Can gNB do HARQ Retransmission(NDI = 0) and Normal Transmission(NDI = 1) at the same TTI?

[Suranjan Daw]

Hi,

I have a doubt with regards to HARQ Retransmission.

Can gNB do HARQ Retransmission(NDI = 0) and Normal Transmission(NDI = 1) at the same TTI in 5G NR?

If yes, then is it possible for the gNB to transmit 2 TBs (1 ReTx and 1 Normal Tx) for 1 UE ?

Also is it possible for gNB to transmit HARQ ReTx for 1 UE and Normal Tx for other UEs?

It would be great if you could help me with some 3GPP docs for the same.

Thanks.

[Biljana B.]

Hi Suranjan,

thank you for your question. 

Indeed, this is not very clearly documented in 5G-LENA documentation. If the user is being scheduled for the HARQ retransmission it will be removed from the list of the active users for that slot, so no new data will be transmitted, and no new DCI, nor new transport block. 

In the old implementation of DP-MIMO, you could find in the traces for the same UE and slot 2TBs, because in the old DP-MIMO implementation, we had two streams being transmitted using two independent transport blocks, so the situation that you explain in that case was possible. But since 5G-LENA 3.0, that is not possible anymore, because according to the new SU-MIMO, all the streams are multiplexed into the same transport block.

Regarding the 3GPP doc, if you find that this is not the correct way, please let us know.

Kind regards,

Biljana