Cash-strapped WiMAX operator Clearwire plans to raise more than $1.1 billion from a debt offering, as it works to maintain its head-start network advantage against looming competition from Verizon Wireless and T-Mobile USA.

The funding will help alleviate a cash crunch that has forced the company to lay off 600 workers, suspend the launch of Clear-branded WiMAX smartphones and threatened Clearwire’s ability to stay afloat.

Clearwire said earlier this year that it was considering selling some of its considerable spectrum assets to raise money, and it was also speculated that Clearwire may try to secure investment capital from T-Mobile USA, which lacks the spectrum to deploy WiMAX or LTE. Clearwire did not say whether such funding options were still on the tablet in its announcement today.

BTIG Research analyst Walter Piecyk says the funding will solve Clearwire’s near-term cash needs, but its long-term financing needs exceed the $1.1 billion that would be raised in its current debt offering. Piecyk speculated that today’s funding announcement may indicate that Clearwire’s first attempt to sell its spectrum was unsuccessful, though there’s still a possibility a spectrum sale could go through.

Separately, Clearwire said it had nominated three candidates to its board of directors to replace the Sprint executives who quit the board earlier this year, citing antitrust concerns. The nominees include consultant and former Embarq executive William Blessing, Springwell Capital Partners executive Mufit Cinali and Ericsson technical advisor Hossein Eslambolchi.

Clearwire is also moving to defend its WiMAX offering against Verizon Wireless’ LTE network, which will cover about one-third of the country when it launches on Sunday. In a blog post yesterday, Clearwire Chief Commercial Officer Mike Sievert pointed out that the company’s WiMAX unlimited plans were cheaper than Verizon’s tiered data plans and emphasized the advantages presented by the company’s spectrum holdings.