ually decreased on the layer to be off-loaded. Correspondingly the target layer cell change margin towards the congested layer may have to be increased to control ping-pong. The process can be continued until the desired average load distribution on the layers is achieved or some system limitation (e.g. drop call increase) is encountered. Figure 15.20 illustrates the simple idea. With path loss exponent A and cell area reduction of 100(1-w) percent the path loss difference would be 5A log10(w). For example, with a path LTE2600 20 MHz layer, priority = 5 New LTE2600 exit point LTE1800 20 MHz layer, priority = 5 Figure 15.20 Example of static load balancing between equal priority layers Inter-layer Mobility Optimization loss exponent of 4 and 30% reduction in cell area the theoretical change in A3 offset would be 5 X 4 X log10(0.7) 22 3 dB. If the UEs are roughly uniformly distributed over the coverage area, a 3 dB reduction in the inter-frequency A3 RSRP offset and idle mode RSRP hysteresis would theoretically result in 30% reduction in the number of UEs served by the cell. For instance, looking at the example shown in Figure 15.20 the coverage area of the LTE1800 layer is about 40% larger based on the path loss difference alone16 (path loss expo- nent = 4). In order to balance the coverage areas of the two layers by the A3, handover margins should be made asymmetrical, and even negative. For example, if the A3 offset and idle mode hysteresis from 2.6G towards 1.8G are set to 3 dB and the reverse direction offset from 1.8G to 2.6G layer is set to -3 dB then the coverage areas would be approximately matched (assuming co-siting) but without any hysteresis. Adding 4 dB hysteresis to the theoretical setting would result in A3 offsets of 5 and -1 dB. Obviously practical systems rarely obey such simplified models due to various system link budget differences between the frequency bands, but such calculations can help in inferring a suitable starting point for further optimization. 15.5.2 Dynamic Load Balancing via eNode