 base stations in mobile systems. LMDS is weather dependent. The range is in the area of around 5 km. It is physically a point-to-multipoint network, and the available bandwidth depends on the number of subscribers connected at the same time. The bandwidth can be up to some tens of Mbit/s downstream. See Figure 13.40. 13.19.3 BLUETOOTH Bluetooth is a cable replacement technology for data and voice communication in the unlicensed 2.4 GHz frequency band. It is based on a low-cost short-range radio link, built into a microchip, and facilitating protected ad hoc connections for stationary and mobile communication environments. Some possible application areas are shown in Figure 13.41. Bluetooth technology allows for the replacement of the many proprietary cables that connect one device to another with one universal short-range radio link. For instance, Bluetooth radio technology could replace the cumbersome cable used today to connect a laptop to a cellular telephone. Printers, PDAs, desktops, fax machines, keyboards, joysticks and virtually any other digital device can be part of the Bluetooth system. Bluetooth radio technology also provides a universal bridge to existing data networks, a peripheral Access Network antennas Small and large businesses Fibre transport Base station LMDS antenna Central office Video Fibre transport Telephony Customer interface PC/Internet Base station Figure 13.40 LMDS network structure and services. LMDS can also feed radio base stations Data/voice Cable access points replacement Ad hoc networking Figure 13.41 Bluetooth applications interface, and a mechanism to form small private ad hoc groupings of connected devices away from fixed network infrastructures. Designed to operate in a noisy radio frequency environment, the Bluetooth radio uses a fast acknowledgement and frequency hopping scheme to make the link robust. Bluetooth radio modules avoid interference from other signals by hopping to a new frequency after transmitting or receiving a packet. Compared with other systems operating 