Performance Evaluation of AQM Schemes in Rate-Varying 3G Links

When TCP is carried over 3G links, overbuffering and buffer overflow at the RLC layer degrades its performance. AQM techniques at the RLC buffer can bring noticeable enhancements to TCP performance without introducing changes in 3G specifications. We show that the optimum parameter setting of AQM algorithms in RLC buffers is strongly related to the radio bearer rate, which can be changed dynamically by control layer protocols. By means of extensive simulation experiments we propose, for each specified nominal rate, optimum configurations that keep the goodput near the maximum while the delay is reduced up to 50%. We consider two AQM schemes, an adapted RED algorithm and a novel deterministic one, SBD described in this paper. We illustrate how an automatic reconfiguration of AQM parameters avoids the degradation caused by sudden changes in the radio bearer rate.