 Direct Broadcast Satellite (DBS), Free Space Optics, and virtual fiber (VF). Wireless systems increasingly offer more options, each of which prom- ises greater speeds, supports QoS, and operates over a wider range of footprints. It is likely that within the next couple years, more than half of the new fixed phone lines installed worldwide each year will be wireless. Fixed wireless is a strong contender to fill the gap where existing wiring is not up to the job or where there is no wiring at all. For example, about one in five people in the United States lives in an area that is too remote to receive any type of fast wireline access to the Internet, and this is an even more prevalent situation in vast but not densely popu- lated parts of Africa, Asia, Eastern Europe, and Latin America. Further, millions of people work in modest industrial parks that do not have fast access and are not able to receive DSL, cable, or fiber connections. Wireless broadband can often be used in such situations. The cost of wireless links has been halving every seven years, and the data capacity of these links has been doubling every three years. These factors com- bined mean that the cost-to-capacity ratio in wireless communications has been dropping by 50% about every two years. For wireless links, the construction costs account for approximately 20% of the total installation cost, and equipment accounts for the other 80%. Wireless systems often operate in a point-to-multipoint mode. The antenna communicates with several different clients' antennas, usually installed within a well-defined region. Because the air is a shared medium, like cable, the maximum transmission rate that can be provided to any one client decreases as more clients are served. Clients that need the greatest bit rate obtainable from a system (e.g., an ISP) may need to arrange for a point-to-point system. Because there are now so many wireless alternatives available, Part IV of this book is dedicated entirely to wireless communications Chapter 13, "Wireless Commun