Application Specific Scheduling in WiMAX: Ensuring QoS in Application Mix Environment
In wireless network deployments, scheduling at MAC is deterministic and of empirical importance to ensure QoS. The Quality of Service centric Medium Access Control architecture of WiMAX helps providing services with different QoS requirement. In WiMAX, Service Specific Convergence Sub-layer (CS) CS-MAC enables service differentiation and thus provides basis for allocating different scheduling types to different applications. The IEEE 802.16 group working on standardization of WiMAX does not explicitly define the scheduling class to be used and has left for vendors and operators to come up with adaptable frameworks to accommodate different applications with differing QoS requirement. In this article we have focused on QoS requirements in application mix environment wherein real time applications with stringent QoS requirements and non-real time applications with very flexible QoS requirements coexist. We used OPNET modeler to simulate a WiMAX network with seven cell sites and IP backbone. MSs in the network are using both the real time voice and non-real time data applications. Network performance is reviewed in terms of load offered, throughput, delay and, application response time. Initially network was configured with UGS class for real time voice and BE for data application. The network response shows that in application mix environment UGS class with fixed size, periodic allocations is not useful and may result in underutilization of BW assigned periodically to application configured with UGS class and on the other hand applications running with BE class may observe Waiting for indefinite time to transmit. Having observed this, we re-simulated network with ertPS class (an adaptable scheduling scheme) for real time applications. From results of the reconfigured network it is followed that using ertPS for real-time applications in application mix environments is advantageous as ertPS class provides polling based assignment to real time flows and thus support non-real time applications using BE class to flow.