military systems, slow adoption of the technology. Over 26 million Wi-Fi which typically use specialized proprietary designs in devices are expected to ship in 2003 [6]. restricted frequency bands. Another exception is spe- cialized private systems, used for such applications as voice dispatch and remote asset monitoring. These sys- Wide area systems tems operate in licensed frequency bands and generally consist of several tower sites and many fixed or mobile Wide area mobile systems generally sacrifice throughput subscriber units operated by a corporate or government for longer propagation paths, user mobility, decreased entity. They go by many different names: SMR (spe- device size, and increased coverage. Paging and cellular cialized mobile radio), MAS (multiaddress system), communication systems are prime examples of wide area trunked radio, PMR (private mobile radio), and others. systems. Without the economies of scale of their mass market CHAPTER Introduction counterparts, the specialized radio systems are often Voice a generation behind comparable commercial equipment, Cellular is the most obvious wireless voice technology. with many still employing analog modulation, for ex- SMR and satellite systems support vertical voice markets, ample, long after cellular has migrated to digital. and various technologies (including Bluetooth) are used for short-range cordless telephony. Efforts are underway to Terrestrial packet systems support voice services over WLAN technologies. Several proprietary systems have been deployed to pro- vide general-purpose packet data services. Mobitex, Messaging originally developed by Ericsson, and Ardis, now oper- Communication via short wireless messages has echoed the ated by Motient, provide shared channels operating at popularity of e-mail in a wired environment. Most usage of about 10 to 20 kbps. Wireless e-mail (similar to two-way the Mobitex, Ardis (packet services), and ReFlex (paging) paging) has been the dominant application for these systems today consists of messaging t