 are not optimized) but this neglected for the time being and left for further optimization. With the 3 dB uplink noise rise assumption, the RSRP trigger to exit to layer due to low uplink throughput changes from -115 to -112 dBm. Finally, to determine the downlink exit point from RSRP requires a network-specific per- formance curve similar to what is shown in Figure 15.9. Skipping the details, it can be fairly easily deduced that the RSRP exit trigger based on downlink throughput target is lower than the uplink trigger, and hence it is the uplink performance that dictates the exit point. Inter-layer Mobility Optimization Uplink noise rise simulation example ISD 0.5 km urban 1800 MHz ISD 1.7 km suburban 1800 MHz ISD 0.5 km urban 800 MHz ISD 1.7 km suburban 800 MHz Uplink noise (dB) Figure 15.13 Uplink noise rise distribution example for full buffer data model with an average of 0.2 UEs scheduled in uplink per TTI. Open-loop power control with P = - -100 dBm and alpha = 1 is used. Downtilt is 4 degrees, antenna height is 30 metres. ISD = inter-site distance Layer RSRP Entry Point for Network with Interference At this point, the layer exit points have been defined based on the throughput target. The next step is to choose the layer entry points SO that some hysteresis remains to avoid ping-pong layer changes. For uplink the exit trigger is based on RSRP, SO the entry trigger should also be based on the same measurement quantity since otherwise hysteresis is difficult to control. The main purpose of the hysteresis is to mitigate the effect of small-scale signal fading, and the hysteresis can be based on timer and level offset in both idle and connected modes. The recommended approach is to rather use small level offset and longer timer value, since this keeps stationary UEs connected to the most suitable layer; the design is optimized for low-mobility UEs since the assumed primary service is data. Using too large level hysteresis can degrade throughput performance since even a 3 dB increase in SINR can improve the s