Method and apparatus for handling circuit switched calls at a user equipment
View Patent ↗A method at a user equipment including detecting that a circuit switched (CS) call has been requested at the user equipment; if a most recent registration attempt or registration update attempt with a network of a first radio access technology (RAT) resulted in an abnormal state, registering with a network of a second RAT; and initiating the CS call with the network of the second RAT.
1. A method at a user equipment comprising:
detecting that a circuit switched (CS) call has been requested at the user equipment and initiating a circuit switched fallback (CSFB) procedure;
determining if a most recent registration attempt or registration update attempt with a network of a first radio access technology (RAT) resulted in an abnormal state;
registering with a network of a second RAT it the abnormal state is detected even if a tracking area code or a location area code of a last successful network registration matches the tracking area code or location area code in a broadcast message from the network of the second RAT;
initiating the CS call with the network of the second RAT; and
reselecting to the network of the second RAT for the CS call.
2. The method of claim 1 , wherein the first RAT is a packet switched only RAT.
3. The method of claim 1 , wherein the reselecting to the network of the second RAT includes the registering with the network of the second RAT.
4. The method of claim 1 , wherein the registering is in the form of a location area update that utilizes a follow_on_request flag.
5. The method of claim 1 , wherein the reselecting comprises sending a CM service request to the network of the second RAT.
6. The method of claim 1 , wherein the most recent registration attempt with the network of the first RAT is in an abnormal state due to a radio link failure or a radio resource control connection release.
7. The method of claim 6 , wherein the abnormal state is based on a reject cause indicating an identifier is unknown in a visitor location registry.
8. The method of claim 1 , further comprising, checking whether the registering is successful, and if not ending the process.
9. The method of claim 1 , further comprising, checking whether the registering is successful, and if not proceeding back to registering with the network of the second RAT.
10. The method of claim 1 , wherein the first RAT is an evolved-universal terrestrial radio access (E-UTRAN) RAT.
11. The method of claim 1 , wherein the second RAT is a global system for mobile communications (GSM) RAT or universal terrestrial radio access network (UTRAN) RAT.
12. The method of claim 1 , wherein the circuit switched call is a voice call.
13. A user equipment comprising a processor configured to:
detect that a circuit switched (CS) call has been requested at the user equipment and initiate a circuit switched fall back procedure;
determine if a most recent registration attempt or registration update attempt with network of a first radio access technology (RAT) resulted in an abnormal state;
register with a network of a second RAT if the abnormal state is determined even if a tracking area code or a location area code of a last successful registration matches the tracking area code or location area code in a broadcast message from the network of the second RAT;
initiate the CS call with the network of the second RAT; and
reselect to the network of the second RAT for the CS call.
14. The user equipment of claim 13 , wherein the first RAT is a packet switched only RAT.
15. The user equipment of claim 13 , wherein the reselect to the network of the second RAT includes registering with the second RAT.
16. The user equipment of claim 13 , wherein the registration with the network of the second RAT is in the form of a location area update that utilizes a follow_on_request flag.