Latency reduction in shared or unlicensed spectrum
Methods, systems, and devices for wireless communication are described. A user equipment (UE) may transmit uplink (UL) messages in unlicensed spectrum with a reduced UL timing delay. The UL timing delay may be reduced by using a shortened transmission time interval (TTI) (e.g., a TTI that is reduced in duration relative to other TTIs in the system or in a legacy system) or by reducing the number of TTIs between a grant and the corresponding UL message. The reduced UL timing delay may decrease the likelihood that the UE will wait for a subsequent transmit opportunity (TxOp) to transmit the UL message. In some cases, the reduced UL timing delay corresponds to a reduced hybrid automatic repeat request (HARM) processing delay. In some cases, a time difference (e.g., measured in TTIs) between a measurement reference TTI a corresponding channel state information (CSI) report may also be reduced.
1. A method for wireless communication at a user equipment (UE), comprising:
establishing a connection with a base station, the connection supporting a first time difference between downlink communication and responsive uplink communication and supporting a second time difference between the downlink communication and the responsive uplink communication;
receiving an indication from the base station of whether to use the first time difference or to use the second time difference, wherein the indication of whether to use the first time difference or to use the second time difference comprises an indication of an offset, from a start of a subframe, for uplink transmissions; and
transmitting an uplink transmission in response to a control message from the base station with an uplink timing that is based at least in part on receiving the indication of whether to use the first time difference or the second time difference.
2. The method of claim 1 , wherein receiving the indication of whether to use the first time difference or to use the second time difference comprises:
receiving the indication in a second control message from the base station.
3. The method of claim 1 , further comprising:
receiving, in a transmission time interval, a grant of resources to transmit the uplink transmission; and
transmitting the uplink transmission with the uplink timing that is based at least in part on a time of the transmission time interval and on the indication of the offset.
4. The method of claim 1 , wherein the indication of whether to use the first time difference or to use the second time difference is based at least in part on a duration of a transmission time interval associated with the control message.
5. A method for wireless communication at a user equipment (UE), comprising:
establishing a connection with a base station, the connection supporting a first time difference between downlink communication and responsive uplink communication and supporting a second time difference between the downlink communication and the responsive uplink communication;
receiving an indication from the base station of whether to use the first time difference or to use the second time difference, wherein the indication of whether to use the first time difference or to use the second time difference comprises an indication of a quantity of transmission time intervals between an uplink grant and a responsive uplink transmission; and
transmitting an uplink transmission in response to a control message from the base station with an uplink timing that is based at least in part on receiving the indication of whether to use the first time difference or the second time difference.
6. The method of claim 1 , wherein the indication of whether to use the first time difference or to use the second time difference comprises an indication of an UL and DL pattern from the base station.
7. The method of claim 1 , wherein receiving the indication of whether to use the first time difference or to use the second time difference comprises:
receiving the indication in a shortened physical downlink control channel (sPDCCH).
8. An apparatus for wireless communication at a user equipment (UE), 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:
establish a connection with a base station, the connection supporting a first time difference between downlink communication and responsive uplink communication and supporting a second time difference between the downlink communication and the responsive uplink communication;
receive an indication from the base station of whether to use the first time difference or to use the second time difference, wherein the indication of whether to use the first time difference or to use the second time difference comprises an indication of an offset, from a start of a subframe, for uplink transmissions; and
transmit an uplink transmission in response to a control message from the base station with an uplink timing that is based at least in part on receiving the indication of whether to use the first time difference or the second time difference.
9. The apparatus of claim 8 , wherein the instructions to receive the indication of whether to use the first time difference or to use the second time difference are executable by the processor to cause the apparatus to:
receive the indication in a second control message from the base station.
10. The apparatus of claim 8 , wherein the instructions are executable by the processor to cause the apparatus to:
receive, in a transmission time interval, a grant of resources to transmit the uplink transmission; and
transmit the uplink transmission with the uplink timing that is based at least in part on a time of the transmission time interval and on the indication of the offset.
11. The apparatus of claim 8 , wherein the indication of whether to use the first time difference or to use the second time difference is based at least in part on a duration of a transmission time interval associated with the control message.
12. An apparatus for wireless communication at a user equipment (UE), 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:
establish a connection with a base station, the connection supporting a first time difference between downlink communication and responsive uplink communication and supporting a second time difference between the downlink communication and the responsive uplink communication;
receive an indication from the base station of whether to use the first time difference or to use the second time difference, wherein the indication of whether to use the first time difference or to use the second time difference comprises an indication of a quantity of transmission time intervals between an uplink grant and a responsive uplink transmission; and
transmit an uplink transmission in response to a control message from the base station with an uplink timing that is based at least in part on receiving the indication of whether to use the first time difference or the second time difference.
13. The apparatus of claim 8 , wherein the indication of whether to use the first time difference or to use the second time difference comprises an indication of an UL and DL pattern from the base station.
14. The apparatus of claim 8 , wherein the instructions to receive the indication of whether to use the first time difference or to use the second time difference are executable by the processor to cause the apparatus to:
receive the indication in a shortened physical downlink control channel (sPDCCH).
15. An apparatus for wireless communication at a user equipment (UE), comprising:
means for establishing a connection with a base station, the connection supporting a first time difference between downlink communication and responsive uplink communication and supporting a second time difference between the downlink communication and the responsive uplink communication;
means for receiving an indication from the base station of whether to use the first time difference or to use the second time difference, wherein the indication of whether to use the first time difference or to use the second time difference comprises an indication of an offset, from a start of a subframe, for uplink transmissions; and
means for transmitting an uplink transmission in response to a control message from the base station with an uplink timing that is based at least in part on receiving the indication of whether to use the first time difference or the second time difference.
16. A non-transitory computer-readable medium storing code for wireless communication at a user equipment (UE), the code comprising instructions executable by a processor to:
establish a connection with a base station, the connection supporting a first time difference between downlink communication and responsive uplink communication and supporting a second time difference between the downlink communication and the responsive uplink communication;
receive an indication from the base station of whether to use the first time difference or to use the second time difference, wherein the indication of whether to use the first time difference or to use the second time difference comprises an indication of an offset, from a start of a subframe, for uplink transmissions; and
transmit an uplink transmission in response to a control message from the base station with an uplink timing that is based at least in part on receiving the indication of whether to use the first time difference or the second time difference.