OptiMOS: Optimal MOS-based scheduling of downlink voice flows in point-to-multipoint access networks

We introduce OptiMOS, a method for selecting deadlines for the scheduling of downlink voice flows in a centralized-scheduling point-to-multipoint network. These include cellular networks such as LTE, UMTS HSDPA, or WiMAX, and WLANs with centralized control. OptiMOS selects the deadline of each packet so as to maximize the expected Mean Opinion Score (MOS) for the talkspurt it belongs to. It requires that absolute time is both included in RTP timestamps at the source and checked for scheduling decisions, in a cross-layer approach. OptiMOS can be employed in conjunction with any deadline-based scheduling algorithm, and does not require a specific playout buffering scheme at the receiver. Simulations of an LTE system show a performance improvement in terms of MOS for the VoIP flows, good tolerance to relatively large synchronization errors and qualitatively similar results with different playout buffers.