What LTE means for Apple's new iPad

By Glenn Fleishman, Macworld |  Mobile & Wireless

Cellular versions of the new iPad come with support for the latest and greatest wireless networking technology, LTE (Long Term Evolution). In the U.S., both AT&T and Verizon have LTE networks. You'd think this would be a recipe for network simplicity for Apple's iPads at long last... but you'd be wrong.

Apple will sell two different LTE-equipped iPads—one for AT&T's network and one for Verizon's. That means that in the U.S. the third-generation iPad comes in 18 versions, like the iPad 2: Wi-Fi, Wi-Fi plus Verizon 3G/4G, and Wi-Fi plus AT&T 2G/3G/4G multiplied by three memory sizes and two colors. (The Verizon 4G iPad also includes worldwide support for 2G and 3G using GSM standards when used outside the United States, just like the iPhone 4S.)

LTE and 4G

LTE is an early version of fourth-generation (4G) cellular technology. But not every version of LTE is interoperable with every other. While all LTE implementations rely on the same underlying networking technology, carriers can make a variety of choices that affect interoperability. In other words, not all LTE is the same.

That complicates Apple's product introductions, because AT&T and Verizon Wireless (not to mention other carriers around the globe) have made different choices in building their LTE networks. The frequencies used, network authentication, and other factors make it presently impossible to roam from AT&T to Verizon or vice-versa over 4G with the same hardware.

LTE is more spectrally efficient than 3G. That is, it packs more data into the same range of frequencies (a radio channel) than 3G protocols. Carriers like that, because spectrum is expensive to license and cell base stations are expensive to deploy. The more data that can be carried over a given allotment of spectrum, the more customers a carrier can serve in a given area covered by a base station, and the more revenue (and, one expects, profit) it can generate.

The technology also reduces latency, which is the lag time usually measured as being the time from initiating a request to a network and receiving the response. Think about turning on a faucet and waiting for the water to flow (latency) compared to the amount of water that comes out (throughput). The latency on 3G networks is like an old pump well in which you have to prime it to get the flow started; on an LTE network, it's the convenience of pressurized indoor plumbing. Less latency means better buffering, quicker starts, and less choppiness for streaming video and less stuttering during Internet telephony calls. LTE's latency can be as low as wired broadband.

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