Sprint has made a buyout bid for the remaining stake of Clearwire that it does not already own, a move that would bolster the company’s spectrum portfolio.

The nation’s third-largest carrier currently owns 51 percent of Clearwire. In a filing Sprint made with the Securities and Exchange Commission, the company outlined a $2.1 billion bid for the other 49 percent at $2.90 per share.

Any deal between Sprint and Clearwire would have to win regulatory approval. It also would have to happen after Sprint finalizes its transaction with Japanese wireless carrier Softbank, which announced plans to buy a 70 percent stake in Sprint in October.

In a filing of its own, Clearwire confirmed that it is in “discussions with Sprint regarding a potential strategic transaction.”