Low latency physical uplink control channel with scheduling request and channel state information
Methods, systems, and devices for wireless communication are described. A user equipment (UE) and a base station may use low latency communications to improve the throughput of a wireless link. To facilitate efficient low latency communication, the UE may send UE-initiated CSI reports in addition to periodic and base station-initiated reports. For example, the UE may, in various examples, send UE-initiated CSI reports using contention based spectrum, using a request-to-transmit, or using a CSI differential (i.e., an indicator of a change in channel conditions). The base station may schedule different UEs for uplink low latency communication by providing resources to each UE for CSI and scheduling requests (SRs) using coherent or non-coherent uplink transmissions. The CSI and SR may also be combined with uplink feedback.
1. A method of wireless communication, comprising:
determining channel state information (CSI) for a communication link that uses a first transmission time interval (TTI) duration in a system that supports operation with the first TTI duration and a second TTI duration that is greater than the first TTI duration, wherein the second TTI duration is a subframe including two slots, and wherein the first TTI duration is one slot or less;
identifying resources of an unscheduled uplink channel on which to transmit a report with the determined CSI, wherein the resources are selected from a set of resources reserved for uplink control information (UCI), selection of the resources being based at least in part on a number of user equipment (UEs) for which the set of resources reserved for UCI is allocated; and
transmitting the report on the identified resources.
2. The method of claim 1 , further comprising:
receiving signaling that indicates the set of resources reserved for UCI.
3. The method of claim 2 , wherein the signaling comprises a downlink grant.
4. The method of claim 1 , wherein the set of resources reserved for UCI comprises resources reserved for a scheduling request (SR), a CSI report, or hybrid automatic repeat request (HARQ) feedback, or any combination thereof.
5. The method of claim 1 , wherein the set of resources reserved for UCI comprises a set of resource blocks of a TTI having the first TTI duration.
6. The method of claim 1 , wherein the number of UEs comprises coherent users or non-coherent users, or both.
7. The method of claim 1 , wherein identifying the resources of the unscheduled uplink channel comprises:
determining that a TTI having the first TTI duration is available for CSI reporting.
8. The method of claim 1 , wherein the report is transmitted with a different cyclic shift from an uplink reference signal.
9. 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:
determine channel state information (CSI) for a communication link that uses a first transmission time interval (TTI) duration in a system that supports operation with the first TTI duration and a second TTI duration that is greater than the first TTI duration, wherein the second TTI duration is a subframe including two slots, and wherein the first TTI duration is one slot or less;
identify resources of an unscheduled uplink channel on which to transmit a report with the determined CSI, wherein the resources are selected from a set of resources reserved for uplink control information (UCI), selection of the resources being based at least in part on a number of user equipment (UEs) for which the set of resources reserved for UCI is allocated; and
transmit the report on the identified resources.
10. The apparatus of claim 9 , wherein the instructions are operable to cause the apparatus to:
receive signaling that indicates the set of resources reserved for UCI.
11. The apparatus of claim 10 , wherein the signaling comprises a downlink grant.
12. The apparatus of claim 9 , wherein the set of resources reserved for UCI comprises resources reserved for an SR, a CSI report, or hybrid automatic repeat request (HARQ) feedback, or any combination thereof.
13. The apparatus of claim 9 , wherein the set of resources reserved for UCI comprises a set of resource blocks of a TTI having the first TTI duration.
14. The apparatus of claim 9 , wherein the number of UEs comprises coherent users or non-coherent users, or both.
15. The apparatus of claim 9 , wherein the instructions operable to cause the apparatus to:
determine that a TTI having the first TTI duration is available for CSI reporting.
16. The apparatus of claim 9 , wherein the instructions are operable to cause the apparatus to:
transmit the report with a different cyclic shift from an uplink reference signal.
17. An apparatus for wireless communication, comprising:
means for determining channel state information (CSI) for a communication link that uses a first transmission time interval (TTI) duration in a system that supports operation with the first TTI duration and a second TTI duration that is greater than the first TTI duration, wherein the second TTI duration is a subframe including two slots, and wherein the first TTI duration is one slot or less;
means for identifying resources of an unscheduled uplink channel on which to transmit a report with the determined CSI, wherein the resources are selected from a set of resources reserved for uplink control information (UCI), selection of the resources being based at least in part on a number of user equipment (UEs) for which the set of resources reserved for UCI is allocated; and
transmitting the report on the identified resources.
18. The apparatus of claim 17 , further comprising:
means for receiving signaling that indicates the set of resources reserved for UCI.
19. The apparatus of claim 17 , wherein the set of resources reserved for UCI comprises resources reserved for a scheduling request (SR), a CSI report, or hybrid automatic repeat request (HARQ) feedback, or any combination thereof.
20. The apparatus of claim 17 , wherein the set of resources reserved for UCI comprises a set of resource blocks of a TTI having the first TTI duration.
21. The apparatus of claim 17 , wherein the number of UEs comprises coherent users or non-coherent users, or both.
22. The apparatus of claim 17 , wherein the means for identifying the resources of the unscheduled uplink channel comprises:
means for determining that a TTI having the first TTI duration is available for CSI reporting.
23. The apparatus of claim 17 , wherein the report is transmitted with a different cyclic shift from an uplink reference signal.
24. A non-transitory computer-readable medium storing code for wireless communication, the code comprising one or more instructions executable to:
determine channel state information (CSI) for a communication link that uses a first transmission time interval (TTI) duration in a system that supports operation with the first TTI duration and a second TTI duration that is greater than the first TTI duration, wherein the second TTI duration is a subframe including two slots, and wherein the first TTI duration is one slot or less;
identify resources of an unscheduled uplink channel on which to transmit a report with the determined CSI, wherein the resources are selected from a set of resources reserved for uplink control information (UCI), selection of the resources being based at least in part on a number of user equipment (UEs) for which the set of resources reserved for UCI is allocated; and
transmit the report on the identified resources.
25. The non-transitory computer-readable medium of claim 24 , wherein the one or more instructions are executable to:
receive signaling that indicates the set of resources reserved for UCI.
26. The non-transitory computer-readable medium of claim 24 , wherein the set of resources reserved for UCI comprises resources reserved for a scheduling request (SR), a CSI report, or hybrid automatic repeat request (HARQ) feedback, or any combination thereof.
27. The non-transitory computer-readable medium of claim 24 , wherein the set of resources reserved for UCI comprises a set of resource blocks of a TTI having the first TTI duration.
28. The non-transitory computer-readable medium of claim 24 , wherein the number of UEs comprises coherent users or non-coherent users, or both.
29. The non-transitory computer-readable medium of claim 24 , wherein the one or more instructions executable to identify the resources of the unscheduled uplink channel comprise instructions executable to:
determine that a TTI having the first TTI duration is available for CSI reporting.
30. The non-transitory computer-readable medium of claim 24 , wherein the report is transmitted with a different cyclic shift from an uplink reference signal.