cheduled throughput by tens of percents if the layers have the same bandwidth. The main drawback from ping-pong cell change is the potential loss of paging in idle mode, and increased risk of dropping a call in connected mode. If ping-pong is too frequent, also an ongoing TCP download would suffer due to delay peaks and packet loss. A web browsing user is, however, unlikely to notice the effect unless the ping-pong is excessive. For native LTE voice service (VoLTE), a different mobility parameter design would be required. LTE Small Cell Optimization Exit-112 dBm Entry -109 dBm LTE1800 layer, priority = 6 Entry -109 dBm LTE800 layer, priority = 4 Exit-112 dBm UMTS900 layer, priority = 2 Loss of network service Figure 15.14 Layer exit and entry points for the network with low load With this philosophy in mind, the RSRP hysteresis is set to a fairly low value of 3 dB and ping-pong will be controlled by increasing time hysteresis as needed. Figure 15.14 summarizes the exit and entry points for the LTE layers. The actual measure- ment triggering events are selected according to the analogy discussed previously. In other words, A5 is used to move within LTE from high- to low-priority layer and A4 is used to move from low- to high-priority layer as these measurement events are the connected mode duals of the corresponding idle mode mobility rules. Further refinements to the baseline case may be needed in high-interference areas where RSRP is strong but SINR is low. In this case the layer exit trigger could in addition be based on RSRQ to have a mobility trigger based on downlink throughput. Mapping the SNR target of -3 dB gives RSRQ threshold of -16.5 dB when serving cell is fully utilized. Assuming a fully utilized serving cell is logical since if the serving cell was not fully loaded the eNodeB could actually allocate more PRBs to the UE thus increasing its throughput. The main problem with mixing RSRP- and RSRQ-based mobility triggers is that after a RSRQ-triggered handover the UE may swing back to the polluted high-