4 ms·
If devices have other radios such as WiFi and GSM these can function as a backup plan (I don't think BT would suffice, unless there would be P2P between Bluetoo
by Fnoord 7y ago
If devices have other radios such as WiFi and GSM these can function as a backup plan (I don't think BT would suffice, unless there would be P2P between Bluetooth devices with devices who can provide coordinates such as WiFi and GSM).
For example, the first iPhone used Apple WiFi positioning; it didn't have GPS. I still remember I had a an iPod Touch with a 3rd party GPS which worked with the predecessor of Cydia.
Check the sources UnifiedNlp [1] can use. Quoting:
> AppleWifiNlpBackend - Uses Apple's service to resolve Wi-Fi locations. It has excellent coverage but the database is proprietary.
> OpenWlanMapNlpBackend - Uses OpenWlanMap.org to resolve user location but the NLP backend did not reach release-quality, yet. Users interested in a freely licensed and downloadable database for offline use should stick with openBmap for now - Last updated in 2015
> OpenBmapNlpBackend - Uses openBmap to resolve user location. Community-created, freely licensed database that can optionally be downloaded for offline operation. The coverage varies from country to country (it's best in central Europe).
> MozillaNlpBackend - Uses the Mozilla Location Service to resolve user location. The coverage is OK. Only the cell tower database is free.
> LocalWifiNlpBackend - Local location provider for Wi-Fi APs using on-phone generated database.
> LocalGSMLocationProvider - Local opencellid based location provider backend. Has been surpassed by LocalGSMBackend which also has an OpenCellID option - Last update in 2014
> LocalGSMBackend - Local location provider for GSM cells. It works offline by downloading freely licensed database files from Mozilla, OpenCellID, or lacells.db.
[1] https://github.com/microg/android_packages_apps_UnifiedNlp https://github.com/microg/android_packages_apps_UnifiedNlp
- ImprovedSilence 7y agoI think a lot of cellular technologies rely on GPS on their base stations as a timing reference. Most cellular capabilities might fall off a cliff if GPS isn’t available.
- myself248 7y agoRight. They have a few hours of holdover before things start to lose sync, and when sync degrades, the towers may stay on the air but handoffs get real rough. They may also take themselves off the air after too long in holdover, but that's a software setting. Conceivably this could be overridden by network operators (in close cooperation with their equipment vendor) in a prolonged GPS outage where it was determined that having the towers on-air as islands without handoff would be better than nothing.
- Fnoord 7y agoWhy though? If the celltower has networking (e.g. 4G), it could use NTP. The databases with GSM just use triangulation. As long as they broadcast, the triangulation should work.
- brohee 7y agoBest case NTP is in the order of millisecond precision. Completely inadequate for this case.
- ckdarby 7y agoAny idea why wifi isn't leveraged more often? Wasn't there a huge deal about Google maps cars collecting wifi ssids? I never understood why this was a privacy issue.
- floatboth 7y ago> I never understood why this was a privacy issue e.g. if you have a rather unique SSID, and someone knows it (say you posted a screenshot of your phone's settings), these databases of access points would pretty much point them to your home address
- Piskvorrr 7y ago1. unreliable + imprecise 2. requires periodic map updates 3. when you actually need it, Murphy guarantees visibility to zero APs
- Fnoord 7y agoOSM and Mozilla both allow to contribute easily to such databases.
- Piskvorrr 7y agoThat's orthogonal to the issue. GNSS gives you a fix anywhere; wireless triangulation gives you a guess in some populated areas (note all the three qualifiers). Moreover, GNSS gives you a 4D fix: [X,Y,Z,t]; triangulation gives you 2D at best: [~X, ~Y]. Worse, easy contribution to a database is still way off from ease-of-use: now the database needs to get to the end devices, which brings in a whole tangled ball of dependencies. Also, last I checked, OSM doesn't deal in wireless maps.