Patent Description:
Using large bandwidths in new radio in unlicensed bands (NR-U) is beneficial because it ensures that large transmissions take place in short amounts of time. This, in turn, reduces the impact of failing to acquire a channel due to listen-before-talk (LBT) not being successful in the allotted time. LBT may be done in portions of at least <NUM>. If the LBT process is defined to only be performed on LBT subbands, multiple LBT processes would need to be performed to acquire a large bandwidth (BW). This may increase channel access complexity. For example, it is unclear how many LBT processes can be performed in parallel. Using a wideband LBT process may reduce the undue complexity. However, a wideband LBT process may fail for the entire BW or bandwidth part (BWP) when only a small portion of the BW is actually occupied. Therefore, adaptability between these two extreme examples is required to benefit from both the reduced complexity of wideband LBT and the greater access granularity of subband LBT.

Additionally, it may be beneficial to ensure that all acquired LBT subbands form a contiguous BW. Therefore, rules may be required when acquiring the channel to ensure that the union of acquired LBT subbands form a contiguous set.

Systems, methods, and devices for addressing wideband unlicensed channel access are disclosed herein. A device may be configured for different types of listen-before-talk (LBT) procedures, where the LBT type may refer to the frequency granularity of the LBT. There is a hierarchical LBT procedure, where the LBT granularity changes at each point in the LBT procedure. There may be a selection of parameters for each LBT type. Some of the parameters may be shared over different points of the LBT procedure. There are LBT subband sets for a subband set LBT type. There may be one or more indications of acquired LBT subbands on a condition of shared channel occupancy time. At one point in the LBT procedure, there may be a selection of a LBT subband or one or more subbands sets for transmission based on one or more criteria.

A wireless transmit/receive unit (WTRU) is configured to perform the disclosed hierarchical LBT procedure. In the hierarchical LBT procedure, the WTRU may change the LBT type at different levels of the process. The WTRU first performs LBT to acquire available resources on an entire bandwidth part (BWP). If the BWP is not acquired, the WTRU then performs LBT to acquire resources on one or more subband sets. If one or more subband sets are not acquired, the WTRU then performs LBT to acquire available resources on one or more subbands. After every LBT attempt on a different LBT type, data may be transmitted if a sufficient number of resources have been acquired. Resources comprising one or more subband sets may be determined by at least one of previous LBT operation, network configuration, measurements, and transmission type. Performing LBT on one or more subband sets may include adjusting at least one LBT parameter, where the at least one LBT parameter may be a number of idle clear channel assessment (CCA) slots required. The hierarchical LBT procedure may further comprise monitoring multiple LBT subbands for a discovery reference signal (DRS) and transmitting a physical random access channel (PRACH) on an acquired LBT subband.

For example, the communications systems <NUM> may employ one or more channel access methods, such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrier FDMA (SC-FDMA), zero-tail unique-word discrete Fourier transform Spread OFDM (ZT-UW-DFT-S-OFDM), unique word OFDM (UW-OFDM), resource block-filtered OFDM, filter bank multicarrier (FBMC), and the like.

As shown in <FIG>, the communications system <NUM> may include wireless transmit/receive units (WTRUs) 102a, 102b, 102c, 102d, a radio access network (RAN) <NUM>, a core network (CN) <NUM>, a public switched telephone network (PSTN) <NUM>, the Internet <NUM>, and other networks <NUM>, though it will be appreciated that the disclosed embodiments contemplate any number of WTRUs, base stations, networks, and/or network elements. By way of example, the WTRUs 102a, 102b, 102c, 102d, any of which may be referred to as a station (STA), may be configured to transmit and/or receive wireless signals and may include a user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a subscription-based unit, a pager, a cellular telephone, a personal digital assistant (PDA), a smartphone, a laptop, a netbook, a personal computer, a wireless sensor, a hotspot or Mi-Fi device, an Internet of Things (IoT) device, a watch or other wearable, a head-mounted display (HMD), a vehicle, a drone, a medical device and applications (e.g., remote surgery), an industrial device and applications (e.g., a robot and/or other wireless devices operating in an industrial and/or an automated processing chain contexts), a consumer electronics device, a device operating on commercial and/or industrial wireless networks, and the like.

Each of the base stations 114a, 114b may be any type of device configured to wirelessly interface with at least one of the WTRUs 102a, 102b, 102c, 102d to facilitate access to one or more communication networks, such as the CN <NUM>, the Internet <NUM>, and/or the other networks <NUM>. By way of example, the base stations 114a, 114b may be a base transceiver station (BTS), a NodeB, an eNode B (eNB), a Home Node B, a Home eNode B, a next generation NodeB, such as a gNode B (gNB), a new radio (NR) NodeB, a site controller, an access point (AP), a wireless router, and the like.

In an embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement a radio technology such as NR Radio Access , which may establish the air interface <NUM> using NR.

The WTRU <NUM> may include a full duplex radio for which transmission and reception of some or all of the signals (e.g., associated with particular subframes for both the UL (e.g., for transmission) and DL (e.g., for reception) may be concurrent and/or simultaneous. In an embodiment, the WTRU <NUM> may include a half-duplex radio for which transmission and reception of some or all of the signals (e.g., associated with particular subframes for either the UL (e.g., for transmission) or the DL (e.g., for reception)).

For example, the CN <NUM> may provide the WTRUs 102a, 102b, 102c with access to circuit-switched networks, such as the PSTN <NUM>, to facilitate communications between the WTRUs 102a, 102b, 102c and traditional landline communications devices.

The AP may have access or an interface to a Distribution System (DS) or another type of wired/wireless network that carries traffic in to and/or out of the BSS. 11e DLS or an <NUM>.

The primary channel may be a fixed width (e.g., <NUM> wide bandwidth) or a dynamically set width. In certain representative embodiments, Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) may be implemented, for example in <NUM> systems.

11af and <NUM>. 11af and <NUM>. 11n, and <NUM>. 11af supports <NUM>, <NUM>, and <NUM> bandwidths in the TV White Space (TVWS) spectrum, and <NUM>. 11ah may support Meter Type Control/Machine-Type Communications (MTC), such as MTC devices in a macro coverage area.

11n, <NUM>. 11ac, <NUM>. 11af, and <NUM>. If the primary channel is busy, for example, due to a STA (which supports only a <NUM> operating mode) transmitting to the AP, all available frequency bands may be considered busy even though a majority of the available frequency bands remains idle.

The WTRUs 102a, 102b, 102c may communicate with gNBs 180a, 180b, 180c using subframe or transmission time intervals (TTIs) of various or scalable lengths (e.g., containing a varying number of OFDM symbols and/or lasting varying lengths of absolute time).

For example, the AMF 182a, 182b may be responsible for authenticating users of the WTRUs 102a, 102b, 102c, support for network slicing (e.g., handling of different protocol data unit (PDU) sessions with different requirements), selecting a particular SMF 183a, 183b, management of the registration area, termination of non-access stratum (NAS) signaling, mobility management, and the like. For example, different network slices may be established for different use cases such as services relying on ultra-reliable low latency (URLLC) access, services relying on enhanced massive mobile broadband (eMBB) access, services for MTC access, and the like. The AMF 182a, 182b may provide a control plane function for switching between the RAN <NUM> and other RANs (not shown) that employ other radio technologies, such as LTE, LTE-A, LTE-A Pro, and/or non-3GPP access technologies such as WiFi.

Operation in an unlicensed frequency band may be subject to some limits on the transmit power control (TPC), the radio frequency (RF) output power and power density given by the mean Equivalent Isotropically Radiated Power (EIRP) and the mean EIRP density at the highest power level. It may further be subject to requirements on the transmitter out of band emissions. Such requirements may be specific to bands and/or geographical locations.

Operation may be further subject to requirements on the Nominal Channel Bandwidth (NCB) and the Occupied Channel Bandwidth (OCB) as defined for unlicensed spectrum in the <NUM> region. The NCB (i.e., the widest band of frequencies inclusive of guard bands assigned to a single channel) may be at least <NUM> at all times. The OCB (i.e., the bandwidth containing <NUM>% of the power of the signal) may be between <NUM>% and <NUM>% of the declared NCB. During an established communication, a device is allowed to operate temporarily in a mode where its OCB may be reduced to as low as <NUM>% of its NCB with a minimum of <NUM>.

Channel access in an unlicensed frequency band may use a Listen-Before-Talk (LBT) mechanism. LBT is typically mandated independently of whether the channel is occupied or not.

For frame-based systems, LBT may be characterized by a Clear Channel Assessment (CCA) time (e.g., ~<NUM>), a Channel Occupancy time (e.g., minimum <NUM>, maximum <NUM>), an idle period (e.g., minimum <NUM>% of channel occupancy time), a fixed frame period (e.g., equal to the channel occupancy time, plus the idle period), a short control signaling transmission time (e.g., maximum duty cycle of <NUM>% within an observation period of <NUM>), and a CAA energy detection threshold.

For load-based systems (e.g., transmit/receive structure may not be fixed in time), LBT may be characterized by a number N corresponding to the number of clear idle slots in extended CCA instead of a fixed frame period. N may be selected randomly within a range.

Deployment for unlicensed operation scenarios may include different standalone NR-based operation, different variants of dual connectivity operation (e.g., E-UTRAN New Radio Dual Connectivity (EN-DC) with at least one carrier operating according to the LTE radio access technology (RAT) or NR DC with at least two set of one or more carriers operating according to the NR RAT), and/or different variants of carrier aggregation (CA) (e.g., possibly also including different combinations of zero or more carriers of each of LTE and NR RATs).

For example, for LTE, the following functionalities may be considered for a Licensed Assisted Access (LAA) system: LBT (i.e., clear channel assessment); discontinuous transmission on a carrier with limited maximum transmission duration; carrier selection; transmit power control; radio resource management (RRM) measurements including cell identification; and/or channel-state information (CSI) measurement, including channel and interference.

A LBT procedure may be defined as a mechanism by which equipment applies a CCA check before using the channel. The CCA may utilize at least energy detection to determine the presence or absence of other signals on a channel in order to determine if a channel is occupied or clear, respectively. European and Japanese regulations mandate the usage of LBT in the unlicensed bands. Apart from regulatory requirements, carrier sensing via LBT is one method for ensuring fair sharing of the unlicensed spectrum and is therefore considered to be a vital feature for fair and friendly operation in the unlicensed spectrum in a single global solution framework.

Discontinuous transmission on a carrier with limited maximum transmission duration may be a required functionality for LAA because in unlicensed spectrum, channel availability cannot always be guaranteed. Further, certain regions such as Europe and Japan may prohibit continuous transmission and impose limits on the maximum duration of a transmission burst in the unlicensed spectrum.

Carrier selection, since there is a large available bandwidth of unlicensed spectrum, may be required for LAA nodes to select the carriers with low interference and with that achieve good coexistence with other unlicensed spectrum deployments.

Transmit Power Control (TPC) is a regulatory requirement in some regions by which the transmitting device should be able to reduce the transmit power in a proportion of <NUM> dB or <NUM> dB compared to the maximum nominal transmit power.

Radio resource management (RRM) measurements such as cell identification may enable mobility between SCells and robust operation in the unlicensed band.

For Channel-State Information (CSI) measurement, including channel and interference, a WTRU operating in an unlicensed carrier may also support the necessary frequency/time estimation and synchronization to enable RRM measurements and for successful reception of information on the unlicensed band.

In NR, a WTRU may operate using bandwidth parts (BWPs) in a carrier. First, a WTRU may access the cell using an initial BWP. It may then be configured with a set of BWPs to continue operation. At any given moment, a WTRU may have <NUM> active BWP. Each BWP may be configured with a set of control resource sets (CORESETs) within which a WTRU may blind decode candidates for scheduling, among other things.

Furthermore, NR may support variable transmission duration and feedback timing. With variable transmission duration, a PDSCH or PUSCH transmission may occupy a contiguous subset of symbols of a slot. With variable feedback timing, the DCI for a DL assignment may include an indication for the timing of the feedback for the WTRU (e.g., by pointing to a specific PUCCH resource).

NR in unlicensed bands (NR-U) may need to consider initial access, Scheduling/HARQ, and mobility, along with coexistence methods with LTE-LAA and other incumbent RATs. Deployment scenarios may include different standalone NR-based operation, different variants of dual connectivity operation (e.g., EN-DC with at least one carrier operating according to the LTE RAT or NR DC with at least two set of one or more carriers operating according to the NR RAT), and/or different variants of CA (e.g., possibly also including different combinations of zero or more carriers of each of LTE and NR RATs).

NR-U may support four categories of channel access schemes for NR-U operations. Channel access categories may include immediate transmission after a short switching gap (i.e., category <NUM> LBT), LBT without random back-off (i.e., category <NUM> LBT) and LBT with random back-off with fixed and variable contention window size (i.e., category <NUM> and <NUM> LBT, respectively).

NR-U may also perform Listen-Before-Talk (LBT) using CCAs on LBT subbands of <NUM>. A BWP may be a single LBT subband or may be composed of multiple LBT subbands.

The time for which a channel has been acquired for transmission may be deemed a channel occupancy time (COT). The COT may be acquired by a WTRU or by a gNB and may be subsequently shared with the other node. The total COT duration - including any sharing - cannot exceed maximum COT.

<FIG> is a diagram <NUM> illustrating examples of different LBT types covering a whole BWP <NUM>. A WTRU may perform LBT for channel access with different bandwidth granularity. A WTRU may be configured with a BWP <NUM> that encompasses multiple LBT subbands <NUM>-<NUM>. In some embodiments, an LBT subband may be the smallest BW on which a WTRU may perform an LBT procedure (e.g. <NUM>). In other embodiments, the size of an LBT subband may be configurable.

To access the BWP <NUM>, or a portion thereof, the WTRU performs an LBT procedure on one or more LBT subbands <NUM>-<NUM> (i.e., subband LBT <NUM>), or a LBT procedure on one or more sets of contiguous LBT subbands forming a subband set <NUM>-<NUM> (i.e., subband set LBT <NUM>), or an LBT procedure on the totality of the BWP <NUM> (i.e. wideband LBT <NUM>). As discussed herein, subband LBT <NUM>, subband set LBT <NUM> or wideband LBT <NUM> may be referred to as types of LBT. Also, as discussed herein, the WTRU may be assumed to be performing the LBT procedure; however, any method discussed may also be applicable to another node (e.g., where the base station may perform the LBT).

The LBT type to be used for a transmission may depend on one or more factors.

One such factor may be the required bandwidth to be acquired. For example, depending on the size of the BW to be acquired for a transmission, the WTRU may use a different LBT type. The WTRU may use the LBT type that best matches the BW to be acquired. For example, if a WTRU must acquire x LBT subbands, the WTRU may use a subband set LBT that covers at least x LBT subbands. In another example, if the WTRU must acquire x LBT subbands, the WTRU may use the wideband LBT type if x LBT subbands is greater than a configurable threshold.

Another factor may be the required BW indicated by the network.

Another factor may be the required BW of an ongoing COT.

Another factor may be the required BW required for an upcoming transmission. For example, it may be the set of frequency resources granted for an UL transmission.

Another factor may be the previous LBT type used. The WTRU acquiring an unlicensed channel may reuse the same LBT type for a same acquisition BW. There may be a validity timer upon whose expiration the LBT type may be reset. For example, if the timer expires, the WTRU may fall back to wideband LBT, subband set LBT or subband LBT.

Another factor may be the previous LBT used by another node. For example, in a gNB initiated shared COT, the WTRU may reuse the same LBT type as that previously used by the gNB.

Another factor may be the indication by the network. The WTRU may be indicated dynamically, semi-statically or statically the LBT type to use for a channel acquisition.

Another factor may be the transmission type. Depending on priority of the transmission or the physical channel to be transmitted, the WTRU may select a specific LBT type for channel acquisition.

Another factor may be the parameters of the LBT procedure. For example, in embodiments, the WTRU may select an LBT type based on the contention window size (CWS) of each LBT type.

A WTRU may determine the set of LBT subbands to perform LBT prior to transmission based on an indication received prior to LBT.

In embodiments, the indication may relate to a function tied to the set of LBT subbands previously acquired by the gNB. For example, in a gNB acquired COT, the WTRU may be indicated the set of LBT subbands acquired by the gNB. The WTRU may then perform LBT on the same set of LBT subbands. In another method, the WTRU may determine a subset of LBT subbands (i.e., subset of that acquired by the gNB) on which to perform LBT.

In embodiments, the indication may relate to resources required for transmission. For example, the WTRU may have a set of resources for a transmission, and the WTRU may perform LBT on at least the set of LBT subbands that cover the resources to be used for the transmission. The resources for a transmission may be indicated to the WTRU dynamically (e.g., grant based scheduling), semi-statically (e.g., grant free scheduling or PUCCH transmission) or statically.

The indication to the WTRU may be an explicit indication. A WTRU may receive an indication from the gNB providing the set of LBT subbands on which it may perform LBT.

The indication received by the WTRU may relate to a type of transmission. For example, for a PUSCH retransmission, the WTRU may be required to acquire a specific subset of LBT subbands (e.g., to match that used for a previous transmission).

The indication may relate to a the use of Code Block Group (CBG) transmissions or retransmissions. For example, if a WTRU is configured to use CBG transmissions or retransmissions, it may be possible to acquire a set of LBT subbands that do not wholly cover the resource allocation of the total transport block.

<FIG> is a flowchart <NUM> illustrating an example of hierarchical LBT with a transmission possibility after every LBT performed. A WTRU may be configured to perform hierarchical LBT. Hierarchical LBT may be defined as a process where the WTRU changes the LBT type at different levels of the process. At <NUM>, the WTRU performs wideband LBT. If the wideband LBT is successful (i.e., the channel is acquired in the allocated time), the WTRU may assume the whole BWP has been acquired for transmission and may proceed to <NUM> and data is transmitted on all subbands. If the wideband LBT is not successful (i.e., the channel is not acquired in the allocated time), the WTRU may proceed to <NUM>, where the WTRU performs one or more subband set LBTs. If one or more of the subband set LBTs is successful, the WTRU may assume that it has acquired the union of all LBT subband sets where subband set LBT was successful and may proceed to <NUM>, where data is transmitted on subbands in the acquired subband sets. If all the subband set LBTs fail, the WTRU may proceed to <NUM>, where the WTRU performs one or more subband LBTs <NUM> by cycling through all configured subbands of a BWP or simultaneously on multiple subbands at one time. If a minimum number of subband LBTs are successful, the WTRU may assume that it has acquired the LBT subbands where subband LBT was successful and may proceed to <NUM>, where data is transmitted on acquired subbands. If the minimum number of subbands are not acquired, channel acquisition has failed <NUM>. The minimum number of subbands required may be a configured value or may be determined from a parameter of an associated transmission or a parameter obtained from a grant for a transmission.

Thus, in the embodiment illustrated in <FIG>, after every LBT attempt on a different LBT type, the WTRU may transmit if it has acquired sufficient resources. Note that it is possible that the LBT subband sets in <NUM> are composed of single LBT subbands, in which case <NUM> may not be required for the process. Note also that more LBTs may be performed. For example, there may be multiple subband set LBTs where for each subsequent group of subband set LBTs performed, the subband set size may vary (e.g. decrease). For example, there may be multiple points within the hierarchical LBT procedure where the WTRU may perform subband set LBT and the WTRU may vary the subband set size at each subband set LBT.

<FIG> is a flowchart <NUM> illustrating an example of hierarchical LBT with a combined subband set and an individual subband channel acquisition. At <NUM>, the WTRU may perform wideband LBT. If the wideband LBT is successful, the process may proceed to <NUM> and data may be transmitted by the WTRU on all subbands. Upon determination that wideband LBT is in not successful, (i.e., the channel is not acquired in the allocated time), the process may proceed to <NUM> where the WTRU may perform one or more subband set LBTs. If all of the subband set LBTs fail, the process may proceed to <NUM>, where the WTRU may perform one or more subband LBTs. If at least one of the subband set LBTs is successful, the WTRU may assume that it has acquired the union of all LBT subband sets where subband set LBT was successful and may proceed to <NUM>. At <NUM>, for the group of LBT subband sets where the channel is not successfully acquired, the WTRU may attempt to acquire individual LBT subbands from the remaining LBT subband sets. In such a case, at <NUM>, all acquired subband sets (from <NUM>) along with all acquired individual LBT subbands (from <NUM>) may be combined to form an over-all acquired channel. If the minimum number of LBT subbands are required, the WTRU may proceed to <NUM> and data may be transmitted over the acquired LBT subbands. If the minimum number of LBT subbands are not acquired, channel acquisition has failed <NUM>.

In embodiments, the hierarchical LBT procedure may occur over multiple attempts. For example, in a first channel access attempt, the WTRU may use a wideband LBT. Upon failure to acquire the channel, the WTRU may use a subband set LBT for a future channel acquisition attempt. Upon failure to acquire the channel using subband set LBT, the WTRU may use subband LBT for a future channel acquisition attempt. The WTRU may also adapt the BW of the LBT in the opposite direction. For example, upon successfully acquiring multiple LBT subbands in a channel acquisition attempt, the WTRU may proceed to subband set LBT for a future channel acquisition attempt. Similarly, upon successfully acquiring multiple subband sets, the WTRU may proceed with wideband LBT for a future channel acquisition attempt.

The WTRU may be configured with a stopping criterion to determine when to stop the hierarchical LBT process. The stopping criterion for wideband LBT may be acquisition of the wideband channel. The stopping criterion for subband set LBT and subband LBT may be more complicated. In embodiments, the WTRU may stop the procedure at subband set LBT upon acquisition of a sufficient number of subband sets. In other embodiments, the WTRU may stop the procedure at subband set LBT upon acquisition of the largest possible contiguous group of subband sets.

<FIG> is a diagram <NUM> illustrating an embodiment where the stopping criterion for the subband set LBT <NUM> occurs when the largest group of contiguous subband sets is acquired. As shown in <FIG>, the WTRU has acquired the first two subband sets <NUM>, <NUM> and then fails to acquire the third <NUM>. Given that there is just a last subband set to acquire <NUM>, it may be impossible to acquire a larger contiguous group of subband sets than that which has already been acquired. Therefore, the WTRU may proceed to add additional contiguous subbands or stop the procedure altogether.

In other embodiments, the WTRU may stop the procedure after subband LBT upon acquisition of a sufficient number of LBT subbands. The sufficient number of LBT subbands may be determined as a function of the maximum and/or minimum required number of resources for the associated transmission. In another example, the WTRU may stop the procedure after subband LBT upon determination that union of the LBT subband sets acquired during the subband set LBT and LBT subbands acquired during the subband LBT is sufficient. In other embodiments, the WTRU may only consider LBT subbands during the subband LBT that are contiguous (e.g., contiguous with other subbands acquired during the subband LBT or with subband sets acquired during subband set LBT). Upon a determination that there are no more contiguous LBT subbands, the WTRU may stop the subband LBT.

Depending on the physical channel to transmit or whether the unlicensed channel is to be acquired by the WTRU in a gNB shared COT or WTRU initiated COT, the WTRU may use different LBT categories (e.g., categories <NUM>-<NUM>). Each LBT category may define a specific LBT procedure to be done to acquire the channel. For example, the LBT category may mean that the WTRU may acquire the channel upon a one-shot CCA deeming the channel idle. Category <NUM> LBT requires the use of full LBT, wherein the WTRU must first determine N CCAs indicate the channel is idle prior to accessing the channel. The value N may be determined as a random number selected from <NUM> to CWS, where the CWS may be adapted (e.g., based on previous transmission performance).

In the hierarchical LBT procedure described herein, the LBT category may change depending on the type of LBT being performed. For example, for a WTRU acquired COT, category <NUM> LBT may be required. As such, in embodiments, the WTRU may perform category <NUM> LBT for wideband LBT. If the channel is deemed busy, the WTRU may perform LBT on each of the subband sets. For the subband set LBT and the subband LBT the WTRU may adapt the LBT category, or parameters thereof. For example, the LBT category for subband set LBT and/or the subband LBT may change to category <NUM> LBT. In other embodiments, for the subband set LBT and/or the subband LBT, the LBT category may remain category <NUM> LBT, however the CWS value may be reduced. In embodiments, the CWS value may be reduced to the number of CCAs required.

In other embodiments, if at least one LBT subband set has been successfully acquired in subband set LBT using category <NUM> LBT, then the remaining LBT subband sets in subband set LBT or any future LBT subband in subband LBT may use a different category (e.g., category <NUM> LBT). Similarly, if at least one LBT subband in subband LBT has been acquired using category <NUM> LBT, then the remaining LBT subbands in subband LBT may use a different LBT category (e.g., category <NUM> LBT).

In other embodiments, the WTRU may be configured with anchor subband sets and/or LBT subbands. On such anchors, the WTRU may use category <NUM> LBT. Further, upon successful acquisition of such an anchor subband set or subband, the WTRU may perform LBT on other subband sets or subbands, using a different LBT category (e.g., category <NUM> LBT).

In other embodiments, the LBT performed on the entire BWP is a category <NUM> LBT. The WTRU may need to determine N idle CCA slots. Assuming the WTRU determines M idle CCA slots in the allowed time (where M<N), the WTRU may perform LBT on subband sets where the WTRU may then perform category <NUM> LBT on each subband set requiring the determination of N-M clear CCA slots in a subband set. For a subband set where the WTRU only determines P clear CCA slots by the end of subband set LBT (where P<N-M), the WTRU may perform subband LBT where, for the subbands in the subband set where P clear CCA slots were determined, the WTRU may perform category <NUM> LBT such that it needs to determine N-M-P clear CCA slots.

<FIG> is a diagram <NUM> illustrating an example hierarchical LBT <NUM> where category <NUM> LBT is used for every LBT type. In this example, the number of required clear CCA slots is N=<NUM>. However, this value may be selected at random from a range determined by the a CWS value. During the time allotted to wideband LBT <NUM>, the WTRU may determine M=<NUM> clear CCA slots in the BWP <NUM>. Therefore, for the subband set LBT <NUM>, the WTRU may now need to find an additional N-M=<NUM> clear CCAs in each subband set. This may be achieved in two of the subband sets <NUM>, <NUM> in the time allotted for subband set LBT <NUM>. One of the subband sets <NUM> may fail. Therefore, subband sets <NUM>, <NUM> may be deemed acquired for transmission. The WTRU may then proceed to subband LBT <NUM> for the remaining subbands <NUM> and <NUM>, where it must find N-M-P=<NUM> clear CCA. In this example, a single LBT subband <NUM> may be deemed acquired at the end of the subband LBT <NUM>. The over-all acquired BW is thus all subbands except for the first LBT subband <NUM>.

In embodiments, a WTRU may maintain CWS values for the whole wideband, and/or per subband set and/or per individual LBT subband. In other embodiments, the WTRU may maintain CWS values per priority of the intended transmission. When performing hierarchical LBT, the WTRU may determine the CWS value for the wideband LBT based on at least one the following: a value maintained and used for wideband LBT, where this value may be determined as a function of a previously used CWS for wideband LBT (e.g., an increment greater or lesser than a previously used CWS value); a function using as input the multiple CWS values of the subband sets that together combine to form the wideband (e.g., one per subband set), where such a function may be an average CWS, a maximum CWS or a minimum CWS; and/or a function using as input the multiple CWS values of the LBT subbands that together combine to form the wideband (e.g., one per LBT subband), where such a function may be an average CWS, a maximum CWS or a minimum CWS.

The WTRU may determine the CWS values for the subband sets (e.g. one per subband set), based on at least one of: a value maintained per subband set, where the WTRU may maintain CWS values per subband set, and the values may be determined as a function of a previously used CWS for the subband set (e.g., an increment greater or lesser than a previously used CWS value); a function using as input the multiple CWS values of the LBT subbands that together combine to form a subband set (e.g., one per LBT subband), where such a function may be an average CWS, maximum CWS or minimum CWS; a function using as input the CWS value used for the wideband LBT performed in a previous LBT; and/or a function using as input the CWS of other subband sets, where, for example, if the WTRU is required to acquire a minimum number of LBT subbands and/or subband sets for a transmission, the WTRU may use as input the CWS values of any possible combination of subband sets achieving the minimum value.

The WTRU may determine the CWS values for the LBT subbands (e.g., one per LBT subband), based on at least one of: a value maintained per LBT subband, where the WTRU may maintain CWS values per LBT subband, and the values may be determined as a function of a previously used CWS for the LBT subband (e.g., an increment greater or lesser than a previously used CWS value); a function using as input the CWS value used for the subband set LBT, of which an LBT subband is a member, performed in a previous LBT; a function using as input the CWS value used for the wideband LBT performed in a previous LBT; a function using as input the CWS of other LBT subbands and/or subband sets, where, for example, if the WTRU is required to acquire a minimum number of LBT subbands for a transmission, the WTRU may use as input the CWS values of any possible combination of LBT subbands and/or subband sets achieving the minimum value; and/or a function using as input the CWS of subband sets acquired in a previous LBT.

In considering the construction of LBT subband sets, for the subband set LBT type, the WTRU may perform a single LBT procedure on a set of LBT subbands. The subband sets may be configurable. Such configuration may be received by the WTRU in a dynamic, semi-static, or static manner. The LBT subbands in a subband set may be contiguous. In another method, any LBT subband may be configured into a subband set, including LBT subbands that do not form a contiguous set.

The contents of a LBT subband set may be determined by at least one of several factors.

One such factor for determining a subband set may be semi-static configuration. For example, the WTRU may be indicated the number of LBT subbands to be included in each subband set and using LBT subband index, the WTRU may determine the LBT subbands to be included in each subband set.

One such factor for determining a subband set may be based on prior use. For example, in a shared COT, if the gNB used a subband set configuration for a previous channel acquisition in the same COT, the WTRU may use the same subband set configuration. In another example, the WTRU may reuse a subband set configuration that it used in a previous channel acquisition.

Another factor for determining a subband set may be measurements. The WTRU may perform measurements on LBT subbands (e.g., channel occupancy measurements). Based on these measurements, the WTRU may determine subband sets (e.g., such that similar channel load is expected for all LBT subbands of a subband set). In another example, the WTRU may perform measurements to determine subband set configuration and may report a preferred configuration to the gNB (e.g., the WTRU may feedback a desired number of LBT subbands per subband set).

Another factor for determining a subband set may be previous LBT performance. For example, the WTRU may determine a subband set based on combining LBT subbands that have similar historical LBT performance. There may be a validity timer, upon whose expiration the WTRU may assume that any historical knowledge is no longer applicable.

Another factor for determining a subband set may be LBT parameters of LBT subbands. For example, the WTRU may combine LBT subbands to form subband sets if the LBT parameters (e.g., CWS) of all the LBT subbands are the same.

Another factor for determining a subband set may be persistent or periodic CCA. For example, in embodiments, the WTRU may be configured to perform periodic CCA on LBT subbands, regardless of whether it has data to transmit. The WTRU may combine LBT subbands to form subband sets depending on the current number of CCAs observed in recent periodic CCA occasions. For example, in embodiments, the WTRU may combine LBT subbands that have a similar number of recent idle CCA slots in order to increase the probability of acquiring the overall subband set. The composition of recent CCA occasions may use a sliding window in order to remove the effect of old CCA measurements.

Another factor for determining a subband set may be the level of a hierarchical LBT procedure. In some hierarchical LBT procedures, there may be multiple levels with varying sizes of subband sets. For example, the size of the subband sets may decrease for each subsequent level.

In some cases there may be an indication of the acquired set of LBT subbands. In a shared COT, the WTRU may acquire a set of LBT subbands that is different than those previously acquired by the gNB. For example, the WTRU may only perform LBT on the set of LBT subbands previously acquired by the gNB and may acquire a subset of the subbands. In another example, the WTRU may perform LBT on a set greater than those acquired by the gNB and may acquire a greater subset of LBT subbands than the gNB. The WTRU may indicate to the gNB the subset that is successfully acquired. This may be especially beneficial in cases where the WTRU acquires a greater subset of LBT subbands compared to that previously acquired by the gNB. It may enable the gNB to perform actions to reserve the unused LBT subbands. The WTRU may also not expect a future switch to the gNB to include any subbands that were not acquired by the WTRU. In other embodiments, the WTRU may expect all gNB transmissions during the COT to use the same BW acquired by the gNB, regardless of the BW acquired by the WTRU.

In embodiments, the WTRU may acquire more than one LBT subband in the UL transmission. In such embodiments, the WTRU may transmit on all acquired subbands. The WTRU may rate match its transmission to fit the resources acquired. The WTRU may define a minimum reliability metric (e.g., MCS, or coding rate, that it may transmit at and transmit enough data to match the minimum reliability metric).

In embodiments where the WTRU acquires more than one LBT band in the UL transmission, the WTRU may transmit on a subset (i.e., one or more) of the acquired subbands. The WTRU may select the one or more subbands based on a priority measure or parameter. In one embodiment, the WTRU may be configured with a priority value for each subband and transmit on that subband only if a randomly drawn number is greater than, or less than, that priority number. In one embodiment, the CAT x LBT deferment duration may implicitly signal the priority by having different CWS or different LBT measurement durations. A WTRU that has larger CWS parameters for a band will have a lower probability of acquiring the channel before it is busy.

In embodiments where a gNB may assign a WTRU multiple resources/subbands, the gNB and WTRU behavior may be modified to increase the transmission efficiency. The gNB may assign each individual WTRU to more than one exclusive resource. This may occur in embodiments where ultra-reliable and/or low latency transmission by the WTRU may be needed and as such, the WTRU may need to have multiple opportunities (i.e., subbands) to transmit. The gNB may allow overlap of resources assigned to WTRUs, where one or more of the following may apply: a WTRU may be granted a resource with some level of priority to increase the chance of transmitting if its primary resource may be busy but not be exclusively assigned to the secondary resource; the WTRU may be assigned to a grant-free/configured grant resource; and the WTRU may be assigned to a non-orthogonal multiple access resource.

In NR-U, a Discovery reference signal is used for initial access, to enable WTRUs to synchronize to the gNB and to acquire broadcast channel information and establish a connection using random access.

In an active COT that is acquired and controlled by the gNB, the discovery reference signal (DRS) may be transmitted at periodic intervals. However, in the case that the transmission of a DRS is scheduled to occur outside an active COT, the DRS may be transmitted at any time within a periodic DRS window. This requires that the gNB perform a wideband LBT before transmission. The WTRU may also need to perform a wideband LBT before transmitting the random access channel (RACH) signals.

Initial access in wideband channels outside the COT may be one of the following: DRS window on primary or anchor band only; independent DRS windows per band; and/or jointly transmitted DRS on all bands.

<FIG> is a diagram <NUM> illustrating an anchor subband. In embodiments, the initial access signals (the DRS <NUM>) may be transmitted on a primary or anchor subband <NUM> only (or anchor subband set). The WTRU may monitor the primary subband only and on receipt of the SS/PBCH and minimum system information, may perform a RACH procedure <NUM> on the anchor band <NUM> only. Additionally or alternatively, the WTRU may monitor the primary subband only and on receipt of the SS/PBCH and minimum system information, may perform a random-access procedure on any other subband <NUM>-<NUM> that it is able to successfully perform a LBT on. The WTRU may use one of the wideband LBT methods discussed above.

<FIG> is a diagram <NUM> illustrating an independent DRS <NUM> with a physical random access channel (PRACH) <NUM> on a DRS subband. In embodiments, the initial access signals (e.g., the DRS <NUM>) may be transmitted independently per LBT subband. The WTRU may monitor all of the LBT subbands <NUM>-<NUM> and on receipt of the SS/PBCH and minimum system information on one or more of the subbands, may perform a random-access procedure on the received subband(s) <NUM> only. The WTRU may use one of the wideband LBT methods discussed above. Note that the WTRU may perform the PRACH <NUM> on a single subband or all the subbands it successfully receives the DRS <NUM> on. The WTRU may skip performing a PRACH or monitoring the DRS if it successfully received a DRS within a minimum duration or time-interval.

<FIG> is a diagram <NUM> illustrating an independent DRS <NUM> with PRACH <NUM> on any subband. The WTRU may monitor all the LBT subbands <NUM>-<NUM> and on receipt of the SS/PBCH and minimum system information on one or more of the subbands, may perform a random-access procedure on any band that is able to successfully perform a LBT on. In the example illustrated in <FIG>, RACH <NUM> is performed on subband <NUM>, as it is able to successfully perform a LBT.

<FIG> is a diagram <NUM> illustrating a joint DRS <NUM> with PRACH <NUM> on any subband. In embodiments, the initial access signals (e.g., the DRS <NUM>) may be transmitted concurrently on all the LBT subbands that have been acquired. In the example illustrated in <FIG>, the gNB may attempt LBTs on all of the subbands <NUM>-<NUM> (e.g., a hierarchical LBT) and on acquisition of a subband, may transmit a dummy signal <NUM> to reserve the subband <NUM>. At a predetermined time, the gNB may transmit DRS signals on all the acquired subbands <NUM>, <NUM>.

In embodiments, the WTRU may monitor all the LBT subbands and on receipt of the SS/PBCH and minimum system information on one or more of the subbands, may perform a RACH on the received subband(s) <NUM> only. The WTRU may use one of the wideband LBT methods discussed above. Note that the WTRU may perform the RACH <NUM> on a single subband or all the subbands it successfully receives the DRS on. The WTRU may skip performing a PRACH or monitoring the DRS if it successfully received a DRS within a minimum duration or time-interval.

In embodiments, the WTRU may monitor all the LBT subbands and on receipt of the SS/PBCH and minimum system information on one or more of the subbands, may perform a random-access procedure on any band that is able to successfully perform a LBT on.

Note that there may be a QCL relationship defined between the DRS transmissions on the different subbands to enable acquisition on one subband to be applicable to another.

Claim 1:
A method of acquiring available resources, the method comprising:
performing (<NUM>; <NUM>) listen before talk, LBT, on an entire bandwidth part (BWP);
on a condition that the BWP is acquired, transmitting (<NUM>; <NUM>) on the acquired BWP;
on a condition that the BWP is not acquired, performing (<NUM>; <NUM>) LBT on one or more subband sets;
on a condition that one or more subband sets are acquired, transmitting (<NUM>; <NUM>) on the one or more subband sets;
on a condition that one or more subband sets are not acquired, performing (<NUM>; <NUM>; <NUM>) LBT on one or more subbands; and
on a condition that one or more subbands are acquired, transmitting (<NUM>; <NUM>) on the one or more subbands.