Wireless LAN Technology

WIRELESS LAN TECHNOLOGY SPREAD SPECTRUM LAN Configuration Except for quite small offices, a spread spectrum wireless LAN makes use of a multiple- cell arrangement Adjacent cells make use of different center frequencies within the same band to avoid interference. Within a given cell, the topology can be either hub or peer to peer

WIRELESS LAN TECHNOLOGY In a hub topology, the hub is typically mounted on the ceiling and connected to a backbone wired LAN to provide connectivity to stations attached to the wired LAN and to stations that are part of wireless LANs in other cells. all stations in the cell transmit only to the hub and receive only from the hub. Alternatively, and regardless of access control mechanism, each station may broadcast using an omnidirectional antenna so that all other stations in the cell may receive; this corresponds to a logical bus configuration.

WIRELESS LAN TECHNOLOGY A peer-to-peer topology is one in which there is no hub. A MAC algorithm such as CSMA is used to control access. This topology is appropriate for ad hoc LANs. Transmission Issues characteristic of a wireless LAN is that it be usable without having to go through a licensing procedure The licensing regulations differ from one country to another, which complicates this objective.

WIRELESS LAN TECHNOLOGY Within the United States, the Federal Communications Commission (FCC) has authorized two unlicensed applications within the ISM band: spread spectrum systems, which can operate at up to 1 watt, and very low power systems, which can operate at up to 0.5 watts. In the United States, three microwave bands have been set aside for unlicensed spread spectrum use:

WIRELESS LAN TECHNOLOGY MHz (915 MHz band), GHz(2.4 GHz band), and GHz (5.8 GHz band). Of these, the 2.4 GHz is also used in this manner in Europe and Japan.

WIRELESS LAN TECHNOLOGY Narrowband Microwave LANS The term narrowband microwave refers to the use of a microwave radio frequency band for signal transmission, with a relatively narrow bandwidth- just wide enough to accommodate the signal. Licensed Narrowband RF Microwave radio frequencies usable for voice, data, and video transmission are licensed and coordinated within specific geographic areas to avoid potential interference between systems.

WIRELESS LAN TECHNOLOGY Within the United States, licensing is controlled by the FCC. Each geographic area has a radius of 28 km and can contain five licenses, with each license covering two frequencies. Motorola holds 600 licenses (1200 frequencies) in the 18-GHz range that cover all metropolitan areas with populations of 30,000 or more. A narrowband scheme typically makes use of the cell configuration Adjacent cells use nonoverlapping frequency bands within the overall 18-GHz band.

WIRELESS LAN TECHNOLOGY Unlicensed Narrowband RF In 1995, RadioLAN became the first vendor to introduce a narrowband wireless LAN using the unlicensed ISM spectrum. This spectrum can be used for narrowband transmission at low power (0.5 watts or less). The RadioLAN product operates at 10 Mbps in the 5.8-GHz band. The product has a range of 50 m in a semiopen office and 100 m in an open office.