Patent Description:
<NPL>, relates to a study item on NR-based access to unlicensed spectrum. <NPL>, relates to another study item on NR-based access to unlicensed spectrum. <CIT> relates to a method and apparatus for measuring a channel and transmitting and receiving data in a wireless communication system supporting an unlicensed band.

The invention is defined by the subject-matter of the appended independent claims.

In wireless communication between a base station and a UE in an unlicensed spectrum, downlink and uplink transmissions may not occur due to listen before talk (LBT) procedure failures. For example, the base station or the UE may not get access to an unlicensed frequency channel. If the channel access problem occurs consistently, the system performance may be degraded.

In order to overcome the channel access problem and to prevent system performance degradation, the present disclosure improves the manner in which the base station may configure the UE to perform a handover (HO) to another cell if the channel access problem happens on a primary cell (PCell) or a primary cell of secondary Node (PSCell). The base station may also configure the UE to de-activate a secondary cell (SCell) if the problem occurs, as well as to activate another configured SCell. Aspects presented herein improve communication reliability by enabling the base station and/or the UE to get access to an unlicensed frequency channel in a shorter amount of time. Aspects presented herein further improve communication data rate, capacity, and spectral efficiency.

The base stations <NUM> configured for 5GNR (collectively referred to as Next Generation RAN (NG-RAN)) may interface with core network <NUM> through second backhaul links <NUM>. The third backhaul links <NUM> may be wired or wireless.

A primary component carrier may be referred to as a PCell and a secondary component carrier may be referred to as a SCell.

Some of the UEs <NUM> may be referred to as loT devices (e.g., parking meter, gas pump, toaster, vehicles, heart monitor, etc.).

Referring again to <FIG>, in certain aspects, the UE <NUM> may be configured to obtain access to an unlicensed frequency channel of the unlicensed frequency spectrum in the event of channel access failures. For example, the UE <NUM> may comprise a switch/HO component <NUM> configured to switch from the first unlicensed frequency channel to a second cell for communication through the second cell in a conditional handover. The UE <NUM> is configured to receive a configuration from the first base station <NUM>/<NUM> for the UE <NUM> to perform a conditional handover. The UE <NUM> is configured to determine a first unlicensed frequency channel is unavailable for a transmission to the first base station or from the first base station. The UE <NUM> is configured to switch from the first unlicensed frequency channel to a second cell for communication through the second cell in the conditional handover upon receiving the configuration and upon determining that the first unlicensed frequency channel is unavailable for the transmission.

<FIG> provide an example of slot configuration <NUM> with <NUM> symbols per slot and numerology µ=<NUM> with <NUM> slots per subframe. The slot duration is <NUM>, the subcarrier spacing is <NUM>, and the symbol duration is approximately <NUM>.

In wireless communications (e.g., <NUM> NR or LTE wireless communication) in an unlicensed spectrum, a channel access procedure (e.g., an LBT procedure) may fail because other UEs, other base stations, or other technologies may use an unlicensed channel in the unlicensed spectrum. Thus, downlink and uplink transmissions may not occur due to the LBT procedure failures. For example, a base station <NUM> or a UE <NUM> may not be able to get access to the channel. When the LBT procedure fails, the base station <NUM> or the UE <NUM> may not get access to the channel, for example, for a long time duration. The channel access problem may degrade system performance, and may further degrade communication data rate, capacity and spectral efficiency.

The present disclosure improves the manner in which a UE may overcome channel access problems, which may assist to prevent system performance degradation.

<FIG> is an example communication flow <NUM> between a UE <NUM> and a base station <NUM>. Optional aspects are illustrated with a dashed line. The base station <NUM> may provide a cell serving the UE <NUM>. For example, in the context of <FIG>, the base station <NUM> may correspond to base station <NUM>/<NUM> and, accordingly, the cell may include a geographic coverage area <NUM> in which communication coverage is provided and/or small cell <NUM>' having a coverage area <NUM>'. Further, the UE <NUM> may correspond to at least UE <NUM>. In another example, in the context of <FIG>, the base station <NUM> may correspond to the base station <NUM> and the UE <NUM> may correspond to the UE <NUM>.

The base station <NUM>, at <NUM>, may configure the UE <NUM> to perform a handover (e.g., conditional handover) to another cell when channel access problems occur on a PCell or a PSCell. The base station <NUM> may also configure the UE <NUM> to de-activate an SCell where the channel access problem occurs as well as activate another configured PCell or PSCell, as illustrated at <NUM>. The UE <NUM> receives the configuration to perform the conditional handover.

For uplink transmissions, in the LBT procedure, the UE <NUM> may apply a CCA check prior to transmission. For downlink transmissions, the UE <NUM> may monitor downlink traffic, as well as reference signals from the base station <NUM>. The UE <NUM> may perform an LBT or an RLM to check or monitor the channel, as illustrated at <NUM>.

At <NUM>, the UE <NUM> may determine whether a first unlicensed frequency channel is available. The UE may determine whether the first unlicensed frequency channel is available for a transmission to the base station <NUM> or for a transmission from the base station <NUM>. In some aspects, such as when the first unlicensed frequency channel is available, the UE <NUM> may utilize the first unlicensed frequency channel to transmit the transmission to the base station <NUM> or to receive the transmission from the first base station <NUM>.

In some aspects, for example at <NUM>, the UE <NUM> may determine that the first unlicensed frequency channel may be unavailable for the transmission. In some aspects, the UE <NUM> may determine the conditions that may cause the first unlicensed frequency channel to be unavailable for the transmission.

In some aspects, for example at <NUM>, the UE to determine that the first unlicensed frequency channel may be unavailable for the transmission, the UE <NUM> may determine that the first unlicensed frequency channel may be unavailable for the transmission based on LBT protocol failures. In some aspects, the UE <NUM> may determine that the first unlicensed frequency channel may be unavailable for the transmission based on at least one of the LBT protocol failing due to a number of failed attempts exceeding a first threshold number of failed attempts or a duration of failed attempts exceeding a first threshold duration. In some aspects, the transmission may be one of a SR, a RACH procedure, data on a PUSCH, or SRS on the first unlicensed frequency channel. For example, for uplink, the base station <NUM> may configure the UE <NUM> with a first number of maximum transmission attempts and/or a first configured maximum duration. The UE <NUM> may trigger the report when LBT procedure fails for transmission attempts. In some aspects, the transmission attempts may include transmission attempts for SR, RACH, PUSCH, or SRS. The transmission attempts may include other types of transmission attempts as well, and is not intended to be limited to the aspects provided herein.

In some aspects, the UE <NUM> may maintain one or more counters associated with the number of failed attempts or one or more timers associated with the duration of failed attempts based on the LBT protocol to transmit one or more of the SR, the RACH, the PUSCH, or the SRS on the first unlicensed frequency channel. In some aspects, each failed attempt may correspond to a determination that the first unlicensed frequency channel may be unavailable for transmission. In some aspects, the UE <NUM> may reset the one or more counters or the one or more timers upon a successful attempt based on the LBT protocol to transmit one or more of the SR, the RACH, the PUSCH, or the SRS on the first unlicensed frequency channel. The successful attempt may correspond to a determination that the first unlicensed frequency channel may be available for the transmission. For example, the UE <NUM> may trigger the report after the transmission attempts for SR, RACH, PUSCH, or SRS fail a configured first maximum number of attempts or a configured first maximum duration. As an example, when a transmission attempt fails, a counter and/or timer may be triggered. The counter and/or timer may start counting or running. After a successful attempt, the counter and/or timer may be reset. The counter may increment by <NUM> after each failed attempt, and the timer may increase after each failed attempt, until the counter and/or timer reaches a first configured maximum number of attempts and/or a first configured maximum duration. The first configured maximum duration may be a duration from the timer being triggered until a successful transmission. For example, the first configured maximum duration may be a duration of a total duration of the failed attempts. In some aspects, the failed attempt may be due to LBT procedure failure.

For uplink transmissions, the base station <NUM> may configure the UE <NUM> with a first number of maximum transmission attempts and/or a first configured maximum duration. The UE <NUM> may trigger the report when LBT procedure fails for transmission attempts. For example, the transmission attempts may include transmission attempts for scheduling request (SR), random access channel (RACH), PUSCH, or SRS. The transmission attempts may include other types of transmission attempts as well.

For example, the UE <NUM> may trigger the report after the transmission attempts for SR, RACH, PUSCH, or SRS fail a configured first maximum number of attempts or a configured first maximum duration, as illustrated at <NUM>. As an example, when a transmission attempt fails, a counter and/or timer may be triggered. The counter and/or timer may start counting or running. After a successful attempt, the counter and/or timer may be reset. The counter may increment by <NUM> after each failed attempt, and the timer may increase after each failed attempt, until reach a first configured maximum number of attempts and/or a first configured maximum duration. The first configured maximum duration may be a duration from the timer being triggered until a successful transmission. For example, the first configured maximum duration may be a duration of a total duration of the failed attempts. For example, the failed attempt may be due to LBT procedure failure.

In some aspects, for an SR transmission, the first configured maximum number of attempts, the first configured maximum duration, the counter, and/or the timer may be different if SR is inside or outside a transmission opportunity (TXOP). TXOP refers to the amount of time a base station can send frames when the base station has won contention for the wireless medium. For example, TXOP may correspond to a transmission duration reserved by the base station after LBT being successful. When SR is inside the TXOP, the base station <NUM> has already contended for the channel. For the duration of TXOP, the base station <NUM> has already obtained access to the channel. Thus, when SR is inside the TXOP, the UE <NUM> may have an LBT procedure with a minimum duration. For example, when SR is inside the TXOP, the UE <NUM> may have the LBT with a duration of <NUM>. When SR is outside the TXOP, the UE <NUM> has to contend for the channel, thus the UE <NUM> may have an LBT with a different duration, based on a contention window. Therefore, the UE <NUM> may have different first configured maximum numbers, first maximum durations, counters, and/or timers if SR is inside or outside the TXOP. Further, for RACH, PUSCH, or SRS transmission attempt, if the RACH, PUSCH, or SRS transmission attempt is inside or outside the TXOP, there may be different first configured maximum numbers, first maximum durations, counters, or timers as well.

In some aspects, separate first configured maximum numbers, first configured maximum durations, counters, and/or timers may be used for different access priorities. To provide differentiation to channel access priorities based on the type of traffic served, there may be different priority classes. For example, there may be four LBT priority classes, <NUM>, <NUM>, <NUM>, or <NUM>, while <NUM> being the highest. Different LBT priority classes may have different contention window sizes (CWS). Each access priority may have a corresponding maximum and minimum CWS. For example, higher access priority may have a lower maximum CWS. The highest access priority may have the lowest maximum CWS. For example, the lowest maximum contention window size may be <NUM>. The UE <NUM> may track different priority classes differently. For example, each access priority may have a corresponding first configured maximum number, duration, counter, and/or timer. For example, the counters and/or timers for higher access priorities may also be reset when a counter and/or a timer for an access priority is reset.

In some aspects, the first configured maximum number of attempts and/or a first configured maximum duration may be different and smaller than the existing one which triggers a radio link failure (RLF).

In some aspects, for example at <NUM>, to determine that the first unlicensed frequency channel may be unavailable for the transmission, the UE <NUM> may determine that the first unlicensed frequency channel may be unavailable for the transmission based on a comparison of one or more signals. In some aspects, the UE <NUM> may determine that the first unlicensed frequency channel may be unavailable for the transmission based on a comparison of one or more of a RSRP, a RSRQ, a RSSI, a SINR, a SNR, or a channel occupancy or interference metric to a corresponding threshold. In some aspects, to determine that the first unlicensed frequency channel may be unavailable for the transmission based on a comparison of one or more signals, the UE <NUM> may maintain one or more counters associated with a number of occasions when one or more of the RSRP, the RSRQ, the SINR, or the SNR is less than the corresponding threshold within a monitoring duration, or when one or more of the RSSI or the channel occupancy or interference metric is greater than the corresponding threshold within the monitoring duration. In some aspects, the UE may determine that the first unlicensed frequency channel may be unavailable for the transmission based on the number of occasions that exceed a threshold number of occasions within the monitoring duration. For example, for downlink, the UE <NUM> may determine that the channel is not available and trigger a report when RSRP, RSRQ, RSSI, SINR, SNR or a channel occupancy or interference metric is above or below a corresponding threshold for an amount of time where the UE counts the number of occasions when the reference signals are missed, e.g., when RSRP < the RSPP threshold, or RSRQ < the RSRQ threshold, or RSSI > the RSSI threshold, or SINR < the SINR threshold, or SNR < the SNR threshold, or the channel occupancy or interference metric > the channel occupancy or interference metric threshold within a duration (per cell or per sub-band). The base station <NUM> may configure the UE <NUM> to report to the base station <NUM> when RSRP, RSRQ, RSSI, SINR, SNR or a channel occupancy or interference metric is above or below a corresponding threshold for an amount of time. The UE <NUM> may count the number of occasions when the reference signals are missed, e.g., when RSRP < the RSPP threshold, or RSRQ < the RSRQ threshold, or RSSI > the RSSI threshold, or SINR < the SINR threshold, or SNR < the SNR threshold, or the channel occupancy or interference metric > the channel occupancy or interference metric threshold within the duration (per cell or per sub-band).

In some aspects, a counter may be triggered when RSRP < the RSPP threshold, or RSRQ < the RSRQ threshold, or RSSI > the RSSI threshold, or SINR < the SINR threshold. The UE <NUM> may count the number of occasions when the reference signals are missed, e.g., when RSRP < the RSPP threshold, or RSRQ < the RSRQ threshold, or RSSI > the RSSI threshold, or SINR < the SINR threshold, or SNR < a threshold, or a channel occupancy or interference metric > a threshold within the duration. The issue may occur at any cell or sub-band, and the UE <NUM> may count the number of occasions per cell or per sub-band. If the number of occasions exceeds the threshold number for the counter, the UE <NUM> may send the report to the base station. In some aspects, the UE <NUM> may send the report to the base station based on a percentage of a time corresponds to the number of occasions when the reference signals are missed over the duration of the monitoring time.

In some aspects, the duration of the monitoring may be configured. The base station <NUM> may configure the UE <NUM> to monitor the channel for an amount of time duration. In some aspects, a threshold for the counter may be configured. The base station <NUM> may configure the UE <NUM> to report when the number of occasions that RSRP < the RSPP threshold, or RSRQ < the RSRQ threshold, or RSSI > the RSSI threshold, or SINR < the SINR threshold, or SNR < the threshold, or a channel occupancy or interference metric > the channel occupancy or interference metric threshold exceeds a threshold number of occasions, within the duration (per cell or per sub-band).

In some aspects, the actual symbols/slots to measure can be configured. The actual symbols/slots are the reference signal, such as a synchronization signal block (SSB), or a channel state information reference signal (CSI-RS), etc. The base station <NUM> may configure the UE <NUM> which reference signal is to be measured, for example, the SSB, or the CSI-RS, etc..

In some aspects, when the base station <NUM> accesses the channel, the base station <NUM> may report missing RS symbols. The base station <NUM> may inform the UE <NUM> that the base station was not able to transmit the RS symbols. In such instances, the base station <NUM> may configure the UE to not account for these missing symbols that the base station may have reported in the UE's counting. In the UE's report, the UE <NUM> may report the missing reference signals not reported by the base station, which may due to the hidden nodes and/or interference issue that the base station <NUM> may not know about. In this case, the channel may be good, but the interference due to the hidden nodes (e.g., a WiFi nearby is interfering) may be large, but the base station <NUM> may not be aware of this issue.

In some aspects, for example at <NUM>, the UE <NUM> may perform one or more virtual transmission attempts. The UE <NUM> may perform the one or more virtual transmission attempts in a periodic manner. In a virtual transmission attempt, the UE <NUM> does not have any data to transmit, but instead the UE <NUM> performs LBT without actual data to transmit in order to determine the quality of the channel. In some aspects, the UE <NUM> may be configured to perform the virtual transmission attempt with a first periodicity for a first type of transmission attempt. In some aspects, the UE <NUM> may be configured to perform the virtual transmission attempt with a second periodicity for a second type of transmission attempt. The first type of the transmission attempt may be inside a transmission opportunity contended for and provided by the first base station. The second type of the transmission attempt may be outside the transmission opportunity contended for and provided by the first base station. The second type of the transmission attempt may be transmitted within a transmission opportunity contended for by the UE <NUM>. For example, the UE <NUM> may perform virtual transmission attempts. In some instances, the UE may wait to perform LBT until transmission data arrives, which may be too late and cause a delay in sending the data. In some aspects, the UE <NUM> may sense the channel beforehand. For example, the base station <NUM> may configure the UE <NUM> to sense the channel to determine if the channel quality is good, even if there is no actual data, e.g. every <NUM>. In this way, when actual data comes, the UE performing LBT will not be too late. Virtual transmission attempts refer to the UE performing LBT without actual data to transmit. Virtual transmission attempts may be performed when there are not sufficient actual uplink attempts. In some aspects, the UE <NUM> may be configured to perform virtual transmission attempts periodically. In some aspects, virtual transmission attempts may be performed separate/conditional within or outside the TXOP. For example, the UE may perform a virtual transmission attempt when the TXOP starts, periodically within TXOP, and/or with a separate periodicity outside the TXOP.

In some aspects, for example at <NUM>, the UE <NUM> may determine the best cell among the cells based on a ranking configured by the base station <NUM>. In some aspects, the ranking may be based on a combination of channel quality and channel load metrics. In some aspects, the ranking may be based on a priority configured by the base station <NUM>. For example, the base station <NUM> may give priority to configured SCells, its own cells, or other base stations (e.g., <NUM>) with less load. In some aspects, the ranking may also be in terms of LBT success events including virtual attempts on these frequencies. In some aspects, the ranking may be based on success events of the LBT protocol for the second cell. For example, the UE <NUM> may perform a handover to the best cell among the cells configured by the base station <NUM>. In some aspects, the UE <NUM> may deactivate a cell and activate a second cell. In some aspects, the UE <NUM> may move to a cell of a second base station <NUM> in the handover. Once the event has been triggered, the UE <NUM> may perform the handover to the best cell among the cells based on a ranking configured by the base station <NUM>.

At <NUM>, the UE <NUM> may switch from the first unlicensed frequency channel to a second cell. The UE <NUM> may switch from the first unlicensed frequency channel to the second cell for communication through the second cell in the conditional handover upon receiving the configuration and upon the determination that the first unlicensed frequency channel may be unavailable for the transmission. In some aspects, the first unlicensed frequency channel may be associated with a first primary cell of the base station <NUM>. In some aspects, the second cell may be associated with a first primary cell of a second base station <NUM> or a second primary cell of the base station <NUM>, such that the UE <NUM> switching from the first unlicensed frequency channel to the second cell for communication may comprise moving from the first primary cell of the base station <NUM> to the first primary cell of the second base station <NUM> or a second primary cell of the base station <NUM>. In some aspects, the first unlicensed frequency channel may be associated with a first secondary cell of the base station <NUM>. In some aspects, the second cell may be associated with a second secondary cell of the base station <NUM>, such that the UE switching from the first unlicensed frequency channel may comprise deactivating the first secondary cell of the base station <NUM>. The second cell may include an unlicensed frequency channel that was previously deactivated due to a failure of a previous transmission. In some aspects, the base station <NUM> may be a secondary node, such that the first unlicensed frequency channel may be associated with a primary cell of the secondary node, and the second cell may be associated with another primary cell of the secondary node.

In some aspects, for example at <NUM>, the UE <NUM> may send a report to the base station <NUM>. The UE <NUM> may send the report to the base station <NUM> to indicate the failure of the transmission upon the determination that the first unlicensed frequency channel is unavailable for the transmission. In some aspects, the report may be sent by the UE <NUM> to the base station <NUM> through a unicast RRC message or a MAC-CE. In some aspects, the report may be sent as part of a set of reports, where each report in the set of reports may be sent periodically to the first base station. For example, when an SCell experiences channel access problems, the UE <NUM> may deactivate the SCell and report the channel access problem to the base station <NUM> in an RRC message or as a MAC-CE via another cell, as shown at <NUM>. The UE <NUM> may send the report to the base station <NUM>, as shown at <NUM>'. In instances where an SCell was previously deactivated due to the channel access problem, the UE <NUM> may continue to perform measurements, possibly at a reduced rate in comparison to an activated cell. The UE <NUM> may use virtual attempts on deactivated cells. The UE <NUM> may activate the deactivated SCell when the metrics discussed above for LBT failure and/or channel quality metrics pass the configured thresholds. The UE may report the information that the cell becoming good again to the base station as an RRC message or as an MAC, as illustrated at <NUM>.

<FIG> is a flowchart of a method <NUM> of wireless communication. communication, according to the claimed invention. The method may be performed by a UE or a component of a UE (e.g., the UE <NUM>, <NUM>, <NUM>; the apparatus <NUM>/<NUM>'; the processing system <NUM>, which may include the memory <NUM> and which may be the entire UE <NUM> or a component of the UE <NUM>, such as the TX processor <NUM>, the RX processor <NUM>, and/or the controller/processor <NUM>). According to various aspects, one or more of the illustrated operations of method <NUM> may be omitted, transposed, and/or contemporaneously performed. Optional aspects are illustrated with a dashed line. The method may enable a UE to obtain access to an unlicensed frequency channel of the unlicensed frequency spectrum in a shorter time duration. The method may improve communication reliability, as well as communication data rate, capacity, and spectral efficiency.

At <NUM>, the UE receives a configuration to perform a conditional handover.

For example, <NUM> may be performed by configuration component <NUM> of apparatus <NUM>. The UE may receive the configuration to perform the conditional handover from a first base station. For example, referring to <FIG>, the base station <NUM> may configure the UE <NUM> to perform a handover to another cell or activate another cell under some conditions without waiting for an instruction from the base station. This handover may be referred to as a conditional handover.

At <NUM>, the UE may determine whether a first unlicensed frequency channel is available. For example, <NUM> may be performed by determination component <NUM> of apparatus <NUM>. The UE may determine whether the first unlicensed frequency channel is available for a transmission to the first base station or for a transmission from the first base station. In some aspects, such as when the first unlicensed frequency channel is available, the UE may utilize, at <NUM>, the first unlicensed frequency channel to transmit the transmission to the first base station or to receive the transmission from the first base station.

At <NUM>, the UE determines that the first unlicensed frequency channel is unavailable for the transmission. For example, <NUM> may be performed by determination component <NUM> of apparatus <NUM>. In some aspects, the UE may determine the conditions that may cause the first unlicensed frequency channel to be unavailable for the transmission.

At <NUM>, to determine that the first unlicensed frequency channel is unavailable for the transmission, the UE determines that the first unlicensed frequency channel is unavailable for the transmission based on LBT protocol failures. For example, <NUM> may be performed by LBT component <NUM> of apparatus <NUM>. The UE determines that the first unlicensed frequency channel may be unavailable for the transmission based on at least one of the LBT protocol failing due to a number of failed attempts exceeding a first threshold number of failed attempts or a duration of failed attempts exceeding a first threshold duration. In some aspects, the transmission may be one of a SR, a RACH procedure, data on a PUSCH, or SRS on the first unlicensed frequency channel. For example, with reference to <FIG>, for uplink, the base station <NUM> may configure the UE <NUM> with a first number of maximum transmission attempts and/or a first configured maximum duration. The UE <NUM> may trigger the report when LBT procedure fails for transmission attempts. In some aspects, the transmission attempts may include transmission attempts for SR, RACH, PUSCH, or SRS. The transmission attempts may include other types of transmission attempts as well, and is not intended to be limited to the aspects provided herein.

In some aspects, the UE may maintain one or more counters associated with the number of failed attempts or one or more timers associated with the duration of failed attempts based on the LBT protocol to transmit one or more of the SR, the RACH, the PUSCH, or the SRS on the first unlicensed frequency channel. In some aspects, each failed attempt may correspond to a determination that the first unlicensed frequency channel may be unavailable for transmission. In some aspects, the UE may reset the one or more counters or the one or more timers upon a successful attempt based on the LBT protocol to transmit one or more of the SR, the RACH, the PUSCH, or the SRS on the first unlicensed frequency channel. The successful attempt may correspond to a determination that the first unlicensed frequency channel may be available for the transmission. For example, with reference to <FIG>, the UE <NUM> may trigger the report after the transmission attempts for SR, RACH, PUSCH, or SRS fail a configured first maximum number of attempts or a configured first maximum duration, as illustrated at <NUM>. As an example, when a transmission attempt fails, a counter and/or timer may be triggered. The counter and/or timer may start counting or running. After a successful attempt, the counter and/or timer may be reset. The counter may increment by <NUM> after each failed attempt, and the timer may increase after each failed attempt, until the counter and/or timer reaches a first configured maximum number of attempts and/or a first configured maximum duration. The first configured maximum duration may be a duration from the timer being triggered until a successful transmission. For example, the first configured maximum duration may be a duration of a total duration of the failed attempts. In some aspects, the failed attempt may be due to LBT procedure failure.

Alternatively, for example at <NUM>, to determine that the first unlicensed frequency channel may be unavailable for the transmission, the UE may determine that the first unlicensed frequency channel may be unavailable for the transmission based on a comparison of one or more signals. For example, <NUM> may be performed by comparison component <NUM> of apparatus <NUM>. In some aspects, the UE may determine that the first unlicensed frequency channel may be unavailable for the transmission based on a comparison of one or more of a RSRP, a RSRQ, a RSSI, a SINR, a SNR, or a channel occupancy or interference metric to a corresponding threshold.

In some aspects, to determine that the first unlicensed frequency channel may be unavailable for the transmission based on a comparison of one or more signals, the UE may maintain one or more counters associated with a number of occasions when one or more of the RSRP, the RSRQ, the SINR, or the SNR is less than the corresponding threshold within a monitoring duration, or when one or more of the RSSI or the channel occupancy or interference metric is greater than the corresponding threshold within the monitoring duration. In some aspects, the UE may determine that the first unlicensed frequency channel may be unavailable for the transmission based on the number of occasions that exceed a threshold number of occasions within the monitoring duration. For example, with reference to <FIG>, for downlink, the UE <NUM> may determine that the channel is not available and trigger a report when RSRP, RSRQ, RSSI, SINR, SNR or a channel occupancy or interference metric is above or below a corresponding threshold for an amount of time where the UE counts the number of occasions when the reference signals are missed, e.g., when RSRP < the RSPP threshold, or RSRQ < the RSRQ threshold, or RSSI > the RSSI threshold, or SINR < the SINR threshold, or SNR < the SNR threshold, or the channel occupancy or interference metric > the channel occupancy or interference metric threshold within a duration (per cell or per sub-band), as illustrated at <NUM>. The base station <NUM> may configure the UE <NUM> to report to the base station <NUM> when RSRP, RSRQ, RSSI, SINR, SNR or a channel occupancy or interference metric is above or below a corresponding threshold for an amount of time. The UE <NUM> may count the number of occasions when the reference signals are missed, e.g., when RSRP < the RSPP threshold, or RSRQ < the RSRQ threshold, or RSSI > the RSSI threshold, or SINR < the SINR threshold, or SNR < the SNR threshold, or the channel occupancy or interference metric > the channel occupancy or interference metric threshold within the duration (per cell or per sub-band).

In some aspects, for example at <NUM>, the UE may perform a virtual transmission attempt. For example, <NUM> may be performed by virtual tx component <NUM> of apparatus <NUM>. The UE may perform the virtual transmission attempt in a periodic manner. In the virtual transmission attempt, the UE does not have any data to transmit, but instead the UE performs LBT without actual data to transmit in order to determine the quality of the channel. In some aspects, the UE may be configured to perform the virtual transmission attempt with a first periodicity for a first type of transmission attempt. In some aspects, the UE may be configured to perform the virtual transmission attempt with a second periodicity for a second type of transmission attempt. The first type of the transmission attempt may be inside a transmission opportunity contended for and provided by the first base station. The second type of the transmission attempt may be outside the transmission opportunity contended for and provided by the first base station. The second type of the transmission attempt may be transmitted within a transmission opportunity contended for by the UE. For example, with reference to <FIG>, the UE <NUM> may perform virtual transmission attempts. In some instances, the UE may wait to perform LBT until the UE has actual data for transmission and may perform the LBT too late. In some aspects, the UE <NUM> may sense the channel beforehand. For example, the base station <NUM> may configure the UE <NUM> to sense the channel to determine if the channel quality is good, even if there is no actual data, e.g. every <NUM>. In this way, when actual data comes, the UE performing LBT will not be too late. Virtual transmission attempts refer to the UE performing LBT without actual data to transmit. Virtual transmission attempts may be performed when there are not sufficient actual uplink attempts. In some aspects, the UE <NUM> may be configured to perform virtual transmission attempts periodically. In some aspects, virtual transmission attempts may be performed separate/conditional within or outside the TXOP. For example, the UE may perform a virtual transmission attempt when the TXOP starts, periodically within TXOP, and/or with a separate periodicity outside the TXOP.

In some aspects, for example at <NUM>, the UE may determine the second cell based on a ranking. For example, <NUM> may be performed by rank component <NUM> of apparatus <NUM>. The UE may determine the second cell based on a ranking configured by the first base station. In some aspects, the ranking may be based on a combination of channel quality and channel load metrics. In some aspects, the ranking may be based on a priority configured by the first base station. For example, the base station <NUM> may give priority to configured SCells, its own cells, or other base stations with less load. In some aspects, the ranking may also be in terms of LBT success events including virtual attempts on these frequencies. In some aspects, the ranking may be based on success events of the LBT protocol for the second cell. For example, with reference to <FIG>, at <NUM>, the UE <NUM> may perform a handover to the best cell among the cells configured by the base station <NUM>. In some aspects, the UE <NUM> may deactivate a cell and activate a second cell. In some aspects, the UE may move to a cell of a second base station <NUM> in the handover. Once the event has been triggered, the UE <NUM> may perform the handover to the best cell among the cells based on a ranking configured by the base station <NUM>.

At <NUM>, the UE switches from the first unlicensed frequency channel to a second cell. For example, <NUM> may be performed by switch component <NUM> of apparatus <NUM>. The UE may switch from the first unlicensed frequency channel to the second cell for communication through the second cell in the conditional handover upon receiving the configuration and upon the determination that the first unlicensed frequency channel may be unavailable for the transmission. In some aspects, the first unlicensed frequency channel may be associated with a first primary cell of the first base station. In some aspects, the second cell may be associated with a first primary cell of a second base station or a second primary cell of the first base station, such that the UE switching from the first unlicensed frequency channel to the second cell for communication may comprise moving from the first primary cell of the first base station to the first primary cell of the second base station or a second primary cell of the first base station. In some aspects, the first unlicensed frequency channel may be associated with a first secondary cell of the first base station. In some aspects, the second cell may be associated with a second secondary cell of the first base station, such that the UE switching from the first unlicensed frequency channel may comprise deactivating the first secondary cell of the first base station. The second cell may include an unlicensed frequency channel that was previously deactivated due to a failure of a previous transmission. In some aspects, the first base station may be a secondary node, such that the first unlicensed frequency channel may be associated with a primary cell of the secondary node, and the second cell may be associated with another primary cell of the secondary node.

In some aspects, for example at <NUM>, the UE may send a report to the first base station. For example, <NUM> may be performed by report component <NUM> of apparatus <NUM>. The UE may send the report to the first base station to indicate the failure of the transmission upon the determination that the first unlicensed frequency channel is unavailable for the transmission. In some aspects, the report may be sent by the UE to the first base station through a unicast RRC message or a MAC-CE. In some aspects, the report may be sent as part of a set of reports, where each report in the set of reports may be sent periodically to the first base station. For example, with reference to <FIG>, when an SCell experiences channel access problems, the UE <NUM> may deactivate the SCell and report the channel access problem to the base station <NUM> in an RRC message or as a MAC-CE via another cell, as shown at <NUM>. The UE <NUM> may send the report to the base station <NUM>, as shown at <NUM>'. In instances where an SCell was previously deactivated due to the channel access problem, the UE <NUM> may continue to perform measurements, possibly at a reduced rate in comparison to an activated cell. The UE <NUM> may use virtual attempts on deactivated cells. The UE <NUM> may activate the deactivated SCell when the metrics discussed above for LBT failure and/or channel quality metrics pass the configured thresholds. The UE may report the information that the cell becoming good again to the base station as an RRC message or as an MAC, as illustrated at <NUM>.

<FIG> is a conceptual data flow diagram <NUM> illustrating the data flow between different means/components in an example apparatus <NUM>. The apparatus may be a UE or a component of a UE. The apparatus includes a reception component <NUM> that may be configured to receive various types of signals/messages and/or other information from other devices, including, for example, the base station <NUM>. The apparatus includes a configuration component <NUM> configured to receive a configuration to perform a conditional handover, e.g., as described in connection with <NUM> of <FIG>. The apparatus includes a determination component <NUM> configured to determine whether a first unlicensed frequency channel is available, e.g., as described in connection with <NUM> of <FIG>. The determination component <NUM> may also be configured to determine that the first unlicensed frequency channel may be unavailable for the transmission, e.g., as described in connection with <NUM> of <FIG>. The apparatus includes an LBT component <NUM> configured to determine that the first unlicensed frequency channel may be unavailable for the transmission based on LBT protocol failures, e.g., as described in connection with <NUM> of <FIG>. The apparatus includes a comparison component <NUM> configured to determine that the first unlicensed frequency channel may be unavailable for the transmission based on a comparison of one or more signals, e.g., as described in connection with <NUM> of <FIG>. The apparatus includes a virtual tx component <NUM> configured to perform a virtual transmission attempt, e.g., as described in connection with <NUM> of <FIG>. The apparatus includes a rank component <NUM> configured to determine the second cell based on a ranking, e.g., as described in connection with <NUM> of <FIG>. The apparatus includes a switch component <NUM> configured to switch from the first unlicensed frequency channel to a second cell, e.g., as described in connection with <NUM> of <FIG>. The apparatus includes a report component <NUM> configured to send a report to the first base station, e.g., as described in connection with <NUM> of <FIG>. The apparatus includes a transmission component <NUM> configured to transmit various types of signals/messages and/or other information to other devices, including, for example, the base station <NUM> and/or <NUM>.

<FIG> is a diagram <NUM> illustrating an example of a hardware implementation for an apparatus <NUM>' employing a processing system <NUM>. The processing system <NUM> may be implemented with a bus architecture, represented generally by the bus <NUM>. The bus <NUM> may include any number of interconnecting buses and bridges depending on the specific application of the processing system <NUM> and the overall design constraints. The bus <NUM> links together various circuits including one or more processors and/or hardware components, represented by the processor <NUM>, the components <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and the computer-readable medium / memory <NUM>. The bus <NUM> may also link various other circuits such as timing sources, peripherals, voltage regulators, and power management circuits, which are well known in the art, and therefore, will not be described any further.

The processing system <NUM> may be coupled to a transceiver <NUM>. The transceiver <NUM> is coupled to one or more antennas <NUM>. The transceiver <NUM> provides a means for communicating with various other apparatus over a transmission medium. The transceiver <NUM> receives a signal from the one or more antennas <NUM>, extracts information from the received signal, and provides the extracted information to the processing system <NUM>, specifically the reception component <NUM>. In addition, the transceiver <NUM> receives information from the processing system <NUM>, specifically the transmission component <NUM>, and based on the received information, generates a signal to be applied to the one or more antennas <NUM>. The processing system <NUM> includes a processor <NUM> coupled to a computer-readable medium / memory <NUM>. The processor <NUM> is responsible for general processing, including the execution of software stored on the computer-readable medium / memory <NUM>. The software, when executed by the processor <NUM>, causes the processing system <NUM> to perform the various functions described supra for any particular apparatus. The computer-readable medium / memory <NUM> may also be used for storing data that is manipulated by the processor <NUM> when executing software. The processing system <NUM> further includes at least one of the components <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>. The components may be software components running in the processor <NUM>, resident/stored in the computer readable medium / memory <NUM>, one or more hardware components coupled to the processor <NUM>, or some combination thereof. The processing system <NUM> may be a component of the UE <NUM> and may include the memory <NUM> and/or at least one of the TX processor <NUM>, the RX processor <NUM>, and the controller/processor <NUM>. Alternatively, the processing system <NUM> may be the entire UE (e.g., see <NUM> of <FIG>).

In some aspects, the apparatus <NUM>/<NUM>' for wireless communication includes means for receiving a configuration from a first base station for the UE to perform a conditional handover. The apparatus includes means for determining a first unlicensed frequency channel is unavailable for a transmission to the first base station or from the first base station. The apparatus includes means for switching from the first unlicensed frequency channel to a second cell for communication through the second cell in the conditional handover upon receiving the configuration and upon determining that the first unlicensed frequency channel is unavailable for the transmission. The apparatus further includes means for determining that the first unlicensed frequency channel is unavailable for the transmission configured to determine the first unlicensed frequency channel is unavailable for the transmission based on at least one of a LBT protocol failing due to a number of failed attempts exceeding a first threshold number of failed attempts or a duration of failed attempts exceeding a first threshold duration. The apparatus further includes means for maintaining one or more counters associated with the number of failed attempts or one or more timers associated with the duration of failed attempts based on the LBT protocol to transmit one or more of the SR, the RACH, the PUSCH, or the SRS on the first unlicensed frequency channel. Each failed attempt corresponding to a determination that the first unlicensed frequency channel is unavailable for the transmission. The apparatus further includes means for resetting the one or more counters or the one or more timers upon a successful attempt based on the LBT protocol to transmit one or more of the SR, the RACH, the PUSCH, or the SRS on the first unlicensed frequency channel. The successful attempt corresponding to a determination that the first unlicensed frequency channel is available for the transmission. The apparatus further includes means for performing virtual transmission attempts. The apparatus further includes means for determining that the first unlicensed frequency channel is unavailable for the transmission configured to determine that the first unlicensed frequency channel is unavailable for the transmission based on a comparison of one or more of a RSRP, a RSRQ, a RSSI, a SINR, a SNR, or a channel occupancy or interference metric to a corresponding threshold. The apparatus further includes means for maintaining one or more counters associated with a number of occasions when one or more of the RSRP, the RSRQ, the SINR, or the SNR is less than the corresponding threshold within a monitoring duration, or when one or more of the RSSI or the channel occupancy or interference metric is greater than the corresponding threshold within the monitoring duration. The apparatus further includes means for determining the second cell based on a ranking configured by the first base station. The apparatus further includes means for sending a report to the first base station indicating the failure of the transmission upon determining that the first unlicensed frequency channel is unavailable for the transmission.

The present disclosure relates to configuring a UE to obtain access to an unlicensed frequency channel of the unlicensed frequency spectrum in the event of channel access failures. The present disclosure improves the manner in which the base station may configure the UE to perform a handover to another cell if the channel access problem occurs on a PCell or a PSCell. The base station may also configure the UE to de-activate an SCell if the channel access problem occurs, as well as to activate another configured SCell. At least one advantage of the disclosure is that the disclosure may improve communication reliability by enabling the base station and/or the UE to access an unlicensed frequency channel in a shorter amount of time, which may further improve communication data rate, capacity, and spectral efficiency.

Claim 1:
A method (<NUM>) of wireless communication performed by an apparatus of a user equipment, UE, the method (<NUM>) comprising:
receiving (<NUM>) a configuration from a first base station for the UE to perform a conditional handover;
determining (<NUM>) that a first unlicensed frequency channel is unavailable for a transmission to the first base station or from the first base station, wherein the determining that the first unlicensed frequency channel is unavailable for the transmission comprises determining the first unlicensed frequency channel is unavailable for the transmission based on at least one of a listen before talk, LBT, protocol failing due to a number of failed attempts exceeding a first threshold number of failed attempts or a duration of failed attempts exceeding a first threshold duration (<NUM>); and
switching (<NUM>) from the first unlicensed frequency channel to a second cell for communication through the second cell in the conditional handover upon receiving the configuration and upon determining that the first unlicensed frequency channel is unavailable for the transmission.