Closed subscriber group cell handover

A serving base station for assisting in handover of a radio terminal connection from the serving base station associated with a serving cell to a closed subscriber group (CSG) cell served by a CSG base station, where only a radio terminal belonging to the CSG, as indicated by a radio terminal identifier qualifying the radio terminal as an authorized subscriber to the CSG, is permitted to access and receive service from the CSG cell, and where information is provided to radio terminals in the serving cell that identify radio terminals that are not to report to the serving base station signal quality measurements of signals transmitted by the CSG base station, the serving base station comprising:

• radio transceiving circuitry, and
• a data processing system including electronic circuitry configured to:
• determine that one of the radio terminals in the serving cell is authorized to access and receive service from the CSG cell;
• send a message to the one radio terminal indicating that the CSG cell may be considered as a handover candidate for the radio terminal;
• based on a signal quality measurement report for the CSG base station, determine that a connection with the one radio terminal may be handed over to the CSG base station;
• and
• facilitate handover of the connection to the CSG base station,
• wherein radio terminals have been informed not to report to the serving base station signal quality measurements of signals transmitted by the CSG base station using a first message that indicates that the CSG cell is forbidden for general access, and wherein the electronic circuitry is configured to generate a second subsequent message to be transmitted via the radio transceiving circuitry to the one radio terminal indicating that the one radio terminal should report signal quality measurements of signals transmitted by the CSG base station.

A serving base station for assisting in handover of a radio terminal connection from the serving base station associated with a serving cell to a closed subscriber group (CSG) cell served by a CSG base station, where only a radio terminal belonging to the CSG, as indicated by a radio terminal identifier qualifying the radio terminal as an authorized subscriber to the CSG, is permitted to access and receive service from the CSG cell, and where information is provided to radio terminals in the serving cell that identify radio terminals that are not to report to the serving base station signal quality measurements of signals transmitted by the CSG base station, the serving base station comprising:

• radio transceiving circuitry, and
• a data processing system including electronic circuitry configured to:
• determine that one of the radio terminals in the serving cell is authorized to access and receive service from the CSG cell;
• send a message to the one radio terminal indicating that the CSG cell may be considered as a handover candidate for the radio terminal;
• based on a signal quality measurement report for the CSG base station, determine that a connection with the one radio terminal may be handed over to the CSG base station;
• and
• facilitate handover of the connection to the CSG base station,
• wherein the radio transceiving circuitry broadcasts information not to report to the serving base station signal quality measurements of signals transmitted by the CSG base station in the serving cell and includes a list identifying cells for which the information is not to be reported or a list of cells identifying only those cells for which the information is to be reported, and
• wherein the radio transceiving circuitry is configured to broadcast a modified cell list in the serving cell to modify those cells for which the information is not to be reported.

A radio terminal for communicating with a serving base station associated with a serving cell, where the radio terminal belongs to a closed subscriber group (CSG) cell served by a CSG base station, and where only a radio terminal belonging to the CSG, as indicated by a radio terminal identifier qualifying the radio terminal as an authorized subscriber to the CSG, is permitted to access and receive service from the CSG cell, comprising:

• radio transceiving circuitry, and
• a data processing system coupled to the radio transceiving circuitry including electronic circuitry configured to:
• receive first information informing the radio terminal not to report to the serving base station signal quality measurements of signals transmitted by CSG base stations;
• obtain a measure of quality of signals transmitted by neighboring base stations other than CSG base stations and report those signal quality measurements to the serving base station for a possible handover operation;
• receive second information overriding the first information and informing the radio terminal to report to the serving base station signal quality measurements of signals transmitted by the CSG base station;
• and
• measure a signal quality of a signal transmitted by the CSG base station and report the CSG base station signal quality measurement to the serving base station.

A central node, comprising:

• an interface for communicating with a serving base station serving a serving cell and with a closed subscriber group (CSG) base station serving a CSG cell in which only a radio terminal belonging to the CSG, as indicated by a radio terminal identifier qualifying the radio terminal as an authorized subscriber to the CSG, is permitted to access and receive service from the CSG cell;
• a memory for storing a CSG authorization list which for each of multiple radio terminals identifies all CSG cells that the radio terminal is authorized to access and receive service from;
• and
• a controller configured to provide a CSG authorization list to the serving base station serving a radio terminal in the serving cell when the CSG authorization list includes CSG cells which the radio terminal is authorized to access, and to otherwise not provide the CSG authorization list to the serving base station,
• wherein the controller is further configured to determine a CSG PLMN identity associated with one or more CSG cells that the radio terminal is authorized to access, and when the central node is notified that the radio terminal has accessed the serving cell, to check whether the CSG PLMN identity corresponds to a compatible PLMN identity associated with the serving cell, and if so, to inform the serving base station about the one or more CSG cells.