mpetitive against large, multinational mobile carriers. Availabil- ity of spectrum and the ability to use spectrum more efficiently are important issues. Using spectrum more efficiently often depends on having state-of-the-art equipment based on new standards that are better able to carry the large quantities of video and e-mail that are transmitted to and from smartphones and tablet computers. One way that carriers add capacity to existing networks is by adding additional, smaller cell sites in densely trafficked metropolitan areas. They can also supplement capacity on mobile networks by using Wi-Fi services both within hot spots and in outside areas. (Wi-Fi is is an abbreviated form of the term "wireless fidelity.") Wi-Fi networks have the advantage of operating on unlicensed spectrum that governments make available at no charge. Determining cost-effective ways to add capacity and upgrade networks is the major challenge facing mobile carriers. Maintaining complex infrastructure with many thousands of cell sites is difficult and costly. Moreover, in countries where there are many competitors, prices tend to be lower, resulting in less capital available for carriers to invest in infrastructure. Mobile and Wi-Fi Networks FIRST-GENERATION ANALOG TECHNOLOGIES A wireless telephone network with connections to the Public Switched Telephone Net- work (PSTN) was first implemented in 1946 in St. Louis, Missouri. One transmitter and receiver covered the entire area, and all users shared the spectrum. This meant that only a limited number of simultaneous calls (25 to 35) could be placed on each city's mobile system. In addition to limited capacity, the quality of service was spotty, with considerable static and calls breaking up. Local telephone companies in each city later deployed this type of mobile system throughout the United States. These services were replaced by analog cellular services, which evolved into advanced generations of digital mobile services capable of carrying data as well as voice. The popularity of mo