Method of enhanced connection recovery and cell selection

• US 9,661,678 B2
• Filed: 05/08/2015
• Issued: 05/23/2017
• Est. Priority Date: 01/18/2012
• Status: Active Grant

• Current Assignee: HFI Innovation, Inc. (MediaTek, Inc.)
• Original Assignee: MediaTek, Inc.
• Inventors: Johansson, Per Johan Mikael, Chen, Yih-Shen, Low, Tze-Ping, Plumb, William
• Primary Examiner(s): Ngo, Chuong A
• Application Number:
  US14/706,967
• Publication Number:
  US 20150245407A1
• Time in Patent Office: 746 Days
• CPC Class Codes: H04W 36/0033 with transfer of context information
• CPC Class Codes: H04W 36/0055 Transmission or use of information for re-establishing the radio link
• CPC Class Codes: H04W 36/0061 of neighbour cell information
• CPC Class Codes: H04W 36/0072 of resource information of target access point
• CPC Class Codes: H04W 36/08 Reselecting an access point
• CPC Class Codes: H04W 36/24 Reselection being triggered by specific parameters
• CPC Class Codes: H04W 40/36 due to handover
• CPC Class Codes: H04W 48/17 Selecting a data network PoA [Point of Attachment]
• CPC Class Codes: H04W 76/18 Management of setup rejection or failure
• CPC Class Codes: H04W 76/19 Connection re-establishment

Abstract

An enhanced connection recovery upon lost RRC connection due to radio link failure (RLF) or handover failure (HOF) is proposed. A UE first establishes an RRC connection in a source cell in a mobile communication network. Later on, the UE detects a failure event and starts an RRC reestablishment procedure in a target cell to restore the RRC connection. In a first novel aspect, a fast RLF process is applied to reduce the outage time in the serving cell. In a second novel aspect, an enhanced cell selection mechanism based on cell prioritization information is applied to reduce the outage time in the target cell. In one embodiment, multi-RAT registration is used to steer cell selection.

Claims

1. A method, comprising:

establishing a radio resource control (RRC) connection by a user equipment (UE) with a base station in a mobile communication network;

detecting a radio link problem of the RRC connection and thereby starting a first timer associated with the radio link problem;

starting a second timer upon detecting a triggering condition while the first timer is not expired;

initiating an RRC reestablishment procedure with a target cell when the second timer expires but before the first timer expires; and

performing the RRC connection reestablishment procedure with the target cell.

2. The method of claim 1, wherein a channel quality of the target cell is better than a channel quality of a serving cell by a non-negative threshold based on reference signal received power or reference signal received quality (RSRP/RSRQ) measurements.

3. The method of claim 1, wherein the triggering condition is satisfied when the UE transmits a measurement report to the base station, wherein the RRC reestablishment procedure is initiated when the second timer expires.

4. The method of claim 1, wherein the triggering condition is satisfied when a channel quality of a serving cell is lower than a channel quality of the target cell by a non-negative threshold, and wherein the RRC reestablishment procedure is initiated when the second timer expires.

5. The method of claim 1, wherein the triggering condition is satisfied when a channel quality of a serving cell is lower than a first threshold and a channel quality of the target cell is higher than a second threshold, wherein the RRC reestablishment procedure is initiated when the second timer expires.

6. The method of claim 1, wherein the RRC reestablishment is initiated before the first timer expires if the target cell is identified as a candidate cell, and wherein the UE receives candidate cell assignment information from the base station.

7. The method of claim 6, wherein the UE receives cell prioritization information from the base station for selecting the target cell.

8. A user equipment (UE), comprising:

a radio resource control (RRC) module that establishes an RRC connection with a base station in a mobile communication network;

a radio link management (RLM) module that initiates a first timer when detecting a radio link problem; and

a cell selection module that selects a target cell based on cell prioritization information when the UE is in a high mobility state, wherein the cell prioritization information comprises information for cell selection as well as for cell reselection, and wherein the UE initiates an RRC reestablishment procedure and performs an RRC connection setup procedure with the selected target cell.

9. The UE of claim 8, wherein the RRC reestablishment procedure is initiated when the first timer expires.

10. The UE of claim 8, wherein the RRC reestablishment procedure is initiated before the first timer expires.

11. The UE of claim 8, wherein the UE receives the cell prioritization information via a broadcast channel from the base station.

12. The UE of claim 8, wherein the UE receives the cell prioritization information via dedicated signaling from the base station.

13. The UE of claim 8, wherein cells are prioritized based on corresponding frequency layers, and wherein the UE receives cell ID information of prioritized cells.

14. The UE of claim 8, wherein cells of the same frequency layer are prioritized based on corresponding mobility coverage, and wherein the UE receives cell ID information of prioritized cells.

15. The UE of claim 8, wherein cells are prioritized based on radio access technology (RAT), and wherein the UE pre-registers in different RATs to facilitate inter-RAT coordination.

16. A user equipment (UE), comprising:

a radio resource control (RRC) management module that establishes an RRC connection with a base station in a mobile communication network;

a radio link management (RLM) module that detects a radio link problem of the RRC connection and thereby starting a first timer, wherein the RLF module also starts a second timer upon detecting a triggering condition while the first timer is not expired, wherein the UE initiates an RRC reestablishment procedure with a target cell when the second timer expires but before the first timer expires; and

a cell selection module that selects a target cell, wherein the UE performs the RRC connection reestablishment with the target cell.

17. The UE of claim 16, wherein the UE detects the triggering condition when the UE transmits a measurement report to the base station, and wherein the RRC reestablishment procedure is initiated when the second timer expires.

18. The UE of claim 16, wherein the RRC reestablishment is initiated before the first timer expires if the target cell is identified as a candidate cell.

19. The UE of claim 16, wherein the UE selects the target cell based on cell prioritization information for the RRC reestablishment procedure or an RRC connection setup procedure.

20. The UE of claim 19, wherein the UE performs cell prioritization based on at least one of a frequency layer, a mobility coverage, and a radio access technology (RAT) of a cell.

21. The UE of claim 19, wherein the UE selectively applies the cell prioritization when the UE is in a high mobility state.