The aim of this chapter is to describe the multiple access of WiMAX/802.16. It will be seen that the mechanisms of multiple access and radio resource sharing are rather complex. It can be said that they are more complex than in other known wireless systems such as GSM, WiFi/IEEE 802.11 or even UMTS. Yet, globally, WiMAX multiple access is an extremely flexible F/TDMA (Frequency and Time Division Multiple Access).
The concept of a service flow on a connection is central to the operation of the MAC protocol. Service flows in the 802.16 standard provide a mechanism for QoS management in both the uplink and downlink. Service flows are integral to the bandwidth allocation process. In this process, an SS requests an uplink bandwidth on a per-connection basis (implicitly identifying the service flow). Bandwidth is granted by the BS to an SS in response to per-connection requests from the SS. WiMAX has been called a Demand Assigned Multiple Access (DAMA) system.
First, duplexing possibilities are described in Section 9.2. Physical frames are described in Section 9.3. WiMAX transmissions take place on totally dynamic bursts. The concept of multiple access is tightly related to burst profile. Frame contents are indicated in DL-MAP and UL-MAP messages, described in Section 9.4. The concept of a burst in the 802.16 standard and the way burst profiles are announced by the BS are detailed in Section 9.5. The specific case of the Mesh mode is tackled in Section 9.6.