 scheduling LTE Small Cell Optimization Cell throughput VS. VoLTE users Dynamic scheduler VoLTE UE per sector Figure 14.22 Cell throughput as a function of simultaneous VoLTE users with different scheduler solutions It has been shown in simulations that SPS can enhance the VoLTE capacity by +5% compared to the dynamic scheduler in voice-only cases. A more relevant use case would be mixed voice and data since a typical LTE cell carries a lot of data on top of VoLTE traffic. Figure 14.22 shows the cell throughput for the packet data as a function of number of simultaneous VoLTE users. The results show that the dynamic scheduler can provide higher efficiency than SPS in the mixed case. The difference can be even 20% more cell throughput. We can conclude that the dynamic scheduling solution with fast CQI feedback is typically the most efficient solution in practical LTE deployment scenarios. 14.4.4 Packet Bundling The PDCCH signalling overhead and Layer 1 and 2 overhead can be minimized by using packet bundling for VoLTE. The idea is to wait until there are two voice packets in the transmission buffer and then send those two packets at once over the air interface. The benefit is that the transmission becomes more efficient and the allocation signalling is cut into half. The concept of packet bundling is shown in Figure 14.23. The benefit of packet bundling is that it can be utilized together with dynamic scheduling while obtaining similar benefits as with SPS in terms of signalling minimization. The packet bundling increases delay variations which need to be considered in terms of number of allowed retransmissions. The impact of packet bundling to the delay variations is shown in Figure 14.30. 20 ms No packet bundling 40 ms With packet bundling Figure 14.23 Packet bundling concept VoLTE Optimization = Radio link failure (((c-m),)) = Re-establishment request 3 = Radio link failure indication Cell A Cell B = UE contex tretrieval by handover request Figure 14.24 Re-establishment procedure 14.4.5 Re-establishment with Ra