1. A PHYSICAL CELL ID (PCI) allocation method for allocating a PCI by a target base station to a target cell belonging to the target base station, comprising:
obtaining, by a target base station, a usable PCI list sent by an Operations And Maintenance (OAM) function entity;
obtaining, by the target base station, E-UTRA Absolute Radio Frequency Channel Number (EARFCN) information of neighbour cells of serving cells via an X2 interface message; and
removing, by the target base station, limited PCIs of the target cell from the usable PCI list to obtain a selectable PCI set according to the obtained the EARFCN information of the neighbour cells of the serving cells;
wherein the removing, by the target base station, limited PCIs of the target cell from the usable PCI list comprises:
obtaining, by the target base station, a first reference PCI set in a predefined manner, wherein cell EARFCN information in the first reference PCI set is different from that of the target cell of the target base station;
forming, by the target base station, a second reference PCI set based on the intersection of the usable PCI list and the first reference PCI set; and
randomly selecting, by the target base station, a PCI from the selectable PCI set as the PCI of the target cell, or randomly selecting, by the target base station, a PCI from the second reference PCI set as the PCI of the target cell if the selectable PCI set is empty.', 'obtaining, by a target base station, a usable PCI list sent by an Operations And Maintenance (OAM) function entity;', 'obtaining, by the target base station, E-UTRA Absolute Radio Frequency Channel Number (EARFCN) information of neighbour cells of serving cells via an X2 interface message; and', 'removing, by the target base station, limited PCIs of the target cell from the usable PCI list to obtain a selectable PCI set according to the obtained the EARFCN information of the neighbour cells of the serving cells;', 'wherein the removing, by the target base station, limited PCIs of the target cell from the usable PCI list comprises:', 'obtaining, by the target base station, a first reference PCI set in a predefined manner, wherein cell EARFCN information in the first reference PCI set is different from that of the target cell of the target base station;', 'forming, by the target base station, a second reference PCI set based on the intersection of the usable PCI list and the first reference PCI set; and', 'randomly selecting, by the target base station, a PCI from the selectable PCI set as the PCI of the target cell, or randomly selecting, by the target base station, a PCI from the second reference PCI set as the PCI of the target cell if the selectable PCI set is empty.

2. The method according to claim 1, wherein the obtaining, by the target base station, a first reference PCI set in a predefined manner comprises:
collecting, by the target base station via an X2 interface, the PCIs and the EARFCN information of cells supported by all base stations in X2 connection with the target base station and the PCIs and the EARFCN information used by neighbour cells of the cells supported by all base stations; and
determining by the target base station the PCIs of one or more cells corresponding to the collected EARFCN information which is different from that of the target cell as the first reference PCI set.', 'collecting, by the target base station via an X2 interface, the PCIs and the EARFCN information of cells supported by all base stations in X2 connection with the target base station and the PCIs and the EARFCN information used by neighbour cells of the cells supported by all base stations; and', 'determining by the target base station the PCIs of one or more cells corresponding to the collected EARFCN information which is different from that of the target cell as the first reference PCI set.

3. The method according to claim 2, wherein
if the selectable PCI set is empty, then the target base station sends a first response message to the OAM function entity to notify the OAM function entity that it has been failed to select a PCI for the target cell from the selectable PCI set; and
after obtaining the response message, the OAM function entity determines whether the target base station has selected a PCI for the target cell from the second reference PCI set and sends the result of the determination to the target base station.', 'if the selectable PCI set is empty, then the target base station sends a first response message to the OAM function entity to notify the OAM function entity that it has been failed to select a PCI for the target cell from the selectable PCI set; and', 'after obtaining the response message, the OAM function entity determines whether the target base station has selected a PCI for the target cell from the second reference PCI set and sends the result of the determination to the target base station.

4. The method according to claim 2, wherein
if the target base station fails to allocate a PCI to the target cell by selecting one from the second reference PCI set, then it sends a second response message to the OAM function entity to notify the OAM function entity that it has been failed to select a PCI for the target cell from the second reference PCI set.', 'if the target base station fails to allocate a PCI to the target cell by selecting one from the second reference PCI set, then it sends a second response message to the OAM function entity to notify the OAM function entity that it has been failed to select a PCI for the target cell from the second reference PCI set.

5. The method according to claim 2, wherein the X2 interface message comprises: an X2 setup request message, an X2 setup response message and an eNB configuration update message.

6. The method according to claim 1, wherein the obtaining, by the target base station, a first reference PCI set in a predefined manner comprises:
collecting, by the target base station collects, via an X2 interface, the PCIs and the EARFCN information used by neighbour cells of cells supported by all base stations in X2 connection with the target base station; and
determining by the target base station the PCIs of one or more cells corresponding to the collected EARFCN information which is different from that of the target cell as the first reference PCI set.', 'collecting, by the target base station collects, via an X2 interface, the PCIs and the EARFCN information used by neighbour cells of cells supported by all base stations in X2 connection with the target base station; and', 'determining by the target base station the PCIs of one or more cells corresponding to the collected EARFCN information which is different from that of the target cell as the first reference PCI set.

7. The method according to claim 6, wherein
if the selectable PCI set is empty, then the target base station sends a first response message to the OAM function entity to notify the OAM function entity that it has been failed to select a PCI for the target cell from the selectable PCI set; and
after obtaining the response message, the OAM function entity determines whether the target base station has selected a PCI for the target cell from the second reference PCI set and sends the result of the determination to the target base station.', 'if the selectable PCI set is empty, then the target base station sends a first response message to the OAM function entity to notify the OAM function entity that it has been failed to select a PCI for the target cell from the selectable PCI set; and', 'after obtaining the response message, the OAM function entity determines whether the target base station has selected a PCI for the target cell from the second reference PCI set and sends the result of the determination to the target base station.

8. The method according to claim 6, wherein
if the target base station fails to allocate a PCI to the target cell by selecting one from the second reference PCI set, then it sends a second response message to the OAM function entity to notify the OAM function entity that it has been failed to select a PCI for the target cell from the second reference PCI set.', 'if the target base station fails to allocate a PCI to the target cell by selecting one from the second reference PCI set, then it sends a second response message to the OAM function entity to notify the OAM function entity that it has been failed to select a PCI for the target cell from the second reference PCI set.', '9. The method according to claim 6, wherein the X2 interface message comprises: an X2 setup request message, an X2 setup response message and an eNB configuration update message.', '10. The method according to claim 1, wherein the obtaining, by the target base station, a first reference PCI set in a predefined manner comprises:
collecting, by the target base station via an X2 interface, the PCIs and the EARFCN information used by neighbour cells of cells supported by all base stations in X2 connection with the target base station; and
removing, by the target base station, the PCIs of all cells whose EARFCN information is different from that of the target cell, reported by user equipment, from the PCIs of one or more cells corresponding to the collected EARFCN information different from that of the target cell to obtain one or more PCIs, and determines these PCIs as the first reference PCI set.', 'collecting, by the target base station via an X2 interface, the PCIs and the EARFCN information used by neighbour cells of cells supported by all base stations in X2 connection with the target base station; and', 'removing, by the target base station, the PCIs of all cells whose EARFCN information is different from that of the target cell, reported by user equipment, from the PCIs of one or more cells corresponding to the collected EARFCN information different from that of the target cell to obtain one or more PCIs, and determines these PCIs as the first reference PCI set.', '11. The method according to claim 10, wherein
if the selectable PCI set is empty, then the target base station sends a first response message to the OAM function entity to notify the OAM function entity that it has been failed to select a PCI for the target cell from the selectable PCI set; and
after obtaining the response message, the OAM function entity determines whether the target base station has selected a PCI for the target cell from the second reference PCI set and sends the result of the determination to the target base station.', 'if the selectable PCI set is empty, then the target base station sends a first response message to the OAM function entity to notify the OAM function entity that it has been failed to select a PCI for the target cell from the selectable PCI set; and', 'after obtaining the response message, the OAM function entity determines whether the target base station has selected a PCI for the target cell from the second reference PCI set and sends the result of the determination to the target base station.', '12. The method according to claim 10, wherein
if the target base station fails to allocate a PCI to the target cell by selecting one from the second reference PCI set, then it sends a second response message to the OAM function entity to notify the OAM function entity that it has been failed to select a PCI for the target cell from the second reference PCI set.', 'if the target base station fails to allocate a PCI to the target cell by selecting one from the second reference PCI set, then it sends a second response message to the OAM function entity to notify the OAM function entity that it has been failed to select a PCI for the target cell from the second reference PCI set.', '13. The method according to claim 10, wherein the X2 interface message comprises: an X2 setup request message, an X2 setup response message and an eNB configuration update message.', '14. The method according to claim 1, wherein the obtaining, by the target base station, a first reference PCI set in a predefined manner comprises:
collecting, by the target base station, the PCIs and the EARFCN information of surrounding cells reported by user equipment, the PCIs and the EARFCN information of cells supported by all base stations in X2 connection with the target base station via an X2 interfaces, the PCIs and the EARFCN information used by neighbour cells of cells supported by all base stations, and the PCIs and the EARFCN information of the surrounding cells monitored by the target base station itself; and
determining, by the target base station the PCIs of one or more cells corresponding to the collected EARFCN information different from that of the target cell as the first reference PCI set.', 'collecting, by the target base station, the PCIs and the EARFCN information of surrounding cells reported by user equipment, the PCIs and the EARFCN information of cells supported by all base stations in X2 connection with the target base station via an X2 interfaces, the PCIs and the EARFCN information used by neighbour cells of cells supported by all base stations, and the PCIs and the EARFCN information of the surrounding cells monitored by the target base station itself; and', 'determining, by the target base station the PCIs of one or more cells corresponding to the collected EARFCN information different from that of the target cell as the first reference PCI set.', '15. The method according to claim 14, wherein
if the selectable PCI set is empty, then the target base station sends a first response message to the OAM function entity to notify the OAM function entity that it has been failed to select a PCI for the target cell from the selectable PCI set; and
after obtaining the response message, the OAM function entity determines whether the target base station has selected a PCI for the target cell from the second reference PCI set and sends the result of the determination to the target base station.', 'if the selectable PCI set is empty, then the target base station sends a first response message to the OAM function entity to notify the OAM function entity that it has been failed to select a PCI for the target cell from the selectable PCI set; and', 'after obtaining the response message, the OAM function entity determines whether the target base station has selected a PCI for the target cell from the second reference PCI set and sends the result of the determination to the target base station.', '16. The method according to claim 14, wherein
if the target base station fails to allocate a PCI to the target cell by selecting one from the second reference PCI set, then it sends a second response message to the OAM function entity to notify the OAM function entity that it has been failed to select a PCI for the target cell from the second reference PCI set.', 'if the target base station fails to allocate a PCI to the target cell by selecting one from the second reference PCI set, then it sends a second response message to the OAM function entity to notify the OAM function entity that it has been failed to select a PCI for the target cell from the second reference PCI set.', '17. The method according to claim 14, wherein the X2 interface message comprises: an X2 setup request message, an X2 setup response message and an eNB configuration update message.', '18. The method according to claim 1, wherein
if the selectable PCI set is empty, then the target base station sends a first response message to the OAM function entity to notify the OAM function entity that it has been failed to select a PCI for the target cell from the selectable PCI set; and
after obtaining the response message, the OAM function entity determines whether the target base station has selected a PCI for the target cell from the second reference PCI set and sends the result of the determination to the target base station.', 'if the selectable PCI set is empty, then the target base station sends a first response message to the OAM function entity to notify the OAM function entity that it has been failed to select a PCI for the target cell from the selectable PCI set; and', 'after obtaining the response message, the OAM function entity determines whether the target base station has selected a PCI for the target cell from the second reference PCI set and sends the result of the determination to the target base station.', '19. The method according to claim 1, wherein
if the target base station fails to allocate a PCI to the target cell by selecting one from the second reference PCI set, then it sends a second response message to the OAM function entity to notify the OAM function entity that it has been failed to select a PCI for the target cell from the second reference PCI set.', 'if the target base station fails to allocate a PCI to the target cell by selecting one from the second reference PCI set, then it sends a second response message to the OAM function entity to notify the OAM function entity that it has been failed to select a PCI for the target cell from the second reference PCI set.

20. The method according to claim 1, wherein the X2 interface message comprises at least one of: an X2 setup request message, an X2 setup response message and an eNB configuration update message.

21. A base station, comprising:
a first obtaining module, which is used for obtaining a usable PCI list sent by an Operations And Maintenance (OAM) function entity and limited PCIs of a target cell;
a first processing module, which is used for removing the limited PCIs of the target cell from the usable PCI list to obtain a selectable PCI set;
a second obtaining module, which is used for obtaining a first reference PCI set in a predefined manner according to E-UTRA Absolute Radio Frequency Channel Number (EARFCN) information of a cell obtained by an X2 interface message, wherein the cell EARFCN information in the first reference PCI set is different from that of the target cell;
a second processing module, which is used for forming a second reference PCI set based on the intersection of the first reference PCI set obtained by the second obtaining module and the usable PCI list;
a selecting module, which is used for selecting a PCI for the target cell; and
a calling module, which is used for calling the selecting module which randomly selects a PCI from the selectable PCI set obtained by the first processing module as the PCI of the target cell, and randomly selects a PCI from the second reference PCI set obtained by the second processing module as the PCI of the target cell if the selectable PCI set is empty.', 'a first obtaining module, which is used for obtaining a usable PCI list sent by an Operations And Maintenance (OAM) function entity and limited PCIs of a target cell;', 'a first processing module, which is used for removing the limited PCIs of the target cell from the usable PCI list to obtain a selectable PCI set;', 'a second obtaining module, which is used for obtaining a first reference PCI set in a predefined manner according to E-UTRA Absolute Radio Frequency Channel Number (EARFCN) information of a cell obtained by an X2 interface message, wherein the cell EARFCN information in the first reference PCI set is different from that of the target cell;', 'a second processing module, which is used for forming a second reference PCI set based on the intersection of the first reference PCI set obtained by the second obtaining module and the usable PCI list;', 'a selecting module, which is used for selecting a PCI for the target cell; and', 'a calling module, which is used for calling the selecting module which randomly selects a PCI from the selectable PCI set obtained by the first processing module as the PCI of the target cell, and randomly selects a PCI from the second reference PCI set obtained by the second processing module as the PCI of the target cell if the selectable PCI set is empty.']