LTE Allocation Type

In PfFfMacScheduler.cc, we have a piece of code for definition of the Allocation type.

int PfType0AllocationRbg[4] = { 10, // RGB size 1 26, // RGB size 2 63, // RGB size 3 110 // RGB size 4}; // see table 7.1.6.1-1 of 36.213To understand the meaning of the values in this int array, we have to go deeper. One challenge in the signaling of the resource allocation is the compromise between flexibility and overhead. The simplest way to signaling the resource allocation would be the the assignment of one bit for each PRB (Physical Resource Block), indicating the allocation of these PRBs for each UE. However, this approach is not scalable. One possible solution would be the combination of a group of PRBs to reduce the overhead.In this sense, the 3GPP created different resource allocation methods with different approaches to perform this combination. NS-3 has adopted the allocation Type 0.In resource allocations of Type 0, a bitmap indicates theResource Block Groups (RBGs) which are allocated to the scheduled UE, where a RBG is aset of consecutive PRBs. The RBG size (P) is a function of the system bandwidth as shownin Table 1. The total number of RBGs (N_RBG) for a downlink system bandwidth of N_RBPRBs is given by N_RBG = N_RB/P [Sesia].Table 1 - RBG size for type 0 resource allocation.

As an example, if a downlink system has N_RB = 25, from the Table 1, P = 2 and N_RBG = 13. In this case, each bit in the bitmap indicates a pair of PRBs.