Originally Posted by BryanHarig
Yeah, touchscreens can be nice but at least 3/4 of the time they are more annoying then anything.
One freqency band for uplink, one for downlink.
AT&T 850, 1900 (different from GSM band)
T-mobile 1700, 2100
World 2100 (different from t-mobile's)
I dont remember the exact freqencies used, suffice to say a true world 3g phone would have to cover a lot of different bands.
Actually the 850 / 900 / 1800 / 1900 have their own uplink and downlink assignments, so it's actually like 8 GSM bands instead of 4 GSM bands.
For example GSM 850 Mhz is actually two separate bands. "GSM 850 Mhz"
Uplink 824.0 - 849.0 Mhz
Downlink 869.0 - 894.0 Mhz
The only reason the uplink/downlink is being mentioned for UMTS and not GSM, is that some UMTS bands (i.e. operating band IV) uses widely separated uplink and downlink channels (1700 Mhz uplink, 2100 Mhz downlink). We can't call it UMTS 1700 because of the 2100 Mhz downlink, and we can't call it UMTS 2100 because of the 1700 Mhz uplink.
(More precise numbers: UMTS-FDD operating band IV that T-Mobile uses, 1710-1755 uplink, 2110-2155 Mhz downlink)
However, GSM also uses uplink and downlink concepts, just that the uplink and downlink frequencies are "pretty much" adjacent to each other rather than far apart as in UMTS...
If you say 1700 Mhz UMTS is 2 bands, then 850/900/1800/1900 GSM is a total of 8 bands if you count uplink and downlink separately
. Please compare apples to apples!
Also, T-Mobile does not use 1700 or 2100 for GSM -- they are using it for next-generation UMTS. They still use 1900 Mhz GSM too, but AT&T/Cingular is the one that has the 850 Mhz band in addition to 1900. Also, Cingular has their own 3G network, so that's additional bands. Also, some carriers may substitute their GSM bands with UMTS, as some available UMTS frequencies overlap the GSM frequencies. (I have no idea if Cingular is doing this, though)
In a nutshell, AT&T has 2 general GSM bands (4 bands if counting uplink/downlink), and T-Mobile has 1 general GSM frequencies (2 bands if counting uplink/downlink). However, this is made complicated by the fact that T-Mobile uses AT&T 850 Mhz network in California, because T-Mobile does not own spectrum in some areas. Now, add to the fact that T-Mobile and Cingular each has 1 general UMTS band (2 bands if counting uplink/downlink). And the fact the Cingular UMTS uses uplink/downlink very close to each other (close to 1900 Mhz) and T-Mobile UMTS uses uplink/downlink frequencies far apart from each other (1700 Mhz versus 2100 Mhz). Yada yada, so on... It gets complicated...
Source: Wikipedia GSM Frequency Ranges Wikipedia UMTS Frequency Ranges
What we need is more universal radios (software defined radios, etc) that can adapt to pretty much any uplink and downlink frequency and demodulate the world's radio data standards. We are 'gradually' getting there...