. In this, the master of the connection (in the case of option 3 architecture, as covered in Chapter 5, this is LTE) is first allocated the power it needs, and the remaining power is left for 5G operation. This ensures that LTE as the connection anchor can be maintained in all cases, while all the remaining power is available for 5G. This is mandatory in Release 15 (with capability signaling to allow testing the feature first against practical networks). The operation is shown in Figure 6.30. Semi-static power sharing between LTE and 5G. In this case, the LTE side reserves some amount of power resources in a semi-static way, and the remaining power is available for the 5G side. This is challenging as LTE side power reservation has to be done with some margin, and on the other hand the unused LTE power is not made available for the 5G side. This is expected to be the case only for some early imple- mentations for the very first UEs and is not foreseen for large commercial use. 6.11.3 Timing Advance The timing advance procedure is very similar to the LTE approach, with the actual timing advance command being provided in the MAC layer. After the RACH preamble has been received, the gNB will respond with the timing advance in the RAR, and it is then main- tained during the connection as frequently as is needed. The step of the timing advance is a function of the SCS. The larger the SCS, the smaller the timing advance adjustment step. Compared to LTE, the timing advance was adjusted to allow very large cells in spe- cial deployments beyond 100 km limit. Now the theoretical limit for cell size (radius) is up to 300 km. 6.12 5G MIMO and Beamforming Operation 6.12.1 Downlink MIMO Transmission Schemes 5G NR downlink transmission schemes have been streamlined to a single transmission scheme, compared to LTE where we have CRS- and DM-RS-based transmission 6 5G Physical Layer schemes. One of the reasons for such a simplification was the fact that the data transmission in NR operates solely on dedicated reference signals. Whi