Comparing
DAS, Small Cells And WiFi
If
you say "wireless" to an IT or LAN person, they think
WiFi. But to a telecom person. wireless means cellular.
FOA's involvement is based on trying to understand the
infrastructure to support wireless, OSP or premises, WiFi
or cellular, tower site or small cell. We're basically
outsiders on the technology side looking at how to provide
the infrastructure to support them. Recently we've been
trying to understand the technologies, markets and
applications for both to better include the two
technologies in our training and certification programs.
The initial question we had dealt with was how to
distinguish DAS (distributed antenna systems for cellular)
and small cells (also cellular). In most ways they seem to
be very similar, except perhaps DAS is indoors and small
cells outdoors. But perhaps more importantly, a DAS is
usually owned by the owner of the space (building, sports
facility, etc) and handles multiple service providers
while small cells are owned by a service provider and
carries only their service.
WiFi is generally owned by the enterprise that is using it
as part of their LAN - a company or organization - and is
not shared except with their employees and/or guests.
The biggest difference is costs to the users - WiFi is
generally free but all cellular systems are charged by
time and/or data usage. But cellular is mobile wireless -
designed to serve users moving around so it can seamlessly
pass a user from one cell site to another. WiFi however,
assumes the user is staying within it's range and may have
to log in to another WiFi access point if they move
around. That mobility aspect of cellular takes some
additional overhead, so WiFi generally has more bandwidth.
We've interviewed insiders in both technologies to try to
understand how they work and why we should have so many
options. Right off, we found that there appears to be a
general lack of technical understanding about the other
from almost everybody we talk to who works with one of
them. And we're talking real basics - what frequencies are
used, protocols, coverage, bandwidth, etc. etc. etc. Even
the jargon is different, but that's not unexpected. So
we've tried to consolidate information on the three
different premises wireless technologies appropriate for
general usage. Over time we expect to refine this
comparison with more data and user feedback. (got any?
send it to us)
Based on the current evaluation, WiFi is essential to
premises spaces and because of the ubiquity of WiFi, it is
inexpensive. However, WiFi connections for cellular mobile
devices appears to have not yet been refined sufficiently
to provide reliable coverage for cellular voice, but data
is good and video, maybe. Given the cost structure of data
plans, using cellular for video can be very expensive but
WiFi is preferable since it is only limited by bandwidth.
The choice between small cell and DAS in premises spaces
is simple - small cells are generally single carrier
connections and that is too limiting for most users. DAS
is similar technology but has the advantage of offering
multiple service providers. If better cellular service is
desired indoors and WiFi connections for cellular calls is
unreliable, a DAS is the best solution.
Small cells appear to be a good solution for better
cellular service outdoors in metropolitan areas but the
capital costs for building systems is quite high -
Deloitte, you might remember from an earlier FOA
Newsletter, forecast a cost of over $200 billion. It makes
one wonder if the carriers can make that investment while
simultaneously investing in 5G.
Premises
Wireless
|
WiFi |
DAS
(Cellular)
|
Small
Cell
(Cellular) |
Connects
to: |
PCs,
tablets, phones, many other devices |
Phones,
tablets, some other devices |
Phones,
tablets, some other devices |
Usage |
Free,
sponsored |
Paid |
Paid |
Origin |
Private,
LAN |
Public,
telco |
Public,
telco |
Frequency
Ranges |
Unlicensed
2.5GHz (802.11n, 14 - 40MHz channels, 3 max
non-overlapping)
5GHz (802.11ac or 802.11n, 24 - 80 MHz
channels, 23 max non-overlapping)(more bandwidth,
less range) |
Licensed
3G: 850, 1700, 1900, 2100 MHz
4G/LTE: 600, 700, 850, 1700, 1900, 2100,
2300, 2500 MHz
CBRS (Citizens band Radio Service, shared,
unlicensed): 3600 MHz, 20MHz channels,
5G: Eur: 24-27GHz, US: 37-48GHz, 71-74GHz |
Licensed
3G: 850, 1700, 1900, 2100 MHz
4G/LTE: 600, 700, 850, 1700, 1900, 2100,
2300, 2500 MHz
CBRS (Citizens band Radio Service, shared,
unlicensed): 3600 MHz, 20MHz
channels,
5G: Eur: 24-27GHz, US: 37-48GHz, 71-74GHz |
Connects
to: |
Internet |
Multiple
telco carriers |
Single
telco carrier |
Mobility |
Log
in to each new private system required, limited
handoffs between WiFi systems or WiFi and cellular
|
Seamless
handoffs |
Seamless
handoffs subject to coverage |
BYOD
(bring your own device) |
OK |
OK |
Depends
on service provider device connects to |
Optimized
for |
Data |
3G:
voice
4G/LTE/5G: data |
3G:
voice
4G/LTE/5G: data |
Data:
Max data rate: |
802.11n:
~35-300Mb/s
802.11ac: ~400Mb/s - 7 Gb/s (MIMO) |
4G/LTE:
~100Mb/s
5G: ~Gb/s (proposed) |
4G/LTE:
~100Mb/s
5G: ~Gb/s (proposed) |
Voice |
VoIP:
good
Cellular on WiFi: not optimal, depends on
device/carrier/implementation
|
Good
with proper coverage |
Good
with proper coverage |
Video |
Good |
4G/LTE:
marginal, expensive
5G: Good (proposed), cost? |
4G/LTE:
marginal, expensive
5G: Good (proposed), cost? |
Cabling
(typical)
|
Fiber
backbone to Cat 5, POE
|
Fiber,
sometimes Cat 5
|
Fiber,
sometimes Cat 5 |
Summary
|
Best
for data on PCs, tablets, smartphones, good for
VoIP systems, marginal on cellular devices
|
Best
for cellular devices since can cover all service
providers, not optimal for high throughput data
(today, future 5G ?)
|
Good
for cellular devices but can cover only one
service provider, not optimal for high throughput
data (today, future 5G ?)
|
Understanding
5G And 802.11ax
Within
all the hype about 5G, one finds little technical details.
It's either how great it's going to be or worries about
the health effects. Finally, we've found some technical
explanations that deal with the actual technology and why
it's possible to have higher bandwidth. Interestingly,
it's a lot like 802.11ax, the latest version of WiFi.
Our information on 5G came from iBwave's
white paper "5G Technology Primer." For
802.11ax, this page on technology from Ruckus
called 802.11ax
Fundamentals was our source. We highly
recommend you read these these papers to help understand
these two systems.
First, we should look at frequency ranges, what has been
the center of most discussion about 5G. 5G has two
frequency ranges within which cellular service providers
have frequency bands licensed to them exclusively. The
band now called FR1 is 450MHz to 6000 MHz and the new band
is FR2, 24,250 MHz to 52,600 MHz, or as it is mostly
described, 24 to 52GHz. It's the new high frequency band
that has attracted most of the attention since it is more
affected by the environment and more readily absorbed,
with the health effects causing much controversy. 802.11ax
works at the same frequency bands as earlier version of
WiFI, unlicensed bands around 900MHz, 2.4 and 5GHz,
although the 2.4 and 5GHz bands are generally used and
the other frequencies are for specialized applications,
new tech (e.g. WiGig at 60GHz) or are licensed bands. The
higher frequencies are desirable because higher
frequencies mean more bandwidth as described by Claude
Shannon at Bell Labs 70 years ago. Higher frequencies are
also problematic because they are more highly absorbed,
shortening link distances and preventing signals from
penetrating walls or glass for example.
The other way to send more information is to use more
efficient protocols. The copper people found out long ago
that one could put more information in one bit by also
encoding data in the pulse height, optical transmission
can also use polarization. Wireless - both cellular and
WiFi - is migrating to OFDMA which stands for Orthogonal
Frequency-Division Multiple Access. Both cellular and WiFi
appear to operate similarly. The system can subdivide
frequencies into subchannels and then divide up frames
using time division multiplexing to allocate bandwidth
where it is needed. Much of the additional throughput
seems to come from using this option to dynamically
allocate bandwidth. 802.11ax is expecting a four-fold
increase in throughput.
802.11ax is using access point intelligence to manage
overlaps in coverage to maximize throughput. 5G meanwhile,
probably willing to spend more money on systems, appears
to have decided to use phased-array antennas, where beam
steering and shaping can be done dynamically to maximize
signal transmission.
All this complicated tech probably shows why the 5G
advocates focus on the higher frequency transmission -
explaining these concepts is not easy. But what's
surprising is that 5G and 802.11ax are so similar, focused
on similar goals, with seemingly the biggest difference is
one is on licensed frequencies and the other unlicensed.
Why do we need both? Why does a building need to have both
a WiFi system and a DAS? Why doe we nead outdoor WiFi?
Practically every phone or tablet has the capability of
connecting to either and laptops can do the same with a
simple plug-in module. Anybody care to comment?
Learn more about how small cells and other technologies
contribute to "smart cities."
More
On Fiber For Wireless
FTTA- Fiber To The
Antenna
Testing FTTC
Fiber
DAS - Distributed
Antenna Systems
WiFi -
Premises Wireless
|