Mixed Traffic HSDPA scheduling - Impact on VoIP Capacity

IMS multimedia telephony (MMTel) for cellular systems is currently being standardized in 3GPP. MMTel comprises a number of media components such as voice over IP (VoIP), real-time video, text messaging and file sharing. In this paper down-link scheduling performance of MMTel services for various scheduling algorithms is investigated in an HSDPA system. The studied service mixes include VoIP and file download (FTP), as well as VoIP and real-time video. The investigation of the schedulers is done over a wide range of traffic mix ratios, in order to give a full understanding of the performance. This paper shows that it is beneficial to have separate schedulers for each media flow. For an MMTel scenario with VoIP and file downloading, the best performance is achieved when using a delay scheduler for VoIP and a proportional fair (PF) scheduler for FTP. An extra priority weight for VoIP over FTP (or v.v.) makes it possible to control the wanted total service mix. With simultaneous VoIP and real-time video the best performance is achieved when both services utilize a delay scheduler, this since the VoIP and video flows shall be synchronized. However, the scheduler for the video flow requires different parameter settings, compared to the VoIP flow, in order to give the best performance.