Sprint is moving to buy an addition stake in Clearwire, giving it control of the broadband firm.

Sprint already owns 48 percent of Clearwire — a partnership that has allowed Sprint to build out the 4G network it needs to compete with AT&T and Verizon.

The news follows Monday’s announcement that Japanese carrier Softbank would buy a 70 percent stake in Sprint for $20.1 billion.

Analysts have expected Sprint to seek more control of Clearwire, especially since the Softbank deal puts the firm in a more secure financial position. Building high-speed networks is a key part of Sprint’s turnaround plan and a high priority for Softbank chief executive Masayoshi Son.

According to a regulatory document filed with the Securities and Exchange Commission,Sprint will buy 30.9 million shares of Class A stock and 2.7 million shares of Class B stock in Clearwire from Eagle River Holdings. Eagle River is owned by Clearwire’s founder, Craig McCaw.

As Dealbook reported, the transaction gives Sprint a majority 50.8 percent stake in the wireless network firm.

Clearwire declined to comment on the filing. Sprint officials could not immediately be reached for comment.