Seven top-tier operators in the United States and abroad have participated in successful LTE roaming trials, reports Syniverse, whose platform is being used in the effort.

"We're addressing everything that's possible to be addressed outside of the frequencies," Syniverse senior vice president Mary Clark says, referring to the incompatibilities between various bands used for LTE, such as the issues between Band 12 and Band 13 in the 700 MHz block. "Through these trials, we're moving everything else off the table that could have been an obstacle before."

The roaming program spans both TD-LTE and FD-LTE. Though the names of the wireless providers participating in the trials have not been released, Clearwire, China Mobile and Softbank are three high-profile TD-LTE operators, while Verizon Wireless, AT&T and Sprint are using FD-LTE.

With LTE networks still in the build-out phase, roaming between networks has remained on the backburner. As a result, customers who exit their provider's LTE coverage area can't piggyback on the LTE network of another provider.

Advancing the test runs will help LTE roaming come to market sooner. The trials are running on Syniverse's IPX network, which is used by nearly 100 carriers worldwide to connect networks for roaming.

"The target architecture that was defined for interoperability between LTE networks, we haven't really seen it in action. We haven't seen how the different interfaces work together," Clark says.

The goal of the end-to-end trials will be to determine how standards defined on paper manifest themselves in real life, looking at all aspects of the technology from customer experience to billing. Another top objective of the trials is to test the handoff between LTE and legacy 2G and 3G networks.

“We’ve had 12 years of 3G interworking and interoperability that has left us with a lot of people with a lot of know-how,” Clark says. “LTE is exactly the same. We have to learn again multiple tactics to ensure seamless roaming. We’re building that experience, building that knowledge base.”