 as the existence of a large number of reflections and transmission paths. These lead to large signal variations and multi-path fading. As discussed in Chapter 10, fading results in highly degraded quality of service, and must be compensated by power control and diversity reception techniques. However, compensation techniques are complex and are not readily practical for inexpensive, simple personal communications systems. Moreover, wireless digital communication techniques were nascent and signal processing requirements for fading compensation well beyond what early devices could deliver. From a business point of view, personal consumer communications devices needed to be of a small size and low cost to allow for integration with and/or within other consumer devices such as mobile phones and PCs. To ensure maximum market size, international standards were needed. Therefore, while most of these standards were developed based on proprietary technologies, standards and global consortia had to be developed. International standards further required harmonisation of unlicensed bands, which required governmental policy cooperation. Considering all these challenges it is surprising that working solutions could be devel- oped in a very short space of time. The first IEEE 802.11 standard for a wireless local area Personal Wireless Communications Systems network (LAN) was published in 1997 and inexpensive access points and data cards were available in the market as early as 1998. The development of Bluetooth technology by Ericsson in the mid-1990s was another solution for inter-device wireless connectivity and soon commercial devices were offered to the market. A number of technologies have been developed since for short- and mid-range wireless communications using a shared spec- trum. Wireless LAN and Bluetooth remain the most successful, although a more recent addition, ZigBee, is finding a niche. IEEE Networking Our wireless connectivity needs can be defined over a wide range of distances and applica- tions: from near-f