The announcement of a new handset using something called Enhanced-GPS started to make my brain hurt. Come'on guys another type of assisted GPS? So before talking about this I decided to research a bit more about this mess.
And trying to make sense of this new technology/product offered in the Assisted-GPS arena, I ran into two great papers that help put GSM and GPS technologies in a pretty clear view. The first paper [PDF] by Craig Scott and others researchers from Sydney describes GSM (Global System for Mobile Communications) and how location services can be implemented.
On a side note at the end of the document the authors discuss non-technical issues saying that:
"The most important point is that people’s locations should not be monitored without their permission or appropriate legal authority. Given that a GSM positioning system will be gathering information on people’s movements, it will be important that sites which gather this data (e.g., the location service center) are highly secure from both physical and computer-based attacks."The second paper [PDF] by Motorola which is a bit more recent gives an overview of location technologies in 2G networks describing techniques very similar to the same one used by GPS receivers to triangulate position.
The thing is that for unsynchronized networks like GSM and W-CDMA things are a bit more complicated when you want to pinpoint the location of a cell phone. Time is the basis for distance measurements and by not having precise, synchronized timing other methods are required. CDMA networks in the other hand are synchronized.
Trying to resume what these papers talk about you could say that for GSM networks you can break the Assisted-GPS camp in two big fields: one where most of the work is done in the cell phone itself and another where most of the work is done in the network. By work we mean obtaining, measuring and processing data that in the end will help pinpoint the location of the cell phone. Check this post under "Aided GPS" for more details about this.
Enhanced-GPS as developed and distributed by Cambridge Positioning Systems makes use of software in the cell phone that works with its embedded GPS receiver plus a network component (Serving Mobile Location Center) that most providers need in order to use the other methods. This paper [PDF] describes this technique in detail.
The goal is to make these technologies cheap enough for volume usage by providing a software layer in the cell phone without requiring changes to the network. This also would help manufactures avoid higher power consumption with the use of dedicated chipsets.