less medium of indoor offices is characterised by signal fading because of the presence of many objects such as chairs, desks, partitions, furniture, false walls and SO on. Moreover, office workers both reflect and absorb electromagnetic waves. The resulting signal fading required very high received signal to noise ratio to maintain an acceptable communications quality, making it impractical to use existing conventional wireless data communication techniques. A number of systems were developed towards the end of the 1980s to facilitate wireless local area networking. WaveLAN, an early system developed by NCR and later on Lucent, used a bandwidth of 26 MHz in a 900 MHz unlicensed band for a 2 megabits per second (Mbps) maximum transmission rate in air. As the fading channel causes the car- rier phase to vary during transmission, a differential modulation technique was used. Another system was Motorola's Altair which operated in the 18 GHz band. Both systems used the channel sense multiple access (CSMA) technique to facilitate sharing of com- munications resources. A test by PC Magazine in 1992 showed that both systems could provide throughput rates of approximately 500 kbps with several active users, which compared well with faster Ethernet transmission rates of approximately three times. Test reports from 1999 by Network World show WaveLAN transmission rates of 1.15 Mbps, an improvement over the 1992 results [3]. While these systems realised wireless indoor data communications, clearly usage of the available spectrum was inefficient (Table 10.1). Broadband Telecommunications Technologies and Management Table 10.1 Wired and wireless local area throughput figures (in megabits per second) in 1992 [4] System 1 User 2 Users 3 Users 4 Users Ethernet WaveLAN Altair Wireless local area network (LAN) standards have been developed under the auspices of the IEEE since the early 1990s and under the 802.11 series. Many technological advancements such as higher processing power devices, more advanced antennas and modulation te