Feedback based adaptation of multicast transmission offset

1. A method for managing multicast transmissions in a cellular network, the method comprising:

a node of the cellular network sending data units to a group of base stations, each data unit configured for conveying multicast data to be sent by the base stations in a synchronized manner at a starting time indicated in the data unit;

the node determining, for each of the data units, the starting time as the sum of the time of sending the data unit from the node and an offset value;

the node obtaining feedback information from the base stations of the group, the feedback information indicating a deviation of the starting time indicated in one of the data units from an earliest possible time of sending the multicast data from the data unit by the base stations of the group; and

depending on the feedback information, the node adapting the offset value.

2. The method of claim 1 , wherein the feedback information comprises, for at least one of the base stations, a value representing the time difference between the earliest possible time of sending the multicast data from the one of the data units by the base station and the starting time indicated in the one of the data units.

3. The method of claim 2 , further comprising:

the node obtaining the value for each of a plurality of the base stations;

the node determining a maximum value from the plurality; and

the node adapting the offset value depending on the maximum value.

4. The method of claim 3 , further comprising:

the node determining a minimum value from the plurality; and

the node monitoring a deviation of the minimum value from the maximum value.

5. The method of claim 1 , wherein the feedback information comprises, for at least one subgroup of the base stations, a value representing a maximum value of, for each base station of the subgroup, the time difference between the earliest possible time of sending the multicast data from the one of the data units by the base station and the starting time indicated in the one of the data units.

6. The method of claim 5 , further comprising:

the node obtaining the value for each of a plurality of the subgroups;

the node determining a maximum value from the plurality; and

the node adapting the offset value depending on the maximum value.

7. The method of claim 6 :

wherein the feedback information comprises, for each of the subgroups, a further value representing a minimum value of, for each base station of the subgroup, the time difference between the earliest possible time of sending the multicast data from the one of the data units by the base station and the starting time indicated in the one of the data units;

further comprising the node:

determining a minimum value from the further values; and

monitoring a deviation of the minimum value from the maximum value.

8. The method of claim 1 , further comprising the node initiating the obtaining of the feedback information in response to addition of a further base station to the group.

9. The method of claim 1 , further comprising the node initiating the obtaining of the feedback information in response to removal of a base station from the group.

10. The method of claim 1 , further comprising the node initiating the obtaining of the feedback information by sending a request toward the base stations of the group.

11. The method claim 1 , further comprising the node indicating, to the base stations of the group, that the one of the data units is utilized for probing.

12. A node for a cellular network, the node comprising:

an interface for communication with a group of base stations; and

at least one processor;

memory containing instructions executable by the at least one processor whereby the node is configured to:

send data units to the group of base stations, each data unit being configured for conveying multicast data to be sent by the base stations in a synchronized manner at a starting time indicated in the data unit;

determine, for each of the data units, the starting time as the sum of the time of sending the data unit from the node and an offset value;

obtain feedback information from the base stations of the group, the feedback information indicating a deviation of the starting time indicated in one of the data units from an earliest possible time of sending the multicast data from the data unit by the base stations of the group; and

depending on the feedback information, adapt the offset value.

13. The node of claim 12 , wherein the feedback information comprises, for at least one of the base stations, a value representing the time difference between the earliest possible time of sending the multicast data from the one of the data units by the base station and the starting time indicated in the one of the data units.

14. The node of claim 13 , wherein the instructions are such that the node is configured to:

obtain the value for each of a plurality of the base stations;

determine a maximum value from the plurality; and

adapt the offset value depending on the maximum value.

15. The node of claim 14 , wherein the instructions are such that the node is configured to:

determine a minimum value from the plurality; and

monitor a deviation of the minimum value from the maximum value.

16. The node of claim 12 , wherein the feedback information comprises, for at least one subgroup of the base stations, a value representing a maximum value of, for each base station of the subgroup, the time difference between the earliest possible time of sending the multicast data from the one of the data units by the base station and the starting time indicated in the one of the data units.

17. The node of claim 16 , wherein the instructions are such that the node is configured to:

obtain the value for each of a plurality of the subgroups;

determine a maximum value from the plurality; and

adapt the offset value depending on the maximum value.

18. The node of claim 16 :

wherein the feedback information comprises, for each of the subgroups, a further value representing a minimum value of, for each base station of the subgroup, the time difference between the earliest possible time of sending the multicast data from the one of the data units by the base station and the starting time indicated in the one of the data units;

wherein the instructions are such that the node is configured to:

determine a minimum value from the further values; and

monitor a deviation of the minimum value from the maximum value.

19. The node of claim 12 , wherein the instructions are such that the node is configured to initiate the obtaining of the feedback information in response to addition of a further base station to the group.

20. The node of claim 12 , wherein the instructions are such that the node is configured to initiate the obtaining of the feedback information in response to removal of a base station from the group.

21. The node of claim 12 , wherein the instructions are such that the node is configured to initiate the obtaining of the feedback information by sending a request toward the base stations of the group.

22. The node of claim 12 , wherein the instructions are such that the node is configured to indicate to the base stations of the group that the one of the data units is utilized for probing.

23. A computer program product stored in a non-transitory computer readable medium for managing multicast transmissions in a cellular network, the computer program product comprising software instructions which, when run on one or more processors of a node of the cellular network, causes the node to:

send data units to a group of base stations, each data unit configured for conveying multicast data to be sent by the base stations in a synchronized manner at a starting time indicated in the data unit;

determine, for each of the data units, the starting time as the sum of the time of sending the data unit from the node and an offset value;

obtain feedback information from the base stations of the group, the feedback information indicating a deviation of the starting time indicated in one of the data units from an earliest possible time of sending the multicast data from the data unit by the base stations of the group; and

depending on the feedback information, adapt the offset value.