later as millimeter-wave
frequencies come online. Industry organizations
typically state the increase in
base stations at ten times those in use
today for 4G (for “hyper densification”
150 small cells per km2). More than 10
million small cells have already been
deployed throughout the world to serve
4G, but this is just the beginning.
Analysts predict that more than 4
million more will be deployed globally
this year alone, and the small cell market,
which had been growing slowly for
lack of a need to make them, is now expanding
at 50% per year to accommodate
LTE-Advanced, representing more
than $4 billion in revenue. These figures
will likely soon be incremented upward
once deployments at 3.5 and 5 GHz
increase. These estimates also do not
include millimeter-wave deployments,
which except for FWA won’t appear for
years (see table 1).
This being said, the same characteristics
the make the millimeter-wavelengths
a poor choice for long-range
communication make them almost ideal
for the very short distances required
for small cell-to-small cell and smartphone
to-smartphone links, as well
as high-speed backhaul. They might
also find homes in some industrial IoT
environments, where they will compete
with entrenched protocols like ZigBee,
Bluetooth, Wi-Fi, Thread, and Z-Wave.
Small cells operating at millimeter-wave
frequencies could also collaborate
with these protocols, providing a more
16 MW March - April 2019 www.mwee.com
/www.mwee.com
