vation for a Massive-MIMO base- station in such scenarios is to boost capacity by improving spectral efficiency. Although we have focused on the downlink, the capacity improvement in the uplink is also expected to be as significant as the downlink in the respective deployment scenarios. In frequency bands at about 700 MHz to 3.5 GHz where current LTE deployments are most prevalent, this seems to be the predominant role of AAS and Massive-MIMO base-stations of the future. It is worth mentioning, however, that in the context of 5G the easier availability of spectrum at higher frequencies but with unfavourable propagation characteristics is also motivating M-MIMO antenna arrays as discussed in Chapter 17. The considerations, however, at a higher band such as 30-100 GHz can be quite different. The pathloss can be higher by about 20-30 dB while at the same time a large number of antenna elements can be packed efficiently in a small area. The number of transceivers driving the array is expected to be limited due to cost and power consumption issues. The design focus may veer towards maintaining connectivity rather than optimizing for spectral efficiency. The aspect that remains relevant, however, is the ability to precisely control a Massive-MIMO array in three dimensions. The evolution of the LTE specifications for supporting Massive-MIMO is progressing as part of Release 13 supported by many operators and vendors worldwide. The focus is to provide an optimized, robust LTE Small Cell Optimization OFDMA Power Power System bandwidth User 1 User 2 User 1 User 2 Figure 11.16 NOMA principle and versatile specification for deploying Massive-MIMO base-stations with a wide range of configurations and cost options. The latest scope for Release 13 is reflected in [10]. 11.7 Release 13 Advanced Receiver Enhancements The cancellation of cell-specific reference signals (CRS) was studied initially in the context of Release 11 heterogeneous networks. In such scenario, pico cell UEs situated in cell range extension are impacted by hi