itoring Other Small Cell Physical Layer Enhancement Release 13 Enhancements Conclusions References 4.1 Introduction This chapter covers the small cell enhancements introduced in Release 12 in 3GPP as well as the items on-going for Release 13. First the architecture impacts from the dual connectivity architecture options specified for Release 12 are introduced, and then the dual connectivity principle is covered, followed with the more detailed impacts for the radio protocols as well as physical layer enhancements including 256 QAM and small cell on/off procedures. The resulting performance is introduced. Finally the chapter is concluded with the Release 13 enhancements, including uplink bearer split. 4.2 Small Cell and Dual Connectivity Principles The 3GPP started the work for the small cell-related improvements following the workshop held in June 2012 on LTE-Advanced evolution, which concluded the need for evolution for LTE Small Cell Optimization: 3GPP Evolution to Release 13, First Edition. Edited by Harri Holma, Antti Toskala and Jussi Reunanen. © 2016 John Wiley & Sons, Ltd. Published 2016 by John Wiley & Sons, Ltd. LTE Small Cell Optimization Scenario 1 Scenario 1 co-channel macro overlay outdoor, small deployment, outdoor cells a) outdoor or b) indoor Figure 4.1 Small cell co-channel and overlay scenarios the small cell operation. The scenario of importance was especially the use of small cells with a dedicated small cell frequency, as shown in Figure 4.1 as earlier Releases contained already solution such as CoMP or eICIC that can be used with the co-channel scenario. In Release 10-based intra-site carrier aggregation, as explained in Chapter 2, all the car- riers are coming from the same co-located eNodeB. The carrier aggregation can be imple- mented also with radio frequency (RF) head behind dark fibre configuration with the baseband units/processes handling the aggregated cells just being in the same location. An important extension to the carrier aggregation principle was adopted in Release 12 with th