What LTE means for Apple's new iPad

By Glenn Fleishman, Macworld |  Mobile & Wireless

So while it might take, on average, half or a quarter as long to download an image or a movie or load a webpage with LTE than with a 3G network in the same physical location, the experience will also be less frustrating, because LTE will work more reliably more of the time. Having just visited Manhattan and suffered the heartbreak of AT&T 3G in that fine city (something I have no trouble with in Seattle), I can fully appreciate how that might reduce people's stress and increase their productivity.

But how fast, really?

Fine, you say, but what does all this mean for actual data rates already, Fleishman? (Please. Call me Mr. Fleishman.) During Wednesday's announcement, Apple senior vice president of worldwide product marketing Phil Schiller spoke of "up to 72 Mbps" downstream rates with LTE. But that's a specious number relative to the modest and more accurate information that carriers provide. It's like the difference between the capacity of a water main on your street and how fast water gushes out of the tap in your kitchen.

72 Mbps is an accurate measurement of the top data rate between an LTE device and a cellular base station on AT&T and Verizon's 4G networks, where they use 2x2 MIMO arrays (two sets of receiving and transmitting antennas with two separate data streams) and 10 MHz wide channels for sending and receiving. (Verizon openly provides that information. AT&T is a little more technically circumspect.)

But neither AT&T nor Verizon nor carriers outside the United States promote that "72 Mbps" number. That rate includes the network overhead outside of pure data transferred among devices if all devices are close enough to communicate at the maximum data rate. In reality, the true throughput is much lower, and each device will be at varying distances from a base station, and thus communicate at different rates. (Like nearly all wireless standards, LTE base stations and devices constantly adjust the optimum data rate by taking less or more time to send hunks of data. Slower transmissions allow more noise in the connection, which produces more reliable results.)

Verizon and AT&T both say their LTE networks will deliver about 5 to 12 Mbps downstream (from their networks or the Internet to a device, like downloading files) and 2 to 5 Mbps upstream. That's two to four times higher than the rates AT&T expects even with its faster HSPA+ 3G deployments, and two to six times faster than Verizon's current 3G network.


Originally published on Macworld |  Click here to read the original story.
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