Question

I want to find the distance using wi-fi and plot the marker on map in iPhone.

So any idea or code i can get for that?

Answer 1

Upon first reading your question, i was under the assumption you were referring to distance to an access point. After writing a bunch about that, i realized you might mean something else. In case that is what you mean, keep reading…

Given your configuration:

• a single fixed receiver (your phone doesn’t have to be fixed, but it is effectively fixed if you’re looking for instantaneous measurements)
• a single fixed base station (the access point)
• an omnidirectional antenna on the receiver
• 802.11 b/g protocol

This cannot be done. Even if you were working at the PHY level, this is an impossible problem to solve. To make it slightly more feasible, you need to triangulate the position of your receiver relative to two (but preferably more) base stations. Even then this is still a hard problem. RF waves travel at the speed of light, so using relay techniques to measure round-trip signal propagation delay won’t give good accuracy (the receivers have to operate extremely fast, and then there’s multipath problems…). Again, this is all assuming you’re basically building your own RF hardware, which obviously you’re not about to do for the iPhone.

Your best bet to track down the location of a base station is to record the WiFi signal strength as you change the position of the phone. By ‘change the position’, you would essentially have to sweep around the area. With some good heuristics, and robustness to handle non-distance related signal degradation, you could achieve decent accuracy (probably on the order of 10 meters).