METHODS AND APPARATUS FOR FACILITATING ROBUST FORWARD HANDOVER IN LONG TERM EVOLUTION (LTE) COMMUNICATION SYSTEMS

• US 20110250892A1
• Filed: 02/16/2011
• Published: 10/13/2011
• Est. Priority Date: 04/09/2010
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Malladi, Durga Prasad, Gupta, Ajay
• Granted Patent: US 8,615,241 B2
• Time in Patent Office: Days
• US Class Current: 455/437
• CPC Class Codes: H04W 36/0011 for data sessions of end-to-end connection
• CPC Class Codes: H04W 36/13 Cell handover without a predetermined boundary, e.g. virtual cells
• CPC Class Codes: H04W 76/27 Transitions between radio resource control [RRC] states

Abstract

Method and apparatus for facilitating inter-cell connections, such as during a forward handover or radio link failure (RLF), are disclosed. A user terminal such as a UE may store identity information associated with a source cell, and use this information in accessing target or other cells subsequent to radio link failure so as to facilitate access to context information of the user terminal. A base station may be configured to improve handover performance by associating context information with a newly assigned terminal identity. Handover performance may be enhanced by facilitating connection processing in the event of inability to retrieve user terminal context from a source cell.

Claims

1. A method for facilitating a forward handover in a communications system, comprising:

receiving, at a user terminal, from a first base station of a first cell, first identity information associated with the first cell;

initiating a forward handover between the user terminal and a second base station of a second cell;

receiving second identity information associated with the second cell;

establishing a Radio Resource Control (RRC) connected state (RRC_Connected) with the second base station;

declaring Radio Link Failure (RLF) between establishment of the RRC connection state and completion of establishment of the connection to the second base station; and

initiating a connection with a third base station of a third cell using the first identity information.

2. The method of claim 1, wherein the first identity information comprises a Physical Cell Identity (PCI) and a Cell Radio Network Temporary Identifier (C-RNTI) associated with the first base station, and a random number generated by the user terminal.

3. The method of claim 1, wherein the first identity information comprises an SAE Temporary Mobile Subscriber Identity (S-TMSI).

4. The method of claim 1, wherein the declaring RLF occurs before completion of an RRCConnectionReconfiguration procedure.

5. The method of claim 1, wherein the third base station is a different base station from the first base station and the second base station.

6. The method of claim 1, wherein the third base station and the first base station are the same base station.

7. The method of claim 1, further comprising:

establishing an RRC_Connected state with the third base station;

receiving second identity information associated with the third cell;

declaring a second RLF associated with the third base station between establishment of the RRC_Connected state with the third base station and completion of establishment of the connection to the third base station; and

initiating a connection with a fourth base station of a fourth cell using the first identity information.

8. The method of claim 7, further comprising:

disregarding the second identity information during the establishing an RRC_Connected state with the third base station.

9. A computer program product comprising a computer-readable medium including codes executable by a processor to:

receive, at a user terminal, from a first base station of a first cell, first identity information associated with the first cell;

initiate a forward handover between the user terminal and a second base station of a second cell;

receive second identity information associated with the second cell;

establish a Radio Resource Control (RRC) connected state (RRC_Connected) with the second base station;

declare Radio Link Failure (RLF) between establishment of the RRC connection state and completion of establishment of the connection to the second base station; and

initiate a connection with a third base station of a third cell using the first identity information.

10. A communications device, comprising:

a receiver module configured to receive, from a first base station of a first cell, first identity information associated with the first cell;

a transmitter module configured to initiate a forward handover with a second base station of a second cell; and

a processor module configured to declare, in conjunction with the receiver module, Radio Link Failure (RLF) between establishment of the RRC connection state and completion of establishment of the connection to the second base station;

wherein the transmitter module is further configured to initiate a connection with a third base station of a third cell using the first identity information and first user terminal information subsequent to the declaration of RLF.

11. The communications device of claim 10, wherein the first identity information comprises a Physical Cell Identity (PCI) and a Cell Radio Network Temporary Identifier (C-RNTI) associated with the first base station, and a random number generated by the user terminal.

12. The communications device of claim 10, wherein the first identity information comprises an SAE Temporary Mobile Subscriber Identity (S-TMSI).

13. The communications device of claim 10, wherein the declaring RLF occurs before completion of an RRCConnectionReconfiguration procedure.

14. A communications device, comprising:

means for receiving, at a user terminal, from a first base station of a first cell, first identity information associated with the first cell;

means for initiating a forward handover between the user terminal and a second base station of a second cell;

means for receiving second identity information associated with the second cell;

means for establishing a Radio Resource Control (RRC) connected state (RRC_Connected) with the second base station;

means for declaring Radio Link Failure (RLF) between establishment of the RRC connection state and completion of establishment of the connection to the second base station; and

means for initiating a connection with a third base station of a third cell using the first identity information.

15. A method for facilitating a forward handover in a communications system, comprising:

receiving, at a target base station, first identity information from a user terminal including information for retrieval of user context information stored at a source base station;

sending second identity information to the user terminal;

receiving a new reestablishment request from the user terminal;

sending third identity information to the user terminal; and

associating the user context information with the third identity information.

16. The method of claim 15, wherein the first identity information comprises a Physical Cell Identity (PCI) and a Cell Radio Network Temporary Identifier (C-RNTI) associated with the first base station, and a random number generated by the user terminal.

17. The method of claim 15, wherein the first identity information comprises an SAE Temporary Mobile Subscriber Identity (S-TMSI).

18. The method of claim 15, wherein the second identity information comprises a first C-RNTI generated by the second base station.

19. The method of claim 18, wherein the third identity information comprises a second C-RNTI generated by the second base station.

20. The method of claim 15, further comprising retrieving the user terminal context information from the source base station.

21. The method of claim 15, further comprising sending an RRCConnectionReestablishment message, wherein the RLF occurs before receipt of the RRCConnectionReestablishment message.

22. A computer program product comprising a computer-readable medium including codes executable by a processor to:

receive, at a target base station, first identity information from a user terminal including information for retrieval of user context information stored at a source base station;

send second identity information to the user terminal;

receive, subsequent to declaration of RLF at the user terminal, the first identity information from the user terminal;

send third identity information to the user terminal; and

associate the user context information with the third identity information.

23. A communications device, comprising:

a receiver module configured to receive first identity information from a user terminal including information for retrieval of user context information stored at a source base station;

a transmitter module configured to send second identity information to the user terminal;

wherein the receiver module is further configured to receive, subsequent to declaration of RLF at the user terminal, the second identity information from the user terminal, and the transmitter module is further configured to send third identity information to the user terminal; and

a processor module configured to associate the user context information with the third identity information.

24. The communications device of claim 23, wherein the first identity information comprises a Physical Cell Identity (PCI) and a Cell Radio Network Temporary Identifier (C-RNTI) associated with the first base station, and a random number generated by the user terminal.

25. The communications device of claim 23, wherein the first identity information comprises an SAE Temporary Mobile Subscriber Identity (S-TMSI).

26. The communications device of claim 23, wherein the second identity information comprises a first C-RNTI generated by the second base station.

27. The communications device of claim 26, wherein the third identity information comprises a second C-RNTI generated by the second base station.

28. The communications device of claim 24, further comprising a backhaul interface module configured to retrieve the user terminal context information from the source base station.

29. The communications device of claim 23, wherein the transmitter module is further configured to send an RRCConnectionReestablishment message, wherein the RLF occurs before receipt of the RRCConnectionReestablishment message.

30. A communications device, comprising:

means for receiving, at a target base station, first identity information from a user terminal including information for retrieval of user context information stored at a source base station;

means for sending second identity information to the user terminal;

means for receiving, subsequent to declaration of RLF at the user terminal, the first identity information from the user terminal;

means for sending third identity information to the user terminal; and

means for associating the user context information with the third identity information.

31. A method for facilitating a forward handover in a communications system, comprising:

receiving, at a target base station, first identity information from a user terminal including information for retrieval of user context information stored at a source base station;

initiating retrieval of the user context from the source base station;

sending, in response to failure to retrieve the user context, a context retrieval fail message to the user terminal; and

receiving, from the user terminal, a connection request message.

32. The method of claim 31, further comprising sending a connection setup message to the user terminal subsequent to receipt of the connection request message.

33. The method of claim 32, wherein the connection setup message is an RRCConnectionSetup message.

34. The method of claim 31, wherein the connection request message is an RRCConnectionRequest message, said connection request message received without receipt of preceding Random Access Channel (RACH) procedure signaling from the user terminal.

35. A computer program product comprising a computer-readable medium including codes executable by a processor to:

receive, at a target base station, first identity information from a user terminal including information for retrieval of user context information stored at a source base station;

initiate retrieval of the user context from the source base station;

send, in response to failure to retrieve the user context, a context retrieval fail message to the user terminal; and

receive, from the user terminal, a connection request message.

36. A communications device, comprising:

a receiver module configured to receive, at a target base station, first identity information from a user terminal including information for retrieval of user context information stored at a source base station;

a processor module configured to initiate retrieval of the user context from the source base station; and

a transmitter module configured to send, in response to failure to retrieve the user context, a context retrieval fail message to the user terminal;

wherein the receiver module is further configured to receive, from the user terminal, a connection request message.

37. The communications device of claim 36, wherein the transmitter module is further configured to send a connection setup message to the user terminal subsequent to receipt of the connection request message.

38. The communications device of claim 36, wherein the connection setup message is an RRCConnectionSetup message.

39. The communications device of claim 36, wherein the connection request message is an RRCConnectionRequest message, said connection request message received at the receiver module without receipt of preceding Random Access Channel (RACH) procedure signaling from the user terminal.

40. A communications device, comprising:

means for receiving, at a target base station, first identity information from a user terminal including information for retrieval of user context information stored at a source base station;

means for initiating retrieval of the user context from the source base station;

means for sending, in response to failure to retrieve the user context, a context retrieval fail message to the user terminal; and

means for receiving, from the user terminal, a connection request message.

41. A method for facilitating a forward handover in a communications system, comprising:

sending, from a user terminal to a target base station, first identity information including information for retrieval of user context information stored at a source base station;

receiving, from the target base station, a context retrieval fail message; and

sending a connection request message to the target base station, without performing a RACH procedure with the target base station, subsequent to receipt of the context retrieval fail message.

42. The method of claim 41, wherein the connection request message is an RRCConnectionRequest message.

43. The method of claim 41, further comprising receiving, from the target base station, a connection setup message.

44. A computer program product comprising a computer-readable medium including codes executable by a processor to:

send, from a user terminal to a target base station, first identity information including information for retrieval of user context information stored at a source base station;

receive, from the target base station, a context retrieval fail message; and

send a connection request message to the target base station, without performing a RACH procedure with the target base station, subsequent to receipt of the context retrieval fail message.

45. A communications device, comprising:

a transmitter module configured to send, from a user terminal to a target base station, first identity information including information for retrieval of user context information stored at a source base station; and

a receiver module configured to receive, from the target base station, a context retrieval fail message;

wherein the transmitter module is further configured to send a connection request message to the target base station without performing a RACH procedure with the target base station subsequent to receipt of the retrieval fail message.

46. A communications device, comprising:

means for sending, from a user terminal to a target base station, first identity information including information for retrieval of user context information stored at a source base station;

means for receiving, from the target base station, a context retrieval fail message; and

means for sending a connection request message to the target base station, without performing a RACH procedure with the target base station, subsequent to receipt of the context retrieval fail message.