 800 MHz same-sector cell has an average of 2 UEs. The load balancing inter-frequency handover is activated in the middle on day 9. As a result hourly average of the number of UEs loading the transmit buffer on the 2.6 GHz layer decreases by about 30% while the load on the 800 MHz layer is almost tripled using the same load measure. The amount of off-loading is controlled by the target number of UEs with data in transmit buffer which in the example was set to 10 on the congested 2.6 GHz layer; it can be seen that the target level is maintained approximately in the source cell. Setting a lower target would result in more aggressive off-loading at the expense of increased number of inter-frequency handovers. In the example the target cell must have RSRP higher than a pre-defined threshold to avoid handing UEs over to bad coverage. In general, the target cell should satisfy some level or quality criterion to custom-pick those UEs that can be handed over to a cell that does not degrade service level too much. Since balancing of network resource usage by adaptive threshold tuning and congestion- triggered handovers will by definition modify the natural cell and layer boundaries the main problem with dynamic load balancing is the increased number of unnecessary layer changes with the increased probability of call drops and ping-pong. In a typical sequence of steps, the UE is first handed over to a less congested cell, and after returning to idle mode it reselects back to the congested cell, restarting the off-load cycle. In the worst case, if handover thresholds are not coordinated between layers, the UE may try to bounce back while still in connected mode Inter-layer Mobility Optimization Intra-sector dynamic load balancing via handover, 2.6 GHz to 800 MHz Low band UEs High band UEs LB handover attempts Day 1 Day 2 Day 3 Day 4 Day 5 Day 6 Day 7 Day 8 Day 9 Day 10 Day 11 Day 12 Day 13 Day 14 Figure 15.21 Dynamic load balancing via inter-frequency handover, from 2.6 GHz to 800 MHz in the target cell. In other words, whi