How LTE-Advanced Will Reach for Gigabit Cellular

By Wesley Fenlon

The successor to LTE promises faster speeds and greater reliability, but we're going to need much more complicated hardware to take advantage of it.

Cell phone carriers and smartphone makers led us down a rocky, windy road to a 4G cellular data standard. It started with the iPhone 4, which many people assumed as a 4G device, and with carriers deliberately labeling buffed-up 3G technology like HSPA+ as a 4G network. Now that most major carriers, like AT&T and Verizon in the US, have finally moved on to LTE, the situation isn't quite as murky as it once was. But, ironically, even LTE isn't the 4G standard we were once promised--the original 4G specification called for speeds up to 1 gigabit per second, which current LTE networks fall far short of. And our next LTE network doesn't look like it'll get there, either.

Technology Review wrote about LTE-Advanced on Wednesday, delving into how the LTE follow-up will increase network speeds for mobile data consumption. And our consumption will need all that speed--according to Cisco Systems, by 2016 our traffic will have increased 18 times over. We're going to need a bigger wireless pipe.

LTE-Advanced won't get anywhere near that lofty 1 gigabit per second goal--at least not right away. Technology Review points out that China Mobile recently tested out LTE-Advanced and hit peak downloads of 223 megabits per second, while Qualcomm showed off an LTE-Advanced chip at this year's CES capable of 150 megabit per second speeds. Sure, that's a far cry from a gigabit, but it's still dramatically faster than the Internet connections most of us have at home. So how do we get there?

The road, as usual, won't be an easy one. We need more antennas. LTE phones are beginning to rely on MIMO (multiple-input and multiple-output) technology, which Wikipedia has a convenient summary of: "[MIMO] offers significant increases in data throughput and link range without additional bandwidth or increased transmit power. It achieves this goal by spreading the same total transmit power over the antennas to achieve an array gain that improves the spectral efficiency (more bits per second per hertz of bandwidth) or to achieve a diversity gain that improves the link reliability (reduced fading)."

Anandtech's review of the iPhone 5 goes into more detail about how the phone uses two antennas for LTE. And that's a simple 2x2 MIMO implementation: two antennas in the phone, two in the base station. Adding more antennas complicates things, but it's the basis of how LTE Advanced offers us faster data: " In essence, the technology stitches together streams of data from as many as five different frequencies—a trick known as 'carrier aggregation,' writes Technology Review. "In addition to that, it can transmit and receive from as many as eight antennas..."

Phone makers will have to figure out how to squeeze at least two more antennas into their phone designs. They'll need more powerful processing to handle those antennas. And they'll need more battery power to operate. Remember how crappy battery life was on the first round of LTE phones? If that situation repeats itself, only when phone SoCs integrate LTE-Advanced processing will the battery use be manageable.

But we do have something to look forward to aside from pure speed: reliability.

More advanced MIMO configurations aggregating multiple frequencies means one can drop without ruining your connection. Cellular data should become more reliable and more efficient, once we have the hardware to support LTE-Advnaced.

So when do we get to take that next step towards true gigabit 4G bliss? AT&T plans to test LTE-Adanced this year--but AT&T won't finish its LTE rollout until sometime in 2014. IT's going to take time for carriers to upgrade, and they probably won't start until they feel the pinch of overtaxed LTE networks. Companies like Qualcomm still have to release their chips, and companies like Apple and Samsung have to integrate them into phones. We don't expect to start down that road until 2015, at the earliest.