QoS Aware HSDPA Congestion Control Algorithm

High speed downlink packet access (HSDPA) is providing increased user data rate by introducing additional functionalities like link adaptation and coding, fast scheduling and hybrid automatic repeat request (HARQ) at the Node B. To achieve optimal radio resource utilization, HSDPA flow control is applied to control the amount of data sent from the radio network controller (RNC) to the Node B over the Iub interface. HSDPA flow control is not taking into account the available transport resources which can lead to situations when HSDPA packets are dropped due to congestion. These drops are triggering radio link control protocol (RLC) retransmissions that are decreasing the HSDPA performance. TCP flow control is not able to detect and resolve in time the congestion situation because RLC retransmissions are hiding the congestion on Iub transport. Therefore a congestion control algorithm is needed that is able to improve the system performance in case of resource limited transport. In this paper we propose a congestion control solution for systems with HSDPA QoS classes and evaluate it with NS2 simulations.