The radio performance in the 3rd Generation (3G) network has been improved greatly. However, from the perspective of commercial operation, the operator needs to reduce costs of network construction and operation so as to win the markets with more cost-efficient network services for the users. The linchpin of reducing the operation cost is to reduce the network planning and network optimization processes that involve manual operation, thereby enhancing the network automation functions. Consequently, PCT automatic allocation is an important content of the radio network system planning and optimization currently.
The automatic allocation of PCIs is performed by an Evolved Node B which is also called an eNB. The automatic allocation aims to allocate a proper PCI automatically for the newly introduced cell of the eNB. According to the protocol, there are 504 available PCIs in total. Therefore, in the practical networking, it is necessary to multiplex such PCIs. If the PCIs are allocated improperly, the PCI may conflict between the cells. Given below are two examples of the conflict:
I. As shown in FIG. 1, there are three cells: cell 1 (101), cell 2 (102), and cell 3 (103). Cell 1 and cell 3 work under the same frequency, and their PCI is the same, namely, PCIA; cell 2 is direct neighbor of cell 1 and cell 3. (Two cells in radio-sense adjacent to each other or (partially) overlapping as regards geographical radio coverage are examples of direct neighbors); and the PCI of cell 2 is PCIB. When the User Equipment (UE) in cell 2 initiates a handover request, the UE detects cell 1 and cell 3. Because cell 1 and cell 3 have the same PCI, the eNB of cell 2 is unable to determine which cell can serve as a target cell according to the PCI, and the eNB is unable to notify the UE to hand over.
II. As shown in FIG. 2, there are two adjacent cells: cell 1 and cell 2. Cell 1 is partially overlapping with cell 2; cell 1 and cell 2 are working under the same frequency and have the same PCI, namely, PCIA. If the UE is in the overlap of cell 1 and cell 2, the UE can detect at most one cell.
In order to avoid the foregoing conflict, precise planning need be performed at the time of allocating the PCI to the cell.
The existing standard provides a mechanism of allocating the PCIs in a same-frequency scenario as follows. When an eNB is started, the eNB obtains the PCI used by one or more cells neighboring the one or more cells of the started eNB through an X2 or S1 interface message. Therefore, a PCI unused by the adjacent cell of the cell under the new eNB is allocated to the cell under the new eNB, and the foregoing conflict is avoided.
The foregoing method provides automatic allocation of PCI for cells operating on the same-frequency. According to prior art, for cells operating on disjoint frequencies, no corresponding mechanism is available to PCI allocation and PCI conflict therefore may occur.