The Google (NSDQ: GOOG) relationship with Clearwire (NSDQ: CLWR) goes fairly deep. Google is investing $500 million into the new Clearwire-Sprint (NYSE: S) venture and will provide search and other applications on top of an advertising platform for the WiMax network. But it will not allow Clearwire to use its fiber optic network for cheap backhaul, Unstrung reported. This may seem a bit esoteric, but in order to provide a mutli-megabit wireless network, there has to be a big enough pipe to haul all the traffic back to the Internet. Clearwire will be relying on some of Sprint’s assets to accomplish this, and build out a microwave network, but it seemed like Google could have been another big source since it has been stock-piling unused fiber around the country for awhile now. Unstrung said a Google spokesman said that isn’t the case. “At this time Google’s involvement in Clearwire is limited to the terms of its investment and does not include providing network infrastructure,” wrote Google’s Andrew Pederson in an email.