HSDPA (High Speed Downlink Packet Access) is an extension of the current UMTS (Universal Mobile Telecommunications System) technology with the objective to increase the data rate and to reduce the latency in the downlink. The main focus of this investigation is to optimise the Iub interface to provide the best end user performance at minimum cost for UMTS HSDPA network. An adaptive credit-based flow control mechanism for UTRAN transport has been developed, tested and validated in the HSDPA simulation model. In this paper, the HSDPA performance with the new adaptive credit-based flow control mechanism is compared with the generic ON/OFF flow control mechanism. The results confirm that the adaptive credit-based flow control mechanism can significantly improve the performance and therefore reduce the required bandwidth at the Iub interface meeting a specified performance: The better bandwidth utilisation and improved statistical multiplexing is achieved by reducing the burstiness of the traffic over the Iub interface. Finally, a recommendation for the required bandwidth at the Iub interface is given for bursty HSDPA traffic.
