
Wi-Fi and LTE in Unlicensed Spectrum Bands - sinak
http://googlepublicpolicy.blogspot.com/2015/06/encouraging-innovation-wi-fi-and-lte-in.html?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed:+GooglePublicPolicyBlog+(Google+Public+Policy+Blog)
======
rayiner
The linked paper is a great read. The punch line is on 6-7 (LTE's duty cycling
co-existence mechanism reduces wifi throughout because it doesn't listen
before transmitting and invariably stomps on a WiFi transmission mid-frame
causing errors and possibly renegotiation to a lower link speed).

Rant: It's sad that we are fighting to put more users in existing unlicensed
bands instead of expanding the amount of unlicensed spectrum available:
[http://www2.itif.org/2015-coase-wifi.pdf;](http://www2.itif.org/2015-coase-
wifi.pdf;)
[http://wireless.fcc.gov/outreach/2004broadbandforum/comments...](http://wireless.fcc.gov/outreach/2004broadbandforum/comments/NewAmericaFoundation.pdf).

Our current approach to unlicensed leaves enormous performance on the table,
and it doesn't have to be that way. Basically the solution is two-fold. First,
there is a lot of spectrum that could be reallocated to unlicensed. Second, we
could get a lot more use out of the band if we imposed least cost avoider type
principles on use of the band (i.e. devices have an affirmative duty to
exercise reasonable measures to be resistant to interference).

If you're interested in the subject, read Bill Lehr's work (at MIT). He's one
of the few people writing about the issue who knows what he's talking about
(he's an engineer who went on to get an Econ PhD).

------
PinguTS
Just to remark, there is much more than Wifi and Bluetooth in the 2.4 GHz and
5 GHz going.

There other users like ZigBee and many industrial users as well. Especially
the industrial users have problems. Because there is no licensed band for
them, they have to work in the unlicensed as well. Industrial users have
stronger real time and reliability requirements than Wifi can offer (response
times in ns).

Technologies like LTE will hurt innovation for industrial usage.

~~~
mentat
Can you expand on "have to use unlicensed"? Is that really saying "don't want
to deal with global regulatory systems"?

~~~
PinguTS
Nope. At least in Europe, there are working on to get their own frequency.
There are also first contacts made to regulating bodies. But we learned, it is
very complicated with lots of intransparent groups and clubs of those
regulating bodies on national, Europe and international level. That means it
will take at least 10 years and than additional years to then transform those
international agreements into national regulations.

So, to be honest nobody believes that it will work out. The industrial
industry is very diverse compared to telcos. There are only 3 different telcos
in Germany. There 3 or 4 telcos for the whole US. So they have a different
market position.

------
jrapdx3
As soon as the article brought up plans of carriers to expand LTE into the
unlicensed 5GHz band, I immediately thought about the implications for current
users of WiFi. Specifically that high-powered LTE would overwhelm the signal
output by home WiFi routers and in other typical scenarios.

The article comes essentially to to the same conclusion, and it will be
unfortunate if new FCC regulations have to be created. It seems to be human
nature that sooner or later powerful interests stop "playing nice", and start
acting like bullies until regulators are forced to step in.

Of course it doesn't have to go that way, but what are the odds that it won't?

~~~
VoightKampff
I would think that everyone operating in unlicenced parts of the spectrum was
subject to the same regulations.

~~~
KB1JWQ
They are-- until you lobby the FCC to change those regulations. Part 15 is
very clear on this.

~~~
TorKlingberg
Part 15 of what?

~~~
luxpir
For US hams it's an extremely often cited regulation, touching on many aspects
of the hobby. There's a good chance 'KB1JWQ' is a ham :)

If you or others care:
[https://en.wikipedia.org/wiki/Title_47_CFR_Part_15](https://en.wikipedia.org/wiki/Title_47_CFR_Part_15)

I'm not based in the States, but it pops up enough everywhere ham-related for
general familiarity.

~~~
hacker234
Part 15 says (amongst many other things) that if a service causes (or suffers)
interference it must go of the air.

Nothing to do with Amateur Radio.

~~~
luxpir
RFI doesn't affect amateur radio? Don't take my word for it, the ARRL have a
few thoughts on Part 15:

[http://www.arrl.org/part-15-radio-frequency-
devices](http://www.arrl.org/part-15-radio-frequency-devices)

------
msoad
It's also called LTE-U. There was a lot debate around this in the recent IEEE
conference. I mean yelling at each other kind of debate!

~~~
yxhuvud
Any more details? What were the two sides of that debate?

~~~
msoad
One side was (is) AT&T and Vrizon and other side was Google and other members

~~~
minot
If AT&T and Verizon are on the same side, I'd probably be on the other side.

~~~
spacecowboy_lon
Its American mobile companies so id agree with you :-)

------
guelo
I thought radios in the unlicensed bands were capped to really weak TX power
levels which would make them useless for broadcasting to large areas.

~~~
dboreham
Not true in most countries (including USA). There is a whole service provider
industry (WISP) with sizable equipment vendors (Miktotik and Ubiquity) that
depends on using the unlicensed bands over wide areas and long range.

~~~
nitrogen
In the absence of a license, aren't those long range and wide area systems
still subject to the same power caps as consumer gear?

~~~
jauer
There's a big difference in how they use the available power.

WISP-type equipment generally uses very directional antennas so the available
power is used more efficiently.

A laptop and a home WiFi router are like people talking in a crowded room.
Long-range systems are like talking into a unpowered megaphone while the other
side is listening with a megaphone on its ear.

~~~
guelo
If what the carriers are talking about is highly directional links for
backhaul then I don't see what the fear is. Directional is not going to
interfere with nearby WiFi.

~~~
dboreham
They're talking about handset to base station, split band -- using licensed
frequencies for downlink and unlicensed for uplink. So, not backhaul.

------
Zigurd
It's spectrum licensing that's obsolete. We know how to make smart radios.
It's time to enable people to use as much spectrum as they need, not as much
as we are willing to pay to rent.

~~~
rayiner
I agree and disagree. Licensing is obsolete for a lot of cases. At the same
time, smart radio technology isn't there yet. In fact, this article is a great
example of that. Both WiFi and LTE have pretty primitive spectrum sharing
technology built in. But it doesn't work that well together.

I worked on spectrum sharing technology as part of the DARPA XG project about
10 years ago. It worked great for many things and had some significant
limitations. Not to mention, the necessary hardware is still very expensive
(high bandwidth analog frontends, extremely sensitive detectors, substantial
CPU and memory to run the algorithms). The simplified version of that sort of
technology you have in LTE on unlicensed band is probably the best you can do
without blowing your budget. And that's not good enough to replace licensing.
The challenge is probably a bit but not tremendously simpler than self-driving
cars, and the relevant cost, size, and power budgets are a couple of orders of
magnitude tighter.

Besides that, the ideal of smart radios interacting in a totally unregulated
world is suboptimal. As Bill Lehr points out, smart radios work way better
when you impose certain rules on everyone. See also Kevin Werbach's work on
the subject:
[http://werbach.com/research/supercommons.pdf](http://werbach.com/research/supercommons.pdf).
The unlicensed band for example isn't totally unregulated. You have strict
power output limitations. But that's sub-optimal. If you're a WiFi access
point in the country, you can probably use a lot more power without causing
interference. At the same time, you don't want to create a shouting match
scenario, where each node ups their power output to drown out the others. More
sophisticated rules help you get more efficient use of your unlicensed band.
For example, you can mandate transmission power control (only enough power to
close the link) you can mandate the use of FEC, so you don't have dumb devices
that can't handle even a tiny bit of interference. Etc.

But you're right about the big picture. Allocating spectrum is not the way
forward. We don't "allocate road" to cars--we just define rules they have to
follow to play nicely with others on the road. Licensing has its place in
enforcing those rules, and doesn't need to imply fixed allocations.

~~~
Zigurd
I wouldn't call current wifi smart any more than I'd call the primitive
beamforming in wifi "SDMA." I'd also agree that smart radios need to observe
some common set of rules, or at least principles, much in the way that self-
driving cars need compatible principles of operation.

I am, however, optimistic about cost and timeline. The amount of hair in your
mobile phone's radio to make it work on 2G FDMA/TDMA, WCDMA, and OFDMA, and
their respective layer 2 protocols, while it certainly adds cost, doesn't add
a multiple of cost compared with, say, a pure wimax 2 radio. Making radios
that use different technologies smart enough to share spectrum is a relatively
cleaner and less compute-intensive problem. I think it could be done now, and
a really huge amount of spectrum could be made available for use cases similar
to today's wifi right now.

------
Spooky23
Uh, no. Leave unlicensed spectrum alone. That belongs to the people.

If licensed spectrum is in finite, constrained supply, let the market take
care of that. Raise the price as it becomes more constrained, and wait a
couple of years for the next technology change that increases the density.

~~~
mentat
What does "belongs to the people" mean in this context? Should Starbuck not be
able to put up Wifi access points? Only private users? Belongs to the people
sounds a lot more like ham radio really.

~~~
Spooky23
It means that it's a commons. You, I or Starbucks doesn't need a lobbyist to
build, buy, or operate a device on unlicensed spectrum that complies with a
few FCC rules. One of the key rules is that you cannot interfere with others.

Licensed telcos shouldn't be able to stomp on the commons because of their
inability to manage the spectrum they have. If Verizon & AT&T lack capacity to
deliver, they can raise the prices, subsidize replacement of older devices
that use more spectrum, or make capital investments in high-density areas.

~~~
mentat
But... wifi interferes with others all the time.

The actual language:

>The primary operating condition for unlicensed devices is that the operator
must accept whatever interference is received and must correct whatever
interference it causes. Should harmful interference occur, the operator is
required to immediately correct the interference problem or cease operation.

Practically wifi at 2.4 GHz is a mess from the density of wifi which is why
that isn't even considered. 5 GHz isn't yet but will be soon enough.

It's the commons, they're not operating outside of the rules unless they're
broadcasting beyond the specifications:
[https://en.wikipedia.org/wiki/U-NII](https://en.wikipedia.org/wiki/U-NII)

Qualcomm's propaganda page is interesting:
[https://www.qualcomm.com/invention/technologies/lte/unlicens...](https://www.qualcomm.com/invention/technologies/lte/unlicensed)

------
chrispeel
The article would have been more complete if it had noted that Google is
attempting to be an 'SAS' database provider for the 3.5GHz band. See
[http://www.fiercewireless.com/tech/story/google-touts-
spectr...](http://www.fiercewireless.com/tech/story/google-touts-spectrum-
access-system-35-ghz-spectrum-management/2015-05-17)

So what Google is saying is "LTE doesn't work well with Wi-Fi in the 5GHz
band, so you should use the 3.5 GHz band. And since we are not evil, we won't
mention that you need to go through yet another Google service to use the 3.5
GHz band."

~~~
minthd
That's a big of an exaggeration.It's surely not the main motivation here.

Being a SAS databse provider won't be very meaningful business for Google.On
the other hand, we know from large efforts and common sense, that Google
really wants faster cheaper internet access to all.

------
ripperdoc
Just FYI, here is response by Qualcomm. They say for example "Qualcomm’s
demonstrations have proven that adding a neighboring LTE Unlicensed node does
not impact an existing Wi-Fi node any more than would adding another Wi-Fi
node. In fact, in many cases, replacing a Wi-Fi node with an LTE-U node
improves throughput for nearby Wi-Fi users"
[http://apps.fcc.gov/ecfs/document/view?id=60001104452](http://apps.fcc.gov/ecfs/document/view?id=60001104452)

~~~
minthd
That's some sneaky wording. the way wifi is viewed in society today - as a
free resource - what matters is the total free capacity for everybody.

And in their example, most definitely , by taking 1 user and converting it to
a non-free method, free capacity decreases.

~~~
TorKlingberg
The unlicensed band was never dedicated to WiFi, and WiFi is not necessarily
free. Carriers like AT&T has rolled out a lot of WiFi hotspots that their
customers devices can connect to.

~~~
minthd
There's a big difference in competition levels between the wifi(i.e. anybody
is able to offer a free or commercial service), and between LTE-U assisted ,
which depends on access to the carrier network which is far from being
competitive.

And that's the reason why carriers added the assisted part to the
standard,according to internal documents:

[http://www.eetimes.com/document.asp?doc_id=1326570](http://www.eetimes.com/document.asp?doc_id=1326570)

~~~
yaantc
I'm sure the big operators are more than happy to limit possible competition,
but that's not the primary reason why LTE-LAA is assisted.

First, LTE-U with its fixed pattern is a quick n' dirty non standard proposal.
It's not even acceptable everywhere, as some countries (Europe for example) do
require LBT in the 5 GHz band, which LTE-U does not do. So I'll skip that
part.

For the 3GPP standard LTE-LAA, a fundamental reason that it requires a primary
channel in licensed bands is that the way LTE works does require an always-on,
reserved channel. This is the way LTE do works in licensed bands: the channel
is fully reserved for LTE, under full eNB control. Changing this fundamental
assumption would be a major breakage, and much much more effort. The result
would be very different. Whereas using LTE carrier aggregation, with a primary
channel in a licensed band and using the unlicensed 5 GHz band for downlink
only (UL has some added challenges that makes it unpractical) secondary
channel(s) with LBT is not too difficult. It's an incremental changes, but
does not require breaking a fundamental assumption. And in this case, LTE-LAA
could perform like other technologies (to be checked, but possible on
principle).

So even if it fits with the operator wishes, the assisted part is also the
sane way to add 5 GHz support to LTE from a pure technological point of view.

~~~
minthd
>> Changing this fundamental assumption would be a major breakage, and much
much more effort.

That's non of the concern of the unlicensed spectrum.The LTE-LAA guys should
do their work and come prepared for what is common in the unlicensed world.
Not the other way around.

And open competitiveness is key in the unlicensed band.

~~~
yaantc
Unfortunately, this is not set in law. And really, that's the level where this
should be enforced. You can count on firms to pursue their own self interest
to the extent allowed by the law. I'm not saying that's good, I'm saying
that's what happens BTW (don't shoot the messenger ;). Here, cellular
operators are seeing all this "free" spectrum, and cellular equipment makers
are building a path to enable them to use it in a practical way for them, and
sell their wares in the process. All legally, as the law is today.

BTW, there are precedents. In the IoT/M2M space Sigfox uses an unlicensed band
around 900 MHz (from memory), and you can't buy their base stations: they make
them for their own use, as their business is to be an operator. If you want to
compete with them, you need to develop your own equipment based on a different
scheme. WiFi and BT are the best known techs working in unlicensed bands, but
there are proprietary systems too.

The legal constraints on the unlicensed bands are varying depending on
country. But as far as I know the strictest constraints are:

\- limited transmission power (LTE-LAA won't be allowed to shout above others
at 5 GHz, at least where this constraint exists);

\- requirements to do listen-before-talk (LBT), at least in Europe (but not in
the US);

\- limit on the amount of consecutive time a given device can hold the medium
(5 ms max.).

LTE-LAA (not LTE-U) will be able to comply with all of this. In this sense,
strictly limited to legal constraints, it will behave as is common in the 5
GHz band. To put more restrictions would need to happen at a legal level. And
not surprisingly, there's intense lobbying on this topic happening right now
from all parties (Google paper is part of this). To be followed...

------
616c
Sorry, this will be off-topic.

Let's say I am a run of the mill IT guy and I wanted to work my way up into
understanding and maybe operating/admin work on cellular networks, how are
guys in the US and abroad getting into this so I understand implementation and
later policy/regulation stuff like this more intimately?

Years ago I considered after college crap work with ATT and Verzion starting
on the bottom ladder just to learn, and every time there is a life crisis I
wonder if I can have a just fuck-it moment and try getting into it.

Any tips?

~~~
Tehnix
You would probably need a good overview of the technologies in use. I can very
much recommend the book "From GSM to LTE"[0]. It goes through all the networks
back from GSM and up to LTE, which are needed, since all are in fact still in
use.

After that you could probably keep an eye on telecom news sites to follow the
ongoing things and regulations.

That should at least get you going.

[0]
[https://books.google.dk/books/about/From_GSM_to_LTE.html?id=...](https://books.google.dk/books/about/From_GSM_to_LTE.html?id=QNyrjwEACAAJ&hl=da)

~~~
616c
Very cool stuff, thanks for the tip. Will find a copy and buy it.

------
lifeisstillgood
I am amazed commercial exploitation of the unlicensed bands is even on
regulators radar. If you are providing commercial use of the spectrum, you
have to get off that band.

It seems that "citizens band" radio was much better "branded" than wifi.
Perhaps we should call it "citizens wifi"

~~~
michaelt

      If you are providing commercial use of the 
      spectrum, you have to get off that band.
    

Goodbye workplace, cafe and hotel wifi?

~~~
minot
I wouldn't mind if wifi had to be at no additional charge or free with
service.

~~~
lifeisstillgood
Well the wifi should be certainly. The issue is the internet backhaul can be
chargeable. Which to all intents and purposes says LTE providers can come
along and offer high powered radio, and effectively block out any low power
wifi routers.

So, if anything this seems like "denial of service" problem more than citizens
band wifi.

But I still say the branding is needed.

------
Aloha
I've thought about trying to do long reach WISP stuff in the 900 MHz band for
similar reasons - its too hard/expensive to get affordable licensed spectrum.
I'd like to see more unlicensed spectrum out there to make this easier,
ideally lower than 2.4 GHz

~~~
Gibbon1
The 900MHz band is great if you can use it, since for the same power 900MHz
goes substantially farther than 2.4 or worse 5GHz.

The old inverse square law is 'in a vacuum' Once you your signal is going
through air, drywall, masonry, or my favorite steel re-enforced concrete,
you're looking at exponents of 2.5 (just air) to 3.5 or worse. This only get
more sad the high frequency you go.

~~~
jdiez17
When you start lowering the frequency and going further, you can have a path
loss exponent of up to 4, so you have to be wary of reflections from the
atmosphere. [1]

Radio engineering is really interesting.

[1]
[https://en.wikipedia.org/wiki/Path_loss#Loss_exponent](https://en.wikipedia.org/wiki/Path_loss#Loss_exponent)

~~~
Aloha
multipath is a pain in the ass - so are atmospheric inversions (which effects
much higher frequencies).

