LTE globally and in the United States is highly fragmented, says Eran Eshed, vice president of marketing for Altair Semiconductor, the Israel-based LTE chipmaker. Without going into details, there are two LTE flavors, and 15-20 different frequencies (some say 30 or more) around the globe designated for them. "In each band, you'd need different components and antennas in some cases to talk to each frequency," he says.
There have been ongoing efforts to "harmonize" a handful of bands for LTE, and some effort to push for an international "roaming band" -- based on 1800MHz -- that phones could support, he says. But nothing is expected soon.
Multi-mode phones will be able to fall back to 3G to support roaming, according to Eshed.
Even in the U.S., where AT&T and Verizon are deploying LTE in the 700MHz spectrum, roaming isn't possible. "You'd expect that one phone could support both, but there are two bands within that spectrum," says Ericsson's Nandlall. "An AT&T [LTE] phone will not roam to the Verizon band."
iPhone 5 impact on LTE networks
If asked, the carriers recite standard assurances that they've carefully designed their networks to handle LTE subscribers. If pressed, they'll repeat those assurances.
But there's going to be big surge of LTE-capable devices thanks to the iPhone 5.
Apple is widely expected to sell millions of the new iPhones in a matter of days: Some are projecting 10 million units. Some number of those may not reach their owners for two or three weeks but within a few months, the number U.S. LTE subscribers could double.
There are roughly 12 million-13 million LTE users in the U.S. now, estimates Bill Moore, CEO and president of RootMetrics in Bellevue, Wash. One analyst thinks Apple could sell up to 5 million units before September ends, and 15 million more in the last quarter of 2012.
Those numbers could, in some locations at some times, congest the access to LTE base stations, or bog down the wireline backhaul from the stations to the carrier's core.
With the early iPhone, solely on AT&T's 2G/3G network, connections bogged down under unexpectedly heavy signaling loads, more than the higher data payloads. The 3G silicon and radio vendors have been addressing that. And LTE is much more efficient than 3G in this regard. In addition, the 3G data experience demonstrated the need for adequate LTE backhaul connections to prevent bottlenecks. And the nature of LTE creates much higher capacity at the outset, according to vendors.
None of the vendors or analysts contacted for this story think any of the U.S. LTE networks will implode. But there may be times or areas where users run into problems.