ic for transmission. If the BS transmits a negative traffic indication to the MS, the BS will not transmit any DL traffic to the MS during the remaining part of the listening window, unless there are UL bandwidth requests or UL MAC PDUs sent from the MS which have not been 6.9 Mobility and power management processed. If a positive traffic indication is sent to a specific MS, the BS transmits at least one DL MAC PDU to the MS in the listening window. If the traffic indication message is lost or not properly detected by the MS, the MS would stay awake for the remainder of the listening window. If the MS receives any unicast data during the listening window, it assumes that the traffic indication had been positive. If neither the traffic indication message nor any unicast data in the listening window is received, the MS remains awake even after the listening window ends. The MS then sends a MAC control message (e.g., a signaling header) to inquire about the traffic indication. The BS responds to the MS by sending a unicast MAC control message containing the traffic indication. The operation of the IEEE 802.16m sleep mode with VoIP (persistent and non-persistent scheduling) and HTTP traffic models are shown in Figure 6-21 and Figure 6-22, respectively. It is shown that the MS power can be considerably conserved and the inactivity intervals of the mobile station can be dynamically adjusted for different types of user traffic [25]. 6.9.2 Idle Mode Operation Idle State provides a power saving mechanism for the MS by allowing the MS to become periodi- cally available for downlink broadcast messages (e.g., paging message) without registration with a specific BS. The network assigns Idle Mode MS to a paging group during Idle Mode entry or location update. This allows the network to minimize the number of location updates performed by the MS and the paging signaling overhead incurred by the BS. The base stations and Idle Mode mobile stations can belong to one or multiple paging groups. Idle mode mobile stations may be assig