le load balancing between layers is achievable it may also result in undesirable side effects such as increased number of handovers and call drops. The conventional solutions of physical cell dominance optimization and addition of new cells should be considered as an alternative. 15.6 Summary In this chapter idle and connected mode UE measurements were described. The classical form of inter-layer mobility applied to LTE is based on the best server-based rule where the cell change margin is implemented via hysteresis or A3 offset. From 3GPP Release 8 onwards it is possible in 3GPP RATs to assign different absolute priority to layers. In this non-equal priority case the layer entry and exit points need to be designed and optimized to satisfy some target service quality criteria. Usually the same exit and entry points are used in both idle connected modes. In case of sporadic network congestion, it may be possible to balance traffic in the network by static or load-adaptive steering. To alleviate long-term intra- and cross-layer congestion, network capacity needs to be increased by physical optimization and addition of new cells. References [1] 3GPPTS 23.122, "Non-Access-Stratum (NAS) functions Related to Mobile Station (MS) in Idle Mode', v.12.5.0, June 2014. [2] 3GPP TS 36.133, 'Requirements for Support of Radio Resource Management', v.12.4.0, July 2014. [3] 3GPP TS 36.304, "Equipment (UE) Procedures in Idle Mode', v.10.8.0, March 2014. LTE Small Cell Optimization [4] 3GPP TS 36.331, 'Radio Resource Control (RRC); Protocol Specification', v.10.13.0, June 2014. [5] H. Holma and A. Toskala, editors. LTE for UMTS - OFDMA and SC-FDMA Based Radio Access, John Wiley & Sons, Ltd (2009). [6] S. Sesia, I. Toufik, and M. Baker, editors. The UMTS Long Term Evolution: From Theory to Practice, John Wiley & Sons, Ltd (2011). B. Rengarajan and G. de Veciana, 'Practical Adaptive User Association Policies for Wireless Systems with Dynamic Interference', IEEE/ACM Transactions on Networking, 19(6), 1690-1703 (2011). [8] Q. Ye, B. Ro