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Cellphones that Work Everywhere?
spoonist asks: "The vast array of available wireless protocols in the US is quite
bewildering: CDMA, TDMA, GSM, AMPS. I spend most of my time in urban areas. Major providers appear to be rolling out GSM, so that seems like the way to go. I also spend a lot of time hiking and climbing in rural areas and like having my mobile phone in case of an emergency. My ancient analog phone gets a signal in all but the most remote of areas
LONG after friends' digital phones loose their signals. Are there any dual mode mobile phones that can talk both GSM and AMPS? Also, I occassionally travel to Europe. From what I understand, GSM in the US uses a different frequency from the rest of the world (WHY!?!).
Are there any phones that talk European GSM, US GSM, and AMPS?"
I think it's because the 900MHz spectrum was already set aside as unlicensed. It's the frequency used by many cordless phones and baby monitors.
--Be human.
Firstly, "3G" is not a standard on its own. There is not going to be a shift away from GSM here in Australia, or in many parts of the world.
:-) where GSM coverage is lacking. But most Australians live in cities.
The term "3G" is nothing more than a stupid marketing term, it explains very little and just confuses people about the technology. Hopefully I can clear up some of this confusing mess of acronyms.
The term GSM however does not refer exclusively to the current "2.xG" digital technology. GSM is constantly evolving, and yes, will become "3G".
The first stage in the GSM "2.5G" evolution towards 3G was GPRS (General Packet Radio Service). This extended GSM to support packet switched data over multiple timeslots (bandwidth per timeslot = 14400bps). It required little change to the GSM network except for software upgrades on the base station and other minor changes to the backbone. Hence GPRS could be called "2.75G". GPRS is implemented by all 3 Australian carriers Optus, Telstra and Vodafone. It is also implemented in many other countries.
The next phase will be EDGE (Enhanced Data rates for GSM Evolution). Also called "E-GPRS" this is much like GPRS however it packs more data onto a single timeslot (upto 3 times as much due to improved coding (8 Phase shift keying as opposed to Gaussian Minimal Shift keying) and error correction transferring up to around 3 times as much data - 3 bits per symbol with a raw symbol rate of 270K). This only generally requires hardware changes to the radio interface of the base station. No official term for this yet, call it "almost 3G - 2.9G??".
Unfortunately Optus scrapped its plans to implement this for now, however I've been told some of the newer GSM base stations do support EDGE.
It is important to note that GPRS & EDGE operate in the normal GSM spectrum (thats 900MHz and 1.8GHz here in Aus and most of the world, 1900 and 800 in the US/Canada).
The next part however is to _supplement_ EDGE in other parts of the spectrum. Branded "3GSM", I am not too familiar with the technology however I believe most GSM countries will use a Wideband-CDMA technology (W-CDMA) in the 2.0-2.2 GHz spectrum. Hence, a 3G GSM phone operates on several frequencies using several coding techniques transparently to the user. The different codings are suited to different environments so I guess you have a more reliable service. EDGE can supposedly transfer around as much as 384Kbps whilst W-CDMA can do around 2megabit or so.
EDGE can coexist peacefully with older GPRS and "plain old GSM" transmissions on the same timeslot, so it's backward compatibility will make it look promising.
In Australia GSM will be the way of the future here, however CDMA is still useful for the rural hicks
Anyway correct me if I've made errors
--JQuirke
GSM uses three frequencies, depending on which bastardization you use: 900, 1800, and 1900 MHz. One is Europe's standard; the other two are used in the US and Canada because the American government enjoys giving away frequencies without stopping to think what they're used for elsewhere in the world. In this case though, I think the Restoftheworldian frequencies are reserved for military use.
Anywho, you can purchase phones that support all frequencies, but they cost more. The Motorola V60 is such a phone, as are any expensive Nokias. You may be looking for a 'world phone', as some people advertise them.
You can also get tri-mode phones. The phone I'm going to pick up next week is such a phone, and has digital 1900 MHz reception if it finds a Telus tower; if not, it looks for a digital NB Tel/Aliant tower (local telco's cheaper PCS service), and if not that, then analog, if any (and most of my country's population is covered by analong at least, with the exception of my roommate's hometown, about which I mock him).
Your best bet is to find a good cellular provider (Verizon in the US), and go in and ask THEM. THey have all the answers about the phones they offer and the services that go with them. Slashdot is a bad place to go for anything but theoretical discussions and anecdotes.
Good luck.
--Dan