[Asterisk-Users] GPS-enabled cell phone/PDA

[Bill Michaelson]

Date: Fri, 24 Feb 2006 14:56:54 +0000

From: Steve Kennedy <steve-asterisk at gbnet.net>
Subject: Re: [Asterisk-Users] GPS-enabled cell phone/PDA

On Fri, Feb 24, 2006 at 07:17:52AM -0600, Rich Adamson wrote:


>> Its my understanding the cell phone coordinates are sent to the cell phone
>> provider and their equipment reads (and holds) that data. Its not part
>> of any data available to you in any form unless you talk to the cell
>> provider and convience them you have a valid need. Highly unlikely in
>> the US anyway. Even if you could convience them to provide it, they
>> would likely demaand some sort of out-of-band data transmission facility.
>  
>

GSM networks have the Cell ID available to the phone, however that's not
much use without the location of the cellsite.

There are now location based services, whereby you can query the network
and they'll give out an approximate location (most cells are sectored
[6 sectors per cell) which gives a direction, the cell also knows what
power the phone is transmitting with, and the power it's received so can
make a good approximation of where the phone is (within 60 degrees
angle). However it's likely a phone will be picked up by several cells,
so the network can triangulate and make a better aproximation.

Making the information available to end-users is problematic due to
privacy issues, unless the user explicitly agrees to give the info away.

With GPS units, the info is stored in the phone and can send it out
using SMS or other means.


-------------
It was my impression that only a handful of cellphones have full GPS 
units in them.  Benefon and some Motorola units made for the former 
Nextel come to mind.  The Benefon units do send SMS reports, and in 
fact, I have written code to control and track these units via SMS using 
a Nokia 31 GSM terminal.  Unfortunately, aside from their unique GPS/SMS 
capability, the Benefons are not very attractive products, in my 
opinion.  And they are expensive.  The Motorola units contain Java 
machines and a well defined API for accessing the location data.  I have 
not worked with them.  There have undoubtedly been changes in the 
marketplace since I did this work about 2 years ago.

As I understand it (but don't have thorough knowledge and could be 
mistaken), other units generally only receive GPS satellite signals and 
relay the data to cellular provider networks where the actual location 
calculation is done.  This can be done with assistance of data obtained 
based on tower proximity, which jumpstarts the iterative process of 
approximation.  I think it is called assisted GPS or some such...
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