Google says the "new" Clearwire LLC venture will not be using its dark fiber to backhaul parts of a planned Mobile WiMax network in the U.S. as the technology is deployed through 2010 and beyond.

The recent $500 million investment by Google into a "new" Clearwire venture threw up the intriguing prospect that the operator might be able to use Google's dark fiber resources to reduce the cost of connecting its cell sites back to the wired Internet. Google, however, got back to Unstrung on Monday to say that such a move isn't in the cards.

"At this time Google's involvement in Clearwire is limited to the terms of its investment and does not include providing network infrastructure," says company spokesman Andrew Pederson in an email.

Google will act as the default search engine for devices on the Clearwire network and develop mobile applications around the service as well as investing $500 million in the venture.

The search giant has been acquiring fiber in the U.S. and beyond for several years. (See Google's Own Private Internet.) The firm says it uses the fiber to interconnect server farms and establish "peering" relationships with major operators. (See Google: Dark Fiber Story Not So Dark .)

Clearwire will still use other fiber in some markets for deploying the mobile WiMax network. CTO John Saw told us last week that the operator will try and use fiber in markets where it makes "financial sense." (See Clearwire's Backhaul Bet.)

Generally, however, Clearwire is focusing on building out more of its microwave backhaul network to support the multi-megabits WiMax base station transmission speeds. The operator already claims to have the largest wireless backhaul network in the U.S. The Kirkland, Wash.-based company says that it will be able to build out a complete network covering up to 140 million Americans for around $5 billion using the wireless links. (See CLWR: Where It's at With WiMax.)

Unstrung has reported recently on the problems carriers, particularly in the U.S., could face with the move to so-called fourth generation (4G) network technologies that support data download speeds of 100 Mbit/s over-taxing the leased-line T1 copper connections that many rely on. (See 4G Backhaul: A Problem for All?)

Sprint Nextel Corp. provided a graphic illustration of the problem last month as it delayed the launch of its initial Xohm WiMax sites, which will eventually form part of the "new" Clearwire network, because of backhaul and billing problems. (See Sprint Quiet on WiMax Launch Date.)

— Dan Jones, Site Editor, Unstrung