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In an application I am building I am using "Fused Location Provider". When the phone is in a WiFi network I am getting an accurate location value (within 14 meters). When the phone is in EDGE Network I am not getting the same accuracy (a value like 1895 meters).

What's the problem with EDGE and WiFi networks? Why I am getting the different values in different networks (Wifi, EDGE, GPS)?

ale
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suneel
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2 Answers2

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Google has a big database of (hashes of) Wi-Fi network SSIDs. When Wi-Fi is enabled on your phone, it scans for Wi-Fi networks, and sends the list to Google (in a hashed form). In cities, networks are plentiful, and Wi-Fi networks are short-range, so the combination of networks it can 'see' gives a very accurate idea of where you are.

A similar thing happens with cellular network cell IDs, but these are spaced more widely apart. The phone itself can't perform triangulation, because it only has the received signal strength for each cell it can 'see': it doesn't know the signal's angle of arrival, the transmit strength of the cell, or what might be occluding the signal. However, it can still use the combination of which cells it can 'see' to estimate position, a little more accurately than the distance between cells.

Even if you're connected to an EDGE network, if Wi-Fi is enabled then the Wi-Fi scanning technique will still be used, so the location estimate will be more accurate.

Both these techniques are far less accurate than GPS, which computes a position based on time differences between signals coming from different satellites. When your device can 'see' enough satellites, the precision is limited mostly by deliberate interference added by the US government (which operates the system) to make it less useful to non-US armed forces.

Dan Hulme
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  • The "deliberate interference" ended on 2000-05-02. The current 3m (or 3cm with averaging on a good chip) is due to financial and technical limitations. http://en.wikipedia.org/wiki/Global_Positioning_System#Timeline_and_modernization – user1133275 Apr 17 '15 at 21:04
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EDGE and WIFI use cell phone tower triangulation and these have a low accuracy level While using GPS, your each device is sending the message to satellite so accuracy is high

In simple terms

For GPS consider you device is sending the signal so accuracy is high

But for WIFI and Edge is based on an average that is calculated from the towers around you so its less accurate

Girish Nair
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    In GPS, your device doesn't send signals to satellites. It's the other way around. How do you think the satellites would handle the millions of GPS receivers in the world if it worked that way? – Dan Hulme Oct 29 '13 at 10:42
  • When determining the location with the GSM network, I doubt that triangulation is involved. – Flow Oct 29 '13 at 17:26