On performance of MAC-c/sh in UMTS

MAC (medium access control) is one of the sublayers of layer 2 of the radio interface protocol stack in UMTS. MAC-c/sh is a part of MAC responsible for handling data transported on common and shared transport channels. The goal of this paper is to analyse the performance of MAC-c/sh, with focus on the MAC-c/sh FACH scheduler and the FACH flow control algorithm between MAC-d and MAC-c/sh. We propose weighted round robin with a dynamically adjusted serving cycle as an effective scheduling algorithm for FACH on the Iub interface. We also introduce an efficient FACH flow control algorithm for FACH on the Iur interface, both for serving radio network controller (SRNC) and drift radio network controller (DRNC). This algorithm grants credits in a fair manner, tries to limit the amount of control traffic and provides a mechanism for revoking unused credits. Additionally, we provide some general MAC-c/sh configuration guidelines, based on implementing a simulator capable of interoperating with commercial UMTS equipment.