Methods and system for performing handover in a wireless communication system
A method and system for performing handover in a third generation (3G) long term evolution (LTE) system are disclosed. A source evolved Node-B (eNode-B) makes a handover decision based on measurements and sends a handover request to a target eNode-B. The target eNode-B sends a handover response to the source eNode-B indicating that a handover should commence. The source eNode-B then sends a handover command to a wireless transmit/receive unit (WTRU). The handover command includes at least one of reconfiguration information, information regarding timing adjustment, relative timing difference between the source eNode-B and the target eNode-B, information regarding an initial scheduling procedure at the target eNode-B, and measurement information for the target eNode-B. The WTRU then accesses the target eNode-B and exchanges layer 1/2 signaling to perform downlink synchronization, timing adjustment, and uplink and downlink resource assignment based on information included in the handover command.
1. A wireless transmit/receive unit (WTRU) for performing handover in a wireless communication system, the WTRU comprising:
a transceiver configured to receive a handover command from a first evolved Node-B (eNode-B); and
a controller configured to:
facilitate a handover from the first eNode-B to a second eNode-B in accordance with the handover command,
perform timing adjustment with the second eNode-B using a random access channel (RACH) access procedure, and
reset radio link control (RLC) and hybrid automatic repeat request (HARQ) after receiving the handover command.
2. The WTRU of claim 1 wherein the handover command comprises at least one of reconfiguration information, information regarding timing adjustment, relative timing difference between the first eNode-B and the second eNode-B information regarding an initial radio resource scheduling procedure at the second eNode-B, and measurement information for the second eNode-B.
3. The WTRU of claim 2 wherein the reconfiguration information is for at least one of a radio resource control (RRC) layer, a radio link control (RLC) layer, a medium access control (MAC) layer or a physical layer.
4. The WTRU of claim 1 wherein the controller is further configured to control the transceiver such that data is exchanged with the first eNode-B after the WTRU receives the handover command.
5. The WTRU of claim 4 wherein the data transmitted comprises an incomplete service data unit (SDU).
6. The WTRU of claim 1 wherein the controller is further configured to control the transceiver such that data transmission to the first eNode-B stops when the WTRU receives the handover command.
7. The WTRU of claim 1 wherein the controller is further configured to autonomously perform the timing adjustment based on a relative timing difference between the first eNode-B and the second eNode-B.
8. The WTRU of claim 1 wherein a plurality of RACH preamble signatures with different orthogonality and different priority are used, and among the plurality of RACH preamble signatures, a RACH preamble signature with higher orthogonality, higher priority and higher power is used for the handover.
9. The WTRU of claim 1 wherein a particular RACH preamble signature is reserved for the handover.
10. The WTRU of claim 1 wherein a reserved RACH preamble signature is indicated in the handover command.
11. The WTRU of claim 1 wherein the controller is further configured to send a resource assignment request to the second eNode-B for scheduling an uplink resource.
12. The WTRU of claim 11 wherein the resource assignment request is sent via a random access channel (RACH).
13. The WTRU of claim 1 wherein the controller performs a radio link failure procedure when the handover command is not successfully received.
14. The WTRU of claim 13 wherein the controller is further configured attempt to access an originally connected cell associated with the first eNode-B.
15. The WTRU of claim 13 wherein the controller is further configured to attempt to access a second cell associated with the first eNode-B if the controller fails to access the originally connected cell.
16. The WTRU of claim 15 wherein the controller is further configured to attempt to access a third cell not associated with the first eNode-B if the controller fails to access the second cell associated with the first eNode-B.
17. The WTRU of claim 13 wherein the controller is further configured to send a first eNode-B identity (ID) to the second eNode-B during a cell reselection procedure.
18. The WTRU of claim 1 wherein the first eNode-B is a source eNode-B and the second eNode-B is a target eNode-B.
19. A method for performing handover from a first evolved Node-B (eNode-B) to a second eNode-B in a wireless communication system, the method comprising:
a wireless transmit/receive unit (WTRU) receiving a handover command from the first eNode-B;
the WTRU performing timing adjustment with the second eNode-B using a random access channel (RACH) access procedure; and
the WTRU resetting radio link control (RLC) and hybrid automatic repeat request (HARQ) after receiving the handover command.
20. The method of claim 19 wherein handover command comprises at least one of reconfiguration information, information regarding timing adjustment, relative timing difference between the first eNode-B and the second eNode-B, information regarding an initial radio resource scheduling procedure at the second eNode-B, and measurement information for the second eNode-B.
21. The method of claim 19 wherein the reconfiguration information is for at least one of a radio resource control (RRC) layer, a radio link control (RLC) layer, a medium access control (MAC) layer or a physical layer.
22. The method of claim 19 wherein the WTRU exchanges data with the first eNode-B after the WTRU receives the handover command.
23. The method of claim 22 wherein the data comprises an incomplete service data unit (SDU).
24. The method of claim 19 wherein the WTRU stops data transmission to the first eNode-B when the WTRU receives the handover command.
25. The method of claim 19 wherein the WTRU autonomously performs the timing adjustment based on a relative timing difference between the first eNode-B and the second eNode-B.
26. The method of claim 19 wherein a plurality of RACH preamble signatures with different orthogonality and different priority are used, and among the plurality of RACH preamble signatures, a RACH preamble signature with higher orthogonality, higher priority and higher power is used for the handover.
27. The method of claim 19 wherein a particular RACH preamble signature is reserved for the handover.
28. The method of claim 19 wherein a reserved RACH preamble signature is indicated in the handover command.
29. The method of claim 19 wherein the WTRU sends a resource assignment request to the second eNode-B for scheduling an uplink resource.
30. The method of claim 29 wherein the resource assignment request is sent via a random access channel (RACH).
31. The method of claim 19 wherein the WTRU sends a first eNode-B identity (ID) to the second eNode-B during cell reselection.
32. The method of claim 19 wherein the first eNode-B is a source eNode-B and the second eNode-B is a target eNode-B.