Cell reselection in communication systems using unlicensed frequency bands
Cell selection in a New Radio-Unlicensed Standalone (NR-U SA) communication system is managed by allowing UE devices to avoid measurements of frequencies that are occupied. A base station (gNB) may indicate to the UE device frequencies that can be skipped or may allow the UE device to skip frequencies for a temporary period after the frequencies have been determined to be occupied.
1. A method performed at a user equipment (UE) device, the method comprising:
receiving a frequency prioritization list identifying a priority of each of a plurality of unlicensed frequencies;
receiving unlicensed frequency occupancy information from a serving base station, the unlicensed frequency occupancy information identifying an occupied unlicensed frequency in the frequency prioritization list;
determining that the UE device is not camped on a highest priority frequency in the frequency prioritization list;
in response to determining that the UE device is not camped on the highest priority frequency in the frequency prioritization list, identifying a higher priority frequency in the frequency prioritization list that has a higher priority than a current frequency of a current cell on which the UE device is camped, the current cell provided by the serving base station;
determining that the higher priority frequency in the frequency prioritization list is not the occupied unlicensed frequency identified by the unlicensed frequency occupancy information; and
in response to determining that the higher priority frequency is not the occupied unlicensed frequency, attempting to measure a reference signal transmitted at the higher priority frequency.
2. The method of claim 1 , further comprising:
reselecting a cell at the higher priority frequency in response to determining a measurement of the higher priority frequency is above a threshold.
3. The method of claim 2 , further comprising:
continuing to camp on the current cell, in response to determining the measurement of the higher priority frequency is below the threshold.
4. The method of claim 1 , further comprising:
receiving, from a serving base station, a temporary occupied frequency skip configuration indicating the time period.
5. The method of claim 4 , wherein the receiving the temporary occupied frequency skip configuration is performed while the UE device is in a CONNECTED mode.
6. The method of claim 4 , wherein the receiving the temporary occupied frequency skip configuration comprises receiving the temporary occupied frequency skip configuration in a System Information Block (SIB).
7. A user equipment (UE) device comprising:
a receiver configured to receive a frequency prioritization list identifying a priority of each of a plurality of unlicensed frequencies, the receiver configured to receive unlicensed frequency occupancy information from a serving base station, the unlicensed frequency occupancy information identifying an occupied unlicensed frequency in the frequency prioritization list; and
a controller configured to:
determine that the UE device is not camped on a highest priority frequency in the frequency prioritization list,
in response to determining that the UE device is not camped on the highest priority frequency in the frequency prioritization list, identify a higher priority frequency in the frequency prioritization list that has a higher priority than a current frequency of a current cell on which the UE device is camped, the current cell provided by the serving base station,
determine that the higher priority frequency in the frequency prioritization list is not the occupied unlicensed frequency identified by the unlicensed frequency occupancy information, and
in response to determining that the higher priority frequency is not the occupied unlicensed frequency, attempt to measure a reference signal transmitted at the higher priority frequency.
8. The UE device of claim 7 , the controller further configured to reselect a cell at the higher priority frequency in response to determining a measurement of the higher priority frequency is above a threshold.
9. The UE device of claim 8 , the controller further configured to cause the UE device to continue to camp on the current cell in response to determining the measurement of the higher priority frequency is below the threshold.
10. The UE device of claim 7 , the receiver further configured to receive, from a serving base station, a temporary occupied frequency skip configuration indicating the time period.
11. The UE device of claim 10 , wherein the receiver is configured to receive the temporary occupied frequency skip configuration while the UE device is in a CONNECTED mode.
12. The UE device of claim 10 , wherein the receiver is configured to receive the temporary occupied frequency skip configuration in a System Information Block (SIB).