, although one competing standard was initially developed by the IEEE. It is possible that the IEEE 802.16 standard, better known as WiMAX, may still serve a niche market of fixed wireless access in a number of markets. However, it is likely that one technology will capture the lion's share of the market. All WAN standards operate within licensed bands and are not considered as personal communications systems (Figure 12.1). Industrial, Scientific and Medical Frequency Band As discussed above, ISM frequency bands were initially set aside internationally for industrial, scientific or medical applications. Originally no communication was allowed within these bands to prevent mutual interference between devices. Applications included microwave ovens (2.45 GHz), plastic welding and physiotherapy diathermy machines. ISM bands cover a range of frequencies in different spectrum bands: from a 14 kHz bandwidth at 13.553-13.567 MHz, to a very wide bandwidth of 2 GHz at 244-246 GHz. Since the 1980s Personal Wireless Communications Systems Table 12.2 ISM frequency bands for telecommunications Frequency range Bandwidth (MHz) Region 433.05-434.79 MHz 902.0-928.0 MHz Americas 2.4-2.5 GHz Worldwide 5.725-5.875 GHz Worldwide 61.0-61.5 GHz Subject to acceptance Source: Electronic Code of Federal Regulations [5]. five ISM bands have been opened internationally to telecommunications applications as shown in Table 12.2. These are used as unlicensed bands where personal communications systems may operate. The first two at 400 and 900 MHz are used by analogue cordless tele- phony systems. PAN and LAN standards such as Bluetooth, ZigBee and Wi-Fi, operate within the 2.4 and 5 GHz bands. The millimetre wave frequency of 61 GHz is a newly proposed addition. Although devices can operate in the ISM band without license, they still need to abide by power emission regulations issued by the relevant authorities in different countries. For example in the United States the Federal Communications Commission (FCC) mandates that the transmission pow