Methods and apparatuses for transmitting control-plane messages in cells using different radio access technologies

A method in a radio terminal, the method comprising:

• communicating with a radio station system comprising one or more radio stations on one or more first cells in accordance with a first radio access technology and one or more second cells in accordance with a second radio access technology and used in addition to and subordinate to the one or more first cells;
• and
• transmitting or receiving a control-plane message to or from the radio station system on the one or more second cells in a case where a predetermined condition is satisfied,
• wherein the control-plane message includes a non-access stratum (NAS) message or a radio resource control (RRC) message or both,
• wherein the predetermined condition relates to a content or type of the control-plane message, and
• wherein the method comprises:
• in a case where the control-plane message includes a measurement report related to the one or more second cells and the measurement report corresponds to a report of a measurement result of the one or more second cells as Inter-Radio Access Technology (RAT) measurement for the one or more first cells, transmitting the control-plane message in the one or more first cells;
• and
• in a case where the control-plane message includes a measurement report related to the one or more second cells and the measurement report does not correspond to a report of a measurement result of the one or more second cells as Inter-RAT measurement for the one or more first cells, transmitting the control-plane message in the one or more second cells.

A radio station system comprising:

• one or more radio stations configured to:
• provide, for a radio terminal, one or more first cells in accordance with a first radio access technology and one or more second cells in accordance with a second radio access technology and used in addition to and subordinate to the one or more first cells;
• and
• transmit or receive a control-plane message to or from the radio terminal on the one or more second cells in a case where a predetermined condition is satisfied,
• wherein the control-plane message includes a non-access stratum (NAS) message or a radio resource control (RRC) message or both,
• wherein the predetermined condition relates to a content or type of the control-plane message, and
• wherein the one or more radio stations are configured to:
• in a case where the control-plane message includes a measurement report related to the one or more second cells from the radio terminal and the measurement report corresponds to a report of a measurement result of the one or more second cells as Inter-Radio Access Technology (RAT) measurement for the one or more first cells, receive the control plane message in the one or more first cells;
• and
• in a case where the control-plane message includes a measurement report related to the one or more second cells from the radio terminal and the measurement report does not correspond to a report of a measurement result of the one or more second cells as Inter-RAT measurement for the one or more first cells, receive the control-plane message in the one or more second cells.

A radio terminal comprising:

• a memory;
• and
• at least one processor coupled to the memory and configured to:
• communicate with a radio station system comprising one or more radio stations on one or more first cells in accordance with a first radio access technology and one or more second cells in accordance with a second radio access technology and used in addition to and subordinate to the one or more first cells;
• and
• transmit or receive a control-plane message to or from the radio station system on the one or more second cells in a case where a predetermined condition is satisfied,
• wherein the control-plane message includes a non-access stratum (NAS) message or a radio resource control (RRC) message or both,
• wherein the predetermined condition relates to a content or type of the control-plane message, and
• wherein the at least one processor is configured to:
• in a case where the control-plane message includes a measurement report related to the one or more second cells and the measurement report corresponds to a report of a measurement result of the one or more second cells as Inter-Radio Access Technology (RAT) measurement for the one or more first cells, transmit the control-plane message in the one or more first cells;
• and
• in a case where the control-plane message includes a measurement report related to the one or more second cells and the measurement report does not correspond to a report of a measurement result of the one or more second cells as Inter-RAT measurement for the one or more first cells, transmit the control-plane message in the one or more second cells.