can be detected by the cells involved in PCID collision regardless of them being neighbors (i.e., both ends of a one-way relationship can detect it). CHAPTER 2 SELF-ORGANIZING NETWORKS IN LTE DEPLOYMENT If two eNodeBs exchange PCIDs and the neighbor lists data via the X2 link, then both cells are in a position to detect and resolve the PCID conflict. A vendor-specific algorithm can determine how the conflict should be resolved. Some of the challenges in PCID conflict resolution may arise when: An operator has chosen a fixed PCID value for a particular cell and SON algorithms are not allowed to override it. An operator has chosen to disable the conflict resolution feature for SON. There are no PCIDs available in the allocated range; this might result in a situation wherein no value would avoid PCID conflict. PCID Confusion When two or more cells on the same neighbor list are using the same PCID value and downlink frequency, it can result in PCID confusion. This condition can be detected at the cell that owns the neighbor list as well as at all of the neighbor cells that are using the same PCID value. Figure 2-5 shows an example of PCID confusion. ENodeB 3 X2-link ENodeB 2 X2-link PCI 3 PCI 8 ENodeB 1 PCI 7 PCI 3 PCI 6 PCI 5 PCI 4 Figure 2-5. Example of PCID confusion In this figure, eNodeB 1 sees that eNodeB 1 and eNodeB 3 have the same PCID (i.e., PCI 3). However, eNodeB 1 and eNodeB 3 do not have an X2 link and are not neighbors, so they cannot resolve the conflict. PCID confusion is detected by eNodeB 2, and it sends an eNodeB configuration update message with Neighbor Information IE (NI) filled appropriately to eNodeB 1 as well as eNodeB 3, which in turn would trigger conflict resolution based on its settings. PCID confusion detection can also be a learned algorithm wherein the eNodeB detects the PCID confusion based on the UE measurement report. For example, consider Figure 2-5 where both eNodeB 1 and eNodeB 3 have a cell with PCI 3. Assuming that the eNodeB 2 is unaware of the cell with PCI 3 within eNodeB 1