or a 20 MHz bandwidth. In resource allocation type 1, a bitmap indicates physical resource blocks inside a selected resource block group subset. The information field for the resource block assignment on PDCCH is divided into three fields: one field indicates the selected resource block group subset; a 1-bit field indicates whether an offset shall be applied when the bitmap is mapped to the resource 470 CHAPTER 9 The IEEE 802. 16m Physical Layer (Part I) 3rd RBG subset 2nd RBG subset 1st RBG subset 0th RBG subset 3rd RBG subset 2nd RBG subset 1st RBG subset One Resource Block Group (RBG) with 4 0th RBG subset Resource Blocks FIGURE 9-74 Resource block groups for resource allocation type 0/1 (example: 20 MHz bandwidth and each resource block group contains 4 resource blocks) blocks; and another field contains the bitmap that indicates specific physical resource blocks inside the resource block group subset. In resource allocation type 2, physical resource blocks are not directly allocated. Instead, virtual resource blocks are allocated which are then mapped to physical resource blocks. The information field for the resource block assignment carried on PDCCH contains a Resource Indication Value (RIV) from which the starting virtual resource block and a length in terms of contiguously allocated virtual resource blocks can be derived. Both localized and distributed virtual resource block assignment is possible; they are differentiated by a one-bit flag within the DCI. In the localized case, there is a one-to-one mapping between virtual and physical resource blocks. In the distributed case of resource allocation type 2, the virtual resource block numbers are mapped to physical resource block numbers according to a certain rule, [30] and inter-slot hopping is applied. Frequency diversity is achieved if the first part of a virtual resource block pair is mapped to one physical resource block and the other part of the virtual resource block pair is mapped to a physical resource block which is at a predefined distance in f