HSUPA Transport Network Congestion Control

The introduction of high speed uplink packet access (HSUPA) greatly improves achievable uplink bitrate but it presents new challenges to be solved in the radio access network. In the transport network, bandwidth reservation for HSUPA is not efficient and TCP cannot efficiently resolve congestion because of lower layer retransmissions. This paper proposes an HSUPA transport network flow control algorithm that handles congestion situations efficiently and supports quality of service differentiation. In the radio network controller (RNC), transport network congestion is detected. Relying on the standardized control frame the RNC notifies the Node B about transport network congestion. In case of transport network congestion the Node B part of the HSUPA flow control instructs the air interface scheduler to reduce the bitrate of the flow to eliminate congestion. The performance analysis concentrates on transport network limited scenarios. It is shown that TCP cannot provide efficient congestion control. The proposed algorithm can achieve high end-user perceived throughput, while maintaining low delay, loss and good fairness in the transport network.