Praise for Fundamentals of WiMAX

9.7 Mobility Management 3279.6.2 Idle ModeIn mobile WiMAX, idle mode is a mechanism that allows the MS to receive broadcast DL transmissionfrom the BS without registering itself with the network. Support for idle mode isoptional in WiMAX and helps mobile MS by eliminating the need for handoff when it is notinvolved in any active data session. Idle mode also helps the BS to conserve its PHY and MACresources, since it does not need to perform any of the handoff-related procedures or signalingfor MSs that are in idle mode.For idle-mode operation, groups of BSs are assigned to a paging group, as shown inFigure 9.11. An MS in idle mode periodically monitors the DL transmission of the network todetermine the paging group of its current location. On detectings that it has moved to a new paginggroup, an MS performs a paging group update, during which it informs the network of thecurrent paging group in which it is present. When, due to pending downlink traffic, the networkneeds to establish a connection with an MS in idle mode, the network needs to page the MS onlyin all the BSs belonging to the current paging group of the MS. Without the concept of the pagingarea, the network would need to page the MSs in all the BSs within the entire network. Eachpaging area should be large enough so that the MS is not required to perform a paging areaupdate too often and should be small enough so that the paging overhead associated with sendingthe page on multiple BSs is low enough.During idle-mode operation, the MS can be in either MS paging-unavailable interval or inMS paging-listen interval. During the MS paging-unavailable interval, the MS is not availablefor paging and can power down, conduct ranging with a neighboring BS, or scan the neighboringBS for the received signal strength and/or signal-to-noise ratio. During the MS paging-listeninterval, the MS listens to the DCD and DL MAP message of the serving BS to determinewhen the broadcast paging message is scheduled. If the MS is paged in the broadcast pagingmessage, the MS responds to the page and terminates its idle-mode operation. If the MS is notpaged in the broadcast paging message, the MS enters the next MS paging-unavailable interval.9.7 Mobility ManagementIn WiMAX, as in any other cellular network, the handoff procedure requires support from layers1, 2, and 3 of the network. Although the ultimate decision for the handoff is determined by layer3, the MAC and PHY layers play a crucial role by providing information and triggers requiredby layer 3 to execute the handoff. In this section, we discuss the mobility-management-relatedfeatures of the WiMAX MAC layer.In order to be aware of its dynamic radio frequency environment, the BS allocates time foreach MS to monitor and measure the radio condition of the neighboring BSs. This process is calledscanning, and the time allocated to each MS is called the scanning interval. Each scanning intervalis followed by an interval of normal operation, referred to as the interleaving interval. In order tostart the scanning process, the BS issues a MOB_SCN-REQ message that specifies to the MS thelength of each scanning interval, the length the of interleaving interval, and the number of scanningevents the MS is required to execute. In order to reduce the number of times such messages as