eSize. The interleaving function is defined by (j)=rC+c+nshifmodNCORESET/LReG;j = 1, R - 1; = 0, 1, C - 1 andC =NCORESET/LREGR where Re {2, 3, 6} is given by the higher layer parameter interleaverSize. Other parameters are defined as fol- lows: = a PDCCH transmitted in a CORESET configured by the PBCH or SIB1, nshift {0, 1, 274} is given by the RRC parameter shiftIndex. The UE is not expected to monitor configurations for which C is not an integer. For both interleaved and non-interleaved mappings, the same precoding is used within an REG bundle, if the higher layer parameter precoderGranularity equals LREG. The same precoding is used across all REGs within the set of contiguous resource blocks in the CORESET, if the higher layer parameter precoderGranularity equals the size of the CORESET in the frequency domain. For a CORESET configured by PBCH, LREG = 6,R = 2 and the same precoding is used within the REG bundle [6]. Unlike LTE, where the length of the control region can vary dynamically as indicated by PCFICH, a CORESET in NR is of fixed size. This is important from an implementation perspective, both for the UE and the network. From the UE perspective, a pipelined implementation is simpler, if the device can directly start to decode PDCCH without having to first decode another control channel. Various REG-to- CCE mapping options are shown in Fig. 4.18. During the PDCCH detection and decoding process, the UE needs to estimate the channel using the reference signals associated with the PDCCH candidate being decoded. A single antenna port is used for PDCCH transmission which means any transmit diversity or multi- user MIMO scheme is handled in a device-transparent manner. The PDCCH has its own DM-RS, based on the same pseudo-random sequence that is used for PDSCH, that is, the pseudo-random sequence is generated across all the common resource blocks in the REG-to-CCE mapping REG-to-CCE mapping (time REG-to-CCE mapping REG-to-CCE mapping (time (frequency first allocation) first allocation) (frequency first alloca