Clearwire and China Mobile want to use their respective unpaired spectrum holdings in the 2.5 GHz band for TD-LTE, but there's a catch: The development of equipment and devices for TD-LTE lags behind FDD-LTE, the standard used in Verizon Wireless and AT&T's LTE networks.

To that end, Clearwire and China Mobile began work in September on devices compatible with the standard. Today, the struggling WiMAX provider and the world's largest wireless operator announced that they are taking their partnership a step further with joint testing.

The goal is to make devices running on Clearwire's planned TD-LTE network in the United States interoperable with China Mobile's TD-LTE network in Asia.

If successful, the effort will expand the potential number of users for the technology and improve economies of scale. This, in turn, will help lower prices for network gear and handsets, making the technology more attractive to other operators with unpaired spectrum holdings in 2.3-2.7 GHz and some other bands.

"Close collaboration with global wireless leader China Mobile accelerates the development of multi-mode, multi-band TD-LTE and LTE FDD devices and provides the common test specifications OEMs, ODMs, chipset vendors and other critical component manufacturers need to rapidly develop and commercialize products to serve this massive global marketplace," Clearwire CTO John Saw said.

China Mobile wants TD-LTE to become a key global standard for unpaired spectrum instead of WiMAX, which also runs on unpaired spectrum. The technology is of special importance after the Chinese government failed to gain widespread adoption of its TD-SCDMA standard for 3G.

Clearwire, China Mobile and other operators participating in the Global TD-LTE Initiative will set up labs this month using joint specifications on testing and interoperability. Clearwire says its testing will take place in Herndon, Va., and Phoenix.

China Mobile will run tests in Beijing and some of the other cities where it is conducting trials of TD-LTE. The joint test platforms will be open to device interoperability testing by "key participants" later this year.

The strengthened ties with China Mobile come as Clearwire is looking for a new strategic investor. The company landed some much-needed funding from Sprint last year but is still looking for more cash to keep itself going and pay for the construction of its TD-LTE network.

Instead of shuttering its WiMAX network, Clearwire wants to overlay key portions of its legacy infrastructure with TD-LTE. Sprint plans to lease capacity on Clearwire's network to add capacity to its own LTE service, and the companies are coordinating construction of their networks.