Methods and apparatus for facilitating robust forward handover in long term evolution (LTE) communication systems

• US 8,615,241 B2
• Filed: 02/16/2011
• Issued: 12/24/2013
• Est. Priority Date: 04/09/2010
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Gupta, Ajay, Malladi, Durga Prasad
• Primary Examiner(s): Kincaid, Lester
• Assistant Examiner(s): Ajayi, Joel
• Application Number:
  US13/028,971
• Publication Number:
  US 20110250892A1
• Time in Patent Office: 1,042 Days
• Field of Search: 455/437
• 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:

establishing, by a user terminal, a connection with a first base station of a first cell, the connection including a Radio Resource Control Connected (RRC_Connected) state and a data connected state;

storing at the user terminal first identity information associated with the connection to the first cell, the identity information comprising a Physical Cell Identity (PCI) and a Cell Radio Network Temporary Identifier (C-RNTI);

selecting, by the user terminal, a second base station of a second cell based on a first criterion determined by the user terminal;

initiating, at the user terminal, a forward handover to the second base station of the second cell;

receiving, at the user terminal, second identity information associated with the second cell;

re-establishing the RRC_Connected state with the second base station;

declaring, by the user terminal, a Radio Link Failure (RLF) between re-establishment of the RRC_Connected state and completion of establishment of the connection to the second base station, based on a second criterion determined by the user terminal; and

initiating, by the user terminal, reestablishment of the connection with a third base station of a third cell using the first identity information.

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

3. 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.

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

5. The method of claim 1, further comprising:

receiving, at the user terminal, third identity information associated with the third cell;

declaring, by the user terminal, 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

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

6. The method of claim 5, further comprising:

disregarding the third identity information received during the re-establishment of the RRC_Connected state with the third base station.

7. A computer program product comprising a non-transitory computer-readable medium including codes executable by a processor of a user terminal to:

establish a connection with a first base station of a first cell, the connection including a Radio Resource Control Connected (RRC_Connected) state and a data connected state;

store first identity information associated with the connection to the first cell, the identity information comprising a Physical Cell Identity (PCI) and a Cell Radio Network Temporary Identifier (C_RNTI);

select a second base station of a second cell based on a first criterion determined by the user terminal;

initiate a forward handover to the second base station of the second cell;

receive second identity information associated with the second cell;

re-establish the RRC_Connected state with the second base station;

declare a Radio Link Failure (RLF) between re-establishment of the RRC_Connected state and completion of establishment of the connection to the second base station, based on a second criterion determined by the user terminal; and

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

8. A user terminal, comprising:

a processor module configured to establish, in conjunction with a receiver module and a transmitter module, a connection with a first base station of a first cell, the connection including a Radio Resource Control Connected (RRC_Connected) state and a data connected state;

a module configured to store first identity information associated with the connection to the first cell, the identity information comprising a Physical Cell Identity (PCI) and a Cell Radio Network Temporary Identifier (C_RNTI);

wherein the processor module is further configured to select a second base station of a second cell based on a first criterion and

the transmitter module, in conjunction with the processor module, is further configured to initiate a forward handover with the second base station of the second cell;

wherein the processor module is further configured to declare, in conjunction with the receiver module, a Radio Link Failure (RLF) between establishment of the RRC_Connected state and completion of establishment of the connection to the second base station, based on a second criterion; and

wherein the transmitter module is further configured to initiate reestablishment of the 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.

9. The communications device of claim 8, wherein the declaring RLF occurs before completion of an RRCConnectionReconfiguration procedure.

10. A user terminal, comprising:

means for establishing a connection with a first base station of a first cell, the connection including a Radio Resource Control Connected (RRC_Connected) state and a data connected state;

means for storing first identity information associated with the connection to the first cell, the identity information comprising a Physical Cell Identity (PCI) and a Cell Radio Network Temporary Identifier (C_RNTI);

means for selecting a second base station of a second cell based on a first criterion determined by the user terminal;

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

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

means for re-establishing the RRC_Connected state with the second base station;

means for declaring a Radio Link Failure (RLF) between re-establishment of the RRC_Connected state and completion of establishment of the connection to the second base station, based on a second criterion determined by the user terminal; and

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

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

establishing, at a user terminal, a connection with a source base station of a source cell, the connection including a Radio Resource Control Connected (RRC_Connected) state and a data connected state;

storing at the user terminal, first identity information associated with the connection with the source cell, the first identity information comprising a Physical Cell Identity (PCI) and a Cell Radio Network Temporary Identifier (C-RNTI);

selecting, by the user terminal, a target base station of a target cell based on a first criterion determined by the user terminal;

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

receiving, at the user terminal, a message from the target base station informing the user terminal to continue the connection process without performing a Random Access Channel (RACH) procedure; and

sending, from the user terminal, a connection request message to the target base station, without performing a RACH procedure with the target base station, subsequent to receipt of the message.

12. The method of claim 11, wherein the connection request message is an RRCConnectionRequest message.

13. The method of claim 11, further comprising receiving, from the target base station, a connection setup message.

14. A computer program product comprising a non-transitory computer-readable medium including codes executable by a processor of a user terminal to:

establish a connection with a source base station of a source cell, the connection including a Radio Resource Control Connected (RRC_Connected) state and a data connected state;

store first identity information associated with the connection with the source cell, the first identity information comprising a Physical Cell Identity (PCI) and a Cell Radio Network Temporary Identifier (C-RNTI);

select a target base station of a target cell based on a first criterion determined by the user terminal;

send to the target base station, a connection reestablishment request including first identity information for retrieval of user context information stored at a source base station;

receive, from the target base station, a message informing the user terminal to continue the connection process without performing a Random Access Channel (RACH) procedure; 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 message.

15. A user terminal, comprising:

a processor module configured to

establish a connection with a source base station of a source cell, the connection including a Radio Resource Control Connected (RRC_Connected) state and a data connected state,

store first identity information associated with the source cell, the first identity information comprising a Physical Cell Identity (PCI) and a Cell Radio Network Temporary Identifier (C-RNTI), and

select a target base station of a target cell based on a first criterion determined by the user terminal;

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

a receiver module configured to receive, from the target base station, a message informing the user terminal to continue the connection process without performing a Random Access Channel (RACH) procedure;

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 message.

16. A user terminal, comprising:

means for establishing a connection with a source base station of a source cell, the connection including a Radio Resource Control Connected (RRC_Connected) state and a data connected state;

means for storing first identity information associated with the source cell, the first identity information comprising a Physical Cell Identity (PCI) and a Cell Radio Network Temporary Identifier (C-RNTI);

means for selecting a target base station of a target cell based on a first criterion determined by the user terminal;

means for sending to the target base station, a connection reestablishment request including first identity information for retrieval of user context information stored at a source base station;

means for receiving, from the target base station, a message informing the user terminal to continue the connection without performing a Random Access Channel (RACH) procedure; 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 message.