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nathalie
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hi guys, I need your help. My group is currently conducting a study about Indoor Wi-Fi Localization using Fingerprinting technique, wherein we need the RSS from three access points to compute the location of the user. Our group provided three routers as access points. The problem is our instructor asked us where are we going to position the three routers and the basis of the position.

Our group think that we can position the access points anywhere since we are just after the signal strength that it will provide. I need further explanation, comments and suggestions. THANK YOU :)

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This comes up every few months. What the biggest problem you're going to run into is the local environment. What are the walls made of? What is on the walls that could affect the signal? What equipment/furniture is in the area that could affect the signal? How do you account for this? You also have to factor in signal bounce. Large mirrors are a problem. Had to install another access point at one client location because of mirrors. They have large mirrors in the restrooms and it was killing the signal. Owner was bummed out he couldn't read Facebook while "taking a break" in the restroom.

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You can calibrate each AP but it's not foolproof. As for location, I would recommend towards the edge of rooms and mounted on the ceiling while maintaining proper signal propagation. At hospitals, wireless access points are used for locating wireless devices integrated in equipment. If you place an AP closer to the room anything outside the access point triangle will be difficult to locate.

Be mindful of channels and tx pwr.

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Basically you are looking for packets. It's true that you will get a lot of noise because of reflecting signals but what you can try is a statistical analysis of the packets. I mean, the packets are sent with a maximum relative signal strength. In a complex environment you will get lots of packets with different relative signal strenght because of the reflections, although nothing is moving yet. Try to collect a certain amount of packets and then look at the highest relative signal strenght and calculate a mean value of them. In theory every reflection should decrease the signal strenght a little bit because of absorption.

Finally it also depends on how precise you want to locate your target. At least that would be my approach.

Edited by whitenoise
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