Patent Description:
Aspects of the present disclosure relate generally to wireless communication systems and to sounding reference signal (SRS) carrier switching with short transmission time interval (sTTI)/short processing time (sPT).

Research and development continue to advance the UMTS technologies not only to meet the growing demand for mobile broadband access, but to advance and enhance the user experience with mobile communications.

Patent application <CIT> relates to techniques for facilitating SRS Switching. User Equipments (UEs) may be assigned a set of aggregated component carriers for downlink carrier aggregation and/or carrier selection. Some UEs may be incapable of transmitting uplink signals over all component carriers in their assigned set of aggregated component carriers. In such scenarios, a UE may need to perform SRS switching in order to transmit SRS symbols over all of the component carriers.

The publication "<NPL> relates to Different aspects of SRS carrier switching, such as the reduction in timeline from N+<NUM> to N+<NUM>, to support of <NUM>-symbol SRS in UpPTS, and to the maximum number of supportable CC.

This disclosure relates generally to providing or participating in authorized shared access between two or more wireless communications systems, also referred to as wireless communications networks. In various embodiments, the techniques and apparatus may be used for wireless communication networks such as code division multiple access (CDMA) networks, time division multiple access (TDMA) networks, frequency division multiple access (FDMA) networks, orthogonal FDMA (OFDMA) networks, single-carrier FDMA (SC-FDMA) networks, LTE networks, GSM networks, as well as other communications networks. As described herein, the terms "networks" and "systems" may be used interchangeably.

A CDMA network may implement a radio technology such as universal terrestrial radio access (UTRA), cdma2000, and the like. UTRA includes wideband-CDMA (W-CDMA) and low chip rate (LCR), CDMA2000 covers IS-<NUM>, IS-<NUM>, and IS-<NUM> standards.

3GPP defines standards for the GSM EDGE (enhanced data rates for GSM evolution) radio access network (RAN), also denoted as GERAN. GERAN is the radio component of GSM/EDGE, together with the network that joins the base stations (for example, the Ater and Abis interfaces) and the base station controllers (A interfaces, etc.). The radio access network represents a component of a GSM network, through which phone calls and packet data are routed from and to the public switched telephone network (PSTN) and Internet to and from subscriber handsets, also known as user terminals or user equipments (UEs). A mobile phone operator's network may comprise one or more GERANs, which may be coupled with UTRANs in the case of a UMTS/GSM network. An operator network may also include one or more LTE networks, and/or one or more other networks. The various different network types may use different radio access technologies (RATs) and radio access networks (RANs).

UTRA, E-UTRA, and GSM are part of universal mobile telecommunication system (UMTS). 3GPP long term evolution (LTE) is a 3GPP project aimed at improving the universal mobile telecommunications system (UMTS) mobile phone standard. For clarity, certain aspects of the apparatus and techniques may be described below for LTE implementations or in an LTE-centric way, and LTE terminology may be used as illustrative examples in portions of the description below; however, the description is not intended to be limited to LTE applications. Indeed, the present disclosure is concerned with shared access to wireless spectrum between networks using different radio access technologies or radio air interfaces.

A new carrier type based on LTE/LTE-A including unlicensed spectrum has also been suggested that can be compatible with carrier-grade WiFi, making LTE/LTE-A with unlicensed spectrum an alternative to WiFi. LTE/LTE-A, when operating in unlicensed spectrum, may leverage LTE concepts and may introduce some modifications to physical layer (PHY) and media access control (MAC) aspects of the network or network devices to provide efficient operation in the unlicensed spectrum and meet regulatory requirements. The unlicensed spectrum used may range from as low as several hundred Megahertz (MHz) to as high as tens of Gigahertz (GHz), for example. In operation, such LTE/LTE-A networks may operate with any combination of licensed or unlicensed spectrum depending on loading and availability. Accordingly, it may be apparent to one of skill in the art that the systems, apparatus and methods described herein may be applied to other communications systems and applications.

System designs may support various time-frequency reference signals for the downlink and uplink to facilitate beamforming and other functions. A reference signal is a signal generated based on known data and may also be referred to as a pilot, preamble, training signal, sounding signal, and the like. A reference signal may be used by a receiver for various purposes such as channel estimation, coherent demodulation, channel quality measurement, signal strength measurement, and the like. MIMO systems using multiple antennas generally provide for coordination of sending of reference signals between antennas; however, LTE systems do not in general provide for coordination of sending of reference signals from multiple base stations or eNBs.

In some implementations, a system may utilize time division duplexing (TDD). For TDD, the downlink and uplink share the same frequency spectrum or channel, and downlink and uplink transmissions are sent on the same frequency spectrum. The downlink channel response may thus be correlated with the uplink channel response. Reciprocity may allow a downlink channel to be estimated based on transmissions sent via the uplink. These uplink transmissions may be reference signals or uplink control channels (which may be used as reference symbols after demodulation). The uplink transmissions may allow for estimation of a space-selective channel via multiple antennas.

In LTE implementations, orthogonal frequency division multiplexing (OFDM) is used for the downlink - that is, from a base station, access point or eNodeB (eNB) to a user terminal or UE. Use of OFDM meets the LTE requirement for spectrum flexibility and enables cost-efficient solutions for very wide carriers with high peak rates, and is a well-established technology. For example, OFDM is used in standards such as IEEE <NUM>. 11a/g, <NUM>, High Performance Radio LAN-<NUM> (HIPERLAN-<NUM>, wherein LAN stands for Local Area Network) standardized by the European Telecommunications Standards Institute (ETSI), Digital Video Broadcasting (DVB) published by the Joint Technical Committee of ETSI, and other standards.

Time frequency physical resource blocks (also denoted here in as resource blocks or "RBs" for brevity) may be defined in OFDM systems as groups of transport carriers (e.g. sub-carriers) or intervals that are assigned to transport data. The RBs are defined over a time and frequency period. Resource blocks are comprised of time-frequency resource elements (also denoted here in as resource elements or "REs" for brevity), which may be defined by indices of time and frequency in a slot. Additional details of LTE RBs and liEs are described in the 3GPP specifications, such as, for example, 3GPP TS <NUM>.

UMTS LTE supports scalable carrier bandwidths from <NUM> down to <NUM>. In LTE, an RB is defined as <NUM> sub-carriers when the subcarrier bandwidth is <NUM>, or <NUM> sub-carriers when the sub-carrier bandwidth is <NUM>. In an exemplary implementation, in the time domain there is a defined radio frame that is <NUM> long and consists of <NUM> subframes of <NUM> millisecond (ms) each. Every subframe consists of <NUM> slots, where each slot is <NUM>. The subcarrier spacing in the frequency domain in this case is <NUM>. Twelve of these subcarriers together (per slot) constitute an RB, so in this implementation one resource block is <NUM>. Six Resource blocks fit in a carrier of <NUM> and <NUM> resource blocks fit in a carrier of <NUM>.

<FIG> shows a wireless network <NUM> for communication, which may be an LTE-A network. The wireless network <NUM> includes a number of evolved node Bs (eNBs) <NUM> and other network entities. An eNB may be a station that communicates with the UEs and may also be referred to as a base station, a node B, an access point, and the like. Each eNB <NUM> may provide communication coverage for a particular geographic area. In 3GPP, the term "cell" can refer to this particular geographic coverage area of an eNB and/or an eNB subsystem serving the coverage area, depending on the context in which the term is used.

An eNB may provide communication coverage for a macro cell or a small cell, such as a pico cell or a femto cell, and/or other types of cell. An eN-B 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. In the example shown in <FIG>, the eNBs 105a, 105b and 105c are macro eNBs for the macro cells 110a, 110b and 110c, respectively. The eNBs 105x, 105y, and 105z are small cell eNBs, which may include pico or femto eNBs that provide service to small cells 110x, 110y, and 110z, respectively. An eNB may support one or multiple (e.g., two, three, four, and the like) cells.

For synchronous operation, the eNBs may have similar frame timing, and transmissions from different eNBs may be approximately aligned in time. For asynchronous operation, the eNBs may have different frame timing, and transmissions from different eNBs may not be aligned in time.

The UEs <NUM> are dispersed throughout the wireless network <NUM>, and each UE may be stationary or mobile. A UE may also be referred to as a terminal, a mobile station, a subscriber unit, a station, or the like. A UE may be a cellular phone, a personal digital assistant (PDA), a wireless modem, a wireless communication device, a handheld device, a tablet computer, a laptop computer, a cordless phone, a wireless local loop (WLL) station, or the like. A UE may be able to communicate with macro eNBs, pico eNBs, femto eNBs, relays, and the like. In <FIG>, a lightning bolt (e.g., communication links <NUM>) indicates wireless transmissions between a UE and a serving eNB, which is an eNB designated to serve the UE on the downlink and/or uplink, or desired transmission between eNBs. Wired backhaul communication <NUM> indicate wired backhaul communications that may occur between eNBs.

LTE/-A utilizes orthogonal frequency division multiplexing (OFDM) on the downlink and single-carrier frequency division multiplexing (SC-FDM) on the uplink. OFDM and SC-FDM partition the system bandwidth into multiple (K) orthogonal subcarriers, which are also commonly referred to as tones, bins, or the like. Each subcarrier may be modulated with data. For example, K may be equal to <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> for a corresponding system bandwidth of <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> megahertz (MHz), respectively. The system bandwidth may also be partitioned into sub-bands. For example, a sub-band may cover <NUM>, and there may be <NUM>, <NUM>, <NUM>, <NUM> or <NUM> sub-bands for a corresponding system bandwidth of <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>, respectively.

<FIG> shows a block diagram of a design of a base station/eNB <NUM> and a UE <NUM>, which may be one of the base stations/eNBs and one of the UEs in <FIG>. For a restricted association scenario, the eNB <NUM> may be the small cell eNB 105z in <FIG>, and the UE <NUM> may be the UE 115z, which in order to access small cell eNB 105z, would be included in a list of accessible UEs for small cell eNB 105z. The eNB <NUM> may also be a base station of some other type. The eNB <NUM> may be equipped with antennas 234a through 234t, and the UE <NUM> may be equipped with antennas 252a through 252r.

At the eNB <NUM>, a transmit processor <NUM> may receive data from a data source <NUM> and control information from a controller/processor <NUM>. The control information may be for the PBCH, PCFICH, PHICH, PDCCH, etc. The data may be for the PDSCH, etc. The transmit processor <NUM> may process (e.g., encode and symbol map) the data and control information to obtain data symbols and control symbols, respectively. The transmit processor <NUM> may also generate reference symbols, e.g., for the PSS, SSS, and cell-specific reference signal. A transmit (TX) multiple-input multiple-output (MIMO) processor <NUM> may perform spatial processing (e.g., precoding) on the data symbols, the control symbols, and/or the reference symbols, if applicable, and may provide output symbol streams to the modulators (MODs) 232a through 232t. Downlink signals from modulators 232a through 232t may be transmitted via the antennas 234a through 234t, respectively.

At the UE <NUM>, the antennas 252a through 252r may receive the downlink signals from the eNB <NUM> and may provide received signals to the demodulators (DEMODs) 254a through 254r, respectively. A MIMO detector <NUM> may obtain received symbols from all the demodulators 254a through 254r, perform MIMO detection on the received symbols if applicable, and provide detected symbols. A receive processor <NUM> may process (e.g., demodulate, deinterleave, and decode) the detected symbols, provide decoded data for the UE <NUM> to a data sink <NUM>, and provide decoded control information to a controller/processor <NUM>,.

On the uplink, at the UE <NUM>, a transmit processor <NUM> may receive and process data (e.g., for the PUSCH) from a data source <NUM> and control information (e.g., for the PUCCH) from the controller/processor <NUM>. The symbols from the transmit processor <NUM> may be precoded by a TX MIMO processor <NUM> if applicable, further processed by the modulators 254a through 254r (e.g., for SC-FDM, etc.), and transmitted to the eNB <NUM>. At the eNB <NUM>, the uplink signals from the UE <NUM> may be received by the antennas <NUM>, processed by the demodulators <NUM>, detected by a MIMO detector <NUM> if applicable, and further processed by a receive processor <NUM> to obtain decoded data and control information sent by the UE <NUM>. The processor <NUM> may provide the decoded data to a data sink <NUM> and the decoded control information to the controller/processor <NUM>.

The controllers/processors <NUM> and <NUM> may direct the operation at the eNB <NUM> and the UE <NUM>, respectively. The controller/processor <NUM> and/or other processors and modules at the eNB <NUM> may perform or direct the execution of various processes for the techniques described herein. The controllers/processor <NUM> and/or other processors and modules at the UE <NUM> may also perform or direct the execution of the functional blocks illustrated in <FIG>, and/or other processes for the techniques described herein. The memories <NUM> and <NUM> may store data and program codes for the eNB <NUM> and the UE <NUM>, respectively.

In advanced versions of LTE, SRS carrier switching allows the ability for a UE to transmit sound reference signals (SRS) in a time division duplex (TDD) secondary cell (SCell) for which there is no uplink configured. In LTE deployments, there may be more downlink-only carriers configured for communications. Thus, some carriers may only be configured for downlink communications. Because downlink and uplink carriers are reciprocal in TDD cells, it may be helpful for channel estimation to configure the UE to transmit SRS on such a TDD cell (referred to herein as a "SRS-SCell" or a "TDD serving cell without PUSCH/PUCCH transmission") configured only for downlink. The SRS may be used for beamforming or channel estimation of the configured downlink channel due to the reciprocal relationship. The UE may switch or retune one of its radio frequency (RF) transmit chains to the SRS-SCell, which creates an interruption in a different SCell/PCell for the switched SRS transmission.

SRS carrier switching may be triggered either via the downlink configured SCell or through the common search space (CSS) of a primary cell (PCell). In some cases (e.g. dual connectivity), the primary cell may be a primary SCell (pSCell). Moreover, the triggering signal in the CSS of the PCell may take the form of a group triggering signal (e.g., group DCI, DCI format 3B), which triggers SRS carrier switching for a group of UEs and/or a group of carriers for at least one UE. The interrruptions/prioritizations of transmissions of the UE may depend on both the information sent on the cell that will be interrupted (the "source cell") as well as whether the SRS is requested as an asynchronous SRS (A-SRS) or periodic SRS (P-SRS). The UE reports the interruption time to retune from the band A carrier to the band B carrier. Example interruption times may be up to <NUM>, but more relaxed interruption times may be allowed, such allowing for dropping such transmissions up to <NUM> before and <NUM> after the UE switches to the target SCell.

Additional advanced networks have introduced the timing capabilities of short transmit time interval (sTTI) and short processing time (sPT). The concepts of sTTI and sPT operate to reduce the timeline of communications. For example, sTTI may reduce the timeline and length of the TTI to sub-slot or slot timing. Thus, sTTI timing may provide transmission units on a per slot basis or even smaller basis, such as on a <NUM>/<NUM> OFDM-symbol sub-slot scheduling. Thus, for a standard subframe, there may be up to six transmission units (e.g., with the <NUM>/<NUM> OFDM-symbol sub-slot scheduling).

While sTTI/sPT work on a faster timescale, SRS carrier switching relies on RF retuning procedures that may operate on a slower timescale. Thus, in order to compute the collision handling rules that may arise with SRS carrier switching for operations that may be configured with sTTI/sPT, the UE may perform a "look ahead" operation, in which, for example, the decision to transmit SRS in subframe N may depend on the data to be transmitted in subframe N+<NUM>.

The current standard timeline allows for a <NUM> interruption before transmitting SRS. Considering that a slot-based sTTI has an "N+<NUM>" timing for SRS, such that a grant received in slot N will trigger transmission of the SRS at slot N+<NUM>, there would be <NUM> to compute any switching times, reconfigure the RF, etc. A UE, thus, may not have enough time to process all this information before switching carriers, even though the RF switching time may be the same as for a standard, <NUM> TTI. Additionally, while a UE may be processing a DCI more quickly in one carrier, it may then receive a DCI on another carrier that is configured for slower timing. The two carriers are coupled together for the SRS carrier switching, but because of the discrepancies of the timing between the two carriers there may be issues coordinating operations on both carriers.

It should be noted that the "interruption time" may be defined herein as the time during which the UE cannot transmit or receive on the "source cell. " However, before the defined interruption time, the UE would process a set of items (e.g. power amplifier (PA) loading, retuning parameters, etc.). Thus, the effective interruption time may be much greater than simply the time while the UE can neither transmit nor receive.

<FIG> is a block diagram illustrating example blocks executed to implement one aspect of the present disclosure. The example blocks will also be described with respect to UE <NUM> as illustrated in <FIG> is a block diagram illustrating UE <NUM> configured according to one aspect of the present disclosure. UE <NUM> includes the structure, hardware, and components as illustrated for UE <NUM> of <FIG>. For example, UE <NUM> includes controller/processor <NUM>, which operates to execute logic or computer instructions stored in memory <NUM>, as well as controlling the components of UE <NUM> that provide the features and functionality of UE <NUM>. UE <NUM>, under control of controller/processor <NUM>, transmits and receives signals via wireless radios 600a-r and antennas 252a-r. Wireless radios 600a-r includes various components and hardware, as illustrated in <FIG> for UE <NUM>, including modulator/demodulators 254a-r, MIMO detector <NUM>, receive processor <NUM>, transmit processor <NUM>, and TX MIMO processor <NUM>.

At block <NUM>, a UE receives, on a first carrier, an SRS trigger for SRS carrier switching to a downlink-configured second carrier for an SRS transmission at a designated subframe. The UE, such as UE <NUM>, may receive the SRS trigger via antennas 252a-r and wireless radios 600a-r. The SRS trigger may be received in a downlink control signal in the common search space (CSS) of a PCell, or in a UE-specific search space of an SRS-SCell.

At block <NUM>, the UE determines whether there are any additional signals scheduled for the UE to transmit on the first carrier at the designated subframe and on the first carrier at a subsequent subframe adjacent to the designated subframe. In order to execute the SRS carrier switching, upon receiving the trigger, UE <NUM>, under control of controller/processor <NUM>, executes SRS switching logic <NUM>, stored in memory <NUM>. The execution environment of SRS switching logic <NUM> allows for UE <NUM> to look ahead to the designated subframe and its adjacent subsequent subframe to determine whether there are any additional signals for UE <NUM> to transmit. UE <NUM> may identify colliding signals for transmission in the designated subframe and/or additional signals scheduled for transmission in the subsequent subframe which may impact the decision to perform the SRS carrier switching for SRS transmission in the designated subframe or not.

At block <NUM>, the UE, in response to detection of a first additional signal scheduled on the designated subframe, resolves a collision between the SRS transmission and the first additional signal to identify a first scheduled transmission for the designated subframe. If a colliding signal is detected in the designated subframe, UE <NUM> accesses transmission prioritization logic <NUM>, stored in memory <NUM>. UE <NUM> compares the priority of the SRS transmission with the signal scheduled at the designated subframe to identify the first transmission to schedule for the designated subframe (the "first scheduled transmission"). As noted further below, the priority may be applied according to the following relation: <MAT>.

Currently, the priority rules depend mainly on the type of transmission (e.g., HARQ-ACK, CQI, etc.) Aspects of the present disclosure provide for resolving collisions by prioritizing SRS switching or transmission in source cell also depending on the TTI length and/or HARQ scheduling time. For example when a standard <NUM> PUSCH collides with SRS, UE <NUM> may drop the PUSCH, but if UE <NUM> accesses TTI capability <NUM> and identifies that the collision is between an sTTI PUSCH and SRS, UE <NUM> may drop SRS. Thus, the rules for resolving the collisions may be different depending on whether UE <NUM> operates in standard TTI (N+<NUM> timing) or sTTI (N+<NUM> timing). Transmit prioritization logic <NUM> may include such rules for resolving collision in consideration of the TTI mode configured for operation.

In an additional and/or alternative aspect of the present disclosure, the rules for resolving collisions may also depend on whether the data carried over the sTTI is marked as high reliability (e.g., URLLC). In implementation of such an aspect, UE <NUM> accesses data priority <NUM> to determine the priority of the data for transmission over the sTTI. UE <NUM> may identify the logic channel identifier (LCID), which may provide the data quality requirements for transmission on the logical channel. In some cases, UE <NUM> may identify a physical layer identifier (e.g. RNTI, field in DCI, DCI format used for scheduling, search space, etc.) associated with the URLLC traffic to determine the data priority. UE <NUM> notes this data priority in memory <NUM> at data priority <NUM>.

At block <NUM>, the UE, in response to detection of a second additional signal scheduled on the subsequent subframe, resolves a transmission priority between the first scheduled transmission and the second additional signal. At block <NUM>, the UE transmits either the first scheduled transmission or the second additional signal according to results of the resolving. If UE <NUM><NUM> detects an additional signal scheduled for transmission in the subsequent subframe, UE <NUM> again identifies the transmission priority between the two signals as provided in transmission prioritization logic <NUM>. If the first scheduled transmission has priority over the second additional signal, then UE <NUM> would drop transmission of the second additional signal if the first scheduled transmission is the SRS transmission or transmit both signals if the first scheduled transmission is the first additional signal. However, if the second additional signal has priority over the first scheduled transmission, then, when the first scheduled transmission is the first additional signal, LIE <NUM> may either transmit both first and second additional signals, as scheduled, or simply transmit the second additional signal. But, when the first scheduled transmission is the SRS signal, then, depending on whether UE <NUM> has already switched carriers, UE <NUM> checks processing time capability <NUM> to determine whether it is capable of sPT. If so, then UE <NUM> may switch back to the first carrier and transmit the first additional signal before transmitting the second additional signal. If UE <NUM> cannot perform sPT, UE <NUM> would switch back to the first carrier, drop transmission of the first additional signal, as there would not be sufficient time to switch back to the first carrier to transmit the first additional signal at the designated subframe. UE <NUM> would, instead, only transmit the second additional signal at the subsequent subframe.

<FIG> is a block diagram illustrating a UE <NUM><NUM> and base station <NUM> configured for SRS carrier switching according to one aspect of the present disclosure. The transmission of SRS in subframe N+<NUM> may depend on the transmitted information in subframe N+<NUM>. As noted above in equation (<NUM>), one example priority rule provides that CQI : SRS < HARQ-ACK. If UE has HARQ-ACK scheduled for subframe N+<NUM>, it only has <NUM> (minus any timing advance (TA)) to determine whether to transmit CQI, which is reduced with respect to legacy timeline.

It should be noted that the examples described with respect to <FIG> refer to CQI as the lower priority transmission. However, the scope of the various aspects of the present disclosure may cover the general case of a "lower priority transmission" that is not planned to be transmitted in subframe N+<NUM> due to an initial trigger for SRS carrier switching until a higher priority transmission arrives in subframe N+<NUM>.

<FIG> illustrates a transmission stream <NUM> between UE <NUM> and base station <NUM> at three different time points. At N-<NUM>, UE <NUM> identifies that it has CQI scheduled for transmission at N+<NUM> on the first carrier, CC1. At N, UE <NUM> receives an aperiodic SRS trigger to perform SRS carrier switching to CC2 for transmission of SRS. In comparing priorities of the two colliding signals, SRS has priority over CQI. Therefore, UE <NUM> drops CQI at N+<NUM> on CC1 to retune to CC2 for transmitting SRS, At N+<NUM>, UE <NUM> receives a downlink data via PDSCH, which would trigger an acknowledgement signal (ACK) to be transmitted at N+<NUM>, UE <NUM> determines the priority between the SRS scheduled for N+<NUM> and ACK scheduled for N+<NUM>. Because HARQ-ACK has priority over SRS, and, after tuning away to CC2. , there would be insufficient time to transmit both SRS on CC2 at N+<NUM> and then retune to CC1 for transmission of ACK. Therefore, UE <NUM> drops transmission of SRS at N+<NUM>. With four sub-frames between the PDSCH and the scheduled ACK, UE <NUM> would have sufficient time to retune to CC1 for transmission.

After dropping the SRS transmission at N+<NUM>, UE <NUM> may determine whether or not it may also transmit the CQ1 at N+<NUM> on CC1 instead, as originally scheduled. In a first optional aspect, in the baseline behavior, where UE <NUM> operates on CCT1 with a standard-length TTI, the lower priority transmission should not be transmitted even if UE <NUM> has not tuned to CC2. For the UE operating in sTTI mode, given the additional (and faster) UE processing, UE <NUM> may be able to transmit the sTTI transmission (e.g., PUSCH at N+<NUM>), but not any other transmission.

Transmission stream <NUM> is an alternate transmission between UE <NUM> and base station <NUM>. The SRS trigger received at N prompts UE <NUM> to drop CQI transmission at N+<NUM> on CC1 to retune to CC2 for SRS transmission. At N+<NUM>, UE <NUM> receives an sTTI grant via sPDCCH granting sPUSCH transmissions at N+<NUM>. However, at N+<NUM>, UE <NUM> has already tuned to CC2. In this case, the transmission of sPUSCH may depend on the separation between the SRS and the sPUSCH. For example, if SRS is in the last symbol of the subframe and sPUSCH is right before that, UE <NUM> may not have time to re-configure the RF to come back to the source cell at CC1. However, where SRS is at N+<NUM> and sPUSCH is at N+<NUM>, UE <NUM> may have enough time to tune back to CC1 for sPUSCH transmission.

In an additional aspect illustrated by <FIG>, if UE <NUM> is operating in a sPT mode for CC1 of transmission stream <NUM>, and the "higher priority transmission" (e.g., ACK at N+<NUM>) is processed using normal processing time (e.g., PDSCH scheduled from a CSS on a PCell), UE <NUM> may be able to transmit the CQI N+<NUM> in addition to the ACK in N+<NUM>. This is for the case when DCI processing is performed assuming a worst case (e.g., the case where the UE has less time to process it according to sPT).

In a further additional aspect illustrated by <FIG>, UE <NUM> has the capability of processing the DCI faster, thus, processing and transmitting with an N+<NUM> timing should not be a problem. In such case, UE <NUM> may transmit the CQI in subframe N+<NUM> after dropping the SRS in response to the data transmission at N+<NUM> that prompts an ACK at N+<NUM> in CC1. Such transmission may depend on the current timing advance (TA) and scheduling signal. UE <NUM> may transmit the CQI in subframe N+<NUM> when the TA is below a threshold (e.g., <NUM>, <NUM>, etc.). For a TA above that threshold, UE <NUM> would drop transmission of the CQI. Additionally, transmission of the CQI by UE <NUM> in subframe N+<NUM> can also depend on whether the "higher priority transmission" is scheduled based on PDCCH or EPDCCH. For PDCCH scheduling, UE <NUM> may transmit the CQI, while for EPDCCH scheduling, because it covers an entire subframe, UE <NUM> may drop transmission of the CQI at N+<NUM>.

Some UEs may be able to perform faster DCI processing and/or prepare two hypotheses in parallel (e.g. prepare the SRS and the CQI transmission) without the need to support sPT. Thus, such UEs, such as UE <NUM> for this example aspect, may transmit CQI when the current TA meets the threshold and the higher priority transmission is scheduled based on PDCCH. However, UE <NUM> does not necessarily have sPT capabilities, but may support a look-ahead procedure as a separate capability.

<FIG> is a block diagram illustrating UEs 115a-115c and base station <NUM> configured according to one aspect of the present disclosure. In current LTE networks, there are generally two ways to trigger SRS carrier switching: (<NUM>) transmitting a trigger signal in the common search space (CSS) of a PCell, such as PCell <NUM>, and (<NUM>) transmitting the trigger signal on an SRS-SCell (an SCell with a downlink-only configuration), such as SCell <NUM>. Triggering from SCell <NUM> may further tighten the UE timeline when sPT is configured due to having to perform RF retuning and RF preparation. In the presently described example aspect, there is a separate capability on whether UE 115a supports triggering SRS carrier switching from SCell <NUM> when configured with sPT.

In a first example aspect, UE 115a may support SRS carrier switching, but the switching cannot be triggered by sPT trigger in SCell <NUM>. While an SRS trigger at CSS DCI <NUM> of subframe N may properly trigger UE 115a to retune to SCell <NUM> for SRS 504a transmission, the SRS trigger at DL DCI 503b would not be valid for UE 115a. Alternatively, if SRS triggering from DL DCI 503b is supported, the timeline may follow N+<NUM> (legacy timing) instead of N+<NUM>. Thus, in the alternative example, DL DCI 503b may cause UE 115a to retune to SCell <NUM> for SRS 504b transmission at N+<NUM>.

In SRS SCells (without PUSCH/PUCCH configured), such as SCells <NUM>, <NUM>, <NUM>, <NUM>, when sPT/sTTI is configured for downlink, a question arises as to whether the uplink channel also shares the sPT/sTTI configuration. In a first alternative aspect, sPT/sTTI configuration may be automatically linked between downlink and uplink channels, such that when sPT/sTTI is configured for the downlink, sPT/sTTI related to HARQ/scheduling timing is also applicable to the uplink. In a second alternative aspect, sPT/sTTI may be separately configured for downlink and uplink, such that UE 115a timing can be further configured for SRS triggering based on sPT/sTTI or legacy <NUM> N+<NUM> timing.

In an additional aspect of the present disclosure, the SRS trigger in CSS DCI 503a may provide a group downlink control as well as power control commands. For either case, different CCs for the same UE and/or for different UEs may have the same or different timing to apply the SRS triggering or power control commands. Thus, there may be the same or different timing configurations for UEs 115a-115c and for SCells <NUM>, <NUM>, <NUM>, and <NUM>. In a first example aspect, the group control does not allow different timings in the same group control. Thus, even though UEs 115a-115c and SCells <NUM>, <NUM>, <NUM>, and <NUM> may have different timing configurations, the group control command at CSS DCI 503a identifies the same timing configuration (e.g., regular N+<NUM> or short N+<NUM>). In a second alternative aspect, when different timing configurations are in the same group, a common timing may be assumed at least for some CCs for a given UE. For example, UE 115b is capable of simultaneous SRS transmissions on SCell <NUM> with N+<NUM> and SCell <NUM> with N +<NUM>, if triggered for both SCells <NUM> and <NUM>. In such an instance, UE 115b can start SRS transmission at N +<NUM> for both SCells <NUM> and <NUM>.

In a third alternative aspect, different timing configurations may be applied separately, but with the shorter timing configurations having a higher priority. For example, SCell <NUM> is configured with N+<NUM>, while SCell <NUM> is configured with N+<NUM>. When UE 115c is triggered simultaneously for SRS carrier switching, SRS for SCell <NUM> is transmitted first, as it has priority over SRS transmissions for SCell <NUM> with an N+<NUM> timing configuration. Such prioritization can be implemented using explicit rules or signaled semi-statically using RRC configuration (e.g., base station <NUM> can configure the SCells having shorter timing configurations with a lower cell index, where the lower cell index CCs take precedence).

The functional blocks and modules in <FIG> may comprise processors, electronics devices, hardware devices, electronics components, logical circuits, memories, software codes, firmware codes, etc., or any combination thereof.

Claim 1:
A method of wireless communication, comprising:
receiving (<NUM>), by a user equipment, UE, a sounding reference signal, SRS, trigger for SRS carrier switching from a first carrier to a downlink-configured second carrier for an SRS transmission at a designated subframe;
determining (<NUM>), by the UE, whether there are any additional signals scheduled for the UE to transmit on the first carrier that overlap with the SRS transmission;
resolving (<NUM>), by the UE in response to detection of a first additional signal scheduled on the designated subframe, a collision between the SRS transmission and the first additional signal to identify a first scheduled transmission for the designated subframe, wherein the resolving the collision includes:
determining, by the UE, one or more of a transmission time interval, TTI, length and a processing time configured for each of the SRS transmission and the first additional signal, or an acknowledgement reporting schedule associated with the first carrier; and
selecting, by the UE, one of the SRS transmission or the first additional signal as the first scheduled transmission according to a priority rule, wherein the priority rule is based at least in part on one or more of the acknowledgement reporting schedule, the TTI length, or the processing time; and
transmitting by the UE, one or more of the SRS transmission or the first additional signal according to results of the resolving.