CODEWITHSUNDEEP
androidiosbluetooth
ItalianPride15
ItalianPride15

Reputation: 51

Finding the direction between two bluetooth devices (localization)

I have an app that scans for a specific UUID that another phone is broadcasting and measures the signal strength between them and tells you whether you're getting closer or further away from them. I want to add an arrow for direction. I know you can use triangulation if you have 3 points but I want to get something somewhat accurate with 2 points.

Any algorithm or suggestion that would help?

My current idea (since for this app's use case one node will be relatively still) is to have some algorithm learning as you walk. Like if you get further away the arrow knows to disregard this direction and keep refining itself as you walk different directions.

I found a bunch of research papers on the topic but I'm not an electrical engineer so it's easy to get lost. Also I read this post and understand the many pitfalls How to measure distance between two iphone devices using bluetooth?

Thanks!

Upvotes: 4

Views: 3847

Answers (1)

Gilles Lesire
Gilles Lesire

Reputation: 1237

Such a solution is extremely convoluted.

Getting the direction of the signal requires far more data than normal app usage can provide. The user would have to slowly rotate the phone while taking many samples of all directions.

Getting the relative distance, as you said like "getting closer" or "going farther away" is kinda possible within a 12 meter range using the formula posted below. Above 12 meters it gets very buggy. But it's quite complex and requires you to use a moving average solution with a length that you consider adequate.

You can calculate the relation between RSSI and distance using the following formula:

RSSI = -(10*n*log10(d) + A)

In this case, n = path loss exponent, since you don't want an exact distance, just a way to check if it's closer or further, you can use 2 as a value, I found this the most realistic one in most cases. A = the measured RSSI value at 1 meter distance, you need to measure this in advance to do your calculations, but since this varies a lot, just use a value like -60dB. Also this one is about average in most situations.

So getting a crudely guessed distance in meters can be achieved by the formula:

distance = 10 ^ ((-RSSI - 60) / (10 * 2));

This isn't very exact but will be sufficient to tell you if it is closer/farther within a limited range.

Upvotes: 3

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