Radio link setup signaling in cellular system

1. A method comprising:

receiving, in a terminal device of a cellular communication system, a message from a network node of the cellular communication system, the message comprising at least one information element indicating at least one candidate cell and at least one validity window for the at least one candidate cell, the at least one validity window defining at least one time window when link setup with the at least one candidate cell will be valid for the terminal device;

selecting, in the terminal device, one of the at least one candidate cell for the link setup; and

initiating, by the terminal device, the link setup with the selected candidate cell within a validity window associated with the selected candidate cell,

wherein the at least one candidate cell comprises a plurality of candidate cells; and the method further comprises:

comparing by the terminal device validity windows of the plurality of candidate cells and wherein said selecting is on a basis of the comparison.

2. The method of claim 1 , further comprising: performing the selection before the validity window associated with the selected candidate cell starts.

3. The method of claim 1 , further comprising: performing the selection after the validity window associated with the selected candidate cell has started.

4. The method of claim 1 , further comprising:

measuring, by the terminal device a reference signal received from each of the plurality of candidate cells; and using the measurements in the comparison.

5. The method of claim 1 , further comprising:

selecting, by the terminal device according to at least one determined criterion, a particular time instance for the triggering the link setup within the validity window associated with the selected candidate cell, wherein the at least one criterion is based on measurements made by the terminal device or a state of the terminal device.

6. An apparatus, comprising:

at least one processor, and

at least one non-transitory memory including a computer program code, wherein the at least one non-transitory memory and the computer program code are configured, with the at least one processor, to cause the apparatus to:

select for a terminal device of a cellular communication system, at least one candidate cell for link setup;

determine at least one validity window for the at least one candidate cell, the at least one validity window defining at least one time window when the link setup with the at least one candidate cell will be valid for the terminal device; and

cause transmission of a message to the terminal device, the message comprising at least one information element indicating the at least one candidate cell and a corresponding validity window for the terminal device to select for link setup based on a comparison of the at least one validity window.

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

determine the at least one validity window on the basis of the mobility of the terminal device.

8. The apparatus of claim 7 , wherein the mobility comprises at least one of direction of movement, location and velocity.

9. The apparatus of claim 6 , wherein at least one of the apparatus and the at least one candidate cell is mobile, and wherein the at least one non-transitory memory and the computer program code are configured, with the at least one processor, to cause the apparatus to:

determine the at least one validity window for the at least one candidate cell on the basis of the mobility of the at least one of the apparatus and the at least one candidate cell.

10. The apparatus of claim 6 , wherein the at least one non-transitory memory and the computer program code are configured, with the at least one processor, to cause the apparatus to:

transfer, before transmitting the message to the terminal device, at least one current connection parameter of the terminal device to the at least one candidate cell to prepare the at least one candidate cell for the link setup.

11. The apparatus of claim 6 , wherein the at least one non-transitory memory and the computer program code are configured, with the at least one processor, to cause the apparatus to:

receive a message comprising at least one information element indicating which one of the at least one candidate cell the terminal device selected for the link setup.

12. The apparatus of claim 6 , wherein the at least one non-transitory memory and the computer program code are configured, with the at least one processor, to cause the apparatus to:

verify, before selecting the at least one candidate cell, whether or not the at least one candidate cell is prepared for the link setup.

13. The apparatus of claim 6 , wherein the message is a handover command or a command for setting up an additional radio link for the terminal device.

14. An apparatus, comprising:

at least one processor, and

at least one non-transitory memory including a computer program code, wherein the at least one non-transitory memory and the computer program code are configured, with the at least one processor, to cause the apparatus to:

receive a message from a network node of a cellular communication system, the message comprising at least one information element indicating at least one candidate cell and at least one validity window for the at least one candidate cell, the at least one validity window defining at least one time window when link setup with the cell will be valid for the apparatus;

select one of the at least one candidate cell for the link setup; and

initiate the link setup with the selected candidate cell within a validity window associated with the selected candidate cell,

wherein the at least one candidate cell comprises a plurality of candidate cells; and the apparatus is further caused to:

compare validity windows of the plurality of candidate cells and wherein said selecting is on a basis of the comparison.

15. The apparatus of claim 14 , wherein the at least one non-transitory memory and the computer program code are configured, with the at least one processor, to cause the apparatus to:

perform the selection before the validity window associated with the selected candidate cell starts.

16. The apparatus of claim 14 , wherein the at least one non-transitory memory and the computer program code are configured, with the at least one processor, to cause the apparatus to:

perform the selection after the validity window associated with the selected candidate cell has started.

17. The apparatus of claim 14 , wherein the at least one non-transitory memory and the computer program code are configured, with the at least one processor, to cause the apparatus to:

measure a reference signal received from each of the plurality of candidate cells and to use the measurements in the comparison.

18. The apparatus of claim 14 , wherein the at least one non-transitory memory and the computer program code are configured, with the at least one processor, to cause the apparatus to:

select, according to at least one determined criterion, a particular time instance for the triggering the link setup within the validity window associated with the selected candidate cell, wherein the at least one criterion is based on measurements or a state of the apparatus.