 option, the downlink and uplink are on separate RF channels. For the half-duplex option, the SS does not transmit and receive simultaneously. Figure 13.9 shows FDD burst framing and how it allows scheduling flexibility. Figure 13.10 shows FDD downlink subframe. Table 13.1 gives an overview of IEEE 802.16 modulation rates and channel sizes. It shows a flexible plan allowing manufacturers to choose according to spectrum requirements. 13.6.1 IEEE 802.16 MAC Requirements The 802.16 MAC design addresses network access in the wireless environment affording very efficient use of the spectrum. Its broadband services support high bit rates and a Scope of standard CS SAP Management Entity Service Specific Convergence Sublayer Service Specific Convergence Sublayers MAC SAP MAC Common Part Sublayer (MAC CPS) Management Entity MAC Common Part Sublayer Privacy Sublayer Security Sublayer PHY SAP Physical Layer Management Entity (PHY) PHY Layer Management Plane Data/Control Plane Figure 13.6 IEEE 802.16 reference model. 13.6 IEEE 802.1 16 STANDARD n PS = (Symbol Rate X Frame Length) / 4 Downlink Subframe Uplink Subframe Adaptive PS n-1 Frame j-2 Frame j-1 Frame j Frame j+1 Frame j+2 Figure 13.7 A typical IEEE 802.16 TDD frame, 10-66 GHz. TDM Portion Broadcast Control DIUC a DIUC b DIUC C DIUC = 0 Tx/Rx Transition Gap DL-MAP UL-MAP Figure 13.8 TDD downlink subframe. DIUC, downlink interval usage code. broad range of QoS requirements. Its broadband services include IPV4, IPV6, ATM, and Ethernet. It has an independent protocol engine. The MAC is connection-oriented and can operate in difficult user environments with hundreds of users per channel. The core MAC protocol engine is a new design for the wireless MAN. We will find the familiar SDUs (service data units), which are data units exchanged between adjacent layers, and PDUs (protocol data units), which are data units exchanged between peer entities. There is a unidirectional flow of MAC PDUs on a connection that provides a particular QoS. It is uniquely identified by an SFID (