Operation in case of radio link failure

1. A method, comprising:

creating a backup user context for a terminal device served currently by a relay base station, wherein the relay base station is a mobile relay base station, relaying a radio connection between the terminal device and fixed cellular network infrastructure comprising a fixed base station communicating with the relay base station, wherein the backup user context is prepared for use in case of an unexpected radio link failure, wherein an unexpected radio link failure is where a drop of the radio link is so sudden that the cellular network cannot prepare for the drop;

applying the backup user context upon detection of a radio link failure in a primary user context being used in the communication and before the terminal device enters an idle state as a result of the radio link failure; and

updating the backup user context when the mobile relay base station is handed over to another fixed base station of the fixed cellular network infrastructure.

2. The method of claim 1 , wherein the terminal device applies the backup user context without reception of a command to apply the backup user context from the relay base station.

3. The method of claim 1 , wherein the backup user context for the terminal device is created regardless of the channel state between the fixed base station and in the terminal device.

4. The method of claim 1 , further comprising:

configuring the terminal device to store an identifier of the fixed base station in the backup user context stored in the terminal device; and

configuring the fixed base station to store an identifier of the terminal device in the backup user context stored in the fixed cellular network infrastructure.

5. The method of claim 1 , further comprising:

accessing by the terminal device the fixed base station associated with the stored backup user context before entering the idle state and upon detection of the radio link failure in the terminal device; and

negotiating recovery of the radio link between the fixed network infrastructure and the terminal device by applying the backup user context as a primary user context.

6. The method of claim 1 , further comprising:

exchanging information related to the primary user context between the relay base station and the fixed base station when applying the backup user context for use between the fixed base station and the terminal device.

7. The method of claim 1 , further comprising:

negotiating, after detection of the radio link failure, release of the primary user context of the terminal device used in communication with the relay base station before the radio link failure.

8. An apparatus comprising:

at least one processor, and

at least one memory including computer program code,

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

create of a backup user context for a terminal device served currently by a relay base station, wherein the relay base station is a mobile relay base station, relaying a radio connection between the terminal device and fixed cellular network infrastructure comprising a fixed base station communicating with the relay base station, wherein the backup user context is prepared for use in case of an unexpected radio link failure, wherein an unexpected radio link failure is where a drop of the radio link is so sudden that the cellular network cannot prepare for the drop;

apply the backup user context upon detection of a radio link failure in a primary user context being used in the communication and before the terminal device enters an idle state as a result of the radio link failure; and

update the backup user context when the relay base station is handed over to another fixed base station of the fixed cellular network infrastructure.

9. The apparatus of claim 8 , wherein the at least one memory and the computer code are further configured to, with the at least one processor, cause the apparatus to at least perform or control the terminal device to apply the backup user context without reception of a command to apply the backup user context from the relay base station.

10. The apparatus of claim 8 , wherein the at least one memory and the computer code are further configured to, with the at least one processor, cause the apparatus to at least perform or control the creation of the backup user context for the terminal device regardless of the channel state between the fixed base station and in the terminal device.

11. The apparatus of claim 8 , wherein at least one memory and the computer code are further configured to, with the at least one processor, cause the apparatus to at least perform or control accessing of the fixed base station associated with the stored backup user context before entering the idle state and upon detection of the radio link failure in the terminal device, and to negotiate the recovery of the radio link between the fixed network infrastructure and the terminal device by applying the backup user context as a primary user context.

12. The apparatus of claim 8 , wherein the at least one memory and the computer code are further configured to, with the at least one processor, cause the apparatus to at least perform or control the exchanging of information related to the primary user context between the relay base station and the fixed base station when applying the backup user context for use between the fixed base station and the terminal device.

13. The apparatus of claim 8 , wherein the at least one memory and the computer code are further configured to, with the at least one processor, cause the apparatus to at least perform or control the configuring of the terminal device to store an identifier of the fixed base station in the backup user context stored in the terminal device.

14. The apparatus of claim 8 , wherein the at least one memory and the computer code are further configured to, with the at least one processor, cause the apparatus to at least perform or control the configuring of the fixed base station to store an identifier of the terminal device in the backup user context stored in the fixed cellular network infrastructure.

15. The apparatus of claim 8 , wherein the at least one memory and the computer code are further configured to, with the at least one processor, cause the apparatus to at least perform or control the releasing of, after the detection of the radio link failure, the primary user context of the terminal device used in communication with the relay base station before the radio link failure.

16. A terminal device of a cellular telecommunication system, comprising the apparatus according to claim 8 , a memory unit configured to store parameters pertaining to the backup user context, and radio interface components providing the terminal device with radio communication capabilities.

17. A base station of a cellular telecommunication system, comprising the apparatus according to claim 12 , an interface to a memory unit storing the backup user context, and radio interface components to providing the base station with radio communication capabilities.

18. A computer program product embodied on a non-transitory computer-readable medium in which a computer program is stored comprising program instructions which, when loaded into an apparatus, execute the method according to claim 1 .

19. A method, comprising:

creating a backup user context for a terminal device served currently by a relay base station relaying a radio connection between the terminal device and fixed cellular network infrastructure comprising a fixed base station communicating with the relay base station, wherein the backup user context is prepared for use in case of an unexpected radio link failure, wherein an unexpected radio link failure is where a drop of the radio link is so sudden that the cellular network cannot prepare for the drop;

applying the backup user context upon detection of a radio link failure in a primary user context being used in the communication and before the terminal device enters an idle state as a result of the radio link failure;

configuring the terminal device to store communication parameters to be used when the backup user context is applied, wherein the stored communication parameters include carrier information of the fixed base station, an identifier of the terminal device in the backup user context, a transmission timing advance used by the relay base station in communication with the fixed base station and a scheduling request configuration; and

accessing the fixed base station by using the stored communication parameters upon detection of the radio link failure.

20. The method of claim 19 , wherein the terminal device applies the backup user context without reception of a command to apply the backup user context from the relay base station.

21. The method of claim 19 , wherein the backup user context for the terminal device is created regardless of the channel state between the fixed base station and in the terminal device.

22. A computer program product embodied on a non-transitory computer-readable medium in which a computer program is stored comprising program instructions which, when loaded into an apparatus, execute the method according to claim 19 .

23. An apparatus comprising:

at least one processor, and

at least one memory including computer program code,

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

create of a backup user context for a terminal device served currently by a relay base station relaying a radio connection between the terminal device and fixed cellular network infrastructure comprising a fixed base station communicating with the relay base station, wherein the backup user context is prepared for use in case of an unexpected radio link failure, wherein an unexpected radio link failure is where a drop of the radio link is so sudden that the cellular network cannot prepare for the drop;

apply the backup user context upon detection of a radio link failure in a primary user context being used in the communication and before the terminal device enters an idle state as a result of the radio link failure;

configure the terminal device to store communication parameters to be used when the backup user context is applied, wherein the stored communication parameters include carrier information of the fixed base station, an identifier of the terminal device in the backup user context, a scheduling request configuration and/or transmission timing advance used by the relay base station in communication with the fixed base station; and

access the fixed base station by using the stored communication parameters upon detection of the radio link failure.

24. The apparatus of claim 23 , wherein the at least one memory and the computer code are further configured to, with the at least one processor, cause the apparatus to at least perform or control the terminal device to apply the backup user context without reception of a command to apply the backup user context from the relay base station.

25. The apparatus of claim 23 , wherein the at least one memory and the computer code are further configured to, with the at least one processor, cause the apparatus to at least perform or control the creation of the backup user context for the terminal device regardless of the channel state between the fixed base station and in the terminal device.