n frequencies separated from the center frequency of the emission by 2.5 X or more of the necessary bandwidth of the emission will generally be considered as emissions in the spurious domain. However, this frequency separation may be dependent on the type of modulation, the maximum symbol rate in the case of digital modulation, the type of transmitter, and frequency coordination factors. For example, in the case of some digital, broadband, or pulse-modulated systems, the frequency separation may need to differ from the 2.5 X factor. For multi-channel or multi-carrier transmitters, where several carriers may be transmitted simultaneously from the PA or an AAS, the center frequency of the emission is taken to be the center of either the assigned bandwidth of the BS or of the - 3 dB bandwidth of the transmitter, using the lesser of the two bandwidths. The above separation of the requirements can be easily applied to systems with fixed chan- nel bandwidth. It does; however, become more difficult for NR, which supports flexible bandwidths, implying that the frequency range where requirements apply would then vary 682 Chapter 5 Table 5.10: Maximum offset of operating band unwanted emission outside the downlink operating bands [5]. BS Type Operating Band (MHz) Afobue (MHz) BS Type 1-H fDL-high - fDL-low < 100 100  DDL-high fDL-low < 900 BS Type 1-C fDL-high - fDL-low < 200 200 fDL-high fDL-low < 900 with the channel bandwidth. The approach taken for defining the boundary in 3GPP is slightly different for BS and the device requirements. With the recommended boundary between OOB emissions and spurious emissions set at 2.5 the channel bandwidth, third- order and fifth-order intermodulation products from the carrier will fall inside the OOB domain, which will cover a frequency range of twice the channel bandwidth on each side of the carrier. For the OOB domain, two overlapping requirements are defined for the BS and the device, namely, spectrum emissions mask (SEM) and ACLR. The OOB emission requirement for the BS transmitt