WO2021028871A1 - Cell reselection triggered by listen-before-talk (lbt) failures - Google Patents

Abstract

A User Equipment (UE) (40) triggers (132) cell reselection responsive to detecting Listen-Before-Talk (LBT) failures, and initiates (138) cell reselection according to specified schemes, or preconfigured conditions and schemes. When the UE determines that the uplink (UL) channel(s) are too busy to provide service(s) for the UE, the UE can select another cell on another frequency.

Description

CELL RESELECTION TRIGGERED BY LISTEN-BEFORE-TALK (LBT) FAILURES

RELATED APPLICATIONS

The present application claims benefit of U.S. Provisional Application 62/887,430, which was filed August 15, 2019, the disclosure of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to channel reselection in wireless systems, and more particularly to user equipment (UEs) that are configured to trigger and initiate channel reselection according to specified schemes or preconfigured conditions and schemes.

BACKGROUND

Next generation systems are expected to support a wide range of use cases with varying requirements ranging from fully mobile devices to stationary Internet of Things (loT) or fixed wireless broadband devices. The traffic pattern associated with many use cases is expected to consist of short or long bursts of data traffic, with varying length waiting periods in between (referred to herein as an “inactive state”). In New Radio (NR), both license assisted access and standalone unlicensed operation are to be supported in 3GPP. Hence, 3GPP investigates the random access procedure and/or scheduling request (SR) transmission in the unlicensed spectrum.

SUMMARY

For NR unlicensed spectrum, NR standalone scenario was the newly defined scenario. For this scenario, the existing Random Access (RA) procedure, sometimes referred to as a Random Access Channel (RACH) procedure, is enhanced to ensure differentiated latency requirements considering the Listen-Before-Talk (LBT) impact. Aspects of the present disclosure addresses such issues and provide enhancements.

Particularly, a first aspect for initiating cell reselection according to the present disclosure is implemented by a user equipment (UE) operating in a first cell. In this aspect, the UE implements a method for triggering cell reselection at the UE responsive to detecting one or more Listen-Before-Talk (LBT) failures, obtaining a channel occupancy for each of one or more cells that are different from the first cell, selecting, from the one or more cells, a second cell having a channel occupancy that is lower than the first cell, and initiating cell reselection to the second cell.

In a second aspect, the present disclosure provides a user equipment (UE) in a wireless communication network. In this aspect, the UE comprises interface circuitry configured for communication with one or more serving cells the wireless communication network, and processing circuitry. The processing circuitry is configured to trigger cell reselection at the UE responsive to detecting one or more Listen-Before-Talk (LBT) failures, obtain a channel occupancy for each of one or more cells that are different from the first cell, select, from the one or more cells, a second cell having a channel occupancy that is lower than the first cell, and initiate cell reselection to the second cell.

The present disclosure also provides a UE configured to perform the method described above, a computer program comprising executable instructions that, when executed by processing circuitry in a UE in a wireless communication network, causes the UE to perform the method described above, and a non-transitory computer-readable storage medium containing a computer program comprising executable instructions that, when executed by processing circuitry in a UE in a wireless communication network, causes the UE to perform the method described above.

The aspects disclosed herein provide benefits and advantages that prior art systems either do not provide, or are not configured to provide. Such benefits and advantages include, but are not limited to:

• The improvement of the user experience served in NR-U system;

• The reduction of latency for service provisioning;

• The ability of the UEs to resolve local congestion issues, which are not visible by the gNB.

• The gNB still controls frequency prioritization and load balancing.

• The gNB may determine, based on exchange of neighbor cell information on channel occupancy, whether it wants to allow the UE to reselect cells on other frequencies or not; and

• The gNB may determine, based on observation, how long channel occupancy issues could apply, as well as determine an appropriate timer value.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 illustrates a New Radio (NR) frequency combination of paired carrier and supplementary uplink carrier (SUL) (for uplink only) according to an aspect.

Figure 2 illustrates a communication network according to one aspect.

Figure 3 is a flow chart illustrating a method for frequency barring triggered by UL-LBT- ISSUES according to one aspect.

Figure 4 is a flow chart illustrating a method for frequency deprioritization triggered by UL-LBT-ISSUES according to one aspect.

Figure 5 is a flow chart illustrating a method for ceasing to bar a frequency according to one aspect.

Figure 6 is a flow chart illustrating a method for re-setting a frequency that was deprioritized to its previous priority according to one aspect.

Figure 7 is a flow chart illustrating a method implemented by a UE for performing cell reselection according to one aspect. Figure 8 is a functional block diagram of a wireless terminal that can be configured as a UE according to one aspect.

Figure 9 is a schematic block diagram of a wireless terminal that can be configured as a UE according to one aspect.

Figure 10 is a functional block diagram of UE processing circuitry and some functional components executed by the processing circuitry according to one aspect.

DETAILED DESCRIPTION

Aspects of the present disclosure detail NR-based Access to the Unlicensed Spectrum (NR-U) and introduce channel access procedures for an unlicensed channel based on Listen- Before-Talk (LBT).

Introduction to NR-U

In order to tackle the ever increasing demand for data, NR is considered in both the licensed and unlicensed spectrums. In the study item on NR-based Access to Unlicensed Spectrum of September 2017, it was determined that NR-U, in contrast to Long Term Evolution (LTE) Licensed Assisted Access (LAA), also needs to support Dual Connectivity (DC) and standalone scenarios where Medium Access Control (MAC) procedures, including the Random Access (RA) and scheduling procedures on the unlicensed spectrum, are subject to LBT failures. In contrast, there are no such restrictions in LTE LAA. Since there are licensed spectrums in LAA scenarios, the RACH and scheduling related signaling can be transmitted on the licensed spectrum instead of the unlicensed spectrum. Channel sensing should be applied to determine the channel availability before a physical signal is transmitted using the channel.

The Radio resource management (RRM) procedures in NR-U are generally similar to those in LAA. This is because NR-U aims to reuse LAA / Enhanced LAA (eLAA) / Further Enhanced LAA (feLAA) technologies as much as possible to handle coexistence of NR-U and other legacy Radio Access Technologies (RATs). RRM measurements and reports comprise special configuration procedures with respect to channel sensing and channel availability. For instance, LAA uses the same carriers as Wi-Fi, and thus, may be congested. Hence, channel access/selection for LAA is one important aspect for co-existence with other RATs, such as Wi Fi. For more information, the interested reader is directed to 3GPP TS 37.213 V16.2.0 (2020- 06) entitles, “3GPP Technical Specification Group Radio Access Network; Physical layer procedures for shared spectrum channel access; (Release 16),” which is incorporated herein by reference in its entirety.

LTE LAA defines Received Signal Strength Indicator (RSSI) measurement timing configuration (RMTC) to support measurements of averaged RSSI and channel occupancy (CO) for measurement reports. For example, the channel occupancy is defined as a percentage of time that the RSSI was measured above a configured threshold. Random Access Procedures in NR unlicensed spectrum

The ordinary four step random access (RA) procedure has been the current standard for legacy systems such as LTE and NR Rel-15. It has been proposed to specify a two-step procedure where the Uplink (UL) messages (PRACH + Msg3) are sent simultaneously, and similarly, the two Downlink (DL) messages (Random Access Response (RAR) and contention resolution information) are sent as a simultaneous response in the DL to reduce the latency.

For NR-U, combining the UL messages and the DL messages advantageously reduces the number of LBT procedures.

Supplementary Uplink (SUL)

NR introduced a supplementary uplink (SUL) carrier for a NR cell (i.e. a NR cell has a SUL carrier plus a NR UL carrier). More particularly, Figure 1 shows a NR cell 10 having a base station 20, and illustrates the coverages of an NR UL carrier 12 and an SUL carrier 14, as well as a NR DL carrier 16 in NR cell 10. The SUL carrier 14 is a low frequency carrier which can be shared (in the time and/or frequency domain) with other RAT systems such as LTE. Since there are two uplink carriers for a NR cell 10 in this case, the random access can be initiated in either NR UL carrier 12 or SUL carrier 14.

For NR in unlicensed operation, the SUL carrier 14 can be deployed in situations where the NR cell 10 is a stand-alone NR cell in the unlicensed band (i.e., single cell architecture). According to the deployment scenarios described in 3GPP TR 38.889 v1 .1 .0 “Study on NR- based access to Unlicensed Spectrum (Release 16),” SUL carrier 14 would be on a licensed band for NR-U. However, in future releases, it could also include scenarios where the SUL carrier 14 is on unlicensed bands.

Deprioritization of Frequencies

When a UE attempts to initialize (random) channel access, or resume a connection from the RRCJNACTIVE state, it selects a RACH preamble randomly and requests a random access to a gNB.

In an unlicensed system, the UE may experience consecutive LBT failures during PRACH, possibly resulting in a situation where the UE reaches the maximum transmission attempts. The UE MAC would then trigger a PRACH problem due to LBT failures.

As a result, the establishment of an Radio Resource Control RRC connection may fail due to the consistent LBT failures that occur (e.g. due to high interference). The UE may select the same serving cell again for initial access since the channel occupancy is not considered on the cells. When the cell reselection is triggered because the UL LBT failures are consistent, the UE may select another cell to avoid the possible RRC establishment failures. However, if the selected new cell and the cell where consistent LBT failures are occurring are in the same frequency, the UE may still face the consistent UL LBT failures when those failures are caused by high interference in this frequency. Consequently, in order to avoid the possible consistent UL LBT failures, the UE should camp on a cell of another frequency. One simple solution is to decrease cell reselection priority of the frequency where the consistent LBT failures occurred, i.e. the priority of the frequency used by the current cell where the failures are occurring, should be deprioritized so that the UE will not choose that frequency during the subsequent cell reselection procedure. This can be done with the RRCRelease message, for example. Using this message, the gNB can control de-prioritization of frequencies.

Therefore, in one NR-U-based aspect, the priority of the frequency where the consistent UL LBT failures occurred is deprioritized for the subsequent cell reselection procedure triggered by the consistent UL LBT failures.

As stated above, one way to handle these situations is to allow the UE to deprioritize the frequency. However, other frequencies may have similar issues. Additionally, such deprioritization is not complete. Deprioritizing a frequency for an unlimited time may cause the UE to end up on a non-optimal frequency.

Apart from the UL LBT issues, additional delay may be caused because different UEs may select the same RACH preamble. Therefore, there is a risk of collision (i.e. contention based RACH). In cases of collision, the competing UEs will have to re-initiate the random access with reselected preambles. Normally, a back-off action is also required before initializing a new random access procedure.

To address these issues, aspects of the present disclosure provide a method for a UE to trigger and initiate channel reselection according to specified schemes or preconfigured conditions and schemes. When the UE determines that the UL channel(s) are too busy to provide service(s) for the UE, the UE can select another cell. Similarly, as in the connected mode where the UE may initiate a Bandwidth Part (BWP) switch or carrier switch procedure, the UE reselects another frequency.

Referring now to the Figures 2-10 of the drawings, an exemplary aspect of the disclosure will be described in the context of a 5G or NR wireless communication network. Those skilled in the art will appreciate that the methods and apparatus herein described are not limited to use in 5G or NR networks, but may also be used in wireless communication networks 30 where multiple beams within a single cell may or may not be used for communication with wireless devices in the cell.

Figure 2 illustrates a wireless communication network 30 according to the NR standard. The wireless communication network 30 comprises one or more base stations 20 providing service to user equipment (UEs) 40 in respective cells 50 of the wireless communication network 30. The base stations 20 are also referred to as Evolved NodesBs (eNBs) and gNodeBs (gNBs) in 3GPP standards. Although only one cell 50 and one base station 20 are shown in Figure 2, those skilled in the art will appreciate that a typical wireless communication network 30 comprises many cells 50 served by many base stations 20. One feature of NR networks is the ability of the base stations 20 to transmit and/or receive on multiple beams 60 in the same cell 30. Figure 2 illustrates two beams 60, although the number of beams 60 in a cell 50 may be different.

The UEs 40 may comprise any type of equipment capable of communicating with the base station 20 over a wireless communication channel. For example, the UEs 40 may comprise cellular telephones, smart phones, laptop computers, notebook computers, tablets, machine-to-machine (M2M) devices (also known as machine type communication (MTC) devices), embedded devices, wireless sensors, or other types of wireless end user devices capable of communicating over wireless communication networks 30.

Aspects of the present disclosure provide methods by which a UE triggers and initiates channel reselection according to specified schemes, or preconfigured conditions and schemes. When the UE determines that the UL channel(s) are too busy to provide service(s) for the UE, the UE can select another cell on another frequency.

LBT issues are local and, for UL LBT, the UE will not change its location when selecting another cell on the same frequency. Therefore, to overcome LBT issues, the UE would have to use another frequency. This is implemented by considering all cells on the serving cell’s frequency as “barred.”

How a UE determines consistent LBT failures during an RA procedure:

According to the present aspects, the UE 40 can determine consistent LBT failures during an RA procedure in at least two ways.

• Option 1 ) LBT failures for preamble transmissions on (P)RACH can be counted separately.

• Option 2) UL LBT failures are counted for all, or a subset of all, physical uplink channels. Issues on PRACH are implicitly derived by the UE when UL LBT failures occur during its random access procedure. If there is congestion, it can be assumed that it was Msg1 transmission (PRACH) which failed rather than Msg3 (PUSCH). However, there is no strong need to distinguish between Msg1 and Msg3 while UL LBT failures are consistent.

After successful initial channel access, a UE 40 may report any UL LBT failure issues including the amount of time in which it suffered from LBT problems. This information could be for a certain frequency. Such information can be used by the gNB and exchanged between neighboring gNBs to optimize network configuration with regard to frequency barring/deprioritization by the UE 40 during the cell reselection procedure.

For example, if the gNB knows that there may be LBT issues on the serving cell’s frequency, and also on other carrier frequencies, it may prevent the UE 40 from barring/deprioritizing that frequency. The gNB may explicitly allow or disallow the UE 40 to autonomously bar a frequency when the UE 40 experiences UL LBT issues during the initial channel access procedure. This can be signaled in the system information, e.g. in SIB1 (as the spare bits in MIB are valuable), using a bit - e.g., “freqBarring” ” or “ul-LBT- TriggeredDeprioritization - which can be set to the states “allowed” or “notAllowed”.

Additionally, the gNB may know typical durations for the LBT congestion issues from UL LBT failure reports received from the UE 40. In such cases, the gNB could configure a corresponding timer parameter to a value that is different than the 300s value that is typically used, thereby guarding against an undesirable situation where a UE bars/deprioritizes a given cell even though the cell should not be barred/deprioritized.

For example, consider a situation where a UE 40 bars/deprioritizes a cell. However, prior to the 300 second timer expiring, the coverage conditions for the cell improve. Because the UE 40 may not know the potential time duration for LBT issues, the UE 40 could continue to bar/deprioritize the cell even though the cell coverage conditions may improve to the point where reading the System Information Block (SIB) may succeed. Therefore, some aspects of the present disclosure allow the network to configure an appropriate value for the timer if it has knowledge of the potential time duration for LBT issues.

There are three options:

• Option 1 ) Bar the frequency temporarily;

• Option 2) Temporarily deprioritize the frequency; and

• Option 3) Have the network select whether to bar the frequency or deprioritize the frequency.

The drawback of frequency barring is that the cells on this frequency will be completely blocked, and the UE 40 will not try to access those cells, even though the channel occupancy on other frequencies may be similar or worse, such that the UE 40 will not try to access on any of those cells. However, deprioritizing the frequencies would put the priority of all frequencies to the lowest priority, so that those frequencies would not be completely barred.

Unnecessary frequency deprioritization/barring procedures, such as those performed in situations where the channel occupancy on all frequencies is known to be quite high, can be avoided if the gNB is aware of this situation (e.g. by frequency observation or being aware of busy hour or people going to a stadium or other bigger event).

Figure 3 illustrates a method 70 in which frequency barring is triggered by UL-LBT- ISSUES according to one aspect. In Figure 3, the following terminologies are used:

• UL-LBT-ISSUES - This state indication is provided in MAC or RRC to determine that there have been UL LBT issues for some period. Alternatively, a separate indication for

RACH-LBT-ISSUES could be used.

• freqBarring - This is a bit that is configured in the system information, or via

RRCRelease, other dedicated RRC signaling or other signaling, that indicates whether frequency barring during the cell reselection procedure is allowed when the UE determines UL LBT issues during the random access procedure.

• freqBarringTimer -This is a timer that is configured in RRC (see 3GPP TS 38.331 v. 15.60) to determine the duration of the temporary frequency barring for cell reselection.

• ul-LBT-TriggeredFreqDeprioritization - This is a bit that is configured in the system information, via RRCRelease, or via other dedicated RRC signaling, and indicates whether frequency deprioritization during the cell reselection procedure is allowed when the UE determines UL LBT issues during the random access procedure.

• ul-LBT-TriggeredFreqDeprioritizationTimer - This is a timer that is configured in RRC (3GPP TS 38.331 ) to determine the duration of the temporary frequency deprioritization for cell reselection.

As seen in Figure 3, the UE 40 begins a RACH procedure (e.g., Msg1 preamble transmission on (P)RACH) (box 72). Then, from the MAC/RRC layers, UL-LBTJSSUES indications are sent (box 74). Based on this information, the UE 40 determines whether it is permitted to bar the frequency or not bar the frequency (box 76). If the UE 40 is permitted to bar the frequency, it begins the freqBarringTimer, bars the frequency (box 78), and continues with the cell reselection procedure (box 80). If not, the UE 40 simply continues with the cell reselection procedure (box 80). Cell reselection continues until a cell is selected (box 82).

Figure 4 illustrates a method 90 in which frequency deprioritization is triggered by UL- LBT-ISSUES according to one aspect. As seen in Figure 4, the UE 40 begins a RACH procedure (e.g., Msg1 preamble transmission on (P)RACH) (box 92). Then, from the MAC/RRC layers, UL-LBTJSSUES indications are sent (box 94). Based on this information, the UE determines whether it is or is not permitted to deprioritize the frequency (box 96). If deprioritization is allowed, the UE 40 stores the priority value of the frequency being deprioritized, deprioritizes the frequency to the lowest priority value, and then begins the ul- LBT-Triggered-FreqDeprioritisationTimer for the deprioritized frequency (box 98) before continuing with cell reselection (box 100). If frequency deprioritization is not permitted, the UE 40 simply continues with cell reselection (box 100). As above, cell reselection continues until a cell is selected (box 102).

Figures 5 and 6 are both implemented at the UE 40 and illustrate respective methods for operation upon expiration of the freqBarringTimer (method 110 in Figure 5) and the ul-LBT- Triggered-FreqDeprioritisationTimer (method 120 in Figure 6). In particular, as seen in method 110 of Figure 5, once the freqBarringTimer for a given frequency expires (box 112), the UE ceases the barring of that frequency (box 114). As seen in method 120 of Figure 6, once the ul-LBT-Triggered-FreqDeprioritisationTimer expires (box 122), the UE sets the priority of the deprioritzed frequency back to its previous stored value (box 124). Any other equivalent parameter names can be used for the above indications/parameters.

In other words, the above methods for triggering cell reselection by the UE can be reformulated as the following. Based on information provided by the PHY layer or upper layer (e.g. RRC or MAC layer), the UE may trigger a cell reselection event by barring the current frequency for a limited amount of time. The frequency barring is triggered because the UE is experiencing a high congestion/collision in the current serving cell. The event can be triggered based on at least one of following criteria:

• When within a preconfigured interval, a maximum number of consecutive LBT failures is reached with respect to the transmission of one or multiple uplink physical channels. Generally, this may occur because transmission on the PRACH could not be performed. However, it may also occur with respect to PUSCH for msg3 transmission. In this case, the PHY layer may need to send an indicator indicating the outcome of the LBT operation to the MAC layer.

• When a maximum time period beginning at the time transmission is triggered at the MAC and ending at the time the transmission gets through on the PHY layer is reached. In this case, the time periods for both the initial transmission and the retransmission attempts are considered. If the UE is experiencing consecutive LBT failures, the UE may only succeed to grasp the channel for the last transmission attempt.

• When a maximum time period beginning at the time the UE detected the last DL control reference signal is reached. In this case, the UE could not receive the DL RLM reference signals (SSB, CSI-RS or DRS) since the gNB may experience LBT failures.

• When the channel occupancy of the UL channels to serve the UE exceeds a preconfigured threshold.

Further, the network may configure a UE based on whether the UE is allowed to bar the frequency of the cell where the congestion is observed. Additionally, the network may configure a frequency barring timer T to control the duration for the frequency barring - i.e. the length of time that the UE is allowed to bar the current frequency. For example, the configurations can be signaled in at least one of following.

• In the system information (e.g., counter, timer for triggering consistent LBT failures);

• The configuration information (e.g., counter, timer for triggering consistent LBT failures)) for the IDLE and inactive states can be included in the RRC signaling message (e.g., RRC reconfiguration) when the UE switches down from the connected mode to RRC idle or RRC inactive;

• The UE may remain in the same configurations as in the RRC connected state, and use them for the RRC IDLE and RRC inactive states. When the UE has finished establishing or resuming its RRC connection to a serving cell, the UE can report any consistent LBT failure that the UE has experienced for other channel/subband/BWP/cell/frequency. Upon receiving the report, the gNB may improve its configuration for that channel/subband/BWP/cell/frequency.

In one example the UE can beconfigured with a SUL (licensed or un-licensed). The UE will try the Random Access procedure on this UL before it will bar the frequency where the first Random Access procedure failed due to consecutive UL LBT failures.

In another example, the UE may base the original selection between the normal UL and the SUL. The UE may base the original selection not only on an RSRP threshold, as is the case with legacy NR, but also on channel occupancy such as LBT statistics.

The UE can send this information to the gNB on a different cell that is active if such a cell exists and responsive to the UE detecting UL LBT failures during random access. The UE may also send this information on a different BWP, if configured, or on a RACH resource that requires an LBT procedure on a subband that is different than where the LBT failed. If such a procedure also fails LBT, then any of the aspects previously described may be used.

The examples below show possible configuration options in SIB1 (see e.g., 3GPP TS 38.331), and possible changes on IDLE/INACTIVE mode UE behavior for cell reselection in 3GPP TS 38.304 v16.0.0 (2020-03) “NR; User Equipment (UE) procedures in Idle mode and RRC Inactive state (Release 16),” for implementing the methods described above.

Option 1 - Frequency Barring

UL-LBT-FailureControl

The IE UL-LBT-FailureControl is used to configure parameters for UL LBT failure control.

UL-LBT-FailureControl Information Element

- ASN1 START

- TAG-UL-LBT-FailureControl-START UL-LBT-FailureControl ::= SEQUENCE { freqBarring ENUMERATED {allowed, notAllowed}, freqBarringTimer ENUMERATED { mini , min2, min3, min4, min5, min10, min15, min30}

}

- TAG-UL-LBT-FailureControl -STOP

- ASN1STOP

Table 1 : New SIB1 parameters.

Additionally, according to section 5.3.1 “Cell status and cell reservations” of 3GPP TS

38.304:

• If the cell is to be treated as if the cell status is "barred" due to being unable to transmit during the random access procedure due to UL-LBT-ISSUES;

• The UE shall exclude the barred cell and the cells on the same frequency as a candidate for cell selection/reselection for freqBarringTimer seconds.

The default value for freqBarringTimer is 300 seconds.

The timer can be defined in the specifications if considered beneficial. Otherwise, the timer will typically be fixed to 300 seconds (5 minutes) as it is for other cell/frequency barring features.

The UL-LBT-ISSUES indication can be associated with transmission failure of the RA preamble on PRACH if the random access procedure is ongoing.

Option 2 - Frequency Deprioritization

UL-LBT-FailureControl

The IE UL-LBT-FailureControl is used to configure parameters for UL LBT failure control.

UL-LBT-FailureControl information element

- ASN1 START

- TAG-UL-LBT-FailureControl-START UL-LBT-FailureControl ::= SEQUENCE { ul-LBT-TriggeredFreqDeprioritisation ENUMERATED {allowed, notAllowed}, ul-LBT-TriggeredFreqDeprioritisationTimer ENUMERATED {mini , min2, min3, min4, min5, min10, min15, min30}

}

- TAG-UL-LBT-FailureControl -STOP

- ASN1STOP

Option 3 - qNB chooses between frequency barrinq and frequency deprioritization UL-LBT-FailureControl

The IE UL-LBT-FailureControl is used to configure parameters for UL LBT failure control.

UL-LBT-FailureControl information element

- ASN1 START

- TAG-UL-LBT-FailureControl-START

UL-LBT-FailureControl ::= CHOICE {freqBarringControl, freqDeprioritisationControl} freqBarringControl ::= SEQUENCE { ul-LBT-TriggeredFreqBarring ENUMERATED {allowed, notAllowed}, ul-LBT-TriggeredFreqBarringTimer ENUMERATED {mini , min2, min3, min4, min5, min10, min15, min30}

} freqDeprioritisationControl ::= SEQUENCE { ul-LBT-TriggeredFreqDeprioritisation ENUMERATED {allowed, notAllowed}, ul-LBT-TriggeredFreqDeprioritisationTimer ENUMERATED {mini , min2, min3, min4, min5, min10, min15, min30}

}

- TAG-UL-LBT-FailureControl -STOP

- ASN1STOP

Additionally, as discussed in Section 5.2.4.1 of TS 38.304 entitled, “Reselection priorities handling”:

In situations where the UE receives an RRCRelease with deprioritizationReq, the UE shall consider the current frequency and stored frequencies due to:

• the previously received RRCRelease with deprioritisation Req; or

• all the frequencies of NR being the lowest priority frequency (i.e. lower than any of the network configured values) while T325 is running irrespective of camped RAT. The UE shall delete the stored deprioritization request(s) when a PLMN selection is performed on request by NAS (TS 23.122).

Additionally, if the UE receives an indication about UL-LBT-ISSUES during the random access procedure and, if the ul-LBT-TriggeredFreqDeprioritization field is received in SIB1 or dedicated signaling is “allowed,” the UE shall:

• store the priority for the current frequency; and

• set the priority for the current frequency to the lowest priority frequency. The UE should search for a higher priority layer for cell reselection as soon as possible after the change of priority. The minimum related performance requirements specified in 3GPP TS 38.133 version 15.3.0 Release 15 entitled, “5G; NR; Requirements for support of radio resource management” remain applicable.

The UE shall delete priorities provided by dedicated signaling when:

• the UE enters a different RRC state; or

• the optional validity time of dedicated priorities (T320) expires; or

• a PLMN selection is performed on request by NAS (see 3GPP TS 23.122 V16.6.1 (2020-07)).

The UE shall restore the priority for a certain frequency with the previously stored value when:

• the UE enters a different RRC state; or

• the validity time (ul-LBT-TriggeredDeprioritisationTimer) for deprioritisation of this frequency expires; or

• a PLMN selection is performed on request by NAS (see 3GPP TS 23.122).

Option A - Trigger controlled in MAC:

According to section 5.1 .3 “Random Access Preamble transmission” of 3GPP TS

38.321 :

Random Access Preamble Transmission The MAC entity shall, for each Random Access Preamble:

• instruct the physical layer to transmit the Random Access Preamble using the selected PRACH occasion, corresponding RA-RNTI (if available), PREAMBLEJNDEX and PREAMBLE RECEIVED TARGET POWER.

• if UL-LBT-ISSUES is set to TRUE,

• OPTION 1 : evaluate frequency barring according to clause 5.3.1 in 3GPP TS 38.304;

• OPTION 2: evaluate frequency deprioritization according to clause 5.2.4.1 in 3GPP TS 38.304;

Option B - Trigger controlled by RRC:

In aspects of the present disclosure:

Initiation

• The UE initiates the procedure when upper layers request establishment of an RRC connection while the UE is in RRCJDLE and it has acquired essential system information as described in section 5.2.2.1 of 3GPP TS 38.331 v. 15.6.0.

• The UE shall ensure having valid and up to date essential system information as specified in section S.2.2.2 of 3GPP TS 38.331 v. 15.6.0 before initiating this procedure. Upon initiation of the procedure, the UE shall:

• initiate transmission of the RRCSetupRequest message in accordance with section 5.3.3.3 of 3GPP TS 38.331 v. 15.6.0;

• if UL-LBT-ISSUES is TRUE · OPTION 1 : evaluate frequency barring according to section 5.3.1 in 3GPP TS

38.304;

• OPTION 2: evaluate frequency deprioritization according to section 5.2.4.1 in 3GPP TS 38.304.

The following aspects are described in the context of the NR unlicensed spectrum (NR- U). However, those of ordinary skill in the art should appreciate that the following aspects are not limited solely to NR-U scenarios. Aspects of the present disclosure are also applicable to other unlicensed operation scenarios, such as LTE LAA/eLAA/feLAA/MuLteFire, as well as for any licensed spectrum network that operates with LBT-type interference avoidance.

Option 1 and 3

Table 2: New timer, freqBarringTimer to control the duration of the frequency barring.

Option 2 and 3

Table 3. New timer, ul-LBT-TriggeredFreqDeprioritsationTimer to control the duration of the frequency deprioritization.

Aspects of the present disclosure allow a UE served by NR-U system to initiate fast cell reselection to continue initial channel access attempts in another cell with lower channel occupancy. Further, it should be noted that the following aspects initiating channel reselection by a UE are exemplified in an NR-U system. However, as stated above, corresponding schemes can be applied in other systems operating in unlicensed spectrum as well. Figure 7 illustrates an exemplary method 130 performed by a UE 40 in a first cell according to an aspect. As seen in Figure 7, method 130 begins with the UE 40 triggering cell reselection responsive to detecting one or more LBT failures (box 132). The UE 40 then obtains a channel occupancy for each of one or more cells (box 134). For example, the UE may obtain the channel occupancy information from a network node, or it may determine the channel occupancy based on measurements performed by the UE or received from the network node. Additionally, although not required, the UE may determine the channel occupancy prior to triggering the cell reselection process. Regardless of how the UE obtains the channel occupancy, however, each of these one or more cells are different than the first cell. The UE 40 selects, from the one or more cells, a second cell having a channel occupancy that is lower than that of the first cell (box 136), and initiates a cell reselection process to the second cell (box 138).

In some aspects, the UE receives an LBT configuration signal from a network node. In this case, the LBT configuration signal comprises configuration information and configures the UE with a maximum number of LBT failures that can occur within a predetermined time interval. In other aspects, the UE is pre-configured with this configuration information (e.g., by the manufacturer), as well as with a particular selection process to use to select/reselect a given cell, such as the second cell.

In some aspects, triggering cell reselection at the UE comprises barring a current frequency for a predetermined time period.

In some aspects, triggering cell reselection at the UE is based on information provided by one of a PHY layer and an upper layer.

In some aspects, the upper layer comprises one of an RRC layer and a MAC layer.

In some aspects, barring the current frequency comprises barring the current frequency responsive to detecting one or both of high congestion and a high collision rate in the first cell.

In some aspects, triggering cell reselection at the UE comprises triggering the cell reselection responsive to determining that a maximum number of consecutive LBT failures within a preconfigured interval has been reached.

In some aspects, an outcome of an LBT operation is indicated to the MAC layer.

In some aspects, triggering cell reselection at the UE comprises triggering the cell reselection responsive to determining that a maximum time period has elapsed.

In some aspects, the maximum time period defines a time period beginning when a transmission is triggered at the MAC layer and ending when the transmission gets through on the PHY layer.

In some aspects, the maximum time period defines a time beginning when the UE detected a last DL control reference signal. In some aspects, triggering cell reselection at the UE comprises triggering the cell reselection responsive to determining that a channel occupancy of the UL channels serving the UE exceeds a preconfigured threshold.

In some aspects, the UE receives configuration information from the network.

In other aspects, the UE is preconfigured with configuration information.

In some aspects, the configuration information indicates whether the UE is permitted to bar a frequency of a cell responsive to detecting congestion on the frequency.

In some aspects, the configuration information comprises a frequency barring timer T that defines a length of time the UE can bar the frequency.

In some aspects, the configuration information is signaled in system information by the network.

In some aspects, the configuration information is signaled by the network responsive to the UE switching from a connected mode to one of an RRC idle state and an RRC inactive state.

In some aspects, the configuration information associated with one or both of an IDLE state and an inactive state for the UE is signaled in an RRC signaling message.

In some aspects, the UE is in a first configuration associated with the UE being in an RRC connected state. In these aspects, the UE remains in the first configuration in one or both of the RRC IDLE and RRC Inactive states.

In some aspects, the UE reports LBT failures experienced by the UE to a network node responsive to the UE establishing or resuming an RRC connection to a serving cell.

In some aspects, the failures experienced by the UE comprise one or more consecutive failures on one or more of another channel, another subband, another BWP, another cell, and another frequency.

In some aspects, the UE is configured with a Supplementary Uplink (SUL) carrier. In these aspects, barring a current frequency for a predetermined time period comprises prior to barring the current frequency, performing a Random Access procedure on the SUL, and barring the current frequency responsive to detecting N consecutive uplink LBT failures, wherein L/is > 2 and is provided to the UE in the configuration information.

In some aspects, the UE also selects one of an uplink (UL) carrier and the SUL carrier based on both an RSRP threshold and on a determined channel occupancy.

In some aspects, the UE also detects UL LBT failures while performing a random access procedure in the first cell, and transmits information indicative of the UL LBT failures to a network node on at least one of the second cell that is different from the first cell, a second Bandwidth Part (BWP) that is different than a first BWP on which the UL LBT failures were detected, and RACH resources requiring an LBT procedure on a subband that is different from a subband on which the UL LBT failures were detected. In some aspects, the one or more LBT failures comprise uplink LBT failures.

An apparatus can perform any of the methods herein described by implementing any functional means, modules, units, or circuitry. In one aspect, for example, the apparatuses comprise respective circuits or circuitry configured to perform the steps shown in the method figures. The circuits or circuitry in this regard may comprise circuits dedicated to performing certain functional processing and/or one or more microprocessors in conjunction with memory. For instance, the circuitry may include one or more microprocessor or microcontrollers, as well as other digital hardware, which may include Digital Signal Processors (DSPs), special-purpose digital logic, and the like. The processing circuitry may be configured to execute program code stored in memory, which may include one or several types of memory such as read-only memory (ROM), random-access memory, cache memory, flash memory devices, optical storage devices, etc. Program code stored in memory may include program instructions for executing one or more telecommunications and/or data communications protocols as well as instructions for carrying out one or more of the techniques described herein, in several aspects. In aspects that employ memory, the memory stores program code that, when executed by the one or more processors, carries out the techniques described herein.

Figure 8 illustrates a UE 40 in accordance with one or more aspects. The UE 40 comprises a trigger module 42, a cell reselect module 44, a channel access module 46, and one or more antennas 48a-48n (collectively herein, 48). The various modules 42, 44, and 46 can be implemented by hardware and/or by software code that is executed by one or more processors or processing circuits.

The trigger module 42 is configured to trigger cell reselection at the UE 40. The cell reselect module 44 is configured to initiate fast cell reselection to a second cell, wherein the second cell is different from the first cell and has a channel occupancy that is lower than the first cell. The channel access module 46 is configured to perform an initial channel access in the second cell.

Figure 9 illustrates a wireless device 40 according to one aspect that may be configured to function as a UE 40 as herein described. The wireless device 40 comprises an antenna array 48 with multiple antenna elements 48a-48n, interface circuitry 140, processing circuitry 142, and memory circuitry 144.

The interface circuitry 140is coupled to the antennas 48 and comprises the radio frequency (RF) circuitry needed for transmitting and receiving signals over a wireless communication channel. The processing circuitry 142controls the overall operation of the wireless device 40 and processes the signals transmitted to or received by the wireless device 40. Such processing includes coding and modulation of transmitted data signals, and the demodulation and decoding of received data signals. The processing circuitry 142may comprise one or more microprocessors, hardware, firmware, or a combination thereof. Memory circuitry 144 comprises both volatile and non-volatile memory for storing computer program code and data needed by the processing circuitry 142for operation. Memory circuitry 144may comprise any tangible, non-transitory computer-readable storage medium for storing data including electronic, magnetic, optical, electromagnetic, or semiconductor data storage. Memory circuitry 144stores a computer program 146 comprising executable instructions that configure the processing circuitry 142to implement the methods according to Figures 3-7 as described herein. A computer program in this regard may comprise one or more code modules corresponding to the means or units described above. In general, computer program instructions and configuration information are stored in a non-volatile memory, such as a ROM, erasable programmable read only memory (EPROM) or flash memory. Temporary data generated during operation may be stored in a volatile memory, such as a random access memory (RAM). In some aspects, computer program 146 for configuring the processing circuitry 142as herein described may be stored in a removable memory, such as a portable compact disc, portable digital video disc, or other removable media. The computer program 146 may also be embodied in a carrier such as an electronic signal, optical signal, radio signal, or computer readable storage medium.

Figure 10 is a functional block diagram illustrating a computer program product executable of processing circuitry 142. As seen in Figure 10, the computer program product comprises a trigger unit 150, a cell reselect unit 152, and a channel access unit 154. The trigger unit 150 is configured to trigger cell reselection at the UE 40. The cell reselect unit 152 is configured to initiate fast cell reselection to a second cell, wherein the second cell is different from the first cell and has a channel occupancy that is lower than the first cell. The channel access unit 154 is configured to perform an initial channel access in the second cell.

Those skilled in the art will also appreciate that aspects herein further include corresponding computer programs. A computer program comprises instructions which, when executed on at least one processor of an apparatus, cause the apparatus to carry out any of the respective processing described above. A computer program in this regard may comprise one or more code modules corresponding to the means or units described above.

Aspects further include a carrier containing such a computer program. This carrier may comprise one of an electronic signal, optical signal, radio signal, or computer readable storage medium.

In this regard, aspects herein also include a computer program product stored on a non- transitory computer readable (storage or recording) medium and comprising instructions that, when executed by a processor of an apparatus, cause the apparatus to perform as described above.

Aspects further include a computer program product comprising program code portions for performing the steps of any of the aspects herein when the computer program product is executed by a computing device. This computer program product may be stored on a computer readable recording medium.

Any appropriate steps, methods, features, functions, or benefits disclosed herein may be performed through one or more functional units or modules of one or more virtual apparatuses. Each virtual apparatus may comprise a number of these functional units. These functional units may be implemented via processing circuitry, which may include one or more microprocessor or microcontrollers, as well as other digital hardware, which may include digital signal processors (DSPs), special-purpose digital logic, and the like. The processing circuitry may be configured to execute program code stored in memory, which may include one or several types of memory such as read-only memory (ROM), random-access memory (RAM), cache memory, flash memory devices, optical storage devices, etc. Program code stored in memory includes program instructions for executing one or more telecommunications and/or data communications protocols as well as instructions for carrying out one or more of the techniques described herein. In some implementations, the processing circuitry may be used to cause the respective functional unit to perform corresponding functions according one or more aspects of the present disclosure.

Generally, all terms used herein are to be interpreted according to their ordinary meaning in the relevant technical field, unless a different meaning is clearly given and/or is implied from the context in which it is used. All references to a/an/the element, apparatus, component, means, step, etc. are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise.

The steps of any methods disclosed herein do not have to be performed in the exact order disclosed, unless a step is explicitly described as following or preceding another step and/or where it is implicit that a step must follow or precede another step. Any feature of any of the aspects disclosed herein may be applied to any other aspect, wherever appropriate. Likewise, any advantage of any of the aspects may apply to any other aspects, and vice versa. Other objectives, features and advantages of the enclosed aspects will be apparent from the description.

Some of the aspects contemplated herein are described more fully with reference to the accompanying drawings. Other aspects, however, are contained within the scope of the subject matter disclosed herein. For example, the aspects herein are described in the framework of New Radio (NR) being developed by 3GPP. However, this is merely for illustrative purposes. Those of ordinary skill in the art should readily appreciate that the aspects described herein are not limited solely to NR, but rather, are applicable to wireless systems in general.

The disclosed subject matter should therefore not be construed as limited to only the aspects set forth herein; rather, these aspects are provided by way of example to convey the scope of the subject matter to those skilled in the art.

Claims

CLAIMS What is claimed is:

1 . A method (130), implemented by a user equipment (UE) (40) operating in a first cell (50), for initiating cell reselection, said method comprising: triggering (132) cell reselection at the UE responsive to detecting one or more Listen- Before-Talk (LBT) failures; obtaining (134) a channel occupancy for each of one or more cells that are different from the first cell; selecting (136), from the one or more cells, a second cell having a channel occupancy that is lower than the first cell; and initiating (138) cell reselection to the second cell.

2. The method of claim 1 further comprising receiving an LBT configuration signal from a network node, wherein the LBT configuration signal configures the UE with a maximum number of LBT failures that can occur within a predetermined time interval.

3. The method of claim 1 wherein triggering cell reselection at the UE comprises barring (78) a current frequency for a predetermined time period.

4. The method of any of claims 1-3 wherein triggering cell reselection at the UE is based on information provided by one of a Physical (PHY) layer and an upper layer.

5. The method of any of claims 2-4 wherein barring the current frequency is further in response to detecting one or both of high congestion and a high collision rate in the first cell.

6. The method of any of claims 1-5 wherein triggering cell reselection at the UE comprises triggering the cell reselection responsive to determining that a maximum number of consecutive LBT failures within a preconfigured interval has been reached.

7. The method of any of claims 1-5 wherein triggering cell reselection at the UE further comprises triggering the cell reselection responsive to determining that a maximum time period has elapsed.

8. The method of claim 7 wherein the maximum time period defines a time period beginning when a transmission is triggered at a Medium Access Control (MAC) layer and ending when the transmission gets through on the PHY layer.

9. The method of claim 7 wherein the maximum time period defines a time beginning when the UE detected a last downlink (DL) control reference signal.

10. The method of any of claims 1-5 further comprising triggering cell reselection at the UE in response to determining that a channel occupancy of uplink (UL) channels serving the UE exceeds a preconfigured threshold.

11 . The method of any of claims 2-10 further comprising receiving configuration information from a network node.

12. The method of any of claims 2-10 wherein the UE is preconfigured with configuration information.

13. The method of claims 11 or 12 wherein the configuration information indicates whether the UE is permitted to bar a frequency of a cell responsive to detecting congestion on the frequency.

14. The method of any one of claims 11-13 wherein the configuration information comprises a frequency barring timer T that defines a length of time the UE can bar the frequency.

15. The method of any one of claims 11-13 wherein the configuration information is signaled in system information by the network node.

16. The method of any one of claims 1-15 wherein the configuration information is signaled by the network node responsive to the UE switching from a connected mode to one of an RRC idle state and an RRC inactive state.

17. The method of any of claims 11-12 wherein the UE is in a first configuration associated with the UE being in an RRC connected state, and wherein the method further comprises the UE remaining in the first configuration in one or both of the RRC IDLE and RRC Inactive states.

18. The method of any of claims 1-17 further comprising reporting LBT failures experienced by the UE to a network node responsive to the UE establishing or resuming an RRC connection to a serving cell.

19. The method of any of claims 2-18 wherein the UE is configured with a Supplementary Uplink (SUL) carrier, and wherein barring a current frequency for a predetermined time period comprises: prior to barring the current frequency, performing a Random Access procedure on the SUL; and barring the current frequency responsive to detecting N consecutive uplink LBT failures, wherein L/ is > 2 and is provided to the UE in the configuration information.

20. The method of claim 19 further comprising selecting one of an uplink (UL) carrier and the SUL carrier based on both an RSRP threshold and on a determined channel occupancy.

21 . The method of any of claims 1 -20 further comprising: detecting UL LBT failures while performing a random access procedure in the first cell; transmitting information indicative of the UL LBT failures to a network node on at least one of: the second cell that is different from the first cell; a second Bandwidth Part (BWP) that is different than a first BWP on which the UL LBT failures were detected; and

RACH resources requiring an LBT procedure on a subband that is different from a subband on which the UL LBT failures were detected.

22. A user equipment (UE) (40) in a wireless communication network, said UE comprising comprising: interface circuitry (140) configured for communication with one or more serving cells; and processing circuitry (142) configured to: trigger (132) cell reselection at the UE responsive to detecting one or more Listen- Before-Talk (LBT) failures; obtain (134) a channel occupancy for each of one or more cells that are different from the first cell; select (136), from the one or more cells, a second cell having a channel occupancy that is lower than the first cell; and initiate (138) cell reselection to the second cell.

23. The user equipment of claim 22 wherein the processing circuitry is further configured to receive, from a network node, an LBT configuration signal that configures the UE with a maximum number of LBT failures that can occur within a predetermined time interval.

24. The user equipment of claim 22 wherein to trigger cell reselection at the UE, the processing circuitry is configured to bar a current frequency for a predetermined time period.

25. The user equipment of any of claims 22-24 wherein the processing circuitry is configured to trigger cell reselection at the UE is based on information provided by one of a Physical (PHY) layer and an upper layer.

26. The user equipment of any of claims 22-25 wherein the processing circuitry is configured to bar the current frequency responsive to further detecting one or both of high congestion and a high collision rate in the serving cell.

27. The user equipment of any of claims 22-26 wherein the processing circuitry is configured to trigger the cell reselection responsive to determining that a maximum number of consecutive LBT failures within a preconfigured interval has been reached.

28. The user equipment of any of claims 22-26 wherein the processing circuitry is configured to trigger the cell reselection responsive to determining that a maximum time period has elapsed.

29. The user equipment of claim 28 wherein the maximum time period defines a time period beginning when a transmission is triggered at a Medium Access Control (MAC) layer and ending when the transmission gets through on the PHY layer.

30. The user equipment of claim 28 wherein the maximum time period defines a time beginning when the UE detected a last Downlink (DL) control reference signal.

31 . The user equipment of any of claims 22-26 wherein the processing circuitry is configured to trigger the cell reselection responsive to further determining that a channel occupancy of the UL channels serving the UE exceeds a preconfigured threshold.

32. The user equipment of any of claims 22-31 wherein the processing circuitry is further configured to receive configuration information from a network node.

33. The user equipment of any of claims 22-31 wherein the UE is preconfigured with configuration information.

34. The user equipment of any of claims 32-33 wherein the configuration information indicates whether the UE is permitted to bar a frequency of a cell responsive to detecting congestion on the frequency.

35. The user equipment of any of claims 32-33 wherein the configuration information comprises a frequency barring timer T that defines a length of time the UE can bar the frequency.

36. The user equipment of any one of claims 32-33 wherein the configuration information is signaled by the network node in system information.

37. The user equipment of claim 32 wherein the configuration information is signaled by the network node responsive to the UE switching from a connected mode to one of an RRC idle state and an RRC inactive state.

38. The user equipment of any one of claims 22-37 wherein the UE is in a first configuration associated with the UE being in an RRC connected state, and wherein the processing circuitry is further configured to maintain the UE in the first configuration in one or both of the RRC IDLE and RRC Inactive states.

39. The user equipment of any of claims 22-38 wherein the processing circuitry is further configured to report LBT failures experienced by the UE to a network node responsive to the UE establishing or resuming an RRC connection to a serving cell.

40. The user equipment of any of claims 22-39 wherein the UE is configured with a Supplementary Uplink (SUL) carrier, and wherein to bar a current frequency for a predetermined time period, the processing circuitry is further configured to: prior to barring the current frequency, perform a Random Access procedure on the SUL; and bar the current frequency responsive to detecting consecutive uplink LBT failures.

41 . The user equipment of claim 40 wherein the processing circuitry is further configured to select one of an uplink (UL) carrier and the SUL carrier based on both an RSRP threshold and on a determined channel occupancy.

42. The user equipment of any of claims 22-41 wherein the processing circuitry is further configured to: detect UL LBT failures while performing a random access procedure in the first cell; and transmit information indicative of the UL LBT failures to a network node on at least one of: the second cell that is different from the first cell; a second Bandwidth Part (BWP) that is different than a first BWP on which the UL LBT failures were detected; and

RACH resources requiring an LBT procedure on a subband that is different from a subband on which the UL LBT failures were detected.

43. A user equipment (40) in a wireless communication network, said user equipment being configured to: trigger (132) cell reselection at the UE responsive to detecting one or more Listen-Before- Talk (LBT) failures; obtain (134) a channel occupancy for each of one or more cells that are different from the first cell; select (136), from the one or more cells, a second cell having a channel occupancy that is lower than the first cell; and initiate (138) cell reselection to the second cell.

44. The user equipment of claim 43 configured to perform any one of the methods of claims 2- 21.

45. A computer program (146) comprising executable instructions that, when executed by a processing circuitry (140) in a user equipment (40) in a wireless communication network, causes the user equipment to perform any one of the methods of claims 1 -21 .

46. A carrier containing a computer program of claim 45, wherein the carrier is one of an electronic signal, optical signal, radio signal, or computer readable storage medium.

47. A non-transitory computer-readable storage medium (144) containing a computer program (146) comprising executable instructions that, when executed by a processing circuitry (140) in a user equipment (40) in a wireless communication network causes the user equipment to: trigger (132) cell reselection at the UE responsive to detecting one or more Listen-Before- Talk (LBT) failures; obtain (134) a channel occupancy for each of one or more cells that are different from the first cell; select (136), from the one or more cells, a second cell having a channel occupancy that is lower than the first cell; and initiate (138) cell reselection to the second cell.