Each method presented has its strengths and weaknesses. None of these is the perfect positioning system, yet they all can collaborate in order to give the estimated position of a user.
GPS, the veteran of the group, has a plethora of satellites at its disposal, offering almost anywhere in the world a precision in meters. The devices which implement this technology are small enough to be inserted even in phones, smart enough to do their job or even more by tracking many satellites in the same time and eating less power, affording the usage of this service for hours in a row. But it needs clear sight to the sky in order to see at least 3 satellites and needs quite a long time in this busy era to get a clear position and be able to pinpoint the location on a map.
Its child, the aGPS helps by relying not only on satellites but also on GSM towers, locating and triangulating them too. Knowing their location, the power of the emitted signal, the user can be easily triangulated. Especially useful in crowded cities, where many GSM antennas are installed removes the need for a clear sky. Thus, it allows even in places surrounded by tall buildings to have a good enough precision while locating the position on the map.
The GSM positioning system continues the movement of the positioning technologies from the sky to ground bases by replacing completely the satellites from the picture. In developed countries there are a lot of GSM towers in urban areas. This is added to the fact that this technology doesn’t eat more power in phones. Since the phone knows by default how to measure and get the tower’s id, there is just a software issue to get the ids, match them to a table with geographical positions and triangulate based on the strength of signal the user’s position. But if you’re in a remote area, like in mountains, where there are few emitters the quality of location falls dramatically.
Wifi, on the other hand, is a newborn technology created out of the people need to communicate. Internet access is getting cheaper and cheaper, being for some business a nice feature to offer. Especially the large fast foods chains offer free wireless Internet access, but also people with enough bandwidth offer this for free. And given the fact that in the big cities these hotspots are countless, some smart guys invented a positioning system based on tracking these hotspots location, offering sometimes a comparable precision in comparison with the classic – the GPS system.
Bottom line, no method is perfect – GPS needs clear sky, aGPS improves this but still needs some satellites to be seen, GSM works like a charm if you have lots of antennas but falls dramatically if you’re in a remote place and WiFi positioning is good in cities, but absolutely lacks in remote zones. Only the composition of all can cover all the situations encountered in a normal life – crowded city when going to work and big, empty spaces when going to mountains to relax.
Note: This is an excerpt from my work during Agile Lab and Seminar in Fall 2009(besides the images whom are taken from internet)