Generation Node-B (GNB), user equipment (UE) and methods for handover based on multi-connectivity in new radio (NR) systems

1. An apparatus, comprising:

memory; and

processing circuitry in communication with the memory, wherein the processing circuitry is configured to:

decode a message for a handover of a User Equipment (UE) to a target base station, wherein a source base station is a primary base station for the UE before the handover;

determine, based on the message, that the target base station is to be the primary base station for the UE after the handover;

encode, for transmission to the source base station, a sequence number (SN) status transfer request message that indicates a highest SN of data packets received from the source base station for relay to the UE;

decode, from the source base station, an SN status transfer message that indicates a starting SN for subsequent data packets;

encode, for transmission to the UE while operating as a secondary base station, a first data packet received from the source base station;

encode, for transmission to the UE while operating as the primary base station, a second data packet received from the network; and

refrain from reception of data packets from the source base station for relay to the UE.

2. The apparatus according to claim 1 , the processing circuitry further configured to:

before the handover occurs, decode one or more data packets from the source base station for relay to the UE; and

after the handover occurs:

decode one or more data packets from a serving gateway (SGW) for relay to the UE.

3. The apparatus according to claim 1 , the processing circuitry further configured to:

encode, for transmission to a mobility management entity (MME), a path switch request message that indicates a request for a serving gateway (SGW) to transmit subsequent data packets to the target base station as part of the handover.

4. The apparatus according to claim 1 , the processing circuitry further configured to:

decode, from the UE, a radio resource control (RRC) message that indicates that an RRC reconfiguration at the UE has been completed; and

encode a path switch request message for transmission to a mobility management entity (MME) at least partly in response to reception of the RRC message from the UE.

5. The apparatus according to claim 1 ,

wherein the message is a secondary base station addition request message, and wherein the processing circuitry is further configured to:

encode, for transmission to the source base station, a secondary base station addition request acknowledge message that includes one or more of:

a cell radio network temporary identifier (C-RNTI) to identify the UE in a random access channel (RACH) procedure between the UE and the target base station, and

a security algorithm identifier of the target base station.

6. The apparatus according to claim 5 , the processing circuitry further configured to:

attempt to detect a RACH preamble from the UE;

encode, for transmission to the UE, a RACH message that indicates reception of the RACH preamble; and

encode, for transmission to the source base station, secondary base station reconfiguration complete message that indicates a successful addition as the secondary base station, the successful addition based at least partly on the reception of the RACH preamble.

7. The apparatus according to claim 1 , the processing circuitry further configured to:

decode, from the UE, a buffer status report (BSR) to request an uplink grant for communication to the target base station on a signaling radio bearer (SRB);

encode, for transmission to the UE, the uplink grant; and

decode, from the UE, a radio resource control (RRC) reconfiguration complete message that indicates that an RRC reconfiguration at the UE has been completed.

8. The apparatus according to claim 1 , the processing circuitry further configured to:

decode, from the UE, a request for an uplink grant for communication to the target base station on a signaling radio bearer (SRB); and

encode, for transmission to the UE, a handover command that includes the uplink grant.

9. The apparatus according to claim 1 , the processing circuitry further configured to:

decode, from the UE, a request for an uplink grant for communication to the target base station on a signaling radio bearer (SRB); and

encode, for transmission to the UE, a physical downlink control channel (PDCCH) that includes the uplink grant.

10. The apparatus according to claim 1 , the processing circuitry further configured to:

decode, from the UE, a buffer status report (BSR) to request an uplink grant for communication to the target base station on a signaling radio bearer (SRB),

wherein a bit field of one or more bits indicates that the BSR is intended for the target base station; and

encode, for transmission to the UE, the uplink grant.

11. The apparatus according to claim 1 , the processing circuitry further configured to:

decode, frorn the UE, a request for an uplink grant for communication to the target base station on a signaling radio bearer (SRB); and

encode, for transmission to the UE, a radio resource control (RRC) message that indicates:

the uplink grant, and

an indication that the target base station has begun operation as the primary base station.

12. The apparatus according to claim 1 , the processing circuitry further configured to:

determine a cell radio network temporary identifier (C-RNTI) to identify the UE after the handover is completed; and

encode, for transmission to the UE:

a radio resource control (RRC) message that includes the C-RNTI, or

a handover command that includes the C-RNTI.

13. The apparatus according to claim 1 , wherein the target base station is arranged to operate in accordance with a Previously Presented Radio (NR) protocol.

14. The apparatus according to claim 1 , wherein the apparatus further includes a transceiver to receive the message and to transmit the first and second data packets.

15. The apparatus according to claim 1 , wherein the processing circuitry includes a baseband processor to decode the message and to encode the first and second data packets.

16. A method, comprising:

decoding a message for a handover of a User Equipment (UE) to a target base station, wherein a source base station is a primary base station for the UE before the handover;

determining, based on the message, that the target base station is to be the primary base station for the UE after the handover;

encoding, for transmission to the source base station, a sequence number (SN) status transfer request message that indicates a highest SN of data packets received from the source base station for relay to the UE;

decoding, from the source base station, an SN status transfer message that indicates a starting SN for subsequent data packets;

encoding, for transmission to the UE while operating as a secondary base station, a first data packet received from the source base station;

encoding, for transmission to the UE while operating as the primary base station, a second data packet received from the network; and

refraining from reception of data packets from the source base station for relay to the UE.

17. The method of claim 16 , further comprising:

decoding, before the handover occurs, one or more data packets from the source base station for relay to the UE; and

decoding, after the handover occurs, one or more data packets from a serving gateway (SGW) for relay to the UE.

18. The method of claim 16 , further comprising:

encoding, for transmission to a mobility management entity (MME), a path switch request message that indicates a request for a serving gateway (SGW) to transmit subsequent data packets to the target base station as part of the handover.

19. A non-transitory computer-readable storage medium that stores instructions for execution by one or more processors to cause a device to:

decode a message for a handover of a User Equipment (UE) to a target base station, wherein a source base station is a primary base station for the UE before the handover;

determine, based on the message, that the target base station is to be the primary base station for the UE after the handover;

encode, for transmission to the source base station, a sequence number (SN) status transfer request message that indicates a highest SN of data packets received from the source base station for relay to the UE;

decode, from the source base station, an SN status transfer message that indicates a starting SN for subsequent data packets;

encode, for transmission to the UE while operating as a secondary base station, a first data packet received from the source base station;

encode, for transmission to the UE while operating as the primary base station, a second data packet received from the network; and

refrain from reception of data packets from the source base station for relay to the UE.

20. The non-transitory computer-readable storage medium of claim 19 ,

wherein the instructions for execution by the one or more processors further cause the device to:

before the handover occurs, decode one or more data packets from the source base station for relay to the UE; and

after the handover occurs, decode one or more data packets from a serving gateway (SGW) for relay to the UE.

21. The non-transitory computer-readable storage medium of claim 19 ,

wherein the instructions for execution by the one or more processors further cause the device to:

encode, for transmission to a mobility management entity (MME), a path switch request message that indicates a request for a serving gateway (SGW) to transmit subsequent data packets to the target base station as part of the handover.

22. The non-transitory computer-readable storage medium of claim 19 ,

wherein the instructions for execution by the one or more processors further cause the device to:

decode, from the UE, a radio resource control (RRC) message that indicates that an RRC reconfiguration at the UE has been completed; and

encode a path switch request message for transmission to a mobility management entity (MEE) at least partly in response to reception of the RRC message from the UE.