"Blunkett u-turn on data privacy plans"

[Brian Gladman]

From: "Roland Perry" <ukcrypto@netcomuk.co.uk>
To: <ukcrypto@chiark.greenend.org.uk>
Sent: Monday, March 03, 2003 2:37 PM
Subject: Re: "Blunkett u-turn on data privacy plans"


> 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 accuracy that can be achieved from differential GPS is very dependent on
how much time is available to make the measurements.

With long integration times (many minutes or even hours) it is certainly
possible to get below a centimetre but I am _very_ sceptical about claims of
measurements accurate to 100 micrometres even under laboratory conditions.

   Brian Gladman