Saturday, July 14, 2012

Some adviсes on WiFi scanning for getting better maps

Indoor positioning based on WiFi signals have not yet grown up to a state of the art technology. It's neither wide-spread nor well-known among most of mobile users. Existing industrial solutions require a special equipment installation on premises, they are very expensive, and therefore they are rare. On the other hand, it's obvious that people need help in finding their way in (every) big building, which can not afford a deployed navigation system for visitors. Just today I saw a notice on a stand in a local shopping center which reads "Please, no inquires about the shopping center". So, that's where WiFiLine should come in handy. And here we come to a problem.

Building of a public and cheap positioning system is a kind of challenge nowadays.

It's so, because prelimiary WiFi scanning should be done by people themselves - without special devices and knowledge. So, what can be done to achieve an acceptable quality of the WiFi map? Here is some basic rules.

First, you should check if a building is well populated with WiFi signals. Normally there must be at least 3 different WiFi hotspots detectable at every point. Of course, it's not reasonale to check hotspots availability after each scanning step. It's enough to make 2-3 test scans in different parts of the building. Then inspect the list of detected WiFi hotspots. If number of listed hotspots in every point is larger than 5, and overall number of hotspots is more than 10, then the building will likely conform to our requirements. Now you can start regular scanning.

Move from point to point. Start scan in a point, wait until the process ends (the message "Scanning" is grayed out), and then proceed to another point. Cover most important (public) parts of the building with approximately 5 meter distance.

WiFiLine allows you to setup number of subscans in each point between 1 and 20. The number 10 is the default value. The larger the number is chosen, the better accuracy is expected, yet the more time must be spent for scanning. I don't recommend to set it to less than 5. It can be used mostly in other mode - for location searching, and if only your device is somewhat laidback in WiFi processing, which can lead to an effect that it marks your actual position with a lag. Most modern devices are equipped with a quick WiFi module capable of prompt scanning at the rate 10.

As WiFi signals are not as stable as GPS signals from satellites, it's advisable to repeat scanning of the same building parts several times.

After all abovementioned measures are taken, we can expect 5 meter accuracy of positioning. Of course, this is not only a question of scanning, but of the algorithmic parts of WiFiLine as well. But this is a theme for another story.

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