First base station, second base station, and method

1. A first base station comprising:

a memory storing instructions; and

one or more processors configured to execute the instructions to:

communicate with a terminal apparatus in accordance with a first radio access technology;

obtain handover result information related to results of handovers from the first base station to other base stations; and

transmit, when a terminal apparatus performs a handover from the first base station to a second base station communicating in accordance with a second radio access technology, an Application Protocol message including the handover result information to the second base station, wherein

the one or more processors are configured to execute the instructions to set, in the Application Protocol message, a RAN-INFORMATION RIM container including the handover result information to transmit the Application Protocol message to the second base station,

the RAN-INFORMATION RIM container is an information element for transparent notification to the second base station via a first core network node in the first radio access technology and a second core network node in the second radio access technology, and

the handover result information includes information indicating a handover success rate of each of handover-target base stations, the handover success rate being determined based on whether a first handover failed to be completed and whether a second handover is needed again within a predetermined period after the first handover is completed.

2. The first base station according to claim 1 , wherein the one or more processors are configured to execute the instructions to include, in the RAN-INFORMATION RIM container, an SN Addition Container IE including the handover result information and set the RAN-INFORMATION RIM container in the Application Protocol message to transmit the Application Protocol message to the second base station, and

the SN Addition Container IE is an information element for addition procedure of secondary base station in dual connectivity with the second base station for the terminal apparatus.

3. A second base station comprising:

a memory storing instructions; and

one or more processors configured to execute the instructions to:

communicate with a terminal apparatus in accordance with a second radio access technology;

receive an Application Protocol message including handover result information related to results of handovers from a first base station to other base stations, the first base station communicating in accordance with a first radio access technology; and

perform, based on the handover result information, communication processing for a terminal apparatus performing a handover from the first base station to the second base station, wherein

a RAN-INFORMATION RIM including the handover result information is set in the Application Protocol message for transmitting the Application Protocol message from the first base station to the second base station,

the RAN-INFORMATION RIM is an information element for transparent notification to the second base station via a first core network node in the first radio access technology and a second core network node in the second radio access technology, and

the handover result information includes information indicating a handover success rate of each of handover-target base stations, the handover success rate being determined based on whether a first handover failed to be completed and whether a second handover is needed again within a predetermined period after the first handover is completed.

4. The second base station according to claim 3 , wherein the one or more processors are configured to execute the instructions to determine, based on the handover result information, a secondary base station with which a terminal apparatus performing a handover from the first base station to the second base station is to communicate in dual connectivity.

5. The second base station according to claim 3 , wherein the one or more processors are configured to execute the instructions to refer to the handover result information to determine, from among one or more base stations of which handover success rates are equal to or larger than a predetermined threshold, a secondary base station with which a terminal apparatus performing a handover from the first base station to the second base station is to communicate in dual connectivity.

6. The second base station according to claim 3 , wherein the second base station is a Master eNB (MeNB) in dual connectivity.

7. A method comprising:

obtaining handover result information related to results of handovers from a first base station to other base stations, the first base station communicating with a terminal apparatus in accordance with a first radio access technology;

setting, in an Application Protocol message, a RAN-INFORMATION RIM container including the handover result information to transmit the Application Protocol message to a second base station communicating in accordance with a second radio access technology, and

transmitting, when a terminal apparatus performs a handover from the first base station to the second base station, the Application protocol message including the handover result information to the second base station, wherein

the RAN-INFORMATION RIM container is an information element for transparent notification to the second base station via a first core network node in the first radio access technology and a second core network node in the second radio access technology, and

the handover result information includes information indicating a handover success rate of each of handover-target base stations, the handover success rate being determined based on whether a first handover failed to be completed and whether a second handover is needed again within a predetermined period after the first handover is completed.