Techniques and apparatuses for acknowledgement (ACK) / negative acknowledgement (NACK) signaling using a reference signal

1. A method of wireless communication, comprising:

determining, by a user equipment (UE), whether acknowledgement or negative acknowledgement (ACK/NACK) signaling is to be included in an uplink transmission in a portion of uplink resources allocated for a data channel;

generating, by the UE, a reference signal that indicates whether the ACK/NACK signaling is present in the uplink transmission, wherein a single symbol of the reference signal indicates whether the ACK/NACK signaling is present in the uplink transmission, and wherein a cyclic shift, of a plurality of cyclic shifts, applied to the single symbol indicates whether the ACK/NACK signaling is present or not present in the uplink transmission; and

transmitting, by the UE, the reference signal that indicates whether the ACK/NACK signaling is present in the uplink transmission.

2. The method of claim 1 , wherein the reference signal is modulated to indicate whether the ACK/NACK signaling is present in the uplink transmission.

3. The method of claim 1 , wherein the reference signal is a demodulation reference signal.

4. The method of claim 1 , wherein the reference signal indicates whether uplink data is rate matched around the ACK/NACK signaling in the uplink transmission.

5. The method of claim 1 , wherein the reference signal indicates whether uplink data is punctured by the ACK/NACK signaling in the uplink transmission.

6. The method of claim 1 , wherein a payload size of the ACK/NACK signaling is indicated using one or more dedicated resource elements.

7. The method of claim 1 , wherein the portion of uplink resources allocated for the data channel is a physical uplink shared channel.

8. The method of claim 1 , wherein the cyclic shift is associated with a value that is equal to a length of a sequence of the single symbol divided by two.

9. The method of claim 8 , wherein the value being equal to the length of the sequence divided by two indicates that the ACK/NACK signaling is not present in the uplink transmission.

10. The method of claim 1 , wherein the cyclic shift is associated with a value that is equal to zero when the ACK/NACK signaling is present in the uplink transmission.

11. A user equipment (UE) for wireless communication, comprising:

memory; and

one or more processors operatively coupled to the memory, the memory and the one or more processors configured to:

determine whether acknowledgement or negative acknowledgement (ACK/NACK) signaling is to be included in an uplink transmission in a portion of uplink resources allocated for a data channel;

generate a reference signal that indicates whether the ACK/NACK signaling is present in the uplink transmission, wherein a single symbol of the reference signal indicates whether the ACK/NACK signaling is present in the uplink transmission, and wherein a cyclic shift, of a plurality of cyclic shifts, applied to the single symbol indicates whether the ACK/NACK signaling is present or not present in the uplink transmission; and

transmit the reference signal that indicates whether the ACK/NACK signaling is present in the uplink transmission.

12. The UE of claim 11 , wherein the reference signal is modulated to indicate whether the ACK/NACK signaling is present in the uplink transmission.

13. The UE of claim 11 , wherein the reference signal is a demodulation reference signal.

14. The UE of claim 11 , wherein the reference signal indicates whether uplink data is rate matched around the ACK/NACK signaling in the uplink transmission.

15. The UE of claim 11 , wherein the reference signal indicates whether uplink data is punctured by the ACK/NACK signaling in the uplink transmission.

16. The UE of claim 11 , wherein a payload size of the ACK/NACK signaling is indicated using one or more dedicated resource elements.

17. The UE of claim 11 , wherein the portion of uplink resources allocated for the data channel is a physical uplink shared channel.

18. The UE of claim 11 , wherein the cyclic shift is associated with a value that is equal to a length of a sequence of the single symbol divided by two when the ACK/NACK signaling is present in the uplink transmission.

19. A method of wireless communication, comprising:

receiving, by a base station, a reference signal that indicates whether acknowledgement or negative acknowledgement (ACK/NACK) signaling is present in an uplink transmission in a portion of uplink resources allocated for a data channel, wherein a single symbol of the reference signal indicates whether the ACK/NACK signaling is present in the uplink transmission, and wherein a cyclic shift, of a plurality of cyclic shifts, applied to the single symbol indicates whether the ACK/NACK signaling is present or not present in the uplink transmission;

determining, by the base station, whether the ACK/NACK signaling was received in the uplink transmission based at least in part on the reference signal; and

decoding, by the base station, the ACK/NACK signaling when the ACK/NACK signaling is received.

20. The method of claim 19 , wherein uplink data in the uplink transmission is decoded based at least in part on whether the ACK/NACK signaling was received.

21. The method of claim 20 , wherein, when the ACK/NACK signaling is received, the uplink data is decoded from a set of resource elements other than resource elements in which the ACK/NACK signaling is received.

22. The method of claim 20 , wherein a set of resource elements are decoded as the ACK/NACK signaling or uplink data based at least in part on the indication in the reference signal.

23. The method of claim 19 , wherein the reference signal is a demodulation reference signal.

24. The method of claim 19 , wherein the single symbol is a DMRS sequence.

25. The method of claim 19 , wherein the cyclic shift is associated with a value that is equal to a length of a sequence of the single symbol divided by two.

26. A base station for wireless communication, comprising:

memory; and

one or more processors operatively coupled to the memory, the memory and the one or more processors configured to:

receive a reference signal that indicates whether acknowledgement or negative acknowledgement (ACK/NACK) signaling is present in an uplink transmission in a portion of uplink resources allocated for a data channel, wherein a single symbol of the reference signal indicates whether the ACK/NACK signaling is present in the uplink transmission, and wherein a cyclic shift, of a plurality of cyclic shifts, applied to the single symbol indicates whether the ACK/NACK signaling is present or not present in the uplink transmission;

determine whether the ACK/NACK signaling was received in the uplink transmission based at least in part on the reference signal; and

decode the ACK/NACK signaling when the ACK/NACK signaling is received.

27. The base station of claim 26 , wherein uplink data in the uplink transmission is decoded based at least in part on whether the ACK/NACK signaling was received.

28. The base station of claim 26 , wherein the reference signal is a demodulation reference signal.

29. The base station of claim 26 , wherein the single symbol is a DMRS sequence.

30. The base station of claim 26 , w wherein the cyclic shift is associated with a value that is equal to a length of a sequence of the single symbol divided by two.