An open broadband wireless network in the US moved one step closer to reality today.

The US Federal Communications Commission (FCC) said that bidding on the 700MHz C-block had surpassed the $4.6bn reserve, meaning that the winner of the auction will be forced to open the network to all mobile devices.

The top bid on the block at 5:30pm Pacific time on 31 January stood at roughly $4.71bn.

The identity of the top bidders is being kept secret to prevent collusion, but Google, AT&T and Verizon are among those expected to be taking part.

A simultaneous multiple-round system means that participants enter their bids during rounds.

At the end of each round, the highest bid is announced and a new round begins. The auction ends when a round closes with no new bids being entered.

While significant, the news was not unexpected. Google pledged in July to bid at least enough in the auction to meet the reserve price, but the final cost of the band is expected to be higher.

The search giant was one of the major backers of FCC president Kevin Martin's plan to open the spectrum to all devices.

Wireless carriers blasted the plan as 'Silicon Valley welfare', however, and accused the FCC of allowing Google to rig the auction in its favour.

Verizon went so far as to sue the FCC over the rule, although the case was dropped shortly after being filed.