UPLINK TRANSMISSION TECHNIQUES IN LOW-LATENCY WIRELESS COMMUNICATION
Methods, systems, and devices for wireless communications are described that provide for indicating transmit power control information to a user equipment (UE) for semi-persistent scheduling (SPS) transmissions in short transmission time intervals (TTIs) from the UE, and for configuring reference signal transmissions in SPS transmissions of short TTIs. A UE may be configured with uplink power control information for SPS transmissions that use sTTIs that is separate from uplink power control for longer TTIs. A UE may receive the power control information and apply it in SPS transmissions that use sTTIs. Uplink transmit power for SPS sTTI transmissions may be independent of power control for regular sTTI transmissions and independent of power control for long TTI transmissions. UEs may apply a cyclic shift to reference signals transmitted is SPS transmissions according to a SPS configuration, rather than a cyclic shift indicated in a SPS activation command.
1 . A method for wireless communication, comprising:
receiving, at a user equipment (UE), a semi-persistent scheduling (SPS) configuration for transmitting uplink transmissions in a first plurality of transmission time intervals (TTIs), wherein the first plurality of TTIs have a first TTI duration that is shorter than a second TTI duration of a second plurality of TTIs, and wherein the SPS configuration indicates configuration information that is to be applied to a demodulation reference signal (DMRS) transmitted in one or more of the first plurality of TTIs;
receiving, during a first TTI of the second plurality of TTIs, an activation command to activate the SPS configuration;
configuring, in accordance with the configuration information, the DMRS for transmission in one or more of the first plurality of TTIs responsive to the activation command; and
transmitting the configured DMRS in at least one of the first plurality of TTIs.
2 . The method of claim 1 , further comprising:
transmitting the configured DMRS in at least the second plurality of TTIs.
3 . The method of claim 1 , wherein configuring the DMRS further comprises:
applying a cyclic shift to the DMRS, wherein the configuration information indicates at least the cyclic shift.
4 . The method of claim 1 , wherein multiple UEs are configured with non-orthogonal SPS resources.
5 . The method of claim 1 , wherein the activation command includes a field indicating a DMRS cyclic shift that is ignored when applying a cyclic shift.
6 . The method of claim 5 , wherein the DMRS cyclic shift is indicated in the activation command.
7 . The method of claim 1 , wherein the activation command is received in downlink control information (DCI) from a base station.
8 . The method of claim 7 , wherein the DCI has a predetermined DCI format for activating the SPS configuration.
9 . The method of claim 7 , wherein the activation command is confirmed by verifying that a cyclic redundancy check (CRC) of the activation command is scrambled by a SPS identification that is configured at the UE, and that one or more fields of the DCI, including a DMRS cyclic shift field, are set to predetermined pattern of values.
10 . A method for wireless communication, comprising:
transmitting, to a user equipment (UE), a semi-persistent scheduling (SPS) configuration for uplink transmissions from the UE in a first plurality of transmission time intervals (TTIs), wherein the first plurality of TTIs have a first TTI duration that is shorter than a second TTI duration of a second plurality of TTIs, and wherein the SPS configuration includes configuration information that is to be applied to a demodulation reference signal (DMRS) transmitted in one or more of the first plurality of TTIs;
transmitting, during a first TTI of the second plurality of TTIs, an activation command to the UE to activate the SPS configuration;
receiving one or more uplink transmissions in the first plurality of TTIs, the one or more uplink transmissions including a DMRS transmission;
processing the DMRS in accordance with the configuration information; and
decoding the one or more uplink transmissions based at least in part on the processed DMRS.
11 . The method of claim 10 , wherein multiple UEs are configured with non-orthogonal SPS resources.
12 . The method of claim 10 , wherein the activation command includes a field indicating a DMRS cyclic shift that is ignored by the UE when applying a cyclic shift to the DMRS.
13 . The method of claim 10 , wherein processing the DMRS further comprises:
applying a cyclic shift to the DMRS, wherein the configuration information indicates the cyclic shift.
14 . 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), a semi-persistent scheduling (SPS) configuration for transmitting uplink transmissions in a first plurality of transmission time intervals (TTIs), wherein the first plurality of TTIs have a first TTI duration that is shorter than a second TTI duration of a second plurality of TTIs, and wherein the SPS configuration includes configuration information that is to be applied to a demodulation reference signal (DMRS) transmitted in one or more of the first plurality of TTIs;
receive, during a first TTI of the second plurality of TTIs, an activation command to activate the SPS configuration;
configure, in accordance with the configuration information, the DMRS for transmission in one or more of the first plurality of TTIs responsive to the activation command; and
transmit the configured DMRS in at least one of the first plurality of TTIs.
15 . The apparatus of claim 14 , wherein the instructions are further executable by the processor to:
transmit the configured DMRS in at least the second plurality of TTIs.
16 . The apparatus of claim 14 , wherein the instructions to configure the DMRS are further executable by the processor to:
apply a cyclic shift to the DMRS, wherein the configuration information indicates at least the cyclic shift.
17 . The apparatus of claim 14 , wherein multiple UEs are configured with non-orthogonal SPS resources.
18 . The apparatus of claim 14 , wherein the activation command includes a field indicating a DMRS cyclic shift that is ignored when applying a cyclic shift.
19 . The apparatus of claim 18 , wherein the DMRS cyclic shift is indicated in the activation command.
20 . The apparatus of claim 14 , wherein the activation command is received in downlink control information (DCI) from a base station.
21 . The apparatus of claim 20 , wherein the DCI has a predetermined DCI format for activating the SPS configuration.
22 . The apparatus of claim 20 , wherein the activation command is confirmed by verifying that a cyclic redundancy check (CRC) of the activation command is scrambled by a SPS identification that is configured at the UE, and that one or more fields of the DCI, including a DMRS cyclic shift field, are set to predetermined pattern of values.
23 . 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), a semi-persistent scheduling (SPS) configuration for uplink transmissions from the UE in a first plurality of transmission time intervals (TTIs), wherein the first plurality of TTIs have a first TTI duration that is shorter than a second TTI duration of a second plurality of TTIs, and wherein the SPS configuration includes configuration information that is to be applied to a demodulation reference signal (DMRS) transmitted in one or more of the first plurality of TTIs;
transmit, during a first TTI of the second plurality of TTIs, an activation command to the UE to activate the SPS configuration;
receive one or more uplink transmissions in the first plurality of TTIs, the one or more uplink transmissions including a DMRS transmission;
process the DMRS in accordance with the configuration information; and
decode the one or more uplink transmissions based at least in part on the processed DMRS.
24 . The apparatus of claim 23 , the processor further operable to cause the apparatus to:
receive one or more uplink transmissions in the second plurality of TTIs, the one or more uplink transmissions including the DMRS transmission.
25 . The apparatus of claim 23 , the processor further operable to process the DMRS by causing the apparatus to:
apply a cyclic shift to the DMRS, wherein the configuration information indicates at least the cyclic shift.
26 . The apparatus of claim 23 , wherein multiple UEs are configured with non-orthogonal SPS resources.
27 . The apparatus of claim 23 , wherein the activation command includes a field indicating a DMRS cyclic shift that is ignored by the UE when applying a cyclic shift to the DMRS.