Based on DCI formats In LTE Three types of allocation are used:
type 0: DCI formats 1, 2, 2A
type 1: DCI formats 1, 2, 2A
type 2: DCI formats1A, 1B, 1C, 1D
One bit in the header is indicating if DCI formats 1, 2, 2A are of type 0 or type 1.

Type 0:
A number of resource blocks forms a resource block group (RBG). A bitmap indicates which RBG(s) is/are allocated in the corresponding TTI. I.e. a group-wise addressing of resources is used. The number of PRBs per group (RBG size) P depends on the cell bandwidth – see Below table.

Type 1:
In type 1 allocation P RGB subsets are in use. There are 3 fields in the allocation to
address single PRBs of an indicated group. Additionally a resource allocation shift
may be applied.

Type 2:
Contiguous allocations are made by type 2. The virtual RBs are localized or distributed. In case of 1A, 1B or 1D the distributed version is signaled by a flag where for 1C this is always the case.

Applicable bandwidths:
- localized: 1 VRB .. system BW
- 1A distributed: 1 .. N_VRB if P-RNTI, RA-RNTI or SI-RNTI scrambled.
- 1B, 1D or 1A distributed, C-RNTI scrambled:1 :: N_VRB (BW = 6 .. 49) and 1 .. 16
(BW = 50..110).
- 1C : N_step .. floor(N_VRB / N_step) * N_step.
N_step = 2 (BW = 6..49), = 4 (BW=50 .. 100).