Method and apparatus for conditional reestablishment and consecutive reestablishment

1 . A user equipment (UE) for wireless communication, comprising:

at least one memory; and

at least one processor coupled with the at least one memory and configured to cause the apparatus to:

receive, at a user equipment (UE), conditional reestablishment configuration information indicating a set of execution conditions for a set of candidate cells,

wherein each candidate cell of the set of candidate cells is associated with at least one execution condition; and

trigger, by the UE, a conditional reestablishment procedure before an occurrence of a radio link failure (RLF), by:

evaluating the set of execution conditions based on the conditional reestablishment configuration information in response to the reception of conditional reestablishment configuration information;

selecting a target cell from the set of candidate cells for conditional reestablishment based on the evaluation, and

initiating the conditional reestablishment procedure with the target cell without starting a timer associated with reestablishment initiation.

2 . The UE of claim 1 , wherein the set of execution conditions includes at least one of the following:

a first execution condition that a first channel quality between the UE and a corresponding candidate cell is an offset better than a second channel quality between the UE and a serving cell of the UE, the second channel quality is less than a first threshold, and the first channel quality is greater than a second threshold;

a second execution condition that a distance between the UE and the serving cell of the UE is greater than a third threshold and a distance between the UE and a corresponding candidate cell is less than a fourth threshold;

a third execution condition indicating an absolute time for performing conditional reestablishment;

a fourth execution condition indicating a value of a timer;

a fifth execution condition that the timing advance value from the UE to a corresponding candidate cell is less than a fifth threshold; and

a sixth execution condition that the timing advance value from the UE to a corresponding candidate cell is less than a sixth threshold and the timing advance value from the UE to the serving cell of the UE is greater than a seventh threshold;

a seventh execution condition that the elevation angle of the serving cell of the UE is less than an eighth threshold, and the elevation angle of a corresponding candidate cell is greater than a ninth threshold.

3 . The UE of claim 2 , wherein the serving cell of the UE is a primary cell (PCell).

4 . The UE of claim 2 , wherein the timer starts at the same time as a physical layer timer starts, and the fourth execution condition is fulfilled in response to the expiry of the timer.

5 . The UE of claim 2 , wherein the first, second, fifth, sixth, or seventh condition is fulfilled when the first, second, fifth, sixth, or seventh condition is satisfied during a timer to trigger (TTT) period.

6 . The UE of claim 1 , wherein the at least one processor is further configured to cause the UE to:

transmit capability information of the UE, wherein the capability information indicates that the UE supports at least one of the following execution conditions:

a measurement-based condition;

a distance-based condition;

a time-based condition;

a timer-based condition;

a timing advance-based condition; and

an elevation angle-based condition.

7 . The UE of claim 1 , wherein the set of candidate cells includes a first candidate cell associated with at least two execution conditions.

8 . The UE of claim 1 , wherein the conditional reestablishment configuration information is received in a radio resource control (RRC) message, and the set of candidate cells includes more than one candidate cell.

9 . The UE of claim 1 , wherein the at least one processor is further configured to cause the UE to:

determine that more than one candidate cell satisfies a reestablishment condition; and

select a target cell for conditional reestablishment from the more than one candidate cell.

10 . The UE of claim 1 , wherein the at least one processor is further configured to cause the UE to:

initiating a reestablishment procedure in response to a radio link failure (RLF);

select a target cell for performing reestablishment; and

transmit a reestablishment request message to the target cell.

11 . An apparatus for wireless communication, comprising:

at least one memory; and

at least one processor coupled with the at least one memory and configured to cause the apparatus to:

transmit, to a user equipment (UE), conditional reestablishment configuration information indicating a set of execution conditions for a set of candidate cells, wherein each candidate cell of the set of candidate cells is associated with at least one execution condition, and

wherein the conditional reestablishment configuration information is associated with triggering, by the UE, a conditional reestablishment procedure before an occurrence of a radio link failure (RLF) at the UE using a target cell selected, before the occurrence of the RLF, from the set of candidate cells and without starting a timer associated with reestablishment initiation.

12 . The apparatus of claim 11 , wherein the set of execution conditions includes at least one of the following:

a first execution condition that a first channel quality between the UE and a corresponding candidate cell is an offset better than a second channel quality between the UE and a serving cell of the UE, the second channel quality is less than a first threshold, and the first channel quality is greater than a second threshold;

a second execution condition that a distance between the UE and the serving cell of the UE is greater than a third threshold and a distance between the UE and a corresponding candidate cell is less than a fourth threshold;

a third execution condition indicating an absolute time for performing conditional reestablishment;

a fourth execution condition indicating a value of a timer;

a fifth execution condition that the timing advance value from the UE to a corresponding candidate cell is less than a fifth threshold;

a sixth execution condition that the timing advance value from the UE to a corresponding candidate cell is less than a sixth threshold and the timing advance value from the UE to the serving cell of the UE is greater than a seventh threshold; and

a seventh execution condition that the elevation angle of the serving cell of the UE is less than an eighth threshold, and the elevation angle of a corresponding candidate cell is greater than a ninth threshold.

13 . The apparatus of claim 11 , wherein the at least one processor is further configured to cause the apparatus to:

receive capability information of the UE, wherein the capability information indicates that the UE supports at least one of the following execution conditions:

a measurement-based condition;

a distance-based condition;

a time-based condition;

a timer-based condition;

a timing advance-based condition; and

an elevation angle-based condition.

14 . The apparatus of claim 11 , wherein the set of candidate cells includes a first candidate cell associated with at least two execution conditions.

15 . The apparatus of claim 11 , wherein the conditional reestablishment configuration information is transmitted in a radio resource control (RRC) message, and the set of candidate cells includes more than one candidate cell.

16 . The apparatus of claim 11 , wherein the at least one processor is further configured to cause the apparatus to:

transmit a message including a UE context of the UE to at least one of the set of candidate cells.

17 . The apparatus of claim 16 , wherein the message indicates a value of a timer associated a validity period of the UE context.

18 . A method performed by a user equipment (UE), the method comprising:

receiving conditional reestablishment configuration information indicating a set of execution conditions for a set of candidate cells, wherein each candidate cell of the set of candidate cells is associated with at least one execution condition; and

triggering a conditional reestablishment procedure before an occurrence of a radio link failure (RLF), by:

evaluating the set of execution conditions based on the conditional reestablishment configuration information in response to the reception of conditional reestablishment configuration information;

selecting a target cell from the set of candidate cells for conditional reestablishment based on the evaluation, and

initiating the conditional reestablishment procedure with the target cell without starting a timer associated with reestablishment initiation.

19 . The method of claim 18 , wherein the set of execution conditions includes at least one of the following:

a first execution condition that a first channel quality between the UE and a corresponding candidate cell is an offset better than a second channel quality between the UE and a serving cell of the UE, the second channel quality is less than a first threshold, and the first channel quality is greater than a second threshold;

a second execution condition that a distance between the UE and the serving cell of the UE is greater than a third threshold and a distance between the UE and a corresponding candidate cell is less than a fourth threshold;

a third execution condition indicating an absolute time for performing conditional reestablishment;

a fourth execution condition indicating a value of a timer;

a fifth execution condition that the timing advance value from the UE to a corresponding candidate cell is less than a fifth threshold; and

a sixth execution condition that the timing advance value from the UE to a corresponding candidate cell is less than a sixth threshold and the timing advance value from the UE to the serving cell of the UE is greater than a seventh threshold;

a seventh execution condition that the elevation angle of the serving cell of the UE is less than an eighth threshold, and the elevation angle of a corresponding candidate cell is greater than a ninth threshold.