When your cool new LTE phone loses touch with your LTE network, the 3G radio inside the phone will immediately connect to the older 3G network for your data service. But 3G is slower, so the downshift needs to be a smooth one—one that doesn't yank you down to a speed so slow, you can't continue what you're doing.
If such a jolt were to happen while you're watching streaming video, your movie might might begin to stutter, playing in fits and starts. It might even stop working altogether.
That's why a comparison of the major national carriers' combined 3G and 4G speed is important. The fastest LTE speeds can be easily forgotten if your backup 3G service slows throughput to a trickle.
TechHive benchmarked nationwide wireless speeds throughout March and April, and our 20-city tests show that AT&T's LTE service and HSPA+ service offer the fastest combination of 4G and 3G for dual-mode smartphones and tablets. AT&T's LTE service showed average download speeds of 13.15 megabits per second, and average upload speeds of a solid 6.45 mbps across our 20 testing cities.
AT&T got a late start relative to rival Verizon in building its LTE network, but it has moved fast and now reaches a respectable 200 million people with its service. Verizon LTE service is now accessible to 287 million Americans, and is generally more accessible as one travels outward from densely populated urban areas.
It's likely, then, that AT&T devices must downshift to HSPA+ service more often than Verizon devices must downshift to CDMA data service--but when they do, AT&T users don't see nearly the drop-off in speed that Verizon subscribers experience upon downshift. The average download speed of AT&T's HSPA+ service was almost 3 mbps in our tests.
The average LTE-to-3G downshift for AT&T customers, from 13.15 mbps to 2.97 mbps, represents a 77 percent drop. The average downshift for Verizon subscribers, from 9.61 mbps down to less than 0.80 mbps, represents a 92 percent drop.
It gets uglier with Sprint service. When Sprint customers lose LTE service and fall back to 3G CDMA, their speeds drop by more than 90 percent. And the drop-off starts from a far lower height: Sprint's average for LTE downloads is only 4.32 mbps. The carrier's backup CDMA 3G service averaged a mere 0.40 mbps in our tests.
T-Mobile didn't produce LTE speeds as fast as AT&T's, but its drop-off of 62 percent from an average 4G download speed of 9.01 mbps to 3.13 mbps was the least of all the carriers.
The new LTE technology is, on average, ten times faster than the 3G service many people are used to, and the carriers are doing their best to upgrade their 3G device-owning customers to new LTE devices, with some success. When we conduct our tests next year, well more than half of U.S. cellular customers will likely have moved over to LTE networks.
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