Ref 36.213 Sec 7.1.6
PDCCH DCI formats 1, 2, 2A, 2B, 2C and 2D with type 0/1
-In Type0 RAT, allocations happen on contiguous RBGs (RB groups) therefore the limitations of Type0 is that it can lead to the wastage of RB's
-In Type1 RAT, allocations happen in a more granular fashion and frequency diversity in the system, by distributing the RBs across freq domain and allocating them subset ids. UE comes to know the subset id eNB has used for allocation based on the subset id and a bitmap.
PDCCH with DCI format 1A, 1B, 1C and 1D have a type 2
-In Type2, RAT the assignment information indicates to a scheduled UE a set of
contiguously allocated localized virtual resource blocks or distributed virtual resource blocks.
For 1A/B/D - 1bit flag indicates whether localized virtual resource blocks or distributed virtual resource
blocks are assigned
For 1C - Always distributed VRBs.