CORESET indicates the number of symbols and RBs occupied by a PDCCH. A CORESET consists of {1, 2, 3} symbols in the time domain (also called PDCCH duration) and many RBs in frequency domain (depends upon number of REGs in a CORESET; 1 REG = 12 RE = 1 PRB). The specific number of symbols and RBs are configured by higher layer parameters. The REG in the CORESET is numbered from 0 according to the time domain priority.
