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Originally Posted by tpeazy
Actually, its not that GSM is able to do voice and data simultaneously. So called GSM carriers open up an additional channed using even more bandwith to accomplish this. So it is not on a shared channel at all.
To be totally correct, GSM as it existed in the past is not even around anymore. Carriers like ATT and T-Not-So-Mobile use WCDMA which stands for wideband CDMA. These networks, so far, are vastly inferior to CDMA 2000 networks because of the difference in frequency allocation and usage. That is why ATT has about 2.5 cells to VZW and Sprint's 1 Cell. (Cellular Towers).
Just a bit of info.
Tp
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Actually, not to nitpick, but right now GSM carriers are still using the 2.5G GSM networks, but are OVERLAYING WCDMA. They're still expanding their native 1900 mhz/850 mhz GSM networks.
And their networks are not vastly inferior to CDMA 2000 networks. The difference in frequency is minimal. AT&T uses Band II and Band III, while T-Mobile uses Band IV (AWS) UMTS. II and III operate on the exact SAME PCS spectrum (850 and 1900 mhz), Band IV operates on 1700 uplink (to the handset) 2100 downlink. 200mhz is NOT a significant difference in building penetration, cell distance, etc.
The reason for more cell sites with GSM networks is that their 3G solutions are a completely new network overlay, capable of handling voice AND data (and thus why you can make a voice call and data call at the same time. You actually connect to two DIFFERENT networks in UMTS areas), and GSM uses time division instead of code division. The technology is capable of extremely high and extremely consistent call quality (significantly better than CDMAs, in theory), however has a hard wired set of "time slots" that users rotate through. CDMA networks theoretically have NO capacity limit, but as more users utilize certain cell sites with certain backhaul call quality exponentially degrades. Even still, 2.5G GSM's timeslot management systems, with vocoders installed are MORE efficient than CDMA. You can have more users on a GSM network with better call quality than on a CDMA2000 network, in both AT&T and T-Mobile's implentations vs. Sprint and Verizon's. The PRIMARY reason for the 2.5 to 1 cell site figure is that there is more coverage OVERLAP with GSM. Verizon and Sprint tend to have very friendly roaming agreements, which T-Mobile and AT&T do not. Also, THREE national carriers were using GSM (Cingular, AT&T Wireless, T-Mobile) versus the TWO that were using CDMA, and had MUCH more friendly roaming agreements to cut down on costs. It's not an issue of the technology, it's an issue of the AT&T/Cingular merger and more hostile GSM roaming agreements of the past (which have since gotten much friendlier, but there's still a LOT more overlap between carriers and even within carriers due to such mergers).
Even if you look at how T-Mobile was formed (Aerial, PowerTel, VoiceStream), those networks had significant overlap, which Verizon and Sprint's formations did NOT. Their networks were more or less built from the ground up or were purchased from operaters in different markets, THEN purchased.
Also, WCDMA also allows for MUCH higher theoretical data speeds, is MUCH more spectrum-efficient, etc.
CDMA vs GSM always was, and always will be a "6 of one, half a dozen of another" battle. They both have their advantages and disadvantages, and really the differences people notice in the technologies have more to do with carrier implementations than anything else. For instance, people always tout GSM for being advantageous because of SIM cards. The same is possible, and is used on several CDMA networks in the world. They're called RUIM cards, however no US carrier has jumped on them.