Buffer Management for Multimedia QoS Control over HSDPA Downlink Suleiman Y. Yerima, Khalid Al-Begain Mobile Computing, Communications and Networking RG Faculty of Advanced Technology, University of Glamorgan Pontypridd (Cardiff) CF37 1DL, Wales, UK E-mail: {syerima,kbegain}@glam.ac.uk Abstract HSDPA specifications include support for a flexible framework for QoS management. In this paper, it is shown how buffer management could be incorporated into HSDPA QoS framework for ‘multimedia’ traffic QoS control in the MAC-hs of the Node-B. A Time- Space-Priority (TSP) scheme is proposed as viable buffer management scheme to this effect. Comparative simulation study with other schemes is presented, demonstrating the effectiveness of the TSP buffer management scheme for ‘multimedia’ service QoS control in HSDPA Node-B data buffers. 1. Introduction Improved support for packet-switched data in UMTS mobile networks introduced in recent 3GPP releases presents opportunities for service providers to introduce novel broadband services. High-Speed Downlink Packet Access (HSDPA) is the 3GPP release 5 specifications that enhances UMTS networks to provide higher data rates and increased capacity for greater support of broadband services like multimedia conferencing, VoIP, audio/video streaming, mobile multimedia gaming, high-speed internet access, etc. The ability to support high data rates enables application developers to create content rich ‘multimedia’ applications, typically consisting of a number of classes of media or data- with different QoS requirements- being concurrently downloaded to a single user [1]. HSDPA significantly reduces downlink transmission latency, enabling theoretical data rates of up to 14.4 Mbps in addition to a three-fold capacity increase in WCDMA UMTS networks [2, 3]. A shared downlink channel is utilized, which adapts transmission capacity to changing radio propagation conditions (fast link adaptation). Fast link adaptation employs adaptive modulation and coding (AMC) whereby different modulation and coding schemes are selected for transmission of traffic to the User Equipments (UE) within the serving HSDPA cell. AMC scheme selection is based on the experienced radio channel quality of the UE. Other features of HSDPA include HARQ for error control and channel- dependent Fast Scheduling. Minimum allocation time or TTI (Transmission Time Interval) on the shared channel is 2ms which improves the tracking of fast channel variations. Not only have these new features been added to the Physical and MAC layers of in the HSDPA specifications, but they have also been implemented in the base station (Node-B). Furthermore, unlike in the UMTS Release 99 architecture, the packet scheduling is moved from the centralized RNC to the base station and embedded in a new MAC entity called MAC-hs. Recent studies, in [4] for example, emphasize the flexible framework for efficient QoS differentiation featured in the Release 5 specifications. Thus, the inclusion of packet scheduling capability (i.e. MAC- hs) in the Node-B presents opportunity to utilize buffer management schemes for QoS management. Hence, in this paper, a combined Time-Space Priority (TSP) buffer management strategy is proposed for multimedia traffic QoS control over HSDPA downlink in Node-B buffers. In particular, the potential of TSP for efficient QoS control of heterogeneous multimedia traffic- comprising flows with diverse QoS requirements- is demonstrated through performance comparisons with the non-priority First-come-first- serve (FCFS), Space Priority (SP), and Time Priority (TP) buffer management schemes. Figure 1 shows aspects of the HSDPA user-plane protocol stack relevant to buffer management based QoS control. Due to the functional split between RNC and Node-Bs, the buffer management parameters could be computed and set by the RNC as an additional Resource Management (RM) function in the control plane as shown in Figure 1.