Wimax standards and Security The Wimax

QoS Support

802.16e defines new scheduling mechanisms: the extended real-time polling service (ErtPS), which is based on two services defined in 802.16-2004; the unsolicited grant service (UGS); and the real-time polling service (rtPS). ErtPS is similar to UGS in providing unicast grants, thus saving the delay incurred for requesting the bandwidth. However, ErtPS allocations are dynamic as rtPS while UGS allocations are fixed. The ErtPS is introduced to support real- time service flows that generate periodical variable sized data packets. Thus, ErtPS is especially important to support VoIP, since it allows for managing traffic rates and improves latency and jitter.

2. 
   Handover Support
   

802.16e includes new MAC-level request/grant mechanisms to achieve sim- ilar seamless mobility as that provided for cellular users. 802.16e includes fast base station switching and hard handoff mechanisms for intercell and intersector handover. In 802.16e, handoff process may be triggered for two reasons. One is due to fading of the signal, interference level, etc. within the current cell or sector. The other is due to the fact that another cell can pro- vide a higher level of QoS for the mobile station (MS). Furthermore, 802.16e supports macrodiversity handovers and intertechnology roaming. Macro- diversity handovers support handoffs between different sized cells, while intertechnology roaming addresses MS handoffs from BS to backhaul or wired network by providing roaming authentication mechanisms.

3. 
   Power Management
   

Power management is a critical process for mobile applications to enable effi- cient operation of the MS. 802.16e defines two power management operations, sleep mode and idle mode.
Idle mode operation is carried out by MS when the MS does not intend to register to a specific BS as the MS traverses a region covered by multiple BS. The advantage of idle mode for the BS is to avoid multiple handoffs and other normal operations while the SS is traversing the region, and for the BS and network is to avoid unnecessary handoffs from an inactive MS. When the MS enters the idle mode, it needs to periodically check for broadcast messages sent by the BS to see if new downlink frames have been sent to it (WiMAX Forum, 2006).

Sleep mode operation is a state in which MS sends a request to be unavail- able to the BS. If the BS responds with approval, the MS is provided with a sleep interval time vector that determines the length of the sleep mode period. The benefit of the sleep mode operation is to minimize MS power usage and utilization of the air interface resources of the BS. While the MS is in the sleep mode, the MS scans other BSs to collect information required for handover during the sleep mode.