Wimax standards and Security The Wimax

MOB_SLP-REQ

MOB_SLP-RSP

MOB_TRF-IND
(Negative)

MOB_TRF-IND
(Negative)

MOB_TRF-IND
(Positive)
BS

MS

Start frame


FIGURE 6.2
Operation of PSC I.

Then, the size of each sleep window increases binary exponentially every sleep but does not exceed the final-sleep window T_max. If the MS has reached T_max, it maintains the sleep window at T_max. That is, the size of sleep window in ith cycle is controlled by

=
_T 2ⁱ⁻¹T_min, if 2ⁱ⁻¹T_min < T_max
ⁱ T_max, otherwise

(6.1)

After each sleep interval the MS wakes up for a fixed-size listening interval, which generally has a short length. During each listening interval, the MS listens to the MOB_TRF-IND message that is broadcasted from the BS, which indicates whether any packets have arrived for the MS during the sleep inter- val. If this message delivers a positive indication, the MS exits sleep mode and enters wake mode to receive all the buffered packets from the BS. In addition, PSC I operation is finished when a BS transmits MAC data during any listen- ing window or when the MS transmits a bandwidth request with respect to the connection belonging to the current PSC.

2. Power-Saving Class of Type II

PSC II is recommended for UGS and real-time variable rate (RT-VR) connec- tions, such as VoIP and video-streaming. Figure 6.3 shows the basic sleep mode operation of PSC II. Similar to the case of PSC I, PSC II is activated by the exchange of MOB_SLP-REQ and MOB_SLP-RSP messages between an MS and a BS. For PSC II to work, it is necessary to set three parameters: initial-sleep window (T_min), listening window, and start frame number. Since real-time traffic is generated periodically, the sleep and listening windows in each sleep cycle have constant size. Therefore, the size of the sleep window is set to the initial-sleep window T_min at all times.


DL packet arrival