Spectrum auctions have become popular for selling radio spectrum after the success of the PCS Auction in 1994. Traditional methods have been replaced by auctions, raising billions of dollars globally. The PCS auction used a multi-round format, which made bidders compete for licenses individually, even if they preferred certain combinations. This led to risks for bidders who might end up winning less desirable licenses. Combinatorial auctions, allowing bids on combinations of licenses, show potential for better performance.