How UE know which MCS will be used for retransmission?

Hi Experts,
MCS 29, 30, 31 are used for retransmission.
How UE know which MCS will be used?

I believe retransmission are all QPSK for reserved MCS.

No, retrans can used other modulation.

Because DL retransmissions are always adaptive. So the DCI will come always.

In DCI it says MCS = 29, 30, 31?

Yes, this is the main part of the DCI.

28, 29 and 30 are used for retransmissions only.
27 is the max MCS you will see I believe.

I think 28 is max, 29 / 30 / 31 are retrans.

This is for 256qam table.

64qam table.

In DCI, eNB send MCS as 29 / 30 / 31, right?

MCS table, left one without 256QAM and right one table having with 256QAM carry 8 bits and retranmission at 28 (QPSK), 29 (16QAM), 30 (64QAM), 31 (256QAM)

It only tell modulation type, how is exact MCS of retrans TB?

It directly specific the MCS index. Which is of 5 bits.
Why don’t you some DCI format? See format 2 in share tech note.