Praise for Fundamentals of WiMAX

250 Chapter 7 • Networking and Services Aspects of Broadband WirelessAKA/SIMTLSTokenCardExtensible Authentication Protocol (EAP)PPP 802.11 802.16Figure 7.12 IEAP architecturemanage this is called handoff management. Location management and handoff managementtogether constitute mobility management.7.4.1 Location ManagementLocation management involves two processes. The first process is called location registration, orlocation update, in which the MS periodically informs the network of its current location, whichleads the network to authenticate the user and update its location profile in a database. The databasesare usually placed in one or more centralized locations within the network. The location istypically defined by an area that encompasses the coverage area of one or more base stations.Making the location area large reduces the number of location updates. Having every MS, includingidle MS, report to the network every time it moves from the coverage range of one BS toanother could cause an unacceptable signaling load on the network, particularly when the basestations are microcells and when the number of subscribers is very large. To lighten this burden,service providers typically define larger location areas that cover several base stations. The frequencyof location update is also an important consideration. If location update is done infrequently,the MS risks moving out of its current location area without the network being notified,which leads to the network having inaccurate location information about the mobile. To supportglobal roaming, location management must be done not only within a single operator’s networkbut also across several operators tied through roaming agreements.The second process related to location management is called paging. When a request forsession initiation, e.g., incoming call, arrives at the network, it looks up the location database todetermine the recipient’s current location area and then pages all the base stations within andaround that area for the subscriber. Obviously, the larger the number of base stations within adefined location area, the greater the paging resources required in the network. Network operatorsneed to make the trade-off between using resources for location update signaling from allthe mobile stations versus paging over a large area.