ce constrained by the eNodeB imple- mentation. Especially for dynamic load balancing the optimization criterion is typically hard- coded in the eNodeB implementation. From end-user experience point possibly the most important performance criterion for non-GBR services is the UE-scheduled throughput. Figure 15.16 shows an example of the average UE throughput versus the average number of UEs sharing a TTI for a busy cell. Such performance curve can be used for capacity management and for load balancing. 15.5.1 Static Load Balancing via Mobility Thresholds Load of the LTE layers can be to a certain extent balanced by tuning exit/entry points or cell change margin (idle mode hysteresis, A3 offset) for non-equal and equal priority layers, respectively. LTE Small Cell Optimization UE downlink scheduled throughput Average number of UEs scheduled in downlink per TTI Figure 15.16 Example of UE downlink-scheduled throughput in a cell versus the number of UEs scheduled per TTI. Each dot corresponds to 1-hour average Non-equal Priority Layers When layers have different priority a natural way to tune the load distribution between the layers is to modify the layer exit and entry points. Since the difference between the two is the hysteresis - which can be kept constant - the number of variables to optimize consists only of a single parameter hence resulting in a simple and easily controllable process. This is illustrated in Figure 15.17 where the higher priority layer is made to absorb more traffic by lowering the layer exit point. The amount of traffic that can be steered from one layer to another depends strongly on the spatial UE distribution. If UEs are concentrated near the cell centre, modification of layer exit/entry points is not likely to help much since mainly a few cell edge UEs are affected. Coverage increase Old exit point Entry point Higher priority LTE layer New exit point Hysteresis LTE entry point Lower priority LTE layer LTE exit point To/from 2G/3G coverage layer Figure 15.17 Principle of inter-layer load ba