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Depending on how you look at it, there can be many benefits, but as with most technologies, they're contextual. CDMA uses 1.25MHz channels. That can be limiting in some ways, but advantageous in others. When deploying UMTS channels, AT&T or T-Mobile would need to clear out 10MHz of spectrum. Back when 3G wireless was first getting off the ground, it was decently common for a carrier to have below 30MHz in a market. To give two examples, Sprint and T-Mobile both had an average spectrum depth of around 25MHz. Sprint was able to get out of the gate fast on 3G requiring only 2.5MHz (around 10% of their spectrum) to deploy. T-Mobile had to wait until it purchased new AWS spectrum years later. The UMTS channels would have taken up 40% of their spectrum. So, it was difficult to clear out enough space to deploy UMTS. You were basically taking a third to half of your spectrum and making it unavailable for current customers. Then, as you launched the network and started selling 3G devices, customers would start moving their usage to the new technology. EV-DO (the CDMA data standard), on the other hand, only required a carrier to free up 2.5MHz of spectrum to deploy 3G. Even today, it can be an issue. As the number of GSM customers dwindle, AT&T and T-Mobile want to allocate more spectrum to UMTS. However, they can only do that in 10MHz chunks. They don't get to say, "ah, there's 3MHz that we should move to UMTS". Likewise, because UMTS does voice and data, it meant that carriers had to install SS7 and mobile switching gear to handle the voice. EV-DO was an all-IP network that wasn't going to handle voice. While that could be a disadvantage in some ways, it provided the benefit of being easier to deploy in terms of equipment. Taking that a step further, the lack of a voice requirement for EV-DO meant that they could launch a network in a much more piecemeal fashion. If one launched a UMTS network with lots of holes, call quality would be poor. Sure, calls could hand-off to GSM, but they might have a "1-bar" UMTS signal with crummy call quality while GSM users got excellent quality. Back then, if data didn't work or was delayed a bit, it didn't matter that much. People used data infrequently compared to calling and call reliability is what people paid for. It should also be noted that when EV-DO was first deployed, it was faster than UMTS. UMTS R99 had a peak data rate of 384kbps, well below the 2.4Mbps of EV-DO Rel 0. Now, the wider band of UMTS made it more future-proof, but initially EV-DO looked very good. To be fair to UMTS, I could talk about problems with CDMA as well. CDMA offered a bit more of a practical, easier transition to 3G for carriers. It's narrower channels made it easy to carve out spectrum, the fact that there wasn't a voice component meant that less equipment was needed and it didn't require the same initial reliability, etc. |