Patent Publication Number: US-2022225399-A1

Title: Configuration of aperiodic sounding reference signal transmission and triggering

Description:
CROSS REFERENCES 
     The present application for Patent is a Continuation of U.S. patent application Ser. No. 16/269,903 by Manolakos et al., entitled “Configuration of Aperiodic Sounding Reference Signal Transmission and Triggering” filed Feb. 7, 2019, which claims the benefit of Greece Provisional Patent Application No. 20180100057 by Manolakos, et al., entitled “Configuration of Aperiodic Sounding Reference Signal Transmission and Triggering,” filed Feb. 15, 2018, assigned to the assignee hereof, and expressly incorporated by reference herein. 
    
    
     BACKGROUND 
     The following relates generally to wireless communication, and more specifically to configuration of aperiodic sounding reference signal transmission and triggering. 
     Wireless communications systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power). Examples of such multiple-access systems include fourth generation (4G) systems such as Long Term Evolution (LTE) systems, LTE-Advanced (LTE-A) systems, or LTE-A Pro systems, and fifth generation (5G) systems which may be referred to as New Radio (NR) systems. These systems may employ technologies such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal frequency division multiple access (OFDMA), or discrete Fourier transform-spread-OFDM (DFT-S-OFDM). A wireless multiple-access communications system may include a number of base stations or network access nodes, each simultaneously supporting communication for multiple communication devices, which may be otherwise known as user equipment (UE). 
     In some examples of a wireless communications system, communications between a UE and a base station may include communication of sounding reference signals (SRSs). An SRS may be signal known by each of the UE and the base station. The UE may transmit the SRS, and the base station may receive and measure the SRS for generating a channel estimate of a wireless channel between the UE and the base station. In some cases, the base station may use the channel estimate for identifying whether a particular frequency band is experiencing high levels of interference and/or noise, and make frequency dependent scheduling determinations based on one or more determined channel estimates. In some examples, an SRS may be transmitted aperiodically, semi-persistently, or periodically. However, SRS transmission schemes in conventional wireless communication systems are deficient. 
     SUMMARY 
     The described techniques relate to improved methods, systems, devices, or apparatuses that support configuration of aperiodic sounding reference signal transmission and triggering. Generally, the described techniques provide for aperiodic triggering of a user equipment (UE) to transmit a sounding reference signal (SRS) in a transmission time interval (TTI) relative to a TTI in which the UE receives a grant. In some examples, a UE may receive a grant that triggers the transmission of an aperiodic SRS, and the UE may identify offset information indicating a TTI offset between the TTI in which the triggering grant is received, and the TTI in which the aperiodic SRS is to be transmitted. In some examples, the TTI in which the aperiodic SRS is to be transmitted may be a function of the amount of time required by the UE to process a grant relative to when the UE is capable of transmitting in accordance with the grant. 
     In some examples, a UE may receive downlink control information (DCI) that includes a downlink grant or an uplink grant, and in response the UE, may transmit SRS to a base station in a TTI relative to a TTI that included the grant. In some examples, the UE may transmit the SRS on SRS resource in an earliest available TTI following a TTI in which the grant is received, which may be as early as the same TTI that included the grant. In some examples, the transmission timing of the SRS may be identified based on TTI offset information. The UE may be preconfigured with the TTI offset information, or the TTI offset information may be received via RRC signaling, or included in DCI. The UE may identify the TTI offset information and determine a TTI offset, and may use the TTI offset to determine in which TTI to transmit the SRS relative to the TTI in which the grant is received. 
     In some cases, a UE may signal its capabilities to the base station, or the base station may be aware of default UE capabilities for UEs operating within a wireless communication system. The base station may determine in which TTI to instruct the UE to transmit uplink data, or to receive downlink data, and generate a grant accordingly. The base station may also identify, based on the signaled UE capabilities or default capabilities, in which TTI the UE is expected to transmit the SRS relative to the grant. The base station may monitor SRS resource of the expected TTI for the SRS. Beneficially, a UE may be configured to transmit an SRS at an earlier or earliest available TTI following the reception of DCI. 
     A method of wireless communication is described. The method may include detecting, within a first TTI, a grant triggering the UE to transmit an aperiodic sounding reference signal (A-SRS), identifying offset information indicating a TTI offset relative to the grant, determining a second TTI for transmitting the A-SRS based at least in part on the TTI offset, and transmitting the A-SRS in an SRS resource of the second TTI. 
     An apparatus for wireless communication is described. The apparatus may include means for detecting, within a first TTI, a grant triggering the UE to transmit an A-SRS, means for identifying offset information indicating a TTI offset relative to the grant, means for determining a second TTI for transmitting the A-SRS based at least in part on the TTI offset, and means for transmitting the A-SRS in an SRS resource of the second TTI. 
     Another apparatus for wireless communication is described. The apparatus may include a processor, memory in electronic communication with the processor, and instructions stored in the memory. The instructions may be operable to cause the processor to detect, within a first TTI, a grant triggering the UE to transmit an A-SRS, identify offset information indicating a TTI offset relative to the grant, determine a second TTI for transmitting the A-SRS based at least in part on the TTI offset, and transmit the A-SRS in an SRS resource of the second TTI. 
     A non-transitory computer-readable medium for wireless communication is described. The non-transitory computer-readable medium may include instructions operable to cause a processor to detect, within a first TTI, a grant triggering the UE to transmit an A-SRS, identify offset information indicating a TTI offset relative to the grant, determine a second TTI for transmitting the A-SRS based at least in part on the TTI offset, and transmit the A-SRS in an SRS resource of the second TTI. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, receiving configuration information that configures the UE to transmit the A-SRS within at least one symbol index of a plurality of different symbol indexes of a TTI, wherein transmitting the A-SRS in the SRS resource of the second TTI further comprises: transmitting the A-SRS within at least one symbol period of the second TTI corresponding to the at least one symbol index. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, identifying the offset information further comprises: receiving the offset information in downlink control information of the first TTI, wherein the offset information indicates a delay corresponding to a number of TTIs occurring between receipt of the grant by the UE and when the UE may be instructed to transmit uplink data in accordance with the grant. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, determining the second TTI further comprises: determining a TTI index following the delay indicated in the offset information, wherein the second TTI corresponds to the TTI index. 
     Some examples of the method, apparatus, and non-transitory computer-readable medium described above may further include processes, features, means, or instructions for transmitting capability information indicating a number of symbol periods between receipt of the grant by the UE and when the UE may be capable of transmitting uplink data in accordance with the grant, wherein the delay corresponds to the capability information. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, the delay corresponds to a specified capability information indicating a number of symbol periods between receipt of the grant by the UE and when the UE may be capable of transmitting uplink data in accordance with the grant. 
     Some examples of the method, apparatus, and non-transitory computer-readable medium described above may further include processes, features, means, or instructions for receiving downlink control information of the first TTI that includes the offset information, wherein the grant indicates resources of a shared data channel allocated to the UE for transmission of uplink data, and wherein the offset information may be a bit flag indicating whether the UE may be to use a first value for the TTI offset indicated in the downlink control information or a second semi-statically configured value for the TTI offset. 
     Some examples of the method, apparatus, and non-transitory computer-readable medium described above may further include processes, features, means, or instructions for receiving downlink control information of the first TTI that includes the offset information, wherein the grant indicates resources of a shared data channel allocated to the UE for transmission of uplink data, and wherein the offset information comprises a bit sequence corresponding to a number of TTIs occurring between receipt of the grant by the UE and when the UE may be instructed to transmit uplink data in accordance with the grant. 
     Some examples of the method, apparatus, and non-transitory computer-readable medium described above may further include processes, features, means, or instructions for receiving downlink control information of the first TTI that includes the offset information, wherein the grant indicates resources of a shared data channel allocated to the UE for transmission of uplink data, and wherein the offset information comprises a bit flag indicating whether the UE may be to use a first value for the TTI offset indicated in the downlink control information or a second value for the TTI offset. 
     Some examples of the method, apparatus, and non-transitory computer-readable medium described above may further include processes, features, means, or instructions for receiving control signaling semi-statically indicating a defined value, wherein the second value for the TTI offset may be a function of the first value for the TTI offset and the defined value. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, the first value indicates a gap in TTIs between the grant requesting the uplink data and transmission of the uplink data, and the second TTI may be a TTI occurring prior to a TTI corresponding to the first value. 
     Some examples of the method, apparatus, and non-transitory computer-readable medium described above may further include processes, features, means, or instructions for receiving downlink control information of the first TTI that includes the offset information, wherein the grant indicates resources of a shared data channel allocated to the UE for reception of downlink data. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, the offset information may be a bit sequence included within downlink control information of the first TTI, the bit sequence corresponding to a number of TTIs occurring between receipt of the grant by the UE and when the UE may be instructed to transmit uplink data in accordance with the grant. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, the bit sequence may be configured to jointly trigger transmission of a zero-power channel state information reference signal (CSIRS) from a base station and transmission of the A-SPS from the UE. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, identifying the second TTI further comprises: identifying the second TTI as being offset from the first TTI by the TTI offset. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, identifying the second TTI comprises: determining that the TTI offset may be a zero TTI offset, wherein the second TTI and the first TTI may be a same TTI. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, identifying the offset information further comprises receiving control signaling that semi-statically configures the UE with the offset information. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, identifying the offset information further comprises: receiving downlink control information of the first TTI that includes the offset information for dynamically configuring the UE with the TTI offset. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, identifying the offset information further comprises retrieving the offset information from memory, wherein the UE may be preconfigured with the offset information. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, the SRS resource corresponds to a subset of symbol periods within the second TTI. 
     A method of wireless communication is described. The method may include detecting, within a first TTI, a grant triggering the UE to transmit an A-SRS, identifying a second TTI based at least in part on a first number of symbol periods between receipt of the grant by the UE and when the UE is capable of transmitting uplink data, the first number of symbol periods meeting or being less than a difference between a number of symbol periods between an SRS resource of the second TTI and a control channel of the first TTI, and transmitting the A-SRS in the SRS resource of the second TTI. 
     An apparatus for wireless communication is described. The apparatus may include means for detecting, within a first TTI, a grant triggering the UE to transmit an A-SRS, means for identifying a second TTI based at least in part on a first number of symbol periods between receipt of the grant by the UE and when the UE is capable of transmitting uplink data, the first number of symbol periods meeting or being less than a difference between a number of symbol periods between an SRS resource of the second TTI and a control channel of the first TTI, and means for transmitting the A-SRS in the SRS resource of the second TTI. 
     Another apparatus for wireless communication is described. The apparatus may include a processor, memory in electronic communication with the processor, and instructions stored in the memory. The instructions may be operable to cause the processor to detect, within a first TTI, a grant triggering the UE to transmit an A-SRS, identify a second TTI based at least in part on a first number of symbol periods between receipt of the grant by the UE and when the UE is capable of transmitting uplink data, the first number of symbol periods meeting or being less than a difference between a number of symbol periods between an SRS resource of the second TTI and a control channel of the first TTI, and transmit the A-SRS in the SRS resource of the second TTI. 
     A non-transitory computer-readable medium for wireless communication is described. The non-transitory computer-readable medium may include instructions operable to cause a processor to detect, within a first TTI, a grant triggering the UE to transmit an A-SRS, identify a second TTI based at least in part on a first number of symbol periods between receipt of the grant by the UE and when the UE is capable of transmitting uplink data, the first number of symbol periods meeting or being less than a difference between a number of symbol periods between an SRS resource of the second TTI and a control channel of the first TTI, and transmit the A-SRS in the SRS resource of the second TTI. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, receiving configuration information that configures the UE to transmit the A-SRS within at least one symbol index of a plurality of different symbol indexes of a TTI, wherein transmitting the A-SRS in the SRS resource of the second TTI further comprises: transmitting the A-SRS within at least one symbol period of the second TTI corresponding to the at least one symbol index. 
     Some examples of the method, apparatus, and non-transitory computer-readable medium described above may further include processes, features, means, or instructions for transmitting capability information indicating the first number of symbol periods. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, the grant indicates resources of a shared data channel allocated to the UE for reception of downlink data. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, identifying the second TTI further comprises: identifying the second TTI based at least in part on a second number of symbol periods between receipt of the grant by the UE and when the UE may be capable of receiving downlink data. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, identifying the second TTI further comprises: determining a maximum of the first number of symbol periods and the second number of symbol periods. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, receiving configuration information that configures the UE to transmit the A-SRS within at least one symbol index of a plurality of different symbol indexes of a TTI, wherein transmitting the A-SRS in the SRS resource of the second TTI further comprises: transmitting the A-SRS within at least one symbol period of the second TTI corresponding to the at least one symbol index, wherein a number of symbol periods between the at least one symbol period of the second TTI and the control channel of the first TTI meets or exceeds the maximum. 
     Some examples of the method, apparatus, and non-transitory computer-readable medium described above may further include processes, features, means, or instructions for transmitting capability information indicating the first number of symbol periods and the second number of symbol periods. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, the first number of symbol periods and the second number of symbol periods may be a specified capability of the UE. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, identifying the second TTI comprises: determining that the second TTI and the first TTI may be a same TTI. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, identifying the second TTI comprises: identifying the second TTI based at least in part on a maximum of a channel state information reference signal (CSIRS) gap and a UE capability delay. 
     Some examples of the method, apparatus, and non-transitory computer-readable medium described above may further include processes, features, means, or instructions for processing a use-case indication that indicates whether the A-SRS may be associated with a channel state information reference signal (CSIRS). 
     A method of wireless communication is described. The method may include transmitting, within a first transmission time interval (TTI), a grant triggering a UE to transmit an A-SRS, identifying offset information indicating a TTI offset relative to the grant, determining a second TTI for the A-SRS based at least in part on the TTI offset, and monitoring an SRS resource of the second TTI for the A-SRS. 
     An apparatus for wireless communication is described. The apparatus may include means for transmitting, within a first TTI, a grant triggering a UE to transmit an A-SRS, means for identifying offset information indicating a TTI offset relative to the grant, means for determining a second TTI for the A-SRS based at least in part on the TTI offset, and means for monitoring an SRS resource of the second TTI for the A-SRS. 
     Another apparatus for wireless communication is described. The apparatus may include a processor, memory in electronic communication with the processor, and instructions stored in the memory. The instructions may be operable to cause the processor to transmit, within a first TTI, a grant triggering a UE to transmit an A-SRS, identify offset information indicating a TTI offset relative to the grant, determine a second TTI for the A-SRS based at least in part on the TTI offset, and monitor an SRS resource of the second TTI for the A-SRS. 
     A non-transitory computer-readable medium for wireless communication is described. The non-transitory computer-readable medium may include instructions operable to cause a processor to transmit, within a first TTI, a grant triggering a UE to transmit an A-SRS, identify offset information indicating a TTI offset relative to the grant, determine a second TTI for the A-SRS based at least in part on the TTI offset, and monitor an SRS resource of the second TTI for the A-SRS. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, transmitting configuration information to configure the UE to transmit the A-SRS within at least one symbol index of a plurality of different symbol indexes of a TTI, wherein monitoring the SRS resource of the second TTI for the A-SRS further comprises: monitoring at least one symbol period of the second TTI corresponding to the at least one symbol index for the A-SRS. 
     Some examples of the method, apparatus, and non-transitory computer-readable medium described above may further include processes, features, means, or instructions for transmitting, within the first TTI, downlink control information that includes the offset information, wherein the offset information indicates a delay corresponding to a number of TTIs occurring between receipt of the grant by the UE and when the UE may be instructed to transmit uplink data in accordance with the grant. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, the offset information corresponds to a TTI index following the delay, and wherein the second TTI corresponds to the TTI index. 
     Some examples of the method, apparatus, and non-transitory computer-readable medium described above may further include processes, features, means, or instructions for receiving capability information indicating a number of symbol periods between receipt of the grant by the UE and when the UE may be capable of transmitting uplink data in accordance with the grant, wherein the delay corresponds to the capability information. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, the delay corresponds to a specified capability information indicating a number of symbol periods between receipt of the grant by the UE and when the UE may be capable of transmitting uplink data in accordance with the grant. 
     Some examples of the method, apparatus, and non-transitory computer-readable medium described above may further include processes, features, means, or instructions for transmitting downlink control information in the first TTI that includes the offset information, wherein the grant indicates resources of a shared data channel allocated to the UE for transmission of uplink data, and wherein the offset information comprises a bit flag indicating whether the UE may be to use a first value for the TTI offset indicated in the downlink control information or a second semi-statically configured value for the TTI offset. 
     Some examples of the method, apparatus, and non-transitory computer-readable medium described above may further include processes, features, means, or instructions for transmitting downlink control information in the first TTI that includes the offset information, wherein the grant indicates resources of a shared data channel allocated to the UE for transmission of uplink data, and wherein the offset information comprises a bit sequence indicating that the TTI offset corresponds to a number of TTIs occurring between receipt of the grant by the UE and when the UE may be instructed to transmit uplink data in accordance with the grant. 
     Some examples of the method, apparatus, and non-transitory computer-readable medium described above may further include processes, features, means, or instructions for transmitting downlink control information in the first TTI that includes the offset information, wherein the grant indicates resources of a shared data channel allocated to the UE for transmission of uplink data, wherein the offset information comprises a bit flag indicating whether the UE may be to use a first value for the TTI offset indicated in the downlink control information or a second value for the TTI offset. 
     Some examples of the method, apparatus, and non-transitory computer-readable medium described above may further include processes, features, means, or instructions for transmitting control signaling semi-statically indicating a defined value, wherein the second value for the TTI offset may be a function of the first value for the TTI offset and the defined value. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, the first value indicates a gap in TTIs between the grant requesting the uplink data and transmission of the uplink data, and the second TTI may be a TTI occurring prior to a TTI corresponding to the first value. 
     Some examples of the method, apparatus, and non-transitory computer-readable medium described above may further include processes, features, means, or instructions for transmitting downlink control information in the first TTI that includes the offset information, wherein the grant indicates resources of a shared data channel allocated to the UE for reception of downlink data. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, the offset information comprises a bit sequence corresponding to a number of TTIs occurring between receipt of the grant by the UE and when the UE may be instructed to transmit uplink data in accordance with the grant. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, the bit sequence may be configured to jointly trigger transmission of a zero power CSIRS from the base station and transmission of the A-SPS from a UE. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, identifying the second TTI further comprises: identifying the second TTI as being offset from the first TTI by the TTI offset. 
     Some examples of the method, apparatus, and non-transitory computer-readable medium described above may further include processes, features, means, or instructions for receiving the A-SRS within the SRS resource of the second TTI. Some examples of the method, apparatus, and non-transitory computer-readable medium described above may further include processes, features, means, or instructions for generating a channel measurement based at least in part on the received A-SRS. Some examples of the method, apparatus, and non-transitory computer-readable medium described above may further include processes, features, means, or instructions for generating a frequency dependent scheduling decision based at least in part on the channel measurement. 
     Some examples of the method, apparatus, and non-transitory computer-readable medium described above may further include processes, features, means, or instructions for transmitting control signaling to semi-statically configure the UE with the offset information. 
     Some examples of the method, apparatus, and non-transitory computer-readable medium described above may further include processes, features, means, or instructions for transmitting downlink control information within the first TTI to dynamically configure the UE with the offset information. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, the UE may be preconfigured with the TTI offset. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, the SRS resource corresponds to a subset of symbol periods within the second TTI. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, identifying the second TTI comprises: determining that the TTI offset may be a zero TTI offset, wherein the second TTI and the first TTI may be a same TTI. 
     A method of wireless communication is described. The method may include transmitting, within a first TTI, a grant triggering a UE to transmit an A-SRS, identifying a second TTI based at least in part on a first number of symbol periods between receipt of the grant by the UE and when the UE is capable of transmitting uplink data, the first number of symbol periods meeting or being less than a difference between a number of symbol periods between an SRS resource of the second TTI and a control channel of the first TTI, and monitoring the SRS resource of the second TTI for the A-SRS. 
     An apparatus for wireless communication is described. The apparatus may include means for transmitting, within a first TTI, a grant triggering a UE to transmit an A-SRS, means for identifying a second TTI based at least in part on a first number of symbol periods between receipt of the grant by the UE and when the UE is capable of transmitting uplink data, the first number of symbol periods meeting or being less than a difference between a number of symbol periods between an SRS resource of the second TTI and a control channel of the first TTI, and means for monitoring the SRS resource of the second TTI for the A-SRS. 
     Another apparatus for wireless communication is described. The apparatus may include a processor, memory in electronic communication with the processor, and instructions stored in the memory. The instructions may be operable to cause the processor to transmit, within a first TTI, a grant triggering a UE to transmit an A-SRS, identify a second TTI based at least in part on a first number of symbol periods between receipt of the grant by the UE and when the UE is capable of transmitting uplink data, the first number of symbol periods meeting or being less than a difference between a number of symbol periods between an SRS resource of the second TTI and a control channel of the first TTI, and monitor the SRS resource of the second TTI for the A-SRS. 
     A non-transitory computer-readable medium for wireless communication is described. The non-transitory computer-readable medium may include instructions operable to cause a processor to transmit, within a first TTI, a grant triggering a UE to transmit an A-SRS, identify a second TTI based at least in part on a first number of symbol periods between receipt of the grant by the UE and when the UE is capable of transmitting uplink data, the first number of symbol periods meeting or being less than a difference between a number of symbol periods between an SRS resource of the second TTI and a control channel of the first TTI, and monitor the SRS resource of the second TTI for the A-SRS. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, transmitting configuration information to configure the UE to transmit the A-SRS within at least one symbol index of a plurality of different symbol indexes of a TTI, wherein monitoring the SRS resource of the second TTI for the A-SRS further comprises: monitoring the A-SRS within at least one symbol period of the second TTI corresponding to the at least one symbol index. 
     Some examples of the method, apparatus, and non-transitory computer-readable medium described above may further include processes, features, means, or instructions for receiving capability information indicating the first number of symbol periods. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, the grant indicates resources of a shared data channel allocated to the UE for reception of downlink data. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, identifying the second TTI further comprises: identifying the second TTI based at least in part on a second number of symbol periods between receipt of the grant by the UE and when the UE may be capable of receiving downlink data. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, identifying the second TTI further comprises: determining a maximum of the first number of symbol periods and the second number of symbol periods. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, transmitting configuration information to configure the UE to transmit the A-SRS within at least one symbol index of a plurality of different symbol indexes of a TTI, wherein monitoring the SRS resource of the second TTI for the A-SRS further comprises: monitoring the SRS resource of the second TTI for the A-SRS within at least one symbol period of the second TTI corresponding to the at least one symbol index, wherein a number of symbol periods between the at least one symbol period of the second TTI and the control channel of the first TTI meets or exceeds the maximum. 
     Some examples of the method, apparatus, and non-transitory computer-readable medium described above may further include processes, features, means, or instructions for receiving capability information indicating the first number of symbol periods and the second number of symbol periods. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, the first number of symbol periods and the second number of symbol periods respectively correspond to defined capability information of the UE. 
     Some examples of the method, apparatus, and non-transitory computer-readable medium described above may further include processes, features, means, or instructions for receiving the A-SRS within the SRS resource of the second TTI. Some examples of the method, apparatus, and non-transitory computer-readable medium described above may further include processes, features, means, or instructions for generating a channel measurement based at least in part on the received A-SRS. Some examples of the method, apparatus, and non-transitory computer-readable medium described above may further include processes, features, means, or instructions for generating a frequency dependent scheduling decision based at least in part on the channel measurement. 
     In some examples of the method, apparatus, and non-transitory computer-readable medium described above, identifying the second TTI comprises: determining that the second TTI and the first TTI may be a same TTI. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an example of a system for wireless communication in accordance with aspects of the present disclosure. 
         FIG. 2  illustrates an example of a wireless communications system in accordance with aspects of the present disclosure. 
         FIG. 3  illustrates an example of a transmission timing in accordance with aspects of the present disclosure. 
         FIG. 4  illustrates an example of a timeline in accordance with aspects of the present disclosure. 
         FIG. 5  illustrates an example of a timeline in accordance with aspects of the present disclosure. 
         FIG. 6  illustrates an example of a process flow that supports reference signal transmission and triggering in accordance with aspects of the present disclosure. 
         FIG. 7  illustrates an example of a process flow in accordance with aspects of the present disclosure. 
         FIGS. 8 through 10  show block diagrams of a device in accordance with aspects of the present disclosure. 
         FIG. 11  illustrates a block diagram of a system including a UE in accordance with aspects of the present disclosure. 
         FIGS. 12 through 14  show block diagrams of a device in accordance with aspects of the present disclosure. 
         FIG. 15  illustrates a block diagram of a system including a base station in accordance with aspects of the present disclosure. 
         FIGS. 16 through 21  illustrate methods for reference signal transmission and triggering in accordance with aspects of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The described techniques relate to improved methods, systems, devices, or apparatuses that support configuration of aperiodic sounding reference signal transmission and triggering. Generally, the described techniques provide for aperiodic triggering of a user equipment (UE) to transmit a sounding reference signal (SRS) in a transmission time interval (TTI) relative to a TTI in which the UE receives a grant of resources. In some examples, a UE may receive a grant that triggers the transmission of an aperiodic SRS, and the UE may identify offset information indicating a TTI offset between the TTI in which the triggering grant is received, and the TTI in which the aperiodic SRS is to be transmitted. In some examples, the TTI in which the aperiodic SRS is to be transmitted may be a function of the amount of time required by the UE to process a grant relative to when the UE is capable of transmitting in accordance with the grant. 
     In some examples, a UE may receive a downlink signal, such as a DCI transmission, and may transmit sounding reference signals (SRS) to a base station in reply. The DCI may include an uplink grant or a downlink grant, which may trigger the transmission of the SRS by the UE in a TTI that is determined relative to a TTI that includes the grant. A TTI may be a slot, a mini-slot, a frame, a subframe, or any collection of consecutive OFDM symbols, or any other time interval. The UE may send the SRS transmission aperiodically, such as in response to receiving downlink control information (DCI) from the base station. In some cases, the SRS may be transmitted within SRS resource in an earliest available transmission time interval (TTI) relative to when a grant is received, which may be as early as the same TTI that included the grant. 
     The base station may measure the received SRS to generate a channel estimate of a wireless channel between the base station and the UE, and may use the channel estimate when making frequency dependent scheduling decisions. For example, the base station may continue to schedule the UE in frequency resources in which the UE transmitted the SRS if the channel estimate is satisfactory, and may schedule the UE in different frequency resources if the channel estimate is unsatisfactory. 
     In some examples, a base station may configure a UE with particular resources within a given TTI on which to transmit aperiodic SRS. The UE may be configured via higher layer signaling (e.g., RRC signaling) or may be preconfigured with SRS resource, which may be one or more adjacent symbol periods located at the end of a TTI (e.g. the final symbol or symbols of a slot). The base station may transmit configuration information that includes one or more symbol indexes for identifying particular symbols periods within a TTI that are SRS resource in which the UE is transmit SRS. The UE may determine, utilizing an aperiodic SRS transmission configuration, in which slot to transmit the SRS on the designated SRS resource. 
     In some examples, the UE may transmit an SRS in an earliest available TTI relative to when a grant is received. The UE may determine the earliest available slot based at least in part on capability information for the UE. That is, when the UE receives DCI including a downlink grant, the UE may take some minimum amount of time (e.g., a first delay) to process the DCI that triggers the UE to transmit an SRS transmission, prior to transmitting the SRS transmission. In some examples, the UE may be able to process the DCI and transmit the SRS within the same slot in which the DCI is received. In some examples, it may take a UE one or more slots to process the DCI and the UE may transmit the SRS in the SRS resource of the next available slot after processing of the DCI is complete (e.g., the next slot index after the slot index in which the DCI is received). The UE may signal its capability information to its base station, or the base station may know default capability information for UEs operating within its wireless communication system. The base station may generate the DCI, and corresponding grant of resources, in accordance with the signaled or default capability information. The base station may determine, in accordance with the signaled or default capability information, an earliest TTI relative to the grant in which the UE is capable of transmitting SRS, and may monitor SRS resource of that TTI for an SRS transmission from the UE. 
     In some examples, the UE may transmit an SRS in an earliest available TTI, determined based on the capability information for the UE, after receiving an uplink grant that grants resources for the UE to transmit uplink data. That is, when the UE receives an uplink grant, the UE may take some minimum amount of time to process the uplink grant, prior to being capable of transmitting uplink data in accordance with the grant. In some examples, the base station may know the capability information for the UE and generate an uplink grant in accordance with when the UE is capable of transmitting uplink data relative to when the grant is received. The grant may allocate one or more TTIs to the UE, and the base station may monitor SRS resource of an earliest of the one or more allocated TTIs for an SRS transmission from the UE. In some examples, the earliest available TTI may be the same TTI in which the DCI is received, or may be a subsequent TTI. In some examples, the base station may not know the capability information for a UE. In such examples, the base station may utilize default capability information for determining a TTI when the UE is expected to transmit the SRS relative to when the grant is transmitted, and may monitor SRS resource of that slot for the SRS. 
     In some examples, the UE may identify a TTI offset relative to when the triggering grant is received for determining in which TTI to transmit the SRS. In some examples, DCI may include a bit flag to indicate whether to use a dynamic TTI offset (e.g., in DCI) or a semi-static offset (e.g., in RRC signaling), and the UE may process the bit flag to determine which offset to use. In some examples, the bit flag may indicate whether to use a dynamic TTI offset (e.g., in DCI) or a second offset that is a function of the dynamic TTI offset. In some examples, the UE may determine that the TTI offset is a zero TTI offset, and hence the SRS transmission may be in the same TTI in which the DCI is received. In some examples, the UE may determine that the TTI offset is one or more TTIs, and the UE may transmit the SRS in a TTI that is offset by one or more TTIs from a TTI that includes the grant. 
     Aspects of the disclosure are initially described in the context of a wireless communications system. The described techniques provide for aperiodic triggering of a UE to transmit an SRS in a TTI relative to a TTI in which the UE receives a grant of resources. Aspects of the disclosure are further illustrated by and described with reference to apparatus diagrams, system diagrams, and flowcharts that relate to configuration of aperiodic sounding reference signal transmission and triggering. 
       FIG. 1  illustrates an example of a wireless communications system  100  in accordance with various aspects of the present disclosure. The wireless communications system  100  includes base stations  105 , UEs  115 , and a core network  130 . In some examples, the wireless communications system  100  may be a Long-Term Evolution (LTE) network, an LTE-Advanced (LTE-A) network, an LTE-A Pro network, or a New Radio (NR) network. In some cases, wireless communications system  100  may support enhanced broadband communications, ultra-reliable (e.g., mission critical) communications, low latency communications, or communications with low-cost and low-complexity devices. 
     Base stations  105  may wirelessly communicate with UEs  115  via one or more base station antennas. Base stations  105  described herein may include or may be referred to by those skilled in the art as a base transceiver station, a radio base station, an access point, a radio transceiver, a NodeB, an eNodeB (eNB), a next-generation Node B or giga-nodeB (either of which may be referred to as a gNB), a Home NodeB, a Home eNodeB, or some other suitable terminology. Wireless communications system  100  may include base stations  105  of different types (e.g., macro or small cell base stations). The UEs  115  described herein may be able to communicate with various types of base stations  105  and network equipment including macro eNBs, small cell eNBs, gNBs, relay base stations, and the like. 
     Each base station  105  may be associated with a particular geographic coverage area  110  in which communications with various UEs  115  is supported. Each base station  105  may provide communication coverage for a respective geographic coverage area  110  via communication links  125 , and communication links  125  between a base station  105  and a UE  115  may utilize one or more carriers. Communication links  125  shown in wireless communications system  100  may include uplink transmissions from a UE  115  to a base station  105 , or downlink transmissions from a base station  105  to a UE  115 . Downlink transmissions may also be called forward link transmissions while uplink transmissions may also be called reverse link transmissions. 
     The geographic coverage area  110  for a base station  105  may be divided into sectors making up only a portion of the geographic coverage area  110 , and each sector may be associated with a cell. For example, each base station  105  may provide communication coverage for a macro cell, a small cell, a hot spot, or other types of cells, or various combinations thereof. In some examples, a base station  105  may be movable and therefore provide communication coverage for a moving geographic coverage area  110 . In some examples, different geographic coverage areas  110  associated with different technologies may overlap, and overlapping geographic coverage areas  110  associated with different technologies may be supported by the same base station  105  or by different base stations  105 . The wireless communications system  100  may include, for example, a heterogeneous LTE/LTE-A/LTE-A Pro or NR network in which different types of base stations  105  provide coverage for various geographic coverage areas  110 . 
     The term “cell” refers to a logical communication entity used for communication with a base station  105  (e.g., over a carrier), and may be associated with an identifier for distinguishing neighboring cells (e.g., a physical cell identifier (PCID), a virtual cell identifier (VCID)) operating via the same or a different carrier. In some examples, a carrier may support multiple cells, and different cells may be configured according to different protocol types (e.g., machine-type communication (MTC), narrowband Internet-of-Things (NB-IoT), enhanced mobile broadband (eMBB), or others) that may provide access for different types of devices. In some cases, the term “cell” may refer to a portion of a geographic coverage area  110  (e.g., a sector) over which the logical entity operates. 
     UEs  115  may be dispersed throughout the wireless communications system  100 , and each UE  115  may be stationary or mobile. A UE  115  may also be referred to as a mobile device, a wireless device, a remote device, a handheld device, or a subscriber device, or some other suitable terminology, where the “device” may also be referred to as a unit, a station, a terminal, or a client. A UE  115  may also be a personal electronic device such as a cellular phone, a personal digital assistant (PDA), a tablet computer, a laptop computer, or a personal computer. In some examples, a UE  115  may also refer to a wireless local loop (WLL) station, an Internet of Things (IoT) device, an Internet of Everything (IoE) device, or an MTC device, or the like, which may be implemented in various articles such as appliances, vehicles, meters, or the like. 
     Some UEs  115 , such as MTC or IoT devices, may be low cost or low complexity devices, and may provide for automated communication between machines (e.g., via Machine-to-Machine (M2M) communication). M2M communication or MTC may refer to data communication technologies that allow devices to communicate with one another or a base station  105  without human intervention. In some examples, M2M communication or MTC may include communications from devices that integrate sensors or meters to measure or capture information and relay that information to a central server or application program that can make use of the information or present the information to humans interacting with the program or application. Some UEs  115  may be designed to collect information or enable automated behavior of machines. Examples of applications for MTC devices include smart metering, inventory monitoring, water level monitoring, equipment monitoring, healthcare monitoring, wildlife monitoring, weather and geological event monitoring, fleet management and tracking, remote security sensing, physical access control, and transaction-based business charging. 
     Some UEs  115  may be configured to employ operating modes that reduce power consumption, such as half-duplex communications (e.g., a mode that supports one-way communication via transmission or reception, but not transmission and reception simultaneously). In some examples half-duplex communications may be performed at a reduced peak rate. Other power conservation techniques for UEs  115  include entering a power saving “deep sleep” mode when not engaging in active communications, or operating over a limited bandwidth (e.g., according to narrowband communications). In some cases, UEs  115  may be designed to support critical functions (e.g., mission critical functions), and a wireless communications system  100  may be configured to provide ultra-reliable communications for these functions. 
     In some cases, a UE  115  may also be able to communicate directly with other UEs  115  (e.g., using a peer-to-peer (P2P) or device-to-device (D2D) protocol). One or more of a group of UEs  115  utilizing D2D communications may be within the geographic coverage area  110  of a base station  105 . Other UEs  115  in such a group may be outside the geographic coverage area  110  of a base station  105 , or be otherwise unable to receive transmissions from a base station  105 . In some cases, groups of UEs  115  communicating via D2D communications may utilize a one-to-many (1:M) system in which each UE  115  transmits to every other UE  115  in the group. In some cases, a base station  105  facilitates the scheduling of resources for D2D communications. In other cases, D2D communications are carried out between UEs  115  without the involvement of a base station  105 . 
     Base stations  105  may communicate with the core network  130  and with one another. For example, base stations  105  may interface with the core network  130  through backhaul links  132  (e.g., via an S1 or other interface). Base stations  105  may communicate with one another over backhaul links  134  (e.g., via an X2 or other interface) either directly (e.g., directly between base stations  105 ) or indirectly (e.g., via core network  130 ). 
     The core network  130  may provide user authentication, access authorization, tracking, Internet Protocol (IP) connectivity, and other access, routing, or mobility functions. The core network  130  may be an evolved packet core (EPC), which may include at least one mobility management entity (MME), at least one serving gateway (S-GW), and at least one Packet Data Network (PDN) gateway (P-GW). The MME may manage non-access stratum (e.g., control plane) functions such as mobility, authentication, and bearer management for UEs  115  served by base stations  105  associated with the EPC. User IP packets may be transferred through the S-GW, which itself may be connected to the P-GW. The P-GW may provide IP address allocation as well as other functions. The P-GW may be connected to the network operators IP services. The operators IP services may include access to the Internet, Intranet(s), an IP Multimedia Subsystem (IMS), or a Packet-Switched (PS) Streaming Service. 
     At least some of the network devices, such as a base station  105 , may include subcomponents such as an access network entity, which may be an example of an access node controller (ANC). Each access network entity may communicate with UEs  115  through a number of other access network transmission entities, which may be referred to as a radio head, a smart radio head, or a transmission/reception point (TRP). In some configurations, various functions of each access network entity or base station  105  may be distributed across various network devices (e.g., radio heads and access network controllers) or consolidated into a single network device (e.g., a base station  105 ). 
     Wireless communications system  100  may operate using one or more frequency bands, typically in the range of 300 MHz to 300 GHz. Generally, the region from 300 MHz to 3 GHz is known as the ultra-high frequency (UHF) region or decimeter band, since the wavelengths range from approximately one decimeter to one meter in length. UHF waves may be blocked or redirected by buildings and environmental features. However, the waves may penetrate structures sufficiently for a macro cell to provide service to UEs  115  located indoors. Transmission of UHF waves may be associated with smaller antennas and shorter range (e.g., less than 100 km) compared to transmission using the smaller frequencies and longer waves of the high frequency (HF) or very high frequency (VHF) portion of the spectrum below 300 MHz. 
     Wireless communications system  100  may also operate in a super high frequency (SHF) region using frequency bands from 3 GHz to 30 GHz, also known as the centimeter band. The SHF region includes bands such as the 5 GHz industrial, scientific, and medical (ISM) bands, which may be used opportunistically by devices that can tolerate interference from other users. 
     Wireless communications system  100  may also operate in an extremely high frequency (EHF) region of the spectrum (e.g., from 30 GHz to 300 GHz), also known as the millimeter band. In some examples, wireless communications system  100  may support millimeter wave (mmW) communications between UEs  115  and base stations  105 , and EHF antennas of the respective devices may be even smaller and more closely spaced than UHF antennas. In some cases, this may facilitate use of antenna arrays within a UE  115 . However, the propagation of EHF transmissions may be subject to even greater atmospheric attenuation and shorter range than SHF or UHF transmissions. Techniques disclosed herein may be employed across transmissions that use one or more different frequency regions, and designated use of bands across these frequency regions may differ by country or regulating body. 
     In some cases, wireless communications system  100  may utilize both licensed and unlicensed radio frequency spectrum bands. For example, wireless communications system  100  may employ License Assisted Access (LAA), LTE-Unlicensed (LTE-U) radio access technology, or NR technology in an unlicensed band such as the 5 GHz ISM band. When operating in unlicensed radio frequency spectrum bands, wireless devices such as base stations  105  and UEs  115  may employ listen-before-talk (LBT) procedures to ensure a frequency channel is clear before transmitting data. In some cases, operations in unlicensed bands may be based on a CA configuration in conjunction with CCs operating in a licensed band (e.g., LAA). Operations in unlicensed spectrum may include downlink transmissions, uplink transmissions, peer-to-peer transmissions, or a combination of these. Duplexing in unlicensed spectrum may be based on frequency division duplexing (FDD), time division duplexing (TDD), or a combination of both. 
     In some examples, base station  105  or UE  115  may be equipped with multiple antennas, which may be used to employ techniques such as transmit diversity, receive diversity, multiple-input multiple-output (MIMO) communications, or beamforming. For example, wireless communications system  100  may use a transmission scheme between a transmitting device (e.g., a base station  105 ) and a receiving device (e.g., a UE  115 ), where the transmitting device is equipped with multiple antennas and the receiving devices are equipped with one or more antennas. MIMO communications may employ multipath signal propagation to increase the spectral efficiency by transmitting or receiving multiple signals via different spatial layers, which may be referred to as spatial multiplexing. The multiple signals may, for example, be transmitted by the transmitting device via different antennas or different combinations of antennas. Likewise, the multiple signals may be received by the receiving device via different antennas or different combinations of antennas. Each of the multiple signals may be referred to as a separate spatial stream, and may carry bits associated with the same data stream (e.g., the same codeword) or different data streams. Different spatial layers may be associated with different antenna ports used for channel measurement and reporting. MIMO techniques include single-user MIMO (SU-MIMO) where multiple spatial layers are transmitted to the same receiving device, and multiple-user MIMO (MU-MIMO) where multiple spatial layers are transmitted to multiple devices. 
     Beamforming, which may also be referred to as spatial filtering, directional transmission, or directional reception, is a signal processing technique that may be used at a transmitting device or a receiving device (e.g., a base station  105  or a UE  115 ) to shape or steer an antenna beam (e.g., a transmit beam or receive beam) along a spatial path between the transmitting device and the receiving device. Beamforming may be achieved by combining the signals communicated via antenna elements of an antenna array such that signals propagating at particular orientations with respect to an antenna array experience constructive interference while others experience destructive interference. The adjustment of signals communicated via the antenna elements may include a transmitting device or a receiving device applying certain amplitude and phase offsets to signals carried via each of the antenna elements associated with the device. The adjustments associated with each of the antenna elements may be defined by a beamforming weight set associated with a particular orientation (e.g., with respect to the antenna array of the transmitting device or receiving device, or with respect to some other orientation). 
     In one example, a base station  105  may use multiple antennas or antenna arrays to conduct beamforming operations for directional communications with a UE  115 . For instance, some signals (e.g. synchronization signals, reference signals, beam selection signals, or other control signals) may be transmitted by a base station  105  multiple times in different directions, which may include a signal being transmitted according to different beamforming weight sets associated with different directions of transmission. Transmissions in different beam directions may be used to identify (e.g., by the base station  105  or a receiving device, such as a UE  115 ) a beam direction for subsequent transmission and/or reception by the base station  105 . Some signals, such as data signals associated with a particular receiving device, may be transmitted by a base station  105  in a single beam direction (e.g., a direction associated with the receiving device, such as a UE  115 ). In some examples, the beam direction associated with transmissions along a single beam direction may be determined based at least in in part on a signal that was transmitted in different beam directions. For example, a UE  115  may receive one or more of the signals transmitted by the base station  105  in different directions, and the UE  115  may report to the base station  105  an indication of the signal it received with a highest signal quality, or an otherwise acceptable signal quality. Although these techniques are described with reference to signals transmitted in one or more directions by a base station  105 , a UE  115  may employ similar techniques for transmitting signals multiple times in different directions (e.g., for identifying a beam direction for subsequent transmission or reception by the UE  115 ), or transmitting a signal in a single direction (e.g., for transmitting data to a receiving device). 
     A receiving device (e.g., a UE  115 , which may be an example of a mmW receiving device) may try multiple receive beams when receiving various signals from the base station  105 , such as synchronization signals, reference signals, beam selection signals, or other control signals. For example, a receiving device may try multiple receive directions by receiving via different antenna subarrays, by processing received signals according to different antenna subarrays, by receiving according to different receive beamforming weight sets applied to signals received at a plurality of antenna elements of an antenna array, or by processing received signals according to different receive beamforming weight sets applied to signals received at a plurality of antenna elements of an antenna array, any of which may be referred to as “listening” according to different receive beams or receive directions. In some examples a receiving device may use a single receive beam to receive along a single beam direction (e.g., when receiving a data signal). The single receive beam may be aligned in a beam direction determined based at least in part on listening according to different receive beam directions (e.g., a beam direction determined to have a highest signal strength, highest signal-to-noise ratio, or otherwise acceptable signal quality based at least in part on listening according to multiple beam directions). 
     In some cases, the antennas of a base station  105  or UE  115  may be located within one or more antenna arrays, which may support MIMO operations, or transmit or receive beamforming. For example, one or more base station antennas or antenna arrays may be co-located at an antenna assembly, such as an antenna tower. In some cases, antennas or antenna arrays associated with a base station  105  may be located in diverse geographic locations. A base station  105  may have an antenna array with a number of rows and columns of antenna ports that the base station  105  may use to support beamforming of communications with a UE  115 . Likewise, a UE  115  may have one or more antenna arrays that may support various MIMO or beamforming operations. 
     In some cases, wireless communications system  100  may be a packet-based network that operate according to a layered protocol stack. In the user plane, communications at the bearer or Packet Data Convergence Protocol (PDCP) layer may be IP-based. A Radio Link Control (RLC) layer may in some cases perform packet segmentation and reassembly to communicate over logical channels. A Medium Access Control (MAC) layer may perform priority handling and multiplexing of logical channels into transport channels. The MAC layer may also use hybrid automatic repeat request (HARQ) to provide retransmission at the MAC layer to improve link efficiency. In the control plane, the Radio Resource Control (RRC) protocol layer may provide establishment, configuration, and maintenance of an RRC connection between a UE  115  and a base station  105  or core network  130  supporting radio bearers for user plane data. At the Physical (PHY) layer, transport channels may be mapped to physical channels. 
     In some cases, UEs  115  and base stations  105  may support retransmissions of data to increase the likelihood that data is received successfully. HARQ feedback is one technique of increasing the likelihood that data is received correctly over a communication link  125 . HARQ may include a combination of error detection (e.g., using a cyclic redundancy check (CRC)), forward error correction (FEC), and retransmission (e.g., automatic repeat request (ARQ)). HARQ may improve throughput at the MAC layer in poor radio conditions (e.g., signal-to-noise conditions). In some cases, a wireless device may support same-slot HARQ feedback, where the device may provide HARQ feedback in a specific slot for data received in a previous symbol in the slot. In other cases, the device may provide HARQ feedback in a subsequent slot, or according to some other time interval. 
     Time intervals in LTE or NR may be expressed in multiples of a basic time unit, which may, for example, refer to a sampling period of T s =1/30,720,000 seconds. Time intervals of a communications resource may be organized according to radio frames each having a duration of 10 milliseconds (ms), where the frame period may be expressed as T f =307,200 T s . The radio frames may be identified by a system frame number (SFN) ranging from 0 to 1023. Each frame may include 10 subframes numbered from 0 to 9, and each subframe may have a duration of 1 ms. A subframe may be further divided into 2 slots each having a duration of 0.5 ms, and each slot may contain 6 or 7 modulation symbol periods (e.g., depending on the length of the cyclic prefix prepended to each symbol period). Excluding the cyclic prefix, each symbol period may contain 2048 sampling periods. In some cases, a subframe may be the smallest scheduling unit of the wireless communications system  100 , and may be referred to as a transmission time interval (TTI). In other cases, a smallest scheduling unit of the wireless communications system  100  may be shorter than a subframe or may be dynamically selected (e.g., in bursts of shortened TTIs (sTTIs) or in selected component carriers using sTTIs). 
     In some wireless communications systems, a slot may further be divided into multiple mini-slots containing one or more symbols. In some instances, a symbol of a mini-slot or a mini-slot may be the smallest unit of scheduling. Each symbol may vary in duration depending on the subcarrier spacing or frequency band of operation, for example. Further, some wireless communications systems may implement slot aggregation in which multiple slots or mini-slots are aggregated together and used for communication between a UE  115  and a base station  105 . 
     The term “carrier” refers to a set of radio frequency spectrum resources having a defined physical layer structure for supporting communications over a communication link  125 . For example, a carrier of a communication link  125  may include a portion of a radio frequency spectrum band that is operated according to physical layer channels for a given radio access technology. Each physical layer channel may carry user data, control information, or other signaling. A carrier may be associated with a pre-defined frequency channel (e.g., an E-UTRA absolute radio frequency channel number (EARFCN)), and may be positioned according to a channel raster for discovery by UEs  115 . Carriers may be downlink or uplink (e.g., in an FDD mode), or be configured to carry downlink and uplink communications (e.g., in a TDD mode). In some examples, signal waveforms transmitted over a carrier may be made up of multiple sub-carriers (e.g., using multi-carrier modulation (MCM) techniques such as OFDM or DFT-s-OFDM). 
     The organizational structure of the carriers may be different for different radio access technologies (e.g., LTE, LTE-A, LTE-A Pro, NR, etc.). For example, communications over a carrier may be organized according to TTIs or slots, each of which may include user data as well as control information or signaling to support decoding the user data. A carrier may also include dedicated acquisition signaling (e.g., synchronization signals or system information, etc.) and control signaling that coordinates operation for the carrier. In some examples (e.g., in a carrier aggregation configuration), a carrier may also have acquisition signaling or control signaling that coordinates operations for other carriers. 
     Physical channels may be multiplexed on a carrier according to various techniques. A physical control channel and a physical data channel may be multiplexed on a downlink carrier, for example, using time division multiplexing (TDM) techniques, frequency division multiplexing (FDM) techniques, or hybrid TDM-FDM techniques. In some examples, control information transmitted in a physical control channel may be distributed between different control regions in a cascaded manner (e.g., between a common control region or common search space and one or more UE-specific control regions or UE-specific search spaces). 
     A carrier may be associated with a particular bandwidth of the radio frequency spectrum, and in some examples the carrier bandwidth may be referred to as a “system bandwidth” of the carrier or the wireless communications system  100 . For example, the carrier bandwidth may be one of a number of predetermined bandwidths for carriers of a particular radio access technology (e.g., 1.4, 3, 5, 10, 15, 20, 40, or 80 MHz). In some examples, each served UE  115  may be configured for operating over portions or all of the carrier bandwidth. In other examples, some UEs  115  may be configured for operation using a narrowband protocol type that is associated with a predefined portion or range (e.g., set of subcarriers or RBs) within a carrier (e.g., “in-band” deployment of a narrowband protocol type). 
     In a system employing MCM techniques, a resource element may consist of one symbol period (e.g., a duration of one modulation symbol) and one subcarrier, where the symbol period and subcarrier spacing are inversely related. The number of bits carried by each resource element may depend on the modulation scheme (e.g., the order of the modulation scheme). Thus, the more resource elements that a UE  115  receives and the higher the order of the modulation scheme, the higher the data rate may be for the UE  115 . In MIMO systems, a wireless communications resource may refer to a combination of a radio frequency spectrum resource, a time resource, and a spatial resource (e.g., spatial layers), and the use of multiple spatial layers may further increase the data rate for communications with a UE  115 . 
     Devices of the wireless communications system  100  (e.g., base stations  105  or UEs  115 ) may have a hardware configuration that supports communications over a particular carrier bandwidth, or may be configurable to support communications over one of a set of carrier bandwidths. In some examples, the wireless communications system  100  may include base stations  105  and/or UEs that can support simultaneous communications via carriers associated with more than one different carrier bandwidth. 
     Wireless communications system  100  may support communication with a UE  115  on multiple cells or carriers, a feature which may be referred to as carrier aggregation (CA) or multi-carrier operation. A UE  115  may be configured with multiple downlink CCs and one or more uplink CCs according to a carrier aggregation configuration. Carrier aggregation may be used with both FDD and TDD component carriers. 
     In some cases, wireless communications system  100  may utilize enhanced component carriers (eCCs). An eCC may be characterized by one or more features including wider carrier or frequency channel bandwidth, shorter symbol duration, shorter TTI duration, or modified control channel configuration. In some cases, an eCC may be associated with a carrier aggregation configuration or a dual connectivity configuration (e.g., when multiple serving cells have a suboptimal or non-ideal backhaul link). An eCC may also be configured for use in unlicensed spectrum or shared spectrum (e.g., where more than one operator is allowed to use the spectrum). An eCC characterized by wide carrier bandwidth may include one or more segments that may be utilized by UEs  115  that are not capable of monitoring the whole carrier bandwidth or are otherwise configured to use a limited carrier bandwidth (e.g., to conserve power). 
     In some cases, an eCC may utilize a different symbol duration than other CCs, which may include use of a reduced symbol duration as compared with symbol durations of the other CCs. A shorter symbol duration may be associated with increased spacing between adjacent subcarriers. A device, such as a UE  115  or base station  105 , utilizing eCCs may transmit wideband signals (e.g., according to frequency channel or carrier bandwidths of 20, 40, 60, 80 MHz, etc.) at reduced symbol durations (e.g., 16.67 microseconds). A TTI in eCC may consist of one or multiple symbol periods. In some cases, the TTI duration (that is, the number of symbol periods in a TTI) may be variable. 
     Wireless communications systems such as an NR system may utilize any combination of licensed, shared, and unlicensed spectrum bands, among others. The flexibility of eCC symbol duration and subcarrier spacing may allow for the use of eCC across multiple spectrums. In some examples, NR shared spectrum may increase spectrum utilization and spectral efficiency, specifically through dynamic vertical (e.g., across frequency) and horizontal (e.g., across time) sharing of resources. 
     In some examples, a base station  105  may transmit downlink control information (DCI) that includes a downlink grant, or an uplink grant for a UE  115 , and in response the UE  115  may transmit an SRS to the base station  105 . The timing of when the UE  115  sends the SRS transmission may be relative to a TTI in which the UE  115  receives the DCI, and may be a function of how long it takes the UE  115  to process the DCI before the UE  115  is capable of transmitting in response to the DCI. In some examples, the UE  115  may transmit the SRS on SRS resource in an earliest TTI following a TTI in which the grant is received, which may be as early as the same TTI that included the grant. In some examples, the transmission timing of the SRS may be identified based on TTI offset information. The UE may be preconfigured with the TTI offset information, or the TTI offset information may be received via RRC signaling, or included in DCI. The UE may process the TTI offset information for determining a TTI offset, and may use the TTI offset to determine in which TTI to transmit the SRS relative to the TTI in which the grant is received. 
     In some cases, a UE  115  may signal its capabilities to the base station  105 , or the base station  105  may be aware of default UE capabilities for UEs operating within wireless communications system  100 . The base station  105  may determine in which TTI to instruct the UE  115  to transmit uplink data, or to receive downlink data, and generate a grant accordingly. The base station  105  may also identify, based on the signaled UE capabilities or default capabilities, in which TTI the UE  115  is expected to transmit the SRS relative to the grant. The base station  105  may monitor SRS resource of the expected TTI for the SRS. Beneficially, a UE  115  may be configured to transmit an SRS at an earlier or earliest available TTI following the reception of DCI. 
       FIG. 2  illustrates an example of a wireless communications system  200  in accordance with various aspects of the present disclosure. In some examples, wireless communications system  200  may implement aspects of wireless communications system  100 . In some examples, the transmission timing of an aperiodic SRS may be triggered by the reception of an uplink grant or a downlink grant. 
     In some cases, an aperiodic SRS may be transmitted on SRS resource in an earliest available TTI following a triggering grant. For example, base station  105 - a  may communicate with various devices within a geographic coverage area  110 - a . Base station  105 - a  may communicate with UE  115 - a  via bidirectional link  205 . Base station  105 - a  may transmit a downlink signal  210  via bidirectional link  205 . In some examples, downlink signal  210  may include DCI. DCI may include a downlink grant or an uplink grant, and additional information regarding the timing of subsequent transmissions. For instance, the DCI included in downlink signal  210  may include TTI offset information (e.g., slot offset information), indicating zero or more TTI subsequent to the reception of downlink signal  210  in which the UE  115 - a  is to transmit an uplink signal  215  that includes an aperiodic SRS. Base station  105 - a  may perform channel estimation using the received SRS, and may generate frequency dependent scheduling decisions based on the channel estimation. 
     An aperiodic SRS transmission configuration may allow a UE to transmit an SRS at a minimum timing, based on the capability information for a UE (e.g., processing capabilities) of UE  115 - a . For example, UE  115 - a  may receive a DCI signal and may be capable of processing the received DCI and transmitting a corresponding SRS within some minimum amount of time. Additionally, an aperiodic SRS transmission configuration may account for the differences in triggering, signaling, and timing constraints based on the capability information for UE  115 - a  when a DCI includes a downlink grant, as well as when DCI includes an uplink grant. In some cases, the minimum amount of processing time used by UE  115 - a  may differ based on whether UE  115 - a  receives a downlink grant or an uplink grant on downlink signal  210 . In some examples, determining when to transmit the SRS may vary based on the different minimum processing times. 
     In some examples, the base station  105 - a  may configure UE  115 - a  with particular resources within a given TTI on which to transmit aperiodic SRS. For example, UE  115 - a  may be configured via higher layer signaling (e.g., RRC signaling) indicate that an SRS resource may be located at the end of a TTI (e.g. the final symbol or symbols of a slot). 
     In some examples, UE  115 - a  may transmit an SRS in an earliest available slot after receiving a downlink grant. The earliest available slot may be a function of the capabilities of the UE  115 - a . That is, when UE  115 - a  receives a downlink grant, UE  115 - a  may take some minimum amount of time (e.g., a first delay including a first number of symbol periods) to process the downlink grant prior to transmitting an SRS. In some examples, the UE may be able to transmit the SRS using SRS resource within the same slot in which the DCI is received, or may take longer to process the DCI and transmit the SRS within SRS resource of a subsequent slot (e.g., the next slot index after the slot index in which the DCI is received). In some examples, UE  115 - a  may transmit capability information, indicating the number of symbol periods between receipt of a grant and when UE  115 - a  is capable of transmitting uplink data in accordance with the grant. Base station  105 - a  may receive the capability information, and may instruct the UE  115 - a  in the DCI to transmit the SRS in the SRS resource of the first slot in which the UE  115 - a  is capable of transmitting the SRS. 
     In some examples, UE  115 - a  may transmit an SRS in an earliest available slot after a receiving triggering uplink grant, in accordance with the capability information for UE  115 - a . When UE  115 - a  receives an uplink grant, UE  115 - a  may take some minimum amount of time (e.g., one or more symbol periods) to process the uplink grant, prior to being capable to transmit uplink data and/or an SRS In some examples, UE  115 - a  may transmit capability information to base station  105 - a , and base station  105 - a  may determine when the UE  115 - a  is capable of transmitting uplink data and/or an SRS relative to when a grant is received. Receipt of the grant may trigger the UE  115 - a  to transmit the SRS in an earliest available slot relative to when the UE  115 - a  receives the grant. The base station  105 - a  may monitor SRS resource of the earliest available slot and receive the SRS transmission in the SRS resource of that slot. The earliest available slot may be the same slot in which the DCI is received, or a subsequent slot. 
     In some examples, base station  105 - a  may not know the capability information for UE  115 - a . In such examples, base station  105 - a  may assume specified capability information (e.g., a default capability) for how long it takes for the UE  115 - a  to transmit an SRS relative to when a grant is received. For example, base station  105 - a  may determine a maximum of the delay of how long it takes a UE  115 - a  to process a downlink grant and when the UE  115 - a  is capable of receiving downlink data, and the delay of how long it takes a UE  115 - a  to process an uplink grant and when the UE  115 - a  capable of transmitting uplink data. The base station  105 - a  may determine, based on the specified capability information, a number of zero or more slots between when the UE  115 - a  receives a grant and when the UE is capable of transmitting uplink data in accordance with the grant. The base station  105 - a  may then generate a grant to instruct the UE  115 - a  to transmit uplink data in accordance with the grant based on the determined number of slots. The UE  115 - a  may transmit the SRS in SRS resource of a first of the slots in which the UE  115 - a  is granted resources to transmit uplink data and/or to receive downlink data. 
     In some examples, UE  115 - a  may identify a slot offset relative to when the triggering grant is received. In some examples, a DCI including an uplink grant may indicate a slot offset between the slot in which the DCI is received, and the slot in which the SRS is to be transmitted. In some examples, the slot offset may be indicated during higher layer signaling (e.g., RRC signaling), or the UE  115 - a  may be preconfigured with the slot offset. UE  115 - a  may utilize the slot offset to determine in which slot to transmit the SRS. For example, UE  115 - a  may determine to transmit the SRS in configured SRS resource in the same slot in which the grant allocates resources to the UE  115 - a  for transmission of uplink data, in a slot occurring one or more slots after a slot in which the grant allocates resources to the UE  115 - a  for transmission of uplink data, or in a slot occurring one or more slots before the slot in which the grant allocates resources to the UE  115 - a  for transmission of uplink data. 
     In some examples, the DCI including an uplink grant may include a bit sequence. The bit sequence may indicate the timing of uplink transmission and offset information to indicate a slot offset. The bit sequence may include bit flag, or the bit flag may be a bit in addition to the bit sequence. The bit flag having a first value (e.g., bit having a value of zero) may indicate to use a dynamic slot offset indicated in DCI and a second value (e.g., bit having a value of one) to indicate to use a semi-static slot offset configured via RRC signaling. In another example, the bit flag may have a first value (e.g., bit having a value of zero) to indicate to use the dynamic slot offset, and a second value (e.g., bit having a value of one) indicating to use a different slot offset that is a function of the dynamic slot offset (e.g., slot immediately prior to or immediately after slot corresponding to the dynamic slot offset). In some examples, instead of adding a bit flag to the DCI, one of the bits of the bit sequence may be repurposed and used as the bit flag, and fewer bits may be available for indicating the timing of an uplink transmission. 
     In some examples, some types of DCI conventionally may not include the bit sequence. For example, typically a downlink DCI does not include such a bit sequence for indicating the timing of an uplink transmission. In such examples, DCI may include an additional field with a bit sequence indicating the timing of an uplink transmission, similar to the discussion of uplink DCI, as described above. The bit sequence may also include a bit flag, as described herein. 
     Some examples of wireless communications system  100  may support SRS transmission timing that is related to HARQ transmission timing and data transmission timing. These transmission timings may be a function of the capabilities of UE  115 .  FIG. 3  illustrates an example of a transmission timing  300  in accordance with various aspects of the present disclosure. Techniques used in transmission timing  300  may be implemented by a UE  115  and a base station  105 , which may be examples of corresponding devices as described with reference to wireless communications systems  100  and  200 . 
     A wireless communications system may support wireless communications, such as new radio (NR) (e.g., 5G). In such a system, a slot may include a control channel  305 , such as controls channels  305 - a  and  305 - b  depicted in slot n and slot n+1, and a shared data channel, corresponding to a remaining one or more symbol periods of a particular slot. The depicted slots are examples of TTIs. Control channel  305  may include DCI that includes a grant of resources to the UE  115  and the control channel  305  may be located in a beginning portion of a slot. In an example, a slot may have 14 symbol periods with a slot index ranging from zero to thirteen, and the control channel  305  may be the first one or more symbol periods of the slot (e.g., symbols corresponding to slot index (SI) 0 and SI 1). 
     UE  115  may support transmission of an SRS on SRS resource  315  of a slot. SRS resource  315  may be located in a last portion of a slot (e.g., SI 13 of slot n) and the SRS resource  315  may span a set of one or more adjacent symbols (e.g., 1, 2, or 4 adjacent symbols). In some examples, SRS resource  315  may correspond to up to 4 ports for every SRS resource. In some cases, all ports of an SRS resource may be sounded in each symbol. 
     The transmission of SRS may be aperiodic, and may be triggered by reception of DCI in control channel  305 , which may carry DCI that includes a downlink grant. In some examples, SRS transmissions may be semi-persistent or periodic, and may be wideband transmissions or subband transmissions. In some cases, SRS bandwidths may be multiples of 4 physical resource blocks (PRB). 
     In some examples, a wireless communications system (e.g., NR) may support various configurations at the UE  115 . For example, the wireless communications system may support switching between partial bands for SRS transmission on a component carrier (CC). Switching may be supported when UE  115  is not capable of simultaneous transmission on partial bands in the CC. In some examples, a partial band may be defined as a bandwidth part. UE  115  may be configured with multiple resources, which may be grouped based on use cases. For example, resource grouping may be different for channel state information (CSI) acquisition, uplink non-codebook precoding, or uplink analog beamforming. In some examples, the wireless communications system may support SRS transmission where numerologies may be configurable for a specific UE or a group of UEs. In some examples, the wireless communications system may support SRS antenna switching within a carrier. 
     SRS transmissions and other uplink transmissions may be determined based on capability information for a UE  115 . That is, capability information for UE  115  may include minimum processing times in terms of symbols together with absolute time (in micro seconds (μs)). For example, UE  115  may utilize a specified number of OFDM symbols (e.g., minimum number of symbols) to process a physical downlink grant. This minimum number of OFDM symbols may be referred to as a first delay, or as N 0 . N 0  may span from the end of a control channel that includes a downlink grant for UE  115  to the beginning of resource of a shared data channel, such as a physical downlink shared channel (PDSCH), allocated to the UE  115  in the downlink grant. In some cases, a UE  115  may utilize a specified number of OFDM symbols (e.g., minimum number) for processing a PDSCH. This specified number of OFDM symbols may be referred to as a second delay, or as N 1 . N 1  may span from the end of control channel  305 , which may include a downlink signal, received on a PDSCH to the earliest possible beginning of a corresponding uplink ACK/NACK from the perspective of UE  115 . 
     UE  115  may utilize a specified number of OFDM symbols (e.g., minimum number) for processing a physical downlink control channel. This specified number of OFDM symbols may be referred to as a third delay, or as N 2 . N 2  may span from the end of a PDCCH containing an uplink grant to the earliest possible transmission of uplink data  325  by the UE  115  on a shared data channel, such as a physical uplink shared channel (PUSCH). In some examples, N 1  and N 2  may or may not include a timing advance (TA). In some examples, a base station  105  may not expect to receive an uplink transmission if a slot offset between receiving a DCI transmission at UE  115  and the transmission of a scheduled uplink transmission does not satisfy capability information for UE  115  (e.g., does not satisfy one or both of N 0  and N 2 ). 
     In some examples, SRS transmissions and other uplink transmissions may be determined based on one or more timing relationships. Timing relationships may be defined by a slot offset. For example, a delay in slots may occur between reception of a DL grant in control channel  305 - a  and reception of corresponding downlink data  310  on a shared data channel (e.g., a PDSCH data). This delay may be known as slot offset K 0 . In some examples, a delay in slots may occur between reception downlink data (e.g., PDSCH data) by UE  115  and when the UE  115  transmits a corresponding uplink ACK/NACK. This delay may be known as slot offset K 1 . A delay may occur between reception of an uplink grant in control channel  305  by UE  115  and when the UE  115  transmits uplink data  325  on a shared data channel (e.g., PUSCH data) in accordance with the grant. This delay may be referred to as slot offset K 2 . In some examples, a delay in slots may occur between when a base station  105  receives an ACK/NACK signal corresponding to downlink data previously transmitted to UE  115 , and retransmits the downlink data corresponding to the ACK/NACK signal. This delay may be referred to as a slot offset K 3 . Slot offsets as described above may be utilized in cases where, for example, a UE is configured with a single numerology with slot-level scheduling and a single transmit power transmission. 
     In some examples, indications of one or more slot offsets may be included in a DCI transmission. For example, as described in greater detail with respect to  FIG. 5 , UE  115  may receive a bit sequence including an indication of slot offset K 2 . Additionally, or alternatively, UE  115  may be preconfigured or configured via higher layer signaling (RRC signaling) to know a default value of slot offset K 2 . In some examples, UE  115  may determine which SRS resource to utilize for transmitting an SRS relative to when a grant is received based at least in part on a slot offset (e.g., K 2 ). 
     In some cases, a wireless communications system may support a minimum value of K 0  such that downlink assignments and scheduled uplink or downlink data transmissions may occur within the same slot. For example, UE  115  may receive a downlink grant in control channel  305 - a  in slot n. If UE  115  has the capability to do so, UE  115  may receive downlink data  310  in one or more symbol periods following the end of control channel  305 . In such a case, K 0 =0, and UE  115  may receive downlink data  310  in the same slot n as control channel  305 - a  that includes the downlink grant. In some examples, if UE  115  has the capability, UE  115  may receive downlink data  310  and transmit uplink ACK/NACK within the same slot n. In such examples, K 1 =0. Similarly, if UE  115  has sufficient processing capabilities, UE  115  may receive an uplink grant in control channel  305 - b  in slot n+1, and may transmit uplink data  325  within the same slot n+1. In such cases, K 2 =0. 
     An aperiodic SRS transmission configuration may specify a minimum timing between receiving DCI and transmitting aperiodic SRS. In some cases, the base station  105  may or may not know the capabilities of UE  115 , and the aperiodic SRS transmission configuration may be determined accordingly. For example, a UE  115  may have established an RRC connection with base station  105  and initiated wireless communications, but the UE  115  may not yet have advertised its capability information to the base station  105 . Furthermore, an aperiodic SRS transmission configuration may be utilized to determine a minimum timing between DCI and SRS transmission when the DCI includes an uplink grant and when the DCI carries a downlink grant. 
     In some examples, an SRS transmission may be sent at an earliest available slot relative to a slot that includes a grant, based on the capability information of a UE  115  indicated to a base station  105 .  FIG. 4  illustrates an example of a timeline  400  in accordance with various aspects of the present disclosure. In some examples, timeline  400  may implement aspects of wireless communications system  100 . Techniques used in transmission timeline  400  may be implemented by a UE  115  and a base station  105 , which may be examples of corresponding devices as described with reference to wireless communications systems  100  and  200 . 
     Symbols of a slot, such as symbol  405 , may be indexed and scheduled across one or more slots (e.g., slot n, slot n+1, slot n+2, etc.). In  FIG. 4 , ‘u’ may represent an uplink symbol, ‘d’ may represent a downlink symbol, and ‘g’ may represent a guard period. In some examples, base station  105  may configure UE  115  with SRS resource, which may be located at the end of a slot. The SRS resource may be adjacent symbol periods, and may be located in the last symbol or symbols of a slot n. In some examples, SRS resource  415  may span 1 symbol, 2 symbols, or 4 symbols. UE  115  may receive a DCI, and may be expected to transmit the SRS in the SRS resource of the earliest available slot in accordance with the capability information of UE  115 . In some cases, base station  105  may transmit configuration information that configures UE  115  to transmit the aperiodic SRS within at least one symbol index of multiple symbol indexes of a slot. The at least one symbol index may correspond to the symbol periods defining the SRS resource  415  within a slot. 
     In some examples, a DCI  410  may include a grant of resources for UE  115 . The base station  105  may allocate resources to the UE  115  in the grant based on the signaled or specified (e.g., default) capability of the UE  115 . The UE  115  may be expected to transmit the SRS in the SRS resource of the first available slot relative to slot that includes the grant, given that enough time has passed according to the signaled or default capability of the UE  115 . 
     In an example, the signaled or default capability of the UE  115  may indicate that the UE  115  is capable of processing the DCI  410  in fewer than 14 symbol periods. The UE  115  may detect, within slot n, a grant in the DCI  410  that triggers the UE  115  to transmit an aperiodic SRS. The UE  115  may identify in which slot to transmit the SRS based on a first number of symbol periods between receipt of the grant by the UE  115  and when the UE  115  is capable of transmitting uplink data. The first number of symbol periods corresponds to the N 0  delay  420 , representing a minimum amount of symbol periods required by the UE  115  to process a downlink grant, in accordance with the signaled or default capability of the UE  115 , and receive downlink data in accordance with the downlink grant. In another example, the first number of symbol periods corresponds to N 2  delay  430  representing a minimum amount of symbol periods required by the UE  115  to process an uplink grant, in accordance with the signaled or default capability of the UE  115 , and transmit in accordance with the uplink grant. 
     In a first example, the UE  115  may signal its capability information to the base station  105 , and the base station  105  may use the capability information when generating DCI  410 - a  that includes a downlink grant for UE  115 . In an example, the base station  105  may process capability information received from the UE  115  for determining the N 0  delay  420 . In slot n, for example, N 0  delay  420 - a  may be less than difference  425 - a . Difference  425 - a  may represent a number of symbol periods between a first symbol period of SRS resource  415 - a , and a last symbol period of a control channel of slot n that includes DCI  410 - a . Base station  105  may identify, based on the capability information, that the UE  115  is capable of processing a grant and transmitting uplink data in a same slot (e.g., within slot n). The base station may generate a downlink grant in DCI  410 - a  that grants resources to the UE  115  in slot n for reception of downlink data. The UE  115  may process the DCI  410 , and identify that it is to transmit the SRS in SRS resource  415 - a  within the same slot that included the downlink grant in the DCI  410 - a . Thus, because N 0  delay  420 - a  is less than difference  425 - a , slot n is the earliest available slot, and the UE  115  may transmit the SRS in SRS resource  415 - a , instead of in a later slot, such as slot n+1. Base station  105  may monitor the SRS resource  415 - a  for an SRS transmitted by the UE  115 . 
     In another example, the capability information may indicate that N 0  delay  420 - b  is greater than difference  425 - a  but less than difference  425 - b , and hence the UE  115  may identify that it is to transmit the SRS in SRS resource  415 - b  within the next slot (e.g., slot n+1) which is after the slot that included the downlink grant in the DCI  410 - a . Base station  105  may monitor the SRS resource  415 - b  for an SRS transmitted by the UE  115 . The techniques described herein may applied for determining to transmit the SRS in subsequent slots for longer N 0  delays. 
     Slot n+2 corresponds to DCI  410 - b  that includes an uplink grant for UE  115 . The base station  105  may use the capability information received from UE  15  when generating DCI  410 - b  that includes the uplink grant for UE  115 . In an example, the base station  105  may process capability information received from the UE  115  for determining the N 2  delay  430 - a . Base station  105  may identify, based on the capability information, that the UE  115  is capable of processing a grant and transmitting uplink data in a same slot. In slot n+2, for example, N 2  delay  430 - a  may be less than difference  425 - c  (e.g., between last symbol period of control channel that includes DCI  410 - b  and a first symbol period of SRS resource  415 - c ), and hence the UE  115  may identify that it is to transmit the SRS in SRS resource  415 - c  within the same slot that included the uplink grant in the DCI  410 - b . Thus, slot n+2 is the earliest available slot, and the UE  115  transmits the SRS in SRS resource  415 - c , instead of in a later slot, such as slot n+3. Base station  105  may monitor the SRS resource  415 - c  for an SRS transmitted by the UE  115 . 
     In another example, N 2  delay  430 - b  may be greater than difference  425 - c  but less than difference  425 - d , and hence the UE  115  may identify that it is to transmit the SRS in SRS resource  415 - d  within the next slot (e.g., slot n+3) which is after slot n+2 that included the uplink grant in the DCI  410 - b . Base station  105  may monitor the SRS resource  415 - d  for an SRS transmitted by the UE  115 . The techniques described herein may applied for determining to transmit the SRS in subsequent slots for longer N 2  delays. 
     In some examples, the UE  115  may not yet have signaled its capability information to the base station  105 , and the base station  105  may use specified (e.g., default) capability information when generating DCI  410  that includes a downlink grant for UE  115 . In  FIG. 4 , for example, N 0  delay  420 - c  may represent a default N 0  delay and N 2  delay  430 - c  may represent a default N 2  delay. The UE  115  is expected to transmit the SRS in the SRS resource of the first available slot corresponding to the grant, given that enough time has passed according to a maximum of the default capability (e.g., maximum of N 0  delay and N 2  delay). In the depicted example, the larger delay is the N 2  delay  430 - c . In slot n, for example, N 2  delay  430 - c  may be larger than difference  425 - a  and smaller than difference  425 - b . Base station  105  may identify, based on the default capability information, that the UE  115  is capable of processing a grant and transmitting uplink data in the next slot (e.g., slot n+1) after the slot that includes DCI  410 - a  with the downlink grant. The UE  115  may identify that it is to transmit the SRS in SRS resource  415 - b  within the next slot (e.g., slot n+1) which is after the slot that included the downlink grant in the DCI  410 - a . Base station  105  may monitor the SRS resource  415 - b  for an SRS transmitted by the UE  115 . The techniques described herein may applied for determining to transmit the SRS in subsequent slots where a maximum of default capability is longer. 
     In some examples, triggering in which TTI the UE  115  transmits may be associated with a channel state information (CSI) reference signal (RS) and a CSIRS gap. In some cases, a specified (e.g., minimum) time interval, (e.g., N in unit of symbols) may occur between DCI triggering and A-SRS transmission, and may have a candidate value range that is the same as N 2 . In some examples, there may be a minimum time interval (e.g., 42 symbols) between reception of an aperiodic channel state information reference signal (A-CSIRS) and when the UE  115  is expected to update its A-SRS precoding. This minimum time interval may be referred to as a CSIRS gap. Prior to the CSIRS gap elapsing, the UE  115  is not expected to have updated its A-SRS precoding. 
     Triggering transmission of an SRS may take into account the minimum time interval (e.g., CSIRS gap) between when the associated CSIRS is transmitted and when transmission of the SRS occurs relative to a grant. In some examples, UE  115  and base station  105  may identify whether the SRS is associated with a CSIRS. When determining the earliest available slot to transmit SRS, the earliest available slot may be determined based on the CSIRS gap (e.g., the minimum time interval) and a UE capability delay (e.g., the N 0  and/or N 2  delay). For downlink transmission, the UE  115  and base station  105  may identify a maximum of the CSIRS gap and the UE capability delay (e.g., N 0  delay). The maximum may be the longer of the two in time or number of symbols. The maximum of the CSIRS gap and the UE capability delay may be used by the UE  115  and base station  105  for determining the earliest available slot (e.g., earliest available TTI) in which the SRS is to be communicated relative to the slot that includes the downlink grant, similar to the above discussion of determining in which SRS resource  415  the SRS is to be transmitted based on the N 0  delay. For uplink transmission, the UE  115  and base station  105  may identify a maximum of the CSIRS gap and the UE capability delay (e.g., the N 2  delay). The maximum of the CSIRS gap and the UE capability delay may be used by the UE  115  and base station  105  for determining the earliest available slot (e.g., earliest available TTI) in which the SRS is to be communicated relative to the slot that includes the uplink grant, similar to the above discussion of determining in which SRS resource  415  the SRS is to be transmitted based on the N 2  delay. In an example, a maximum between 42 symbols and an earliest available slot (e.g., earliest possible TTI) may be determined such that the UE capability (e.g., N 0  and/or N 2 ) is satisfied. 
     In some instances, an aperiodic SRS resource associated with a CSIRS may be an SRS resource corresponding to an uplink non-codebook precoding use-case, and may correspond to a use-case or use-case indication that follows (e.g., is equal to) uplink non-codebook precoding. DCI, for example, may include a use-case indication having a first value to indicate that the SRS resource is associated with a CSIRS, and a second value to indicate that the SRS resource is not associated with a CSIRS. The use-case indication may trigger whether the UE  115  is to use the maximum of the CSIRS delay and the N 0  delay and/or the N 2  delay, or the N 0  delay or the N 2  delay when determining in which TTI (e.g., slot) to transmit the SRS relative to a TTI that included the grant. 
     A transmission timing of an SRS relative to a grant received in DCI may be determined based on slot offset information. The slot offset information may be received in DCI, via RRC signaling, or may preconfigured at UE  115  and base station  105 .  FIG. 5  illustrates an example of a timeline  500  in accordance with various aspects of the present disclosure. In some examples, timeline  500  may implement aspects of wireless communications system  100 . Techniques used in timeline  500  may be implemented by a UE  115  and a base station  105 , which may be examples of corresponding devices as described with reference to wireless communications systems  100  and  200 . 
     The transmission timing of the SRS relative to a grant may be based on slot offset information. In some examples, base station  105  may transmit configuration information that configures UE  115  with an SRS resource  515  of a TTI. A TTI (e.g., slot) may be composed of a set of symbol periods and a set of symbol indexes may correspond to a respective symbol period in the set of symbol periods. The configuration information may identify, for example, a set of one or more symbol indexes to identify the SRS resource  515  within a slot. In  FIG. 5 , slot n may include 14 symbols and the configuration information may indicate that a symbol index corresponding to a last symbol period of the slot is to be used as the SRS resource  515 . The configuration information may identify more than one symbol index, and hence the SRS resource  515  may be more than one symbol period of a slot. 
     The timing of an SRS transmission relative to a grant may depend at least in part on whether the capability information for UE  115  is known at base station  105 . For example, if base station  105  knows the capability information of UE  115  (e.g., the amount of time or number of symbols utilized by UE  115  to process DCI  510 ), base station  105  may communicate slot offset information via RRC signaling or in DCI. The slot offset information may indicate information for identifying a slot offset (e.g., slot offset  525 ). The slot offset information may permit the UE  115  to determine in which slot to transmit SRS relative to a slot that includes DCI  510  having a grant of resources for the UE  115 . 
     In some examples, the base station  105  may configure the UE  115  with the slot offset information via RRC signaling. The slot offset information may indicate a slot offset, and the UE  115  may use the slot offset for determining in which slot to transmit an SRS relative a slot that includes a grant for the UE  115 . The slot offset information may indicate a slot offset of zero or more slots. For example, slot offset  520  may correspond to a zero slot offset  520 , a single slot offset  525 , and or a multi-slot offset  530  (e.g., a two slot offset). A slot offset configured via RRC signaling may be referred to as a semi-static slot offset. If, for example, DCI  510 - a  includes a grant of resources to the UE  115 , the UE  115  may identify the semi-static slot offset. For a zero slot offset, the UE  115  may transmit the SRS in SRS resource  515 - a  (e.g., in the same slot that included the grant). For a single slot offset, the UE  115  may transmit the SRS in SRS resource  515 - b  (e.g., in the next slot after the slot that included the grant). For a two slot offset, the UE  115  may transmit the SRS in SRS resource  515 - c  (e.g., in two slots after the slot that included the grant). The base station  105  that transmitted DCI  510 - a  knows the semi-static slot offset, and monitor for an SRS transmission in the SRS resource  515  corresponding to the semi-static slot offset. The techniques may be extended to a semi-static slot offset having any number slot offset. 
     In some examples, the base station  105  may configure the UE  115  with the slot offset information in DCI. Similar to the discussion provided above, the slot offset information in DCI may indicate in which slot the UE  115  is to transmit an SRS relative a slot that includes a grant for the UE  115 . In an example, the DCI  510  may include a grant of uplink resources and offset information indicating a slot index. The slot index may identify a slot in which the UE  115  is to transmit uplink data (e.g., slot index may follow a K2 value reported in DCI  510 ). The UE  115  may transmit the SRS in the SRS resource  515  of the slot corresponding to the same slot index indicated in DCI  510 . In an example, if DCI  510 - a  includes a grant of resources to the UE  115 , the offset information may include a slot index for a zero slot offset (e.g., in the same slot that included the grant), a one slot offset (e.g., in slot n+1 that is one slot after slot n that included the grant), or a two slot offset (e.g., in slot n+2 that is two slots after slot n that included the grant). The slot index may indicate additional offsets. As the UE  115  is configured with the location of the SRS resource  515  in each slot, the UE  115  may transmit the SRS in the slot corresponding to the slot index indicated in DCI  510 - a  (e.g., in one of SRS resource  515 - a ,  515 - b , or  515 - c ). Similarly, the base station  105  that transmitted DCI  510 - a  knows the offset information included in DCI  510 - a , and monitor for an SRS transmission in the SRS resource  515  corresponding to the offset information indicated in DCI  510 - a.    
     For DCI  510 - a  that includes a grant of resources to the UE  115  for transmission of uplink data, the offset information in DCI  510 - a  may be a bit sequence to indicate uplink timing. In some examples, the bit sequence may include three bits to indicate a K 2  offset relative to the slot that included the grant (e.g., a K 2  offset to indicate PUSCH timing). The UE  115  may transmit the SRS in the SRS resource  515  of the same slot indicated in the K 2  offset. For example, the base station  105  may set the K 2  offset in DCI  510 - a  as K2=1, to instruct the UE  115  to transmit uplink data in the next slot (e.g., slot n+1). The UE  115  may process the DCI  510 - a  in slot n to identify the K 2  offset, and transmit the SRS in SRS resource  515 - b  of slot n+1. In some examples, the UE  115  may transmit the SRS in the SRS resource  515  of slot occurring after the slot indicated in the K 2  offset. 
     In some examples, one of the bits in the bit sequence of DCI  510 - a  may be a bit flag, or the bit flag may be an additional bit that is in addition to the bit sequence. In some examples, instead of adding an addition 1-bit flag to a 3-bit sequence, the 3-bit sequence may be reduced to a 2-bit sequence (e.g., signal K 2  offset using the two bits), and the third bit may be repurposed as the above described 1-bit flag. 
     In some cases, the base station  105  may toggle the bit flag to indicate which slot offset of multiple slot offsets to use. In an example, the base station  105  may toggle the bit flag in DCI  510 - a  to indicate whether the UE  115  is to use a dynamic slot offset or a semi-static offset. If the UE  115  is to use a dynamic slot offset, the bit flag may have a first value (e.g., bit value of zero) indicating that the UE  115  is to use offset information included in DCI  510 - a  for identifying the dynamic slot offset. If the UE  115  is to use a semi-static slot offset, the bit flag may have a second value (e.g., bit value of one) indicating that the UE  115  is to use the semi-static slot offset received via RRC signaling. In an example, the dynamic slot offset be that the UE  115  is to transmit SRS in SRS resource of the same slot that includes a grant of resources for UE  115 , and the semi-static slot offset may be that the UE  115  is to transmit SRS in SRS resource of a slot occurring two slots after a slot is received that includes a grant of resources for UE  115 . In  FIG. 5 , for example, bit flag having a first value may instruct the UE  115  to transmit SRS in SRS resource  515 - a  (e.g., transmit SRS in the slot n that also includes the grant in DCI  510 - a ), and bit flag having a second value may instruct the UE  115  to transmit SRS in SRS resource  515 - c  (e.g., transmit SRS in slot n+2 occurring two slots after slot n that includes the grant in DCI  510 - a ). 
     The base station  105  may toggle the bit flag to indicate whether to use a dynamic slot offset or a second offset that is a function of the dynamic slot offset. For example, the bit flag having a first value (e.g., bit value of zero) for a TTI offset may be offset K 2  indicated in DCI  510 - a , and the bit flag having a second value (e.g., bit value of zero) for the TTI offset may be offset K 2  plus a constant offset c. In some cases, c may be a constant value from a set of integer values (e.g., −1 and 1). The value of c may be RRC configured, or may be configured by a media access control (MAC) control element (CE) transmitted by the base station  105  to the UE  115 . In some examples, the first value may indicate a gap in TTIs between the grant requesting the uplink data and transmission of the uplink data (e.g., indicate offset K 2 ), and the constant value c may be used to cause the UE  115  to transmit the SRS prior to or after the TTI in which the UE transmits uplink data (e.g., prior to or after TTI corresponding to offset K 2 . In some such examples, for slot offset K 2  is equal to slot offset  525  (e.g., to indicate slot n+1), then the 1 bit flag may indicate whether UE  115  should transmit the SRS at slot offset  520  in slot n (e.g., K 2 −1) or at slot offset  530  in slot n+2 (e.g., K 2 +1). The base station  105  may use the bit flag in DCI  510 - a  to control whether the UE  115  transmits SRS prior to, in the same, or in a subsequent slot, relative to the slot granting the UE  115  resources for transmitting uplink data (e.g., before or after slot corresponding to the slot indicated in the offset K 2 ). 
     Unlike an uplink grant, a downlink grant in DCI does not conventionally include bits for indicating PUSCH timing (e.g., offset K 2 ). To remedy this deficiency, in accordance with the examples described herein, the slot offset information may be communicated via RRC signaling. When the DCI  510 - a  includes a grant of downlink resources for the UE  115 , the UE  115  may determine a slot offset using slot offset information configured via RRC signaling (e.g., identify a semi-static slot offset), and determine which slot to use for transmitting the SRS relative to the slot that includes the grant. In an example, the semi-static slot offset may be that the UE  115  is to transmit SRS in SRS resource of a slot occurring in the next slot after a slot is received that includes a grant of resources for UE  115 . In  FIG. 5 , for example, the UE  115  may transmit SRS in SRS resource  515 - b  (e.g., transmit SRS in slot n+1 that is one slot after the slot that the grant in DCI  510 - a ). RRC signaling may be used to configure slot offset information corresponding to a semi-static slot offset that is one or more slots after the slot that includes the grant. 
     In some examples, DCI  510  that includes a downlink grant be configured to include a bit sequence similar to the bit sequence indicating the K 2  offset for PUSCH timing as described with respect to DCI that includes an uplink grant. The bit sequence may include, for example, up to 3 bits. One of the 3 bits may be configured as a 1-bit flag as described herein for toggling between a dynamic slot offset and a semi-static offset, or for toggling between a dynamic slot offset and a dynamic slot offset plus or minus a constant value. 
     In some examples, the DCI  510  may be a bit sequence that is a joint field for indicating transmission of a reference signal and for triggering the UE  115  to transmit SRS. For instance, DCI  510  may include a field for jointly indicating that the base station  105  is transmitting a zero power channel state information reference signal (ZP-CSIRS) and for triggering the UE  115  to transmit SRS. The bit sequence may include a set of bits (e.g., 1 to 3 bits) to indicate that the base station  105  is transmitting ZP-CSIRS, and for indicating offset information for identifying a slot offset. The UE  115  may process the bit sequence to determine that it is to monitor for the ZP-CSIRS transmitted by base station  105 , and to transmit an SRS in a slot relative to a slot that includes the DCI  510 . The UE  115  may determine in which slot to transmit the SRS in accordance with the techniques described herein. 
       FIG. 6  illustrates an example of a process flow  600  in accordance with various aspects of the present disclosure. In some examples, process flow  600  may implement aspects of wireless communications system  100 . Techniques used in process flow  600  may be implemented by a UE  115 - b  and a base station  105 - b , which may be examples of corresponding devices as described with reference to wireless communications systems  100  and  200 . 
     At  605 , base station  105 - b  transmits a triggering grant to UE  115 - b . The triggering grant may be an uplink grant or a downlink grant. The triggering grant may be included in a DCI transmission. At  610 , UE  115 - b  detects the triggering grant in a first TTI. The grant may trigger the UE to transmit an aperiodic SRS. 
     At  615 , UE  115 - b  identifies offset information indicating a TTI offset relative to the grant received at  605 . The offset information may be a TTI offset that is preconfigured at UE  115 - b , may be indicated via RRC signaling, or may be included in the same DCI transmission in which the triggering grant of  605  is received. In some cases, the offset information may be based on an uplink grant, and the time between the grant of  605  and the corresponding scheduled uplink transmission (e.g., K 2 ). In some cases, the offset information may be based on K 2  and some additional value (e.g., −1 or 1) indicating that the second TTI is previous to, equal to, or subsequent to K 2 . In some examples, the offset information is a bit sequence that may include a bit flag. 
     At  620 , UE  115 - b  determines a second TTI for transmitting the aperiodic SRS based at least in part on the TTI offset identified at  615 . UE  115 - b  may identify SRS resource that are located, for example, in the final 1, 2, or 4 symbols of a plurality of TTIs. The UE  115 - a  may determine the second TTI as being offset from the first TTI that included the grant by the TTI offset. In some examples, the TTI offset may be a zero TTI offset, and hence the second TTI and the first TTI may be the same TTI. Having identified the second TTI based on the offset information, UE  115 - b  may identify the SRS resource corresponding to the second TTI. 
     At  625 , base station  105 - b  may identify offset information indicating a TTI offset relative to the grant transmitted at  605 . Base station  105 - b  may identify offset information based on the same considerations as described with respect to UE  115 - b  at  615 , and with respect to  FIGS. 4-5 . At  630 , base station  105 - b  determines a second TTI for the aperiodic SRS based at least in part on the TTI offset. Base station  105 - b  may determine the second TTI based on the same considerations as described with respect to UE  115 - b  at  620 , and with respect to  FIGS. 4-5 . 
     At  635 , base station  105 - b  monitors, for the aperiodic SRS, at least on symbol period of the second TTI corresponding to at least on symbol index of the SRS resource. At  640 , UE  115 - b  transmits and base station  105 - b  receives the aperiodic SRS in the SRS resource of the second TTI. 
     At  645 , base station  105 - b  generates a channel measurement based at least in part on the aperiodic SRS received at  640 . At  650 , base station  105 - b  generates a frequency dependent scheduling decision based at least in part on the channel measurement. Base station  105 - b  may perform subsequent communications with UE  115 - b  based on the generated scheduling decision. 
       FIG. 7  illustrates an example of a process flow  700  in accordance with various aspects of the present disclosure. In some examples, process flow  700  may implement aspects of wireless communications system  100 . Techniques used in process flow  700  may be implemented by a UE  115 - c  and a base station  105 - c , which may be examples of corresponding devices as described with reference to wireless communications systems  100  and  200 . 
     At  705 , UE  115 - c  may transmit capability information to the base station  105 - c . The capability information may indicate, for example, one or both of N 0  delay and N 2  delay of the UE  115 - c . Operation  705  is optional and maybe skipped. If skipped, the base station  105 - c  may utilize specified capability information (e.g., default capability information that indicates default N 0  delay and N 2  delay) for UEs operating within a wireless communication system, such as system  100 . 
     At  710 , base station  105 - c  transmits DCI in a TTI that grants the UE  115 - a  resources, wherein the grant is in accordance with the signaled or specified capability information. The grant may trigger UE  115 - c  to transmit an aperiodic SRS. The triggering grant may be an uplink grant or a downlink grant. At  715 , UE  115 - c  may detect the grant triggering the transmission of an aperiodic SRS. The grant may be detected within a first TTI. 
     At  720 , UE  115 - c  may identify a second TTI based at least in part on a first number of symbol periods between receipt of the grant by the UE and when the UE is capable of transmitting uplink data (e.g., based on N 0  delay or N 2  delay). The first number of symbol periods may meet or be less than a difference between a number of symbol periods between an SRS resource of the second TTI and a control channel of the first TTI. The first number of symbol periods may be the number of symbol periods indicated in the capability information transmitted by UE  115 - c  at  705 . That is, if the first number of symbol periods is less than or equal to the difference (e.g., different  425 - a  in  FIG. 4 ) between the control channel (e.g., of slot n in  FIG. 4 ) and the SRS resource of the first TTI (e.g., SRS resource  415 - a ), then the second TTI may be the same as the first TTI (e.g., the aperiodic SRS may be transmitted in the same TTI in which the triggering grant of  710  was received). However, if the first number of symbol periods is greater than the difference between the control channel and the SRS resource of the first TTI (e.g., different  425 - b ), then the second TTI may be a subsequent TTI to the first TTI (e.g., the aperiodic SRS may be transmitted on the SRS resource  415 - b  of a slot n+1 that is subsequent to the slot n that included the grant). At  725 , base station  105 - c  may identify the second TTI for the aperiodic SRS, similar to the process described with respect to UE  115 - c  at  720 . 
     At  730 , base station  105 - c  may monitor the SRS resource of the second TTI. The monitoring may occur within at least on symbol period of the second TTI configured with an SRS resource. At  735 , UE  115 - c  may transmit, and base station  105 - c  may receive, the aperiodic SRS in the SRS resource of the second TTI. 
     At  740 , base station  105 - c  may generate a channel measurement based at least in part on the received aperiodic SRS. At  745 , base station  105 - c  may generate a frequency dependent scheduling decision based at least in part on the channel measurement. Base station  105 - c  may subsequently communicate with UE  115 - c  based on the generated scheduling decision. 
     Beneficially, the techniques described herein may provide for triggering a UE to transmit an SRS in a TTI relative to a TTI that includes a grant. 
       FIG. 8  shows a block diagram  800  of a wireless device  805  in accordance with aspects of the present disclosure. Wireless device  805  may be an example of aspects of a user equipment (UE)  115  as described herein. Wireless device  805  may include receiver  810 , UE communications manager  815 , and transmitter  820 . Wireless device  805  may also include a processor. Each of these components may be in communication with one another (e.g., via one or more buses). 
     Receiver  810  may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to reference signal transmission and triggering, etc.). Information may be passed on to other components of the device. The receiver  810  may be an example of aspects of the transceiver  1135  described with reference to  FIG. 11 . The receiver  810  may utilize a single antenna or a set of antennas. 
     UE communications manager  815  may be an example of aspects of the UE communications manager  1115  described with reference to  FIG. 11 . 
     UE communications manager  815  and/or at least some of its various sub-components may be implemented in hardware, software executed by a processor, firmware, or any combination thereof. If implemented in software executed by a processor, the functions of the UE communications manager  815  and/or at least some of its various sub-components may be executed by a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), an field-programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described in the present disclosure. The UE communications manager  815  and/or at least some of its various sub-components may be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations by one or more physical devices. In some examples, UE communications manager  815  and/or at least some of its various sub-components may be a separate and distinct component in accordance with various aspects of the present disclosure. In other examples, UE communications manager  815  and/or at least some of its various sub-components may be combined with one or more other hardware components, including but not limited to an I/O component, a transceiver, a network server, another computing device, one or more other components described in the present disclosure, or a combination thereof in accordance with various aspects of the present disclosure. 
     UE communications manager  815  may detect, within a first transmission time interval (TTI), a grant triggering the UE to transmit an aperiodic sounding reference signal (A-sounding reference signal (SRS)), identify offset information indicating a TTI offset relative to the grant, determine a second TTI for transmitting the A-SRS based on the TTI offset, and transmit the A-SRS in an SRS resource of the second TTI. The UE communications manager  815  may also detect, within a first TTI, a grant triggering the UE to transmit an aperiodic sounding reference signal (A-SRS), identify a second TTI based on a first number of symbol periods between receipt of the grant by the UE and when the UE is capable of transmitting uplink data, the first number of symbol periods meeting or being less than a difference between a number of symbol periods between an SRS resource of the second TTI and a control channel of the first TTI, and transmit the A-SRS in the SRS resource of the second TTI. 
     Transmitter  820  may transmit signals generated by other components of the device. In some examples, the transmitter  820  may be collocated with a receiver  810  in a transceiver module. For example, the transmitter  820  may be an example of aspects of the transceiver  1135  described with reference to  FIG. 11 . The transmitter  820  may utilize a single antenna or a set of antennas. 
       FIG. 9  shows a block diagram  900  of a wireless device  905  in accordance with aspects of the present disclosure. Wireless device  905  may be an example of aspects of a wireless device  805  or a UE  115  as described with reference to  FIG. 8 . Wireless device  905  may include receiver  910 , UE communications manager  915 , and transmitter  920 . Wireless device  905  may also include a processor. Each of these components may be in communication with one another (e.g., via one or more buses). 
     Receiver  910  may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to reference signal transmission and triggering, etc.). Information may be passed on to other components of the device. The receiver  910  may be an example of aspects of the transceiver  1135  described with reference to  FIG. 11 . The receiver  910  may utilize a single antenna or a set of antennas. 
     UE communications manager  915  may be an example of aspects of the UE communications manager  1115  described with reference to  FIG. 11 . 
     UE communications manager  915  may also include detecting component  925 , offset information component  930 , A-SRS component  935 , and TTI identifier component  940 . 
     Detecting component  925  may detect, within a first TTI, a grant triggering the UE to transmit an aperiodic sounding reference signal (A-SRS) and receive downlink control information of the first TTI that includes the offset information, where the grant indicates resources of a shared data channel allocated to the UE for transmission of uplink data, and where the offset information includes a bit sequence corresponding to a number of TTIs occurring between receipt of the grant by the UE and when the UE is instructed to transmit uplink data in accordance with the grant. In some cases, the grant indicates resources of a shared data channel allocated to the UE for reception of downlink data. 
     Offset information component  930  may identify offset information indicating a TTI offset relative to the grant, receive downlink control information of the first TTI that includes the offset information, where the grant indicates resources of a shared data channel allocated to the UE for transmission of uplink data, and where the offset information is a bit flag indicating whether the UE is to use a first value for the TTI offset indicated in the downlink control information or a second semi-statically configured value for the TTI offset, receive downlink control information of the first TTI that includes the offset information, where the grant indicates resources of a shared data channel allocated to the UE for transmission of uplink data, and where the offset information includes a bit flag indicating whether the UE is to use a first value for the TTI offset indicated in the downlink control information or a second value for the TTI offset, and receive control signaling semi-statically indicating a defined value, where the second value for the TTI offset is a function of the first value for the TTI offset and the defined value. In some cases, identifying the offset information further includes retrieving the offset information from memory, where the UE is preconfigured with the offset information. In some cases, identifying the offset information further includes: receiving the offset information in downlink control information of the first TTI, where the offset information indicates a delay corresponding to a number of TTIs occurring between receipt of the grant by the UE and when the UE is instructed to transmit uplink data in accordance with the grant. In some cases, identifying the second TTI further includes: identifying the second TTI as being offset from the first TTI by the TTI offset. In some cases, identifying the second TTI includes: determining that the TTI offset is a zero TTI offset, where the second TTI and the first TTI are a same TTI. In some cases, identifying the offset information further includes receiving control signaling that semi-statically configures the UE with the offset information. In some cases, identifying the offset information further includes: receiving downlink control information of the first TTI that includes the offset information for dynamically configuring the UE with the TTI offset. In some cases, the first value is K2 and the second TTI is a TTI occurring prior to a TTI corresponding to the first value. 
     A-SRS component  935  may determine a second TTI for transmitting the A-SRS based on the TTI offset, transmit the A-SRS in an SRS resource of the second TTI, and transmit the A-SRS in the SRS resource of the second TTI. In some cases, determining the second TTI further includes: determining a TTI index following the delay indicated in the offset information, where the second TTI corresponds to the TTI index. In some cases, the SRS resource corresponds to a subset of symbol periods within the second TTI. 
     TTI identifier component  940  may identify a second TTI based on a first number of symbol periods between receipt of the grant by the UE and when the UE is capable of transmitting uplink data, the first number of symbol periods meeting or being less than a difference between a number of symbol periods between an SRS resource of the second TTI and a control channel of the first TTI. In some cases, identifying the second TTI further includes: identifying the second TTI based on a second number of symbol periods between receipt of the grant by the UE and when the UE is capable of receiving downlink data. In some cases, identifying the second TTI further includes: determining a maximum of the first number of symbol periods and the second number of symbol periods. In some cases, the first number of symbol periods and the second number of symbol periods are a specified capability of the UE. In some cases, identifying the second TTI includes: determining that the second TTI and the first TTI are a same TTI. 
     Transmitter  920  may transmit signals generated by other components of the device. In some examples, the transmitter  920  may be collocated with a receiver  910  in a transceiver module. For example, the transmitter  920  may be an example of aspects of the transceiver  1135  described with reference to  FIG. 11 . The transmitter  920  may utilize a single antenna or a set of antennas. 
       FIG. 10  shows a block diagram  1000  of a UE communications manager  1015  in accordance with aspects of the present disclosure. The UE communications manager  1015  may be an example of aspects of a UE communications manager  815 , a UE communications manager  915 , or a UE communications manager  1115  described with reference to  FIGS. 8, 9, and 11 . The UE communications manager  1015  may include detecting component  1020 , offset information component  1025 , A-SRS component  1030 , TTI identifier component  1035 , configuration information component  1040 , capability information component  1045 , and control information component  1050 . Each of these modules may communicate, directly or indirectly, with one another (e.g., via one or more buses). 
     Detecting component  1020  may detect, within a first TTI, a grant triggering the UE to transmit an aperiodic sounding reference signal (A-SRS) and receive downlink control information of the first TTI that includes the offset information, where the grant indicates resources of a shared data channel allocated to the UE for transmission of uplink data, and where the offset information includes a bit sequence corresponding to a number of TTIs occurring between receipt of the grant by the UE and when the UE is instructed to transmit uplink data in accordance with the grant. In some cases, the grant indicates resources of a shared data channel allocated to the UE for reception of downlink data. 
     Offset information component  1025  may identify offset information indicating a TTI offset relative to the grant, receive downlink control information of the first TTI that includes the offset information, where the grant indicates resources of a shared data channel allocated to the UE for transmission of uplink data, and where the offset information is a bit flag indicating whether the UE is to use a first value for the TTI offset indicated in the downlink control information or a second semi-statically configured value for the TTI offset, receive downlink control information of the first TTI that includes the offset information, where the grant indicates resources of a shared data channel allocated to the UE for transmission of uplink data, and where the offset information includes a bit flag indicating whether the UE is to use a first value for the TTI offset indicated in the downlink control information or a second value for the TTI offset, and receive control signaling semi-statically indicating a defined value, where the second value for the TTI offset is a function of the first value for the TTI offset and the defined value. In some cases, identifying the offset information further includes retrieving the offset information from memory, where the UE is preconfigured with the offset information. In some cases, identifying the offset information further includes: receiving the offset information in downlink control information of the first TTI, where the offset information indicates a delay corresponding to a number of TTIs occurring between receipt of the grant by the UE and when the UE is instructed to transmit uplink data in accordance with the grant. In some cases, identifying the second TTI further includes: identifying the second TTI as being offset from the first TTI by the TTI offset. In some cases, identifying the second TTI includes: determining that the TTI offset is a zero TTI offset, where the second TTI and the first TTI are a same TTI. In some cases, identifying the offset information further includes receiving control signaling that semi-statically configures the UE with the offset information. In some cases, identifying the offset information further includes: receiving downlink control information of the first TTI that includes the offset information for dynamically configuring the UE with the TTI offset. In some cases, the first value is K2 and the second TTI is a TTI occurring prior to a TTI corresponding to the first value. 
     A-SRS component  1030  may determine a second TTI for transmitting the A-SRS based on the TTI offset, transmit the A-SRS in an SRS resource of the second TTI, and transmit the A-SRS in the SRS resource of the second TTI. In some cases, determining the second TTI further includes: determining a TTI index following the delay indicated in the offset information, where the second TTI corresponds to the TTI index. In some cases, the SRS resource corresponds to a subset of symbol periods within the second TTI. 
     TTI identifier component  1035  may identify a second TTI based on a first number of symbol periods between receipt of the grant by the UE and when the UE is capable of transmitting uplink data, the first number of symbol periods meeting or being less than a difference between a number of symbol periods between an SRS resource of the second TTI and a control channel of the first TTI. In some cases, identifying the second TTI further includes: identifying the second TTI based on a second number of symbol periods between receipt of the grant by the UE and when the UE is capable of receiving downlink data. In some cases, identifying the second TTI further includes: determining a maximum of the first number of symbol periods and the second number of symbol periods. In some cases, the first number of symbol periods and the second number of symbol periods are a specified capability of the UE. In some cases, identifying the second TTI includes: determining that the second TTI and the first TTI are a same TTI. 
     Configuration information component  1040  may receive configuration information that configures the UE to transmit the A-SRS within at least one symbol index of a set of different symbol indexes of a TTI, where transmitting the A-SRS in the SRS resource of the second TTI further includes: transmitting the A-SRS within at least one symbol period of the second TTI corresponding to the at least one symbol index. In some cases, receiving configuration information that configures the UE to transmit the A-SRS within at least one symbol index of a set of different symbol indexes of a TTI, where transmitting the A-SRS in the SRS resource of the second TTI further includes: transmitting the A-SRS within at least one symbol period of the second TTI corresponding to the at least one symbol index. In some cases, receiving configuration information that configures the UE to transmit the A-SRS within at least one symbol index of a set of different symbol indexes of a TTI, where transmitting the A-SRS in the SRS resource of the second TTI further includes: transmitting the A-SRS within at least one symbol period of the second TTI corresponding to the at least one symbol index, where a number of symbol periods between the at least one symbol period of the second TTI and the control channel of the first TTI meets or exceeds the maximum. 
     Capability information component  1045  may transmit capability information indicating a number of symbol periods between receipt of the grant by the UE and when the UE is capable of transmitting uplink data in accordance with the grant, where the delay corresponds to the capability information, transmit capability information indicating the first number of symbol periods, and transmit capability information indicating the first number of symbol periods and the second number of symbol periods. In some cases, the delay corresponds to a specified capability information indicating a number of symbol periods between receipt of the grant by the UE and when the UE is capable of transmitting uplink data in accordance with the grant. 
     Control information component  1050  may receive downlink control information of the first TTI that includes the offset information, where the grant indicates resources of a shared data channel allocated to the UE for reception of downlink data. In some cases, the offset information is a bit sequence included within downlink control information of the first TTI, the bit sequence corresponding to a number of TTIs occurring between receipt of the grant by the UE and when the UE is capable of transmitting uplink data in accordance with the grant. In some cases, the bit sequence is configured to jointly trigger transmission of a zero power channel state information reference signal (channel state information (CSI)-RS) from a base station and transmission of the A-SPS from the UE. 
       FIG. 11  shows a diagram of a system  1100  including a device  1105  in accordance with aspects of the present disclosure. Device  1105  may be an example of or include the components of wireless device  805 , wireless device  905 , or a UE  115  as described above, e.g., with reference to  FIGS. 8 and 9 . Device  1105  may include components for bi-directional voice and data communications including components for transmitting and receiving communications, including UE communications manager  1115 , processor  1120 , memory  1125 , software  1130 , transceiver  1135 , antenna  1140 , and I/O controller  1145 . These components may be in electronic communication via one or more buses (e.g., bus  1110 ). Device  1105  may communicate wirelessly with one or more base stations  105 . 
     Processor  1120  may include an intelligent hardware device, (e.g., a general-purpose processor, a DSP, a central processing unit (CPU), a microcontroller, an ASIC, an FPGA, a programmable logic device, a discrete gate or transistor logic component, a discrete hardware component, or any combination thereof). In some cases, processor  1120  may be configured to operate a memory array using a memory controller. In other cases, a memory controller may be integrated into processor  1120 . Processor  1120  may be configured to execute computer-readable instructions stored in a memory to perform various functions (e.g., functions or tasks supporting reference signal transmission and triggering). 
     Memory  1125  may include random access memory (RAM) and read only memory (ROM). The memory  1125  may store computer-readable, computer-executable software  1130  including instructions that, when executed, cause the processor to perform various functions described herein. In some cases, the memory  1125  may contain, among other things, a basic input/output system (BIOS) which may control basic hardware or software operation such as the interaction with peripheral components or devices. 
     Software  1130  may include code to implement aspects of the present disclosure, including code to support reference signal transmission and triggering. Software  1130  may be stored in a non-transitory computer-readable medium such as system memory or other memory. In some cases, the software  1130  may not be directly executable by the processor but may cause a computer (e.g., when compiled and executed) to perform functions described herein. 
     Transceiver  1135  may communicate bi-directionally, via one or more antennas, wired, or wireless links as described above. For example, the transceiver  1135  may represent a wireless transceiver and may communicate bi-directionally with another wireless transceiver. The transceiver  1135  may also include a modem to modulate the packets and provide the modulated packets to the antennas for transmission, and to demodulate packets received from the antennas. 
     In some cases, the wireless device may include a single antenna  1140 . However, in some cases the device may have more than one antenna  1140 , which may be capable of concurrently transmitting or receiving multiple wireless transmissions. 
     I/O controller  1145  may manage input and output signals for device  1105 . I/O controller  1145  may also manage peripherals not integrated into device  1105 . In some cases, I/O controller  1145  may represent a physical connection or port to an external peripheral. In some cases, I/O controller  1145  may utilize an operating system such as iOS®, ANDROID®, MS-DOS®, MS-WINDOWS®, OS/2®, UNIX®, LINUX®, or another known operating system. In other cases, I/O controller  1145  may represent or interact with a modem, a keyboard, a mouse, a touchscreen, or a similar device. In some cases, I/O controller  1145  may be implemented as part of a processor. In some cases, a user may interact with device  1105  via I/O controller  1145  or via hardware components controlled by I/O controller  1145 . 
       FIG. 12  shows a block diagram  1200  of a wireless device  1205  in accordance with aspects of the present disclosure. Wireless device  1205  may be an example of aspects of a base station  105  as described herein. Wireless device  1205  may include receiver  1210 , base station communications manager  1215 , and transmitter  1220 . Wireless device  1205  may also include a processor. Each of these components may be in communication with one another (e.g., via one or more buses). 
     Receiver  1210  may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to reference signal transmission and triggering, etc.). Information may be passed on to other components of the device. The receiver  1210  may be an example of aspects of the transceiver  1535  described with reference to  FIG. 15 . The receiver  1210  may utilize a single antenna or a set of antennas. 
     Base station communications manager  1215  may be an example of aspects of the base station communications manager  1515  described with reference to  FIG. 15 . 
     Base station communications manager  1215  and/or at least some of its various sub-components may be implemented in hardware, software executed by a processor, firmware, or any combination thereof. If implemented in software executed by a processor, the functions of the base station communications manager  1215  and/or at least some of its various sub-components may be executed by a general-purpose processor, a DSP, an ASIC, an FPGA or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described in the present disclosure. The base station communications manager  1215  and/or at least some of its various sub-components may be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations by one or more physical devices. In some examples, base station communications manager  1215  and/or at least some of its various sub-components may be a separate and distinct component in accordance with various aspects of the present disclosure. In other examples, base station communications manager  1215  and/or at least some of its various sub-components may be combined with one or more other hardware components, including but not limited to an I/O component, a transceiver, a network server, another computing device, one or more other components described in the present disclosure, or a combination thereof in accordance with various aspects of the present disclosure. 
     Base station communications manager  1215  may transmit, within a first TTI, a grant triggering a UE to transmit an aperiodic sounding reference signal (A-SRS), identify offset information indicating a TTI offset relative to the grant, determine a second TTI for the A-SRS based on the TTI offset, and monitor an SRS resource of the second TTI for the A-SRS. The base station communications manager  1215  may also transmit, within a first TTI, a grant triggering a UE to transmit an aperiodic sounding reference signal (A-SRS), identify a second TTI based on a first number of symbol periods between receipt of the grant by the UE and when the UE is capable of transmitting uplink data, the first number of symbol periods meeting or being less than a difference between a number of symbol periods between an SRS resource of the second TTI and a control channel of the first TTI, and monitor the SRS resource of the second TTI for the A-SRS. 
     Transmitter  1220  may transmit signals generated by other components of the device. In some examples, the transmitter  1220  may be collocated with a receiver  1210  in a transceiver module. For example, the transmitter  1220  may be an example of aspects of the transceiver  1535  described with reference to  FIG. 15 . The transmitter  1220  may utilize a single antenna or a set of antennas. 
       FIG. 13  shows a block diagram  1300  of a wireless device  1305  in accordance with aspects of the present disclosure. Wireless device  1305  may be an example of aspects of a wireless device  1205  or a base station  105  as described with reference to  FIG. 12 . Wireless device  1305  may include receiver  1310 , base station communications manager  1315 , and transmitter  1320 . Wireless device  1305  may also include a processor. Each of these components may be in communication with one another (e.g., via one or more buses). 
     Receiver  1310  may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to reference signal transmission and triggering, etc.). Information may be passed on to other components of the device. The receiver  1310  may be an example of aspects of the transceiver  1535  described with reference to  FIG. 15 . The receiver  1310  may utilize a single antenna or a set of antennas. 
     Base station communications manager  1315  may be an example of aspects of the base station communications manager  1515  described with reference to  FIG. 15 . 
     Base station communications manager  1315  may also include resource grant component  1325 , offset information component  1330 , TTI identifier component  1335 , and monitoring component  1340 . 
     Resource grant component  1325  may transmit, within a first TTI, a grant triggering a UE to transmit an aperiodic sounding reference signal (A-SRS). In some cases, the grant indicates resources of a shared data channel allocated to the UE for reception of downlink data. 
     Offset information component  1330  may identify offset information indicating a TTI offset relative to the grant. In some cases, the offset information corresponds to a TTI index following the delay, and where the second TTI corresponds to the TTI index. In some cases, the offset information includes a bit sequence corresponding to a number of TTIs occurring between receipt of the grant by the UE and when the UE is instructed to transmit uplink data in accordance with the grant. In some cases, the bit sequence is configured to jointly trigger transmission of a zero power channel state information reference signal (CSIRS) from the base station and transmission of the A-SPS from a UE. In some cases, the UE is preconfigured with the TTI offset. 
     TTI identifier component  1335  may determine a second TTI for the A-SRS based on the TTI offset and identify a second TTI based on a first number of symbol periods between receipt of the grant by the UE and when the UE is capable of transmitting uplink data, the first number of symbol periods meeting or being less than a difference between a number of symbol periods between an SRS resource of the second TTI and a control channel of the first TTI. In some cases, identifying the second TTI further includes: identifying the second TTI as being offset from the first TTI by the TTI offset. In some cases, identifying the second TTI includes: determining that the TTI offset is a zero TTI offset, where the second TTI and the first TTI are a same TTI. In some cases, identifying the second TTI further includes: identifying the second TTI based on a second number of symbol periods between receipt of the grant by the UE and when the UE is capable of receiving downlink data. In some cases, identifying the second TTI further includes: determining a maximum of the first number of symbol periods and the second number of symbol periods. In some cases, identifying the second TTI includes: determining that the second TTI and the first TTI are a same TTI. 
     Monitoring component  1340  may monitor an SRS resource of the second TTI for the A-SRS and monitor the SRS resource of the second TTI for the A-SRS. 
     Transmitter  1320  may transmit signals generated by other components of the device. In some examples, the transmitter  1320  may be collocated with a receiver  1310  in a transceiver module. For example, the transmitter  1320  may be an example of aspects of the transceiver  1535  described with reference to  FIG. 15 . The transmitter  1320  may utilize a single antenna or a set of antennas. 
       FIG. 14  shows a block diagram  1400  of a base station communications manager  1415  in accordance with aspects of the present disclosure. The base station communications manager  1415  may be an example of aspects of a base station communications manager  1515  described with reference to  FIGS. 12, 13, and 15 . The base station communications manager  1415  may include resource grant component  1420 , offset information component  1425 , TTI identifier component  1430 , monitoring component  1435 , configuration information component  1440 , control information component  1445 , capability information component  1450 , A-SRS component  1455 , measuring component  1460 , and scheduling component  1465 . Each of these modules may communicate, directly or indirectly, with one another (e.g., via one or more buses). 
     Resource grant component  1420  may transmit, within a first TTI, a grant triggering a UE to transmit an aperiodic sounding reference signal (A-SRS). In some cases, the grant indicates resources of a shared data channel allocated to the UE for reception of downlink data. 
     Offset information component  1425  may identify offset information indicating a TTI offset relative to the grant. In some cases, the offset information corresponds to a TTI index following the delay, and where the second TTI corresponds to the TTI index. In some cases, the offset information includes a bit sequence corresponding to a number of TTIs occurring between receipt of the grant by the UE and when the UE is instructed to transmit uplink data in accordance with the grant. In some cases, the bit sequence is configured to jointly trigger transmission of a zero power channel state information reference signal (CSIRS) from the base station and transmission of the A-SPS from a UE. In some cases, the UE is preconfigured with the TTI offset. 
     TTI identifier component  1430  may determine a second TTI for the A-SRS based on the TTI offset and identify a second TTI based on a first number of symbol periods between receipt of the grant by the UE and when the UE is capable of transmitting uplink data, the first number of symbol periods meeting or being less than a difference between a number of symbol periods between an SRS resource of the second TTI and a control channel of the first TTI. In some cases, identifying the second TTI further includes: identifying the second TTI as being offset from the first TTI by the TTI offset. In some cases, identifying the second TTI includes: determining that the TTI offset is a zero TTI offset, where the second TTI and the first TTI are a same TTI. In some cases, identifying the second TTI further includes: identifying the second TTI based on a second number of symbol periods between receipt of the grant by the UE and when the UE is capable of receiving downlink data. In some cases, identifying the second TTI further includes: determining a maximum of the first number of symbol periods and the second number of symbol periods. In some cases, identifying the second TTI includes: determining that the second TTI and the first TTI are a same TTI. 
     Monitoring component  1435  may monitor an SRS resource of the second TTI for the A-SRS and monitor the SRS resource of the second TTI for the A-SRS. 
     Configuration information component  1440  may transmit configuration information to configure the UE to transmit the A-SRS within at least one symbol index of a set of different symbol indexes of a TTI, where monitoring the SRS resource of the second TTI for the A-SRS further includes: monitoring at least one symbol period of the second TTI corresponding to the at least one symbol index for the A-SRS. In some cases, transmitting configuration information to configure the UE to transmit the A-SRS within at least one symbol index of a set of different symbol indexes of a TTI, where monitoring the SRS resource of the second TTI for the A-SRS further includes: monitoring the A-SRS within at least one symbol period of the second TTI corresponding to the at least one symbol index. In some cases, transmitting configuration information to configure the UE to transmit the A-SRS within at least one symbol index of a set of different symbol indexes of a TTI, where monitoring the SRS resource of the second TTI for the A-SRS further includes: monitoring the SRS resource of the second TTI for the A-SRS within at least one symbol period of the second TTI corresponding to the at least one symbol index, where a number of symbol periods between the at least one symbol period of the second TTI and the control channel of the first TTI meets or exceeds the maximum. 
     Control information component  1445  may transmit, within the first TTI, downlink control information that includes the offset information, where the offset information indicates a delay corresponding to a number of TTIs occurring between receipt of the grant by the UE and when the UE is instructed to transmit uplink data in accordance with the grant, transmit downlink control information in the first TTI that includes the offset information, where the grant indicates resources of a shared data channel allocated to the UE for transmission of uplink data, and where the offset information includes a bit flag indicating whether the UE is to use a first value for the TTI offset indicated in the downlink control information or a second semi-statically configured value for the TTI offset, transmit downlink control information in the first TTI that includes the offset information, where the grant indicates resources of a shared data channel allocated to the UE for transmission of uplink data, and where the offset information includes a bit sequence indicating that the TTI offset corresponds to a number of TTIs occurring between receipt of the grant by the UE and when the UE is instructed to transmit uplink data in accordance with the grant, transmit downlink control information in the first TTI that includes the offset information, where the grant indicates resources of a shared data channel allocated to the UE for transmission of uplink data, where the offset information includes a bit flag indicating whether the UE is to use a first value for the TTI offset indicated in the downlink control information or a second value for the TTI offset, transmit control signaling semi-statically indicating a defined value, where the second value for the TTI offset is a function of the first value for the TTI offset and the defined value, transmit downlink control information in the first TTI that includes the offset information, where the grant indicates resources of a shared data channel allocated to the UE for reception of downlink data, transmit control signaling to semi-statically configure the UE with the offset information, and transmit downlink control information within the first TTI to dynamically configure the UE with the offset information. In some cases, the first value is K2 and the second TTI is a TTI occurring prior to a TTI corresponding to the first value. 
     Capability information component  1450  may receive capability information indicating a number of symbol periods between receipt of the grant by the UE and when the UE is capable of transmitting uplink data in accordance with the grant, where the delay corresponds to the capability information, receive capability information indicating the first number of symbol periods, and receive capability information indicating the first number of symbol periods and the second number of symbol periods. In some cases, the delay corresponds to a specified capability information indicating a number of symbol periods between receipt of the grant by the UE and when the UE is capable of transmitting uplink data in accordance with the grant. In some cases, the first number of symbol periods and the second number of symbol periods respectively correspond to defined capability information of the UE. 
     A-SRS component  1455  may receive the A-SRS within the SRS resource of the second TTI. In some cases, the SRS resource corresponds to a subset of symbol periods within the second TTI. 
     Measuring component  1460  may generate a channel measurement based on the received A-SRS. 
     Scheduling component  1465  may generate a frequency dependent scheduling decision based on the channel measurement. 
       FIG. 15  shows a diagram of a system  1500  including a device  1505  in accordance with aspects of the present disclosure. Device  1505  may be an example of or include the components of base station  105  as described above, e.g., with reference to  FIG. 1 . Device  1505  may include components for bi-directional voice and data communications including components for transmitting and receiving communications, including base station communications manager  1515 , processor  1520 , memory  1525 , software  1530 , transceiver  1535 , antenna  1540 , network communications manager  1545 , and inter-station communications manager  1550 . These components may be in electronic communication via one or more buses (e.g., bus  1510 ). Device  1505  may communicate wirelessly with one or more UEs  115 . 
     Processor  1520  may include an intelligent hardware device, (e.g., a general-purpose processor, a DSP, a CPU, a microcontroller, an ASIC, an FPGA, a programmable logic device, a discrete gate or transistor logic component, a discrete hardware component, or any combination thereof). In some cases, processor  1520  may be configured to operate a memory array using a memory controller. In other cases, a memory controller may be integrated into processor  1520 . Processor  1520  may be configured to execute computer-readable instructions stored in a memory to perform various functions (e.g., functions or tasks supporting reference signal transmission and triggering). 
     Memory  1525  may include RAM and ROM. The memory  1525  may store computer-readable, computer-executable software  1530  including instructions that, when executed, cause the processor to perform various functions described herein. In some cases, the memory  1525  may contain, among other things, a BIOS which may control basic hardware or software operation such as the interaction with peripheral components or devices. 
     Software  1530  may include code to implement aspects of the present disclosure, including code to support reference signal transmission and triggering. Software  1530  may be stored in a non-transitory computer-readable medium such as system memory or other memory. In some cases, the software  1530  may not be directly executable by the processor but may cause a computer (e.g., when compiled and executed) to perform functions described herein. 
     Transceiver  1535  may communicate bi-directionally, via one or more antennas, wired, or wireless links as described above. For example, the transceiver  1535  may represent a wireless transceiver and may communicate bi-directionally with another wireless transceiver. The transceiver  1535  may also include a modem to modulate the packets and provide the modulated packets to the antennas for transmission, and to demodulate packets received from the antennas. 
     In some cases, the wireless device may include a single antenna  1540 . However, in some cases the device may have more than one antenna  1540 , which may be capable of concurrently transmitting or receiving multiple wireless transmissions. 
     Network communications manager  1545  may manage communications with the core network (e.g., via one or more wired backhaul links). For example, the network communications manager  1545  may manage the transfer of data communications for client devices, such as one or more UEs  115 . 
     Inter-station communications manager  1550  may manage communications with other base station  105 , and may include a controller or scheduler for controlling communications with UEs  115  in cooperation with other base stations  105 . For example, the inter-station communications manager  1550  may coordinate scheduling for transmissions to UEs  115  for various interference mitigation techniques such as beamforming or joint transmission. In some examples, inter-station communications manager  1550  may provide an X2 interface within a Long Term Evolution (LTE)/LTE-A wireless communication network technology to provide communication between base stations  105 . 
       FIG. 16  shows a flowchart illustrating a method  1600  for reference signal transmission and triggering in accordance with aspects of the present disclosure. The operations of method  1600  may be implemented by a UE  115  or its components as described herein. For example, the operations of method  1600  may be performed by a UE communications manager as described with reference to  FIGS. 8 through 11 . In some examples, a UE  115  may execute a set of codes to control the functional elements of the device to perform the functions described below. Additionally or alternatively, the UE  115  may perform aspects of the functions described below using special-purpose hardware. 
     At  1605  the UE  115  may detect, within a first transmission time interval (TTI), a grant triggering the UE to transmit an aperiodic sounding reference signal (A-SRS). The operations of  1605  may be performed according to the methods described herein. In certain examples, aspects of the operations of  1605  may be performed by a detecting component as described with reference to  FIGS. 8 through 11 . 
     At  1610  the UE  115  may identify offset information indicating a TTI offset relative to the grant. The operations of  1610  may be performed according to the methods described herein. In certain examples, aspects of the operations of  1610  may be performed by an offset information component as described with reference to  FIGS. 8 through 11 . 
     At  1615  the UE  115  may determine a second TTI for transmitting the A-SRS based at least in part on the TTI offset. The operations of  1615  may be performed according to the methods described herein. In certain examples, aspects of the operations of  1615  may be performed by a A-SRS component as described with reference to  FIGS. 8 through 11 . 
     At  1620  the UE  115  may transmit the A-SRS in an SRS resource of the second TTI. The operations of  1620  may be performed according to the methods described herein. In certain examples, aspects of the operations of  1620  may be performed by a A-SRS component as described with reference to  FIGS. 8 through 11 . 
       FIG. 17  shows a flowchart illustrating a method  1700  for reference signal transmission and triggering in accordance with aspects of the present disclosure. The operations of method  1700  may be implemented by a UE  115  or its components as described herein. For example, the operations of method  1700  may be performed by a UE communications manager as described with reference to  FIGS. 8 through 11 . In some examples, a UE  115  may execute a set of codes to control the functional elements of the device to perform the functions described below. Additionally, or alternatively, the UE  115  may perform aspects of the functions described below using special-purpose hardware. 
     At  1705  the UE  115  may detect, within a first transmission time interval (TTI), a grant triggering the UE to transmit an aperiodic sounding reference signal (A-SRS). The operations of  1705  may be performed according to the methods described herein. In certain examples, aspects of the operations of  1705  may be performed by a detecting component as described with reference to  FIGS. 8 through 11 . 
     At  1710  the UE  115  may receive downlink control information of the first TTI that includes offset information, wherein the grant indicates resources of a shared data channel allocated to the UE for transmission of uplink data, and wherein the offset information is a bit flag indicating whether the UE is to use a first value for the TTI offset indicated in the downlink control information or a second semi-statically configured value for the TTI offset. The operations of  1710  may be performed according to the methods described herein. In certain examples, aspects of the operations of  1710  may be performed by an offset information component as described with reference to  FIGS. 8 through 11 . 
     At  1715  the UE  115  may identify the offset information indicating a TTI offset relative to the grant. The operations of  1715  may be performed according to the methods described herein. In certain examples, aspects of the operations of  1715  may be performed by an offset information component as described with reference to  FIGS. 8 through 11 . 
     At  1720  the UE  115  may determine a second TTI for transmitting the A-SRS based at least in part on the TTI offset. The operations of  1720  may be performed according to the methods described herein. In certain examples, aspects of the operations of  1720  may be performed by a A-SRS component as described with reference to  FIGS. 8 through 11 . 
     At  1725  the UE  115  may transmit the A-SRS in an SRS resource of the second TTI. The operations of  1725  may be performed according to the methods described herein. In certain examples, aspects of the operations of  1725  may be performed by a A-SRS component as described with reference to  FIGS. 8 through 11 . 
       FIG. 18  shows a flowchart illustrating a method  1800  for reference signal transmission and triggering in accordance with aspects of the present disclosure. The operations of method  1800  may be implemented by a UE  115  or its components as described herein. For example, the operations of method  1800  may be performed by a UE communications manager as described with reference to  FIGS. 8 through 11 . In some examples, a UE  115  may execute a set of codes to control the functional elements of the device to perform the functions described below. Additionally, or alternatively, the UE  115  may perform aspects of the functions described below using special-purpose hardware. 
     At  1805  the UE  115  may detect, within a first transmission time interval (TTI), a grant triggering the UE to transmit an aperiodic sounding reference signal (A-SRS). The operations of  1805  may be performed according to the methods described herein. In certain examples, aspects of the operations of  1805  may be performed by a detecting component as described with reference to  FIGS. 8 through 11 . 
     At  1810  the UE  115  may identify a second TTI based at least in part on a first number of symbol periods between receipt of the grant by the UE and when the UE is capable of transmitting uplink data, the first number of symbol periods meeting or being less than a difference between a number of symbol periods between an SRS resource of the second TTI and a control channel of the first TTI. The operations of  1810  may be performed according to the methods described herein. In certain examples, aspects of the operations of  1810  may be performed by a TTI identifier component as described with reference to  FIGS. 8 through 11 . 
     At  1815  the UE  115  may transmit the A-SRS in the SRS resource of the second TTI. The operations of  1815  may be performed according to the methods described herein. In certain examples, aspects of the operations of  1815  may be performed by a A-SRS component as described with reference to  FIGS. 8 through 11 . 
       FIG. 19  shows a flowchart illustrating a method  1900  for reference signal transmission and triggering in accordance with aspects of the present disclosure. The operations of method  1900  may be implemented by a UE  115  or its components as described herein. For example, the operations of method  1900  may be performed by a UE communications manager as described with reference to  FIGS. 8 through 11 . In some examples, a UE  115  may execute a set of codes to control the functional elements of the device to perform the functions described below. Additionally, or alternatively, the UE  115  may perform aspects of the functions described below using special-purpose hardware. 
     At  1905  the UE  115  may transmit capability information indicating the first number of symbol periods. The operations of  1905  may be performed according to the methods described herein. In certain examples, aspects of the operations of  1905  may be performed by a capability information component as described with reference to  FIGS. 8 through 11 . 
     At  1910  the UE  115  may detect, within a first transmission time interval (TTI), a grant triggering the UE to transmit an aperiodic sounding reference signal (A-SRS). The operations of  1910  may be performed according to the methods described herein. In certain examples, aspects of the operations of  1910  may be performed by a detecting component as described with reference to  FIGS. 8 through 11 . 
     At  1915  the UE  115  may identify a second TTI based at least in part on a first number of symbol periods between receipt of the grant by the UE and when the UE is capable of transmitting uplink data, the first number of symbol periods meeting or being less than a difference between a number of symbol periods between an SRS resource of the second TTI and a control channel of the first TTI. The operations of  1915  may be performed according to the methods described herein. In certain examples, aspects of the operations of  1915  may be performed by a TTI identifier component as described with reference to  FIGS. 8 through 11 . 
     At  1920  the UE  115  may transmit the A-SRS in the SRS resource of the second TTI. The operations of  1920  may be performed according to the methods described herein. In certain examples, aspects of the operations of  1920  may be performed by a A-SRS component as described with reference to  FIGS. 8 through 11 . 
       FIG. 20  shows a flowchart illustrating a method  2000  for reference signal transmission and triggering in accordance with aspects of the present disclosure. The operations of method  2000  may be implemented by a base station  105  or its components as described herein. For example, the operations of method  2000  may be performed by a base station communications manager as described with reference to  FIGS. 12 through 15 . In some examples, a base station  105  may execute a set of codes to control the functional elements of the device to perform the functions described below. Additionally, or alternatively, the base station  105  may perform aspects of the functions described below using special-purpose hardware. 
     At  2005  the base station  105  may transmit, within a first transmission time interval (TTI), a grant triggering a user equipment (UE) to transmit an aperiodic sounding reference signal (A-SRS). The operations of  2005  may be performed according to the methods described herein. In certain examples, aspects of the operations of  2005  may be performed by a resource grant component as described with reference to  FIGS. 12 through 15 . 
     At  2010  the base station  105  may identify offset information indicating a TTI offset relative to the grant. The operations of  2010  may be performed according to the methods described herein. In certain examples, aspects of the operations of  2010  may be performed by an offset information component as described with reference to  FIGS. 12 through 15 . 
     At  2015  the base station  105  may determine a second TTI for the A-SRS based at least in part on the TTI offset. The operations of  2015  may be performed according to the methods described herein. In certain examples, aspects of the operations of  2015  may be performed by a TTI identifier component as described with reference to  FIGS. 12 through 15 . 
     At  2020  the base station  105  may monitor an SRS resource of the second TTI for the A-SRS. The operations of  2020  may be performed according to the methods described herein. In certain examples, aspects of the operations of  2020  may be performed by a monitoring component as described with reference to  FIGS. 12 through 15 . 
       FIG. 21  shows a flowchart illustrating a method  2100  for reference signal transmission and triggering in accordance with aspects of the present disclosure. The operations of method  2100  may be implemented by a base station  105  or its components as described herein. For example, the operations of method  2100  may be performed by a base station communications manager as described with reference to  FIGS. 12 through 15 . In some examples, a base station  105  may execute a set of codes to control the functional elements of the device to perform the functions described below. Additionally, or alternatively, the base station  105  may perform aspects of the functions described below using special-purpose hardware. 
     At  2105  the base station  105  may transmit, within a first transmission time interval (TTI), a grant triggering a user equipment (UE) to transmit an aperiodic sounding reference signal (A-SRS). The operations of  2105  may be performed according to the methods described herein. In certain examples, aspects of the operations of  2105  may be performed by a resource grant component as described with reference to  FIGS. 12 through 15 . 
     At  2110  the base station  105  may identify a second TTI based at least in part on a first number of symbol periods between receipt of the grant by the UE and when the UE is capable of transmitting uplink data, the first number of symbol periods meeting or being less than a difference between a number of symbol periods between an SRS resource of the second TTI and a control channel of the first TTI. The operations of  2110  may be performed according to the methods described herein. In certain examples, aspects of the operations of  2110  may be performed by a TTI identifier component as described with reference to  FIGS. 12 through 15 . 
     At  2115  the base station  105  may monitor the SRS resource of the second TTI for the A-SRS. The operations of  2115  may be performed according to the methods described herein. In certain examples, aspects of the operations of  2115  may be performed by a monitoring component as described with reference to  FIGS. 12 through 15 . 
     It should be noted that the methods described above describe possible implementations, and that the operations and the steps may be rearranged or otherwise modified and that other implementations are possible. Further, aspects from two or more of the methods may be combined. 
     Techniques described herein may be used for various wireless communications systems such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal frequency division multiple access (OFDMA), single carrier frequency division multiple access (SC-FDMA), and other systems. A CDMA system may implement a radio technology such as CDMA2000, Universal Terrestrial Radio Access (UTRA), etc. CDMA2000 covers IS-2000, IS-95, and IS-856 standards. IS-2000 Releases may be commonly referred to as CDMA2000 1×, 1×, etc. IS-856 (TIA-856) is commonly referred to as CDMA2000 1×EV-DO, High Rate Packet Data (HRPD), etc. UTRA includes Wideband CDMA (WCDMA) and other variants of CDMA. A TDMA system may implement a radio technology such as Global System for Mobile Communications (GSM). 
     An OFDMA system may implement a radio technology such as Ultra Mobile Broadband (UMB), Evolved UTRA (E-UTRA), Institute of Electrical and Electronics Engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDM, etc. UTRA and E-UTRA are part of Universal Mobile Telecommunications System (UMTS). LTE, LTE-A, and LTE-A Pro are releases of UMTS that use E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A, LTE-A Pro, NR, and GSM are described in documents from the organization named “3rd Generation Partnership Project” (3GPP). CDMA2000 and UMB are described in documents from an organization named “3rd Generation Partnership Project 2” (3GPP2). The techniques described herein may be used for the systems and radio technologies mentioned above as well as other systems and radio technologies. While aspects of an LTE, LTE-A, LTE-A Pro, or NR system may be described for purposes of example, and LTE, LTE-A, LTE-A Pro, or NR terminology may be used in much of the description, the techniques described herein are applicable beyond LTE, LTE-A, LTE-A Pro, or NR applications. 
     A macro cell generally covers a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by UEs  115  with service subscriptions with the network provider. A small cell may be associated with a lower-powered base station  105 , as compared with a macro cell, and a small cell may operate in the same or different (e.g., licensed, unlicensed, etc.) frequency bands as macro cells. Small cells may include pico cells, femto cells, and micro cells according to various examples. A pico cell, for example, may cover a small geographic area and may allow unrestricted access by UEs  115  with service subscriptions with the network provider. A femto cell may also cover a small geographic area (e.g., a home) and may provide restricted access by UEs  115  having an association with the femto cell (e.g., UEs  115  in a closed subscriber group (CSG), UEs  115  for users in the home, and the like). An eNB for a macro cell may be referred to as a macro eNB. An eNB for a small cell may be referred to as a small cell eNB, a pico eNB, a femto eNB, or a home eNB. An eNB may support one or multiple (e.g., two, three, four, and the like) cells, and may also support communications using one or multiple component carriers. 
     The wireless communications system  100  or systems described herein may support synchronous or asynchronous operation. For synchronous operation, the base stations  105  may have similar frame timing, and transmissions from different base stations  105  may be approximately aligned in time. For asynchronous operation, the base stations  105  may have different frame timing, and transmissions from different base stations  105  may not be aligned in time. The techniques described herein may be used for either synchronous or asynchronous operations. 
     Information and signals described herein may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof. 
     The various illustrative blocks and modules described in connection with the disclosure herein may be implemented or performed with a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA) or other programmable logic device (PLD), discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices (e.g., a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration). 
     The functions described herein may be implemented in hardware, software executed by a processor, firmware, or any combination thereof. If implemented in software executed by a processor, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Other examples and implementations are within the scope of the disclosure and appended claims. For example, due to the nature of software, functions described above can be implemented using software executed by a processor, hardware, firmware, hardwiring, or combinations of any of these. Features implementing functions may also be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations. 
     Computer-readable media includes both non-transitory computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A non-transitory storage medium may be any available medium that can be accessed by a general purpose or special purpose computer. By way of example, and not limitation, non-transitory computer-readable media may comprise random-access memory (RAM), read-only memory (ROM), electrically erasable programmable read only memory (EEPROM), flash memory, compact disk (CD) ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other non-transitory medium that can be used to carry or store desired program code means in the form of instructions or data structures and that can be accessed by a general-purpose or special-purpose computer, or a general-purpose or special-purpose processor. Also, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. Disk and disc, as used herein, include CD, laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above are also included within the scope of computer-readable media. 
     As used herein, including in the claims, “or” as used in a list of items (e.g., a list of items prefaced by a phrase such as “at least one of” or “one or more of”) indicates an inclusive list such that, for example, a list of at least one of A, B, or C means A or B or C or AB or AC or BC or ABC (i.e., A and B and C). Also, as used herein, the phrase “based on” shall not be construed as a reference to a closed set of conditions. For example, an exemplary step that is described as “based on condition A” may be based on both a condition A and a condition B without departing from the scope of the present disclosure. In other words, as used herein, the phrase “based on” shall be construed in the same manner as the phrase “based at least in part on.” 
     In the appended figures, similar components or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar components. If just the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label, or other subsequent reference label. 
     The description set forth herein, in connection with the appended drawings, describes example configurations and does not represent all the examples that may be implemented or that are within the scope of the claims. The term “exemplary” used herein means “serving as an example, instance, or illustration,” and not “preferred” or “advantageous over other examples.” The detailed description includes specific details for the purpose of providing an understanding of the described techniques. These techniques, however, may be practiced without these specific details. In some instances, well-known structures and devices are shown in block diagram form in order to avoid obscuring the concepts of the described examples. 
     The description herein is provided to enable a person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other variations without departing from the scope of the disclosure. Thus, the disclosure is not limited to the examples and designs described herein, but is to be accorded the broadest scope consistent with the principles and novel features disclosed herein.