Clearwire plans to conduct trials of LTE (Long-Term Evolution) network infrastructure, the company announced Wednesday.

The trials will take place in Phoenix in the fall of this year and early next year, Clearwire said. It will use equipment from Huawei Technologies and Samsung Electronics. It will work with dual-mode 4G chip maker Beceem and other partners to "determine the best methods for enabling end-user devices to take advantage of a potential multi-mode WiMax/LTE network," the company said. The trials will use the existing spectrum Clearwire already holds.

Clearwire is building a national WiMax network across the US, due to reach 120 million residents by the end of this year, but in recent months has given hints that it is open to adopting LTE. A large majority of the world's mobile operators that plan to build 4G networks plan to use LTE. The two technologies are fairly similar.

In the trials, Clearwire said it will test LTE on the common Samsung base station platform it is using for parts of its WiMax network.

Also on Wednesday, Clearwire announced a second-quarter net loss of US$125.9 million, or $0.61 per share, which includes $79 million in costs related to inventory allowance increases and write-offs. Clearwire had a net loss of $73.4 million, or $0.38 per share, in the second quarter of last year.

The carrier, which sells WiMax services on its own and through wholesale partners including Sprint Nextel, Comcast and Time Warner Cable, now has nearly 1 million retail subscribers and more than 1 million wholesale. It has raised its forecast for the end of this year to about 3 million total WiMax subscribers, up from an earlier forecast of just over 2 million, CEO Bill Morrow said on a conference call after the results were announced.

Clearwire remains committed to WiMax for its current build plan and is considering multiple options for the coexistence of WiMax and LTE on its network in the future, Morrow said. An LTE deployment could use off-the-shelf equipment and take advantage of Clearwire's existing backhaul and core network, he said.

"Part of our technical due diligence at Clearwire is to be ready to leverage a number of possible opportunities as we future-proof our network, and that's our goal with these tests," Morrow said.

If it deployed LTE, Clearwire could offer much higher speeds than any 4G rival because it has so much radio spectrum to use, between 20M bps (bits per second) and 70M bps, compared with 5M bps to 12M bps expected from other operators, Morrow said.

"We are the only service provider in the nation with the spectrum to conduct tests of this nature and on this scale," Morrow said. The pooled spectrum licenses of Clearwire and its majority owner, Sprint Nextel, total between 120MHz and 150MHz in most markets. A Sprint executive said recently that only about 30MHz is being used.

Clearwire will test both FDD (frequency-division duplex) and TDD (time-division duplex) technologies, according to CTO John Saw. With FDD, Clearwire could use two bands of 20MHz each, whereas competitors will be limited to 10MHz bands, he said.

Verizon plans to introduce an LTE service by the end of this year that reaches 100 million U.S. residents. It says it has seen downstream speeds between 5M bps and 12M bps in tests. AT&T plans to start offering LTE in 2011.

Clearwire's WiMax network reaches about 56 million people. The next major market to get the service will be Boston, beginning in a few weeks, Morrow said. Also on Wednesday, the company announced a new wholesale deal with Cbeyond, a small-business network services company, which will resell access to the WiMax network.