We Claim:
1. A communication system, comprising:
a communication terminal device; and
a base station device that performs radio communication with the communication terminal device via a radio beam,
wherein a cell configured by the base station device is spatially separated by a plurality of radio beams being served by the base station device, and
the base station device shares, between two or more of the plurality of radio beams, a radio resource control (RRC) parameter to be applied to the communication terminal device.
2. A communication system, comprising:
a communication terminal device; and
a base station device that performs radio communication with the communication terminal device via a radio beam,
wherein a cell configured by the base station device is spatially separated by a plurality of radio beams being served by the base station device, and
the base station device changes a radio resource control (RRC) parameter to be applied to the communication terminal device from a first RRC parameter for a first radio beam to a second RRC parameter for a second radio beam when the communication terminal device moves from a range of the first radio beam to a range of the second radio beam.
3. The communication system according to claim 2,
wherein the base station device includes:

at least one distributed unit (DU) that outputs the plurality of radio beams; and
a central unit (CU) that controls the at least one DU, the CU has a medium access control (MAC) function, and the CU gives:
a notification of the second RRC parameter to the communication terminal device; and
a notification of a switching instruction from the first radio beam to the second radio beam to the communication terminal device via the first radio beam.
4. The communication system according to claim 2, wherein the base station device includes:
at least one distributed unit (DU) that outputs the plurality of radio beams; and
a central unit (CU) that controls the at least one DU,
the CU has a medium access control (MAC) function, and
the CU makes:
a notification of the second RRC parameter to the communication terminal device via the second radio beam; and
a notification of a switching instruction from the first radio beam to the second radio beam to the communication terminal device via the first radio beam.
5. The communication system according to claim 2, wherein the base station device includes:
at least one distributed unit (DU) that outputs the plurality of radio

beams; and
a central unit (CU) that controls the at least one DU,
the at least one DU has a medium access control (MAC) function, and
the CU makes:
a notification of the second RRC parameter to the communication terminal device via the first radio beam with an L1/L2 signaling or a MAC signaling; and
a notification of a switching instruction from the first radio beam to the second radio beam to the communication terminal device via the first radio beam with the L1/L2 signaling or the MAC signaling.
6. The communication system according to claim 2,
wherein the base station device includes:
at least one distributed unit (DU) that outputs the plurality of radio beams; and
a central unit (CU) that controls the at least one DU,
the at least one DU has a medium access control (MAC) function, and
the base station device makes:
a notification of the second RRC parameter to the communication terminal device via the second radio beam with an L1/L2 signaling or a MAC signaling; and
a notification of a switching instruction from the first radio beam to the second radio beam to the communication terminal device via the first radio beam with the L1/L2 signaling or the MAC signaling.
7. A communication system, comprising:
a communication terminal device; and

a base station device that performs radio communication with the communication terminal device via a radio beam,
wherein a cell configured by the base station device is spatially separated by a plurality of radio beams being served by the base station device, and
the base station device sets carrier aggregation per radio beam.
8. A communication system, comprising:
a communication terminal device;
a plurality of base station devices to be radio communicatively connected to the communication terminal device; and
a core network that manages communication between the communication terminal device and each of the plurality of base station devices,
wherein when a first base station device connected to the communication terminal device requests a second base station device to set a bearer for the communication terminal device, the first base station device notifies the second base station device of information on Quality of Service (QoS), and the second base station device sets the bearer for the communication terminal device based on the notified information on the QoS, the information being obtained from the core network on a PDU session.
9. A communication system, comprising:
a communication terminal device;
a plurality of base station devices to be radio communicatively connected to the communication terminal device; and
a core network that manages communication between the communication

terminal device and each of the plurality of base station devices,
wherein when a first base station device connected to the communication terminal device requests a second base station device to set a bearer for the communication terminal device, the first base station device sets the bearer for the communication terminal device based on Quality of Service (QoS) obtained from the core network on a PDU session, and notifies the second base station device of information on the set bearer.