Your car runs off the interstate during a blizzard. You're in a ditch, stuck in the front seat with multiple injuries, and snow is pouring in through the smashed windscreen. You can reach your cellphone. You dial 911, but you're out of service range. Do you really care about having two more days of standby power on your mobile, when you're likely to die of internal haemorraging or exposure within a few hours?

You hit the "Emergency Power Boost" button. It increments the transmit power of your handset upwards in stages until it finds a tower it can link to. An onscreen graphic provides an indication of estimated call time. You also have the option of sending a pre-composed SMS with a single button if you are unable to speak, or if talk time is likely to be short.
-- BunsenHoneydew, Jul 16 2005

Signal boosters are Widely Baked http://www.dazer.com/booster.jsp
...but nothing's gonna help you if you're really out of service range. [DrCurry, Jul 17 2005]

Good idea, but would it work? I'm sure you could have a phone with a "high power send" option, but what about receiving? I think (not sure) that communication has to be two-way even to 'send', since the phone has to negotiate with the tower. So, you'd need a more sensitive ariel on the phone. Or is this not the limitation?
-- Basepair, Jul 16 2005


I'm disappointed - I was hoping this was going to be a way of getting a few extra horsepower out of my turbocharged flat-six.
-- TolpuddleSartre, Jul 17 2005


Absolutely this would work. It's not even close to hard. Marine radios have two settings: 1 Watt / 25 Watts. You try 1, and if it doesn't go through you use 25.
-- Madcat, Jul 17 2005


//Absolutely this would work.// Not if using your cell-phone depends on receiving signals from the tower it won't. I think.
-- Basepair, Jul 17 2005


Exactly - but even 'sending' requires negotiation between the phone and the base-station, as I understand it.
-- Basepair, Jul 17 2005


Haven't Porches enough power as it is?
-- Ling, Jul 17 2005


//You may be able to send but it's doubtful you would receive, unless the network signal is also boosted// But wouldn't the phone send a message as part of the negotiation saying that power had been boosted, so that the base-station could reply in a similar fashion?
-- AbsintheWithoutLeave, Jul 18 2005


Before the phone can do anything under the GSM standard it has to authenticate to the network. Even allowing that this may not be the case for emergency calls (I'm not sure on that point) 2-way negotiation is still required in order to set the timing advance of the phone's transmissions. The maximum diameter of a GSM cell as governed by this limiting factor is approximately 35km. Nice idea but [-] impractical.
-- DocBrown, Jul 18 2005


How about an emergency helium bottle and weather balloon contained in the phone? Then, suspended from the balloon, the phone could rise and its signal easily cover a much wider area. How it would be traced back to the ditch-ridden would-be rescuee...I haven't worked out yet.
-- AbsintheWithoutLeave, Jul 18 2005


Based on the comparative size of the two transmitters, it seems reasonable to assume that the cellphone is usually the limiting factor for range, does it not?
-- Madcat, Jul 18 2005


Nope [Madcat], unfortunately not. The main limiting factor is as I described above the timing advance.

Because a phone is allocated a timeslot to use, if it is a long way away from the base station then in order for its signals to arrive in said slot it must set a timing advance so that it transmits earlier as compensation for the time its signals spend in transit. This advance figure can only get so big before the phone arrives at a situation where it needs to transmit its signal and receive one from the BTS simultaneously. There are other more complicated reasons why it won't work but my head hurts thinking about them.

The practical limit on GSM cell size is 35km across if you're prepared to tolerate shoddy call quality. You could get bigger cells if you lost some channels, perhaps a scheme worth considering for sparsely populated areas. This idea, however, will *not* work.
-- DocBrown, Jul 18 2005


Just put all the ditches near cellphone towers.
-- Basepair, Jul 18 2005


[basepair], no, that's impractical. I suggest that the cellphone towers be put near the ditches. Planning permission for ditches must include foundations for a cellphone tower.
-- Ling, Jul 18 2005


CDMA is an entirely distinct kettle of aquatic life [UB]. I'm only just getting to grips with 3G/UMTS so I'll let someone with more knowledge field that one!
-- DocBrown, Jul 19 2005


CDMA stands for Code Division Multiple Access. GSM stands for Global System for Mobiles or something, but my understanding is it works on TDMA (Time Division) - hence [DocBrown]'s anno.

Here in Australia, CDMA was commissioned as a replacement for the scrapped analogue network in rural areas, with some promises of better range than GSM (which is mostly urban).

So -maybe- this would work with CDMA phones.
-- BunsenHoneydew, Sep 04 2005



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