Best method to determin distance with WI-FI signal strength

Question

I start working in an android application that determin the position with the WI-FI Signal Strength.well i read a lot of theses and every time a found a new idea and new concepts ,and that made me confused about the method i'm going to choose. Finely i found in my point of view that the geometric technique like triangulation and trilateration are not bad.(i knew that to use those methods we need to be root at an android phone).

I read a lot of question and answer about this topic , and i would like to know the opinion of people who worked in this domain, and what they think about my final conclusion. PS: i remaked that those questions where on 2011,2012..now we are on 2014 ,I hope that there will be a solution :) Thank you

Answer 1

FSPL depends on two parameters: First is the frequency of radio signals；Second is the wireless transmission distance. The following formula can reflect the relationship between them.

FSPL (dB) = 20log10(d) + 20log10(f) + K

d = distance
f = frequency
K= constant that depends on the units used for d and f
If d is measured in kilometers, f in MHz, the formula is:

FSPL (dB) = 20log10(d)+ 20log10(f) + 32.44

From the Fade Margin equation, Free Space Path Loss can be computed with the following equation.

Free Space Path Loss=Tx Power-Tx Cable Loss+Tx Antenna Gain+Rx Antenna Gain - Rx Cable Loss - Rx Sensitivity - Fade Margin

With the above two Free Space Path Loss equations, we can find out the Distance in km.

Distance (km) = 10^((Free Space Path Loss – 20log10(f) + 32.44)/20)

The Fresnel Zone is the area around the visual line-of-sight that radio waves spread out into after they leave the antenna. You want a clear line of sight to maintain strength, especially for 2.4GHz wireless systems. This is because 2.4GHz waves are absorbed by water, like the water found in trees. The rule of thumb is that 60% of Fresnel Zone must be clear of obstacles. Typically, 20% Fresnel Zone blockage introduces little signal loss to the link. Beyond 40% blockage the signal loss will become significant.

FSPLr=17.32*√(d/4f)

d = distance [km]
f = frequency [GHz]
r = radius [m]

Check this link

http://www.tp-link.com/en/support/calculator/