(keitai-l) Re: closing down cellphones in cinemas

Most Cellular Protocols have the handset listen first. If you are in a no
reception area -- i.e. the handshake frequencies are silent, the phone will
not attempt a communication.

-----Original Message-----
From: Ben Hutchings [mailto:ben.hutchings@roundpoint.com] 
Sent: α 01 ιεμι 2002 17:39
To: keitai-l@appelsiini.net
Subject: (keitai-l) Re: closing down cellphones in cinemas


On Fri, 28 Jun 2002, Nick May wrote:

>
> http://news.bbc.co.uk/hi/english/sci/tech/newsid_2067000/2067672.stm
>
> Sorry - another link, about efforts to close down cellphones in cinemas
> and the like.
>
> When an incoming signal is very weak, cellphones presumably ramp up the
> power of their own signals. So if this tech. "half worked" it would lead
> to all the cellphones in the cinema blasting away on full power all
> trying to contact the nearest base station....
>
> What do cellphones do when the signal is non-existant? Do they  just put
> out a very low power signal? Or do they blast away?

If a handset loses the signal from its current cell without being
handed-off then it should presumably try to search for a new cell by
itself.  Until the handset has identified the frequencies, timing, etc.
used by the cell, it's quite useless for it to attempt to transmit
anything.  I don't think there's going to be any 'blasting away on full
power'.  (For GSM at least, handsets are not allowed to change power
level; the base station makes the decision.)  On the other hand, the base
station probably might well spend a while increasing signal power before
giving the handset up for lost.

(The process of searching for a new cell can apparently consume quite a
bit of power even though the transmitter isn't active.  My Motorola GSM
handset has various options for speed of search to allow the user to
trade-off battery life against speed of reconnection to a network.)


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