e reduced either by avoiding scheduling some of the resource blocks in some of the cells (reuse-n, n > 1, or fractional reuse; see Figure 4.10) or by coordinating the © 2009 by Taylor & Francis Group, LLC Architecture and Protocol Support for RRM Reuse-1 Collision = > Interference Interference User A User B User B Empty resource block User A Figure 4.9 Intercell interference in a reuse-1 system (showing the uplink case). allocation of the resource blocks in neighbor cells. In case of fractional reuse, cer- tain resource blocks are barred for use on the cell edge, as illustrated in Figure 4.11. Because reuse-n systems tend to underutilize radio resources, the consensus within the 3GPP is that LTE should be a reuse-1 system [46]. Similar arguments can be raised against fractional reuse systems with certain resource blocks barred on the cell edge. Therefore, in LTE such (static) barring will not be employed, either. Building on the reuse-1 agreement, the coordination of the scheduler operation as an optional means to improve the cell edge SINR distribution is, however, supported. Reuse-n/Fractional Reuse User A User B User B User A Empty resource block Barred for exterior users (Fractional reuse) Barred for use completely (Reuse-n) Figure 4.10 Intercell interference in a reuse-n or in a fractional reuse system. © 2009 by Taylor & Francis Group, LLC Long Term Evolution: 3GPP LTE Radio and Cellular Technology Cell-o Random Cell-1 Cell-o Coordinated Cell-1 Allocation Barred of exteriors RBs (R1) for exteriors Collision Collision Zone (CZ) Zone (CZ) Barred RBs (RO) Allocation for exteriors of exteriors Figure 4.11 Example of fractional reuse with (static) barring of resource blocks on the cell edge. In a random allocation, both cells select the RBs to schedule UEs randomly in the frequency domain (or based on the frequency-dependent chan- nel quality of RBs). In the coordinated allocation, the two cells start the alloca- tion of RBs from the two ends of the frequency band, starting the allocation with the exterior UEs f