Uplink control channel for low latency communications
Methods, systems, and devices for wireless communication are described. A wireless device such as a user equipment (UE) or a base station may identify a set of resource element groups (REGs) for low latency communication, and each REG may include a portion of a different resource block (RB) of a set of RBs (e.g., a set of non-contiguous RBs). The device may then map an uplink control channel to the selected REGs and communicate on the uplink control channel accordingly. Reference signals may also be transmitted in the same RBs, and the REGs may be mapped around the resources used for reference signals. In some cases, multiple UEs may transmit uplink control data using the same resources using code division multiplexing (CDM) (e.g., if the control payload is relatively small). In other cases, multiple UEs may be frequency division multiplexed (FDM).
1. A method of wireless communication comprising:
identifying a set of uplink resource element groups (REGs), wherein each uplink REG of the set of uplink REGs comprises a set of uplink resource elements (REs) that span, in a frequency domain, a portion of a respective resource block (RB) of a set of RBs;
mapping an uplink control channel for a wireless communication link to the set of uplink REGs; and
communicating on the uplink control channel using the set of uplink REGs.
2. The method of claim 1 , wherein the set of RBs comprises a plurality of RBs during a transmission time interval (TTI) that are non-contiguous in the frequency domain during the TTI.
3. The method of claim 1 , further comprising:
identifying an offset associated with a user equipment (UE); and
transmitting an uplink reference signal using the offset in each RB of the set of RBs.
4. The method of claim 3 , wherein the uplink reference signal is transmitted during one or more symbol periods that comprise the uplink control channel.
5. The method of claim 3 , wherein the uplink reference signal is transmitted during one or more symbol periods indicated by a base station.
6. The method of claim 3 , wherein the uplink reference signal is associated with the uplink control channel or an uplink shared channel, or both.
7. The method of claim 1 , wherein the set of uplink REGs is semi-statically configured according to an indication communicated using radio resource control (RRC) signaling.
8. The method of claim 1 , wherein the set of uplink REGs is dynamically configured using an indication communicated in a downlink message.
9. The method of claim 1 , wherein a waveform of the uplink control channel comprises an orthogonal frequency division multiplexing (OFDM) waveform.
10. The method of claim 1 , further comprising:
identifying a code division multiplexing (CDM) cover code, wherein communicating over the wireless communication link is based at least in part on the CDM cover code.
11. The method of claim 10 , wherein the CDM cover code comprises resource elements of two or more different subcarriers in the frequency domain, or resource elements of two or more different symbol periods in a time domain, or a combination thereof.
12. The method of claim 10 , further comprising:
determining a payload size of the uplink control channel, wherein identifying the CDM cover code is based at least in part on the payload size.
13. The method of claim 1 , wherein the set of uplink REs in each of the uplink REGs includes REs that comprise data interleaved with REs that comprise a reference signal, wherein the interleaving comprises alternating, in the frequency domain, one of the REs that comprise data with one of the REs that comprise the reference signal during a symbol period of an RB of the set of RBs.
14. The method of claim 1 , wherein the set of uplink REs in each of the uplink REGs includes REs that comprise data interleaved with REs that comprise a reference signal, wherein the interleaving comprises alternating, in the frequency domain, two of the REs that comprise data with one of the REs that comprise the reference signal during a symbol period of an RB of the set of RBs.
15. The method of claim 1 , further comprising:
identifying a quantity of uplink REGs in the set of uplink REGs based at least in part on a content of the uplink control channel.
16. The method of claim 1 , wherein the communicating comprises:
transmitting a reference signal and first data in a first uplink REG of the set of uplink REGs during a first symbol period; and
transmitting second data in each RE of a second uplink REG of the set of uplink REGs during a second symbol period that follows the first symbol period.
17. The method of claim 1 , further comprising:
identifying a transmit antenna or a transmit port for each uplink REG of the set of uplink REGs.
18. The method of claim 1 , wherein the communicating comprises:
transmitting a sounding reference signal (SRS) during a last symbol period of a transmission time interval that comprises the uplink control channel.
19. The method of claim 1 , further comprising:
identifying a first REG structure associated with a first user equipment (UE) and a second REG structure associated with a second UE; and
receiving a first uplink reference signal from the first UE using the first REG structure in an RB of the set of RBs.
20. The method of claim 19 , further comprising:
receiving a second uplink reference signal from the second UE using the second REG structure in another RB of a set of RBs.
21. The method of claim 20 , wherein the first REG structure and the second REG structure differ at least in one of a frequency offset, a number of REs for reference signals, or a code division multiplexing (CDM) cover code, or a combination thereof.
22. The method of claim 19 , further comprising:
receiving data or control information in each RE of an uplink REG associated with the first UE in another RB during a second symbol period, the set of uplink REGs comprising the uplink REG associated with the first UE.
23. An apparatus for wireless communication, comprising:
a processor;
memory in electronic communication with the processor; and
instructions stored in the memory and operable, when executed by the processor, to cause the apparatus to:
identify a set of uplink resource element groups (REGs), wherein each uplink REG of the set of uplink REGs comprises a set of uplink resource elements (REs) that span, in a frequency domain, a portion of a respective resource block (RB) of a set of RBs;
map an uplink control channel for a wireless communication link to the set of uplink REGs; and
communicate on the uplink control channel using the set of uplink REGs.
24. The apparatus of claim 23 , further comprising instructions operable to cause the apparatus to:
identify an offset associated with a user equipment (UE); and
transmit an uplink reference signal using the offset in each RB of the set of RBs.
25. The apparatus of claim 23 , wherein the set of uplink REGs is semi-statically configured according to an indication communicated using radio resource control (RRC) signaling.
26. The apparatus of claim 23 , wherein the set of uplink REGs is dynamically configured using an indication communicated in a downlink message.
27. The apparatus of claim 23 , wherein a waveform of the uplink control channel comprises an orthogonal frequency division multiplexing (OFDM) waveform.
28. The apparatus of claim 23 , further comprising instructions operable to cause the apparatus to:
identify a code division multiplexing (CDM) cover code, wherein communicating over the wireless communication link is based at least in part on the CDM cover code.
29. An apparatus for wireless communication comprising:
means for identifying a set of uplink resource element groups (REGs), wherein each uplink REG of the set of uplink REGs comprises a set of uplink resource elements (REs) that span, in a frequency domain, a portion of a respective resource block (RB) of a set of RBs;
means for mapping an uplink control channel for a wireless communication link to the set of uplink REGs; and
means for communicating on the uplink control channel using the set of uplink REGs.
30. A non-transitory computer-readable medium storing code for wireless communication, the code comprising instructions executable to:
identify a set of uplink resource element groups (REGs), wherein each uplink REG of the set of uplink REGs comprises a set of uplink resource elements (REs) that span, in a frequency domain, a portion of a respective resource block (RB) of a set of RBs;
map an uplink control channel for a wireless communication link to the set of uplink REGs; and
communicate on the uplink control channel using the set of uplink REGs.