Using Bluetooth for finding location.

[Pommie]

In the UK there is a very well known hospital called Christies. They have recently introduced an app to help people navigate through the hospital. It uses 70 stategically place bluetooth beacons for navigation. Details **broken link removed**. How can you find position simply from bluetooth? Can the app simultaneously connect to multiple beacons and use signal strength to deduce position?

Mike.

 

[Reloadron]

The Global Positioning System (GPS) is a network of about 30 satellites orbiting the Earth at an altitude of 20,000 km. ... Once it has information on how far away at least three satellites are, your GPS receiver can pinpoint your location using a process called trilateration.

So what if I replace 30 satellites with over 70 bluetooth beacons have been located around the hospital. Each bluetooth station knows exactly where it is so using the bluetooth capability of a cell phone the app likely uses the same trilateration math functions which GPS uses off satellites. You only need any three bluetooth beacons to nail your location. That would be my guess.

Ron

 

[dknguyen]

Can the app simultaneously connect to multiple beacons and use signal strength to deduce position?

There is part of the Bluetooth spec that allows for multiple simultaneous connections, but not all devices support this. I don't think any phone supports this and I've never seen a laptop that does. It's more for wireless speaker systems where you have multiple bluetooth speakers slaved to a central control unit. Also, while phones can't connect to multiple Bluetooth devices simultaneously, they seem to be able to detect the SSID broadcast of multiple devices simultaneously and that's probably all you need if you're using signal strength.

That's all moot though since you don't need truly simultaneous connections if you're using signal strength for localization. You just need to alternate between signal-strength measurements much faster than you can actually move. You only need true simultaneous for time-of-arrival stuff.

The Global Positioning System (GPS) is a network of about 30 satellites orbiting the Earth at an altitude of 20,000 km. ... Once it has information on how far away at least three satellites are, your GPS receiver can pinpoint your location using a process called trilateration.

So what if I replace 30 satellites with over 70 bluetooth beacons have been located around the hospital. Each bluetooth station knows exactly where it is so using the bluetooth capability of a cell phone the app likely uses the same trilateration math functions which GPS uses off satellites. You only need any three bluetooth beacons to nail your location. That would be my guess.

Ron

I don't think that's what they did because it requires two exceedingly unlikely things to be in place:
1. Phones not only need to be able to measure time-of-arrival but and they would need to be able to do it while being obfuscated by the Bluetooth protocol. They definitely can't do the former, let alone the latter.
2. The beacons would also need to be accurately time-synced to each other.

How big is this facility and how accurate is this system? Class II and III Bluetooth devices only have a a range of 10meters/33 feet or less. With such a short range, all you would have to do is scatter so many beacons and just determine which one you are receiving the strongest signal from so you know which one you are nearest to. 70 of these Class II beacons can cover a rectangular space of 142,414 square feet with no deadzones while the average hospital is apparently only 74,600 square feet. No need for time-of-arrival, time syncing, or simultaneous connections, or even alternating connections to anything.

 

[dr pepper]

If you had 70 points of reference, even in a large hospital you'd have a good fix on where you are, another thing you could do is record what transponders you have been past and how quick, then you'd have direction & speed, if you pre programmed a certain zone and you went past a transponder you werent sposed to you'd instantly know you went the wrong way.

 

[Pommie]

A friend of mine told me about the system and one thing that intrigued me is she said it only works in the corridors. I'm wondering if the beacons contain directional aerials and so seeing the beacon combined with the compass will give you the direction you need to walk.

Mike.

 

[jpanhalt]

Public announcement: **broken link removed**
More detail: **broken link removed**

"Blue dot" technology: https://www.androidauthority.com/google-map-direction-detection-717523/ Somehow related to Google maps.

Still doesn't answer the original question, though.
John

 

[dknguyen]

Public announcement: **broken link removed**
More detail: **broken link removed**

"Blue dot" technology: https://www.androidauthority.com/google-map-direction-detection-717523/ Somehow related to Google maps.

Still doesn't answer the original question, though.
John

The bluedot website says it has an accuracy of 5m so it doesn't look like they are only figuring out what beacon you are nearest to, like I suggested.

 

[ClydeCrashKop]

The bluedot website says it has an accuracy of 5m

I just ordered this GPS. They brag about horizontal position accuracy of 2.5m.
I couldn't find that #6 footnote. We will see.

OPEN-SMART GPS Serial GPS Module for Arduino, APM2.5 Flight Control
<$8.00
https://www.dx.com/p/open-smart-gps...jMyPvDUcYC6a160EWaYaAlQBEALw_wcB#.WhC1YFWnH4Y

 

[KeepItSimpleStupid]

Google used something (Street View) to view the inside of their data center: https://www.google.com/about/datacenters/inside/streetview/