Verizon CTO: 4G LTE international roaming is coming

International travelers on Verizon Wireless should rejoice, as the company's chief technology officer promises the company will offer global roaming on 4G LTE. But don't expect much 4G LTE interoperability among carriers here at home.

Global roaming is coming to Verizon Wireless 4G LTE devices, but subscribers shouldn't expect to be able to use those devices on other U.S. carrier LTE networks, according to Verizon Communications chief technology officer.

Speaking at a press event at the Telecommunications Industry Association event here today, Tony Melone, Verizon's chief technology officer, said that Verizon Wireless will eventually offer global roaming for its 4G LTE smartphones, tablets and network cards for both 3G HSPA networks as well as other 4G LTE networks operating overseas. But he gave no indication that Verizon would alter its radio technology to allow Verizon 4G LTE devices to be used on other carrier networks in the U.S. or vice versa.

"There will absolutely be roaming for 4G LTE devices," he said. "And where 4G LTE isn't available or it's not economical to support those LTE frequencies, we'll allow customers to fall back on 3G HSPA networks."

Currently, roaming onto other 4G LTE networks or even onto 3G networks is unavailable for the more than 8 million 4G LTE subscribers using Verizon Wireless subscribers. It's also impossible for Verizon 4G LTE devices to be used on other U.S. LTE networks, such as ones built by AT&T or other smaller carriers that are building wireless networks that use similar 700MHz wireless spectrum.

Why? It comes down to the specific radio frequencies that carriers around the world and here in the U.S. are using to build their 4G LTE networks. Devices built for one band of radio frequency won't work on a network that uses a different band. And sometimes even devices using the same radio frequency have enough technical differences that they're still not interoperable.

Because wireless spectrum has become so scarce throughout the world, wireless operators in the U.S. and abroad are using different frequency bands to build their networks. What this means for consumers is that even though most of the world's carriers will be using the same network technology, they will still be using different spectrum frequencies, which will make devices incompatible. In order to get global roaming support, devices will have to support radios supporting multiple frequencies. The same issues exist for 2G and 3G when it comes to roaming. But for those networks, there are more common bands used, which makes the number of radios that must be supported low in comparison to the emerging 4G LTE networks.

A recent report published by the GSMA's Wireless Intelligence Service predicts that at least 38 different radio frequency combinations may be used in LTE deployments in the next few years. These differences make it very difficult for manufacturers to make devices with enough radios to support true global roaming.

The problem also exists for domestic 4G LTE deployments, even among carriers using the same spectrum frequencies. For instance, customers with a Verizon 4G LTE device, such a the new iPad, are not able to use that device on AT&T's 4G LTE network and vice versa even though AT&T and Verizon each use the 700 MHz frequency band for their services.

Why? The 700 MHz band of spectrum does not use a single "band plan" across the entire frequency. So companies that own different slivers of that spectrum must build devices with different radios.

Melone said that international roaming is important to Verizon, and he downplayed the importance of domestic roaming, since there is an inherent limit to the number of radios that can be supported on a device. Today, he believes roughly eight different radios can be supported. As technology progresses, that number may increase to 12.

But because Verizon must support multiple radio technologies for its own network, the number of "roaming radios" is further limited. For example, Verizon's 2G and 3G services use 850 MHz and 1900 MHz spectrum. Its 4G LTE network supports 700 MHz and will eventually also support AWS spectrum in 1710-1755MHz and 2110-2155 MHz. And because 4G LTE won't be deployed ubiquitously, a global 4G LTE device will also have to support frequency bands for GSM services globally.

"The number of radios that you have to use adds up quickly," Melone said. "So we need to look at what band plans countries around the world are planning for with their 4G LTE deployments. And then we have to make some bets. There's so much uncertainty now, we are limited in saying which ones we'll support and when."

Melone said that adding this support depends on when the spectrum is allocated and how quickly carriers build their networks.

As for domestic roaming, Melone didn't offer much hope there. He said that it's unlikely that Verizon would add support for its devices to roam on other slivers of 700 MHz spectrum used by other U.S. carriers.

"We will drive our OEMs to build for our network specifications," he said. "We are not going to ask them to invest in and increase our cost to do something we don't need. AT&T will do the same thing."

He continued that if other carriers have access to Verizon's flavor of 700MHz, the company is happy to offer roaming arrangements. In fact, Verizon is working with rural carriers to let them use Verizon's 700MHz spectrum to build out 4G LTE service. But he said the company has no intention to interoperate with other operators using different slices of 700MHz spectrum.

"The challenge we face is that there isn't much real estate on devices for these radios," he said. "And our customers want to roam in Europe. So we have to make those decisions on what frequency bands to support to enable that. If we add 700MHz bands in the U.S., it's just one less frequency band we can offer for global roaming."