Method and apparatus for improving random access procedure in a wireless communication system
A method and apparatus are disclosed, from the perspective of the UE, for performing random access procedure. In one embodiment, the method includes the UE receives a first back-off information from the network in a broadcast message, wherein the first back-off information includes a start offset of back-off interval. The method further includes the UE transmits a first preamble to the network. In addition, the method includes the UE determines a back-off interval based on the first back-off information and a second back-off information, wherein the second back-off information is received when the UE monitors a response for the first preamble. The method also includes the UE transmits a second preamble to the network after the back-off interval is finished.
1. A method of a UE (User Equipment) for performing random access procedure, comprising:
the UE receives a first back-off information from a first base station in a dedicated message, wherein the first back-off information includes a granularity information;
the UE transmits a first preamble to a second base station;
the UE determines a back-off interval based on the first back-off information and a second back-off information, wherein the second back-off information is received when the UE monitors a response for the first preamble; and
the UE transmits a second preamble to the second base station after a back-off time, wherein the back-off time is randomly selected within the back-off interval.
2. The method of claim 1 , wherein the first back-off information includes a start offset of back-off interval.
3. The method of claim 1 , wherein the second back-off information includes a back-off indicator.
4. The method of claim 1 , further comprising:
the UE selects the first back-off information based on a resource set of the first preamble, if the dedicated message includes multiple back-off information.
5. The method of claim 1 , further comprising:
the UE selects the first back-off information based on a purpose of the random access procedure.
6. The method of claim 1 , further comprising:
the UE selects the first back-off information based on highest priority logical channel in all logical channels with data available for transmission.
7. The method of claim 1 , further comprising:
the UE selects the second back-off information based on a resource set of the first preamble, if the UE receives multiple back-off information when the UE monitors the response for the first preamble.
8. The method of claim 1 , further comprising:
the UE selects the second back-off information based on a purpose of the random access procedure, if the UE receives multiple back-off information when the UE monitors the response for the first preamble.
9. The method of claim 1 , further comprising:
the UE selects the second back-off information based on highest priority logical channel in all logical channels with data available for transmission, if the UE receives multiple back-off information when the UE monitors the response for the first preamble.
10. The method of claim 5 , wherein the purpose of the random access procedure is requesting system information.
11. The method of claim 5 , wherein the purpose of the random access procedure is for control plane establishment.
12. The method of claim 5 , wherein the purpose of the random access procedure is for handover.
13. The method of claim 2 , further comprising:
the UE determines the back-off interval based on multiplying the granularity information in the first back-off information by the back-off indicator in the second back-off information.
14. The method of claim 2 , further comprising:
the UE determines the back-off interval based on multiplying the granularity information in the first back-off information by a second value derived from the back-off indicator in the second back-off information.
15. The method of claim 1 , further comprising:
the UE determines the back-off time if the UE does not receive the response for the first preamble.
16. The method of claim 1 , wherein the first base station and the second base station are different base stations.
17. The method of claim 1 , wherein the first base station and the second base station are the same base station.
18. The method of claim 1 , wherein the granularity information includes a granularity of the back-off interval.
19. The method of claim 1 , wherein the granularity information includes a granularity of the start offset of back-off interval.
20. The method of claim 1 , wherein the dedicated message is a RRC (Radio Resource Control) reconfiguration message.
21. A User Equipment (UE) for performing random access procedure, comprising:
a control circuit;
a processor installed in the control circuit; and
a memory installed in the control circuit and operatively coupled to the processor;
wherein the processor is configured to execute a program code stored in the memory to:
receive a first back-off information from a first base station in a dedicated message, wherein the first back-off information includes a granularity information;
transmit a first preamble to a second base station;
determine a back-off interval based on the first back-off information and a second back-off information, wherein the second back-off information is received when the UE monitors a response for the first preamble; and
transmit a second preamble to the second base station after a back-off time, wherein the back-off time is randomly selected within the back-off interval.