METHODS FOR PRACH IN HIGHER FREQUENCIES

Methods and devices to extend the Channel Occupancy Time (COT) for LBT-free PRACH transmission across consecutive ROs based on blind detection are disclosed. Methods and devices to extend the COT for LBT-free PRACH transmission in case of one or more unused ROs across the consecutive ROs based on dynamic indication from gNB are disclosed. Methods and devices to determine the mode of operation based on the cover-codes are disclosed. Method and devices to support the PRACH transmission from a WTRU in multiple consecutive ROs are disclosed.

BACKGROUND

New Radio (NR) beyond 52.6 GHz is being explored. This technology could be the great foundation for the future high data rate frameworks. The realization of beyond 52.6 GHz systems is subject to resolving the key challenges raised due to the special channel and radiation characteristics.

An update WID to extend the NR operation to 71 GHz considering both licensed and unlicensed operation is being explored. As part of the WID, the study for RO configuration was included for non-consecutive RACH occasions (RO) in time domain for operation in shared spectrum. The 120 kHz subcarrier spacing (SCS) was agreed to be supported for the initial access related signals/channels in initial BWP. Also, additional SCS (480 kHz, 960 kHz) for initial access related signals/channels in initial BWP are part of the studies.

SUMMARY

Methods and devices to extend the Channel Occupancy Time (COT) for LBT-free PRACH transmission across consecutive ROs based on blind detection are disclosed.

Methods and devices to extend the COT for LBT-free PRACH transmission in case of one or more unused ROs across the consecutive ROs based on dynamic indication from gNB are disclosed.

Methods and devices to determine the mode of operation based on the cover-codes are disclosed.

Methods and devices to support the PRACH transmission from a WTRU in multiple consecutive ROs are disclosed.

Methods and devices to support the decomposition of PRACH occasions for operation without beam switching gaps between consecutive ROs are disclosed. The WTRU re-allocates original ROs by halving the frequency resources into two consecutive ROs in time domain denoted as RO-pairs. The WTRU expects the switching of the antennas corresponding to the ROs mapped to the first RO within a RO-pair (first half of the original RO) to take place during the second RO within the RO-pair (second half of the original ROs) without switching gaps.

A system and method in a wireless transmit/receive unit (WTRU) for physical random-access channel (PRACH) transmission is disclosed. The system and method include receiving a configuration of PRACH information, the PRACH information including at least one candidate cover-code, performing listen before talk (LBT) in a first random-access channel (RACH) occasion (RO) that is prior to a second RO, on a condition that the LBT is not successful, detecting if there is a first PRACH preamble transmission in the first RO scrambled with a first cover-code from among the at least one candidate cover-code, and based on the detecting, transmitting a second PRACH preamble scrambled with a second cover-code from among the at least one candidate cover-code in the second RO.

The system and method may include the transmitting occurs when the first cover-code is successfully detected in the first RO.

The system and method further comprising based on the detecting, no PRACH preamble is to be transmitted in the second RO due to the LBT failure. The system and method wherein the not transmitting occurs if none of the at least one candidate cover-codes is successfully detected in the first RO.

The system and method further comprising, on a condition that the LBT is successful, transmitting a third PRACH preamble scrambled with a third cover code from among the at least one candidate cover-code in the second RO.

The system and method wherein the detecting if there is a first PRACH preamble transmission in the first RO scrambled with a first cover-code from among the at least one candidate cover-codes enables the WTRU to further determine if the channel is busy.

When the cover-code is detected, the system and method further comprising transmitting PRACH preamble scrambled with the determined cover-code.

The system and method in a wireless transmit/receive unit (WTRU) for physical random-access channel (PRACH) transmission including receiving a configuration of PRACH information, the PRACH information including at least one candidate cover-code, performing listen before talk (LBT) in a first random-access channel (RACH) occasion (RO) that is prior to a second RO, on a condition that the LBT is not successful, detecting if there is a first PRACH preamble transmission in the first RO scrambled with a first cover-code from among the at least one candidate cover-code, and on a condition that the first PRACH preamble transmission scrambled with the first cover-code is detected in the first RO, transmitting a second PRACH preamble scrambled with a second cover-code from among the at least one candidate cover-code in the second RO.

The system and method including, on a condition that no PRACH preamble transmission scrambled with a cover-code from among the at least one candidate cover-code is detected in the first RO, no PRACH preamble is to be transmitted in the second RO due to the LBT failure.

The system and method further comprising, on a condition that the LBT is successful, transmitting a third PRACH preamble scrambled with a third cover code from among the at least one candidate cover-code in the second RO.

DETAILED DESCRIPTION

Methods and devices to extend the Channel Occupancy Time (COT) for LBT-free PRACH transmission across consecutive ROs based on blind detection are disclosed.

Methods and devices to extend the COT for LBT-free PRACH transmission in case of one or more unused ROs across the consecutive ROs based on dynamic indication from gNB are disclosed.

Methods and devices to determine the mode of operation based on the cover-codes are disclosed.

Methods and devices to support the PRACH transmission from a WTRU in multiple consecutive ROs are disclosed.

Methods and devices to support the decomposition of PRACH occasions for operation without beam switching gaps between consecutive ROs are disclosed. The WTRU re-allocates original ROs by halving the frequency resources into two consecutive ROs in time domain denoted as RO-pairs. The WTRU expects the switching of the antennas corresponding to the ROs mapped to the first RO within a RO-pair (first half of the original RO) to take place during the second RO within the RO-pair (second half of the original ROs) without switching gaps.

In an embodiment, the base station114aand the WTRUs102a,102b,102cmay implement a radio technology such as NR Radio Access, which may establish the air interface116using NR.

The RAN104may be in communication with the CN106, which may be any type of network configured to provide voice, data, applications, and/or voice over internet protocol (VoIP) services to one or more of the WTRUs102a,102b,102c,102d. The data may have varying quality of service (QoS) requirements, such as differing throughput requirements, latency requirements, error tolerance requirements, reliability requirements, data throughput requirements, mobility requirements, and the like. The CN106may provide call control, billing services, mobile location-based services, pre-paid calling, Internet connectivity, video distribution, etc., and/or perform high-level security functions, such as user authentication. Although not shown inFIG.1A, it will be appreciated that the RAN104and/or the CN106may be in direct or indirect communication with other RANs that employ the same RAT as the RAN104or a different RAT. For example, in addition to being connected to the RAN104, which may be utilizing a NR radio technology, the CN106may also be in communication with another RAN (not shown) employing a GSM, UMTS, CDMA 2000, WiMAX, E-UTRA, or WiFi radio technology.

The CN106shown inFIG.1Cmay include a mobility management entity (MME)162, a serving gateway (SGW)164, and a packet data network (PDN) gateway (PGW)166. While the foregoing elements are depicted as part of the CN106, it will be appreciated that any of these elements may be owned and/or operated by an entity other than the CN operator.

The CN106may facilitate communications with other networks. For example, the CN106may include, or may communicate with, an IP gateway (e.g., an IP multimedia subsystem (IMS) server) that serves as an interface between the CN106and the PSTN108. In addition, the CN106may provide the WTRUs102a,102b,102cwith access to the other networks112, which may include other wired and/or wireless networks that are owned and/or operated by other service providers. In one embodiment, the WTRUs102a,102b,102cmay be connected to a local DN185a,185bthrough the UPF184a,184bvia the N3 interface to the UPF184a,184band an N6 interface between the UPF184a,184band the DN185a,185b.

In new radio (NR) unlicensed bands, the initial access and PRACH procedures need enhancements in the corresponding shared spectrum in beyond 52.6 GHz. The random-access occasion (RO) configuration is based on consecutive allocation of ROs within a RACH slot with no gap between them, as illustrated inFIG.2.

FIG.2illustrates an example 200 of consecutive RO configurations in a RACH slot. As illustrated in example 200, a slot grid210is provided. The slot grid210is divided into 14 symbol grids220. The 14 symbol grids220are generally numbered from symbol 0 through symbol 13. The slot grid210includes an A1 format230with 6 ROs included in the slot. Format230includes ROs that are generally numbered from RO 0 through RO 5. Associated with each RO is a PRACH transmission240. As illustrated, PRACH 1 corresponds with RO 0, PRACH 2 corresponds with RO 1, and PRACH 3 corresponds with RO 2.

On the other hand, in shared spectrum operation, the Listen Before Talk (LBT) is mandatory in many regions. As such, the Clear Channel Assessment (CCA) is performed before every single transmission using energy sensing. A WTRU may use Type 1 channel access procedure with p=1 for PRACH transmissions. However, the consecutive ROs may result in LBT failure at the succeeding ROs due to the PRACH transmission in the previous ROs, as shown inFIG.3.

FIG.3illustrates PRACH transmission in consecutive ROs. Similar to that described with respect toFIG.2, an A1 format with 6 ROs is included in the slot. Format230includes ROs that are generally numbered from RO 0 through RO 5. Associated with each RO is a PRACH transmission240. As illustrated PRACH 1 corresponds with RO 0, PRACH 2 corresponds with RO 1, and PRACH 3 corresponds with RO 2. A WTRU may not transmit PRACH due to the LBT failure due to PRACH transmission from another WTRU. A WTRU that transmits PRACH in RO 0 may prevent another WTRU from transmitting in RO 1 as a result the LBT failure. If an LBT in a previous RO, i.e., RO 0, fails, the second WTRU may attempt recover a cover-code. If the recovery of the cover-code is successful, the second WTRU may continue with PRACH transmission in RO 1. In this scenario, the second WTRU may effectively skip or ignore the LBT results.

As explained in further detail herein, a methodology for accounting for the LBT in RO configurations is described. The methodology is based on extending the channel occupancy time (COT) through the RACH slot so that the WTRUs transmit PRACH without a need to perform the LBT.

In accounting for LBT in RO configuration, enhancements on the PRACH transmission in consecutive Random-Access Occasions (RO) for the NR-U with LBT operation are described. The extending and sharing of the Channel Occupancy Time (COT) based on blind detection of the WTRU and the indication of the gNB is described.

In several examples described herein, extending the COT for LBT-free PRACH transmission across consecutive ROs based on blind detection of a WTRU may occur. A WTRU may receive a configuration of PRACH information for blind detection. If the WTRU intends to transmit PRACH, the WTRU determines the mode of operation prior to PRACH transmission. Upon successful LBT, the WTRU transmits PRACH preamble scrambled with a cover-code, i.e., another Zadoff-Chu (ZC) sequence by using reserved root and cyclic shift, within a RACH slot, as is illustrated and described with respect toFIGS.4-7. Upon LBT failure, based on the configured PRACH information for blind detection, the WTRU may attempt to detect if the channel is occupied due to the PRACH or other signals by performing the “sequence match” with the cover code using equation Eq. 1:

Upon successful detection of the cover code, the WTRU may skip the LBT and may transmit PRACH. The WTRU optionally may select the preambles for the PRACH transmission from the subset of preambles that were not identified during the sequence-match procedure.

The COT for LBT-free PRACH transmission may be extended for one or more unused ROs across consecutive ROs. A WTRU may receive a configuration of PRACH information, a first cover code and a second cover code. The WTRU may receive a DCI-based signaling from a different frequency band as an indication for LBT-free PRACH transmission or LBT free COT extension. Upon reception of the triggering signaling and the LBT free PRACH transmission, the WTRU may transmit PRACH with a configured sequence scrambled by the first cover code, and may skip the LBT. Upon reception of the triggering signaling and the LBT free COT extension, the WTRU may transmit a PRACH only with the second cover code, and may skip the LBT.

A determination of the mode of operation based on the cover-codes may occur. A WTRU may receive a configuration of PRACH information for blind detection including a set of cover codes. If the WTRU wants to transmit PRACH, the WTRU may determine a mode of operation prior to PRACH transmission. Upon successful LBT, the WTRU may transmit PRACH preamble while each sequence within the PRACH transmission is scrambled with one of the cover-codes, for example the first sequence with the first cover-code and the second sequence with the second cover-code. Upon LBT failure, based on the configured PRACH information for blind detection, the WTRU may attempt to detect if the channel is occupied due to the PRACH or other signals by performing the “sequence match” with the set of the cover codes.

Upon successful detection of the cover code, the WTRU may skip the LBT and may determine one or more ROs to transmit the PRACH based on the configured PRACH information and the cover-code the WTRU has recovered in the previous RO. The WTRU may transmit PRACH while scrambling the preamble with respective cover-codes from the set of cover-codes. The WTRU may select the respective cover-code for PRACH transmission based on the cover-codes recovered from the previous RO, a sequence that can go on cyclically.

A WTRU may transmit or receive a physical channel signal or reference signal according to at least one spatial domain filter. The term “beam” may be used to refer to a spatial domain filter. The WTRU may transmit a physical channel or signal using the same spatial domain filter as the spatial domain filter used for receiving an RS (such as CSI-RS) or a SS block. The WTRU transmission may be referred to as “target”, and the received RS or SS block may be referred to as “reference” or “source”. The WTRU may transmit the target physical channel signal or reference signal according to a spatial relation with a reference to such RS or SS block.

The WTRU may transmit a first physical channel signal or reference signal according to the same spatial domain filter as the spatial domain filter used for transmitting a second physical channel or signal. The first and second transmissions may be referred to as “target” and “reference” (or “source”), respectively. The WTRU may transmit the first (target) physical channel signal or reference signal according to a spatial relation with a reference to the second (reference) physical channel or signal.

A spatial relation may be implicit, configured by RRC or signaled by MAC CE or DCI. For example, a WTRU may transmit PUSCH and DM-RS of PUSCH according to the same spatial domain filter as an SRS indicated by an SRI indicated in DCI or configured by RRC. In another example, a spatial relation may be configured by RRC for an SRS resource indicator (SRI) or signaled by MAC CE for a PUCCH. Such spatial relation may also be referred to as a “beam indication”.

The WTRU may receive a first (target) downlink channel signal according to the same spatial domain filter or spatial reception parameter as a second (reference) downlink channel signal. For example, such association may exist between a physical channel such as PDCCH or PDSCH and its respective DM-RS. At least when the first and second signals are reference signals, such association may exist when the WTRU is configured with a quasi-colocation (QCL) assumption type D between corresponding antenna ports. Such association may be configured as a transmission configuration indicator (TCI) state. A WTRU may be indicated with an association between a CSI-RS or SS block and a DM-RS by an index to a set of TCI states configured by RRC and/or signaled by MAC CE. Such indication may also be referred to as a “beam indication”.

The Channel Occupancy Time (COT) for LBT-Free PRACH Transmission may be extended based on blind detection of a WTRU, based on dynamic indication from gNB, using a determination of the mode of operation based on the cover-codes, and with support of the PRACH transmission from a WTRU in multiple consecutive ROs.

The PRACH occasions for operation without beam switching gaps may be decomposed between consecutive ROs. The WTRU may re-allocate original ROs by halving the frequency resources into two consecutive ROs in time domain denoted as RO-pairs. The WTRU may expect the switching of the antennas corresponding to the ROs mapped to the first RO within a RO-pair (first half of the original RO) to take place during the second RO within the RO-pair (second half of the original ROs) without switching gaps.

Operation with or without shared spectrum channel access can be interchangeably used with unlicensed or licensed bands, respectively. The term unlicensed spectrum may be used to refer to license exempt spectrum and lightly licensed spectrum. The terms CORESET #0, Type0-PDCCH, and/or SIB1 may be used interchangeably but still consistent herein. Random access (RA) operation, random access occasion (RO), preamble transmission, PRACH occasion, or PRACH transmission occasion may be used interchangeably but still consistent herein.

The COT for LBT-free PRACH transmission may be extended based on blind detection of a WTRU. The extension may use a random-access procedure in the NR shared spectrum. A WTRU may perform the random-access (RA) procedure to access a cell. The random-access procedure may be initiated upon a request of a Physical Random-Access Channel (PRACH) transmission by higher layers or a PDCCH order. The PRACH configuration may include one or more of preamble index, preamble SCS, PRACH format, corresponding RA-RNTI, and PRACH time and frequency allocation resources.

A WTRU may be provided with the number N of SS/PBCH block indexes that are associated with one RACH Occasion (RO) by parameter ssb-perRACH-OccasionAndCB-PreamblesPerSSB. For a PRACH transmission, a PRACH mask index is indicated to the WTRU which implies the ROs for the PRACH transmission, wherein the ROs are associated with the SS/PBCH block index selected by the WTRU.

The ROs may be mapped consecutively per respective SS/PBCH block index and the WTRU may select the ROs for the PRACH transmission based on the PRACH mask index associated with the chosen SS/PBCH block index in the first available mapping cycle.

The extension may use a PRACH. The basic random-access preambles are Zadoff-Chu (ZC) sequences generated based on a given root sequence and a given cyclic shift. The WTRU may determine the logical root sequence index obtained from the higher-layer parameter prach-RootSequenceIndex or rootSequenceIndex-BFR, or by msgA-PRACH-RootSequenceIndex. The WTRU may determine the cyclic shift based on the zeroCorrelationZoneConfig index along with the preamble's code-length. As per time-frequency RO, the WTRU may select from 64 preamble sequences generated first by increasing order of cyclic shift from the given logical root sequence, and then by increasing order of the given logical root sequence index.

The main properties of the ZC codes used to generate the random-access preambles may be the normalized cross-correlation between two ZC sequences generated from two different root sequences is as low as one over the preamble's code length. The cross correlation between the cyclic shifts of a ZC sequence is zero, i.e., they are orthogonal to each other.

Random access preambles are transmitted within the frequency resources specified by higher layer parameters msg1-FrequencyStart or msgA-RO-FrequencyStart, if configured. The time resource allocations are determined based on the PRACH configuration index, which is given by the higher-layer parameter prach-ConfigurationIndex, or by msgA-PRACH-ConfigurationIndex if configured. The PRACH preamble formats are provided including the length of Cyclic Prefix (CP), the number of sequences, and the guard time (if any).

The extension may use channel access for shared spectrum. The channel access in shared spectrum includes the procedures to evaluate the channel's availability and the Clear Channel Assessment (CCA) before transmission. The energy detection is accomplished as part of Listen-Before-Talk (LBT) procedure and before the channel access. The defer duration Tdconsists of duration Tf=16 us immediately followed by mpconsecutive slot durations where each slot duration is Tsl=9 us, and Tfincludes an idle slot duration Tslat start of Tf. Thus, the minimum length for LBT is 25 us.

Upon successful evaluation on channel's availability, the channel occupancy takes effect by transmission on the channel. The Channel Occupancy Time (COT) refers to the total time the transmissions on the channel are performed that can be shared between a gNB and the corresponding WTRUs. Within a COT, the gaps less than or equal to 25 us are counted in the channel occupancy time, whereas separate LBT may be required if the gaps are greater than 16 us.

As for the PRACH transmission in shared spectrum, a WTRU may use Type 1 channel access procedure with priority class p=1. In other words, WTRUs may be required to accomplish LBT procedure before initiating the corresponding PRACH transmissions. The extending the COT for LBT-Free PRACH transmission may be based on blind detection of a WTRU. A WTRU may be configured with PRACH resources including one or more of the preamble root sequence indices, preamble cyclic shift, preamble SCS, corresponding RA-RNTI, PRACH time and frequency resources. The WTRU may use the preamble root sequence index and preamble cyclic shift parameters to generate a pool of preamble sequences that includes up to 64 sequences. The WTRU may select a preamble sequence randomly from the set of the sequences to be used during PRACH transmission in the corresponding RACH Occasions (RO). The parameters to generate the preambles may be determined for contention-based or contention-free RACH. The pool of preamble sequences may be cell-specific and common for all WTRUs that may further cause contentions as the different WTRUs may select the same preamble, denoted as contention-based RACH. The preamble sequences may be WTRU-specific indicated through RRC or DCI-based signaling that implies the contention-free RACH. The term RACH/PRACH may be used interchangeably to refer to contention-based RACH/PRACH and contention-free RACH/PRACH but still consistent herein.

In an example for the shared spectrum channel access, a WTRU may be configured with one or more of the Zadoff-Chu sequences as PRACH cover codes. The PRACH cover codes may have the same length as the preamble sequences. The WTRU may scramble the PRACH cover codes with the respective preamble code. The WTRU may not select the respective preamble sequence from one of the codes configured as the PRACH cover code. If the randomly selected preamble sequence for the PRACH transmission is the same as one of the sequences that are configured as the PRACH cover code, the WTRU may skip the preamble and go on with another random draw from the pool of preamble sequences. The WTRU may use the PRACH cover codes to implicitly send an indication to declare that a PRACH transmission is ongoing. The WTRU may send the indication to declare that a COT is reserved for the PRACH transmission, and that the reserved COT can be shared and extended by other WTRUs that may want to transmit PRACH while skipping the LBT, i.e., LBT-free PRACH transmission.

In an example, the WTRU may be configured with the PRACH cover codes based on one or more of the following where the WTRU may determine the number of PRACH cover codes based on the preamble's format, preamble's SCS, and the number of time-domain PRACH occasions within a PRACH slot. The WTRU may explicitly determine the PRACH cover codes. The PRACH cover codes may be preconfigured. In an example, for a PRACH scenario with four PRACH cover codes, the first four preamble sequences from the pool of sequences could be considered as the PRACH cover codes. The PRACH cover codes defined in each time-frequency PRACH occasion, may be enumerated in increasing order of first increasing cyclic shift of a logical root sequence, and then in increasing order of the logical root sequence index, starting with the index obtained from the higher-layer parameter.

In another example, the PRACH cover codes may be different from the sequences that are included in the pool of the preamble sequences. For instance, in a PRACH scenario with four PRACH cover codes, the first four sequences following the last, i.e., 64th, preamble sequence may be configured as the PRACH cover codes. It is as if there were four additional sequences generated at the end of the pool of the preamble sequences to be used as the PRACH cover codes. The additional PRACH cover codes may be generated in increasing order of the cyclic shift of the logical root sequence used to generate the last, i.e., 64th, preamble sequence, and then, if required, in increasing order of the logical root sequence index.

In another example, to avoid the conflict of the cover codes in between the cells, the PRACH cover codes may be determined based on a preconfigured arrangement. The cover codes may be selected based on the Physical Cell ID (PCID) or a modulus function of the PCID, or the cover codes may be selected based on the order of the sequences in the pool of sequences, such as odd sequences, even sequences, or based on the sequences with a specific modulus function result. The PRACH cover codes may be determined based on an RRC signaling. The PRACH cover codes may be determined based on a DCI signaling. The PRACH cover codes may be determined as part of the initial access signaling through the MIB or SIB1.

In an example, the WTRU may select a preamble to perform the PRACH transmission, and may perform Listen-Before-Talk (LBT) to assure a Clear Channel Assessment (CCA) before PRACH transmission. For LBT with p=1, the minimum length for LBT is 25 us which translates into a minimum of 3, 13, and 25 symbols in the SCS of 120 kHz, 480 kHz, and 960 kHz, respectively. The WTRU may initiate the LBT procedure earlier than the RACH slot and the corresponding RO. The LBT may start from multiple symbols, ROs, or slots in advance, depending on the preamble SCS, the preamble format and the number of time-domain PRACH occasions within a PRACH slot. In an example, for PRACH with 960 kHz SCS and the PRACH A1 format, the number of sequences within each RO is two, and the number of time-domain PRACH occasions within a PRACH slot is six. The WTRU that wishes to transmit in one or more of the ROs within the RACH slot may initiate the LBT at least 25 symbols in advance which implies one or two slots before the RACH slot.

In an example, the WTRU may perform PRACH transmission in the corresponding RO within the RACH slot upon successful LBT. The WTRU may use the PRACH cover code to scramble with the respective selected preamble sequence. The WTRU may then send the scrambled preamble for the PRACH transmission.

FIG.4illustrates a scrambling of the preamble sequence with the cover code400. InFIG.4, the xu, is the preamble sequence selected by WTRU that is scrambled by xC, which is the PRACH cover code. The WTRU may send the scrambled preamble, i.e., xu,C, as the Respective Preamble for the PRACH Transmission. The LRAis the length of the selected preamble which is the same for the PRACH cover code. The preamble sequence selected by the WTRU for PRACH transmission410is defined in Eq. 2:

Added to the preamble sequence selected by the WTRU for PRACH transmission is the cover code420. The cover code420may be as provided in Eq. 3:

The result430is the preamble sequence to be transmitted by the WTRU for PRACH. The result430is provided in Eq. 4:

In an example, if there is an LBT-failure, the WTRU may initiate a blind detection to determine if the LBT-failure is caused by a PRACH transmission during the previous RO within the RACH slot. The WTRU may buffer the signals within the previous ROs to perform the blind detection. The WTRU may use the configuration of the RACH slot, including the preamble SCS, the preamble format, and the time and frequency location of the RACH slot, to determine the buffer length. The WTRU may initiate the AGC convergence to get the baseband received signal to the desired level. The AGC deals with the aggregate of energy received, including the energy from all WTRUs that transmitted PRACH in the previous ROs. The WTRU may use the first preamble sequence to converge AGC and then continue with the next sequences for the blind detection. The WTRU may perform sequence matching on one or more of the PRACH cover-codes. The sequence matching may be performed through a cross-correlation function that may be accomplished by IFFT filters.FIG.5illustrates the signal processing500in a graphical depiction. The signal processing500includes an input of a received signal505in the time domain and the cover code510in the time domain. The received signal505has an FFT applied to received signal505to produce the corresponding received signal515in the frequency domain. The cover code510has an FFT applied to cover code510to produce the corresponding cover code signal520in the frequency domain. The corresponding received signal515is multiplied with the corresponding cover code signal520to produce signal530. An inverse FFT is performed on signal530to produce the resultant signal540, the output of the IFFT filter. The spike550in the resultant signal540denotes the existence of the “cover code”, implying that the channel is reserved for the PRACH transmission and LBT could be skipped. InFIG.5, the received signals505are multiplied by the respective PRACH cover code510(after converting each using the FFT) and then passed to the IFFT filter. Upon detection of a spike550at the output of the IFFT, the WTRU may evaluate the spike550to conclude that the respective “cover code” is detected.

Upon successful detection of the one or more of the PRACH cover codes, the WTRU may consider the former LBT-failure to be due to PRACH transmission in the previous ROs, implying that the COT is reserved for the PRACH transmission. The WTRU may extend the PRACH COT by skipping the LBT and going on with the PRACH transmission in the corresponding RO.

FIG.6illustrates an example PRACH transmission600. A WTRU610and another WTRU620perform PRACH transmission in RO 0. A WTRU630and another WTRU640perform LBT-free and gap-free PRACH transmission in RO 1, upon successful recovery of the cover code in the RO 0 within the RACH slot providing an example to account the LBT in consecutive ROs.

As illustrated inFIG.6, WTRU1610and WTRU2620are considered to perform PRACH transmission in the first RO, and WTRU3630and WTRU4640are considered to perform PRACH transmission in the second RO that follows the first RO consecutively in time. Each WTRU610,620,630,640transmits respective preamble scrambled with the cover-code. In the first RO, WTRU1610transmits xu1+xCand WTRU2620transmits xu2+xC. WTRU3630and WTRU4640may perform blind detection to identify if the COT is reserved for the PRACH transmission by “sequence matching” with one or more of the PRACH cover-codes. Upon successful detection of the PRACH cover-code in the first RO, WTRU3630and WTRU4540may skip the LBT and perform PRACH transmission in the second RO by sharing and extending the COT. In the second RO, WTRU3630transmits xu3+xCand WTRU4640transmits xu4+xC.

As illustrated inFIG.6, the COT may be shared while complying with the fair channel occupancy. After successful detection of the PRACH channel occupancy cover code and/or reservation signal, the WTRU may continue with transmission of a PRACH preamble, MsgA, and/or Msg3 without LBT or with a shortened LBT. The WTRU's transmission duration may be limited to a period of time, corresponding to at least one of the following: the remaining time in the COT initiated by first other WTRU in the cell using the detected PRACH cover code/signal, the slot boundary, a predefined period, a configured period, a number of slot and/or symbols, and/or a number of slots till the next Fixed Frame Period (FFP) LBT opportunity/IDLE period in a Frame Based Equipment (FBE) frame configuration.

The WTRU may transmit a RACH message without LBT after successful detection of the PRACH channel occupancy cover code and/or reservation signal, conditioned on at least on the following: the remaining time in the COT initiated by a first other WTRU in the cell using the detected PRACH cover code/signal is greater than a configured or predetermined threshold period, the remaining time (or number of symbols) till slot boundary is greater than a predetermined or configured threshold period, and/or the number of PRACH occasion already transmitted in the same COT (e.g., by other WTRUs) is less than a configured or predetermined threshold.

In an example, the WTRU may transmit a RACH message without LBT upon detection of the cover code for period corresponding to the MCOT minus the duration of consecutive PRACH occasions already transmitted in the COT. In another example, the WTRU may transmit RACH messages without LBT. In an example, the WTRU may count the number of RACH transmission occasions using the cover code during the LBT channel sensing procedure. Upon failing LBT, the WTRU may transmit a RACH message without LBT -or with shortened LBT—if the number of RACH occasions transmitted during the LBT procedure is less than a configured or predetermined threshold.

The WTRU may transmit a RACH message without LBT -or with shortened LBT—if it detects or receives signaling from the gNB. The WTRU may determine the maximum number of symbols or slots it can transmit on without LBT if it receives signaling from the gNB, whereby the signaling: indicates the maximum number of slots or symbols, indicates the PRACH cover code sequence or sequence ID, and/or is received on specific symbols or slots prior to the RACH occasion.

The WTRU may determine the remaining time in the COT from the detected cover code during the LBT procedure or prior to the RACH occasion. For example, the WTRU may be configured with a cover code pattern, such that the WTRU determines the previous number of PRACH occasions transmitted in the same COT. The WTRU may increase or change the cover code sequence (e.g., by adding a cyclic shift to the detected cover code in the RACH occasion prior to the WTRU's transmission time).

Efficient selection of preamble sequences may be used. In an example, during the blind detection (e.g., IFFT cross-correlation procedure), the WTRU may identify one or more of the preambles used in the previous ROs at the output of the IFFT (i.e., but for other WTRUs). The IFFT filtering allows detecting all the cyclic shifts used within the given root sequence in a single IFFT operation. The WTRU may detect the preambles that are used within the same root sequence as the root sequence used for PRACH cover-code. The WTRU may expect that the same preambles may be reused in the following ROs by the corresponding WTRUs. The WTRU may avoid selecting the identified preambles to prevent further preambles' collisions and conflicts.

AGC symbols/samples for PRACH blind detection at the WTRU may be used. When PRACH cover code (or COT extension cover code) is used for a PRACH transmission to indicate that one or more subsequent ROs in the same RACH slot may be used for LBT-free PRACH transmission, one or more of following may apply: AGC symbol or sample may be added at the beginning of each RO. For example, AGC symbol or sample may be a copy of the first N symbols or M samples of a PRACH format used for each RO, wherein N and M may be positive integer number including 1. Alternatively, AGC symbol or sample may be repetition of cyclic prefix of the PRACH format. The number ROs in a RACH slot may be determined based on one or more of PRACH format, number of symbols used for uplink, whether AGC symbol/sample is used or not, and whether pre-configured cover code is used or not. The presence of AGC symbol in each RO may be configured or indicated by gNB. The presence of AGC symbol in a RO may be determined based on at least one of PRACH format, number of PRACH preamble repetition, CP length, Gap length.

The COT for LBT-free PRACH transmission may be extended based on dynamic indication from gNB. In an embodiment, a WTRU may receive a set of configurations and/or an indication to transmit LBT free PRACH transmission. The LBT free PRACH transmission may be used to extend the COT when one or more ROs are unused. For example, the WTRU may receive a set of configurations for LBT free PRACH transmission (e.g., via one or more RRC messages). The separate PRACH configuration may be configured for the extension of PRACH and LBT free PRACH transmission, respectively. The set of PRACH configurations may include one or more of one or more of PRACH configuration indices. One or more of following configurations may be configured by providing one or more of PRACH configuration indices including preamble format (e.g., 0, 1, 2, 3 A1, A2, A3, B1, B2, B3 and etc.), x and y for nSFNmod x=y, subframe number, starting symbol. number of PRACH slots within a subframe, PRACH occasions, number of time-domain PRACH occasions within a PRACH slot, PRACH duration, and other configurations related to PRACH configuration. Alternatively, the WTRU may be directly configured with one or more of the above configurations. For example, the WTRU may be configured with preamble formats and PRACH occasions without receiving the PRACH configuration indices.

One or more of PRACH Root sequences for RACH transmission may be in the set of PRACH configurations. The WTRU may be configured with one or more PRACH root sequences for PRACH transmission. For example, the WTRU may apply PRACH root sequences by generating Zadoff-Chu sequences based on one or more PRACH Root sequence indices which are configured by RRC.

One or more of PRACH Root sequences for blind detection may be in the set of PRACH configurations. The WTRU may be configured with one or more PRACH Root sequences for blind detection. For example, the WTRU may scramble the generated PRACH sequences by using the one or more PRACH Root sequences for blind detection. The application of the one or more PRACH Root sequences for blind detection may be based on one or more resources. For example, the WTRU may be configured with a first PRACH Root sequences and a second PRACH Root sequences for blind detection. Based on the configuration, the WTRU may scramble a PRACH sequence with the first PRACH Root sequence for the first resource. The WTRU may scramble a PRACH sequence with the second PRACH Root sequence for the second resource. The resource may be one or more of following: time domain resource (e.g., one or more of RACH Slot, Symbol, Slot and ms), RACH occasion, PRACH Root sequence for RACH transmission, etc.

One or more of PRACH Root sequence indices for COT extension may be in the set of PRACH configurations. For example, the WTRU may scramble the generated PRACH sequences by using the one or more PRACH Root sequences for blind detection. The application of the one or more PRACH Root sequences for blind detection may be based on one or more resources. For example, the WTRU may be configured with a first PRACH Root sequences and a second PRACH Root sequences for blind detection. Based on the configuration, the WTRU may scramble a PRACH sequence with the first PRACH Root sequence for the first resource. The WTRU may scramble a PRACH sequence with the second PRACH Root sequence for the second resource. The resource may be one or more of following: time domain resource (e.g., one or more of RACH Slot, Symbol, Slot and ms), RACH occasion, PRACH Root sequence for RACH transmission, etc.

Transmission type may be included in the set of PRACH configurations. Transmission type may configure one or more of LBT based PRACH transmission, LBT free PRACH transmission and COT extension.

msg1-FDM may be included in the set of PRACH configurations. The number of PRACH transmission occasions FDMed in one-time instance. msg1-FrequencyStart may be included in the set of PRACH configurations. Offset of lowest PRACH transmission occasion in frequency domain with respective to PRB 0. The value is configured so that the corresponding RACH resource is entirely within the bandwidth of the UL BWP.

msg1-SubcarrierSpacing, subcarrier spacing of PRACH, zeroCorrelationZoneConfig, Nos value for Unrestricted set, Restricted set type A or Restricted set type B, preambleReceivedTargetPower including the target power level at the network receiver side, preambleTransMax including max number of RA preamble transmission performed before declaring a failure, and powerRampingStep including power ramping steps for PRACH, may be included in the set of PRACH configurations.

ra-ResponseWindow may be included in the set of PRACH configurations. This includes Msg2 (RAR) window length in number of slots. The network configures a value lower than or equal to 10 ms when Msg2 is transmitted with licensed spectrum channel access and 40 ms when Msg2 is transmitted with shared spectrum channel access.

Total number of RA preambles may be included in the set of PRACH configurations. Total number of preambles used for contention based and contention free random access in the RACH resources defined in RACH-ConfigCommon, excluding preambles used for other purposes (e.g. for SI request).

ssb-perRACH-OccasionAndCB-PreamblesPerSSB may be included in the set of PRACH configurations. The meaning of this field is twofold: the CHOICE conveys the information about the number of SSBs per RACH occasion.

rsrp-ThresholdSSB may be included in the set of PRACH configurations. WTRU may select the SS block and corresponding PRACH resource for path-loss estimation and (re)transmission based on SS blocks that satisfy the threshold

msg3-transformPrecoder may be included in the set of PRACH configurations. This enables the transform precoder for Msg3 transmission. If the field is absent, the WTRU disables the transformer precoder.

restrictedSetConfig may be included in the set of PRACH configurations. This is the configuration of an unrestricted set or one of two types of restricted sets.

Based on the configuration, the WTRU may receive an indication to transmit one or more of PRACH transmission. The indication may be based on one or more of RRC configuration, MAC CE and DCI (WTRU specific DCI and/or group DCI). Based on the indication, the WTRU may determine to transmit one or more of LBT based PRACH transmission, LBT free PRACH transmission and COT extension. Based on the determination, the WTRU may support one or more of following operations:

For LBT based PRACH transmission operation, if the WTRU determines to transmit LBT based PRACH, the WTRU may use LBT before PRACH transmission. If the WTRU does not detect any signal based on the LBT, the WTRU may transmit PRACH based on the associated configurations. The WTRU may scramble the PRACH by using the PRACH by using the one or more PRACH sequences for blind detection.

For LBT free PRACH transmission, if the WTRU determines to transmit LBT free PRACH, the WTRU may transmit PRACH without LBT based on the associated configurations. The WTRU may scramble the PRACH by using the one or more PRACH sequences for blind detection.

For COT extension, if the WTRU determines to transmit COT extension, the WTRU may transmit PRACH without LBT based on the associated configurations. The WTRU may scramble the PRACH by using the one or more PRACH sequences for COT extension. Alternatively, if the WTRU determines to transmit COT extension, the WTRU may transmit PRACH by only using the one or more PRACH sequences for COT extension.

The WTRU determination may be based on the indicated information by the gNB. For example, the transmission type. The indication may indicate one or more of LBT based PRACH transmission, LBT free PRACH transmission and COT extension. For example, if the WTRU receives a transmission type as LBT free PRACH transmission, the WTRU may transmit one or more PRACH based on a set of PRACH configurations associated with LBT free PRACH transmission. If the WTRU receives a transmission type as COT extension, the WTRU may transmit one or more PRACH for COT extension based on a set of PRACH configurations associated with COT extension.

Another example includes a trigger of LBT free PRACH transmission and/or COT extension. The WTRU may receive a trigger of LBT free PRACH transmission and/or COT extension. The indication may be based on one or more of following: The WTRU may receive an explicit indication from a gNB. For example, the WTRU may receive one or more of triggers by receiving MAC CE message and/or DCI to transmit LBT free PRACH transmission and/or COT extension.

Another example includes a trigger of a set of PRACH configuration. For example, the WTRU may receive an indication for a set of PRACH configuration among multiple sets of PRACH configurations. The set of PRACH configuration may include a transmission type. Based on the indicated set of PRACH configuration, the WTRU may determine configurations for LBT free PRACH transmission and/or COT extension.

Another example to base WTRU determination includes a trigger of one or more of RACH occasions. For example, the WTRU may receive an indication of one or more of RACH occasions. Based on the indicated one or more of RACH occasions, the WTRU may determine to transmit PRACH based on the configurations associated with the indicated one or more of RACH occasions.

Also, a trigger of one or more of preambles may be used. For example, the WTRU may receive an indication of one or more of preambles. Based on the indicated one or more of preambles, the WTRU may determine to transmit PRACH based on the configurations associated with the indicated one or more of preambles.

WTRU blind detection may be used in the WTRU determination. The WTRU may determine to transmit PRACH for one or more of LBT based PRACH transmission, LBT free PRACH transmission and COT extension if the WTRU blindly detects one or more of signals. The blind detection can be based on the configured PRACH configurations for one or more of PRACH transmission, blind detection and COT extension. For example, the WTRU may try to blindly detect the configured PRACH sequences (e.g., for PRACH transmission and/or COT extension) within the configured RACH occasions and/or RACH slots. The WTRU may determine RACH resources to transmit PRACH based on results of WTRU blind detection. For example, the WTRU may estimate end of the existing PRACH transmission based on the detected sequences and the configured PRACH configurations (e.g., PRACH format). Based on the estimated end of the transmission, the WTRU may transmit PRACH (e.g., for PRACH transmission and/or COT extension) after the estimated end of the transmission.

The application of the one or more PRACH Root sequences (e.g., for blind detection and/or COT extension) may be based on two or more resources. For example, the WTRU may be configured with a first PRACH Root sequence and a second PRACH Root sequence. Based on the configured sequences, if the WTRU determines to transmit PRACH, the WTRU may scramble a PRACH sequence with the first PRACH Root sequence for the first resource. and the second PRACH Root sequence for the second resource, respectively. The resource may be one or more of following: RACH Slots, Symbols, Slots, Subframes, PRACH duration, PRACH configuration, Absolute time (e.g., ms or ns), and RACH occasions, PRACH Root sequences for RACH transmission, etc.

According to an embodiment, a WTRU may receive an indication to transmit one or more PRACHs for a first cell (e.g., one or more of unlicensed band, high frequency band (e.g., FR2-2) and UL cell) from a second cell (e.g., one or more of licensed band, low frequency band (e.g., FR1 or FR2-1) and DL cell). In order to associate the first cell and the second cell, following association methods may be used.

An association method includes configuration of associated PRACH configuration ID of the first cell in one or more control resources in the second cell. The WTRU may receive a configuration of associated PRACH configuration ID of the first cell in one or more control resources in the second cell (e.g., via one or more of RRC and MAC CE). Based on the association, the WTRU may receive one or more of DCIs which indicates PRACH transmission (e.g., one or more of LBT based, LBT free and COT extension) in the one or more control resources of the second cell. Based on the association, the WTRU may transmit PRACH based on the PRACH configuration associated with a control resource which the WTRU detects DCI.

An association method includes configuration of associated control resource ID of the second cell in one or more PRACH configurations of the first cell. The WTRU may receive a configuration of associated control resource ID of the second cell in one or more PRACH configurations of the first cell (e.g., via one or more of RRC and MAC CE). Based on the association, the WTRU may receive one or more of DCIs which indicates PRACH transmission (e.g., one or more of LBT based, LBT free and COT extension) in the one or more control resources of the second cell. Based on the association, the WTRU may transmit PRACH based on the PRACH configuration associated with a control resource which the WTRU detects DCI.

The one or more control resources may be one or more of CORESETs and Search Spaces.

For COT extension using one or more PRACH transmission types, one or more of PRACH transmission types may be used, defined, or determined, wherein a first PRACH transmission type may be a PRACH preamble scrambled with a pre-configured cover code to indicate that a subsequent RO may be used as LBT free PRACH transmission within the RACH slot; a second PRACH transmission type may be just pre-configured cover code without PRACH preamble. A WTRU may send the first PRACH transmission type for LBT based PRACH transmission and/or LBT free PRACH transmission. Therefore, the WTRU may send PRACH to a target gNB as well as indicating to other WTRUs that the subsequent ROs in the same RACH slot may be used for LBT-free PRACH transmission. A WTRU may send the second PRACH transmission type for COT extension when the WTRU is indicated to perform. The second PRACH transmission may be used only to keep the COT (or extend COT) and may allow other WTRUs to perform LBT-free PRACH transmission in a subsequent RO in the same RACH slot. The WTRU may send the second PRACH transmission type in a RACH slot if one or more of following conditions are met. The WTRU is indicated to perform COT extension in one or more RACH slots or ROs (e.g., via RRC, MAC-CE, and/or DCI). The WTRU detected a pre-configured cover code in a previous RO. The remaining number of ROs in the RACH slot is larger than a threshold. Subcarrier spacing is larger (or smaller) than a threshold. The WTRU is not scheduled for UL transmission in the RACH slot. The WTRU has no scheduled/configured UL transmission overlapping with the RO.

When a conflict between second PRACH transmission and an uplink transmission is scheduled/configured for a WTRU, one or more of following may apply. If the conflict occurred in time domain (e.g., symbol or slot), a predefined priority rule may be used to determine which uplink signal is transmitted. For example, the second PRACH transmission type may be higher priority than PUSCH, PUCCH for CSI reporting and SRS transmission; while lower priority than PUCCH for HARQ reporting.

If the conflict occurred in frequency domain (e.g., in different RBs), one or more of following may apply: Option-1: a predefined priority rule may be used to determine which uplink signal is transmitted; and Option-2: transmit both signals (e.g., second PRACH transmission and UL signal scheduled/configured). Either Option-1 or Option-2 may be determined to use based on uplink transmission power. If UL transmission power does not reach to Pc,max-deltamarginwith Option-2, the Option-2 may be used. Otherwise, Option-1 may be used. The deltamarginmay be a configured/pre-determined value including 0′.

A WTRU may send the first PRACH transmission type (e.g., LBT-based or LBT-free) in a first RO which may be selected for a PRACH transmission, and the WTRU may send the second PRACH transmission type (e.g., COT extension) in one or more subsequent ROs within the RACH slot.

PRACH transmission type may be interchangeably used with PRACH preamble type, PRACH sequence, PRACH resource type, PRACH resource, PRACH time/frequency resource, PRACH format, and PRACH sequence type. In addition, a pre-configured cover code which may be used to scramble PRACH sequence to indicate a status of one or more subsequent ROs (e.g., in the same RACH slot) may be interchangeably used with RO status indicator, subsequent RO status indicator, COT extension indicator, COT extension code, COT extension cover code, and COT extension sequence.

The COT for LBT-free PRACH transmission may be extended using a determination of the mode of operation based on the cover-codes. A WTRU may be configured to detect presence of a sequence of at least one cover code associated to a PRACH occasion or transmission. The number of cover codes in the sequence may be a function of at least one of the preamble format and subcarrier spacing. Such sequence of at least one cover code may be referred to as “cover code sequence” in the following. A WTRU may scramble a PRACH transmission using a sequence of cover codes. Each cover code of the sequence may scramble a specific portion of the PRACH transmission in time or frequency domains. For example, a PRACH transmission may consist of two portions in time domain. The WTRU may scramble first and second portions with first and second cover codes of the sequence respectively. A WTRU may be configured to detect one of a set of at least one cover code sequence in a RACH occasion using one of the solutions described in the above, such as sequence matching. The set of at least one cover code sequence may be referred to as “candidate set” in the following. The WTRU may perform at least one action depending on which cover code sequence of the candidate set is detected, as described.

The cover code sequence for PRACH transmission may depend on detected cover code sequence may be used. In a solution, the WTRU may determine whether to transmit a PRACH or a PRACH scrambled by a first cover code sequence in a first RACH occasion (or set of thereof) based on the identity of a second cover code sequence detected in a second RACH occasion. The first and second RACH occasion may have a pre-defined timing relationship. For example, the first occasion may immediately follow the second occasion in time. The identity of the first cover code sequence may also be a function of the identity of a second cover code sequence within a candidate set. In an example, the WTRU may determine to transmit a PRACH scrambled by a specific cover code sequence of a candidate set if it determines that the channel is not busy (LBT success) during a preceding period. For example, a candidate set may consist of four (4) cover code sequences.

A WTRU may apply the following behaviors. In case the WTRU determines that the channel is not busy (LBT success), the WTRU may transmit a PRACH scrambled by the first cover code sequence of the set in the subsequent RACH occasion. In case the WTRU detects the first cover code sequence of the set in a RACH occasion, the WTRU may transmit a PRACH scrambled by the second cover code sequence of the set in a subsequent RACH occasion. In case the WTRU detects the second cover code sequence of the set in a RACH occasion, the WTRU may transmit a PRACH scrambled by the third cover code sequence of the set in a subsequent RACH occasion. In case the WTRU detects the third cover code sequence of the set in a RACH occasion, the WTRU may transmit a PRACH scrambled by the fourth cover code sequence of the set in a subsequent RACH occasion. In case the WTRU detects the fourth cover code sequence of the set in a RACH occasion, the WTRU may not transmit a PRACH in a subsequent RACH occasion. In case the WTRU determines that the channel is busy (LBT failure) and does not detect a cover code sequence (or detects the fourth cover code sequence), the WTRU may not transmit a PRACH in a subsequent RACH occasion.

The above example provides implementation of a maximum number of successive RACH occasions that can be reserved by a set of WTRUs for PRACH transmission. Such maximum may correspond to a maximum channel occupation time (COT) duration.

The number of RACH occasions may be determined from detected cover code sequence. In an example, the WTRU may determine a set of RACH occasions on which it may transmit PRACH (or PRACH scrambled by a cover code sequence) based on the identity of a cover code sequence detected in a previous RACH occasion.

Examples for obtaining candidate set of cover code sequences are also provided. A candidate set of cover code sequences may be a function of at least time (e.g. system frame number, slot, symbol position), RACH occasion, PRACH format, subcarrier spacing or PRACH configuration according to a pre-defined function. A cover code sequence may be derived from at least one parameter such as an index. A candidate set of cover code sequence may be derived from at least one parameter such as an index or a set of indexes. The at least one parameter may be referred as candidate set information in the following.

The WTRU may determine candidate set information from physical layer, MAC, RRC signaling or a combination thereof. For example, the candidate set information may be included as part of an enhanced PRACH configuration. In another example, candidate set information may be received from group-common PDCCH or WTRU-specific PDCCH such as a PDCCH order for RACH.

In an example with multiple detected cover code sequences, the WTRU detects the presence of more than one cover code sequence from the candidate set, the WTRU may perform actions according to one (i.e. single one) of the detected cover code sequences. The WTRU may determine such cover code sequence according to a pre-determined rule such as the order of the cover code sequence within a set. For example, the WTRU may select the sequence with the highest order within the candidate set. Alternatively, the WTRU may select the cover code sequence for which sequence matching results in the largest likelihood.

The COT for LBT-free PRACH transmission may be extended with support of the PRACH transmission from a WTRU in multiple consecutive ROs. A WTRU may transmit PRACH in multiple ROs in one or more RACH slots. The WTRU may select the set of ROs on which to transmit a PRACH preamble (or to attempt to acquire a channel to transmit a PRACH preamble) based on a number of factors.

For example, the associated SSB(s) may be used. For example, the WTRU may transmit PRACH on one or more ROs based on whether the ROs are associated to a single SSB. This may be considered PRACH repetition. In another example, the WTRU may transmit PRACH on one or more ROs based on the set of SSBs to which the set of ROs are associated. In this example, the WTRU may transmit PRACH in the ROs for which the associated SSBs are for the same beam, or for QCL beams. In another example, the WTRU may transmit PRACH on one or more ROs based on the set of SSBs to which the set of ROs are associated. In this example, the WTRU may transmit PRACH in the ROs for which the set of SSBs are configured for a set of associated beams. The association between beams forming a set of associated beams may be pre-configured, indicated by higher layers, determined from measurements, or determined from an associated to a single LBT procedure or a single set of LBT parameters. For example, a WTRU may transmit PRACH in a set of ROs, associated to a set of SSBs, if the set of SSBs is associated in a manner that a single LBT is required to initiate a COT that is applicable to the set of beams associated to the set of SSBs.

The timing of the ROs may be used. For example, a WTRU may transmit on a set of ROs if they are adjacent to each other without any gaps. In another example, a WTRU may transmit on a set of ROs only if there are gaps between at least one (e.g. all) ROs. In another example, a WTRU may transmit on a set of ROs only if there are gaps between subsets of ROs, where each subset of ROs may be associated to a single LBT procedure and different subsets of ROs may be associated to different LBT procedures. In such a case, gaps between subsets of ROs may be required.

Reception of an indication that a COT has been initiated by a serving cell or by another WTRU within the serving cell. For example, a WTRU may only transmit on a set of ROs if the WTRU has detected a cover code transmission from another WTRU within the cell indicating that a COT has been initiated. The WTRU may determine the set or subset of ROs to which the COT is associated and may transmit without LBT only on the set or subset of ROs to which the COT is associated.

LBT for multiple PRACH transmissions in multiple ROs may be used. A WTRU may perform LBT prior to transmission of one or more PRACH preambles on one or more ROs. Upon determining the channel is idle, the WTRU may transmit one or more PRACH preambles on one or more ROs without needing subsequent LBT. The WTRU may determine whether to perform LBT prior to a PRACH preamble in a RO based on a variety of factors.

The timing of the RO may be used. For example, the WTRU may perform LBT prior to the first RO that it intends to use. In another example, the WTRU may perform LBT prior to the first RO of a set of associated RO. The set of associated ROs may be defined as a set of ROs for which a single LBT is required.

The timing of a last LBT applicable to the RO may be used. For example, a WTRU may perform an LBT prior to a first RO in a set of associated ROs. The WTRU may initiate a COT of a specific duration for transmissions of RO without requiring LBT. The WTRU may perform a second LBT for transmission on a RO if the COT duration has elapsed.

Parameters associated to the ROs may be used. For example, a WTRU may transmit PRACH preambles on a set of ROs. Such a set may be subdivided into subsets, each associated to a different beam or different QCL index or different associated SSB. The WTRU may perform LBT prior to each subset(s) of ROs.

LBT type or parameter of a previous LBT operation may be used. For example, a WTRU may perform a first LBT of a first LBT type or first set of LBT parameters, for transmission of PRACH preamble on a first (sub)set of ROs. The WTRU may determine that a second (sub)set of ROs may require a second LBT of a second LBT type of a second set of LBT parameters. In such a case, the WTRU may perform the second LBT prior to transmission of PRACH preamble on the second (sub)set of ROs. In an example, the WTRU may perform LBT on a first beam associated to a first subset of ROs. The WTRU may perform LBT on a second beam, prior to transmitting PRACH preamble on a second subset of ROs associated to a second beam.

Whether there are gaps between ROs may be used. A WTRU may perform LBT before a second RO if there is a gap between a first and second consecutive ROs.

Size of a gap between two consecutive ROs may be used. The WTRU may perform LBT prior to a second RO if the gap between the first and second RO is greater than a threshold.

Reception of an indication may be used. For example, a WTRU may receive an indication to perform or not to perform an LBT prior to an RO. Such an indication may be received from the gNB or may be received from a second WTRU (e.g. indicating that the second WTRU has initiated a COT that may be shared with the first WTRU).

A WTRU may be configured with time instances when to perform LBT for a (sub)set of ROs. If the WTRU successfully initiates a COT during one of the configured time instances, the WTRU may transmit PRACH preambles in the (sub)set of ROs without needing further LBT. The WTRU may be required to transmit PRACH preambles in all of the associated (sub)set or ROs. If the WTRU does not transmit a PRACH preamble in one of the associated ROs, a gap may be created. The WTRU may need to perform an LBT procedure prior to transmitting a PRACH preamble in a subsequent RO of the (sub)set.

According to an example, if the WTRU determines the channel is busy during an LBT procedure, the WTRU may not transmit PRACH preamble in any (e.g. all) of the ROs in the (sub)set.

According to an example, if the WTRU determines the channel is busy during an LBT procedure for a (sub)set of ROs, the WTRU may perform LBT at another time (e.g. prior to a subsequent RO) to enable transmission of PRACH preamble on some of the (sub)set of ROs. For example, a subset of ROs may be composed of x ROs (possibly all associated to the same SSB). The WTRU may perform LBT prior to the first RO. If the WTRU successfully initiates a COT, the WTRU may transmit PRACH preambles on all ROs without needing a subsequent LBT procedure. On the other hand, if the WTRU determines that the channel is busy prior to the first RO, it may not transmit PRACH preamble in the first RO. The WTRU may perform LBT prior to a subsequent RO (e.g. the second RO). If the WTRU is determines the channel is idle, the WTRU may transmit PRACH preamble in the second RO and all subsequent ROs in the (sub)set without requiring further LBT. On the other hand, if the LBT prior to the second RO determines the channel is busy, the WTRU may not transmit in the second RO and may perform LBT in a future occasion within the (sub)set of ROs.

A set of ROs may be associated with an SSB or a beam or a QCL index. In the case where all ROs in the set are associated to the same beam, the WTRU may perform LBT on the beam prior to transmitting PRACH preamble on one or more ROs of the set. In another method, a set of ROs may be associated with a set of SSBs or multiple beams or multiple QCL indices. In such a case, the WTRU may perform LBT on a beam that is determined from the beams associated to one or more ROs in the set. The WTRU may determine the LBT beam as a function of at least one of: Beam or SSB or QCL index of one RO in the set. For example, a set may have a primary RO from which the WTRU may determine the LBT beam. The primary RO may be the first RO of a set of ROs; Beam covering all beams of the ROs in the set. For example, the WTRU may perform LBT on a beam that covers or encompasses all the beams in the set of ROs. Beam covering may be defined such that the main beam of the LBT overlaps all the main beams associated to each RO in the set; and Beam covering all beams of the remaining ROs in the set. For example, if a WTRU performs LBT for a subset of the ROs in the set, the beam may cover all the beams in the subset of the set of ROs.

A WTRU may determine if an LBT procedure is required prior to the transmission of a PRACH preamble in a RO based on whether a previous LBT used for a still valid COT covers the beam associated to the RO. For example, a WTRU may perform a first LBT on a beam prior to a first set of ROs. The WTRU may determine the first LBT beam as a function of the beam(s) associated to the ROs in the first set of ROs. Prior to transmitting PRACH preamble in a second set of ROs, the WTRU may determine that the first LBT beam is also applicable to the second set of ROs. If the COT is still valid (i.e. the COT duration has not expired), the WTRU may transmit PRACH preambles in the second set of ROs without performing LBT.

A WTRU may be configured with multiple RO types. Each RO type may be associated to different PRACH preamble formats (e.g. SCS, sequence length, duration). A first RO type may enable time to perform LBT prior to the transmission of the PRACH preamble. A second RO type may not include a gap to perform LBT prior to the transmission of the PRACH preamble. The WTRU may select the RO type based on whether or not LBT is required prior to the transmission of the PRACH preamble. According to an embodiment, the RO type may be configured for specific time instances. In another solution, the WTRU may determine the RO type to use for one or more time instances. A WTRU may also be configured with multiple RACH slot configurations. In a first RACH slot configuration, a WTRU may be configured with adjacent ROs without LBT gaps. In a second RACH slot configuration, a WTRU may be configured with LBT gaps between some or all ROs. The WTRU may receive an indication from the gNB on which RACH slot configuration to use prior to the RACH slot. For example, a WTRU may receive an SSB or PBCH or DCI indicating the RACH slot configuration of one or more subsequent RACH slots. In another method, a WTRU may determine which RACH slot configuration to use as a function of reception of a signal from another WTRU. In yet another method, a WTRU may determine which RACH slot configuration to use as a function of measurements or LBT performance or PRACH parameter.

FIG.7illustrates a method700performed for PRACH. In association with the description above, method700includes the WTRU receiving PRACH configuration including at least one candidate cover-code at710. The PRACH configuration may also include resources and PRACH format. At720, method700includes the WTRU performing LBT prior to PRACH transmission based on channel sensing, for example, performing LBT in a first RACH RO that is prior to a second RO. At730, method700includes determining if the LBT is successful, i.e., is the channel idle.

If the determination in730is no, then method700includes the WTRU determining if the channel is busy with PRACH by monitoring previous ROs and attempting to detect candidate cover-codes at750, for example, detecting if there is a first PRACH preamble transmission in the first RO scrambled with a first cover-code from among the at least one candidate cover-code. The WTRU determining if the channel is busy with PRACH by monitoring previous ROs and attempting to detect candidate cover-codes at750is described above in greater detail with respect toFIG.5.

A determination is made at760if the cover-code is detected. If the cover-code is detected, then method700includes the WTRU transmitting PRACH preamble scrambled with the determined cover-code (Zadoff-Chu sequence xc(n)at740. For example, on a condition that the first PRACH preamble transmission scrambled with the first cover-code is detected in the first RO, the WTRU transmits a second PRACH preamble scrambled with a second cover-code from among the at least one candidate cover-code in the second RO.

Optionally, if the cover-code is not detected, then method700includes no PRACH transmission due to LBT failure at770. For example, on a condition that no PRACH preamble transmission scrambled with a cover-code from among the at least one candidate cover-code is detected in the first RO, no PRACH preamble is to be transmitted in the second RO due to the LBT failure.

Optionally, if the determination in730is yes, then method700includes the WTRU transmitting PRACH preamble scrambled with the determined cover-code (Zadoff-Chu sequence xc(n)) at740, for example, transmitting a third PRACH preamble scrambled with a third cover code from among the at least one candidate cover-code in the second RO. The WTRU transmitting PRACH preamble scrambled with the determined cover-code (Zadoff-Chu sequence xc(n)) at740is described above in greater detail with respect toFIG.4.

According to method700performed for PRACH, it is possible to perform PRACH transmissions in consecutive ROs.

Decomposition of PRACH occasions for operation without beam switching gaps between consecutive ROs is disclosed. A WTRU may receive, identify, or be configured with the time domain resource allocations for the consecutive ROs based on the higher-layer parameter prach-ConfigurationIndex, or by msgA-PRACH-ConfigurationIndex if configured. These parameters, higher-layer parameter prach-ConfigurationIndex, or by msgA-PRACH-ConfigurationIndex, denote the PRACH configuration index corresponding to tables that include random access parameters.

One or more of the following parameters may be derived from the table that include random access parameters. Preamble format may refer to one of the possible formats, namely: A1, A2, A3, B1, A1/B1, A2/B2, A3/B3, B4, C0, C2. The preamble format identifies the corresponding Cyclic Prefix (CP) duration, sequence part duration, and guard time duration (if applicable). The frame number and slot number indicates the frames that may be used for the PRACH transmission and the PRACH slot within the corresponding frame. The starting symbol determines the symbol-level index corresponding to the starting position of the first RO transmission within the PRACH slot. The number of PRACH slots within a 60 kHz slot, defines the number of PRACH slots within the reference PRACH slot, e.g., for higher SCS such as 120 kHz, 480 kHz, 960 kHz, considering the 60 kHz PRACH slot as the reference slot. The number of time-domain PRACH occasions within a PRACH slot (Nt_RAslot),defines the number of consecutive ROs that are located within a PRACH slot in time domain. The PRACH duration corresponds to the preamble format implying the number of sequence part within an RO.

Alternatively, a WTRU may receive the frequency domain resource allocations for the ROs based on one or more of the following higher-layer parameters: msg1-FrequencyStart or msgA-RO-FrequencyStart if configured, indicates the offset of the lowest PRACH transmission occasion in frequency domain with respect to the PRB 0; and msg1-FDM or msgA-RO-FDM if configured, indicates the number of PRACH transmission occasions that are FDMed in one time-domain RO. The WTRU may receive, identify, or be configured with the number of ROs in frequency domain (M) per each time-domain PRACH occasion based on the higher parameter msg1-FDM, msg1-FDM-16, or msgA-RO-FDM if configured, msg1-FDM={one, two, four, eight}. The WTRU may number the PRACH frequency resources nRA={0,1, . . . ,M-1}, starting from the lowest frequency, in increasing order in the initial uplink BWP during the initial access or the active uplink BWP otherwise.

The WTRU may receive the association and mapping between the SS/PBCH block indexes and PRACH transmission occasions based on higher layer parameter ssb-perRACH-OccasionAndCB-PreamblesPerSSB={⅛, ¼, ½, 1,2,4,8,16}. The higher layer parameter indicates the number of SS/PBCH block indexes associated with a PRACH transmission occasion in addition to the number of preambles per SS/PBCH block index per PRACH occasion.

FIG.8illustrates an example of a PRACH RO configuration800with prach-ConfigurationIndex equal to zero. As described, without loss of generality, the index prach-ConfigurationIndex equal to zero is considered, however the same principles can be applied for other PRACH configurations. The PRACH slot810is typically provided as illustrated inFIG.8with preamble format A1, starting symbol=0, PRACH duration=2, number of time domain PRACH occasions within a PRACH slot=6, msg1-FDM=8, and ssb-perRACH-OccasionAndCB-PreamblesPerSSB=1. Symbols820may include symbol 08200, symbol 18201, symbol 28202, symbol 38203, symbol 48204, symbol 58205, symbol 68206, symbol 78207, symbol 88208, symbol 98209, symbol 1082010, symbol 1182011, symbol 1282012, symbol 1382013, (collectively referred to as symbols820). RO1, RO2, . . . , RO6830represent the ROs in time domain where each RO implies 8 PRACH occasion in frequency resources. ROs830may include RO18301, RO28302, RO38303, RO48304, RO58305, RO68306(collectively referred to as ROs830). The PRACH RO configuration800provides PRACH transmissions corresponding to up to 48 SSB indexes in a single PRACH slot. When operating in high frequencies with high subcarrier spacings, e.g., SCS 960 kHz, the cyclic prefix (CP) length may not be long enough to accommodate the beam switching delays between consecutive ROs.

Modes of operation for PRACH transmission are described. According to a configuration, a WTRU may receive, determine, or be configured with the CP length in the PRACH transmission for the corresponding SCS that is not long enough to accommodate beam switching gap between consecutive ROs. The WTRU may determine or be configured to perform the PRACH transmission based on one of the following modes.

In a first mode, the WTRU performs a PRACH transmission while considering one or more symbol gaps in time-domain between the consecutive ROs. In another mode, the WTRU performs a PRACH transmission without any gaps in time-domain, by decomposing the PRACH transmission occasions.

According to a configuration, a WTRU may perform PRACH transmission based on the first mode. In Mode 1, the WTRU may be configured to insert/consider one or more symbol-level switching gaps based on one of the following between time-domain PRACH occasion and based on indication. For example, between time-domain PRACH occasions, the WTRU may insert/consider one or more symbol-level gap between consecutive ROs830. The WTRU may not consider/insert a gap before the first RO within a PRACH slot. The WTRU may not consider/insert a gap after the last RO within a PRACH slot. The WTRU may accommodate as many ROs as possible within a PRACH slot.

Alternatively, the WTRU may accommodate ROs830within a PRACH slot only up to the symbol indexes that were supposed to be used for PRACH transmission based on the original configurations. In an example, illustrated inFIG.9described below, there are no more PRACH transmission performed after symbol index 1082010in the first PRACH slot. The WTRU may continue to the next PRACH slot8202to send the remaining ROs830. The WTRU may determine or be configured with the location of the next PRACH slot based on one of the following: WTRU may receive, identify, or be configured with the frame number and the slot number of the corresponding frame for the next PRACH slot by higher layer parameters, e.g., DCI, RRC; WTRU may determine the next PRACH slot to be the next consecutive slot, and WTRU may determine the next PRACH slot to be the next available PRACH slot.

For example, based on indication, the WTRU may receive, identify, or be configured with the specific time-domain ROs830before/after which WTRU may insert/consider one or more symbol-level gaps. The WTRU may receive a bitmap indicating the time-domain ROs830that require gaps before/after their transmission. In an example, for the RO830configuration with prach-ConfigurationIndex equal to zero, the WTRU may consider a switching gap only after RO18301, RO28302, RO38303, RO48304, or RO58305. Alternatively, for the RO830configuration with prach-ConfigurationIndex equal to zero, the WTRU may consider a switching gap only before RO28302, RO38303, RO48304, RO58305, or RO68306. The WTRU may receive an index to a table indicating the combination for which WTRU may insert/consider switching gaps before/after the time-domain ROs830. The WTRU may receive one or more indexes to determine the combination of the ROs830that need insertion gaps before/after, e.g. combination(Nt_RAslot,g), where g is the number of ROs830that need insertion gaps before/after them. In an example, the first mode is illustrated inFIG.9, where a symbol gap910is inserted in time-domain and between each of the consecutive ROs. Specifically,FIG.9illustrates an example PRACH RO configuration prach-ConfigurationIndex equal to zero with switching gaps910.

PRACH transmission in another mode is described below. According to a configuration, a WTRU may perform PRACH transmission based on another mode. In this mode, the WTRU may perform PRACH transmission without any gaps in time-domain between consecutive ROs830.

According to a configuration, the WTRU may decompose the PRACH transmission occasions in frequency domain into two parts and accommodate the transmission within two time-domain ROs830. In this configuration the total PRB resources may be the same as the original configuration.

In an example, due to the decomposition of the ROs, the WTRU may consider the new configuration of the consecutive ROs830as RO-pairs1010. As illustrated, RO pairs1010may include RO-pair 110101, RO-pair 210102, RO-pair 310103, RO-pair 410104, RO-pair 410105, RO-pair 610106(collectively referred to as RO-pairs1010). The WTRU may adjust each original RO830, that is affected by decomposition, into two consecutive ROs in time domain denoted as RO-pairs1010. Each RO-pair1010may span across two time-domain PRACH occasions in time, and M′ frequency-domain PRACH occasions in frequency as illustrated inFIG.10. Each RO-pair1010may include the mappings allocated to one original RO830in the original configuration800inFIG.8.

The WTRU may continue to the next PRACH slot to send the remaining ROs. The WTRU may determine or be configured with the location of the next PRACH slot based on one of the following: WTRU may receive, identify, or be configured with the frame number and the slot number within the corresponding frame for the next PRACH slot by higher layer parameters, e.g., DCI, RRC; WTRU may determine the next PRACH slot to be the next consecutive slot, and WTRU may determine the next PRACH slot to be the next available PRACH slot.

In an example, the WTRU may operate with the switching of the antennas corresponding to the ROs taking place alternatively. The WTRU may determine that since gNB may handle and receive the frequency-domain PRACH occasions within a single original RO in time-domain without a beam switching, the gNB does not need to perform beam switching once they are re-allocated/decomposed into two consecutive PRACH occasions in time-domain. For example, as illustrated inFIG.10, an example of PRACH transmission occasion where the consecutive ROs may take place within a RO-pair1010without a need for beam switching gap is described.

FIG.10illustrates an example PRACH RO configuration with reallocated RO resources1000. The WTRU may use the switching of the antennas corresponding to the ROs that are mapped to the first RO within a RO-pair1010(first half of the original RO) takes place during the second RO within the RO-pair1010(second half of the original RO). In example1000, illustrated inFIG.10, where RO-Pair 110101represent RO18301in the original PRACH occasion configuration and RO1,110201.1and RO1,210201.2denote the first half and the second half of the original PRACH occasion configuration, respectively. Since the antenna switching corresponding to the first set of ROs within RO-Pair 110101, i.e. RO1,110201.1, takes place during the second PRACH occasion within RO-pair-110101, i.e. RO1,210201.2, then there is no need for the beam switching gap before the next PRACH occasion or RP-pair1010, e.g., RO2,110202.1or RO-Pair 210102.

The WTRU operates with the switching of the antennas corresponding to the ROs830that are mapped to the second RO10201.2within a RO-pair10101(second half of the original RO) takes place during the first RO within the next RO-pair10102(first half of the next original RO). InFIG.10, where RO-Pair 110101represent RO18301in the original PRACH occasion configuration and RO1,110201.1and RO1,210201.2denote the first half and the second half of the original PRACH occasion configuration, respectively. RO-Pair210102represent RO28302in the original PRACH occasion configuration and RO2,110201.1and RO2,210202.2denote the first half and the second half of the original PRACH occasion configuration, respectively. Since the antenna switching corresponding to the second set of ROs within RO-Pair 110101, i.e., RO1,210201.2, takes place during the first PRACH occasion within RO-pair-210102, i.e., RO2,110202.1, then there is no need for the beam switching gap before the next PRACH occasion, e.g., RO2,210202.2. The WTRU may assume the same sequential PRACH occasions and beam switching for the rest of the PRACH occasions within the PRACH slot without any need for a beam switching gap.

Alternatively, a WTRU may determine the decomposition of PRACH occasions without considering RO-pairs1010. The WTRU may determine the PRACH occasion frequency-domain resources to be half the original configuration, e.g., M′=M/2. The WTRU may perform the mapping of PRACH occasions through the consecutive ROs in time, frequency, and PRACH slots if required. The WTRU may determine the need for the switching gap based on one of the following modes of operation:

Between two ROs830resulting from decomposition: the WTRU may determine that the two consecutive PRACH occasions in time domain are parts of an original RO830in time domain that was decomposed into two consecutive ROs830as part of the solution. The WTRU may assume that gNB could receive the PRACH transmissions mapped to the corresponding SS/PBCH block indexes in the original RO830at the same time and without switching gap. The WTRU may determine that gNB may receive the two parts of the original PRACH occasion, decomposed into two consecutive time-domain ROs, without switching gap. The WTRU may not consider/insert any switching gaps in between such consecutive ROs.

Otherwise, between two originally separate ROs: the WTRU may determine that the two consecutive ROs are parts of two consecutive original ROs in time domain and not parts of a decomposition. The WTRU may operate as if the decomposition was already accomplished in the previous PRACH occasion. The WTRU may operate as if the former original PRACH occasion was decomposed into two consecutive time-domain ROs. The WTRU may operate as if the antenna switching was accomplished during the previous PRACH occasion and thorough the decomposition solution. The WTRU may not consider/insert any switching gaps in between such consecutive ROs.

A system and method in a wireless transmit/receive unit (WTRU) for physical random-access channel (PRACH) transmission is disclosed. The system and method include receiving a configuration of PRACH information, the PRACH information including at least one candidate cover-code, performing listen before talk (LBT) in a first random-access channel (RACH) occasion (RO) that is prior to a second RO, on a condition that the LBT is not successful, detecting if there is a first PRACH preamble transmission in the first RO scrambled with a first cover-code from among the at least one candidate cover-code, and based on the detecting, transmitting a second PRACH preamble scrambled with a second cover-code from among the at least one candidate cover-code in the second RO.

The system and method may include the transmitting occurs when the first cover-code is successfully detected in the first RO.

The system and method further comprising based on the detecting, no PRACH preamble is to be transmitted in the second RO due to the LBT failure. The system and method wherein the not transmitting occurs if none of the at least one candidate cover-codes is successfully detected in the first RO.

The system and method further comprising, on a condition that the LBT is successful, transmitting a third PRACH preamble scrambled with a third cover code from among the at least one candidate cover-code in the second RO.

The system and method wherein the detecting if there is a first PRACH preamble transmission in the first RO scrambled with a first cover-code from among the at least one candidate cover-codes enables the WTRU to further determine if the channel is busy.

When the cover-code is detected, the system and method further comprising transmitting PRACH preamble scrambled with the determined cover-code.

The system and method in a wireless transmit/receive unit (WTRU) for physical random-access channel (PRACH) transmission including receiving a configuration of PRACH information, the PRACH information including at least one candidate cover-code, performing listen before talk (LBT) in a first random-access channel (RACH) occasion (RO) that is prior to a second RO, on a condition that the LBT is not successful, detecting if there is a first PRACH preamble transmission in the first RO scrambled with a first cover-code from among the at least one candidate cover-code, and on a condition that the first PRACH preamble transmission scrambled with the first cover-code is detected in the first RO, transmitting a second PRACH preamble scrambled with a second cover-code from among the at least one candidate cover-code in the second RO.

The system and method including, on a condition that no PRACH preamble transmission scrambled with a cover-code from among the at least one candidate cover-code is detected in the first RO, no PRACH preamble is to be transmitted in the second RO due to the LBT failure.

The system and method further comprising, on a condition that the LBT is successful, transmitting a third PRACH preamble scrambled with a third cover code from among the at least one candidate cover-code in the second RO.