
Wi-Fi TimeSync - phr4ts
http://www.wi-fi.org/discover-wi-fi/wi-fi-timesync
======
johnm1019
This is huge news to me. Standardized microsecond level wireless time sync
available on cheap commodity hardware. We could've used this at the startup I
was at 4 years ago. I see lots of uses in the AR space, along with device
tracking algorithms.

~~~
johnhenry
Not entirely relevant, but I'm curious about that startup... is it still
around? Did the company ever find a way around the need for this?

~~~
johnm1019
Hah yes we did. Wires. Of course everyone wants wireless though and while it
would've improved the overall experience I'm not sure it would've saved the
company. Other market factors were making more of a problem than just
delivering good tech :/

In further thinking about the idea, once the wifi devices are time synced like
this, you can also begin to use that signal for localization in addition to
the traditional optical or electromagnetic tracking. Fun!

~~~
kbaker
You need better sync than ~1 microsecond to do time-of-arrival localization
for Wi-Fi style signals, though... since RF waves travel at around 1 ft per
_nano_ second.

Ultra-Wideband devices can get this synchronization though, and can be used
for localization.

~~~
sargun
How can you use UWB for this? Doppler?

~~~
webmaven
The Doppler effect would only help with a moving source or target, so probably
not.

I would guess that what was meant was using two (or more) frequencies at the
same time would produce harmonics that reinforce and cancel the combined
signal at set distances from the source that can be used to get distance info,
and if you can get distance to three different points, you get a 3D
location[0]. The technique dates back to WWII.

Further, I _think_ it works best if the frequencies are each a different prime
(otherwise you get many beats). There are probably additional tricks you can
do by varying the precise frequency combination to extract _very_ fine-grained
location data.

[0] Technically, you get _two_ solutions, one on each side of the plane
connecting the three points, but they can be disambiguated as long as
direction can at least crudely be determined within 180°.

------
jlgaddis
A long time ago I wondered why home routers didn't run (or include, at least)
an instance of ntpd in broadcast mode on the internal interface that clients
could sync to.

You can run an NTP instance on your own, of course, and point clients at it
via DHCP options but I thought something like that would be kinda handy for
easily keeping time synchronized across all one's devices.

That doesn't really fit this use case, of course, but it reminded me of it.
With more and more "home devices" being network-enabled, something like that
would be extremely useful (and could put to an end "12 o'clock flashers").

~~~
oneplane
Mine does, but I suppose we're talking about standard CPE devices. They indeed
only do the minimum and are often locked down to prevent you from adding or
changing anything. All in the name of stability and customer experience. The
reality is, of course, that it is way too expensive to support millions of
home users when they start relying on the CPE for more services or start
changing the settings.

~~~
tech2
And to allow the manufacturer to use a lower-power (and cheaper) processor
with half the RAM and less storage.

Software (something like the OSS ntpd at least) is free, parts on a board,
physical board size, routing etc. not so much.

------
oneplane
I wanted to read the stuff on the wi-fi.org website, but due to the many cases
of the capitalized word "CERTIFIED" I ran away...

I'm not sure why, but somehow it feels like walking into the lion's den if a
page has that many occurrences of that word.

------
cbhl
How does this work? I assume it's not just ntp over TCP/IP/Wi-Fi...

~~~
TD-Linux
Probably just the wifi TSF:
[https://en.wikipedia.org/wiki/Timing_Synchronization_Functio...](https://en.wikipedia.org/wiki/Timing_Synchronization_Function)

Notably used by the Wii U:
[https://patchwork.kernel.org/patch/5865651/](https://patchwork.kernel.org/patch/5865651/)

~~~
chemag
TSF is not scalable[0].

[0] [http://web.cse.ohio-
state.edu/~lai/788-Au03/2-scalibility.pd...](http://web.cse.ohio-
state.edu/~lai/788-Au03/2-scalibility.pdf)

~~~
chemag
I should have mention this only applies to IBSS (ad-hoc), not to (infra) BSS,
where the AP sends the beacon

------
azinman2
Lovely to see. Is this just a spec? What does it need for me to use it as a
developer? Drivers? Hardware support? Kernel support?

~~~
themihai
Most likely all of them.

------
rocky1138
I'm completely ignorant on the need for this technology. Can anyone explain a
potential use-case? The website simply states "Home entertainment systems,
automotive infotainment systems, and industrial sensor-based systems rely on
precisely synchronized components to deliver optimum results."

What are "optimum results?"

~~~
STRiDEX
My friend was using wireless speakers for his projector. Noticeable lag
between the speakers and the mouths on screen. Ended up throwing wires to the
speakers to fix it.

~~~
tech2
Many systems (hell, even my almost ten year old mid-range Sony TV) have
options to adjust audio offset. I'm surprised something like a projector or AV
Amp wouldn't.

------
ars
I wonder if this can time-sync wifi and ethernet devices together, because I
feel like a lot of installations will have a mix.

------
anonymousDan
Does this require an access point or would it work with ad-hoc wi-fi or wi-fi
Direct?

~~~
gubby
Says in the article, either.

------
swatkat
Specs are not out yet? I couldn't find any on wi-fi.org.

------
sargun
Any chance we're going to see this result in TDMA?

------
themihai
I'm wondering how this compares to tsn (aka audio video bridge[0]). Their
conclusion was wifi is not reliable enough for time sensitive applications.
Great av networking is not only about clock sync anyway so this looks more
like a half baked standard, nevertheless a good step towards lag free av.

[0]
[https://en.m.wikipedia.org/wiki/Audio_Video_Bridging](https://en.m.wikipedia.org/wiki/Audio_Video_Bridging)

------
andreiw
I tried to look something up but there is no mention of underlying tech... is
this at all related to PTP?

------
digi_owl
Now how about adding a two way data/file transfer spec to WIFI Direct?

------
cicloid
So basically what a Sonos does, as a standard.

~~~
intopieces
Sonos doesn't have the ability to sync audio with video, only audio with
audio, correct? We recently acquired a Sonos Playbar and the interplay between
HDMI/Optical Out/TV processing made the lip syncing a nightmare. Still not
sure it's entirely solved.

~~~
themihai
I thought sonos can't even do multi channel audio. It's just a kind of mesh
network. Wisa was supposed to fix that but for some reasons it seems it failed
to get mainstreem

~~~
wyager
No, you can have multiple speakers synced together with Sonos. It works very
well; I've never noticed any drift. As I recall, this is why Sonos devices
can't just run off a home wifi network and require a bridge.

~~~
themihai
Ok, but can you play multi-channel? Like a 5.1 system in a home theater ? As
far as I know it's not possible. Multiple speakers playing the same content is
not really multi channel.

~~~
jonknee
They sell 5.1 systems:

[http://www.sonos.com/en-us/shop/wireless-5-1-surround-
sound-...](http://www.sonos.com/en-us/shop/wireless-5-1-surround-sound-
package.html)

~~~
themihai
That's right but in my defence that's really a 3.1 system as you have lf, rf
and center in a single speaker. It's also worth to note that lf, rf and center
speakers are the most demanding/used channels so IMHO the problems were
avoided not fixed. Putting all your channels into a single speaker is not
really what I thought when I heard of wireless multi-channel audio. I also
don't know what resolution they use because it's not mentioned in their specs
but something tells me it's not 24 bit at least not for the separate speakers.
I've tried multichannel wifi audio but it just doesn't work either due the
buffering or the sync issues. I ended up with some proprietary technology with
multiple antennas based on the 5GHz band but you need clear line of sight and
that's not always convenient. Anything obstructing the line of sight may make
your speaker fail to play. To sum it up: it's true that sonos has a 5.1 system
but that's really a half backed solution. It's actually a 3.1 configuration.
This may work for some people just like bluetooth speakers work for so many.
Can they play in a real/native 5.1 configuration(6 separate speakers)? that's
hard to say. What about real 7.1 or the latest configurations such Atmos/DTS:X
( 5.1.4 or 7.1.4)? That's impossible without hardware changes. Some would say
that even standard ethernet is not good enough for multi channel audio(thus
avb[0] or [1]powerlink) so I can't really see how standard wifi could work.

[0]
[https://en.wikipedia.org/wiki/Audio_Video_Bridging](https://en.wikipedia.org/wiki/Audio_Video_Bridging)

[1]
[https://en.wikipedia.org/wiki/Ethernet_Powerlink](https://en.wikipedia.org/wiki/Ethernet_Powerlink)

