MEDF - A Simple Scheduling Algorithm for Two Real-Time Transport Service Classes with Application in the UTRAN

In this paper, we consider speech traffic, circuit-switched data (CSD) and packetswitched data (PSD) in the UMTS Terrestrial Radio Access Network (UTRAN). The focus is on the single low-bandwidth link that interconnects the Radio Network Controller (RNC) and the base station (Node B). We show that all traffic on this link has real-time characteristics. But we take advantage of the upper layer protocols and formulate suitable quality of service (QoS) criteria that lead to two different transport service classes (TSC): A stringent TSC for speech traffic and CSD, and a tolerant TSC for PSD. The RNC transmits packets from both TSCs via a single lowbandwidth link to the Node B. Since transmission capacity on this interface is a serious cost factor in the UTRAN, the link utilization should be optimized while respecting the QoS requirements of both TSCs. We propose a modified version (MEDF) of the Earliest Deadline First (EDF) algorithm for that task. It is easy to implement and does not require the knowledge of the traffic mix to set its parameters. The simulation results show its superiority over FIFO, Static Priority (SP), and Weighted Round Robin (WRR) scheduling. The analysis of the waiting time distribution explains why MEDF is better than the other scheduling strategies.