5.10 Mobile WiMAX: 802.16e
To improve the position of WiMAX in competition with UMTS and other 3G standards, the IEEE and the WiMAX forum have decided to enhance the standard with mobility functionality. As described in the following section, the 802.16e standard introduces a number of enhancements on all layers of the protocol stack. On the physical layer, a new multiple access scheme is used. On the MAC layer, many additions were made to enable true mobility for wireless devices in between networks. In addition, efficient power management functionalities for battery-driven devices have been defined. As client devices are enabled to roam through the network, they are now referred to as mobile stations. For national and international roaming, a network infrastructure has been standardized to support mobility management and subscriber authentication over network boundaries. These functions are outside the scope of the 802.16 standard, as it only describes the air interface. The WiMAX forum thus extended its work beyond promoting and certifying the technology and established a networking group to define and standardize how the network behind the base stations supports roaming and subscriber management. By specifying an end-to-end network topology, large and even nationwide networks can be built with components from different vendors.
5.10.1 OFDM Multiple Access for 802.16e Networks
For the 802.16e standard, the IEEE decided not to use the 256-OFDM PHY used in first-generation networks. ...