I am working on an indoor positioning system where I need to:
- Compute distance based on RSSI (I understand this won't be 100% accurate)
- Then do trilateration to pinpoint the location of the wifi signal. This part might be solved via this solution: Trilateration using 3 latitude and longitude points, and 3 distances
I am stuck with (1).
The relationship b/w RSSI and Distance is (source PPT): Where:
Fm = Fade Margin - ?? N = Path-Loss Exponent, ranges from 2.7 to 4.3 Po = Signal power (dBm) at zero distance - Get this value by testing Pr = Signal power (dBm) at distance - Get this value by testing F = signal frequency in MHz - 2412~2483.5 MHz for Ralink 5370
But I am not able to figure out how to calculate the fade margin.
Based on some findings,
fade margin = sensitivity of receiver - received signal
But then again, how do I get sensitivity of the receiver?
I have an Ralink RT5370 chipset wifi dongle with this specification: Ralink 5370 spec
Any suggestions will help!
Notes from: http://www.tp-link.sg/support/calculator/ suggest that fade margin varies from 14dB to 22dB
Excellent: Link should work with high reliability, ideal for applications demanding high link quality. Fade Margin level is more than 22dB. Good: Link should give you a good surfing experience. Fade Margin level is 14~22dB. Normal: Link would not be stable all the time, but should work properly. Fade Margin level is 14dB or lower