Wimax standards and Security The Wimax

FIGURE 6.11
Paging operation.

idle mode management purposes. If the idle mode timer has expired, the MS should reenter the network, because the paging controller has discarded all MS information.

When the MS initiates idle mode, it selects a preferred BS, which can be a current serving BS or the neighboring BS that has the best air interface DL properties. The MS synchronizes and decodes the DCD and DL-MAP from the preferred BS to extract the frame size and current frame number. The MS uses these to determine the time interval between the present and the next regular paging time from the preferred BS. This calculated time interval becomes an MS paging unavailable interval. During this interval, the MS can power down, scan neighboring BSs, reselect a preferred BS, conduct the ranging, or perform other activities for which the MS will not guarantee availability to any BS for DL traffic. At the end of the MS paging unavailable interval, an MS paging listening interval starts. During this interval, the MS receives an MOB_PAG-ADV message broadcasted by the BS. The MOB_PAG-ADV is a notification message for MSs in idle mode, which indicates the presence of DL

traffic pending or requests a location update. The paging listening interval has a frame unit of constant size and is repeated every paging cycle. After a paging listening interval, another paging unavailable interval begins. That is, the paging unavailable interval and paging listening interval are repeated alternately when the MS is in idle mode.

Idle mode is terminated when an MS reenters the network; when the paging controller fails to receive a response to paging messages and so realizes that the MS is unavailable, or when the idle mode system timer has expired. An MS terminates idle mode and reenters the network if it decodes an MOB_PAG- ADV message that contains an action code of enter network. In the event that an MOB_PAG-ADV message contains an action code of perform ranging, the MS updates its location to the network. In both cases, ranging code and transmission opportunities are assigned to the MS in the MOB_PAG-ADV message, so the MS can reenter the network or update its location by using the dedicated code and transmission opportunity without access collision.

2.