Sounding reference signal transmissions in enhanced machine type communication

1. A method for wireless communications by a user equipment (UE), comprising:

determining one or more narrowband regions partitioned from wider system bandwidth for communicating with a base station;

determining resources, within the one or more narrowband regions of a first subframe, for transmission of sounding reference signals (SRS) by the UE, wherein the resources are determined based, at least in part, on resources used for transmitting a physical uplink shared channel (PUSCH);

deciding whether or not to transmit SRS on the determined resources of the first subframe based, at least in part, on whether the UE has to retune from a first narrowband region of the one or more narrowband regions of the first subframe to a second narrowband region of a second subframe, wherein deciding whether or not to transmit the SRS comprises deciding not to transmit the SRS when a direction of the first subframe is different than a direction of the second subframe; and

transmitting or not transmitting the SRS on the determined resources of the first subframe based on the decision.

2. The method of claim 1 , wherein deciding whether or not to transmit the SRS is further based, at least in part, on at least one of a frequency location of the first narrowband region of the first subframe or a frequency location of the second narrowband region of the second subframe.

3. The method of claim 2 , wherein deciding whether or not to transmit the SRS comprises deciding not to transmit the SRS if the frequency location of the first narrowband region is different from the frequency location of the second narrowband region.

4. The method of claim 2 , wherein deciding whether or not to transmit the SRS is further based, at least in part, on an operating mode of the UE, wherein operating modes comprise at least one of a frequency division duplex (FDD) mode or a time division duplex (TDD) mode.

5. The method of claim 4 , wherein, for TDD mode, deciding whether or not to transmit the SRS is further based, at least in part, on at least one of a duration of a partial downlink subframe or a duration of a partial uplink subframe.

6. The method of claim 1 , wherein the resources are determined, at least in part, based on upper layer information for a subset of narrowbands, comprising one or more of a cyclic shift or a comb index.

7. The method of claim 1 , further comprising receiving signaling to trigger transmission of SRS.

8. The method of claim 7 , wherein deciding whether or not to transmit the SRS is based, at least in part, on the received signaling being valid for a given narrowband region.

9. The method of claim 7 , further comprising:

determining a first set of narrowband regions for which a trigger to transmit SRS is valid;

determining a hopping sequence of transmission resources;

determining transmission parameters according to the first set of narrowband regions for which a trigger is valid and the determined hopping sequence; and

wherein deciding whether or not to transmit the SRS comprises deciding to transmit the SRS in a first subframe of the first set of narrowband regions for which a trigger is valid based, at least in part, on the determined transmission parameters.

10. The method of claim 7 , wherein the signaling comprises a downlink grant, and wherein determining the resources for transmitting SRS is based, at least in part, on resources indicated in the downlink grant.

11. The method of claim 7 , further comprising:

receiving a plurality of SRS configurations from a base station;

receiving a grant from the base station, comprising a trigger to perform SRS and an indication of an SRS configuration of the plurality of SRS configurations to use for transmitting the SRS, and wherein deciding whether or not to transmit an SRS is based, at least in part, on the trigger and the indication of the SRS configuration.

12. The method of claim 1 , further comprising:

receiving a grant from a base station comprising a trigger to perform SRS;

determining a physical downlink shared channel (PDSCH) reception will collide with the SRS transmission; and

dropping at least one of the SRS transmission, the PDSCH transmission, or the grant.

13. The method of claim 1 , further comprising;

receiving higher layer information for SRS;

receiving a grant from a base station comprising a trigger to perform SRS;

determining transmission parameters based, at least in part, on the higher layer information and the trigger, wherein the higher layer information comprises at least one of a code division multiplexing (CDM) index, a comb index, or a cyclic shift; and

wherein deciding whether or not to transmit an SRS is based on the determined transmission parameters.

14. The method of claim 13 , wherein deciding whether or not to transmit an SRS comprises deciding to transmit the SRS over more than one orthogonal frequency division multiplexing (OFDM) symbol.

15. The method of claim 1 , further comprising performing rate matching for a physical uplink channel around a last symbol in the first subframe regardless of the decision of whether or not to transmit SRS on the determined resources of the first subframe, wherein the physical uplink channel is a physical uplink shared channel (PUSCH) or a physical uplink control channel (PUCCH).

16. The method of claim 1 , wherein the UE decides not to transmit the SRS on the determined resources of the first subframe, and further comprising:

determining whether or not to perform rate matching for a physical uplink channel around a last symbol in the first subframe based, at least in part, on whether the SRS is dropped due to a transmission in the first subframe or in a subsequent subframe, wherein the physical uplink channel is a physical uplink shared channel (PUSCH) or a physical uplink control channel (PUCCH).

17. An apparatus for wireless communications, comprising:

at least one processor configured to:

determine one or more narrowband regions partitioned from wider system bandwidth for communicating with a base station;

determine resources, within the one or more narrowband regions of a first subframe, for transmission of sounding reference signals (SRS) by the UE, wherein the resources are determined based, at least in part, on resources used for transmitting a physical uplink shared channel (PUSCH);

decide whether or not to transmit SRS on the determined resources of the first subframe based, at least in part, on whether the UE has to retune from a first narrowband region of the one or more narrowband regions of the first subframe to a second narrowband region of a second subframe, wherein deciding whether or not to transmit the SRS comprises deciding not to transmit the SRS when a direction of the first subframe is different than a direction of the second subframe; and

a transmitter configured to transmit or not transmit the SRS on the determined resources of the first subframe based on the decision.

18. The apparatus of claim 17 , wherein the at least one processor is further configured to decide whether or not to transmit the SRS based, at least in part, on at least one of a frequency location of the first narrowband region of the first subframe or a frequency location of the second narrowband region of the second subframe.

19. The apparatus of claim 18 , wherein the at least one processor is configured to decide not to transmit the SRS if the frequency location of the first narrowband region is different from the frequency location of the second narrowband region.

20. The apparatus of claim 18 , wherein the at least one processor is further configured to decide whether or not to transmit the SRS based, at least in part, on an operating mode of the UE, wherein operating modes comprise at least one of a frequency division duplex (FDD) mode or a time division duplex (TDD) mode.

21. The apparatus of claim 20 , wherein, for TDD mode, the at least one processor is configured to decide whether or not to transmit the SRS based further based, at least in part, on at least one of a duration of a partial downlink subframe or a duration of a partial uplink subframe.

22. The apparatus of claim 17 , wherein the at least one processor is configured to determine the resources based, at least in part, on upper layer information for a subset of narrowbands, comprising one or more of a cyclic shift or a comb index.

23. The apparatus of claim 17 , further comprising a receiver configured to receiving signaling to trigger transmission of SRS.

24. The apparatus of claim 23 , wherein the at least one processor is configured to decide whether or not to transmit the SRS based, at least in part, on the received signaling being valid for a given narrowband region.

25. The apparatus of claim 23 , wherein the at least one processor is further configured to:

determine a first set of narrowband regions for which a trigger to transmit SRS is valid;

determine a hopping sequence of transmission resources;

determine transmission parameters according to the first set of narrowband regions for which a trigger is valid and the determined hopping sequence; and

decide whether or not to transmit the SRS by deciding to transmit the SRS in a first subframe of the first set of narrowband regions for which a trigger is valid based, at least in part, on the determined transmission parameters.

26. The apparatus of claim 23 , wherein the signaling comprises a downlink grant, and wherein the at least one processor is configured to determine the resources for transmitting SRS is based, at least in part, on resources indicated in the downlink grant.

27. The apparatus of claim 23 , wherein the receiver is further configured to:

receive a plurality of SRS configurations from a base station;

receive a grant from the base station, comprising a trigger to perform SRS and an indication of an SRS configuration of the plurality of SRS configurations to use for transmitting the SRS; and

wherein the at least one processor is further configured to decide whether or not to transmit an SRS based, at least in part, on the trigger and the indication of the SRS configuration.

28. The apparatus of claim 17 , further comprising a receiver configured to receive a grant from a base station comprising a trigger to perform SRS; and

wherein the at least one processor is configured to:

determine a physical downlink shared channel (PDSCH) reception will collide with the SRS transmission; and

drop at least one of the SRS transmission, the PDSCH transmission, or the grant.

29. The apparatus of claim 17 , further comprising:

a receiver configured to:

receive higher layer information for SRS;

receive a grant from a base station comprising a trigger to perform SRS; and

wherein the at least one processor is further configured to:

determine transmission parameters based, at least in part, on the higher layer information and the trigger, wherein the higher layer information comprises at least one of a code division multiplexing (CDM) index, a comb index, or a cyclic shift; and

decide whether or not to transmit an SRS based on the determined transmission parameters.

30. The apparatus of claim 29 , wherein the at least one processor configured to decide whether or not to transmit an SRS by deciding to transmit the SRS over more than one orthogonal frequency division multiplexing (OFDM) symbol.

31. The apparatus of claim 17 , wherein the at least one processor is further configured to perform rate matching for a physical uplink channel around a last symbol in the first subframe regardless of the decision of whether or not to transmit SRS on the determined resources of the first subframe, wherein the physical uplink channel is a physical uplink shared channel (PUSCH) or a physical uplink control channel (PUCCH).

32. The apparatus of claim 17 , wherein the apparatus decides not to transmit the SRS on the determined resources of the first subframe, and wherein the at least one processor is configured to determine whether or not to perform rate matching for a physical uplink channel around a last symbol in the first subframe based, at least in part, on whether the SRS is dropped due to a transmission in the first subframe or in a subsequent subframe, wherein the physical uplink channel is a physical uplink shared channel (PUSCH) or a physical uplink control channel (PUCCH).

33. An apparatus for wireless communications, comprising:

means for determining one or more narrowband regions partitioned from wider system bandwidth for communicating with a base station;

means for determining resources, within the one or more narrowband regions of a first subframe, for transmission of sounding reference signals (SRS) by the UE, wherein the resources are determined based, at least in part, on resources used for transmitting a physical uplink shared channel (PUSCH);

means for deciding whether or not to transmit SRS on the determined resources of the first subframe based, at least in part, on whether the UE has to retune from a first narrowband region of the one or more narrowband regions of the first subframe to a second narrowband region of a second subframe, wherein deciding whether or not to transmit the SRS comprises deciding not to transmit the SRS when a direction of the first subframe is different than a direction of the second subframe; and

means for transmitting or not transmitting the SRS on the determined resources of the first subframe based on the decision.

34. A non-transitory computer-readable medium for wireless communications, comprising code, which when executed by at least one processor, causes the at least one processor to:

determine one or more narrowband regions partitioned from wider system bandwidth for communicating with a base station;

determine resources, within the one or more narrowband regions of a first subframe, for transmission of sounding reference signals (SRS) by the UE, wherein the resources are determined based, at least in part, on resources used for transmitting a physical uplink shared channel (PUSCH);

decide whether or not to transmit SRS on the determined resources of the first subframe based, at least in part, on whether the UE has to retune from a first narrowband region of the one or more narrowband regions of the first subframe to a second narrowband region of a second subframe, wherein deciding whether or not to transmit the SRS comprises deciding not to transmit the SRS when a direction of the first subframe is different than a direction of the second subframe; and

transmit or not transmit the SRS on the determined resources of the first subframe based on the decision.