r cellular networks to date, for example, millimeter waves. Physical control resources, over which the PDCCH is transmitted, are configured using COntrol REsource SETs (CORESET). In the frequency domain, a CORESET other than zero is configured on a BWP in full chunks of 6 RBs on a 6RB grid as shown in Figure 6.22. The 6RB grid originates in Point A, which determines also the start of the cell's common RB (CRB) grid. Consequently, the gNB may configure CORESET to be discontinuous in frequency, to, for example, accommodate a narrow-band system within the serving cell or to improve frequency diversity. On the other hand, CORESET zero used in initial access is contiguous, does not need to be 6RB grid aligned, and is config- ured using 4 bits in the Master Information Block (MIB) with a limited set of parameters (Figure 6.25). An additional property of CORESET is its time-domain length of 1 to 3 OFDM symbols. The physical resources of a configured CORESET are separated into Resource CORESET grid CORESET= 0 CORESET # 0 CORESET # 0 BWP (48 PRB) Figure 6.25 CORESET configuration in frequency domain. 6.10 Downlink Signaling Transmission REG bundle Interleaved CORESET of length 2OS and size 24 RB Non-interleaved CORESET of length 2OS and size 24 RB Figure 6.26 CORESET structure. Element Groups (REGs), each containing 9 Resource Elements (REs) to carry the payload and 3 REs of Demodulation Reference Signals (DMRSs) in an RB-symbol cluster. These REGs are further clustered into REG bundles of 2, 3, or 6 REGs, for which the precoder is constant. The REG bundles may be further interleaved and mapped to the logical control channel element (CCE) consisting of 6 REGs. Figure 6.26 illustrates the units of a CORESET. Whether REG bundles are interleaved or not as well as the REG bundle size is configurable for a CORESET, addressing the operator's needs for frequency diversity and channel estimation quality in its deployment. Up to 3 CORESETs can be configured per BWP. However, the minimum requirement for a UE is to support CORESET z