ry GHz ISM band, Bluetooth (named for Harald Bluetooth, mechanism for short text strings, such as phone num- an ancient Danish Viking king) is intended for low cost bers. With simplex data delivery, strategically placed and high interoperability. It is variously described as high-power transmitters and robust encoding, excellent a personal area network (PAN) or a cable replacement reliability was achieved. To compete with evolving cell technology, and should eventually be routinely embed- phone services in the 1990s, many paging systems were ded in cell phones, computers, PDAs, printers, and upgraded to provide two-way transfers and larger mes- a plethora of other products that today require a cable for sage sizes, making them similar in function to the ter- communications. Over time, more applications (as de- restrial packet systems described in the following. Now fined by Bluetooth "Profile" specifications) will be avail- the Motorola proprietary two-way paging protocol able in such diverse areas as video conferencing and ReFlex is the most widely deployed paging technology. automotive support. With many big names behind it Faced with the increased coverage and penetration of (Bluetooth Promoter companies are 3Com, Agere, cellular service, paging subscribership peaked in 1999 Ericsson, IBM, Intel, Microsoft, Motorola, Nokia, and [7]. Motorola, the traditional leader among paging man- Toshiba) and over 900 distinct Bluetooth [5] products (as ufacturers, has announced that it is transitioning away of this writing), Bluetooth has a lot of momentum. It also from both one- and two-way paging equipment in favor has detractors and competitors. of advanced cellular products and services [8]. Wireless local area networks Mobile satellite services The big news in wireless communications over the last The 1990s saw the design of a number of LEO and year or two has not been the much-hyped third genera- MEO (low and medium earth orbit) satellite systems. Of tion (3G) cellular, but rather wireless local area net- these, only