ABSTRACT
Differentiated traffic treatment is a key aspect in providing heterogeneous media flows with quality of service (QoS) at a network level. Heterogeneousmedia may have very different QoS requirements and may ask the network for very different levels of throughput, delay, jitter, and packet losses. This gives rise to the significant challenge of designing a QoS-aware broadband wireless network, and worldwide interoperability for microwave access (WiMAX) is one of the best candidates to play this role. It follows that the success of WiMAX strongly relies on how the underlying network can meet individual QoS requirements of a wide variety of multimedia applications. Integration of a QoS framework into the Medium Access Control (MAC) layer of the IEEE 802.16 protocol [1] is the WiMAX choice for such an endeavor. In the WiMAX QoS framework, a very critical role is played by the packet scheduler within the base station (BS). This component is expected to coordinate all QoS-related functions to provide differentiated QoS guarantees and fair resource allocation to multiple users andmultiple media flows. Themost challenging aspect in this context originates from the wireless nature of the WiMAX channel, which may impair the scheduler QoS-support capability and may invalidate its theoretical fairness in assigning the available bandwidth. This suggests a cross-layer approach that exploits the time-varying nature of the wireless channel to take decisions on the data to deliver to each user. According to this approach, based on channel status awareness, the scheduler performs an opportunistic packet selection and allocates resources to users experiencing good channel conditions. On the one hand, by allocating resources to userswith better channel quality,
the scheduler can maximize the overall system throughput. On the other hand, it may degrade other QoS metrics such as delay, because the scheduler postpones transmissions toward users sensing low-quality channels until the relevant channel conditions recover.
