 mix of five private companies including American Movil, a cellular company owned by Mexican mogul Carlos Slim and his family. The American Movil spectrum is used in Puerto Rico. In 2017, the FCC held a reverse auction of 600Mhz spectrum. T-Mobile won the largest percentage of this spectrum. AT&T and Dish Network won lesser amounts. AT&T subsequently began selling the spectrum it won because it purchased FirstNet for its nationwide spectrum. Other winners included U.S. Cellular and Comcast. Verizon did not bid, possibly because it is concentrating on building out a network of small cells using GHz spectrum able to carry large amounts of data. Enhancing Spectral Efficiency to Increase Capacity The ability to carry more traffic within a given amount of spectrum is crucial to keeping up with the growing amounts of mobile data traffic. Carrying more traffic www.TechnicalPDF.com using the same amount of spectrum is called spectral efficiency. Each successive generation of wireless protocols is more spectrally efficient than the previous one. For example, 4th generation (4G) wireless technologies are capable of carrying more high-speed wireless data and video than third-generation (3G) technologies and 5G is expected to be more spectrally efficient than 4G. The successive spectral efficiency in newer generations of mobile services is gained by building more efficient antennas, faster chips in radios located at cell sites and in users' mobile devices. Profits from Unused Spectrum on the Secondary Market In addition to obtaining spectrum at auctions, carriers purchase spectrum on the secondary market from organizations that purchased it at earlier auctions but either did not build a network on it or were unsuccessful in their service offerings. For example, beginning in 2011, Dell computer owner, Michael Dell bought up TV and radio stations for the value of their spectrum, which he sold in the 2016 incentive auction for billions of dollars. Taxpayers currently receive no revenue from the sale of unused spectrum by non-go