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Performance analysis of the Iub interface in UMTS networks for high speed down link packet access
Publikationstyp
Journal Article
Publikationsdatum
2005-06-01
Sprache
English
Enthalten in
Issue
187
Start Page
51
End Page
52
Citation
ITG-Fachberichte (187): 51-52 (2005-06-01)
Scopus ID
Publisher
VDE
HSDPA is a cost effective upgrade to the current UMTS technology to fulfil the current mobile user demands which grow exponentially day by day. It is an asymmetric solution that enables a faster downlink throughput to the end user. The operator has to cope with the demand of advanced quality of service capabilities and data speeds in a cost effective manner. Therefore the HSDPA technology has to be developed in such a way that it provides significantly improved network capacity at relatively low cost. In a UMTS network, the Node B acts as the transmission and the reception station for the mobile users to the network that handles the network traffic over the scarce radio resources. The radio network controller (RNC) has the overall control of the resources in the Node B up to the user entity. The Node B schedules the HSDPA capable users over the shared downlink channel by matching the user priority, the channel quality and other criteria. It uses adaptive modulation and coding schemes (AMC) to ensure the maximum capacity at the best possible data rates to the user. Hybrid ARQ provides the error correction mechanism over the air interface for better reliability and improved overall throughput of the network. Therefore the HSDPA technology can enhance the user throughput by serving the particular users who currently experience the best channel conditions. On the Iub interface between RNC and Node B the flexible, efficient and high speed Asynchronous Transfer Mode (ATM) transport technology is used for data transport. Statistical multiplexing properties of ATM are suited for handling bursty traffic to optimise the bandwidth utilisation of the Iub. AAL2 is used as the adaptation layer technology for the effective combination of both real-time and best-effort traffic demands. The optimisation of the transport network layer for HSDPA support is one of the key aspects to minimise the operator costs. To guarantee the requested quality of service, class based service differentiation is applied and an additional flow control mechanism is used to avoid link congestion. Therefore, the per user flow control at frame protocol level meets the real time traffic requirement at the Node B by optimising the wireless channel utilization adaptively. The main focus of the simulations presented in this work is to ensure effective bandwidth utilisation over the Iub interface while guaranteeing QoS for the HSDPA traffic. Simulation is performed by employing standard traffic models like ETSI, MWIF and FTP as the end user's traffic profiles. FTP is used as a worst case scenario for downloading large files by all users simultaneously. All experiments are carried out under the OPNET simulation platform with required modifications applied on the OPNET standard ATM modules. For the simulation setup, there are 20 users in the cell and 3 cells are assigned to one Node B entity. The Node B MAC-hs scheduler emulates an air interface based on the per user throughput distribution derived from traces of a detailed air interface simulation.Different simulation scenarios have been analysed to examine the effect of the transport network layer (TNL) flow control under various traffic loads generated by varying user constellations. The overall performance is evaluated on a per user basis at the application layer. The application layer results show the effect of the TCP flow control between the end user entities on the overall user performance. Throughput and delay statistics are measured at different levels from the link layer to the application layer. These results together with the modelling approach are presented in this paper.
DDC Class
004: Informatik