information cannot rely on a UE-specific search space as different devices would monitor different CCEs despite the message being intended for all of them. Thus common search spaces are defined, where a common search space is similar in structure to a UE-specific search space with the differ- ence that the set of CCEs is predefined and known to all devices irrespective of their own identity [14]. Chapter 4 Common search space Common search space UE-specific search space (monitoring periodicity (monitoring periodicity Dedicated RRC [RRC configured per serving cell] and offset and number of and offset and number of configuration (monitoring periodicity and offset and candidates per candidates per number of candidates per aggregation level) aggregation level) aggregation level) CORESET CORESET 1 CORESET One slot OFDM symbol No monitoring in Aggregation Level 4 is No monitoring in this occasion of monitored this occasion of the search space the search space CORESETs containing search spaces with aggregation level 2 Figure 4.22 Procedure for PDCCH search space configuration and example search spaces [68]. The number of blind decoding attempts is proportional to subcarrier spacing and the slot duration. For 15/30/60/120 kHz subcarrier spacing, up to 44/36/22/20 blind decoding attempts per slot can be supported across all DCI payload sizes, respectively. It must be noted that the number of blind decoding attempts is not the only measure of UE complexity, channel estimation efforts also need to be taken in consideration. The number of channel estimations for subcarrier spacings of 15/30/60/120 kHz has been limited to 56/56/48/32 CCEs across all CORESETs in a slot [8]. Depending on the configuration, the number of PDCCH candidates may be limited either by the number of blind decoding attempts, or by the number of channel estimates. In order to minimize the device complexity, a device monitors a maximum of three different DCI sizes using C-RNTI and one DCI size using other RNTIs. In carrier aggregation scenarios, the gener