How do we get RSSI values from Bluetooth beacons (estimote to be specific) in Linux?

Question

I need to get distances from multiple bluetooth beacons for triangulation so that I can do indoor positioning. I have tried to give as many relevant details as possible. This project is for an RPi, but I am currently trying to test it through my laptop first. I have tried most of what I can find on the internet about this:

The best way I could find to get the rssi values was hcitool rssi <address of beacon>

From here Bluetooth LE Signal Strength Linux

To test this, I tried to get it for my mobile first. It showed "Not Connected". I thought I need to connect first, so I tried many ways to connect my mobile:

a) hcittol cc <address of mobile>

b) gatttool -b <address of mobile> -t random --interactive

c) rfcomm connect 0 <address of mobile> 10

In each case, when I clicked pair in my mobile, connection terminated.

Then, I paired my mobile the usual way from bluetooth menu, and then tried hcitool rssi <Address of mobile> which then finally returned a value -8.

Now that I had it for my mobile, I now moved to beacons.

Then, I tried the same for my beacons. This time I had to first do hcitool lescan to get addresses of available beacons then connect to one of the beacons using the command hcitool lecc <address of beacon> which returned the error Could not create connection: Connection timed out So next, I again tried connecting with the other two ways:

rfcomm connect 0 <address of beacon> 10 which returned the error Can't connect RFCOMM socket: Host is down when I can be sure hci0 was up.

Then I tried with sudo gatttool -b F1:15:A7:E3:17:63 --interactive after which interactive mode opened up and I gave the command connect. This gave different errors after Attempting to connect to <address of beacon>, mainly connect error : Connection timed out and Error: connect error: Connection refused (111)

Then I read I need to use -t random from Bluetooth LE on Raspbian , https://ubuntuforums.org/showthread.php?t=2204808 and one another source which I can't find right now.

So I entered sudo gatttool -b F1:15:A7:E3:17:63 -t random --interactive in which when I gave the connect command, I got error Error: connect error: Device or resource busy (16) and also sometimes Error: connect error: Input/Output Error

then I read that I perhaps need to restart my hci0 by hciconfig hci0 down and then hciconfig hci0 up which did the trick, the beacon now got connected.

But then, it quickly got disconnected after saying `GLib-WARNING **: Invalid file descriptor.

` I read here https://raspberrypi.stackexchange.com/questions/53982/how-to-fix-gatttools-glib-warning-invalid-file-descriptor that this is because of poor connections. I tried keeping the beacons closer, but it did the same.

So I tried to anyway at least get one rssi value during the short duration it is connected. But, even when it was thus connected, I did hcitool rssi <address of beacon> the error came like this:

hcitool rssi F1:15:A7:E3:17:63
Get connection info failed: No such file or directory

To which I haven't yet found a proper solution.

I tried another way of reading the rssi value, which gave the following :

hcidump -R
HCI sniffer - Bluetooth packet analyzer ver 5.37
device: hci0 snap_len: 1500 filter: 0xffffffffffffffff
> 04 0E 04 01 0B 20 00 
> 04 0E 04 01 0C 20 00 
> 04 0E 04 01 0C 20 00 
> 04 0F 04 00 01 0D 20 
> 04 0F 04 00 01 16 20 
> 04 0F 04 00 01 13 20 

This was before it got disconnected. I read here Obtain RSSI with hcidump which said to read the 14th byte. since all these seemed to be hex numbers, this would mean that each number is 1 byte. But this way, I only have 7 numbers per line, how can I read the 14th byte?

Getting distance from beacons has been troubling me a lot, and has used up a a lot of my time. Please help me out on this issue. If you can help me find a resource to help me do so, I'd appreciate the help.

Answer 1

You don't need to connect to a device to get the signal strength RSSI values, just use the following code and pipe that to a script that extracts values from the devices you are after:

btmon &
hcitool lescan --duplicates