The popularization of computers at home created the need to interconnect several devices, such as desktops, switches, laptops, printers, cable modems, and so on. WLAN (Wireless Local Area Network) became attractive as it did not require wires and gave mobility to laptops, but to be implemented it required the RF spectrum.
The RF spectrum is regulated by government agencies, requiring that users obtain licenses to use it. Industries, universities and radio amateurs were assigned unlicensed bands for use in laboratories and short range communications, as is the case of the ISM (Industrial, Scientific and Medical Equipment) bands and the U-NII (Unlicensed National Information Infrastructure) band. These bands were used in microwave ovens, car alarms, wireless phones and other similar devices. Over time, regulators conceded that these bands could also be used for short range broadband communications. ISM bands are listed in Table 12.1 and UNII bands in Table 12.2. UNII bands are subject to DFS (Dynamic Frequency Selection) because they are shared with radar operations and have to switch frequencies if a radar signal is detected.
|ISM band as per ITU-R|