at may be in the spuri- ous domain also have to align with the regulatory limits from ITU-R. The shape of the mask is generic for all channel bandwidths, which has to align with ITU-R limits starting 10-40 MHz from the channel edges. The OBUE is defined with a 100 kHz measurement bandwidth and is aligned to some extent with the corresponding emission masks for the LTE systems. In the case of carrier aggregation for a BS, the OBUE requirement is applied as for any multicarrier transmission, where the OBUE will be defined relative to the carriers on the edges of the RF bandwidth. In the case of non-contiguous carrier aggregation, the OBUE within a subblock gap is partly calculated as the cumulative sum of contributions from each subblock [10]. In addition to a SEM, the OOB emissions are defined by the ACLR requirement. The ACLR concept is very useful for analysis of coexistence between two systems that operate on adjacent frequencies. The ACLR defines the ratio of the power transmitted within the Chapter 5 BS operating band unwanted emission limit BWchannel 10-40 MHz 10-40 MHz BS spurious emission limit Operating band for BS transmitter Spurious OOB domain Spurious domain domain +2.5x channel O'OBUE Downlink operating band Operating band BS RF Operating band Spurious unwanted emissions bandwidth unwanted emissions Spurious emissions emissions Figure 5.9 Illustration of the unwanted and spurious emissions applicable to NR base stations [5,8,9]. assigned channel bandwidth to the power of the unwanted emissions transmitted on an adja- cent channel. There is a corresponding receiver requirement known as ACS, which defines the receiver's ability to suppress a signal on an adjacent channel. The definitions of ACLR and ACS are illustrated in Fig. 5.10 for a wanted and an interfering signal received in adja- cent channels. The interfering signal's leakage of unwanted emissions at the wanted signal receiver is given by the ACLR and the ability of the receiver of the wanted signal to sup- press the interfering signal in the 