Device and method of handling dual connectivity

A communication device for handling dual connectivity, comprising:

• a storage device, for storing instructions of:
• configuring a radio resource control (RRC) connection with a first cell, wherein the first cell belongs to a first base station (BS);
• receiving a RRC message via the RRC connection on the first cell from the first BS, wherein the RRC message configures a secondary cell group (SCG) configuration to the communication device and includes an indication indicating no need to perform a random access (RA) procedure to a second cell indicated in the SCG configuration;
• synchronizing to a downlink (DL) of the second cell, wherein the second cell belongs to a second BS;
• transmitting a RRC complete message to the first cell or a third cell of the first BS in response to the RRC message;
• not performing the RA procedure to the second cell in response to the indication;
• determining that the SCG configuration is successfully configured, when the synchronization to the DL of the second cell is completed in a first time period;
• simultaneously connecting to the first BS and the second BS, after successfully configuring the SCG configuration;
• and
• a processing circuit, coupled to the storage device, configured to execute the instructions stored in the storage device.

A method for handling dual connectivity for a communication device, comprising:

• configuring a radio resource control (RRC) connection with a first cell, wherein the first cell belongs to a first base station (BS);
• receiving a RRC message via the RRC connection on the first cell from the first BS, wherein the RRC message configures a secondary cell group (SCG) configuration to the communication device and includes an indication indicating no need to perform a random access (RA) procedure to a second cell indicated in the SCG configuration;
• synchronizing to a downlink (DL) of the second cell, wherein the second cell belongs to a second BS;
• transmitting a RRC complete message to the first cell or a third cell of the first BS in response to the RRC message;
• not performing the RA procedure to the second cell in response to the indication;
• and
• determining that the SCG configuration is successfully configured, when detecting a Radio Network Temporary Identifier (RNTI) on a DL channel from the second cell in a first time period;
• and
• simultaneously connecting to the first BS and the second BS, after successfully configuring the SCG configuration.