
Steve Perlman's Wireless Technology Is Finally Here - amalag
http://www.businessweek.com/articles/2014-02-18/steve-perlmans-amazing-wireless-machine-is-finally-here
======
lutusp
An unfortunate title -- the method doesn't rely on hardware, on "machines", it
uses hardware already in place but calculates, then generates, a unique signal
for each device. The method depends on the calculation, the mathematical
theory, not machines.

Calling this a machine is like calling the first car a horseless carriage.

~~~
Mindless2112
> Calling this a machine is like calling the first car a horseless carriage.

Um, they did do that, you know. I agree with your point, but the analogy is
broken.

~~~
lutusp
Not broken. I know that was the term used at the time, and it was a classic
case of trying to describe something new in outdated terminology.

------
lutusp
I've been playing with antenna phasing and I have a preliminary result for
three cellular antennas:

[http://i.imgur.com/tyyVh0j.png](http://i.imgur.com/tyyVh0j.png)

The antenna locations are marked with blue dots.

In this diagram the size of the high-signal-strength lobes is much larger than
would be true at cellular frequencies, but it gives a sense of how this idea
works. By adjusting the phase at each antenna, the lobes can be moved around
to accommodate different devices within their range.

As I expected, increasing the number of antennas past three doesn't really
improve the outcome enough to justify the increased complexity.

~~~
TTPrograms
This is called phased array, and it's been around since WWII for radar
applications:

[https://en.wikipedia.org/wiki/Phased_array](https://en.wikipedia.org/wiki/Phased_array)

More antennas can enable you to narrow lobes more - you may have not been
phasing them properly to get that effect.

~~~
lutusp
My sole reason for posting the example was to show how a small number of
individual antennas could produce focusing lobes within a 2D space. Phased
array radars use many more elements, much higher control over the wavefront,
and for a different purpose.

In a cellular antenna scenario, unlike phased array radar, you cannot avoid
multiple lobes, but the advantage of phasing is still present. Adding antennas
to the system (beyond three or four) becomes a case of diminishing returns.

> More antennas can enable you to narrow lobes more - you may have not been
> phasing them properly to get that effect.

There are paradoxical effects with more than a few antennas -- apart from the
complexity issue. In some cases you will see lobes with strange shapes in
locations having no benefit. With a circular array of antennas, you sometimes
get concentric circles of high signal strength, not what you're after in the
described system. Example:

[http://i.imgur.com/hK9BZnF.png](http://i.imgur.com/hK9BZnF.png)

~~~
TTPrograms
I'd recommend you make your system scale appropriate. Considering that
cellular transmissions are on the order of GHz, you're effectively simulating
a circle of antennas around 1 m wide looking at what happens in the middle.
That doesn't seem particularly relevant to the case of antennas being very far
away (far-field vs near-field etc).

~~~
lutusp
Yes, understood. The diagram was only meant to show how interference works,
not at all to represent the problem under discussion.

------
uhno
Sounds like MegaMIMO, which allows wireless network throughput to increase
linear in the number of APs added (they call this joint multiuser MIMO):

[http://groups.csail.mit.edu/netmit/wordpress/projects/spectr...](http://groups.csail.mit.edu/netmit/wordpress/projects/spectrum-
usage-coverage-data-rates/megamimo/)

------
muaddirac
> Despite such demonstrations, Perlman has been unable to tempt venture
> capitalists with the technology. “They invariably bring in experts who say
> it doesn’t really work,” he says. “I am showing them a demo, but they remain
> convinced that it’s something else.”

Then it's not an adequate demo?

~~~
raverbashing
Maybe

But they said that of the iPhone as well.

There's always going to be skeptical people, even if your demo is perfect and
your product is a machine that turns "crap into gold"

The ratio of rejections to acceptances unfortunately is very high even for a
great product (and it's possibly very low for bad products as well)

~~~
clhodapp
Are you actually claiming that subject-matter experts argued the technology in
Apple's original iPhone was impossible and that the demos at its unveiling
were just tricks? If so, your claim is pretty hard for me to believe, as I
don't remember reading articles arguing anything like this at the time.

~~~
konstruktor
Here is one:
[http://www.electronista.com/articles/10/12/27/rim.thought.ap...](http://www.electronista.com/articles/10/12/27/rim.thought.apple.was.lying.on.iphone.in.2007/)

------
foobarqux
Anybody familiar with wireless comms know what this actually does and what the
innovation is?

Is this distributed beamforming?

~~~
ChuckMcM
Reading Perlman's descriptions it does sound like distributed beamforming.
Perlman is a smart guy, although I expect he would be more successful selling
this technology initially to crowded venues (think large stadiums, or
conference centers) which would allow those venues to both offer consistent
high performance access to fans as well as high performance wireless channels
for things like flying cameras (which is currently quite the mismash of
technologies).

That said, I continue to remain dubious because his claims are fairly out
there in terms of bandwidth. I don't know if Claude Shannon were alive today
if he could figure out if there was an upper limit of directed traffic in a
channel but that is the principle that feels like its being violated here. All
of my training has taught me to think of a bit of spectrum like a single wire,
and sure you can attach a bunch of things to that wire, but there isn't a lot
of theory around how that becomes a bunch of separate but equivalent channels.

~~~
wmf
AFAIK the Shannon limit applies to a channel with a single transmit antenna
and a single receive antenna. MIMO can get a factor of N more throughput
without breaking Shannon by using N antennas.

~~~
lutusp
Not if the antennas are all carrying the same signal. In the described system,
the antennas get phase adjustments, but they do not get different signals, and
this idea doesn't rely on multiple, independent data channels. So the Nyquist-
Shannon sampling theorem still applies.

~~~
cma
I imagine it is something like a XOR-swap:
[http://en.wikipedia.org/wiki/XOR_swap_algorithm](http://en.wikipedia.org/wiki/XOR_swap_algorithm)

I imagine two phones X and Y and one antenna sends X XOR Y while the other
sends X XOR Y XOR Y. A phone getting both signals could determine X and Y, but
it would take twice as much bandwidth. If you can XOR the signals in the air
through superposition somehow, X might be received in one location, and Y in
another.

So 2 antennas cant service more than 2 phones at full speed, but they can
service those two phones at full bandwidth. This might not seem like an
advantage over directional antennas, but it relaxes the physical constraint of
making sure the phones are in two separate enough places to be serviceable by
the two antennas. Like maybe your phone would have two antennas and get twice
the data--not very feasible if your phone were somehow serviced by two
directional antennas.

I haven't worked out how superposition could do something exactly like XOR, or
if it maybe has a minimum of 3 antennas to start being possible, etc., but it
seems plausible.

Anyway, the idea would be sending signal X and Y. You want X interfering with
Y at some time offset to yield desired phone signal A, and X interfering with
Y at some other time offset to yield phone signal B. The phones never receive
X or Y, but some superposition of the two, The phones couldn't cheat and just
record the two waves and timeshift internally to yield twice the bandwidth,
because they don't receive the two waves separately, they only get the
superposition of the two.

~~~
bsder
It's called CDMA:
[https://en.wikipedia.org/wiki/Code_division_multiple_access](https://en.wikipedia.org/wiki/Code_division_multiple_access)

XOR is just a primitive way of making an orthogonal code.

------
oneiric
My summary, beamforming plus wider bandwidth.

His white paper probably addresses the more inquisitive and technical readers'
questions:
[http://www.rearden.com/DIDO/DIDO_White_Paper_110727.pdf](http://www.rearden.com/DIDO/DIDO_White_Paper_110727.pdf)

802.11ac beamforming justs boosts signal quality. It does not take advantage
of more bandwidth.

I don't think the math is actually that complicated to explain. I think of it
as the electromagnetic equivalent of visual cryptography:
[http://datagenetics.com/blog/november32013/index.html](http://datagenetics.com/blog/november32013/index.html)

An antenna not integrated into the system would see noise. The designated
phone would see the exact interference pattern it needs to get the "picture."

~~~
rasz_pl
Nice example with visual crypto, but does this scale? Are there algorithms
able to generate arbitrary number of patterns where groups of two or more of
those patterns form desired groups of signals? Basically generate 10 visual
crypto pictures and be able to get different messages by combining random
pairs of pictures.

Because this is whats needed for this to work.

------
amalag
Previous Discussion:
[https://news.ycombinator.com/item?id=2817730](https://news.ycombinator.com/item?id=2817730)

------
outside1234
I don't get it. Wouldn't it just be easier to install more base stations with
a lower transmission strength (essentially leveraging the same transmission
frequency more times)?

~~~
aidenn0
I can think of at least two reasons why this is superior:

1) You need to have multiple base stations installed roughly equally spaced.
This seems to support heterogenous spacing of the stations

2) With lots of low-powered base-stations interference and obstructions start
to become bigger issues. With many reachable antennas, a small fraction that
have interference or obstructions should merely decrease SNR a bit rather than
drop completely.

Of course advantage #2 seems (to me) to be theoretical; I'd like to see how
this performs in the real-world.

The other issue I can see is moving receivers and/or moving reflectors.
Imagine having this work, for example, when you are near a wind-farm, with
many moving reflectors changing the apparent signal strength continuously.

I know someone who worked on a similar problem in the past, and temporal
coherence in real-world situations was close enough to the feasible round-trip
delay to the data-center. (e.g. if you need to recalculate every 150ms and it
takes 125ms round-trip to the data center, you only get 1/6 the theoretical
benefit).

------
zwieback
Still seems hard to believe you can scale up the math and deal with
intermittent changes in the RF (e.g. cars passing by) but I guess now we'll
find out if it works.

~~~
msandford
It's not terribly difficult provided that you've got enough directional
antennas in your base station. If you do, then every receiver is independent.

In other words it could very well scale as O(n), n = the number of devices.

~~~
lutusp
> It's not terribly difficult provided that you've got enough directional
> antennas in your base station.

This scheme doesn't rely on directional antennas, it relies on computing an
optimal set of phase solutions for multiple antennas to maximize reception
quality. Each antenna is an ordinary omnidirectional dipole, but several of
them working together, with calculated phase delays, provide a kind of
directionality if you want to think about it that way.

~~~
msandford
How do you know it doesn't rely on directional antennas in addition to the
multi-phase solution? If I were trying to do something like this I would
ABSOLUTELY use multiple directional antennas in each base station AND phase
things appropriately.

I don't mean trying to make a ball of yagis or other narrow beam antennas. But
at the very least try and take advantage of splitting a base station into
multiple (2, 4, 8, etc) slices. I can't see how that would hurt performance
(though it would probably make things more expensive) and it would certainly
make it easier to get more bandwidth.

Here's an excerpt from the patent: [0120]FIG. 3 provides additional detail of
one embodiment of the Base Station 200 and Client Devices 203-207 shown in
FIG. 2. For the purposes of simplicity, the Base Station 300 is shown with
only three antennas 305 and only three Client Devices 306-308. It will be
noted, however, that the embodiments of the invention described herein may be
implemented with a virtually unlimited number of antennas 305 (i.e., limited
only by available space and noise) and Client Devices 306-308.

Obviously I haven't studied the patent in detail but that does sound to me
like there are multiple antennas per base station.

~~~
lutusp
> How do you know it doesn't rely on directional antennas in addition to the
> multi-phase solution?

Because:

1\. The article claims it can use the existing cell tower system.

2\. Cell tower antennas are simple dipoles, not directional antennas.

> If I were trying to do something like this I would ABSOLUTELY use multiple
> directional antennas in each base station AND phase things appropriately.

Yes, that would improve the performance, but this would make it a hard sell to
cell companies who are trying to reduce the cost of their installed equipment.
Also, to use directional antennas in a high-speed dynamic network, for a given
beam width N, you would need 360/N directional antennas. For a beam width of
30 degrees, you would need 12 antennas where one exists now, and you would
need a way to switch between antennas on each transmitted packet to multiple
served devices. That would be a nightmare.

> Obviously I haven't studied the patent in detail but that does sound to me
> like there are multiple antennas per base station.

Yes, the basic idea requires multiple antennas whose relative phase can be
adjusted. But not directional antennas.

~~~
msandford
> 2\. Cell tower antennas are simple dipoles, not directional antennas.

This is where you went wrong. They are in fact directional antennas. From a
wikipedia article:

"Due to the sectorized arrangement of antennas on a tower, it is possible to
vary the strength and angle of each sector depending on the coverage of other
towers in view of the sector."

[http://en.wikipedia.org/wiki/Cell_site#Channel_reuse](http://en.wikipedia.org/wiki/Cell_site#Channel_reuse)

That certainly sounds to me like a cell base station not only already has
multiple antennas (which you can see with your own eyes) but that it makes use
of said multiple antennas in some kind of semi-intelligent way. Obviously not
as smart as the pCell, but sorta.

> For a beam width of 30 degrees, you would need 12 antennas where one exists
> now, and you would need a way to switch between antennas on each transmitted
> packet to multiple served devices. That would be a nightmare.

As we've established there are already multiple antennas. Maybe not 12, but
several. And this is a trivial problem to solve actually. The same technology
that tracks you from mast to mast can be used to track you from antenna to
antenna. This is the job of the base station controller. Here's a clip:

"By using directional antennas on a base station, each pointing in different
directions, it is possible to sectorise the base station so that several
different cells are served from the same location. Typically these directional
antennas have a beamwidth of 65 to 85 degrees. This increases the traffic
capacity of the base station (each frequency can carry eight voice channels)
whilst not greatly increasing the interference caused to neighboring cells (in
any given direction, only a small number of frequencies are being broadcast).
Typically two antennas are used per sector, at spacing of ten or more
wavelengths apart. This allows the operator to overcome the effects of fading
due to physical phenomena such as multipath reception. Some amplification of
the received signal as it leaves the antenna is often used to preserve the
balance between uplink and downlink signal."

[http://en.wikipedia.org/wiki/Base_station_controller#Sectori...](http://en.wikipedia.org/wiki/Base_station_controller#Sectorization)

I appreciate your enthusiasm for debate but please do some more research into
cellular radio before you weigh in further. You've got a lot of the basic
concepts right but not the particulars of the implementation. If that comes
across harsh; I'm sorry. I don't know how to communicate this more gently.

~~~
lutusp
>> 2\. Cell tower antennas are simple dipoles, not directional antennas.

> This is where you went wrong. They are in fact directional antennas.

No, they (simple dipoles) are not. Read my quote above -- a simple dipole is
not directional. Your reply says that an array of such dipoles can be made
directional, which is true and a point I made as well, but it's a different
topic.

> I appreciate your enthusiasm for debate but please do some more research
> into cellular radio before you weigh in further.

That's my advice to you -- before you change the subject, learn enough to
realize that you're changing the subject.

> If that comes across harsh

Harsh? How about wrong? Dipoles are not directional. Cell tower antennas are
vertically polarized dipoles, therefore they aren't directional. An array of
dipoles is directional in a crude sense and as expressed in your linked
article, but not remotely comparable to a phased array, the topic of the
present discussion.

> I don't know how to communicate this more gently.

Let's see if you gently recognize your error. If you move the goal posts,
obviously the game changes.

~~~
msandford
Okay I can't tell if you're trolling me or what. Let's start with one really
simple thing and from that we can learn a lot.

You have claimed repeatedly that cell tower antennas are simple dipoles. What
do you base this claim upon?

And when I say "base" I'd really like some links to in-depth explanations. I
don't want to see a simple hexagonal cell system like this with A-G labeled
cells and a repeating pattern
([http://www.ofcom.org.uk/static/archive/ra/topics/mpsafety/sc...](http://www.ofcom.org.uk/static/archive/ra/topics/mpsafety/school-
audit/mobilework.htm)). That's how cell phones got started back when there
weren't many users and there was a LOT of ground to cover. These days there
are many, many more users and as such things have gotten more sophisticated. I
included links to wikipedia articles that contain more current information.

If you can prove that they are in fact simple dipoles I have no problems
accepting that they are not directional; a simple dipole is an omni. You learn
that as a 3rd year EE.

~~~
lutusp
> You have claimed repeatedly that cell tower antennas are simple dipoles.
> What do you base this claim upon?

The fact that the vast majority of cell tower antennas are simple dipoles --
it's the basis of the system. You want to argue -- go somewhere else. I was
doing this before you were born.

[http://www.unisonsite.com/pdf/resource-
center/How%20Towers%2...](http://www.unisonsite.com/pdf/resource-
center/How%20Towers%20Work.pdf)

> I don't want to see a simple hexagonal cell system ...

No, of course not -- that would imply that you were wrong. This discussion
revolves around a scheme to phase ordinary cellular antennas to improve the
performance of a classic cellular system, the kind of system you don't want to
talk about.

The big advantage of the scheme under discussion is that it works with a
classic cellular antenna system (plus some additional electronics and
mathematical processing). That makes a classic cellular system the topic.

Typical collection of vertically polarized cellular dipole transmitting and
receiving antennas:

[http://upload.wikimedia.org/wikipedia/commons/2/2d/Cell_Phon...](http://upload.wikimedia.org/wikipedia/commons/2/2d/Cell_Phone_Tower.jpg)

~~~
msandford
In the first document you linked here's an excerpt:

"Wireless carriers have taken the reduce and reuse approach a step further
with the use of directional antennas, illustrated in Figure 5. Rather than
using a single omni-directional antenna that covers a circular radius around a
tower, carriers introduced directional antennas, to further segment cell sizes
and enable the reuse of additional frequencies. For example, placing three
antennas operating in separate frequencies on a tower allows sectors to be
created within a cell, essentially tripling capacity per cell."

And a clip from a wikipedia page
([http://en.wikipedia.org/wiki/Cellular_network#Directional_an...](http://en.wikipedia.org/wiki/Cellular_network#Directional_antennas)):

"Cell towers frequently use a directional signal to improve reception in
higher traffic areas. In the United States, the FCC limits omni-directional
cell tower signals to 100 watts of power. If the tower has directional
antennas, the FCC allows the cell operator to broadcast up to 500 watts of
effective radiated power (ERP).[7]"

Furthermore here is a diagram of how this is done:
[http://en.wikipedia.org/wiki/File:CellTowersAtCorners.gif](http://en.wikipedia.org/wiki/File:CellTowersAtCorners.gif)

The picture that you linked to on the wikimedia site shows what are clearly
referred to by another wikipedia page as "sector antennas". See for yourself.
[http://en.wikipedia.org/wiki/Sector_antenna](http://en.wikipedia.org/wiki/Sector_antenna)

Here's what a single one looks like:
[http://en.wikipedia.org/wiki/File:Sector_antenna2.png](http://en.wikipedia.org/wiki/File:Sector_antenna2.png)

And here's what many of them at the top of a tower look like:
[http://en.wikipedia.org/wiki/File:Transmitting_tower_top_us....](http://en.wikipedia.org/wiki/File:Transmitting_tower_top_us.jpg)

Compare those with the picture that you linked which you claim is of simple
dipoles. I see very little difference between the two. Which is more likely?
That they're making dipoles which just happen to look exactly like sector
antennas AND that they're putting up well more than they need to (since
dipoles are omni they'd only need one) or they're actually sector antennas?

Finally if you're going to invoke the "I was doing this before you were born"
I'm more than happy to quit now. I had this foolish idea that you (as most
people on HN do) wanted to understand the world as it really is. I see now
that I was mistaken, you simply want to be right. That's fine, I can't fault
you for it. It's human nature. But please take that kind of corrosive attitude
elsewhere. The reason this community is so great is that people here listen to
data or evidence. Please don't dilute those values for the sake of "winning" a
stupid internet argument.

~~~
lutusp
> Finally if you're going to invoke the "I was doing this before you were
> born" I'm more than happy to quit now. I had this foolish idea that you (as
> most people on HN do) wanted to understand the world as it really is.

I understand these issues perfectly well, and you are trolling. I proved my
case, or weren't you paying attention? The conversation is about an
unconventional scheme that relies on a conventional cellular system.

As I said before, go argue with someone else until your earlobes dry.

~~~
msandford
> 2\. Cell tower antennas are simple dipoles, not directional antennas.

> Cell tower antennas are vertically polarized dipoles

> The fact that the vast majority of cell tower antennas are simple dipoles --
> it's the basis of the system

You stated three times that cell tower antennas are simple dipoles. That's the
problem. They're not simple dipoles. 20 or 30 years ago they absolutely were.
Then a lot of users joined the system and the carriers all rolled out
directional antennas in all but the most rural of places.

I'm trying to make sure that you understand that this is the point I'm
arguing.

I fully agree that a 1/4 wave dipole is an omni. I fully agree that pCell
probably uses omnis (at least initially). I fully agree that many years ago
the cellular system used omnis.

Where I don't agree is the idea that the current cellular system uses omnis.
By and large, anywhere suburban or urban, and even many rural base stations
all use directional antennas. I've provided tons of links showing that the
carriers use directional antennas to further break up the large cells that
existed when they put all the towers up (and used omnis) into smaller cells
today which can support more users.

> I proved my case, or weren't you paying attention?

Just asserting that some statement is true doesn't make it so. I've provided
plenty of evidence that carriers today use multiple directional antennas to
service extra customers from their existing towers. "Directional antenna"
doesn't necessarily mean a 5 degree beam width, an antenna can have a 30 or 60
or 90 or 180 degree beam width and still be directional. The towers used to be
in the middle of the hexagonal cells, now they're at the place where three
hexagons meet.

Here is a patent by Nortel for a six-sector system in 2004.

[http://www.freepatentsonline.com/6745051.html](http://www.freepatentsonline.com/6745051.html)

You'll notice the familiar triangle shape holding the antennas and that there
are a total of 12 antennas.

[http://www.freepatentsonline.com/6745051-0-large.jpg](http://www.freepatentsonline.com/6745051-0-large.jpg)

What does that look an awful lot like? To me it looks exactly like the middle
antenna array in this picture:

[http://upload.wikimedia.org/wikipedia/commons/2/2d/Cell_Phon...](http://upload.wikimedia.org/wikipedia/commons/2/2d/Cell_Phone_Tower.jpg)

I don't know how to make it any clearer than that.

------
eyeareque
This is great, but I'm doubting the FCC will approve this unless he has found
a way to not cause interference on the other frequencies his system uses.

~~~
toomuchtodo
If the system needs to calculate interference on the fly, it should be trivial
to prevent interference to other interconnected systems.

------
jenwike
Is anyone going to see the demo at Columbia University on Wednesday?

------
Codhisattva
The noise is the signal.

Mind. Blown.

------
owenversteeg
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