LTE's theoretical maximum download speed will increase to 450 Mbps next year -- but the upgrade will be out of reach for most users, as many mobile operators simply don't have enough radio spectrum.

The broadband speed users get depends on a myriad of different factors, but in the network it all starts with the amount of spectrum their operator uses. Future increases will be fueled by a technology called carrier aggregation, which lets operators treat up to three radio channels in different frequency bands as if they were one.

This month, chip maker Qualcomm and network equipment manufacturer Ericsson have been doing their best to let the world know speeds at up to 450Mbps will be possible next year, with product launches, interoperability tests and a demo with Australian network operator Telstra.

The demonstration used 60MHz of spectrum made up of three separate 20 MHz LTE channels in the 2600MHz, 1800MHz and 700MHz bands. That the mobile operators need 20MHz in each of threebands to get to 450Mbps makes the technology an option for only a select few.

For example, because spectrum in the U.S. is often licensed in 10 MHz chunks, North American subscribers are unlikely to see 450Mbps anytime soon, according to Malik Saadi, practice director at ABI Research. In Europe, LTE penetration is still low, so mobile operators are more focused on migrating subscribers to regular LTE. The first to get 450Mbps will instead be users in Asia, Saadi said.

Ericsson and Qualcomm are more upbeat, and think there is potential in North America and Europe as well. But the bulk of the deployments will use carrier aggregation at slower speeds, according to Peter Carson, senior director of marketing at Qualcomm. Speeds of 300Mbps or even 375Mbps are within reach of many more mobile operators, and that's still a big step for users.

The upgrade isn't just about really high speeds when users are close to a base station.

"The great thing about carrier aggregation is that it improves performance across the whole coverage area. That's one of the main reasons for using it," said Thomas Norén, vice president and head of product area Radio at Ericsson.

The ability to download data faster because of the higher speeds is also good for battery consumption and network congestion, according to Carson.

The network equipment and modems coming out next year will be able to mix and match LTE TDD (Time-Division Duplex) and LTE FDD (Frequency-Division Duplex), which gives mobile operators more flexibility. The former uses one channel for both uploads and downloads, with traffic alternating between the two directions, while the latter uses separate channels for download and upload traffic.

Operators will be able to use carrier aggregation to increase upload speeds to 100Mbps, as well.

However, what the latest equipment can do and what mobile operators actually install are two completely different things.

Carrier aggregation hasn't set the world on fire yet. Out of 331 commercially launched LTE networks just 21 had been upgraded by the middle of September, according to Alan Hadden, president at industry organization GSA (Global mobile Suppliers Association). By the end of the next year that number will be approaching 100 networks, he said.

A lack of smartphones compatible with carrier aggregation hasn't helped the technology's progress. That has slowly started to change with the launch of products such as Samsung's Galaxy Alpha and Note 4, and Huawei's Ascend Mate 7, which use two channels to get to 300Mbps.

There have been some recent disappointments, though. The Moto X from Motorola doesn't support carrier aggregation and Apple's new iPhones use a version of carrier aggregation that tops out at 150Mbps instead of 300 ]Mbps. They can combine two 10MHz channels, instead of two times 20MHz. The latter omission was especially surprising since Apple's smartphones can handle more bands than any competing product. That might not be an issue today, but for users that plan to keep their phone for at least two years it will be.

Looking at the chipsets that will power next year's smartphones, those disappointments will quickly become a thing of the past.

Qualcomm isn't just laying the groundwork for making carrier aggregation a standard feature on high-end smartphones. The Snapdragon 210 will make it possible to build more affordable smartphones with carrier aggregation, but users will have to make do with a maximum speed of 150Mbps. The first products, allowing devices to combine two 10 MHz channels, are expected to arrive during the first half of next year.

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