4 ms·

Android provides carrier phase access for a while now, and with that relative positioning between such devices in about the same neighborhood can be done with e

by namibj 2y ago

Android provides carrier phase access for a while now, and with that relative positioning between such devices in about the same neighborhood can be done with enough precision that you have to care about where in the device the GNSS antenna lurks. That alone isn't too fancy; it gets good once you throw in the accelerometer and gyroscope in each device. Because with that you get this not only in realtime, but also with only minor degradation due to the changes in the GNSS pseudo-range measurements being predictable despite not holding still. Other interesting things enabled by it are e.g. auto-land of a model plane in a truck bed without needing wheels on the plane (and still preventing it from getting scratched up/depending on a grass landing strip). Even fairly good GNSS receivers aren't expensive to build, as long as power consumption isn't very critical, so why can't I just buy a pair for a hundred bucks?

patze 2y ago
Sounds interesting! Does this approach work in indoor scenarios? Would you mind to provide some further links/papers to this topic?
- bongodongobob 2y ago
  [flagged]
- michaelt 2y ago
  Combining GPS with accelerometer and gyroscope is sometimes called "sensor fusion" - one common way of doing it is with a "Kalman filter" and if you google that you'll find a wealth of information. If you've got plenty of money, companies like https://www.oxts.com/ https://www.oxts.com/ have working systems available off the shelf. They're used for things like measuring the dynamic performance of cars. Such systems will sorta work indoors but not very well. The gyroscope/accelerometer will gradually drift; when you're outdoors with a clear view of the sky, the GPS can compensate for that but when you're indoors that isn't possible. How fast the drift happens depends on how much money you spend to get the highest performance gyroscopes and accelerometers. It's also possible to integrate other sensors, but that's application-dependent; for a car going through a tunnel, an odometer is a great addition, for a smartphone not so much.
- johnwalkr 2y ago
  GPS-denied navigation is the search term. It works well enough for driving through a tunnel, because eventually you get a known location to correct previous estimates. For a fully-indoor environment it's very difficult to get good results and the technique depends on the use-case. "Indoor GPS" using bluetooth beacons is technically possible but the space is filled with proprietary protocols/apps that try to make money by serving ads. It unfortunately doesn't seem to be evolving into a more useful extension of google maps.
- ragebol 2y ago
  For indoor, there's UWB, ultra wide band. Can also use Bluetooth or even lights blinking at different (high, non-humanly-visible) frequencies to do indoor positioning.
- namibj 2y ago
  For indoor you will prefer UWB[0] where you can set up base stations yourself that offer a service pretty much like GNSS signals (i.e., you can passively receive them from 4+ base stations and turn those pseudoranges into a position, provided you are told where they are and kept updated about their clock drift relative to each other (e.g. by them listening to their neighbors and piggybacking 2-way-ranging sessions on top of the beacons they already broadcast, each offering the clock offset to their neighbors in the data payload of their own beacon)), with the added benefit that by using a shared-key CSPRNG to generate the bitstream of the ranging code instead of a fixed known sequence, you can get authenticated ranging where MITM attacks are limited to artificially inflating the range (i.e., a trigger of "has to be close enough to the door handle that e.g. a pair of cameras looking at the areas right in front of either side of the door have it in view" can't be faked with a wireless MITM). There are some links/papers in the publications section[2] of [1]. [0]: https://www.firaconsortium.org/ https://www.firaconsortium.org/ [1]: https://developer.android.com/develop/sensors-and-location/sensors/gnss https://developer.android.com/develop/sensors-and-location/s... [2]: https://developer.android.com/develop/sensors-and-location/sensors/publications https://developer.android.com/develop/sensors-and-location/s...
slow_typist 2y ago
Can‘t you? https://www.mouser.de/ProductDetail/u-blox/ZED-F9P-02B?qs=DPoM0jnrROVJit2O2Grdqw%3D%3D https://www.mouser.de/ProductDetail/u-blox/ZED-F9P-02B?qs=DP...
- namibj 2y ago
  They are 114.62 USD each if you buy at least 100 of them. And you still need to add an active antenna and a good crystal. Considering those, this module is about 3x the price I asked.
  - slow_typist 2y ago
    The crystal is already included. Of course you need an antenna and several other parts and most importantly communication between base and rover for correction data. Integration is the elephant in the room here. Ready to use boards go for like US$ ~ 300 (without board to board communication). Admittedly I misread your post - you asked for $ 100 a pair. But a few hundreds is possible - at least in costs.
    - namibj 2y ago
      I misread the block diagram. It indeed only needs power communications and an antenna.
toast0 2y ago
https://www.bestbuy.com/site/tracfone-blu-view-5-64gb-prepaid-black/6577431.p?skuId=6577431 https://www.bestbuy.com/site/tracfone-blu-view-5-64gb-prepai... Here's a GNSS receiver for $30. It comes with some other junk you don't really need though.

by namibj 2y ago

patze 2y ago

Sounds interesting! Does this approach work in indoor scenarios? Would you mind to provide some further links/papers to this topic?

bongodongobob 2y ago
[flagged]
michaelt 2y ago
Combining GPS with accelerometer and gyroscope is sometimes called "sensor fusion" - one common way of doing it is with a "Kalman filter" and if you google that you'll find a wealth of information. If you've got plenty of money, companies like https://www.oxts.com/ https://www.oxts.com/ have working systems available off the shelf. They're used for things like measuring the dynamic performance of cars. Such systems will sorta work indoors but not very well. The gyroscope/accelerometer will gradually drift; when you're outdoors with a clear view of the sky, the GPS can compensate for that but when you're indoors that isn't possible. How fast the drift happens depends on how much money you spend to get the highest performance gyroscopes and accelerometers. It's also possible to integrate other sensors, but that's application-dependent; for a car going through a tunnel, an odometer is a great addition, for a smartphone not so much.
johnwalkr 2y ago
GPS-denied navigation is the search term. It works well enough for driving through a tunnel, because eventually you get a known location to correct previous estimates. For a fully-indoor environment it's very difficult to get good results and the technique depends on the use-case. "Indoor GPS" using bluetooth beacons is technically possible but the space is filled with proprietary protocols/apps that try to make money by serving ads. It unfortunately doesn't seem to be evolving into a more useful extension of google maps.
ragebol 2y ago
For indoor, there's UWB, ultra wide band. Can also use Bluetooth or even lights blinking at different (high, non-humanly-visible) frequencies to do indoor positioning.
namibj 2y ago
For indoor you will prefer UWB[0] where you can set up base stations yourself that offer a service pretty much like GNSS signals (i.e., you can passively receive them from 4+ base stations and turn those pseudoranges into a position, provided you are told where they are and kept updated about their clock drift relative to each other (e.g. by them listening to their neighbors and piggybacking 2-way-ranging sessions on top of the beacons they already broadcast, each offering the clock offset to their neighbors in the data payload of their own beacon)), with the added benefit that by using a shared-key CSPRNG to generate the bitstream of the ranging code instead of a fixed known sequence, you can get authenticated ranging where MITM attacks are limited to artificially inflating the range (i.e., a trigger of "has to be close enough to the door handle that e.g. a pair of cameras looking at the areas right in front of either side of the door have it in view" can't be faked with a wireless MITM). There are some links/papers in the publications section[2] of [1]. [0]: https://www.firaconsortium.org/ https://www.firaconsortium.org/ [1]: https://developer.android.com/develop/sensors-and-location/sensors/gnss https://developer.android.com/develop/sensors-and-location/s... [2]: https://developer.android.com/develop/sensors-and-location/sensors/publications https://developer.android.com/develop/sensors-and-location/s...

slow_typist 2y ago

Can‘t you? https://www.mouser.de/ProductDetail/u-blox/ZED-F9P-02B?qs=DPoM0jnrROVJit2O2Grdqw%3D%3D https://www.mouser.de/ProductDetail/u-blox/ZED-F9P-02B?qs=DP...

namibj 2y ago
They are 114.62 USD each if you buy at least 100 of them. And you still need to add an active antenna and a good crystal. Considering those, this module is about 3x the price I asked.
- slow_typist 2y ago
  The crystal is already included. Of course you need an antenna and several other parts and most importantly communication between base and rover for correction data. Integration is the elephant in the room here. Ready to use boards go for like US$ ~ 300 (without board to board communication). Admittedly I misread your post - you asked for $ 100 a pair. But a few hundreds is possible - at least in costs.
  - namibj 2y ago
    I misread the block diagram. It indeed only needs power communications and an antenna.

toast0 2y ago

https://www.bestbuy.com/site/tracfone-blu-view-5-64gb-prepaid-black/6577431.p?skuId=6577431 https://www.bestbuy.com/site/tracfone-blu-view-5-64gb-prepai... Here's a GNSS receiver for $30. It comes with some other junk you don't really need though.