Terminal device, base station device, and wireless communication system

A base station device comprising:

• a transmitter that transmits, to a terminal device, a first signal including change destination information that designates a first cell and a second cell as cell change destination candidates and a second signal including information related to a cell change;
• a controller that, by sending the second signal, causes the terminal device to perform first processing of switching a serving cell from a third cell to the first cell in accordance with the information related to the cell change, and perform second processing including processing of maintaining some of values of state variables with a value of a first state variable and returning to a third configuration applied in the third cell to execute a reestablishment procedure when the first processing fails;
• and
• a receptor that receives a signal of random access transmitted from the terminal device in third processing of applying a second configuration applied in the second cell to switch the serving cell to the second cell in a case where the second cell is selected as a change destination cell and a first condition is satisfied in the second processing.

A wireless communication system comprising:

• a base station device that transmits a first signal including change destination information that designates a first cell and a second cell as cell change destination candidates and a second signal including information related to a cell change;
• and
• a terminal device that receives the first signal and the second signal and performs first processing of switching a serving cell from a third cell to the first cell in accordance with the information related to the cell change included in the second signal, wherein
• the terminal device performs second processing including processing of maintaining some of values of state variables with a value of a first state variable and returning to a third configuration applied in the third cell to execute a reestablishment procedure when the first processing fails,
• the terminal device performs third processing of applying the second configuration applied in the second cell to switch the serving cell to the second cell in a case where the second cell is selected as a change destination cell and a first condition is satisfied in the second processing, and
• the third processing is switching processing using random access.