In Step 504, the UE 3 (i.e., the E-UTRA AS layer) sends an RRC Connection Reconfiguration Complete message to the MeNB 1 in the E-UTRA cell of the MeNB 1 (i.e., PCell). Meanwhile, the UE 3 (i.e., the NR AS layer) starts a procedure for synchronizing with the SgNB 2 (e.g., Random Access Procedure).

In Step 505, the MeNB 1 sends an SgNB Reconfiguration Complete message to the SgNB 2 in response to receiving the RRC Connection Reconfiguration Complete message from the UE 3.

As can be understood from the above description, the SgNB 2 according to this embodiment is configured to send the NR radio resource configuration for E-UTRA-NR DC to the UE 3 via the master eNB (MeNB) 1, and the NR radio resource configuration indicates at least one dedicated numerology that is included in the multiple numerologies supported by one or more NR cells of the SgNB 2 and is different from the reference numerology. This allows the SgNB 2 to configure the UE 3 with the numerology(ies) of the SCG cell(s) served by the SgNB 2 in E-UTRA-NR DC. The UE 3 thus can know the numerology(ies) that should be used in the SCG cell(s) served by the SgNB 2.

A configuration example of a radio communication network according to this embodiment is similar to that shown in FIG. 4. This embodiment provides an improvement that enables the MeNB 1 to use a UE measurement report indicating a measurement result of an NR cell(s) of the SgNB 2 based on a reference numerology(ies) in E-UTRA-NR DC.