imum control channel overhead is 21% assuming three symbols and the entire carrier bandwidth used for CORESET, while a more typical overhead is 7% when one-third of the time and frequency New Radio Access Physical Layer Aspects (Part 2) 417 Table 4.1: Various downlink reference signals and their corresponding overhead [73,74]. Reference Description Overhead Signal Type PDSCH DM-RS The DM-RS can occupy 1/3, 1/2 or one full 2.4%-29% OFDM symbol. 1, 2, 3 or 4 symbols per slot can be configured to carry DM-RS. PDSCH PT-RS One resource element in frequency domain 0.2%-0.5% every second or fourth resource block. PT-RS is mainly intended for FR2. CSI-RS One resource element per resource block per 0.25% for eight antenna ports antenna port per CSI-RS periodicity transmitted every 20 ms with 15 kHz subcarrier spacing Two slots with two symbols in each with comb- 0.36% or 0.18% for 20 ms and 40 ms 4 configuration periodicity, respectively and 15 kHz subcarrier spacing resources in the first three symbols of a slot are allocated to PDCCH. The overhead due to the SS/PBCH block is given by the number of SS/PBCH blocks transmitted within the SS/ PBCH block period, the SS/PBCH block periodicity and the subcarrier spacing. Assuming 100 resource blocks across the carrier, the overhead for 20 ms periodicity is in the range of 0.6%-2.3% if the maximum number of SS/PBCH blocks is transmitted [73,74]. 4.1.2.1 Demodulation Reference Signals The main application of DM-RS in NR is to estimate the channel coefficients for coherent detection of the physical channels. In the downlink, the DM-RS is used for channel estima- tion and is subject to the same precoding as PDSCH; thus the (transmit-side) precoding is transparent to the receiver and is viewed as part of the overall channel. There is a trade-off between the channel estimation accuracy and DM-RS density/overhead. If the channel exhi- bits severe frequency-selectivity (i.e., narrower channel coherence bandwidth), the DM-RS density in the frequency-domain should be increased. Similarl