MAC layer allocates the multiple contiguous RBs, but there is no guarantee that they are aligned contiguously when they get transmitted at PHY layer. It means that there should be a some rule to convert this logical/virtual RB allocation in MAC to PRB allocation in PHY.
There are two type of the conversion, one is Localized and the other is Distributed.
- Localized when both virtual allocation and physical allocation are mapped one to one.
- Distributed, when the VRB allocation is contiguous, but PRB allocation is not contiguous. It means that , PRBs may get distributed over wider frequency ranges because there is high possibility that you may not find contiguous PRBs throughout your bandwidth.
I hope it helps !!