Preventive and Reactive Based TNL Congestion Control Impact on the HSDPA Performance

High speed downlink packet access (HSDPA) is an extension of the Universal Mobile Telecommunications System (UMTS) technology of 3GPP Rel-99, with the objective to increase the data rate and reduce the latency in the downlink. The main focus of the work presented is to analyse the effect of congestion at the Iub interface on the HSDPA performance. The data flows should be adequately controlled in order to avoid congestion in the transport network. The 3GPP (3rd Generation Partnership Project) Rel. 5 specifications highlight two congestion detection mechanisms which are based on the frame sequence number (FSN) and the delay reference time (DRT) fields of HSDPA data frame. In addition to these, a third congestion detection mechanism based of Checksum of HSDPA data frame is considered. This paper discusses a congestion control scheme deploying all three congestion detection methods. It is shown, that a congestion control algorithm can effectively work using these congestion detection triggers and can control the offered load to the transport network. The simulation results presented in this paper confirm that the congestion in the transport network can be avoided, and hence the performance of HSDPA network can be significantly improved in all aspects.