More than a phone with a GPS navigator

Alexey Feldgendler alexey at
Fri Mar 28 14:15:30 CET 2008

On Fri, 28 Mar 2008 12:27:56 +0100, Andy Green <andy at> wrote:

> | What's the advantage of the other ways of locating yourself (GSM, WiFi)
> | over GPS?

> Power, and they work inside buildings away from windows.

Inside a building your essential location (as read from the GPS receiver  
the last time before entering the building) stays the same. Once you've  
come home, you're staying home until you go outside and get a GPS signal  
that tells you're somewhere else.

> GSM at least will be powered anyway in the normal case, so polling that
> every 10 minutes

Or whenever we get an interrupt from the accelerometers -- you can't  
really move if you don't accelerate.

> or whatever is relatively cheap.  WLAN just needs to
> come up long enough for a scan and can go back to sleep if not already
> in use.  It can use GPS as an input too, I don't know the power
> consumption but I know in my work room anyway where I spend most time,
> at least the proprietary satnav we have here cannot get a signal unless
> I go outside.  I guess it is the same in most buildings and that is
> where people are most time so it can't be relied on I think.

That's the point: while you're inside a building, all you have to know is  
that you're still inside.

> I really would love WLAN to scavenge open connections as well at the
> same time (Holger mentioned this idea but I already cherished it).  So
> if you walk down a street and you didn't have Internet connection for a
> while, it keeps seeing new APs each scan and on the basis it deduces you
> are moving, it can increase the frequency of waking for scan and trying
> for association and DHCP on anything it finds, update mail and rss,
> maybe alert you it scored a connection.

One has to be careful about that. IANAL, but it might be illegal in some  
countries to use someone's private network even if it's left unencrypted  
(compare: if an apartment door is left unlocked, it doesn't mean that it's  
ok for everyone to come in). Also, in many public places you'll get a page  
telling you that you have to pay or log in instead of any web page you  
request, and it can confuse the RSS parser, screw up page caches etc.

Alexey Feldgendler <alexey at>
[ICQ: 115226275]

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