Enhanced mechanism of uplink time alignment maintenance for inter-eNB carrier aggregation
Apparatus and method are provided to configure two-tier identifiers for serving cells of a UE configured with inter-eNB carrier aggregation (CA). In one novel aspect, cell group identifiers are configured. The cell group identifier is a super set of one or more uplink group identifiers that are associated with serving cells served by the same base station. In one embodiment, different MAC entities are associated with different cell group identifiers. The UE performs uplink alignment, monitoring and management procedures linking to the cell group identifier. In another novel aspect, a group TAG, which is a super set identifier of one or more cell TAGs associated with serving cells served by the same base station, is configured. In one embodiment, the UE performs uplink alignment procedure based on the status of the group TAG, which is determined based on the status of the cell TAGs associated with the group TAG.
1. A method comprising:
detecting an inter-eNB carrier aggregation configuration by a user equipment (UE) in a wireless network with serving cells served by a first and a second base station, wherein each serving cell is configured with an uplink group identifier;
determining a first cell group with a first cell group identifier and a second cell group with a second cell group identifier, wherein the first cell group containing one or more serving cells with the same or different uplink group identifiers served by the first base station and the second cell group with the second cell group identifier containing one or more serving cells with the same or different uplink group identifiers served by the second base station, and wherein the uplink group identifier is associated with a time advancing group and the group identifier is associated with a group TAG, and wherein each TAG associates with the same base station belongs to the same group TAG, and wherein each TAG has a time advance timer (TAT); and
performing uplink alignment, monitoring and management procedures linking to the first or the second cell group identifier.
2. The method of claim 1 , further comprising:
associating a first MAC entity with the first cell group identifier; and
associating a second MAC entity with the second cell group identifier.
3. The method of claim 1 , wherein the first base station is an anchor base station and the second base station is a drift base station.
4. The method of claim 1 , wherein the UE determines a cell group identifier to a serving cell based on a signaling command from the wireless network, and wherein the signaling command is associated with the serving cell and the cell group identifier.
5. The method of claim 1 , wherein the UE determines a cell group identifier to a serving cell based on an eNB ID that the serving cell is associated with, and wherein the UE derives the eNB ID either through a predefined serving cell configuration or through resolving an E-UTRAN Cell Global Identifier (ECGI) of the serving cell.
6. The method of claim 1 , the step of performing uplink alignment further comprising:
obtaining initial uplink time alignment through a random access procedure;
monitoring timing advance commands (TAC) associated with cell TAGs; and
determining if the group TAG is uplink synchronized.
7. The method of claim 6 , wherein the group TAG is uplink synchronized when the UE detects one or more conditions comprising: all cell TAGs in the group TAG is uplink synchronized, a serving cell with PUCCH in the group TAG is uplinked synchronized, and a primary cell TAG in the group TAG is uplink synchronized.
8. The method of claim 6 , wherein the group TAG is not uplink synchronized if the UE detects one or more conditions comprising: all cell TAGs in the group TAG are not uplink synchronized, a serving cell with PUCCH in the group TAG is not uplinked synchronized, and the primary cell TAG in the group TAG is not uplink synchronized.
9. The method of claim 6 , further comprising:
stopping all running TATs belonging to the group TAG when the group TAG is not uplink synchronized; and
continuing running TATs not belonging to the non-synchronized group TAG.
10. The method of claim 9 , further comprising:
notifying the first base station a failure of the second base station when the group TAG associated with the second base station is no longer uplink synchronized.
11. A user equipment (UE), comprising:
a transceiver that transmits and receives radio signals;
a memory; and
a processor coupled to the memory, the processor configured to detect an inter-eNB CA and assigns serving cells with uplink group identifiers, wherein the serving cells are served by a first or a second base station in a wireless network;
retrieve a first cell group with a first cell group identifier containing one or more serving cells with the same or different uplink group identifiers served by the first base station and a second cell group with a second cell group identifier containing one or more serving cells with the same or different uplink group identifiers served by the second base station, and wherein the uplink group identifier is associated with a cell time advancing group (TAG) and the cell group identifier is associated with a group TAG, and wherein each cell TAG associates with the same base station belongs to the same group TAG, and wherein each cell TAG has a time advance timer (TAT); and perform uplink alignment, monitoring and management procedures linking to the first or the second cell group identifier.
12. The UE of claim 11 , further comprising:
a first MAC entity, wherein the first MAC entity is associated with the first cell group identifier; and
a second MAC entity, wherein the second MAC entity is associated with the second cell group identifier.
13. The UE of claim 11 , wherein the first base station is an anchor base station and the second base station is a drift base station.
14. The UE of claim 11 , wherein the processor configured to determines a cell group identifier to a serving cell based on a signaling command from the wireless network, and wherein the signaling command is associated the serving cell with the cell group identifier.
15. The UE of claim 11 , wherein the processor configured to assign a cell group identifier to a serving cell based on an eNB ID that the serving cell is associated with, and wherein the UE derives the eNB ID either through a predefined serving cell configuration or through resolving an E-UTRAN Cell Global Identifier (ECGI) of the serving cell.
16. The UE of claim 11 , wherein the processor further configured to:
obtain initial uplink time alignment through a random access procedure;
monitor timing advance commands (TAC) associated with cell TAGs; and
determine if the group TAG is uplink synchronized.
17. The UE of claim 16 wherein the group TAG is uplink synchronized when the processor detects one or more the conditions comprising:
all cell TAGs in the group TAG is uplink synchronized, a serving cell with PUCCH in the group TAG is uplinked synchronized, and a primary cell TAG in the group TAG is uplink synchronized.
18. The UE of claim 16 wherein the group TAG is not uplink synchronized when the processor detects one or more the conditions comprising:
all cell TAGs in the group TAG are not uplink synchronized, a serving cell with PUCCH in the group TAG is not uplink synchronized, and a primary cell TAG in the group TAG is not uplink synchronized.
19. The UE of claim 16 , wherein the processor stops all running TATs belonging to a group TAG when the group TAG is not uplink synchronized; and continues running TATs not belonging to the non-synchronized group TAG.
20. The UE of claim 16 , wherein the processor further configured to notify the first base station a failure of the second base station when the group TAG associated with the second base station is no longer uplink synchronized.