Transport block size indication for retransmissions in wireless communications

1. A method for wireless communication, comprising:

receiving, at a user equipment (UE), first downlink control information (DCI) for a downlink retransmission from a base station;

determining, based at least in part on information in the first DCI, that a prior DCI associated with the downlink retransmission from the base station to the UE was lost; and

transmitting, responsive to the determining, a negative acknowledgment to the base station and an indication that the prior DCI was lost.

2. The method of claim 1 , wherein the transmitting comprises transmitting the negative acknowledgment and the indication that the prior DCI was lost in uplink control information (UCI) transmitted to the base station.

3. The method of claim 2 , wherein the UCI is transmitted to the base station via a physical uplink control channel (PUCCH) transmission.

4. The method of claim 1 , wherein the determining comprises determining that a transport block size (TBS) of the downlink retransmission is unable to be derived from the first DCI.

5. The method of claim 1 , wherein the determining is based at least in part on one or more of a new data indicator (NDI), an acknowledgment feedback process number, and a modulation and coding scheme (MCS) for the downlink retransmission in the first DCI.

6. The method of claim 1 , further comprising:

retransmitting the negative acknowledgment and the indication that the prior DCI was lost to the base station, wherein the indication that the prior DCI was lost is based at least in part on the first DCI comprising a first new data indicator that is toggled.

7. The method of claim 1 , further comprising:

buffering, at the UE, the downlink retransmission;

receiving, at the UE, a second DCI for a second downlink retransmission, the second DCI containing information for decoding the downlink retransmission and the second downlink retransmission;

combining, at the UE, the downlink retransmission and the second downlink retransmission; and

decoding, at the UE, the combined downlink retransmissions.

8. The method of claim 1 , further comprising:

discarding the downlink retransmission from a buffer at the UE, based at least in part on determining that the prior DCI associated with the downlink retransmission from the base station to the UE was lost.

9. The method of claim 1 , further comprising:

buffering the downlink retransmission;

receiving a second DCI that contains information for decoding the downlink retransmission; and

decoding the downlink retransmission based at least in part on the second DCI.

10. The method of claim 9 , further comprising:

receiving a third DCI associated with a second downlink retransmission;

buffering the second downlink retransmission;

combining the downlink retransmission and the second downlink retransmission; and

decoding the combined downlink retransmissions based at least in part on information from the second DCI.

11. A method for wireless communication, comprising:

transmitting, to a user equipment (UE), first downlink control information (DCI) and a first downlink transmission, the first DCI including information for decoding of the first downlink transmission at the UE;

transmitting, to the UE, a second DCI and a first downlink retransmission of the first downlink transmission, wherein the second DCI includes a subset of the information for decoding the first downlink retransmission at the UE; and

receiving, from the UE, a negative acknowledgment of the first downlink retransmission and an indication that the first DCI was lost.

12. The method of claim 11 , wherein the negative acknowledgment and the indication that the first DCI was lost is received in uplink control information (UCI).

13. The method of claim 12 , wherein the UCI is received at via a physical uplink control channel (PUCCH) transmission.

14. The method of claim 11 , further comprising:

transmitting, based at least in part on the receiving, a third DCI and a second downlink retransmission to the UE, the third DCI including information for decoding the first downlink retransmission and the second downlink retransmission at the UE.

15. The method of claim 11 , further comprising:

discontinuing further retransmissions of the first downlink transmission, based at least in part on receiving, from the UE, the negative acknowledgment of the first downlink retransmission and the indication that the first DCI was lost.

16. The method of claim 15 , further comprising:

transmitting, to the UE, a third DCI and a second downlink transmission, the third DCI including information for decoding of the second downlink transmission, and wherein the second downlink transmission contains information from the first downlink transmission and the third DCI and the second downlink transmission are independent of the first DCI and the first downlink transmission.

17. The method of claim 11 , further comprising:

transmitting, based at least in part on the receiving, a third DCI including information for decoding the first downlink retransmission at the UE.

18. The method of claim 17 , further comprising:

transmitting, to the UE, a fourth DCI and a second downlink retransmission.

19. The method of claim 18 , wherein the fourth DCI includes information that is insufficient for decoding the first downlink retransmission and the second downlink retransmission at the UE.

20. An apparatus for wireless communication, comprising:

a processor;

memory in electronic communication with the processor; and

instructions stored in the memory and executable by the processor to cause the apparatus to:

receive, at a user equipment (UE), first downlink control information (DCI) for a downlink retransmission from a base station;

determine, based at least in part on information in the first DCI, that a prior DCI associated with the downlink retransmission from the base station to the UE was lost; and

transmit, responsive to the determining, a negative acknowledgment to the base station and an indication that the prior DCI was lost.

21. The apparatus of claim 20 , wherein the instructions to transmit are further executable by the processor to cause the apparatus to:

transmit the negative acknowledgment and the indication that the prior DCI was lost in uplink control information (UCI) transmitted to the base station.

22. The apparatus of claim 21 , wherein the UCI is transmitted to the base station via a physical uplink control channel (PUCCH) transmission.

23. The apparatus of claim 20 , wherein the instructions are further executable by the processor to cause the apparatus to determine that a transport block size (TBS) of the downlink retransmission is unable to be derived from the first DCI.

24. The apparatus of claim 20 , wherein the instructions are further executable by the processor to cause the apparatus to:

buffer, at the UE, the downlink retransmission;

receive, at the UE, a second DCI for a second downlink retransmission, the second DCI containing information for decoding the downlink retransmission and the second downlink retransmission;

combine, at the UE, the downlink retransmission and the second downlink retransmission; and

decode, at the UE, the combined downlink retransmissions.

25. The apparatus of claim 20 , wherein the instructions are further executable by the processor to cause the apparatus to:

discard the downlink retransmission from a buffer at the UE, based at least in part on determining that the prior DCI associated with the downlink retransmission from the base station to the UE was lost.

26. An apparatus for wireless communication, comprising:

a processor;

memory in electronic communication with the processor; and

instructions stored in the memory and executable by the processor to cause the apparatus to:

transmit, to a user equipment (UE), first downlink control information (DCI) and a first downlink transmission, the first DCI including information for decoding of the first downlink transmission at the UE;

transmit, to the UE, a second DCI and a first downlink retransmission of the first downlink transmission, wherein the second DCI includes a subset of the information for decoding the first downlink retransmission at the UE; and

receive, from the UE, a negative acknowledgment of the first downlink retransmission and an indication that the first DCI was lost.

27. The apparatus of claim 26 , wherein the negative acknowledgment and the indication that the first DCI was lost is received in uplink control information (UCI).

28. The apparatus of claim 27 , wherein the UCI is received via a physical uplink control channel (PUCCH) transmission.

29. The apparatus of claim 26 , wherein the instructions are further executable by the processor to cause the apparatus to:

transmit, based at least in part on the receiving, a third DCI and a second downlink retransmission to the UE, the third DCI including information for decoding the first downlink retransmission and the second downlink retransmission at the UE.

30. The apparatus of claim 26 , wherein the instructions are further executable by the processor to cause the apparatus to:

discontinue further retransmissions of the first downlink transmission, based at least in part on receiving, from the UE, the negative acknowledgment of the first downlink retransmission and the indication that the first DCI was lost.