r challenge with static load balancing via mobility threshold tuning: namely, that it can be difficult to force off-loading of the desired layer as the effectiveness of the method is strongly dependent on the UE distribution in the cell. In the example of Figure 15.19, the UEs congesting the LTE2600 cell are very near the site in good RF conditions and hence even several decibels shift in the exit point will not move the traffic away from the layer. Besides static tuning of exit/entry triggers, basic 3GPP specification includes the option to send to the UE dedicated idle mode layer priorities in the RRC release. This can be used for load balancing purposes. For example, a certain percentage of UEs can be randomly assigned reversed layer priorities (relative to default layering) in order to make the UEs to reselect to the LTE Small Cell Optimization Intra-sector static load balancing with mobility thresholds, 2.6 GHz to 800 MHz Sector total traffic High band traffic Low band traffic Figure 15.19 Example of intra-sector traffic balancing via static exit/entry mobility threshold tuning, from higher carrier frequency to lower less congested layer. The main problem with this approach is that the dedicated priorities are erased when the UE establishes a new RRC connection. This can result in the UE being restored the default priorities from BCCH if the same dedicated priorities are not reassigned in a sub- sequent RRC release, thus resulting in ping-pong cell reselection back to the congested layer. Equal Priority Layers With equal priority layers traffic balancing can be done by suitably modifying the layer change offset, that is, A3 event offset and idle mode reselection hysteresis. The benefit compared to the non-equal priority case is that steering is not limited to cell edge UEs only, but is more uniform across the coverage area (assuming co-sited layers). The optimization process in this case would be basically the same as with non-equal priority layers. In other words, A3 offset and idle mode hysteresis are grad