Broadcast and group-based handover in NR-based LEO-NTN
This innovation describes methods for an NR-based, LEO Non-Terrestrial Networks (NTN) to improve handover process by sending broadcast or group-cast downlink handover (HO) Command message to all (or group of) UEs in the coverage area (cell or beam-spot) of the LEO satellite. Subsequently, on receiving the broadcast (or group-cast) HO Command message, all the UEs in the source cell transmit HO Complete message to the source cell of the LEO-NTN. In order to reduce or avoid heavy Random Access (RA), generating from all the UEs, the LEO-NTN can either send Contention Free Random Access (CFRA), or instruct the UE to perform a random backoff before sending the uplink HO Complete message. Moreover, improvements to configure Conditional Handover (CHO) and delaying the transmission of HO Complete message are also provided.
1. A method comprising:
establishing a radio resource control (RRC) connection by a user equipment (UE) with a source base station in a new radio (NR) based Low Earth Orbit (LEO) Non-Terrestrial Network (NTN);
receiving a handover command that is broadcasted or groupcasted to multiple UEs by the source base station via an RRC connection reconfiguration message, wherein the handover command comprises a backoff indicator indicating a maximum backoff time interval;
performing a random-access (RA) procedure over a random-access channel (RACH) with a target base station, wherein the UE applies a random backoff time based on the backoff indicator before transmitting a RACH preamble, wherein the random backoff time is derived from the maximum backoff time interval; and
receiving a random-access response (RAR) for handing over to the target base station.
2. The method of claim 1 , wherein the RRC connection reconfiguration message comprises at least an addressing configuration and a security configuration.
3. The method of claim 1 , wherein the RRC connection reconfiguration message is sent over a separate broadcast or groupcast signaling radio bearer (SRB).
4. The method of claim 1 , wherein the UE does not apply Hybrid Automatic Repeat reQuest (HARQ) for the RRC connection reconfiguration message.
5. The method of claim 1 , wherein UE applies configuration provided by the RRC connection reconfiguration message without sending a subsequent confirm or complete RRC message.
6. The method of claim 1 , wherein the UE delays sending a subsequent confirm or complete RRC message or delays performing the subsequent random-access procedure until another uplink transmission or until timeout.
7. The method of claim 1 , wherein the UE receives the RRC connection reconfiguration message for performing a conditional handover upon satisfying a predefined condition.
8. The method of claim 1 , wherein the UE transmits measurement reports to the source base station only when a predefined triggering condition is satisfied.
9. A User Equipment (UE), comprising:
a radio resource control (RRC) connection handling circuit that establishes an RRC connection with a source base station in a new radio (NR) based Low Earth Orbit (LEO) Non-Terrestrial Network (NTN);
a receiver that receives a handover command that is broadcasted or groupcasted to multiple UEs by the source base station via an RRC connection reconfiguration message, wherein the handover command comprises a backoff indicator indicating a maximum backoff time interval;
a random-access handling circuit that performs a random-access channel (RACH) procedure with a target base station, wherein the UE applies a random backoff time based on the backoff indicator before transmitting a RACH preamble, wherein the random backoff time is derived from the maximum backoff time interval; and
a handover handling circuit that handovers the UE to the target base station upon receiving a random-access response from the target base station.
10. The UE of claim 9 , wherein the RRC connection reconfiguration message comprises at least an addressing configuration and a security configuration.
11. The UE of claim 9 , wherein the RRC connection reconfiguration message is sent over a separate broadcast or groupcast signaling radio bearer (SRB).
12. The UE of claim 9 , wherein the UE does not apply Hybrid Automatic Repeat reQuest (HARQ) for the RRC connection reconfiguration message.
13. The UE of claim 9 , wherein UE applies configuration provided by the RRC connection reconfiguration message without sending a subsequent confirm or complete RRC message.
14. The UE of claim 9 , wherein the UE delays sending a subsequent confirm or complete RRC message or delays performing the subsequent random-access procedure until another uplink transmission or until timeout.
15. The UE of claim 9 , wherein the UE receives the RRC connection reconfiguration message for performing a conditional handover upon satisfying a predefined condition.
16. The UE of claim 9 , wherein the UE transmits measurement reports to the source base station only when a predefined triggering condition is satisfied.
17. A method, comprising:
establishing a radio resource control (RRC) connection by a new radio source base station (NR gNB) with a plurality of user equipments (UEs) in a new radio Low Earth Orbit (LEO) Non-Terrestrial Network (NTN);
grouping a number of UEs that are located within a predefined distance with each other into a UE group;
configuring measurements and reporting parameters and receiving measurement reports from the group of UEs upon a triggering condition is satisfied; and
broadcasting or groupcasting a handover command message to the group of UEs via an RRC connection reconfiguration message, wherein the handover command message comprises a backoff indicator, wherein the backoff indicator includes a maximum backoff time interval for the group of UEs to perform random backoff of a subsequent access procedure.
18. The method of claim 17 , wherein the grouping involves estimating UE locations and LEO satellites mobility patterns.
19. The method of claim 17 , wherein the triggering condition involves timer-based neighbor Physical Cell IDs (PCIs) in specific interval.