Impact of Iub flow control on the proportional fair scheduler in HSDPA

One of the key elements of the High Speed Downlink Packet Access (HSDPA) is the fast scheduler located at the base station. For the scheduler to operate efficiently, sufficient amount of traffic needs to be buffered at the base station. However, the users´ buffers at the base station are managed by a flow control protocol in order to minimize data loss during handover. We evaluate the necessity of such protocol under reliable higher layer protocols such as RLC and TCP especially at low traffic load and less frequent handover conditions. The impact of this flow control on the Proportional Fair scheduler (PF) is analyzed by comparing two flow control algorithms to the hypothetical case when flow control is eliminated from the system. The results indicate that eliminating the flow control greatly improves the scheduler performance and increases the overall system throughput at low traffic load. However, at high traffic load, eliminating the flow control increases handover data loss to a point that negates the positive improvement of the scheduler performance and reduces the effective system throughput.