ds Defined in AWMA non-collaborative approach recommended are adaptive frequency hopping, adaptive packet selection and transmit power control. A collaborative TDMA mode termed alternating wireless medium access (AWMA) has also been recommended, where the available transmission time is divided between WLAN and WPAN transmissions, as shown in Figure 9-3. Because of the need for a communication link between the two networks, this collaborative mechanism can only operate if the two radios are located in a single host device - for example a laptop enabled for both Bluetooth and Wi-Fi. A further collaborative mechanism is termed deterministic frequency nulling. The concept here is to reduce the narrow band interference from the 1 MHz wide FHSS signal by nulling out this frequency at the 802.11b receiver. To do this the 802.11b receiver has to follow the hopping pattern and timing of the Bluetooth transmitter, and this is achieved by embedding a Bluetooth receiver within the 802.11b receiver. Although the Task Group is now officially in hibernation, a range of publications can be found at http://grouper.ieee.org/groups/802/15/pub. If Bluetooth interference is suspected as a cause of WLAN performance problems, an analyser such as AirMagnet's free BlueSweep utility can be used to identify active devices within the range of the WLAN operating area. Summary of Part III The implementation of a successful and secure wireless LAN requires attention to a broad range of issues. Chapter Nine Insight into the wide variety of technologies applied at the PHY and MAC layer in the different 802.1 WLAN standards provides the basis for understanding the technical capabilities of each standard and the reason behind their specific limitations, enabling the most appropriate technology to be selected for any WLAN application. An understanding of the basic RF propagation concepts, described in Part II, provides the background to the issues that need to be considered when selecting antenna equipment and planning the physical WLAN layout for 