Clearwire LLC (Nasdaq: CLWR) is looking to overtake 4G rivals by deploying a data-friendly Long Term Evolution Time Division Duplex (LTE TDD) overlay on its WiMax network that has achieved download speeds exceeding 100 Mbit/s in initial tests.

The catch is that the Kirkland, Wash.-based operator needs to raise "substantial additional capital" before it can say when it might deploy the technology.

"We have not announced a date," a company spokesman tells LR Mobile. "Rollout would be contingent on additional funding."

Nonetheless, Clearwire Chief Operating Officer Eric Prusch was on the company\'s second-quarter call Wednesday to sell the benefits of an LTE overlay, which would run concurrently with the WiMax network. He said it will cost $600 million to roll out and that "a typical market overlay should take 12 months." The company would deploy the new technology in high-traffic urban areas first.

So, despite the current funding crunch, Prusch says that this is the most economical way to deploy a 4G network with what would likely be cutting-edge download speeds.

That\'s because of LTE TDD. Time-division networks use one synchronized channel for upstream and downstream signals, rather than the more common frequency division (FDD) technology, which uses two channels separated by a guard band. TDD is well suited for the bursty nature of data traffic, whereas FDD lends itself to voice calls.

Clearwire would likely be the first major carrier to use LTE TDD technology in the U.S. It has been testing the technology with Huawei Technologies Co. Ltd. in Phoenix for months now.

The LTE move could potentially help Clearwire get ahead of the pack as the world starts to move to 100Mbit/s "LTE Advanced" next year, says Heavy Reading Senior Consultant Berge Ayvazian.

"The key is that Clearwire will be overlaying the LTE TDD on its existing WiMax network, and leveraging its deep spectrum position and participation in the GTI TDD ecosystem with 20-plus other operators to help drive network and device convergence through LTE Advanced beginning in 2012," he says.

He also sees the move as an attempt by Clearwire to get a new bargaining chip in its dealings with majority owner Sprint Nextel Corp. (NYSE: S) after Dan Hesse and company inked an LTE deal with LightSquared .

"Given the response of Standard & Poor’s and Wall Street to the Sprint/LightSquared deal, the Clearwire announcement to overlay LTE TDD on its existing WiMax network should be viewed as a counter to Sprint\'s Network Vision," Ayvazian notes.

"Clearwire is portraying Sprint\'s Network Vision as \'too expensive\' and too late. This approach is intended to differentiate Clearwire\'s plans from LightSquared and enhance their negotiating position with Sprint."