Spectrum and existing infrastructure are the keys to Clearwire's plans. It holds more than 100MHz of spectrum in many metropolitan areas, typically exceeding any other mobile operator's holdings. Clearwire said it would start out using 20MHz for the LTE networks, twice what Verizon Wireless is using in most areas, and would add to that as needed. It could make extensive use of existing base stations, wired backhaul and leases on cell towers, though in some cases backhaul would have to be expanded and radios and antennas added on top of the new line cards, executives said.

As expected, the company plans to use TDD (time-division duplex) LTE, which uses a single channel for upstream and downstream traffic. Verizon and other early adopters of LTE use FDD (frequency-division duplex), which uses two separate channels. But Clearwire expects that within a year, almost all LTE handsets will be equipped for use of both TDD and FDD networks. Some of the world's largest carriers are committed to TDD-LTE and to the same frequency band, around 2.5GHz, where Clearwire has its holdings, said John Stanton, Clearwire's acting CEO.

Though the company posted another operating loss for the second quarter, it expects to have positive cash flow by early next year, ahead of its previous forecasts, executives said on a conference call. Clearwire has enough capital on hand today to continue operating for at least 12 months, they said. The company continues to look for outside sources of funding in addition to the capital it needs to raise for the LTE rollout.

In the second quarter, pro forma revenue was $293.7 million, up 151 percent from last year's second quarter. Clearwire posted a net gain of about 1.54 million subscribers, representing a gain of 39,000 customers for its own Clear service and 1.5 million users for the services of its partners, such as Sprint and Comcast.

In after-hours trading late Wednesday, Clearwire's shares on the Nasdaq (CLWR) were down $0.19 at $2.28.