8 ms·
Wi-Fi TimeSync
- johnm1019 10y agoThis 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 10y agoNot 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 10y agoHah 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 10y agoYou 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 nanosecond. Ultra-Wideband devices can get this synchronization though, and can be used for localization.
- sargun 10y agoHow can you use UWB for this? Doppler?
- webmaven 10y agoThe 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°.
- jburgess777 10y agoDecaWave sell UWB modules that perform real-time location to ~10cm in a controlled environment: http://www.decawave.com/ http://www.decawave.com/ I imagine that they use a system which is not too different to the way GPS combines the signals from multiple satellites to calculate the receiver location. When you receive have a receive lock against multiple receivers, the spreading code allows you to determine time of flight to the nearest carrier cycle, and the carrier phase can provide even more precise timing. See also: https://en.wikipedia.org/wiki/Multilateration https://en.wikipedia.org/wiki/Multilateration
- cicloid 10y agoSo basically what a Sonos does, as a standard.
- n1000 10y ago...or Airplay.
- themihai 10y agoAirplay works on top of wifi and it can't play multichannel audio. Not to mention the crappy experience when the video is "buffering". Hopefully this standard will fix such issues but I have big doubts.
- thebradbain 10y agoI thought this too until recently, but Airplay does, in fact, support multichannel audio in sync–but only through playing music to speakers through iTunes Desktop [1], as its the only client to officially implement it. Of course, we don't see more multichannel Airplay clients because it is my understanding the standard is proprietary... [1] https://support.apple.com/kb/PH19497?locale=en_US https://support.apple.com/kb/PH19497?locale=en_US
- themihai 10y agoIs there ANY multi channel client? I tell you: no! And it can't really be because Apple specifically limits AirPlay output to one single destination. It's because wifi sucks and as it is and it just can't work on multi channel(things will get out of sync, some channels will buffer while others will play etc). If you read the avb specs you will underatand why. Wifi needs hw changes. https://en.m.wikipedia.org/wiki/Audio_Video_Bridging https://en.m.wikipedia.org/wiki/Audio_Video_Bridging
- pkulak 10y agoSonos was the first. But now everyone is doing it, so it's cool to see it standardized.
- cbhl 10y agoHow does this work? I assume it's not just ntp over TCP/IP/Wi-Fi...
- TD-Linux 10y agoProbably just the wifi TSF: https://en.wikipedia.org/wiki/Timing_Synchronization_Function https://en.wikipedia.org/wiki/Timing_Synchronization_Functio... Notably used by the Wii U: https://patchwork.kernel.org/patch/5865651/ https://patchwork.kernel.org/patch/5865651/
- chemag 10y agoTSF is not scalable[0]. [0] http://web.cse.ohio-state.edu/~lai/788-Au03/2-scalibility.pdf http://web.cse.ohio-state.edu/~lai/788-Au03/2-scalibility.pd...
- chemag 10y agoI should have mention this only applies to IBSS (ad-hoc), not to (infra) BSS, where the AP sends the beacon
- theon144 10y ago>On a commercial level, industry vendors assume the 802.11 TSF's synchronization to be within 25 microseconds. Meh. Still cool, but a far cry from the sub-MICROsecond accuracy the page suggest, which would indeed be quite revolutionary.
- chemag 10y agoI'm curious which are the use cases for sub-microsecond time sync. Entertainment can probably do with millisecond accuracy. Other use cases mentioned by the Wifi Alliance preso are healthcare, industrial, automotive, and IoT. Do you know any precise use cases?
- swatkat 10y agoSpecs are not out yet? I couldn't find any on wi-fi.org.
- digi_owl 10y agoNow how about adding a two way data/file transfer spec to WIFI Direct?
- azinman2 10y agoLovely 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 10y agoMost likely all of them.
- themihai 10y agoI'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
- ars 10y agoI wonder if this can time-sync wifi and ethernet devices together, because I feel like a lot of installations will have a mix.
- rocky1138 10y agoI'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?"
- massel 10y agoI'm super hopeful this could simply be used in my microwave, stove, car, really anything with a cheap clock in it to sync the time between them to some accurate source, and automatically apply DST.
- lucaspiller 10y agoMost countries have radio signals that transmit the time (including DST). The issue is there has traditionally been no global standard on how it works - each country/region has their own implementation: https://en.m.wikipedia.org/wiki/Radio_clock https://en.m.wikipedia.org/wiki/Radio_clock
- jamestnz 10y agoRelated: this post [1] from the other week on HN, describing a neat little project to build a low-power radio station which emulates the output of radio station WWVB (a fairly well-known station out of Colorado, which transmits the time signal to large parts of North America). You could build one of those in case you aren't within range of one of the NIST-operated stations :-) [1] https://news.ycombinator.com/item?id=13258631 https://news.ycombinator.com/item?id=13258631
- rtkwe 10y agoIf you're playing the same audio from multiple sources but slightly out of sync the effect can be pretty unpleasant depending on the delay and how sensitive you are to timing.
- STRiDEX 10y agoMy 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.
- jlgaddis 10y agoA 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 10y agoMine 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 10y agoAnd 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.
- voltagex_ 10y agoWhy run your own instance when you can just flog the crap out of the public pool for free? [1] Digging into the internals of a few "high end" consumer modem/routers, I wouldn't trust any manufacturer to provide a secure ntpd, so we'd probably just end up with NTP amplification attacks [2] on a Mirai scale. 1: https://www.lightbluetouchpaper.org/2006/04/07/when-firmware-attacks-ddos-by-d-link/ https://www.lightbluetouchpaper.org/2006/04/07/when-firmware... 2: https://blog.cloudflare.com/technical-details-behind-a-400gbps-ntp-amplification-ddos-attack/ https://blog.cloudflare.com/technical-details-behind-a-400gb...
- oneplane 10y agoI 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.
- andreiw 10y agoI tried to look something up but there is no mention of underlying tech... is this at all related to PTP?
- sargun 10y agoAny chance we're going to see this result in TDMA?
- anonymousDan 10y agoDoes this require an access point or would it work with ad-hoc wi-fi or wi-fi Direct?
- gubby 10y agoSays in the article, either.