Wimax standards and Security The Wimax

FIGURE 4.2
WiMAX P2MP network.


P2MP network has one BS and multiple SSs. The BS is the central control point and regulates all the traffic on the network. IEEE 802.16 is a connection- oriented service with which each SS needs to establish a service connection to the BS. An SS first sends a message to the BS for requesting services on the network. The connection between the BS and an SS could be either DL (from BS to SS) or UL (from SS to BS). The protocol stack of WiMAX is illustrated in Figure 4.3 and the connection-oriented service is defined in the MAC sublayer. The multiple access schemes in WiMAX include both frequency division duplex (FDD) and time division duplex (TDD). The QoS discussion in this chapter is on TDD only because TDD is more flexible than FDD for QoS implementation. Within a given frequency bandwidth, IEEE 802.16 supports an adaptive scheme to allocate time slots on UL and DL channels as illustrated in Figure 4.4. Each frame is broken into multiple time slots, and the BS can dynamically allocate different time slots for DL and UL. In the case of Inter- net application where the data transfer is mostly from the Internet down to a subscriber, the BS allocates more time slots for DL and fewer for UL. For VoIP
applications, the BS allocates the same number of time slots for DL and UL.

Upper layer
Service specific convergence sublayer
MAC sublayer common part
Security sublayer
Transmission sublayer
QPSK	QAM-16	QAM-64	QAM-256