Vonage Selects TCS For VoIP E911 Service

Wed Jul 20 13:02:38 UTC 2005

Michael.Dillon at btradianz.com wrote:
>>In the US, that might be true, but, I'm betting that could be very wrong
>>in places like London.  I'm betting the station where you boarded the
>>Tube could be a LONG way from where you make the 911 call.
> 
> There are very few places in the underground tube system where you
> can make calls on your mobile. Outside central London where the tube
> runs aboveground I would expect that GPS reception would be available 
> wherever mobile reception is available, after all the tube trains
> have lots of windows.

This is unlikely.  GPS reception is usually determined by sight of
horizon.  For example the navigation system in my car has trouble
from time to time spotting enough GPS satellites when I'm driving
in the inner city of Zurich.  It keeps itself updated by compass
and tracking the movements/velocity of the car.  If a car mounted
GPS has trouble keeping up with GPS in a city I highly doubt that
a small mobile phone without any line of sight at all would be able
to get any meaningful GPS signal reception.  The low number of active
GPS satellites and their concentration over the middle east don't
help getting accuracy and reception higher up in US and EU.  The
new EU system called Galileo has a larger number of satellites
planned which makes chances higher to have a number of the in sight
all the time.  On top of that it is 20 years further in technology
refinement than GPS.  OTO it ain't there yet and any speculation
on how good it will be is moot until we can see ourselfs.

-- 
Andre