The FCC's Auction 105 continues into its third week Monday, having sold off more than $2.4 billion worth of priority access to the Citizen's Broadband Radio Service since kicking off on July 23.\n\n5G resources\n\nWhat is 5G? Fast wireless technology for enterprises and phones\nHow 5G frequency affects range and speed\nPrivate 5G can solve some problems that Wi-Fi can\u2019t\nPrivate 5G keeps Whirlpool driverless vehicles rolling\n5G can make for cost-effective private backhaul\nCBRS can bring private 5G to enterprises\n\n\nCBRS is a hot topic in the wireless world for several reasons, not least of which is its unique three-tiered access system that carries with it the potential for an almost endless array of new services. Enterprises can use the spectrum \u2013 which sits between 3550MHz and 3700MHz \u2013 to roll their own IoT networks, MSPs can offer various services like smart buildings, and the carriers can fold it into their networks.\nThe tiered system is what makes CBRS different from other regulated spectrum in the U.S. First, there are incumbent users in this frequency band, most notably the U.S. Navy, which uses it for radar. Incumbents always take priority over other users. The second tier is Priority Access, which is what Auction 105 covers. Priority Access Licenses (PAL) have to accept interference from incumbents, and must not interfere with their signals, but otherwise take priority over the third tier of users, called General Authorized Access. GAA users can still use CBRS frequencies, but have to give way to signals from PAL holders and incumbents.\nAll of this is managed by a spectrum access system, which is licensed by the FCC but operated by the private sector. The SAS uses environmental sensors to detect signals in a given CBRS access area and assigns channels and prioritizes traffic based on a given user's access tier. At least in theory, this ensures that any kind of CBRS user can access the spectrum without interference, subject to the rules involved.\n\nThe licenses being auctioned off are 10MHz wide, and each license gives its holder priority access to that piece of spectrum in a single U.S. county. Prices have ranged from $1,000 for remote, sparsely inhabited areas, up to $34 million and counting for urban cores like Los Angeles County and Chicago's Cook County.\nThe auction's structure means that it has an unusual end condition \u2013 according to the FCC, auction 105 will not end until there are no counties left in which demand for licenses exceeds total supply. Of the 3,233 counties in the U.S., just 240 meet that criteria, which implies that the auction is heading into its final stages.\nThe FCC will auction off seven PALs for each of those counties, meaning that a total of 22,631 total licenses were available at the outset. PAL holders can combine up to four of them at a time for an up to 40MHz-wide channel in a given county, and the licenses can be sold or traded.\nThis last point is significant, according to Don Price, senior vice president of technology at cloud-based carrier software provider Mavenir, since at least some of the 271 qualified bidders for Auction 105 may be participating with arbitrage in mind.\n"I think it's a pretty clever scheme they've come up with \u2013 either use spectrum or sell it," he said.\nBut the opportunity for enterprises and other kinds of service provider are equally compelling.\n"This is the first time that enterprises have had the opportunity to deploy a private 5G or LTE network without the traditional dependence on [mobile carriers]," Price said.