METHOD AND APPARATUS FOR FALLBACK HANDLING

1 . A method for fallback handling, comprising:

operating a user equipment in a fifth-generation (5G) radio access technology;

maintaining second-generation (2G) and third-generation (3G) physical layer components in a warm state; and

maintaining 2G and 3G layer 2 components in an inactive state.

2 . The method of claim 1 , further comprising:

powering up at least one of the 2G and 3G layer 2 components when it is determined that fallback should occur.

3 . The method of claim 1 , further comprising:

reselecting from the 5G radio access technology to a fourth-generation (4G) radio access technology, wherein the maintaining the 2G and 3G physical layer components in the warm state and maintaining the 2G and 3G layer 2 components in the inactive state continues after the reselecting to the 4G radio access technology.

4 . The method of claim 1 , wherein the user equipment is configured to operate in at least one standalone mode or non-standalone mode in the 5G radio access technology.

5 . The method of claim 1 , further comprising:

maintaining fourth-generation (4G) physical layer components in a warm state; and

maintaining 4G layer 2 components in an inactive state.

6 . An apparatus for fallback handling, comprising:

at least one processor; and

at least one memory including computer program code,

wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to perform:

operating a user equipment in a fifth-generation (5G) radio access technology; and

transitioning to a second-generation (2G) or third-generation (3G) radio access technology only when out of service (OOS) coverage or internet protocol (IP) multimedia subsystem (IMS) failure occurs.

7 . The apparatus of claim 6 , wherein the at least one memory and the computer program code are further configured to, with the at least one processor, cause the apparatus to perform:

detecting that the user equipment is experiencing an OOS coverage of 5G,

wherein the transitioning is based on the OOS coverage.

8 . The apparatus of claim 6 , wherein the at least one memory and the computer program code are further configured to, with the at least one processor, cause the apparatus to perform:

detecting an IMS failure,

wherein the transitioning is based on the detected IMS failure.

9 . The apparatus of claim 6 , wherein the user equipment is configured to operate in at least one standalone mode or non-standalone mode in the 5G radio access technology.

10 . A method for fallback handling, comprising:

operating a user equipment in a fifth-generation (5G) radio access technology; and

at least one of:

determining a likelihood of fallback to at least one of a second-generation (2G) or third-generation (3G) radio access technology, and falling back to the 2G or 3G radio access technology only when the likelihood exceeds a threshold; or

falling back to at least one of a 2G, 3G, or fourth-generation (4G) radio access technology, and when attempting to return to the 5G radio access technology from the 2G, 3G, or 4G radio access technology, performing only idle mode search of the 5G radio access technology system.

11 . The method of claim 10 , wherein the determining comprises taking into account a location of a neighboring legacy base station.

12 . The method of claim 10 , wherein the determining comprises taking into account signal characteristics of signals received at the user equipment.

13 . The method of claim 10 , wherein the determining comprises taking into account average data buffer queue size at the user equipment.

14 . The method of claim 10 , wherein the determining comprises taking into account a smallest latency value of a packet data application at the user equipment.

15 . The method of claim 10 , wherein the determining is performed contingent upon a determination that received power has fallen below a threshold power level for a predetermined time period.

16 . An apparatus for fallback handling, comprising:

at least one processor; and

at least one memory including computer program code,

wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to perform:

operating the apparatus in a fifth-generation (5G) radio access technology;

maintaining second-generation (2G) and third-generation (3G) physical layer components in a warm state; and

maintaining 2G and 3G layer 2 components in an inactive state.

17 . The apparatus of claim 16 , wherein the at least one memory and the computer program code are further configured to, with the at least one processor, cause the apparatus to perform:

powering up at least one of the 2G and 3G layer 2 components when it is determined that fallback should occur.

18 . The apparatus of claim 16 , wherein the at least one memory and the computer program code are further configured to, with the at least one processor, cause the apparatus to perform:

reselecting from the 5G radio access technology to a fourth-generation (4G) radio access technology, wherein the maintaining the 2G and 3G physical layer components in the warm state and maintaining the 2G and 3G layer 2 components in the inactive state continues after the reselecting to the 4G radio access technology.

19 . The apparatus of claim 16 , wherein the apparatus is configured to operate in at least one standalone mode or non-standalone mode in the 5G radio access technology.

20 . The apparatus of claim 16 , wherein the at least one memory and the computer program code are further configured to, with the at least one processor, cause the apparatus to perform:

maintaining fourth-generation (4G) physical layer components in a warm state; and

maintaining 4G layer 2 components in an inactive state.