Methods and apparatuses for group transmissions

1. A method performed by a first user equipment, (UE), for group transmission, the group comprising multiple UEs transmitting a same Hybrid Automatic Repeat request, (HARQ) buffer data packets to a network node in a synchronous manner, the method comprising:

receiving a predetermined number of negative acknowledgments (NACKs) from the network node in response to transmitting the HARQ buffer data packets;

performing a checksum calculation on a HARQ buffer associated with the HARQ buffer data packets;

receiving a computed checksum from a second UE that relays control data from the network node to the multiple UEs in the group, the computed checksum being associated with the HARQ buffer data packets;

comparing, by the first UE the calculated checksum with the received computed checksum; and

refraining, by the first UE from further transmission of the HARQ buffer data packets to the network node when the calculated checksum and the received computed checksum differ.

2. The method according to claim 1 , further comprising informing the second UE at least one of that:

the first UE has its HARQ buffer out-of-synch; and the first UE stops transmitting HARQ buffer data to the network node.

3. The method according to claim 2 , wherein receiving the computed checksum and informing the second UE is performed using one of a Device-2-Device, D2D, and a sidelink communication protocol.

4. The method according to claim 3 , further comprising synchronizing the HARQ buffer of the first UE with the HARQ buffer of the second UE, by receiving the HARQ buffer data content from the second UE and by receiving from the second UE information on a time instance when new transmissions start again at the first UE.

5. The method according to claim 2 , further comprising synchronizing the HARQ buffer of the first UE with the HARQ buffer of the second UE, acting as the coordinator, by receiving the HARQ buffer data content from the second UE and by receiving from the second UE information on a time instance when new transmissions start again at the first UE.

6. The method according to claim 1 , comprising increasing a NACK counter for each received NACK; and

when the NACK counter expired, performing the checksum calculation.

7. A method performed by a second user equipment, (UE) that relays control data from a network node to a group, the group comprising multiple UEs transmitting same Hybrid Automatic Repeat request, (HARQ) buffer data packets to a network node in a synchronous manner, the method comprising:

receiving a predetermined number of negative acknowledgements (NACKs) from the network node in response to transmitting the HARQ buffer data packets;

performing a checksum computation on a HARQ buffer associated with the HARQ buffer data packets;

transmitting the computed checksum to the multiple UEs in the group; and

receiving a notification from at least one of the multiple UEs in the group when the computed checksum differs from a calculated checksum associated with the HARQ buffer data packets that is performed by at least one of the multiple UEs in the group, wherein at least one of the multiple UEs in the group discovers it is out-of-synch based on receiving and/or not receiving the computed checksum, the notification notifying that the at least one of the multiple UEs in the group refrains from further transmission of the HARQ buffer data to the network node based on discovering it is out-of-synch.

8. The method according to claim 7 , further comprising determining whether an out-of-sync rate is above a threshold, and when the out-of-sync rate is above the threshold:

synchronizing the HARQ buffer with the HARQ buffer of the at least one of the multiple UEs in the group, by transmitting a HARQ buffer data content to the at least one other UE in the group; and

informing the at least one of the multiple UEs in the group on of a time instance when the at least another group starts a new transmission.

9. The method according to claim 8 , wherein the out-of-sync rate being above the threshold is determined when the number of unsynchronized UEs in the group per predefined time is above the threshold.

10. The method according to claim 8 , further comprising notifying the network node of the time instance when the at least one of the multiple UEs in the group starts a new transmission.

11. A first user equipment, (UE) for group transmission, the group comprising multiple UEs transmitting a same Hybrid Automatic Repeat request, (HARQ) buffer data packets to a network node in a synchronous manner the first UE comprising a processor and a memory, the memory containing instructions executable by the processor to configure the first UE to:

receive a predetermined number of negative acknowledgments (NACK) from the network node in response to transmitting the HARQ buffer data packets;

perform a checksum calculation on a HARQ buffer associated with the HARQ buffer data packets;

receive a computed checksum from a second that relays control data from the network node to the multiple UEs in the group, the computed checksum being associated with the HARQ buffer data packets;

compare, by the first UE the calculated checksum with the received computed checksum; and

refrain, by the first UE from further transmission of the HARQ buffer data packets to the network node when the calculated checksum and the received computed checksum differ.

12. The first UE according to claim 11 , further configured to inform the second UE at least one of that:

the first UE has its HARQ buffer out-of-synch; and

the first UE stops transmitting HARQ buffer data to the network node.

13. The first UE according to claim 12 , further configured to receive the computed checksum and inform the second UE using one of a Device-2-Device, (D2D) and a sidelink communication protocol.

14. The first UE according to claim 12 , further configured to synchronize the HARQ buffer of the first UE with the HARQ buffer of the second UE by receiving the HARQ buffer data content from the second UE and by receiving information from the second UE on a time instance when new transmissions start again at the first UE.

15. The first UE according to claim 11 , further configured to:

increase a NACK counter for each received NACKU; and

when the NACK counter expired, perform the checksum calculation.

16. A second user equipment UE for group transmission, the second UE configured to relay control data form a network node to a group, the group comprising multiple UEs transmitting a same Hybrid Automatic Repeat request, (HARQ) buffer data packets to a network node in a synchronous manner, the second UE comprising a processor and a memory, the memory containing instructions executable by the processor to configure the second UE to:

receive a predetermined number of negative acknowledgements (NACK) from the network node in response to transmitting the HARQ buffer data packets;

perform a checksum computation on a HARQ buffer associated with the HARQ buffer data packets;

transmit the computed checksum to multiple UEs in the group; and

receive a notification from at least one of the multiple UEs in the group when the computed checksum differs from a calculated checksum associated with the HARQ buffer data packets that is performed by at least one of the multiple UEs in the group, wherein at least one of the multiple UEs in the group discovers it is out-of-synch based on receiving and/or not receiving the computed checksum, the notification notifying that the at least one of the multiple UEs in the group refrains from further transmission of the HARQ buffer data to the network node based on discovering it is out-of-synch.

17. The second UE according to claim 16 , further configured to determine whether an out-of-sync rate is above a threshold, and when the out-of-sync rate is above the threshold:

synchronize the HARQ buffer with the HARQ buffer of the at least one of the multiple UEs of the group, by transmitting a HARQ buffer data content to the at least one other UE in the group; and

notify the at least one of the multiple UEs in the group on a time instance when the at least one of the multiple UEs in the group starts a new transmission.

18. The second UE according to claim 17 , wherein the out-of-sync rate being above the threshold is determined when a number of unsynchronized UEs in the group per predefined time is above the threshold.

19. The second UE according to claim 17 , further configured to notify the network node of the time instance when the at least one of the multiple UEs in the group starts a new transmission.