The MAC as the "Smarts" for the Physical Layer

The WiMAX MAC provides intelligence for the PHY and ensures a number of QoS measures not seen on other wireless standards. Perhaps its greatest value is providing for dynamic bandwidth allocation that defeats the usual degradations of wireless services jitter and latency.

The WiMAX MAC protocol was designed for point-to-multipoint broadband wireless access applications. It addresses the need for very high bit rates, both UL (to the BS) and DL (from the BS). With WiMAX, unlike with its Wi-Fi predecessors, access and bandwidth allocation algorithms accommodate hundreds of terminals per channel, and multiple end users might share those terminals. End users require services that are varied in nature including legacy TDM voice and data, IP connectivity, and packetized VoIP. To support these various services, the WiMAX MAC accommodates both continuous and bursty traffic. Additionally, these services expect to be assigned QoS parameters in keeping with the traffic types.

The WiMAX MAC protocol supports a variety of backhaul requirements including both ATM and packet-based protocols. Convergence sublayers map the transport-layer-specific traffic to a MAC that is flexible enough to efficiently carry any traffic type. The convergence sublayers and MAC work together using payload header suppression, packing, and fragmentation to carry traffic more efficiently than the original transport mechanism.

The MAC and WiMAX Architecture

The WiMAX DL from the BS to the user operates on a point-tomultipoint basis as illustrated in Figure 3-1. The WiMAX wireless link operates with a central BS with a...