We’ve been starting to hear more about an LTE-Advanced technology called carrier aggregation lately, as mobile operators in South Korea, Australia and the U.S. start rolling out new supercharged networks capable of doubling download speeds to the device. But with an exception or two, carriers are making very little noise about these new capabilities.
I recently reported that AT&T already has carrier aggregation up and running in Chicago and other cities, capable of boosting its speeds by 50 to 100 percent. But AT&T has publicly made little fuss about it, and it’s only revealed a single device — a 4G hotspot — that can tap the network. We’re starting to take the first steps into LTE-Advanced networking, but the normally self-promoting mobile industry is staying mum. What gives?
The explanation, according to Ericsson CEO Hans Vestberg: We’re in a nebulous transition period in mobile networking, and all of the pieces necessary to make the technology commercially viable haven’t yet fallen into the place. Those pieces aren’t just technical, they’re political and economic. Carriers can’t simply flip a switch and turn carrier aggregation on — they need to feed those networks with new spectrum, and they need more advanced smartphones that can actually tap into that increased bandwidth.
“It is a vital component to meeting mobile data demand,” Vestberg told me an interview on Wednesday. “We’ve started with carrier aggregation, but we’re definitely still in the beginning.”
First, let me explain how carrier aggregation works. A single LTE cell is called a “carrier” in telco parlance, and it transmits on a specific block of frequencies. That LTE carrier can only be as big as the amount of the contiguous spectrum an operator has access to. So if you’re AT&T and have 10 MHz of 700 MHz downlink spectrum, you can get a maximum possible capacity of 75 Mbps out of your network.
But AT&T also owns 4G spectrum in the Advanced Wireless Service (AWS) and PCS airwaves at the further end of the spectrum map. It can deploy separate LTE networks at those bands, but they function like separate networks. A device can connect to one or the other, but not both. Carrier aggregation allows those networks to bridge that spectral divide, transmitting on both channels to a single device and creating a big fat bandwidth pipe in the process.
That’s exactly what AT&T has started doing to its networks in Chicago and other places, but it’s been quiet about it. That’s likely because, as Vestberg mentioned, not only does the network have to be configured for carrier aggregation, but also the device. In the U.S., two smartphones I know of have the requisite chips: the Samsung Galaxy S5 and the HTC One M8, both of which launched this month. AT&T offers both devices, but I’m still waiting to hear whether it’s actually switched on the capability in either device.
That leaves the vast majority of smartphones, tablets and other data devices unsupported, and even those exceptions are limited in their capabilities. The GS5 and M8 both sport early generation carrier aggregation chips that can’t tap the blazing 300 Mbps or higher speeds that LTE-Advanced promises.
It’s all about the spectrum
While U.S. operators like AT&T, Verizon and Sprint have alternate spectrum in the bank — or have picked up more through strategic acquisitions — not everyone has that luxury. Even in Europe, where operators do own LTE spectrum in different bands, many of them haven’t deployed their second LTE networks. In order to launch carrier aggregation, you need more than one carrier to aggregate.
That’s going to be the biggest limiting factor facing many countries in moving to LTE-Advanced, Vestberg said. Until operators get new 4G spectrum, they’re limited in the kinds of networks they can build. While it’s a matter of debate whether carriers need more spectrum to serve their customers, there’s no question that carrier aggregation requires lots of frequencies to thrive.
As for network technology, Vestberg said the industry is almost there. Ericsson has been supporting the few individual deployments of LTE-Advanced technologies out there on a one-off basis. But in September it will release a major update to its LTE networking platform that will upgrade its networks from core to tower with carrier aggregation capabilities.
Soon, almost every Ericsson LTE network in the world — and, given Ericsson’s market lead, there are a lot of them — will be carrier aggregation–ready, Vestberg said. But operators will still have to wait for devices and spectrum to fall into place before they can turn it on.