Handover control method and communications device

1. A handover control method performed by a source master base station (BS), the handover control method comprising:

transmitting a conditional handover request to a target BS;

when a handover request confirmation message is received from the target BS, transmitting a conditional handover message to a user equipment (UE);

receiving a conditional handover complete message from the target BS in response to a Radio Resource Control (RRC) connection reconfiguration complete message being sent from the UE to the target BS; and

when the UE is configured to operate in dual connectivity operation by communicating additionally with a source secondary BS, transmitting a secondary BS release request message to the source secondary BS in response to receiving the conditional handover complete message from the target BS.

2. The handover control method according to claim 1 , further comprising:

in response to receiving the conditional handover complete message, forwarding data to the target BS.

3. The handover control method according to claim 1 , wherein the source secondary BS receives a conditional handover activation message from the UE in response to a conditional handover is triggered based on the conditional handover message received by the UE.

4. The handover control method according to claim 3 , wherein the conditional handover activation message is received by the source secondary BS before the RRC connection reconfiguration complete message is received by the target BS.

5. The handover control method according to claim 3 , wherein the conditional handover activation message is included in a Medium Access Control (MAC) control element (CE) or an RRC message.

6. The handover control method according to claim 3 , wherein:

the source secondary BS no longer forwards data to the UE after receiving the conditional handover activation message and transmits an indication message to the source master BS indicating that the conditional handover is triggered; and

the source master BS no longer forwards data to the UE after receiving the indication message.

7. A source master base station (BS) performing handover control, the source master BS comprising:

at least one processor; and

at least one memory coupled to the at least one processor and storing one or more instructions that, when executed by the at least one processor, cause the source master BS to:

transmit a conditional handover request to a target BS;

when a handover request confirmation message is received from the target BS, transmit a conditional handover message to a user equipment (UE);

receive a conditional handover complete message from the target BS in response to a Radio Resource Control (RRC) connection reconfiguration complete message being sent from the UE to the target BS; and

when the UE is configured to operate in dual connectivity operation by communicating additionally with a source secondary BS, transmit a secondary BS release request message to the source secondary BS in response to receiving the conditional handover complete message from the target BS.

8. The source master BS according to claim 7 , wherein the one or more instructions, when executed by the at least one processor, further cause the source master BS to:

when the conditional handover complete message is received, forward data to the target BS.

9. The source master BS according to claim 7 , wherein when a conditional handover is triggered based on the conditional handover message received by the UE, the source secondary BS receives a conditional handover activation message from the UE.

10. The source master BS according to claim 9 , wherein the conditional handover activation message is received by the source secondary BS before the RRC connection reconfiguration complete message is received by the target BS.

11. The source master BS according to claim 9 , wherein the conditional handover activation message is included in a Medium Access Control (MAC) control element (CE) or an RRC message.

12. The source master BS according to claim 9 , wherein:

the source secondary BS no longer forwards data to the UE after receiving the conditional handover activation message and transmits an indication message to the source master BS indicating that the conditional handover is triggered, and

the source master BS no longer forwards data to the UE after receiving the indication message.