Handover management in communication systems using unlicensed frequency bands
Handovers in a New Radio-Unlicensed Standalone (NR-U SA) communication system are managed by invoking one of a plurality of handover procedures based on conditions related to the communication device and channel status. One example of one of the plurality of handover procedures includes sending a handover command with an inactivity indicator to the UE device where the UE device transitions to an Inactive State (such as RRC_INACTIVE) in response to a handover failure (HOF) resulting from an occupied unlicensed channel. The UE device provides the 1-RNTI allocated by the last serving gNB when resuming from the RRC_INACTIVE to the active state; thereby reducing the latency associated with a new connection from the idle mode. The target gNB uses the 1-RNTI to retrieve the UE context from the last serving gNB.
1. A method performed at a communication device, the method comprising:
receiving, from a serving gNB, measurement report trigger information indicative of criteria for sending a measurement report, the criteria comprising:
a measurement report trigger threshold indicative of at least one of a minimum received signal strength threshold and a minimum received signal quality threshold;
a measurement report trigger validity period indicative of a time period that the measurement report trigger threshold is valid, the time period from receipt of the measurement report trigger information; and
a threshold offset value indicative of a maximum offset below the measurement report trigger threshold after expiration of the measurement report trigger validity period;
evaluating a channel occupancy level of an unlicensed channel to the serving gNB; and
transmitting, if the channel occupancy level is below a channel occupancy threshold and only if the criteria are met, a measurement report over the unlicensed channel to the serving gNB, the measurement report indicative of at least one of a received signal strength and a received signal quality at the communication device of at least one received signal transmitted from the target gNB;
receiving, from the serving gNB, a handover command with an inactivity indicator, the handover command identifying a handover procedure to a target gNB;
in response to failing the handover procedure at least partially as a result of another unlicensed channel to the target gNB being occupied, transitioning to a New Radio (NR) Radio Resource Control (RRC) Inactive state; and
executing an RRC Resume procedure to transition to the RRC Connected state to establish communication service with a new serving gNB located within a same Radio Access Network (RAN)-based Notification Area (RNA) as the serving gNB.
2. The method of claim 1 , wherein the new serving gNB is the target gNB.
3. The method of claim 1 , further comprising:
transmitting, over the another unlicensed channel, an I-Radio Network Temporary Identifier (I-RNTI) to the new serving gNB.
4. The method of claim 1 , further comprising:
in response to failing the handover procedure as a result of a radio link failure (RLF), executing a NR RRC re-establishment procedure.
5. The method of claim 1 , further comprising:
transmitting, to the serving gNB and in response to a determination that the occupancy level is not below the channel occupancy threshold, occupancy information indicative of the occupancy level.
6. A user equipment communication device (UE device) comprising:
a receiver configured to receive, from a serving gNB, measurement report trigger information indicative of criteria for sending a measurement report, the criteria comprising:
a measurement report trigger threshold indicative of at least one of a minimum received signal strength threshold and a minimum received signal quality threshold;
a measurement report trigger validity period indicative of a time period that the measurement report trigger threshold is valid, the time period from receipt of the measurement report trigger information; and
a threshold offset value indicative of a maximum offset below the measurement report trigger threshold after expiration of the measurement report trigger validity period;
a controller configured to evaluate an occupancy level of an unlicensed channel to the serving gNB,
a transmitter configured to transmit, if the occupancy level of the unlicensed channel to the serving gNB is below a channel occupancy threshold and only if the criteria are met, a measurement report over the unlicensed channel to the serving gNB, the measurement report indicative of at least one of a received signal strength and a received signal quality at the UE device of at least one received signal transmitted from the target gNB,
the receiver configured to receive a handover command with an inactivity indicator, the handover command identifying a handover procedure to a target gNB, the controller configured to:
in response to failing the handover procedure at least partially as a result of another unlicensed channel to the target gNB being occupied, transition to a New Radio (NR) Radio Resource Control (RRC) Inactive state; and
execute an RRC Resume procedure to transition to the RRC Connected state to establish communication service with a new serving gNB located within a same Radio Access Network (RAN)-based Notification Area (RNA) as the serving QNB.
7. The UE device of claim 6 , wherein the new serving gNB is the target gNB.
8. The UE device of claim 6 , further comprising:
a transmitter configured to transmit, over the another unlicensed channel, an I-Radio Network Temporary Identifier (I-RNTI) to the new serving gNB.
9. The UE device of claim 6 , the controller further configured to execute a NR RRC re-establishment procedure in response to failing the handover procedure as a result of a radio link failure (RLF).
10. The UE device of claim 6 , the transmitter configured to transmit, to the serving gNB and in response to a determination that the occupancy level is not below the channel occupancy threshold, occupancy information indicative of the occupancy level.