433MHz RSSI

I am working on an indoor positioning system, and I'd like to do this using cheap 433MHz beacons, each of which are serial devices. If you're wondering why I'm only using 433MHz, here's the plan:

  1. There will be at least 3 beacons, each will be programmed with a specific "identity" (such as A, B, C, and so on).
  2. All of these beacons will sit idly, not transmitting anything (yet).
  3. The robot has it's own 433MHz transmitter, receiver, and some sort of RSSI module for sensing dB. It also has it's own identification, which could be a number (for now, let's say that number is 0).
  4. The robot will send the string "A0" over its transmitter. When beacon A sees this, it will send back the string A0.
  5. The robot will read beacon A's signal, and using RSSI, detect the signal strength.
  6. Repeat these steps for each other beacon.
  7. Collect the signal strength data, and triangulate on a map.

This idea is inspired by indoor positioning done by wifi, but I don't want wifi because it's much more expensive, more power consuming, harder to manipulate, more vulnerable to disruption, and harder to interface with an arduino. These 433MHz transmitters/receivers are dirt cheap, small, power efficient, and have a somewhat short range (which is fine).

I'm not really fluent with electronics though. So, I was wondering if someone knows how to set up a way to read the signal strength of a 433MHz radio, or if this is even a good idea. I found the AD8307, but I'm not sure if this does what I want and I'm not exactly sure what to do with it.

Signal strength doesnt tell you anything about distance, as there are too many variables that affect it.

I'm aware signal strength from 1 beacon alone tells me nothing, but with at least 3 it has been proven (at least with wifi) that it does in fact work. If the beacons are mounted toward the ceiling and I'm only focusing on 1 room, the only variables to focus on are humidity, temperature, and battery life. If this is located in a building with decent climate control, then I don't think the first 2 are really a problem. If, within the same room, all 3+ beacons are affected by the variables the same way at roughly the same time, I don't think I'll need any absolute values either.

If you're thinking interference is a problem, that's one of the reasons why I'm using a ping system with everything on the same wavelength. That way, assuming there are no other devices using 433MHz, I should get a relatively clean signal.

So that being said, aside from walls, other objects, temperature, humidity, interference, and battery life, what other variables matter?

If, within the same room, all 3+ beacons are affected by the variables the same way at roughly the same time

Not true. Constructive and destructive interference affects the signal from each beacon independently and completely differently from any other.

So that being said, aside from walls, other objects, temperature, humidity, interference, and battery life, what other variables matter?

The relative orientation of the receiving and transmitting antennas has an enormous effect on the RSSI. It is one of the primary factors that makes RSSI nearly useless for distance estimation.

You might find this blog interesting, where the effects of constructive and destructive interference on wifi signal strength are visualized within an apartment: http://jasmcole.com/2014/08/25/helmhurts/

Let us know if you succeed with this project!