WiFi Location Technology

WiFi location is a new application service after the iphone has been upgraded to 1.1.3, and after getting the machine, start experimenting with WiFi positioning. In Dallas, USA, the location button was pressed and rotated for about 2 seconds, and the street immediately flashed to the center of the screen. No wonder Jobs also said: "It's really cool", this function is really amazing.

Previously used GSM positioning, the error can be large to several kilometers, and WiFi location of the center point is 50 meters from where I am. Then I went to the internet to look up the article on this technology, learned about the following situation.

The technology was established in 2003 by a company called Skyhook Wireless (http://www.skyhookwireless.com/). On the Skyhook home page, you can download a software called Loki, which is used on PCs and also supports WiFi positioning, but it seems to be available only in XP. iphone users who have not yet risen to 1.1.3 can try Loki first.

The principle of this technique is to take advantage of the following three facts: WiFi hotspots (ie, AP, or wireless router) are more and more, in the city more space to receive at least one AP signal. (in the United States, there are quite a few cases where 3 or 5 AP signals are received per point.) China will also be more and more hot spots as long as power, no matter how it is encrypted, will certainly send signals around. The unique global ID that contains this hotspot in the signal. The connection cannot be established even if it is far away from this hotspot, but it can still be heard. Hot spots are generally rarely variable position, relatively fixed.

In this way, the locator end simply listens to what hotspots are nearby, detects the signal strength of each hotspot, and sends the information to the Skyhook server on the network. The server based on this information, query each hotspot in the database records the coordinates, and then operation, you can know the specific location of the client, the final coordinates to tell the client. It is easy to understand that the more AP signal received, the more accurate the positioning.

However, a successful positioning requires two prerequisites: The client can be heard on the Internet to detect the coordinates of the hotspot in the Skyhook database has

The first is not to say, whether it is WiFi or edge, as long as you can connect to the Skyhook server on the line.

The second one is the Skyhook gold mine. There are two arguments for how Skyhook knows each AP's coordinate information:

1. There is a saying is to rely on netizens to collect their own, and then sent to Skyhook,skyhook will pay money.
2. However, the official website of the saying is driving around the streets, while walking to collect AP signal, and GPS positioning, so that the coordinate information. And they will periodically restart their data to accommodate the changes in the hot spots.

In contrast, the 2nd is more reliable, and the cost is not high. For example, the acquisition of Beijing, equipment on a GPS and WiFi pda enough, and then loaded into a taxi, to the driver 200, 300 per month, so that he is normal soliciting people. As long as there are 3 or 5 drivers working together, the data is collected and constantly updated. The driver will also be very happy, this is purely a cost-free additional revenue ah, but also enjoy the GPS.

Here is an electronic map of the area that this service has covered: http://www.skyhookwireless.com/howitworks/coverage.php. We can see that this service is available in Beijing, Hong Kong and Taipei. So at this stage only Beijing can use the mainland, do not know if there are other Internet applications in China to achieve WiFi positioning.

WiFi positioning accuracy is lower than the GPS, limited by the scope of services, and no direction, speed and other data, can not navigate, but also can not be used offline. But it has more advantages than GPS, that is, in the population, the more densely populated areas, the use of the effect will be better. GPS startup time is long, in the room is ineffective, bad weather performance is also poor, the buildings are too dense place is not very easy to use. These factors have been overcome by WiFi positioning.

I think it's not really a positioning, it's a toy, the real location is to use WiFi signal positioning, I'm studying this