CSI feedback in LTE/LTE-advanced systems with unlicensed spectrum

1. A method of wireless communication, comprising:

identifying, by a user equipment (UE), at least one carrier utilizing a contention based access radio frequency spectrum;

detecting a transmission signal indicative of clear channel assessment (CCA) result information for the at least one carrier, wherein the transmission signal indicative of CCA result information includes one or more channel usage reference signals transmitted, by one or more base stations, in response to successful listen before talk (LBT) performed on the at least one carrier by the one or more base stations;

determining whether a reference signal for channel state information measurement is present in a subframe based on the detected transmission signal; and

transmitting, by the UE, a measurement report, wherein the measurement report is based at least in part on the determining the reference signal is present.

2. The method of claim 1 , wherein the transmission signal indicative of CCA result information is detected for a transmission frame comprising of a plurality of subframes, including the subframe in which the determining is performed.

3. The method of claim 1 , wherein the one or more channel usage reference signals includes channel usage beacon signals (CUBS) or channel state information reference signals (CSI-RS).

4. The method of claim 1 , further including:

determining, by the UE, the reference signal presence over a plurality of transmission frames;

processing interference conditions, as part of the measurement report, for a first set of transmission frames of the plurality of transmission frames in which the reference signal is determined to be present, separately from for a second set of frames in which the reference signal is determined to be absent.

5. The method of claim 1 , further including:

performing a first interference measurement for a first subframe in a transmission frame;

performing a second interference measurement for a second subframe in the transmission frame; and

transmitting a measurement report comprising a first measurement based on the first interference measurement and a second measurement based on the second interference measurement.

6. The method of claim 5 , wherein the first subframe is a regular and the second subframe is a special subframe, wherein the first measurement is not averaged with the second measurement in the measurement report.

7. The method of claim 5 , wherein the first subframe is configured with a first reference signal configuration and the second subframe is configured with a second reference signal configuration different from the first reference signal configuration.

8. The method of claim 1 , further including performing interference measurement based on a set of resource elements present in substantially all symbols in the subframe.

9. The method of claim 8 , wherein the set of resource elements are arranged in one of:

a hopping pattern across each frequency of the subframe; or

one or more predetermined frequencies of the subframe.

10. The method of claim 1 , further including:

transmitting a report indicative of the CCA result information over a predetermined duration for the at least one carrier.

11. The method of claim 1 , wherein the carrier utilizing a contention based access radio frequency spectrum is in an unlicensed spectrum.

12. The method of claim 1 , further including:

determining, by the UE, there are two or more channel state feedback processes configured for the at least one carrier, wherein the determining the reference signal for channel measurement is performed separately for each of the two or more channel state feedback processes.

13. The method of claim 1 , wherein the UE determines the reference signal is not present, the method further including one of:

omitting, by the UE, the measurement report; or

transmitting the measurement report, wherein the measurement report is based, at least in part, on a previous measurement report.

14. The method of claim 1 , further including:

receiving, by the UE, a presence signal, wherein the presence signal indicates whether the reference signal is present in the subframe.

15. The method of claim 1 , further including:

determining, by the UE, that the subframe is an empty subframe; and

performing interference measurement, by the UE, over the entire subframe in response to the determining the reference signal is present.

16. The method of claim 1 , further including:

performing a first interference measurement for a first subframe in a transmission frame;

performing a second interference measurement for a second subframe in the transmission frame;

transmitting a first measurement report associated with the first interference measurement; and

transmitting a second measurement report associated with the second interference measurement, wherein the second measurement report provides a differential between the second interference measurement and the first interference measurement.

17. The method of claim 1 , further including:

generating, by the UE, the measurement report, wherein the measurement report includes feedback of interference based on one of:

averaged interference observed by the UE over a duration of the subframe; or

symbol-dependent interference associated with one or more symbols of the subframe.

18. The method of claim 17 , wherein the feedback of interference is based on symbol-dependent interference, the generating further including:

averaging first symbols interference observed by the UE over each symbol of a first slot of the subframe; and

averaging second symbols interference observed by the UE over each symbol of a second slot of the subframe, wherein one or more of the first symbols interference and the second symbols interference is included in the measurement report.

19. The method of claim 1 , further including:

determining the subframe is an uplink subframe; and

omitting the detecting, determining, and transmitting in response to the determining the subframe is the uplink subframe.

20. The method of claim 1 , further including:

measuring, by the UE, interference in the subframe when a corresponding CCA is not cleared; and

transmitting the measurement report, wherein the measurement report is based at least in part on the measured interference in the subframe.

21. The method of claim 1 , where the reference signal is at least one of a non-zero-power channel state information reference signal (CSI-RS) or a zero-power CSI-RS.

22. The method of claim 21 , wherein the non-zero CSI-RS is for a channel measurement of the CSI feedback and the zero CSI-RS is for an interference measurement of the CSI feedback.

23. The method of claim 1 , wherein a non-zero-power reference signal is determined to be present in a subframe if a corresponding CCA is cleared.

24. The method of claim 1 , wherein a zero-power reference signal is determined to be present in a subframe irrespective of whether a corresponding CCA is cleared or not.

25. An apparatus configured for wireless communication, comprising:

means for identifying, by a user equipment (UE), at least one carrier utilizing a contention based access radio frequency spectrum;

means for detecting a transmission signal indicative of clear channel assessment (CCA) result information for the at least one carrier, wherein the transmission signal indicative of CCA result information includes one or more channel usage reference signals transmitted, by one or more base stations, in response to successful listen before talk (LBT) performed on the at least one carrier by the one or more base stations;

means for determining whether a reference signal for channel state information measurement is present in a subframe based on the detected transmission signal; and

means for transmitting, by the UE, a measurement report, wherein the measurement report is based at least in part on the determining the reference signal is present.

26. A non-transitory computer-readable medium having program code recorded thereon, the program code including:

program code for causing a computer to identify, by a user equipment (UE), at least one carrier utilizing a contention based access radio frequency spectrum;

program code for causing the computer to detect a transmission signal indicative of clear channel assessment (CCA) result information for the at least one carrier, wherein the transmission signal indicative of CCA result information includes one or more channel usage reference signals transmitted, by one or more base stations, in response to successful listen before talk (LBT) performed on the at least one carrier by the one or more base stations;

program code for causing the computer to determine whether a reference signal for channel state information measurement is present in a subframe based on the detected transmission signal; and

program code for causing the computer to transmit, by the UE, a measurement report, wherein the measurement report is based at least in part on the determining the reference signal is present.

27. An apparatus configured for wireless communication, the apparatus comprising:

at least one processor; and

a memory coupled to the at least one processor,

wherein the at least one processor is configured:

to identifying, by a user equipment (UE), at least one carrier utilizing a contention based access radio frequency spectrum;

to detect a transmission signal indicative of clear channel assessment (CCA) result information for the at least one carrier, wherein the transmission signal indicative of CCA result information includes one or more channel usage reference signals transmitted, by one or more base stations, in response to successful listen before talk (LBT) performed on the at least on carrier by the one or more base stations;

to determine whether a reference signal for channel state information measurement is present in a subframe based on the detected transmission signal; and

to transmit, by the UE, a measurement report, wherein the measurement report is based at least in part on the determining the reference signal is present.

28. The apparatus of claim 27 , wherein the transmission signal indicative of CCA result information is detected for a transmission frame comprising of a plurality of subframes, including the subframe in which the determining is performed.

29. The apparatus of claim 27 , further including configuration of the at least one processor:

to determine, by the UE, the reference signal presence over a plurality of transmission frames;

to process interference conditions, as part of the measurement report, for a first set of transmission frames of the plurality of transmission frames in which the reference signal is determined to be present, separately from for a second set of frames in which the reference signal is determined to be absent.

30. The apparatus of claim 27 , further including configuration of the at least one processor:

to perform a first interference measurement for a first subframe in a transmission frame;

to perform a second interference measurement for a second subframe in the transmission frame; and

to transmit a measurement report comprising a first measurement based on the first interference measurement and a second measurement based on the second interference measurement.