ero and one additional configured CORESET. A CCE carries exactly 108 bits, that is, 54 REs modulated by QPSK. To improve reli- ability and/or coverage, the PDCCH payload can be transmitted over 1, 2, 4, 8, and 16 CCEs, the so-called aggregation levels. Before the payload is mapped to one or more CCEs, it is channel-coded with polar code and concatenated with CRC. To reduce pars- ing and false alarms, NR increased CRC from 16 to 24 bits compared to LTE. The time-domain location of the first symbol of a CORESET is determined by mon- itoring occasions configured by a search space set. Slots where monitoring occasions occur are determined on the basis of search-space-set S periodicity k, offset o, and dura- tion d. This is illustrated in Figure 6.27, where a common (CSS) set S= 0 is configured with periodicity k = 5, offset 0= 1, and duration d= 2 corresponding to grey blocks. In addition, a search space set is configured with number of PDCCH candidates for ALs 1, 2, 4, 8, and 16, which are randomized using a hashing function similar to LTE EPDCCH. Frame nf Slot n01234567890123456789 ns CSS set S = 0 (k = 5,0=1,d= 2) USS set s = 1 A (k=1,o=0,d=1) USS set 3 A (k=1,o=0,d=1) CCEs total Figure 6.27 Search space sets. 6 5G Physical Layer In a monitoring occasion, a UE blindly decodes the configured PDCCH candidates to find a transmitted PDCCH. Monitoring occasions within a slot are determined by a bitmap. NR supports features where multiple monitoring occasions are also allowed within a slot, to reduce latency. In general, a gNB may configure up to 10 SS sets per BWP. However, UEs capabilities are limited by the number of blind decodings (BDs) UEs are able to perform and the number of CCEs UEs are able to channel-estimate in a slot of a given subcarrier spacing. For example, with 60 kHz subcarrier spacing (SCS), a UE is capable of performing 22 blind decodes and estimating 48 CCEs. If the number of CCEs a UE is configured to monitor in a slot exceeds 48, the UE will not monitor the SS sets with the highest indices; in oth