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Improved Cell Selection Method when UMTS UE Is Instructed to Return to Idle State and Bar Currently Used Cells

IP.com Disclosure Number: IPCOM000131192D
Publication Date: 2005-Nov-09
Document File: 1 page(s) / 25K

Publishing Venue

The IP.com Prior Art Database

Abstract

If a UMTS UE detects an authentication failure, it may bar the currently used cells and return to Idle. The NAS instructs the RRC to do this by sending an RRC Connection Release message. The UE acts according to 25.331 v3.14.0 section 8.1.4a.2 and bars the active set (if it was in Cell_DCH) or the cell on which the UE was camped (if it was in other connected modes). In 25.304 v3.12.0, section 5.2.7 "Cell Selection when Leaving Connected Mode" states "Candidate cells for this selection are the cell(s) used immediately before leaving connected mode." This seems to suggest that section 5.2.3.1.1.b should be followed, and in this case it means that UE should try and select one of the barred calls. Rather than just selecting from barred cells, additional cells should be considered. It may be inappropriate to just consider neighbouring cells reported in SIBs 11 and 12, as these cell lists may be transmitted by a network that has just failed authentication, and so shouldn't necessarily be trusted. Trying to select the best cell on the current frequency is one option. Other options include selecting a cell on a different frequency, using stored information about good frequencies and cells. That ensures all cells on the frequency which is deemed untrustworthy are excluded.

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CALL SELECTION WHEN CELL IS BARRED

Improved Cell Selection Method when UMTS UE Is Instructed to Return to Idle State and Bar Currently Used Cells

Disclosed Anonymously

If a UMTS UE detects an authentication failure, it may bar the currently used cells and return to Idle.  The NAS instructs the RRC to do this by sending an RRC Connection Release message.  The UE acts according to 25.331 v3.14.0 section 8.1.4a.2 and bars the active set (if it was in Cell_DCH) or the cell on which the UE was camped (if it was in other connected modes).

In 25.304 v3.12.0, section 5.2.7 "Cell Selection when Leaving Connected Mode" states "Candidate cells for this selection are the cell(s) used immediately before leaving connected mode." This seems to suggest that section 5.2.3.1.1.b should be followed, and in this case it means that UE should try and select one of the barred calls.

Rather than just selecting from barred cells, additional cells should be considered.  It may be inappropriate to just consider neighbouring cells reported in SIBs 11 and 12, as these cell lists may be transmitted by a network that has just failed authentication, and so shouldn't necessarily be trusted.  Trying to select the best cell on the current frequency is one option.  Other options include selecting a cell on a different frequency, using stored information about good frequencies and cells.  That ensures all cells on the frequency which is deemed untrustworthy are excluded.