
Alphabet wants to deliver Internet access via laser beams - spacemanspiffy
https://arstechnica.com/gadgets/2017/12/alphabet-wants-to-deliver-internet-access-via-laser-beams/
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ethagknight
I was hoping the article would provide more detail for why this is better or
different from existing microwave radio methods. Higher bandwidth appears to
the answer. It appears that some laser systems feature a hybrid system with
laser and rf technologies, and will automatically downgrade to RF when
weather, pollution, or other obstructions come up.

[http://www.lightpointe.com/airebridge-
lx-1.html](http://www.lightpointe.com/airebridge-lx-1.html)

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sandworm101
Be more pragmatic. It's about licensing. The microwave frequencies are
licensed. Laser frequencies are not. Want to setup a network without first
securing government permission, the obvious choice is laser. This is also a
primary reason COPs switch to lasers for speed enforcement.

The bandwidth of individual connections is only half the equation, and largely
irrelevant imho. What matters for the network is the lack of interference.
Laser connections can spider across a city without real risk of contaminating
one signal with another. So even if the point-to-point bandwidth is the same,
the total potential bandwidth of the installed network will be much higher.

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oktobercrisis
There are a lot of microwave connections (E.G. 24Ghz, 5.7Ghz) that are in the
unlicensed spectrum. We are using these extensively in our network. See
[https://en.wikipedia.org/wiki/ISM_band](https://en.wikipedia.org/wiki/ISM_band)

~~~
sandworm101
Unlicensed, but not unregulated. There are very detailed limitations on
transmitter/antenna powers in those areas, limitations that are very country-
specific. The rules for laser, where they exist, are more akin to "don't burn
our people's eyes".

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KirinDave
This technique works and is in fact quite simple. I suspect it's simply a
matter of competing business interests that it hasn't been tried before.

Even near visible laser communication systems can operate at harmless power
levels for miles, can be aligned by hand in many cases (you provide a
"collection" dish to reflect the light in) and they're dirt cheap.

I actually built one as a project in my required EE classes for my CS degree
back in 2002 using a pair of (rather expensive and overpowered) helium neon
lasers. In 2002 and with these lasers the speed we had build was quite slow
because of the switching time for the lasers, but the point was to build the
hardware so we were good.

Given the absurdly low cost of these systems w/ modern components and their
phenomenally low power budget, I'm not surprised.

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amelius
Relevant quote:

> If you're like me and immediately asked "how can a line-of-sight laser
> system work when it rains?" The answer is "it doesn't." Atmospheric
> disturbances like rain, snow, fog, dust, and heat can all interfere with the
> light beam, and they have been the major limiting factor in this
> communication method.

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jpm_sd
In the past it has been proposed that a dense mesh network of FSO links could
deal with interfering weather by dynamically routing around it. But that's a
lot of lasers on a lot of moutain tops.

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libraryatnight
I just had this vision of aliens finding us and thinking in their own way
"they have some sort of laser mesh defense system..."

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ASalazarMX
"Lasers can't even penetrate our navigation shields. Don't they know that?"

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foxyv
Errr... I guess go to yellow alert?

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hedora
I used to have a Motorola Canopy dish at home. It was much more reliable than
cable or dsl. The idea is to have one omnidirectional tower, and directional
dishes at each house. This scales beautifully, because you can simply add more
and more towers to increase density (having directional dishes on one side
fixes the crosstalk in both directions, up to a point).

It was doing 6mbit with better latencies than cable, back when cable was <
6mbit in my area. I have no idea what similar bandwidth microwave systems can
push these days, but it worked fine in rain and fog.

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cr0sh
If anyone wants to play around with a system like this, that is basically
"open source" \- and to see firsthand the difficulties of implementing such a
system on a DIY budget, check the following project out:

[http://ronja.twibright.com/](http://ronja.twibright.com/)

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Havoc
>Existing systems have stuck to using eye-safe laser power densities and can
achieve around 10Gbit/s.

Implying that google's 20Gbit system isn't eye-safe?

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Doxin
Implying that googles system didn't exist before.

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killjoywashere
Military has been using this kind of network on ships at sea for decades.

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tyingq
That's interesting...aligning a laser spot beam between two ships moving,
pitching, and rolling seems non trivial.

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nightcracker
Actually, considering the distances I would assume that high-entropy high-
frequency noise near the laser such as people walking nearby, engines roaring,
air currents, etc are much harder to deal with than the low-frequency
predictable movement of the ship caused by large waves.

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tyingq
>low-frequency predictable movement of the ship caused by large waves.

Well, I was thinking that combined with whatever navigation is going on as
well. As a layperson, waves don't seem predictable to me.

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killjoywashere
On micro- to millisecond intervals, plus the dampening effect of a 10K to 100K
ton ship, waves are pretty managable.

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DougN7
I'm (naively) surprised this works in practice. It seems like the sending
laser and receiver would have to be very immovable such that big wind gusts,
or a large truck driving by, or large temperature changes in the structure
holding the laser, etc, didn't cause enough vibration/movement to cause the
laser to miss its target when several miles away. Is this a non-issue? Or
maybe the laser spreads out enough at several miles it compensates for the
movement?

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InvisibleCities
Why is this better than using a fiber optic cable? I guess light travels
slightly faster through the air compared to either glass or plastic (the two
typical optical media used for cables) which would reduce the transmission
time, but I can't imagine that the slight decrease in latency is worth the
massive increase in downtime due to atmospheric interference.

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kevin_b_er
Less cable installation. Put it on a pole pointed toward the tower and you're
done. It'd be nice in the US where the corporate cartels like
Comcast/Charter/Verizon can't as easily blockade access to internet by
manipulating control over utility poles through bribery of local and state
officials.

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gruez
nice laser link, would be a real shame if we built a tower in between...

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knicholes
I'm thinking that it'd be cheap enough to route the beam around a tower that
this would be cost prohibitive, but it made me laugh.

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doommius
The main issue I see with this system is that there are so many factors that
will disrupt the signal. assuming India, How will they handle rain and heavy
pollution degrading the quality of the signal? or will it just be a? "Oh, it's
monsoon season so no internet?"

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grahamburger
I've seen some systems like this that will fall back to 5ghz or 2.4ghz RF
connections when the lasers are blocked, so the throughput goes way down but
at least the service isn't out completely. Maybe they'll do something like
that.

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westbywest
Fallback to other unlicensed bands like 24GHz or 60GHz would probably work
better. The higher frequencies at least retain a compact dish size, smaller
fresnel zone, and sharper directionality. That is, imagine hanging several of
these optical devices + 5GHz fallback at ~1 meter vertical spacing on a pole.
A weather event triggering failover on all optical links could lead to enough
5.8GHz self-interference to kill the fallback links as well. 5.8GHz devices
that aren't synchronized in phase with each other often call for 3meter+
separation, eating up tower real estate.

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betterunix2
Weather will also degrade 24GHz and 60GHz links. A friend of mine used to work
at an ISP that relied on wireless links, and he said that even at 2.4GHz
moisture was a significant problem (especially concentrated moisture in living
things like trees). In general as the frequency increases attenuation due to
water increases; at 60GHz particulates will also become a problem (consider
that a selling point of 60GHz is that it does not penetrate walls, so you will
have less interference in apartments or large office buildings).

(Edit: Looked it up; 2.4GHz is more readily absorbed by plants than 5.8GHz.
Still, attenuation due to moisture seems to be a problem for microwave
frequencies generally.)

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westbywest
Indeed the 24GHz and 60GHz gear has its unique rain fade issues not shared by
5.8GHz. Increased atmospheric attenuation of higher bands is the general
trade-off for higher throughput and more compact physical isolation
requirements. UBNT 24GHz gear is being using for ~10km links, but looks like
the ~5km is the preferred limit. My original comment would have been better
written to stress need to prove out the signal path over all intended bands,
e.g. primary link over (near) optical and fallback over whatever RF band
proves viable.

