"Blunkett u-turn on data privacy plans"

[Roland Perry]

In message <03030310195100.13025@bbzen.edsc.ulst.ac.uk>, Brian Beesley
<BJ.Beesley@ulster.ac.uk> writes
 >On Saturday 01 March 2003 10:52, Roland Perry wrote:
 >>
 >> >I gather that GPS receivers are on the list of
 >> >"wanted" features. This would enable the phone to be located to a few cm.
 >>
 >> IMHO they are much over-sold for this kind of application, needing a
 >> clear view of lots of sky,
 >
 >Or access to a few local repeaters - which should be easy enough to
 >locate on mobile phone masts. The repeaters could easily operate on a
 >sub-band of the mobile phone "carrier" signal; the phones would not actually
 >need to receive actual GPS satellite signals.

I have no idea how such a repeater would rebroadcast the signals from
the several satellites involved, sufficiently faithfully (eg in phase)
to make that work. You aren't confusing this with the fixed receivers
used to implement differential GPS, are you?

 >Don't forget specialised GPS receiving
 >stations are used to track minute movements (down to the order of 100
 >microns) in e.g. earthquake research.

I have never heard of such a thing. Most claim even differential GPS is
only good to a metre.

 >The fact that _raw_ GPS positioning is already used in e.g. car sat-nav
 >equipment suggests that tracking targets around a city is very much feasible,
 >despite the constricted skyline and the presence of a great deal of other
 >equipment causing interference.

Of course. It's a very good application of the technology. Such cars
have a nice stable aerial, rarely go indoors or inside other cars or
trains, and so on. Positioning to 20m is overkill for map-reading.

 >It will be very interesting to see how badly affected these applications will
 >be affected when the US "detunes" GPS for military reasons during the
 >forthcoming attempt to singe Saddam's moustache.

That rather depends if they've equipped their own soldiers with
expensive sets to decrypt [yo! on topic!] the Precise Positioning
Service signals. Last time they had a war, the squaddies only had
commercial receivers so they turned off the wooble. It's been off
permanently since mid-2000. Although "permanently" is a moveable feast
these days :-(
-- 
Roland Perry