RAT SELECTION IN CASE OF AMBIGUOUS RAT IDENTIFIER

摘要

The application relates to PLMN and RAT selection as e.g. standardised by 3GPP TS 23.122. According to this standard, the selection utilises priority lists stored in the [U]SIM card comprising PLMN entries and associated access technologies for each PLMN entry. However, under certain circumstances (such as the present standards used by the China Mobile Communications Corporation (CMCC)), the so-called "access technology field" in the USIM card that indicates the RAT associated with the PLMN does not differentiate between TD-SCDMA and WCDMA. In either case, a common setting referred to as "UTRAN" is used. As a consequence the UE might attempt to acquire service with TD-SCDMA when WCDMA is actually desired, or vice-versa. Since the connection attempt with the undesired RAT will fail, performance will be lost. This problem is solved by the application in that when the RAT is ambiguous, i.e. UTRAN in the given example (704), an additional indicator in non- volatile memory is checked (710) to see which more specific RAT, i.e. TD-SCDMA (714) or WCDMA (716) in the present example, should be given priority when acquiring the RAT (716). The indicator is set either according to the last RAT acquired or according to the RAT history with regard to RAT coverage.