estion by means of off-loading traffic to another layer is the topic of this section. The load balancing methods can be divided to two basic approaches: Static load balancing via mobility threshold tuning. Especially in the case where the load distribution between layers is uneven over a larger coverage area (instead of just few isolated sites or cells), load balancing can be achieved by changing the layer exit and entry points (unequal priority layers) or the cell change offset (equal priority layers). In idle mode, UE dedicated layer priorities can also be used. These methods are mostly based on 3GPP and can be used in a wide range of networks regardless of the eNodeB implementation. Dynamic load balancing via eNodeB algorithms. These methods include congestion- triggered load balancing handover and adaptive tuning of mobility thresholds based on cell load. The methods are vendor specific and hence not defined by 3GPP. The advantage of these methods is that they can dynamically adapt to the traffic fluctuation at cell level, unlike the static methods. The static approach tunes the average load of layers over the coverage area while the dynamic methods can further fine-tune traffic load at cell level. A combination of both may be needed for satisfactory results since applying the dynamic methods alone can easily result in excessive ping-pong layer changes unless the average load of the layers within the coverage area is first tuned by the static mobility thresholds; cell-level local tuning is then handled by the dynamic load balancing. To tune any system, some optimization criterion is needed. For load balancing purposes, several different criteria can be considered. The criteria can be applied to both static and dynamic load balancing. Example criteria include Balancing the number of RRC-connected UEs Balancing radio utilization (e.g. PRBs, PDCCH CCEs) Minimizing the number of UEs having throughput less than the minimum requirement Maximizing UE throughput The choice of which criterion to use is often in practi