Patent Description:
A wireless network may include a number of base stations (BSs) that can support communication for a number of user equipments (UEs).

<CIT> describes methods and apparatus for multi-carrier communication systems with automatic repeat request (arq).

In some aspects, a method of wireless communication, performed by a base station, includes receiving, from a user equipment (UE), a message that indicates whether the UE received a downlink transmission from the base station in a first frequency range; scheduling one or more reference signal (RS) transmissions in the first frequency range and one or more RS transmissions in a second frequency range based at least in part on the message received from the UE; and rescheduling the downlink transmission on a component carrier in either the first frequency range or the second frequency range based at least in part on channel quality information that is determined from the one or more RS transmissions in the first frequency range and the one or more RS transmissions in the second frequency range.

In some aspects, a method of wireless communication, performed by a UE, includes transmitting, to a base station, a message that indicates whether the UE received a downlink transmission from the base station in a first frequency range; receiving, from the base station, information related to one or more RS transmissions that are scheduled in the first frequency range and one or more RS transmissions that are scheduled in a second frequency range based at least in part on the message transmitted to the base station; and receiving the downlink transmission on a component carrier in either the first frequency range or the second frequency range based at least in part on channel quality information that is determined from the one or more RS transmissions in the first frequency range and the one or more RS transmissions in the second frequency range.

In some aspects, a base station includes a memory and one or more processors operatively coupled to the memory. The memory and the one or more processors may be configured to: receive, from a UE, a message that indicates whether the UE received a downlink transmission from the base station in a first frequency range; schedule one or more RS transmissions in the first frequency range and one or more RS transmissions in a second frequency range based at least in part on the message received from the UE; and reschedule the downlink transmission on a component carrier in either the first frequency range or the second frequency range based at least in part on channel quality information that is determined from the one or more RS transmissions in the first frequency range and the one or more RS transmissions in the second frequency range.

In some aspects, a UE includes a memory and one or more processors operatively coupled to the memory. The memory and the one or more processors may be configured to: transmit, to a base station, a message that indicates whether the UE received a downlink transmission from the base station in a first frequency range; receive, from the base station, information related to one or more RS transmissions that are scheduled in the first frequency range and one or more RS transmissions that are scheduled in a second frequency range based at least in part on the message transmitted to the base station; and receive the downlink transmission on a component carrier in either the first frequency range or the second frequency range based at least in part on channel quality information that is determined from the one or more RS transmissions in the first frequency range and the one or more RS transmissions in the second frequency range.

It should be noted that while aspects may be described herein using terminology associated with a <NUM> or NR radio access technology (RAT), aspects of the present disclosure can be applied to other RATs, such as a <NUM> RAT, a <NUM> RAT, and/or a RAT subsequent to <NUM> (e.g., <NUM>).

A network controller <NUM> may be coupled to a set of BSs and may provide coordination and control for these BSs.

<FIG> is a diagram illustrating an example <NUM> of a base station <NUM> in communication with a UE <NUM> in a wireless network, in accordance with various aspects of the present disclosure.

Transmit processor <NUM> may also generate reference symbols for reference signals (e.g., a cell-specific reference signal (CRS), a demodulation reference signal (DMRS), and/or the like) and synchronization signals (e.g., the primary synchronization signal (PSS) and secondary synchronization signal (SSS)).

On the uplink, at UE <NUM>, a transmit processor <NUM> may receive and process data from a data source <NUM> and control information (e.g., for reports that include RSRP, RSSI, RSRQ, CQI, and/or the like) from controller/processor <NUM>. The transceiver may be used by a processor (e.g., controller/processor <NUM>) and memory <NUM> to perform aspects of any of the methods described herein, for example, as described with reference to <FIG>, <FIG>, <FIG>, and/or <FIG>.

The transceiver may be used by a processor (e.g., controller/processor <NUM>) and memory <NUM> to perform aspects of any of the methods described herein, for example, as described with reference to <FIG>, <FIG>, <FIG>, and/or <FIG>.

Controller/processor <NUM> of base station <NUM>, controller/processor <NUM> of UE <NUM>, and/or any other component(s) of <FIG> may perform one or more techniques associated with event-triggered reference signal transmission for carrier selection, as described in more detail elsewhere herein. For example, controller/processor <NUM> of base station <NUM>, controller/processor <NUM> of UE <NUM>, and/or any other component(s) of <FIG> may perform or direct operations of, for example, process <NUM> of <FIG>, process <NUM> of <FIG>, and/or other processes as described herein. Memories <NUM> and <NUM> may store data and program codes for base station <NUM> and UE <NUM>, respectively. In some aspects, memory <NUM> and/or memory <NUM> may include a non-transitory computer-readable medium storing one or more instructions (e.g., code, program code, and/or the like) for wireless communication. For example, the one or more instructions, when executed (e.g., directly, or after compiling, converting, interpreting, and/or the like) by one or more processors of the base station <NUM> and/or the UE <NUM>, may cause the one or more processors, the UE <NUM>, and/or the base station <NUM> to perform or direction operations of, for example, process <NUM> of <FIG>, process <NUM> of <FIG>, and/or other processes as described herein. In some aspects, executing instructions may include running the instructions, converting the instructions, compiling the instructions, interpreting the instructions, and/or the like.

In some aspects, base station <NUM> may include means for receiving, from a UE (e.g., UE <NUM>), a message that indicates whether the UE received a downlink transmission from the base station in a first frequency range, means for scheduling one or more reference signal (RS) transmissions in the first frequency range and one or more RS transmissions in a second frequency range based at least in part on the message received from the UE, and means for rescheduling the downlink transmission on a component carrier in either the first frequency range or the second frequency range based at least in part on channel quality information that is determined from the one or more RS transmissions in the first frequency range and the one or more RS transmissions in the second frequency range, and/or the like. In some aspects, such means may include one or more components of base station <NUM> described in connection with <FIG>, such as antenna <NUM>, DEMOD <NUM>, MIMO detector <NUM>, receive processor <NUM>, controller/processor <NUM>, transmit processor <NUM>, TX MIMO processor <NUM>, MOD <NUM>, antenna <NUM>, and/or the like.

In some aspects, UE <NUM> may include means for transmitting, to a base station (e.g., base station <NUM>), a message that indicates whether UE <NUM> received a downlink transmission from the base station in a first frequency range, means for receiving, from the base station, information related to one or more RS transmissions that are scheduled in the first frequency range and one or more RS transmissions that are scheduled in a second frequency range based at least in part on the message transmitted to the base station, means for receiving the downlink transmission on a component carrier in either the first frequency range or the second frequency range based at least in part on channel quality information that is determined from the one or more RS transmissions in the first frequency range and the one or more RS transmissions in the second frequency range, and/or the like. In some aspects, such means may include one or more components of UE <NUM> described in connection with <FIG>, such as controller/processor <NUM>, transmit processor <NUM>, TX MIMO processor <NUM>, MOD <NUM>, antenna <NUM>, DEMOD <NUM>, MIMO detector <NUM>, receive processor <NUM>, and/or the like.

For example, the functions described with respect to the transmit processor <NUM>, the receive processor <NUM>, and/or the TX MIMO processor <NUM> may be performed by or under the control of processor <NUM>.

In some aspects, "wireless communication structure" may refer to a periodic time-bounded communication unit defined by a wireless communication standard and/or protocol.

In some aspects, the base station may transmit the PSS, the SSS, and/or the PBCH in a synchronization signal block (SSB).

An interlace structure may be used for each of the downlink and uplink for FDD in certain telecommunications systems (e.g., NR). For example, Q interlaces with indices of <NUM> through Q - <NUM> may be defined, where Q may be equal to <NUM>, <NUM>, <NUM>, <NUM>, or some other value. Each interlace may include slots that are spaced apart by Q frames. In particular, interlace q may include slots q, q + Q, q + 2Q, and/or the like, where q ∈ <NUM>,. , Q - <NUM>}.

Received signal quality may be quantified by a signal-to-interference-plus-noise ratio (SINR), a reference signal received power (RSRP), a log likelihood ratio (LLR), a reference signal received quality (RSRQ), or some other metric.

"New Radio" (NR) may refer to radios configured to operate according to a new air interface (e.g., other than Orthogonal Frequency Divisional Multiple Access (OFDMA)-based air interfaces) or fixed transport layer (e.g., other than Internet Protocol (IP)). In some aspects, NR may utilize OFDM with a CP (herein referred to as cyclic prefix OFDM or CP-OFDM) and/or SC-FDM on the uplink, may utilize CP-OFDM on the downlink and include support for half-duplex operation using time division duplexing (TDD). In some aspects, NR may, for example, utilize OFDM with a CP (herein referred to as CP-OFDM) and/or discrete Fourier transform spread orthogonal frequency-division multiplexing (DFT-s-OFDM) on the uplink, may utilize CP-OFDM on the downlink and include support for half-duplex operation using TDD.

<FIG> is a diagram <NUM> showing an example of a DL-centric slot or wireless communication structure. The DL-centric slot may include a control portion <NUM>. The control portion <NUM> may exist in the initial or beginning portion of the DL-centric slot. The control portion <NUM> may include various scheduling information and/or control information corresponding to various portions of the DL-centric slot. In some aspects, the control portion <NUM> may include legacy PDCCH information, shortened PDCCH (sPDCCH) information), a control format indicator (CFI) value (e.g., carried on a physical control format indicator channel (PCFICH)), one or more grants (e.g., downlink grants, uplink grants, and/or the like), and/or the like.

The DL-centric slot may also include a DL data portion <NUM>. The DL data portion <NUM> may sometimes be referred to as the payload of the DL-centric slot.

The DL-centric slot may also include an uplink (UL) short burst portion <NUM>. The UL short burst portion <NUM> may sometimes be referred to as an uplink burst, an uplink burst portion, a common uplink burst, a short burst, an uplink short burst, a common uplink short burst, a common uplink short burst portion, and/or various other suitable terms. In some aspects, the UL short burst portion <NUM> may include one or more reference signals. Additionally, or alternatively, the UL short burst portion <NUM> may include feedback information corresponding to various other portions of the DL-centric slot. For example, the UL short burst portion <NUM> may include feedback information corresponding to the control portion <NUM> and/or the DL data portion <NUM>. Non-limiting examples of information that may be included in the UL short burst portion <NUM> include an ACK signal (e.g., a physical UL control channel (PUCCH) ACK, a physical UL shared channel (PUSCH) ACK, an immediate ACK), a NACK signal (e.g., a PUCCH NACK, a PUSCH NACK, an immediate NACK), a scheduling request (SR), a buffer status report (BSR), a hybrid automatic repeat request (HARQ) indicator, a channel state indication (CSI), a channel quality indicator (CQI), a sounding reference signal (SRS), a demodulation reference signal (DMRS), PUSCH data, and/or various other suitable types of information. The UL short burst portion <NUM> may include additional or alternative information, such as information pertaining to random access channel (RACH) procedures, scheduling requests, and various other suitable types of information.

The foregoing is one example of a DL-centric wireless communication structure, and alternative structures having similar features may exist without necessarily deviating from the aspects described herein.

<FIG> is a diagram <NUM> showing an example of an uplink-centric slot or wireless communication structure. The UL-centric slot may include a control portion <NUM>. The control portion <NUM> may exist in the initial or beginning portion of the UL-centric slot. The control portion <NUM> in <FIG> may be similar to the control portion <NUM> described above with reference to <FIG>. The UL-centric slot may also include an uplink long burst portion <NUM>. The UL long burst portion <NUM> may sometimes be referred to as the payload of the UL-centric slot. The communication resources utilized to communicate UL data from the subordinate entity (e.g., UE) to the scheduling entity (e.g., UE or BS) may be referred to as the UL portion. In some configurations, the control portion <NUM> may be a physical DL control channel (PDCCH).

The UL-centric slot may also include an uplink (UL) short burst portion <NUM>. The UL short burst portion <NUM> in <FIG> may be similar to the UL short burst portion <NUM> described above with reference to <FIG>, and may include any of the information described above in connection with <FIG>. The foregoing is one example of an uplink-centric wireless communication structure, and alternative structures having similar features may exist without necessarily deviating from the aspects described herein.

<FIG> is a diagram illustrating an example <NUM> of cross-carrier retransmission, in accordance with various aspects of the present disclosure.

In carrier aggregation, a UE and a base station may communicate via multiple carriers that may have different frequencies. For example, in NR, frequency bands may be separated into different frequency ranges, which may include Frequency Range <NUM> (FR1) that includes frequency bands below <NUM> gigahertz (GHz) (also known as sub-<NUM>) and Frequency Range <NUM> (FR2) that includes millimeter wave (mmW) frequency bands. In general, carrier aggregation features can enable increased bandwidth, increased throughput, increased reliability, and/or the like for communications between the UE and the base station (e.g., using cross-carrier retransmissions across different carriers). For example, although mmW frequencies in FR2 offer higher bandwidth than frequencies in FR1, radio waves in mmW frequencies have very short wavelengths, from one to ten millimeters. Accordingly, transmissions in FR2 are sensitive to blockage and atmospheric attenuation, which tends to limit propagation to a few kilometers or less (e.g., line-of-sight). As a result, in some cases, a transmission (e.g., of a transmission block (TB), a control block group (CBG), and/or the like) in FR2 may fail to reach an intended recipient, may degrade in quality while in transit to the intended recipient, and/or the like.

For example, as shown in <FIG>, and by reference number <NUM>, a base station may attempt to send a scheduled downlink transmission to a UE via a PDSCH on a first component carrier in FR2, and the UE may fail to receive the downlink transmission (e.g., due to atmospheric absorption, blocking caused by reliability issues, or for some other reason that affects link quality). In this case, as shown by reference number <NUM>, the UE may use a PUCCH to send a negative acknowledgement (NACK) to the base station on a second component carrier in FR2 to indicate that the downlink transmission was not received. Accordingly, as shown by reference number <NUM>, a Medium Access Control (MAC) layer cross-carrier retransmission may be performed to reschedule the failed transmission on a different component carrier for improved reliability. For example, as shown in <FIG>, and by reference number <NUM>, the base station has rescheduled the failed transmission on a particular component carrier in FR1. In particular, the base station may send information to schedule the retransmission to the UE via a PDCCH and then send the same transmission block that the UE initially failed to receive. As further shown in <FIG>, and by reference number <NUM>, the UE may send an acknowledgement (ACK) to the base station on another component carrier in FR1 to indicate that the rescheduled transmission was received.

While cross-carrier retransmission can be used to improve reliability, as described above, a scheduler (e.g., the base station) may need to decide whether to reschedule the failed transmission on a component carrier in FR1, a different component carrier in FR2, and/or the like in order to make an informed decision and efficiently use the other component carriers that may be available for the cross-carrier retransmission. In general, this decision can be based on one or more parameters that relate to channel quality on FR1 and/or FR2 (and/or individual component carriers in FR1 and/or FR2) (e.g., SINR, RSRP, LLR, and/or the like), which can be indicated in a report that the base station requests from the UE based on the NACK indicating that the initial transmission failed. However, this approach of requesting that the UE report the channel quality on FR1 and/or FR2 on-demand (e.g., based on the NACK) introduces latency issues because the base station has to initially request the channel quality report and then wait for the UE to provide the channel quality report before selecting the component carrier to be used for the retransmission. Accordingly, in applications that have strict latency requirements or short cycle durations (e.g., URLLC, Industrial IoT (IIoT), and/or the like), there may be insufficient time for the base station to request, receive, and process the channel quality report within timing constraints. Furthermore, although the base station may request that the UE always report the most recent channel quality measurements in uplink feedback to address the latency issue, this approach introduces additional uplink overhead that may cause network congestion or otherwise interfere with network reliability.

<FIG> are diagrams illustrating examples <NUM> of event-triggered transmission of a reference signal on a non-serving component carrier to enable cross-carrier retransmission, in accordance with various aspects of the present disclosure. For example, in <FIG>, a UE may transmit, to a base station, uplink feedback that includes carrier selection information to enable cross-carrier scheduling and retransmission with low latency and overhead. More particularly, as shown in <FIG>, and by reference number <NUM>, a base station may attempt to send a PDSCH transmission to a UE on a first component carrier in a first frequency range (e.g., FR2 in the illustrated example), and as further shown by reference number <NUM>, the base station may also send Channel State Information Reference Signals (CSI-RS) to the UE on downlink via multiple component carriers in a second frequency range (e.g., FR1 in the illustrated example). For example, the UE may use the CSI-RS to estimate channels associated with the multiple component carriers in the second frequency range and report the channel quality information back to the base station. In general, the CSI-RS transmissions can be periodic, semi-persistent, or aperiodic (e.g., due to downlink control information (DCI) triggering), and the CSI-RS can start at any OFDM symbol in a slot and occupy <NUM>, <NUM>, or <NUM> OFDM symbols depending on a configured quantity of ports.

As further shown in <FIG>, and by reference number <NUM>, the UE may send a NACK to the base station based on a failure to receive the initial PDSCH transmission. Furthermore, as shown by reference number <NUM>, the NACK that the UE transmits to the UE may include uplink feedback with carrier selection information based on the most recent CSI-RS that the UE received from the base station. For example, in some aspects, the uplink feedback provided by the UE may include one or more indicators that relate to a preferred frequency range, a preferred frequency band within the preferred frequency range, a preferred component carrier within the preferred frequency band, and/or the like, which may generally be defined from coarse to fine for at least a next transmission (or retransmission). Furthermore, in some aspects, the uplink feedback may include a request to suspend and/or resume scheduling on a particular frequency range, frequency band, component carrier, and/or the like. For example, if the UE fails to receive several transmissions on FR2, the UE may request that further transmissions on FR2 be blocked or otherwise suspended for some time, and the UE may subsequently request that the base station resume transmissions on FR2 if and/or when channel conditions recover (e.g., as determined based on the latest CSI-RS). Additionally, or alternatively, the uplink feedback may include one or more general quality indicators for a given frequency range, frequency band, component carrier, and/or the like (e.g., measurements related to SINR, RSRP, LLR, RSRQ, and/or the like, which may be determined instantaneously based on the latest CSI-RS, averaged over time, and/or the like).

Accordingly, in some aspects, the base station may select a frequency range, frequency band, component carrier, and/or the like for scheduling a retransmission based on the uplink feedback that the UE provides with the NACK to indicate that the initial transmission failed. For example, as shown in <FIG>, the base station may select a particular component carrier in FR1 based on the NACK indicating that the initial transmission failed and based on the uplink feedback provided by the UE. In particular, as shown by reference number <NUM>, the base station may send a PDCCH transmission to indicate the selected component carrier in FR1, and as shown by reference number <NUM>, may reschedule the PDSCH transmission on the selected component carrier. As further shown by reference number <NUM>, the UE may transmit, to the base station, an ACK to indicate that the rescheduled PDSCH transmission was received.

As further shown in <FIG>, and by reference number <NUM>, the base station may send another PDSCH transmission to the UE in a subsequent cycle. For example, as shown in <FIG>, the base station may send the next PDSCH transmission via a component carrier in FR2 (e.g., the same component carrier that was used for the previous transmission that failed). Alternatively, in some aspects, the base station may send the next PDSCH transmission via a different component carrier, such as the component carrier used for the previous retransmission, a different component carrier in FR2, and/or the like (e.g., where the uplink feedback provided with the NACK requests suspension of scheduling on the component carrier used for the failed transmission). For example, in cases where a PDSCH transmission fails and is rescheduled one or more times on a different component carrier in the same frequency range or a different frequency range (e.g., over a number of consecutive slots), the base station may reschedule subsequent occasions of the PDSCH transmission on the other component carrier (e.g., because the rescheduling may indicate that channel conditions are better on the other component carrier).

As further shown in <FIG>, and by reference number <NUM>, the UE may send an ACK message to the base station on a PUCCH to indicate that the next PDSCH transmission was received. However, in some aspects, the UE may determine that the received PDSCH transmission was received with marginal quality (e.g., with an RSRP, SINR, LLR, and/or the like below a threshold value). Accordingly, as shown by reference number <NUM>, the UE may provide uplink feedback based on the most recent CSI-RS together with the ACK message based on the marginal transmission quality.

In this way, the UE may provide the base station with updated carrier selection information that the base station can use to select a frequency range, a frequency band, a component carrier, and/or the like for rescheduling a failed transmission based on the latest CSI-RS, which may reduce latency, ensure compliance with timing requirements, and/or the like because the base station is provided with the carrier selection information without having to affirmatively request that the UE provide the carrier selection information. Furthermore, by reactively providing the updated carrier selection information in uplink feedback when an initial transmission fails and/or proactively when a transmission is received with marginal quality, the UE does not have to provide the uplink feedback in each cycle, which may reduce overhead.

<FIG> is a diagram illustrating an example of event-triggered transmission of a reference signal by a UE on a non-serving component carrier to enable cross-carrier retransmission, in accordance with various aspects of the present disclosure. For example, as described in further detail herein, <FIG> illustrates an approach in which the base station schedules or otherwise triggers an uplink sounding reference signal (SRS) transmission from the UE to assess the latest component carrier quality. Accordingly, the SRS transmission from the UE may enable the base station to obtain channel state information that describes how signals propagate from the UE to the base station over the component carriers used for the SRS transmission, which may represent a combined effect from scattering, fading, power decay with distance, and/or the like.

More particularly, as shown in <FIG>, and by reference number <NUM>, the UE may provide serving component carrier quality to the base station when providing a NACK to indicate that the UE did not receive a scheduled PDSCH transmission. For example, in some aspects, the UE may provide the serving component carrier quality based on a semi-persistent scheduling (SPS) configuration for a Demodulation Reference Signal (DMRS) on the serving component carrier. Furthermore, as shown by reference number <NUM>, the base station may preconfigure one or more SRS resources to be used to send the SRS transmissions on the non-serving component carriers, and to save overhead, the SRS resources may be activated only when an initial attempt to send a PDSCH transmission to the UE fails. For example, as shown by reference number <NUM>, the base station may activate the preconfigured SRS resources based on the UE providing the NACK to indicate that the initial PDSCH transmission was not received. Additionally, or alternatively, the base station may activate the preconfigured SRS resources based on discontinuous transmission (DTX) by the UE (e.g., non-receipt of an ACK/NACK by the base station) after an attempted downlink transmission.

Accordingly, the UE may send the SRS transmissions to the base station using the preconfigured SRS resources that are activated based on the NACK and/or DTX following the initial attempt of the base station to send the PDSCH transmission to the UE. As shown by reference number <NUM>, the base station may select a component carrier for the retransmission based on the serving component carrier quality information that the UE provided with the NACK and based on channel state information that the base station determines based on the SRS transmissions from the UE. Furthermore, as shown by reference number <NUM>, the base station may deactivate the preconfigured SRS resources based on the UE providing an ACK to indicate that an initial attempted transmission was received. In this way, interference is reduced by the base station scheduling the SRS transmissions only in cases where the base station receives a NACK or no reply (DTX) from the UE after an attempted transmission. Furthermore, compared to a DCI-based SRS scheduling, triggering the SRS transmissions based on the NACK/DTX saves DCI and scheduling offsets.

<FIG> are diagrams illustrating various examples <NUM> of event-triggered transmissions of reference signals on serving and non-serving component carriers to enable cross-carrier retransmission, in accordance with various aspects of the present disclosure.

More particularly, <FIG> illustrates an example approach in which a base station may schedule uplink SRS transmissions from the UE to the base station on serving and non-serving component carriers to obtain channel quality information to be used when selecting a frequency range, frequency band, component carrier, a beam within a component carrier, and/or the like to be used when rescheduling a failed transmission. For example, as shown by reference number <NUM>, the base station may preconfigure SRS resources on each component carrier in a non-serving frequency range, and as shown by reference number <NUM>, the base station may preconfigure SRS resources on each component carrier in a serving frequency range. In some aspects, the preconfigured SRS resources in the non-serving frequency range and the preconfigured SRS resources in the serving frequency range may be staggered in time to enable the base station to process the uplink transmissions for each frequency range sequentially. Furthermore, as shown by reference number <NUM>, the SRS transmissions in FR2 may be scheduled to be sent in a beam sweep to enable the base station to measure different candidate beams for each candidate component carrier in FR2. For example, beamforming may generally be supported on component carriers in FR2 (e.g., mmW frequencies) but not for FR1 (e.g., sub-<NUM> frequencies). Accordingly, in some aspects, the SRS transmissions in FR2 may be sent by the UE and received by the base station in a beam sweep, but the SRS transmissions in FR1 may be single (e.g., unidirectional) transmissions.

In some aspects, as shown by reference number <NUM>, the base station may receive a NACK from the UE that does not include any component carrier quality information following an initial PDSCH transmission attempt (e.g., in contrast to the example shown in <FIG>, where the NACK included quality information for serving component carriers). Additionally, or alternatively, the base station may not receive any response from the UE following the initial PDSCH transmission attempt. Accordingly, as shown by reference number <NUM>, the base station may activate the preconfigured SRS resources on the component carriers in both the serving and non-serving component carriers, which may cause the UE to send the SRS transmissions to the base station. Furthermore, as mentioned above, the SRS transmissions on the serving and non-serving component carriers may be staggered in time to enable the base station to process the SRS transmissions sequentially for each frequency range, and the UE may send the SRS transmissions on FR2 in a beam sweep to enable the base station to measure channel quality for different candidate beams for each candidate component carrier in FR2 (e.g., <FIG> illustrates an example in which the SRS transmissions in FR1 are sent prior to the beamswept transmissions in FR2).

As further shown in <FIG>, and by reference number <NUM>, the base station may select a component carrier for rescheduling the failed transmission based on the channel quality information determined by the base station from the SRS transmissions on the serving and non-serving component carriers. For example, in <FIG>, the base station may select a particular component carrier in FR1 based on FR1 having better channel conditions than FR2, based on the selected component carrier having the best channel quality among multiple component carriers in FR1, and/or the like. Furthermore, in cases where the base station selects a component carrier in FR2, the component carrier selection may further include a selection of one or more particular beams to be used for the retransmission. Additionally, in some aspects, as shown by reference number <NUM>, the base station may deactivate the preconfigured SRS transmissions such that the UE does not send the SRS transmissions when the UE provides an ACK to indicate that the initial transmission was received. In this way, the base station may save overhead by only scheduling the uplink SRS transmissions when the UE fails to receive or otherwise fails to acknowledge an attempted downlink transmission. Furthermore, by preconfiguring the SRS resources to be used for the SRS transmissions and dynamically activating the SRS resources based on a NACK or DTX following an attempted downlink transmission, the base station may obtain the channel quality information for the serving and non-serving component carriers with less latency, which may enable the base station to reschedule the failed transmission within the same cycle and thereby satisfy latency and/or other timing requirements.

Furthermore, in some aspects, the base station may schedule one or more subsequent downlink transmission occasions in one or more subsequent cycles on the component carrier that is selected for the retransmission. For example, in cases where a downlink transmission fails and is rescheduled one or more times on a different component carrier in the same frequency range or a different frequency range (e.g., over a number of consecutive slots), the base station may reschedule subsequent occasions of the downlink transmission on the other component carrier (e.g., because the rescheduling may indicate that channel conditions are better on the other component carrier). Accordingly, in such cases, the base station may transmit, and the UE may receive, information indicating the change to the component carrier on which the subsequent downlink transmission occasions are scheduled.

<FIG> illustrates an example approach in which a base station may schedule uplink SRS transmissions using SRS resources that are persistently reserved on serving and non-serving component carriers to obtain channel quality information that the base station may use to select a frequency range, a frequency band, a component carrier, a beam within a component carrier, and/or the like when rescheduling a failed transmission. For example, as shown by reference number <NUM>, the base station may reserve a set of SRS resources on each component carrier in a non-serving frequency range, and as shown by reference number <NUM>, the base station may reserve SRS resources on each component carrier in a serving frequency range. In some aspects, the SRS resources in the serving and non-serving frequency ranges may be reserved within a short offset from a slot, a symbol, and/or the like in which the UE is scheduled to send an ACK/NACK message to indicate whether a downlink transmission was received. Furthermore, as shown in <FIG>, the reserved SRS resources in the non-serving frequency range and the reserved SRS resources in the serving frequency range may be staggered in time to enable the base station to process the uplink transmissions for each frequency range sequentially. Furthermore, as shown by reference number <NUM>, the SRS transmissions in FR2 may be scheduled to be sent in a beam sweep to enable the base station to measure different candidate beams for each candidate component carrier in FR2.

In some aspects, as shown by reference number <NUM>, the base station may schedule or otherwise trigger uplink SRS transmissions from the UE using the reserved SRS resources based on receiving a NACK from the UE following an initial PDSCH transmission attempt. Additionally, or alternatively, the base station may not receive any response from the UE following the initial PDSCH transmission attempt. In either case, the base station may trigger the SRS transmissions using the reserved SRS resources on the component carriers in both the serving and non-serving component carriers based on the NACK (or DTX or other non-acknowledgement), which may cause the UE to send the SRS transmissions to the base station. Furthermore, as mentioned above, the SRS transmissions on the serving and non-serving component carriers may be staggered in time to enable the base station to process the SRS transmissions sequentially for each frequency range, and the UE may send the SRS transmissions on FR2 in a beam sweep to enable the base station to measure channel quality for different candidate beams for each candidate component carrier in FR2 (e.g., <FIG> illustrates an example in which the SRS transmissions in FR1 are sent prior to the beamswept transmissions in FR2).

Accordingly, the base station may select a component carrier for rescheduling the failed transmission based on the channel quality information determined by the base station from the SRS transmissions on the serving and non-serving component carriers. In some aspects, compared to the approach shown in <FIG>, the base station may select a particular component carrier for the rescheduled transmission with a lower latency because the SRS resources are reserved with a shorter offset from the scheduled ACK/NACK transmission relative to the preconfigured SRS resources. Furthermore, in some aspects, the approach shown in <FIG> may offer additional overhead savings (e.g., saving PUCCH resources) by only using the SRS transmissions to indicate NACK/ACK for the attempted downlink transmission. For example, the UE may send the SRS transmissions to indicate a NACK for the attempted downlink transmission or perform DTX (e.g., non-transmission) of the SRS transmissions to indicate an ACK for the attempted downlink transmission. Additionally, or alternatively, as shown by reference number <NUM>, the base station may not trigger the SRS transmissions using the reserved SRS resources based on receiving an ACK from the UE to indicate that the UE received an attempted downlink transmission.

<FIG> illustrates another example approach in which a base station may schedule uplink SRS transmissions using SRS resources that are preconfigured and/or persistently reserved on serving and non-serving component carriers to obtain channel quality information that the base station may use to select a frequency range, a frequency band, a component carrier, a beam within a component carrier, and/or the like when rescheduling a downlink transmission. In general, the approach shown in <FIG> may be similar to the approaches shown in <FIG>, except that the uplink SRS transmissions are scheduled (e.g., by activating preconfigured SRS resources and/or triggering reserved SRS resources) based on an ACK message that indicates that serving component carrier quality fails to satisfy a threshold value.

For example, in some aspects, the base station may configure one or more threshold values that relate to channel quality on serving component carriers, which may be based on SINR, RSRP, LLR, and/or other suitable parameters. Accordingly, based on the UE receiving an attempted downlink transmission and determining that one or more parameters on the serving component carrier fail to satisfy a threshold value configured by the base station, the UE may send an ACK to the base station with one or more indicators to indicate that the serving component carrier quality fails to satisfy the applicable threshold value(s), as shown by reference number <NUM>. In some aspects, as shown by reference number <NUM>, the base station may schedule uplink SRS transmissions (e.g., using persistently reserved SRS resources, preconfigured SRS resources, and/or the like) based on the ACK indicating that the serving component carrier quality fails to satisfy the threshold value(s), and select a component carrier for rescheduling the downlink transmission and/or the like based on channel quality information determined by the base station based on the uplink SRS transmissions.

<FIG> illustrates an example approach in which a base station may schedule one or more downlink reference signal transmissions (e.g., CSI-RS transmissions) to a UE to request a channel quality report for serving and non-serving component carriers, to obtain information for selecting a frequency range, a frequency band, a component carrier, a beam within a component carrier, and/or the like after a failed retransmission that relates to a service having a cycle duration that satisfies a threshold value. For example, in cases where latency is not a concern or timing requirements are not strict, there may be enough time for the base station to request that the UE obtain measurements that relate to channel quality on the serving and non-serving component carriers and provide a channel quality report indicating current conditions on the serving and non-serving component carriers. In this way, the channel quality information that the base station uses to select the frequency range, a frequency band, a component carrier, a beam within a component carrier, and/or the like for cross-carrier retransmission may more accurately reflect downlink channel conditions that are experienced at the UE.

For example, as shown by reference number <NUM>, the base station may preconfigure CSI-RS resources on each component carrier in a non-serving frequency range, and as shown by reference number <NUM>, the base station may preconfigure CSI-RS resources on each component carrier in a serving frequency range. In some aspects, the preconfigured CSI-RS resources in the non-serving frequency range and the preconfigured CSI-RS resources in the serving frequency range may be staggered in time to enable the UE to process the downlink CSI-RS transmissions for each frequency range sequentially. Furthermore, as shown by reference number <NUM>, the base station may send the CSI-RS transmissions in FR2 in a beam sweep to enable the UE to measure different candidate beams for each candidate component carrier in FR2.

In some aspects, the base station may receive a NACK from the UE that does not include any component carrier quality information following an initial PDSCH transmission attempt. Additionally, or alternatively, the base station may not receive any response from the UE following the initial PDSCH transmission attempt. Accordingly, as shown by reference number <NUM>, the base station may activate the preconfigured CSI-RS resources on the component carriers in both the serving and non-serving component carriers and subsequently send the CSI-RS transmissions to the UE on a downlink. In some aspects, to further save overhead, the CSI-RS resources may be activated and used to send the CSI-RS transmissions only on the non-serving component carriers, based on the NACK received from the UE including channel quality information for the serving component carriers.

As further shown in <FIG>, and by reference number <NUM>, the UE may send a PUCCH transmission to the base station that includes a channel quality report for the non-serving component carriers based on channel state information that the UE determines from the downlink CSI-RS transmissions on the non-serving component carriers. Furthermore, in some aspects (e.g., where the NACK does not include any channel quality information for the serving component carriers), the UE may send a PUCCH transmission to the base station that includes a channel quality report for the serving component carriers based on channel state information that the UE determines from the downlink CSI-RS transmissions on the serving component carriers, as shown by reference number <NUM>. As further shown in <FIG>, and by reference number <NUM>, the base station may select a component carrier for rescheduling the failed transmission based on the channel quality report(s) received from the UE, any channel quality information that the UE may have provided with the NACK, and/or the like. Additionally, in some aspects, the base station may deactivate or otherwise cancel downlink resources allocated to the CSI-RS transmissions and uplink resources allocated to the channel quality report when the UE provides an ACK to indicate that the initial transmission was received. In this way, the base station may save overhead by only scheduling the downlink CSI-RS transmissions and the uplink channel quality report when the UE fails to receive an attempted downlink transmission, fails to acknowledge an attempted downlink transmission, and/or the like. Furthermore, by preconfiguring and/or reserving the CSI-RS resources to be used for the CSI-RS transmissions and dynamically triggering the CSI-RS transmissions based on a NACK or DTX following an attempted downlink transmission, the base station may obtain the channel quality information for the serving and non-serving component carriers with less latency compared with other approaches that typically use DCI to trigger CSI-RS transmissions. For example, the NACK-triggered approach shown in <FIG> may save time by avoiding a DCI and scheduling offset, which is at least greater than a beam switch latency threshold from a beam sweep based CSI-RS transmission on FR2.

<FIG> is a diagram illustrating an example process <NUM> performed, for example, by a base station, in accordance with various aspects of the present disclosure. Example process <NUM> is an example where a base station (e.g., base station <NUM>) schedules one or more reference signal transmissions to assess channel quality on component carriers in different frequency ranges in order to select a suitable carrier (e.g., to enable cross-carrier retransmission with low latency and reduced overhead).

As shown in <FIG>, in some aspects, process <NUM> may include receiving, from a UE, a message that indicates whether the UE received a downlink transmission from the base station in a first frequency range (block <NUM>). For example, the base station (e.g., using receive processor <NUM>, controller/processor <NUM>, memory <NUM>, and/or the like) may receive, from a UE, a message that indicates whether the UE received a downlink transmission from the base station in a first frequency range, as described above.

As further shown in <FIG>, in some aspects, process <NUM> may include scheduling one or more reference signal (RS) transmissions in the first frequency range and one or more RS transmissions in a second frequency range based at least in part on the message received from the UE (block <NUM>). For example, the base station (e.g., using transmit processor <NUM>, receive processor <NUM>, controller/processor <NUM>, memory <NUM>, and/or the like) may schedule one or more RS transmissions in the first frequency range and one or more RS transmissions in a second frequency range based at least in part on the message received from the UE, as described above.

As further shown in <FIG>, in some aspects, process <NUM> may include rescheduling the downlink transmission on a component carrier in either the first frequency range or the second frequency range based at least in part on channel quality information that is determined from the one or more RS transmissions in the first frequency range and the one or more RS transmissions in the second frequency range (block <NUM>). For example, the base station (e.g., using transmit processor <NUM>, receive processor <NUM>, controller/processor <NUM>, memory <NUM>, and/or the like) may reschedule the downlink transmission on a component carrier in either the first frequency range or the second frequency range based at least in part on channel quality information that is determined from the one or more RS transmissions in the first frequency range and the one or more RS transmissions in the second frequency range, as described above.

In a first aspect, the one or more RS transmissions in the first frequency range are transmitted in a beam sweep to enable the channel quality information to be determined for multiple candidate beams associated with one or more component carriers in the first frequency range.

In a second aspect, alone or in combination with the first aspect, the base station may receive, from the UE, the one or more RS transmissions in the first frequency range in the beam sweep, and determine the channel quality information for the multiple candidate beams associated with the one or more component carriers in the first frequency range based at least in part on the one or more RS transmissions received in the beam sweep.

In a third aspect, alone or in combination with one or more of the first and second aspects, the base station may transmit the one or more RS transmissions in the first frequency range to the UE in the beam sweep, to enable the UE to determine the channel quality information for the multiple candidate beams associated with the one or more component carriers in the first frequency range based at least in part on the one or more RS transmissions transmitted in the beam sweep.

In a fourth aspect, alone or in combination with one or more of the first through third aspects, the one or more RS transmissions in the first frequency range and the one or more RS transmissions in the second frequency range are scheduled at different times.

In a fifth aspect, alone or in combination with one or more of the first through fourth aspects, the message received from the UE is a negative acknowledgement to indicate that the downlink transmission was not received.

In a sixth aspect, alone or in combination with one or more of the first through fifth aspects, the one or more RS transmissions in the first frequency range and the second frequency range are scheduled on preconfigured resources that are activated based on the negative acknowledgement.

In a seventh aspect, alone or in combination with one or more of the first through sixth aspects, the one or more RS transmissions in the first frequency range and the second frequency range are scheduled on reserved resources that have a predefined offset from the negative acknowledgement.

In an eighth aspect, alone or in combination with one or more of the first through seventh aspects, the message received from the UE is an acknowledgement to indicate that the downlink transmission was received on a serving component carrier with one or more parameters failing to satisfy a threshold value.

In a ninth aspect, alone or in combination with one or more of the first through eighth aspects, the one or more parameters include at least one of a signal-to-interference-plus-noise ratio, a reference signal received power, or a log likelihood ratio.

In a tenth aspect, alone or in combination with one or more of the first through ninth aspects, the base station may configure the threshold value.

In an eleventh aspect, alone or in combination with one or more of the first through tenth aspects, the one or more RS transmissions comprise uplink SRS transmissions from the UE to the base station based at least in part on the downlink transmission relating to a low-latency service.

In a twelfth aspect, alone or in combination with one or more of the first through eleventh aspects, the base station may determine the channel quality information based at least in part on the uplink SRS transmissions.

In a thirteenth aspect, alone or in combination with one or more of the first through twelfth aspects, the uplink SRS transmissions are used as the message to indicate that the downlink transmission was not received by the UE.

In a fourteenth aspect, alone or in combination with one or more of the first through thirteenth aspects, the one or more RS transmissions comprise downlink CSI-RS transmissions to the UE based at least in part on the downlink transmission relating to a service having a cycle duration that satisfies a threshold value.

In a fifteenth aspect, alone or in combination with one or more of the first through fourteenth aspects, the UE determines the channel quality information based at least in part on the downlink CSI-RS transmissions, and the base station may receive, from the UE, a report containing the channel quality information and select the component carrier for rescheduling the downlink transmission based at least in part on the report containing the channel quality information.

In a sixteenth aspect, alone or in combination with one or more of the first through fifteenth aspects, the downlink CSI-RS transmissions are scheduled on only a set of non-serving component carriers in the first frequency range based at least in part on the message received from the UE including channel quality information relating to a serving component carrier in the first frequency range.

In a seventeenth aspect, alone or in combination with one or more of the first through sixteenth aspects, the first frequency range is a millimeter wave frequency range and the second frequency range is a sub-<NUM> gigahertz frequency range.

In an eighteenth aspect, alone or in combination with one or more of the first through seventeenth aspects, process <NUM> further includes scheduling a next occasion of the downlink transmission in one or more subsequent cycles on the component carrier in either the first frequency range or the second frequency range based at least in part on the channel quality information determined from the one or more RS transmissions.

<FIG> is a diagram illustrating an example process <NUM> performed, for example, by a UE, in accordance with various aspects of the present disclosure. Example process <NUM> is an example where a UE (e.g., UE <NUM>) transmits one or more reference signals, channel quality reports, and/or the like to a base station to enable the base station to select a suitable carrier (e.g., to enable cross-carrier retransmission with low latency and reduced overhead).

As shown in <FIG>, in some aspects, process <NUM> may include transmitting, to a base station, a message that indicates whether the UE received a downlink transmission from the base station in a first frequency range (block <NUM>). For example, the UE (e.g., using transmit processor <NUM>, controller/processor <NUM>, memory <NUM>, and/or the like) may transmit, to a base station, a message that indicates whether the UE received a downlink transmission from the base station in a first frequency range, as described above.

As further shown in <FIG>, in some aspects, process <NUM> may include receiving, from the base station, information related to one or more RS transmissions that are scheduled in the first frequency range and one or more RS transmissions that are scheduled in a second frequency range based at least in part on the message transmitted to the base station (block <NUM>). For example, the UE (e.g., using receive processor <NUM>, controller/processor <NUM>, memory <NUM>, and/or the like) may receive, from the base station, information related to one or more RS transmissions that are scheduled in the first frequency range and one or more RS transmissions that are scheduled in a second frequency range based at least in part on the message transmitted to the base station, as described above.

As further shown in <FIG>, in some aspects, process <NUM> may include receiving the downlink transmission on a component carrier in either the first frequency range or the second frequency range based at least in part on channel quality information that is determined from the one or more RS transmissions in the first frequency range and the one or more RS transmissions in the second frequency range (block <NUM>). For example, the UE (e.g., using receive processor <NUM>, controller/processor <NUM>, memory <NUM>, and/or the like) may receive the downlink transmission on a component carrier in either the first frequency range or the second frequency range based at least in part on channel quality information that is determined from the one or more RS transmissions in the first frequency range and the one or more RS transmissions in the second frequency range, as described above.

In a second aspect, alone or in combination with the first aspect, the UE may transmit, to the base station, the one or more RS transmissions in the first frequency range in the beam sweep to enable the base station to determine the channel quality information for the multiple candidate beams associated with the one or more component carriers in the first frequency range.

In a third aspect, alone or in combination with one or more of the first and second aspects, the UE may receive, from the base station, the one or more RS transmissions in the first frequency range in the beam sweep, and determine the channel quality information for the multiple candidate beams associated with the one or more component carriers in the first frequency range based at least in part on the one or more RS transmissions received in the beam sweep.

In a fifth aspect, alone or in combination with one or more of the first through fourth aspects, the message transmitted to the base station is a negative acknowledgement to indicate that the downlink transmission was not received.

In an eighth aspect, alone or in combination with one or more of the first through seventh aspects, the message transmitted to the base station is an acknowledgement to indicate that the downlink transmission was received on a serving component carrier with one or more parameters failing to satisfy a threshold value.

In a tenth aspect, alone or in combination with one or more of the first through ninth aspects, the threshold value is configured by the base station.

In a twelfth aspect, alone or in combination with one or more of the first through eleventh aspects, the base station determines the channel quality information based at least in part on the uplink SRS transmissions.

In a fifteenth aspect, alone or in combination with one or more of the first through fourteenth aspects, the UE may receive the downlink CSI-RS transmissions from the base station and determine the channel quality information based at least in part on the downlink CSI-RS transmissions, and the base station may reschedule the downlink transmission on the component carrier in either the first frequency range or the second frequency range based at least in part on the report containing the channel quality information.

In a sixteenth aspect, alone or in combination with one or more of the first through fifteenth aspects, the downlink CSI-RS transmissions are scheduled on only a set of non-serving component carriers in the first frequency range based at least in part on the message transmitted to the base station including channel quality information relating to a serving component carrier in the first frequency range.

In an eighteenth aspect, alone or in combination with one or more of the first through seventeenth aspects, process <NUM> further includes receiving, from the base station, information indicating that a next occasion of the downlink transmission is scheduled in one or more subsequent cycles on the component carrier in either the first frequency range or the second frequency range based at least in part on the channel quality information determined from the one or more RS transmissions.

Claim 1:
A method of wireless communication performed by a base station, comprising:
receiving (<NUM>), from a user equipment, UE, a message that indicates whether the UE received a downlink transmission from the base station in a first frequency range;
scheduling (<NUM>) one or more reference signal, RS, transmissions in the first frequency range and one or more RS transmissions in a second frequency range based at least in part on the message received from the UE; and
rescheduling (<NUM>) the downlink transmission on a component carrier in either the first frequency range or the second frequency range based at least in part on channel quality information that is determined from the one or more RS transmissions in the first frequency range and the one or more RS transmissions in the second frequency range.