Method and apparatus for determining preamble and RACH timing for 2-step random access

Abstract

The present disclosure relates to a communication method and system for converging a 5th generation (5G) communication system and an Internet of Things (IoT) technology, wherein the 5G communication system is used to support a higher data rate than a 4th generation (4G) system. The present disclosure can be applied to smart services based on 5G communication technology and IoT-related technologies, such as smart homes, smart buildings, smart cities, smart cars, connected cars, health care, digital education, smart retail, safety and confidentiality services. The present disclosure provides a method and apparatus for determining a preamble and RACH timing for a 2-step random access.

Description

Technical Field

[0001] The present disclosure relates to a wireless communication system. Specifically, the present disclosure relates to a device, method and system for determining a preamble code and a random access channel (RACH) timing of a 2-step random access in a wireless communication system. Background Art

[0002] In order to meet the increased demand for wireless data services since the deployment of 4G communication systems, efforts have been made to develop an improved 5G or quasi-5G communication system. Therefore, 5G or quasi-5G communication systems are also referred to as "super 4G networks" or "post-LTE systems". 5G communication systems are considered to be implemented at higher frequency (millimeter wave) bands (e.g., 60GHz bands) to achieve higher data rates. In order to reduce the propagation loss of radio waves and increase the transmission distance, beamforming, massive multiple input multiple output (MIMO), full-dimensional MIMO (FD-MIMO), array antennas, analog beamforming, and massive antenna technology are discussed in 5G communication systems. In addition, in 5G communication systems, development of system network improvements based on advanced small cells, cloud radio access networks (RAN), ultra-dense networks, device-to-device (D2D) communications, wireless backhaul, mobile networks, collaborative communications, coordinated multipoint (CoMP), receiving end interference elimination, etc. is underway. In 5G systems, hybrid FSK with QAM modulation (FQAM) and sliding window superposition coding (SWSC) have been developed as advanced coded modulation (ACM), as well as filter bank multi-carrier (FBMC), non-orthogonal multiple access (NOMA) and sparse code multiple access (SCMA) as advanced access technologies.

[0003] The Internet, which is a human-centered connectivity network in which humans generate and consume information, has now evolved into the Internet of Things (IoT), in which distributed entities such as things exchange and process information without human intervention. The Internet of Everything (IoE) has emerged, which is a combination of IoT technology and big data processing technology through connection with cloud servers. Since IoT specific implementation requires technical elements such as "sensing technology", "wired / wireless communication and network infrastructure", "service interface technology" and "security technology", sensor networks, machine-to-machine (M2M) communication, machine type communication (MTC), etc. have been recently studied. Such IoT environments can provide smart Internet technology services that create new value for human life by collecting and analyzing data generated between connected things. IoT can be applied to a variety of fields including smart homes, smart buildings, smart cities, smart cars or connected cars, smart grids, health care, smart appliances, and advanced medical services through the integration and combination between existing information technology (IT) and various industrial applications.

[0004] Therefore, various efforts have been made to apply 5G communication systems to IoT networks. For example, technologies such as sensor networks, machine type communication (MTC), and machine to machine (M2M) communication can be implemented through beamforming, MIMO, and array antennas. By applying a cloud radio access network (RAN) as described above, big data processing technology can also be regarded as an example of the convergence between 5G technology and IoT technology.

[0005] Meanwhile, there have been various studies recently on 2-step random access in 5G communication systems.

[0006] The above information is presented as background information only to assist in understanding the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above may be used as prior art for the present disclosure. Summary of the invention

[0007] Technical issues

[0008] Recently, there is a need to improve the current 2-step random access procedure.

[0009] Solution to the problem

[0010] Aspects of the present disclosure are intended to at least address the above-mentioned problems and / or disadvantages, and to provide at least the advantages described below. Therefore, one aspect of the present disclosure is to provide a communication method and system for a converged fifth generation (5G) communication system, which is used to support higher data rates than the fourth generation (4G).

[0011] According to one aspect of the present disclosure, a method performed by a terminal is provided. The method includes: determining a random access preamble of the 2-step random access based on first information associated with the number of synchronization signal blocks (SSBs) of each physical random access channel (PRACH) opportunity of the 2-step random access and second information associated with the number of preambles of each SSB of the 2-step random access; determining the PRACH opportunity of the 2-step random access based on third information associated with a PRACH configuration index; and transmitting a message A (MSGA) including the random access preamble to a base station based on the PRACH opportunity.

[0012] According to another aspect of the present disclosure, a method performed by a base station is provided. The method includes: transmitting a message to a terminal, the message including first information associated with the number of synchronization signal blocks (SSBs) of each physical random access channel (PRACH) opportunity of a 2-step random access, second information associated with the number of preambles of each SSB of the 2-step random access, and third information associated with a PRACH configuration index; and receiving a message A (MSG A) including a random access preamble of the 2-step random access from the terminal based on a PRACH opportunity, wherein the random access preamble of the 2-step random access is determined based on the first information and the second information, and wherein the PRACH opportunity of the 2-step random access is determined based on the third information.

[0013] According to another aspect of the present disclosure, a terminal is provided. The terminal includes: a transceiver configured to transmit and receive signals; and a controller configured to: determine a random access preamble of the 2-step random access based on first information associated with the number of synchronization signal blocks (SSBs) of each physical random access channel (PRACH) opportunity of the 2-step random access and second information associated with the number of preambles of each SSB of the 2-step random access; determine the PRACH opportunity of the 2-step random access based on third information associated with a PRACH configuration index; and transmit a message A (MSG A) including the random access preamble to a base station based on the PRACH opportunity.

[0014] According to another aspect of the present disclosure, a base station is provided. The base station includes: a transceiver configured to transmit and receive signals; and a controller configured to: transmit a message to a terminal, the message including first information associated with the number of synchronization signal blocks (SSBs) of each physical random access channel (PRACH) opportunity of a 2-step random access, second information associated with the number of preambles of each SSB of the 2-step random access, and third information associated with a PRACH configuration index; and receive a message A (MSG A) including a random access preamble of the 2-step random access from the terminal based on a PRACH opportunity, wherein the random access preamble of the 2-step random access is determined based on the first information and the second information, and wherein the PRACH opportunity of the 2-step random access is determined based on the third information.

[0015] Before proceeding to the following detailed description, it may be helpful to set forth definitions of certain words and phrases used throughout this patent document: the term "including" and its derivatives mean including but not limited to; the term "or" is inclusive, meaning and / or; the phrases "associated with" and "associated with" and their derivatives may mean including, included within, interconnected with, including, included within, connected to or connected with, coupled to or coupled with, capable of communicating with, cooperating with, interleaved, juxtaposed, proximate to, bound to or bound with, having, having the property of, etc.; and the term "controller" means any device, system, or part thereof that controls at least one operation, which device may be implemented in hardware, firmware, or software, or some combination of at least two thereof. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether local or remote.

[0016] In addition, the various functions described below can be implemented or supported by one or more computer programs, each of which is formed by a computer-readable program code and embodied in a computer-readable medium. The terms "application" and "program" refer to one or more computer programs, software components, instruction sets, processes, functions, objects, classes, instances, related data or a portion thereof that are suitable for implementation with a suitable computer-readable program code. The phrase "computer-readable program code" includes any type of computer code, including source code, object code and executable code. The phrase "computer-readable medium" includes any type of medium that can be accessed by a computer, such as a read-only memory (ROM), a random access memory (RAM), a hard drive, a compact disk (CD), a digital video disc (DVD) or any other type of memory. "Non-transitory" computer-readable media excludes wired, wireless, optical or other communication links that transmit instantaneous electrical signals or other instantaneous signals. Non-transitory computer-readable media include media that can permanently store data, and media that can store data and then rewrite data, such as rewritable optical disks or erasable memory devices.

[0017] Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases.

[0018] Advantageous Effects of the Invention

[0019] According to various embodiments of the present disclosure, the 2-step random access procedure can be effectively enhanced. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The above and other aspects, features and advantages of certain embodiments of the present disclosure will become more apparent through the following description in conjunction with the accompanying drawings, in which:

[0021] Figure 1 A 2-step random access procedure according to one embodiment of the present disclosure is shown.

[0022] Figure 2 A flow chart of determining a RACH (or physical RACH, ie, PRACH) opportunity according to an embodiment of the present disclosure is shown.

[0023] Figure 3 A flow chart of determining a RACH (or PRACH) opportunity according to an embodiment of the present disclosure is shown.

[0024] Figure 4 A flow chart of determining a RACH (or PRACH) opportunity according to an embodiment of the present disclosure is shown.

[0025] Figure 5 A flow chart of determining a RACH (or PRACH) opportunity according to an embodiment of the present disclosure is shown.

[0026] Figure 6 A random access preamble determination process according to an embodiment of the present disclosure is shown.

[0027] Figure 7 A random access preamble determination process according to an embodiment of the present disclosure is shown.

[0028] Figure 8 A flow chart of determining a random access preamble according to an embodiment of the present disclosure is shown.

[0029] Fig. 9 A flow chart of determining a random access preamble according to an embodiment of the present disclosure is shown.

[0030] Fig.10 A flow chart of determining a random access preamble according to an embodiment of the present disclosure is shown.

[0031] Fig.11 A flow chart of determining a random access preamble according to an embodiment of the present disclosure is shown.

[0032] Fig.12 A flow chart of determining a random access preamble according to an embodiment of the present disclosure is shown.

[0033] Fig.13 is a block diagram of a terminal according to an embodiment of the present disclosure.

[0034] Fig.14 is a block diagram of a base station according to one embodiment of the present disclosure.

[0035] Throughout the drawings, like reference numerals will be understood to refer to like parts, components and structures. DETAILED DESCRIPTION

[0036] The following discussion Figures 1 to 14 The various embodiments used to describe the principles of the present disclosure in this patent document are only for illustration and should not be interpreted in any way as limiting the scope of the present disclosure. Those skilled in the art will understand that the principles of the present disclosure can be implemented in any appropriately arranged system or device.

[0037] The following description is provided with reference to the accompanying drawings to assist in a comprehensive understanding of the various embodiments of the present disclosure as defined by the claims and their equivalents. The following description includes various specific details that are helpful for understanding, but these should be considered as exemplary only. Therefore, it will be appreciated by those of ordinary skill in the art that various changes and modifications may be made to the various embodiments described herein without departing from the scope and spirit of the present disclosure. In addition, for the sake of clarity and brevity, descriptions of well-known functions and configurations may be omitted.

[0038] The terms and words used in the following description and claims are not limited to the bibliographical meanings, but are merely used by the inventor to enable a clear and consistent understanding of the present disclosure. Therefore, it should be apparent to those skilled in the art that the following description of various embodiments of the present disclosure is provided for illustrative purposes only and not for the purpose of limiting the present disclosure as defined by the appended claims and their equivalents.

[0039] It is to be understood that the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a component surface" includes reference to one or more of such surfaces.

[0040] The term "substantially" means that the features, parameters or values ​​described need not be achieved precisely, but may deviate or vary by an amount that does not eliminate the effect the feature is intended to provide, including, for example, tolerances, measurement errors, measurement precision limitations and other factors known to those skilled in the art.

[0041] It is known to those skilled in the art that blocks and combinations of flowcharts (or sequence diagrams) can be represented and executed by computer program instructions. These computer program instructions can be loaded on a processor of a general-purpose computer, a special-purpose computer, or a programmable data processing device. When the loaded program instructions are executed by the processor, they create a device for performing the functions described in the flowchart. Since computer program instructions can be stored in a computer-readable memory that can be used in a special-purpose computer or a programmable data processing device, it is also possible to create an article that performs the functions described in the flowchart. Since computer program instructions can be loaded on a computer or a programmable data processing device, when executed as a process, it can perform the operations of the functions described in the flowchart.

[0042] The blocks of the flow chart may correspond to a module, segment or code containing one or more executable instructions that implement one or more logical functions, or may correspond to a portion thereof. In some cases, the functions described by the blocks may be performed in an order different from the order listed. For example, two blocks listed in sequence may be performed simultaneously or in reverse order.

[0043] In this description, the words "unit", "module" etc. can refer to software components or hardware components that can perform functions or operations, such as field programmable gate arrays (FPGAs) or application specific integrated circuits (ASICs). However, "units" etc. are not limited to hardware or software. Units etc. can be configured to reside in addressable storage media or drive one or more processors. Units etc. can refer to software components, object-oriented software components, category components, task components, processes, functions, attributes, procedures, subroutines, program code fragments, drivers, firmware, microcodes, circuits, data, databases, data structures, tables, arrays or variables. The functions provided by components and units can be a combination of smaller components and units, and can be combined with other components and units to form larger components and units. Components and units can be configured to drive devices or one or more processors in a secure multimedia card.

[0044] Before the detailed description, terms or definitions necessary for understanding the present disclosure are described. However, these terms should be interpreted in a non-limiting manner.

[0045] A “base station (BS)” is an entity that communicates with a user equipment (UE) and may be referred to as a BS, base transceiver station (BTS), node B (NB), evolved NB (eNB), access point (AP), 5G NB (5GNB), or gNB.

[0046] 'UE' is an entity communicating with a BS and may be referred to as UE, a device, a mobile station (MS), a mobile equipment (ME), or a terminal.

[0047] In recent years, several broadband wireless technologies have been developed to meet the growing number of broadband subscribers and provide more and better applications and services. The second generation of wireless communication systems has been developed to provide voice services while ensuring user mobility. The third generation of wireless communication systems supports not only voice services but also data services. In recent years, the fourth generation of wireless communication systems has been developed to provide high-speed data services. However, at present, the fourth generation of wireless communication systems suffers from insufficient resources and cannot meet the growing demand for high-speed data services. Therefore, the fifth generation of wireless communication systems is being developed to meet the growing demand for high-speed data services, supporting ultra-reliability and low latency applications.

[0048] The fifth generation wireless communication system will be implemented not only in lower frequency bands, but also in higher frequency (mm Wave) bands such as 10 GHz to 100 GHz bands to achieve higher data rates. In order to mitigate the propagation loss of radio waves and increase the transmission distance, beamforming, massive MIMO, full-dimensional MIMO (FD-MIMO), array antennas, analog beamforming, and massive antenna technology are considered in the design of the fifth generation wireless communication system. In addition, the fifth generation wireless communication system is expected to solve different use cases with quite different requirements in terms of data rate, latency, reliability, mobility, etc. However, it is expected that the design of the air interface of the fifth generation wireless communication system will be flexible enough to serve UEs with completely different performance, depending on the use cases and market segments that the UE provides services to end customers. For example, the use cases in the fifth generation wireless communication system wireless system are expected to solve the following problems: enhanced mobile broadband (eMBB), large machine type communication (m-MTC), ultra-reliable low latency communication (URLL), etc. The eMBB requirements (such as tens of Gbps data rates, low latency, high mobility, etc.) solve the market segments that actively need Internet connectivity on behalf of conventional wireless broadband subscribers anytime, anywhere. m-MTC requirements (such as very high connection density, infrequent data transmission, very long battery life, low mobility address, etc.) address the market segment representing the connectivity of billions of devices envisioned by the Internet of Things (IoT) / Internet of Everything (IoT). URLL requirements (such as very low latency, very high reliability, and variable mobility) address the market segment representing industrial automation applications (i.e., vehicle-to-vehicle / vehicle-to-infrastructure communications, which is foreseen as one of the enablers of autonomous vehicles).

[0049] In 5th generation (also known as NR or New Radio) wireless communication systems, a random access (RA) procedure is used to achieve uplink time synchronization. The RA procedure is used during the following actions: initial access, handover, radio resource control (RRC) connection re-establishment procedure, scheduling request transmission, secondary cell group (SCG) addition / modification, and data or control information transmission in the uplink by an unsynchronized UE in the RRC CONNECTED state.

[0050] Traditional CBRA procedure: This is also called 4-step CBRA. In this type of random access, the UE first transmits a random access preamble (also called Msg1 (Message 1)), and then waits for a random access response (RAR) or Msg2 in the RAR window corresponding to its random access preamble transmission. The next generation Node B (gNB) transmits the RAR on the Physical Downlink Shared Channel (PDSCH) addressed to the RA Radio Network Temporary Identifier (RNTI). The RA-RNTI identifies the time-frequency resources (also called PRACH opportunity or PRACH TX opportunity or RACH opportunity) where the gNB detects the random access preamble. The maximum size of the RAR window is one radio frame, i.e., 10ms. The RA-RNTI is calculated as follows: RA-RNTI=1+s_id+14*t_id+14*80*f_id+14*80*8*ul_carri er_id, where

[0051] -s_id is the index of the first orthogonal frequency division multiplexing (OFDM) symbol of the PRACH opportunity in which the UE has transmitted Msg1 (i.e., RA preamble), 0≤s_id<14,

[0052] - t_id is the index of the first time slot of the PRACH opportunity (0≤t_id<80),

[0053] - f_id is the index of the PRACH opportunity within the time slot in the frequency domain (0≤f_id<8)

[0054] -ul_carri er_id is the UL carrier used for Msg1 transmission (0 for NUL (normal uplink carrier) and 1 for SUL (supplementary carrier)).

[0055] The gNB may multiplex several RARs of various random access preambles detected by the gNB in ​​the same RAR Media Access Control (MAC) Protocol Data Unit (PDU). If the Random Access Preamble Identifier (RAPID) of the random access preamble transmitted by the UE is included, the RAR in the MAC PDU corresponds to the random access preamble transmission of the UE. If no RAR corresponding to its random access preamble transmission is received during the RAR window, and the UE has not transmitted a random access preamble a configurable (configured by the gNB in ​​the RACH configuration) number of times, the UE returns to the first step, i.e., selecting a random access resource (preamble / RACH opportunity) and transmitting a RA preamble. A backoff may be applied before returning to the first step.

[0056] The RA process is considered successful if a RAR corresponding to its random access preamble transmission is received and the UE has transmitted a dedicated random access preamble. If the UE transmits a non-dedicated (i.e., contention-based) random access preamble after successful reception of the RAR, the UE transmits Msg3 in the UL grant received in the RAR. Msg3 includes messages such as RRC connection request, RRC connection reestablishment request, RRC handover confirmation, scheduling request, etc. Msg3 also includes a UE identity (i.e., cell RNTI (C-RNTI) or service temporary mobile subscriber identity (S-TMSI) or a random number). After transmitting Msg3, the UE starts a contention resolution timer. While the contention resolution timer is running, if the UE receives a physical downlink control channel (PDCCH) addressed to the C-RNTI included in Msg3, contention resolution is considered successful, the contention resolution timer stops and the RA process is completed. While the contention resolution timer is running, if the UE receives a contention resolution MAC control element (CE) including the UE's contention resolution identifier (the first X bits of the common control channel (CCCH) service data unit (SDU) transmitted in Msg3), the contention resolution is considered successful, the contention resolution timer is stopped and the RA procedure is completed. If the contention resolution timer expires and the UE has not transmitted a configurable number of random access preambles, the UE returns to the first step, i.e., selecting a random access resource (preamble / RACH opportunity) and transmitting a RA preamble. A backoff may be applied before returning to the first step.

[0057] Contention-free random access (CFRA): In 5th generation (also known as NR or new radio) wireless communication systems, a contention-free RA (CFRA) procedure is also supported. The contention-free RA procedure is used for situations such as handover requiring low latency, timing advance establishment of Scel l, etc. The GNB allocates a non-contention RA preamble to the UE in dedicated signaling. The UE transmits the allocated non-contention RA preamble. The GNB transmits a RAR on the PDSCH addressed to the RA-RNTI. The RAR conveys the RA preamble identifier and timing alignment information. The RAR may also include a UL grant. The RAR is transmitted in a RAR window similar to the contention-based RA procedure. After receiving the RAR including the RA preamble identifier (RAPID) of the RA preamble transmitted by the UE, the CFRA is considered to be successfully completed. In the case of initiating RA for beam failure recovery, if a PDCCH addressed to the C-RNTI is received in the search space for beam failure recovery, the CFRA is considered to be successfully completed. If the RAR window expires and the RA is not completed successfully, and the UE has not transmitted the RA preamble a configurable (configured by the gNB in ​​the RACH configuration) number of times, the UE retransmits the RA preamble.

[0058] For certain events, such as handover and beam failure recovery, if one or more dedicated preambles are assigned to the UE, the UE determines whether to transmit a dedicated preamble or a non-dedicated preamble during the first step of random access, i.e., during random access resource selection for Msg1 transmission. Dedicated preambles are usually provided for a subset of SSB / CSI-RS. If no SSB / CSI-RS has a DL RSRP above a threshold among the SSB / CSI-RS for which the gNB provides contention-free random access resources (i.e., dedicated preambles / RO), the UE selects a non-dedicated preamble. Otherwise, the UE selects a dedicated preamble. Therefore, in the RA procedure, one random access attempt can be CFRA, while the other random access attempt can be CBRA.

[0059] 2-step contention based random access (2-step CBRA): In the first step, the UE transmits a random access preamble on PRACH and a payload (i.e., MAC PDU) on PUSCH. The random access preamble and payload transmission is also referred to as MsgA. In the second step, after the MsgA transmission, the UE monitors the response from the network (i.e., gNB) within the configured window. The response is also referred to as MsgB. If a CCCH SDU is transmitted in the MsgA payload, the UE performs contention resolution using the contention resolution information in the MsgB. Contention resolution is successful if the contention resolution identifier received in the MsgB matches the first 48 bits of the CCCH SDU transmitted in the MsgA. If the C-RNTI is transmitted in the MsgA payload, contention resolution is successful if the UE receives a PDCCH addressed to the C-RNTI. If contention resolution is successful, the random access procedure is considered to be successfully completed. Instead of the contention resolution information corresponding to the transmitted MsgA, MsgB may include backoff information corresponding to the random access preamble transmitted in MsgA. If the backoff information is received, the UE transmits Msg3 and performs contention resolution using Msg4 as in the CBRA process. If the contention resolution is successful, the random access process is considered to be successfully completed. If the contention resolution fails at the backoff (i.e., when Msg3 is transmitted), the UE retransmits MsgA. If the configured window for the UE to monitor the network response after transmitting MsgA expires and the UE has not received MsgB including contention resolution information or backoff information as described above, the UE retransmits MsgA. If the random access process is not successfully completed even after a configurable number of MsgA transmissions, the UE falls back to the 4-step RACH process, i.e., the UE only transmits the PRACH preamble.

[0060] The MsgA payload may include one or more of the following: a common control channel (CCCH) service data unit (SDU), a dedicated control channel (DCCH) SDU, a dedicated traffic channel (DTCH) SDU, a buffer status report (BSR) MAC control element (CE), a power headroom report (PHR) MAC CE, SSB information, a C-RNTI MAC CE, or padding. MsgA may include a UEIID (e.g., a random IID, S-TMSI, C-RNTI, recovery ID, etc.) and the preamble in the first step. The UEID may be included in the MAC PDU of MsgA. A UEID such as a C-RNTI may be carried in a MAC CE, wherein the MAC CE is included in the MAC PDU. Other UEIDs (such as a random ID, S-TMSI, C-RNTI, recovery ID, etc.) may be carried in a CCCH SDU. The UE|ID may be one of a random ID, S-TMSI, C-RNTI, recovery ID, I MSI, idle mode ID, inactive mode ID, etc. In different situations where the UE performs the RA process, the UE|ID may be different. When the UE performs RA after power-on (before it is attached to the network), the UE ID is a random ID. When the UE performs RA in an idle state after being attached to the network, the UEID is an S-TMSI. If the UE has an assigned C-RNTI (for example, in a connected state), the UEID is a C-RNTI. In the case where the UE is in an inactive state, the UEID is a recovery ID. In addition to the UE ID, some additional ct rl information may be sent in MsgA. The control information may be included in the MAC PDU of MsgA. The control information may include one or more of the following: a connection request indication, a connection recovery request indication, an SI request indication, a buffer status indication, beam information (for example, one or more DL TX beam IDs or one or more SSB|IDs), a beam failure recovery indication / information, a data indicator, a cell / BS / TRP switching indication, a connection reconstruction indication, a reconfiguration completion or handover completion message, etc.

[0061] 2-step Contention-Free Random Access (2-step CFRA): In this case, the gNB allocates to the UE one or more dedicated random access preambles and one or more PUSCH resources to be used for MsgA transmission. One or more ROs to be used for preamble transmission may also be indicated. In the first step, the UE transmits a random access preamble on PRACH and a payload on PUSCH using contention-free random access resources (i.e., dedicated preamble / PUSCH resources / RO). In the second step, after the MsgA transmission, the UE monitors the response from the network (i.e., gNB) within the configured window. If the UE receives a PDCCH addressed to the C-RNTI, the random access procedure is considered to be successfully completed. If the UE receives backoff information corresponding to the preamble it transmitted, the random access procedure is considered to be successfully completed.

[0062] For certain events, such as handover and beam failure recovery, if one or more dedicated preambles and one or more PUSCH resources are allocated to the UE, then during the first step of random access, i.e., during random access resource selection for MsgA transmission, the UE determines whether to transmit a dedicated preamble or a non-dedicated preamble. Dedicated preambles are usually provided for a subset of SSB / CSI-RS. If no SSB / CSI-RS has a DL RSRP above a threshold among the SSB / CSI-RS for which the gNB provides contention-free random access resources (i.e., dedicated preambles / RO / PUSCH resources), the UE selects a non-dedicated preamble. Otherwise, the UE selects a dedicated preamble. Therefore, during the RA procedure, one random access attempt can be a 2-step CFRA, while the other random access attempt can be a 2-step CBRA.

[0063] When initiating a random access procedure, the UE first selects a carrier (SUL or NUL). If the gNB explicitly signals the carrier to be used for the random access procedure, the UE selects the signaled carrier to perform the random access procedure. If the gNB does not explicitly signal the carrier to be used for the random access procedure; and if the serving cell of the random access procedure is configured with a supplementary uplink, and if the RSRP referenced by the downlink path loss is less than the rsrp-threshold SSB-SUL. The UE selects the SUL carrier to perform the random access procedure. Otherwise, the UE selects the NUL carrier to perform the random access procedure. After selecting the UL carrier, the UE determines the UL and DL BWP for the random access procedure, as specified in Section 5.15 of TS 38.321. The UE then determines whether to perform a 2-step or 4-step RACH for the random access procedure.

[0064] - If the random access procedure is initiated by a PDCCH order and if the ra-PreambleIndex (Random Access-Preamble Index) explicitly provided by the PDCCH is not 0b000000, the UE selects 4-step RACH.

[0065] - Otherwise, if the gNB signals 2-step contention-free random access resources for this random access procedure, the UE selects 2-step RACH.

[0066] - Otherwise, if the gNB signals 4-step contention-free random access resources for this random access procedure, the UE selects 4-step RACH.

[0067] - Otherwise, if the UL BWP selected for this random access procedure is configured with only 2-step RACH resources, the UE selects 2-step RACH.

[0068] - Otherwise, if the UL BWP selected for this random access procedure is configured with only 4-step RACH resources, the UE selects 4-step RACH.

[0069] - Otherwise, if the UL BWP selected for this random access procedure is configured with both 2-step and 4-step RACH resources,

[0070] - If the downlink path loss referenced RSRP is below the configured threshold, the UE selects 4-step RACH. Otherwise, the UE selects 2-step RACH.

[0071] To perform CBRA, the RACH configuration is signaled in the system information (ie, SIB1) and dedicated RRC signaling. The RACH configuration in SIB1 is used by the UE in RRC IDLE and RRC NACTI VE.

[0072] -The contention-based RACH configuration includes a prach-ConfigurationIndex, which indicates a set of available PRACH opportunities for transmitting a random access preamble. The number of PRACH opportunities in a PRACH configuration period is predefined for each PRACH configuration index. The PRACH configuration period for each PRACH configuration index is also predefined. The predefined PRACH configuration table lists s configurations, where each configuration indicates the number of PRACH opportunities in a PRACH configuration period, the PRACH configuration period, and the position of the PRACH opportunities in the PRACH configuration period. The PRACH configuration index is an index to an entry in the PRACH configuration table.

[0073] -Content-based RACH configuration also includes ssb-perRACH-OccasionAndCB-PreamblesPerSSB. ssb-perRACH-OccasionAndCB-PreamblesPerSSB indicates CB-PreamblesPerSSB (R) and ssb-perRACH-Occasion (N).

[0074] - Based on ssb-perRACH-Occasion and the number of SSBs transmitted in the cell, the PRACH opportunities configured by prach-ConfigurationIndex are mapped to SSBs. The number of SSBs transmitted in the cell is signaled by the gNB in ​​system information and dedicated RRC signaling messages. PRACH opportunities are mapped to SSBs within an association period. The association period starting from system frame number (SFN) 0 is the period in which all SSBs are mapped to PRACH opportunities at least once. In one example, the association period can be equal to {1,2,4,8,16} PRACH configuration periods.

[0075] - If N < 1, one SSB is mapped to 1 / N consecutive valid PRACH opportunities, and the R-contention based preamble with consecutive indices associated with the SSB of each valid PRACH opportunity starts from preamble index 0. If N ≥ 1, the R-contention based preamble with consecutive indices associated with the SSB of each valid PRACH opportunity n0 ≤ n ≤ N-1 starts from preamble index 0. Start, where Provided by the total Number Of RA-Preambles and is an integer multiple of N. The total Number Of RA-Preambles is signaled by the gNB in ​​the RACH configuration.

[0076] In 4-step CBRA, the UE first selects a suitable SSB, where an SSB is suitable if the synchronization signal reference signal received power (SS-RSRP) of the SSB is higher than rsrp-ThresholdSSB. The selection of a suitable SSB among multiple suitable SSBs depends on the UE specific implementation. If there is no suitable SSB, the UE can select any SSB. Then the random access preamble and PRACH opportunity corresponding to the selected SSB are selected.

[0077] In 2-step RA, the gNB needs to transmit MsgB upon receiving MsgA. In order for the gNB to avoid transmitting msgB in the direction of all SSBs, the SSB should be selected in the same way as for Msg1 and the gNB should be notified via msgA. The random access preamble and PRACH opportunity corresponding to the selected SSB should then be selected. In one cell, both 2-step and 4-step CBRA can be configured. The question is how to determine which PRACH opportunities and preambles are associated with 2-step CBRA and which PRACH opportunities and preambles are associated with 4-step CBRA.

[0078] [Example 1-Determination of PRACH timing]

[0079] Figure 2 and Figure 3 A flowchart of determining a PRACH opportunity according to Embodiment 1-1 of the present disclosure is shown.

[0080] Embodiment 1-1: In one embodiment of the present disclosure, it is recommended to separately signal the parameter prach-ConfigurationIndex (210, 310) for 2-step CBRA and 4-step CBRA in SIB1 and dedicated RRC signaling messages (e.g., RRC reconfiguration). If the CBRA initiated by the UE / GNB is a 2-step CBRA (220, 230, 320, 330), the UE determines the PRACH timing of the 2-step CBRA according to the prach-ConfigurationIndex configured / signaled by the gNB for the 2-step CBRA (250, 260). If the CBRA initiated by the UE / GNB is a 4-step CBRA, the UE determines the PRACH timing of the 4-step CBRA according to the prach-ConfigurationIndex configured / signaled by the gNB for the 4-step CBRA (240, 245, 340, 345). The predefined PRACH configuration table lists multiple configurations, where each configuration indicates the PRACH configuration period, the number of PRACH opportunities in the PRACH configuration period, and the location (ie, OFDM symbol / time slot) of the PRACH opportunities in the PRACH configuration period. The PRACH configuration index is an index to an entry in the PRACH configuration table.

[0081] The prach-ConfigurationIndex for 2-step CBRA may be configured / signaled by the gNB in ​​the 2-step CBRA configuration (e.g., in the RACH-ConfigCommon IE for 2-step), and the prach-ConfigurationIndex for 4-step CBRA may be configured / signaled by the gNB in ​​the 4-step CBRA configuration (e.g., in the RACH-ConfigCommon IE for 4-step). Alternatively, the prach-ConfigurationIndex for 2-step CBRA and the prach-ConfigurationIndex for 4-step CBRA may be configured / signaled by the gNB in ​​the CBRA configuration (i.e., in the RACH-ConfigCommon IE, which is common for both 2-step and 4-step CBRA). Note that the RACH configuration is signaled by the gNB per bandwidth part (BWP), and the UE uses the RACH configuration corresponding to the BWP on which the random access preamble is transmitted to the UE. The RACH configuration is signaled in SIB1 and dedicated RRC signaling messages.

[0082] Figure 3 A flow chart of determining a PRACH opportunity according to an embodiment of the present disclosure is shown.

[0083] In an embodiment of the method, among PRACH opportunities (350) determined for 2-step CBRA based on prach-ConfigurationIndex configured / signaled by the gNB for 2-step CBRA, the UE excludes PRACH opportunities (360, 370) that overlap with PRACH opportunities for 4-step CBRA. The PRACH opportunities for 4-step CBRA are determined based on prach-ConfigurationIndex configured / signaled by the gNB for 4-step CBRA.

[0084] The remaining PRACH opportunities after exclusion are mapped to SSBs. Note that the PRACH opportunities in the associated period are first numbered sequentially in the frequency domain and then in the time domain. The SSBs are mapped to these PRACH opportunities in ascending order of the SSB index. The SSBs associated with the PRACH opportunities are numbered sequentially from lower SSB index to higher SSB index. If ssb-perRACH-Occasion(N1) is less than 1, only one SSB is mapped to one PRACH opportunity, and each SSB is mapped to 1 / N1 PRACH opportunities. If ssb-perRACH-Occasion(N1)>=1, N1 SSBs are mapped to each PRACH opportunity. The UE selects a PRACH opportunity from the remaining PRACH opportunities after exclusion for transmitting the random access preamble. The PRACH opportunity is selected from the PRACH opportunities corresponding to the SSB selected by the UE.

[0085] Figure 4 and Figure 5 A flowchart of determining a PRACH opportunity according to Embodiments 1-2 of the present disclosure is shown.

[0086] Embodiment 1-2: In one embodiment of the present disclosure, it is recommended to separately signal the parameter prach-ConfigurationIndex for 2-step CBRA and 4-step CBRA in SIB1 and dedicated RRC signaling messages (e.g., RRC reconfiguration). The gNB may choose to signal or not signal prach-ConfigurationIndex for 2-step CBRA.

[0087] If the CBRA initiated by the UE / GNB is a 2-step CBRA (410, 510), then in the case where the prach-ConfigurationIndex for the 2-step CBRA is signaled by the gNB, the UE determines the PRACH timing for the 2-step CBRA according to the prach-ConfigurationIndex configured / signaled by the gNB for the 2-step CBRA (420, 440, 450, 540, 560, 570). If the prach-ConfigurationIndex for the 2-step CBRA is not signaled by the gNB, the UE determines the PRACH timing for the 2-step CBRA according to the prach-ConfigurationIndex configured / signaled by the gNB for the 4-step CBRA (420, 430, 435, 540, 550, 555). If the CBRA initiated by the UE / GNB is a 4-step CBRA, the UE determines the PRACH opportunity for the 4-step CBRA according to the prach-ConfigurationIndex configured / signaled by the gNB for the 4-step CBRA (520, 530, 535). The predefined PRACH configuration table lists multiple configurations, each of which indicates the PRACH configuration period, the number of PRACH opportunities in the PRACH configuration period, and the location (symbol / time slot) of the PRACH opportunities in the PRACH configuration period. The PRACH configuration index is an index to an entry in the PRACH configuration table.

[0088] The prach-ConfigurationIndex for 2-step CBRA may be configured / signaled by the gNB in ​​the 2-step CBRA configuration (e.g., in the RACH-ConfigCommon IE for 2-step), and the prach-ConfigurationIndex for 4-step CBRA may be configured / signaled by the gNB in ​​the 4-step CBRA configuration (e.g., in the RACH-ConfigCommon IE for 4-step). Alternatively, the prach-ConfigurationIndex for 2-step CBRA and the prach-ConfigurationIndex for 4-step CBRA may be configured / signaled by the gNB in ​​the CBRA configuration (i.e., in the RACH-ConfigCommon IE, which is common for both 2-step and 4-step CBRA). Note that the RACH configuration is per BWP, and the UE uses the RACH configuration corresponding to the BWP on which the random access preamble is transmitted to the UE. The RACH configuration is signaled in SIB1 and dedicated RRC signaling messages.

[0089] PRACH opportunities are mapped to SSBs. Note that the PRACH opportunities in the associated period are first numbered sequentially in the frequency domain and then in the time domain. The SSBs are mapped to these PRACH opportunities in ascending order of the SSB index. The SSBs associated with the PRACH opportunities are numbered sequentially from lower SSB index to higher SSB index. If ssb-perRACH-Occasion(N1) is less than 1, only one SSB is mapped to one PRACH opportunity, and each SSB is mapped to 1 / N1 PRACH opportunities. If ssb-perRACH-Occasion(N1)>=1, N1 SSBs are mapped to each PRACH opportunity. The UE selects a PRACH opportunity for transmitting a random access preamble. The PRACH opportunity is selected from the PRACH opportunities corresponding to the SSB selected by the UE.

[0090] [Embodiment 2-Determination of Random Access Preamble Code]

[0091] Figure 6 , Figure 7 and Figure 8 A random access preamble determination process according to an embodiment of the present disclosure is shown.

[0092] Embodiment 2-1: In one embodiment of the present disclosure, it is recommended that the parameter ssb-perRACH-OccasionAndCB-PreamblesPerSSB be signaled separately by the gNB for 2-step CBRA and 4-step CBRA in SIB1 and dedicated RRC signaling messages (e.g., RRC reconfiguration). For 2-step CBRA, the parameter PreambleStartIndex is additionally signaled by the gNB. For 4-step CBRA, the parameter PreambleStartIndex is not signaled.

[0093] The ssb-perRACH-OccasionAndCB-PreamblesPerSSB for 2-step CBRA may be configured / signaled by the gNB in ​​the 2-step CBRA configuration (e.g., in the RACH-ConfigCommon IE for 2-step), and the ssb-perRACH-OccasionAndCB-PreamblesPerSSB for 4-step CBRA may be configured / signaled by the gNB in ​​the 4-step CBRA configuration (e.g., in the RACH-ConfigCommon IE for 4-step). Alternatively, the ssb-perRACH-OccasionAndCB-PreamblesPerSSB for 2-step CBRA and the ssb-perRACH-OccasionAndCB-PreamblesPerSSB for 4-step CBRA may be configured / signaled by the gNB in ​​the CBRA configuration (i.e., in the RACH-ConfigCommon IE, which is common to both 2-step and 4-step CBRA). Note that the RACH configuration is per BWP, and the UE uses the RACH configuration corresponding to the BWP on which the random access preamble is transmitted to the UE.

[0094] If the CBRA initiated by the UE / GNB is a 2-step CBRA (810, 820), the UE determines the PRACH preamble code for the 2-step CBRA as follows (850, 860, 870):

[0095] -N1: ssb-perRACH-Occasion configured / signaled by gNB for 2-step CBRA.

[0096] - R1: CB-PreamblesPerSSB configured / signaled by the gNB for 2-step CBRA.

[0097] - If N1<1: Preambles starting from PreambleStartIndex to "PreambleStartIndex+R1-1" are used for 2-step CBRA (860). The same set of preambles is used for each SSB of each PRACH opportunity. In other words, R1 contention-based preambles with consecutive indices associated with the SSBs of each valid PRACH opportunity start from preamble index PreambleStartIndex.

[0098] - If N1>=1, the R1 contention-based preambles with consecutive indices associated with SS / PBCH blocks nO≤n≤N1-1 for each valid PRACH opportunity are indexed from the preamble Start (where Provided by totalNumberOf RA-Preambles)(870). In one embodiment, totalNumberOf RA-Preambles is the total number of preambles used for random access (contention-based as well as contention-free) and is configured by the gNB. In another embodiment, it is the total number of preambles used for 2-step CBRA. It may be configured by the gNB. Alternatively, it is not configured but it is equal to [CB-preambles-per-SSBxmax(1,SSB-per-rach-occasion)]. Figure 6 An example of N1=2 and R1=16 is shown. Total Number Of RA-Preambles is the total number of preambles used for random access (contention-based and contention-free). Figure 7 The case where the total Number Of RA-Preambles is equal to [CB-preambles-per-SSBxmax(1,SSB-per-rach-occasion)] is shown.

[0099] If the CBRA initiated by the UE / GNB is a 4-step CBRA (820), the UE determines the PRACH preamble code for the 4-step CBRA as follows (830, 835, 840):

[0100] -N1: ssb-perRACH-Occasion configured / signaled by gNB for 4-step CBRA

[0101] -R1: CB-PreamblesPerSSB configured / signaled by gNB for 4-step CBRA

[0102] - If N1<1: Preambles starting from preamble index zero to "R1-1" are used for 4-step CBRA (835). The same set of preambles is used for each SSB. In other words, R1 contention-based preambles with consecutive indices associated with the SSB of each valid PRACH opportunity start from preamble index zero.

[0103] - If N1>=1, the R1 contention-based preambles with consecutive indices associated with SS / PBCH blocks n0≤n≤N1-1 for each valid PRACH opportunity are indexed from the preamble Start, where Provided by total Number Of RA-Preambles (840). In one embodiment, total Number Of RA-Preambles is the total number of preambles used for random access (contention-based and contention-free) and is configured by the gNB. In another embodiment, total Number Of RA-Preambles is the total number of preambles used for random access (4-step contention-based and contention-free random access) and is configured by the gNB.

[0104] Fig. 9 A flow chart of determining a random access preamble according to an embodiment of the present disclosure is shown.

[0105] Embodiment 2-2: In one embodiment of the present disclosure, it is recommended that the parameter ssb-per RACH-OccasionAndCB-PreamblesPerSSB be signaled separately by the gNB for 2-step CBRA and 4-step CBRA in SIB1 and dedicated RRC signaling messages (e.g., RRC reconfiguration). For 2-step CBRA, ssb-per RACH-OccasionAndCB-PreamblesPerSSB is optionally signaled by the gNB. If ssb-perRACH-OccasionAndCB-PreamblesPerSSB is not signaled by the gNB for 2-step CBRA, the UE uses the ssb-per RACH-OccasionAndCB-PreamblesPerSSB signaled for 4-step CBRA for 2-step CBRA.

[0106] For 2-step CBRA, the parameter PreambleStartIndex is optionally signaled by the gNB. If PreambleStartIndex is not signaled by the gNB for 2-step CBRA, the UE assumes that PreambleStartIndex is zero. For 4-step CBRA, the parameter PreambleStartIndex is not signaled.

[0107] The ssb-perRACH-OccasionAndCB-PreamblesPerSSB for 2-step CBRA may be configured / signaled by the gNB in ​​the 2-step CBRA configuration (e.g., in the RACH-ConfigCommon IE for 2-step), and the ssb-perRACH-OccasionAndCB-PreamblesPerSSB for 4-step CBRA may be configured / signaled by the gNB in ​​the 4-step CBRA configuration (e.g., in the RACH-ConfigCommon IE for 4-step). Alternatively, the ssb-perRACH-OccasionAndCB-PreamblesPerSSB for 2-step CBRA and the ssb-perRACH-OccasionAndCB-PreamblesPerSSB for 4-step CBRA may be configured / signaled by the gNB in ​​the CBRA configuration (i.e., in the RACH-ConfigCommon IE, which is common for both 2-step and 4-step CBRA). Note that the RACH configuration is per BWP.

[0108] If the CBRA initiated by the UE / GNB is a 2-step CBRA (910), the UE determines the PRACH preamble code for the 2-step CBRA as follows:

[0109] - N1: ssb-perRACH-Occasion configured / signaled by gNB for 2-step CBRA (915, 935, 945). If ssb-perRACH-Occasion is not signaled for 2-step CBRA, the UE applies ssb-perRACH-Occasion configured / signaled by gNB for 4-step CBRA (935, 940).

[0110] - R1: CB-PreamblesPerSSB configured / signaled by the gNB for 2-step CBRA (915, 935, 945). If CB-PreamblesPerSSB is not signaled for 2-step CBRA, the UE applies CB-PreamblesPerSSB configured / signaled by the gNB for 4-step CBRA (935, 940).

[0111] - If N1 < 1: Preambles starting from PreambleStartIndex to "PreambleStartIndex + R1-1" are used for 2-step CBRA (950, 970). The same set of preambles is used for each SSB. In other words, R1 contention-based preambles with consecutive indices associated with the SSB of each valid PRACH opportunity start from preamble index PreambleStartIndex. If PreambleStartIndex is not signaled by the gNB for 2-step CBRA, the UE assumes that PreambleStartIndex is zero (950, 955).

[0112] - If N1>=1, the R1 contention-based preambles with consecutive indices associated with SS / PBCH blocks n0≤n≤N1-1 for each valid PRACH opportunity are indexed from the preamble Start, where Provided by total NumberOf RA-Preambles (950, 980). In one embodiment, total Number Of RA-Preambles is the total number of preambles used for random access (contention-based as well as contention-free) and is configured by the gNB. In another embodiment, it is the total number of preambles used for 2-step CBRA. It may be configured by the gNB. Alternatively, it is not configured and it may be equal to [CB-preambles-per-SSB x max(1,SSB-per-rach-occasion)]. If PreambleStartIndex is not signaled for 2-step CBRA, the UE assumes that PreambleStartIndex is zero (950, 960).

[0113] If the CBRA initiated by the UE / GNB is a 4-step CBRA (915), the UE determines the PRACH preamble code for the 4-step CBRA as follows:

[0114] - N1: ssb-perRACH-Occasion configured / signaled by gNB for 4-step CBRA (920)

[0115] -R1: CB-Preambles Per SSB (920) configured / signaled by gNB for 4-step CBRA

[0116] - If N1<1: Preambles starting from preamble index zero to "R1-1" are used for 4-step CBRA (925). The same set of preambles is used for each SSB. In other words, R1 contention-based preambles with consecutive indices associated with the SSB of each valid PRACH opportunity start from preamble index zero.

[0117] - If N1>=1, the R1 contention-based preambles with consecutive indices associated with SS / PBCH blocks nO≤n≤N1-1 for each valid PRACH opportunity are indexed from the preamble Start, where Provided by totalNumberOfRA-Preambles (930). In one embodiment, totalNumberOfRA-Preambles is the total number of preambles used for random access (contention-based and contention-free) and is configured by the gNB. In another embodiment, totalNumberOfRA-Preambles is the total number of preambles used for random access (4-step contention-based and contention-free random access) and is configured by the gNB.

[0118] Fig.10 and Fig.11 A flow chart of determining a random access preamble according to an embodiment of the present disclosure is shown.

[0119] Embodiment 2-3: In one embodiment of the present disclosure, it is recommended that the parameter ssb-perRACH-OccasionAndCB-PreamblesPerSSB be signaled separately by the gNB for 2-step CBRA and 4-step CBRA in SIB1 and dedicated RRC signaling messages (e.g., RRC reconfiguration). For 2-step CBRA, the parameter ssb-per RACH-OccasionAndCB-PreamblesPerSSB is optionally signaled by the gNB. If ssb-per RACH-OccasionAndCB-PreamblesPerSSB is not signaled by the gNB for 2-step CBRA, the UE uses the ssb-perRACH-OccasionAndCB-PreamblesPerSSB signaled for 4-step CBRA for 2-step CBRA.

[0120] The ssb-perRACH-OccasionAndCB-PreamblesPerSSB for 2-step CBRA may be configured / signaled by the gNB in ​​the 2-step CBRA configuration (e.g., in the RACH-ConfigCommon IE for 2-step), and the ssb-perRACH-OccasionAndCB-PreamblesPerSSB for 4-step CBRA may be configured / signaled by the gNB in ​​the 4-step CBRA configuration (e.g., in the RACH-ConfigCommon IE for 4-step). Alternatively, the ssb-perRACH-OccasionAndCB-PreamblesPerSSB for 2-step CBRA and the ssb-perRACH-OccasionAndCB-PreamblesPerSSB for 4-step CBRA may be configured / signaled by the gNB in ​​the CBRA configuration (i.e., in the RACH-ConfigCommon IE, which is common to both 2-step and 4-step CBRA). Note that the RACH configuration is per BWP, and the UE uses the RACH configuration corresponding to the BWP on which the random access preamble is transmitted to the UE.

[0121] If the CBRA initiated by the UE / GNB is a 2-step CBRA (1010, 1020, 1110, 1120), the UE determines the PRACH preamble code for the 2-step CBRA as follows:

[0122] - N1: ssb-perRACH-Occasion configured / signaled by gNB for 2-step CBRA (1050, 1140, 1150). In one embodiment, if ssb-perRACH-Occasion is not signaled by gNB for 2-step CBRA, the UE applies ssb-perRACH-Occasion configured / signaled by gNB for 4-step CBRA (1140, 1145); in this case, N1 is equal to N2, where N2 is ssb-perRACH-Occasion configured / signaled by gNB for 4-step CBRA.

[0123] - R1: CB-PreamblesPerSSB configured / signaled by the gNB for 2-step CBRA (1050, 1140, 1150). In one embodiment, if CB-PreamblesPerSSB is not signaled for 2-step CBRA, the UE applies CB-PreamblesPerSSB configured / signaled by the gNB for 4-step CBRA (1140, 1145); in this case, R1 is equal to R2, where R2 is the CB-PreamblesPerSSB configured / signaled by the gNB for 4-step CBRA.

[0124] - N2: ssb-perRACH-Occasion configured / signaled by the gNB for 4-step CBRA. If 4-step CBRA is not configured, the UE assumes N2 is equal to zero.

[0125] - R2: CB-PreamblesPerSSB configured / signaled by the gNB for 4-step CBRA.

[0126] - If N1<1: preambles starting from R2 to R2+R1-1 are used for 2-step CBRA (1060, 1160). The same set of preambles is used for each SSB. In other words, R1 contention-based preambles with consecutive indices associated with the SSB of each valid PRACH opportunity start from preamble index R2. In one embodiment, if 4-step CBRA is not configured, the UE assumes R2 equal to zero, i.e., R1 contention-based preambles with consecutive indices associated with the SSB of each valid PRACH opportunity start from preamble index 0. In one embodiment, if the PRACH opportunity is not configured separately for 2-step and 4-step CBRA, R2 is assumed to be zero, i.e., R1 contention-based preambles with consecutive indices associated with the SSB of each valid PRACH opportunity start from preamble index 0. If the PRACH configuration index is configured separately for 2-step and 4-step, the PRACH opportunity is configured separately for 2-step and 4-step CBRA. In one embodiment, if the PRACH preamble is not allocated between 2-step and 4-step CBRA, R2 is assumed to be zero, ie, R1 contention-based preambles with consecutive indices associated with the SSBs of each valid PRACH opportunity start from preamble index 0.

[0127] - If N1>=1, the R1 contention-based preambles with consecutive indices associated with SS / PBCH blocks nO≤n≤N1-1 for each valid PRACH opportunity are indexed from the preamble Start, where Provided by total Number Of RA-Preambles (1070, 1170). In one embodiment, total Number Of RA-Preambles is the total number of preambles used for random access (contention-based as well as contention-free) and is configured by the gNB. In another embodiment, it is the total number of preambles used for 2-step CBRA. It may be configured by the gNB. Alternatively, it is not configured and may be equal to [CB-preambles-per-SSBxmax(1,SSB-per-rach-occasion)]. In one embodiment, if 4-step CBRA is not configured, the UE assumes R2 is equal to zero, i.e., R1 contention-based preambles with consecutive indices associated with SS / PBCH blocks nO≤n≤N1-1 for each valid PRACH opportunity are indexed from the preamble Start, where In one embodiment, if the PRACH opportunity is not configured separately for 2-step and 4-step CBRA, then R2 is assumed to be zero, i.e., R1 contention-based preambles with consecutive indices associated with SS / PBCH blocks nO≤n≤N1-1 for each valid PRACH opportunity are indexed from the preamble Start, where Provided by the total Number Of RA-Preambles. If the PRACH configuration index is configured separately for 2-step and 4-step, then the PRACH occasions are configured separately for 2-step and 4-step CBRA. In one embodiment, if the PRACH preambles are not allocated between 2-step and 4-step CBRA, then R2 is assumed to be zero, i.e., R1 contention-based preambles with consecutive indices associated with SS / PBCH blocks nO≤n≤N1-1 for each valid PRACH opportunity are assigned from the preamble index Start, where Provided by total Number Of RA-Preambles.

[0128] If the CBRA initiated by the UE / GNB is a 4-step CBRA (1020, 1120), the UE determines the PRACH preamble code for the 4-step CBRA as follows:

[0129] - N1: ssb-perRACH-Occasion (1030, 1125) configured / signaled for 4-step CBRA.

[0130] - R1: CB-PreamblesPerSSB (1030, 1125) configured / signaled for 4-step CBRA.

[0131] - If N1<1: Preambles starting from preamble index zero to "R1-1" are used for 4-step CBRA (1035, 1130). The same set of preambles is used for each SSB. In other words, R1 contention-based preambles with consecutive indices associated with the SSB of each valid PRACH opportunity start from preamble index zero.

[0132] - If N1>=1, the R1 contention-based preambles with consecutive indices associated with SS / PBCH blocks nO≤n≤N1-1 for each valid PRACH opportunity are indexed from the preamble Start, where Provided by totalNumberOfRA-Preambles (1040, 1135). In one embodiment, totalNumberOfRA-Preambles is the total number of preambles used for random access (contention-based and contention-free) and is configured by the gNB. In another embodiment, totalNumberOfRA-Preambles is the total number of preambles used for random access (4-step contention-based and contention-free random access) and is configured by the gNB.

[0133] For 2-step CBRA, the gNB may configure / signal the parameter groupBconfigured separately from 4-step CBRA. The UE may determine the random access preambles of random access preamble groups A and B for 2-step CBRA based on the parameter groupBconfigured and numberOfRA-Preambles GroupA configured / signaled by the gNB for 2-step CBRA as follows:

[0134] - Among the contention-based random access preambles associated with an SSB (determined using the method explained previously), the first number Of RA-Preambles Group A random access preambles belong to Random Access Preamble Group A. The remaining random access preambles associated with an SSB belong to Random Access Preamble Group B (if configured).

[0135] In one embodiment, the group B configured / signaled by the gNB for 4-step CBRA and number Of RA-Preambles GroupA are also used for 2-step CBRA.

[0136] The UE selects a preamble among the preambles associated with the selected SSB and the selected preamble group (if multiple groups are configured). If random access preamble group B is configured, the UE selects random access preamble group A or group B based on the Msg3 size or based on the Msg3 size and path loss. The UE also selects a PRACH opportunity from the PRACH opportunities associated with the selected SSB. The UE then transmits the selected preamble in the selected PRACH opportunity.

[0137] Fig.12 A flow chart of determining a random access preamble according to an embodiment of the present disclosure is shown.

[0138] Embodiment 2-4: In one embodiment of the present disclosure, it is recommended that the parameter ssb-perRACH-OccasionAndCB-PreamblesPerSSB be signaled separately by the gNB for 2-step CBRA and 4-step CBRA in SIB1 and dedicated RRC signaling messages (e.g., RRC reconfiguration). For 2-step CBRA, ssb-perRACH-OccasionAndCB-PreamblesPerSSB is optionally signaled by the gNB. If ssb-perRACH-OccasionAndCB-PreamblesPerSSB is not signaled by the gNB for 2-step CBRA, the UE uses the ssb-perRACH-OccasionAndCB-PreamblesPerSSB signaled for 4-step CBRA for 2-step CBRA.

[0139] For 2-step CBRA, the parameter PreambleStartIndex is optionally signaled by the gNB. If PreambleStartIndex is not signaled by the gNB for 2-step CBRA, the UE assumes that PreambleStartIndex is zero. For 4-step CBRA, the parameter PreambleStartIndex is not signaled.

[0140] The ssb-perRACH-OccasionAndCB-PreamblesPerSSB for 2-step CBRA may be configured / signaled by the gNB in ​​the 2-step CBRA configuration (e.g., in the RACH-ConfigCommon IE for 2-step), and the ssb-perRACH-OccasionAndCB-PreamblesPerSSB for 4-step CBRA may be configured / signaled by the gNB in ​​the 4-step CBRA configuration (e.g., in the RACH-ConfigCommon IE for 4-step). Alternatively, the ssb-perRACH-OccasionAndCB-PreamblesPerSSB for 2-step CBRA and the ssb-perRACH-OccasionAndCB-PreamblesPerSSB for 4-step CBRA may be configured / signaled by the gNB in ​​the CBRA configuration (i.e., in the RACH-ConfigCommon IE, which is common for both 2-step and 4-step CBRA). Note that the RACH configuration is per BWP.

[0141] If the CBRA initiated by the UE / GNB is a 2-step CBRA (1210, 1215), the UE determines the PRACH preamble code for the 2-step CBRA as follows:

[0142] -N1: ssb-perRACH-Occasion configured / signaled by gNB for 2-step CBRA (1235, 1245). If ssb-perRACH-Occasion is not signaled for 2-step CBRA, the UE applies ssb-perRACH-Occasion configured / signaled by gNB for 4-step CBRA (1235, 1240). In one embodiment, ssb-perRACH-Occasion is configured in the RACH configuration and is common for both 2-step CBRA and 4-step CBRA.

[0143] - R1: CB-PreamblesPerSSB configured / signaled by the gNB for 2-step CBRA (1235, 1245). If CB-PreamblesPerSSB is not signaled for 2-step CBRA, the UE applies CB-PreamblesPerSSB configured / signaled by the gNB for 4-step CBRA (1235, 1240). In one embodiment, CB-PreamblesPerSSB is configured in the RACH configuration and is common for both 2-step CBRA and 4-step CBRA.

[0144] - If N1<1: Preambles starting from PreambleStartIndex to "PreambleStartIndex+R1-1" are used for 2-step CBRA (1250, 1270). The same set of preambles is used for each SSB. In other words, R1 contention-based preambles with consecutive indices associated with the SSBs for each valid PRACH opportunity start from the preamble index PreambleStartIndex. If PreambleStartIndex is not signaled by the gNB for 2-step CBRA, the UE assumes that PreambleStartIndex is zero (1250, 1255). For example, assume that there are two SSBs with SSB index X and SSB index Y, and N1=1 / 2. SSBX is associated with PRACH opportunity 1 and PRACH opportunity 2; SSBY is associated with PRACH opportunity 3 and PRACH opportunity 4. Note that N1 is 1 / 2, so one SSB is associated with two PRACH opportunities in the association period. SSBX is associated with the R1 preamble starting with preamble index PreambleStartIndex. SSBY is associated with the R1 preamble starting with preamble index PreambleStartIndex.

[0145] -If N1>=1, the R1 contention-based preamble with consecutive indices associated with SSB n0≤n≤N1-1 for each valid PRACH opportunity starts from the preamble index "PreambleStartIndex+nxR1" (1250, 1280). If PreambleStartIndex is not signaled by the gNB for 2-step CBRA, the UE assumes that PreambleStartIndex is zero (1250, 1260). For example, assume that there are four SSBs with SSB index 1, SSB index 2, SSB index 3, and SSB index 4, and N1=2. When N1 is 2, this means that 2 SSBs are associated with one PRACH opportunity. SSB index 1 and SSB index 2 are associated with PRACH opportunity 1; SSB index 3 and SSB index 4 are associated with PRACH opportunity 2. Note that the PRACH opportunities in the association period are numbered sequentially first in the frequency domain and then in the time domain. The SSBs are then mapped to these PRACH opportunities in ascending order of SSB index. The SSBs associated with the PRACH opportunities are numbered sequentially from lower SSB index to higher SSB index. Since SSB index 1 and SSB index 2 are associated with the same PRACH opportunity, the "n" corresponding to these are 0 and 1, respectively. Similarly, SSB index 3 and SSB index 4 are associated with the same PRACH opportunity, so the "n" corresponding to these are 0 and 1, respectively. Therefore, based on the above formula, the R1 preamble associated with SSB index 1 and SSB index 3 starts from "PreambleStartIndex+0*R1" (i.e., PreambleStartIndex). The R1 preamble associated with SSB index 2 and SSB index 4 starts from "PreambleStartIndex+1*R1".

[0146] If the CBRA initiated by the UE / GNB is a 4-step CBRA (1215), the UE determines the PRACH preamble code for the 4-step CBRA as follows:

[0147] - N1: ssb-perRACH-Occasion configured / signaled by gNB for 4-step CBRA (1220). In one embodiment, ssb-perRACH-Occasion is configured in the RACH configuration and is common for both 2-step CBRA and 4-step CBRA.

[0148] - R1: CB-PreamblesPerSSB (1220) configured / signaled by gNB for 4-step CBRA. In one embodiment, ssb-perRACH-Occasion is configured in the RACH configuration and is common for both 2-step CBRA and 4-step CBRA.

[0149] - If N1<1: Preambles starting from preamble index zero to "R1-1" are used for 4-step CBRA (1225). The same set of preambles is used for each SSB. In other words, R1 contention-based preambles with consecutive indices associated with the SSB of each valid PRACH opportunity start from preamble index zero.

[0150] - If N1>=1, the R1 contention-based preambles with consecutive indices associated with SS / PBCH blocks n0≤n≤N1-1 for each valid PRACH opportunity are indexed from the preamble Start, where Provided by totalNumberOfRA-Preambles (1230). In one embodiment, totalNumberOfRA-Preambles is the total number of preambles used for random access (contention-based and contention-free) and is configured by the gNB. In another embodiment, totalNumberOfRA-Preambles is the total number of preambles used for random access (4-step contention-based and contention-free random access) and is configured by the gNB.

[0151] Note that in embodiments where ssb-perRACH-OccasionAndCB-PreamblesPerSSB is always signaled for 2-step CBRA, the condition to check whether ssb-perRACH-OccasionAndCB-PreamblesPerSSB is configured for 2-step CBRA is not performed. Fig.12 The condition to check whether preambleStartIndex is configured for 2-step CBRA is not performed.

[0152] Fig.13 is a block diagram of a terminal according to an embodiment of the present disclosure.

[0153] refer to Fig.13 The terminal includes a transceiver 1310, a controller 1320, and a memory 1330. The controller 1320 may refer to a circuit, an application specific integrated circuit (ASIC), or at least one processor. The transceiver 1310, the controller 1320, and the memory 1330 are configured to execute the following steps: Figures 1 to 12Or the operation of the UE described above. Although the transceiver 1310, the controller 1320, and the memory 1330 are shown as separate entities, they may be implemented as a single entity like a single chip. Alternatively, the transceiver 1310, the controller 1320, and the memory 1330 may be electrically connected or coupled to each other.

[0154] The transceiver 1310 may transmit and receive signals to and from other network entities (eg, base stations).

[0155] The controller 1320 may control the terminal to perform a function according to one of the embodiments described above. For example, the controller 1320 controls the transceiver 1310 and / or the memory 1330 to determine a random access preamble based on the configuration information received from the base station, determine a PRACH opportunity based on the configuration information received from the base station, and transmit a 2-step random access preamble to the base station based on the determination.

[0156] In one embodiment, the operation of the terminal can be implemented using a memory 1330 storing corresponding program codes. Specifically, the terminal can be equipped with a memory 1330 to store program codes for implementing desired operations. In order to perform the desired operation, the controller 1320 can read and execute the program codes stored in the memory 1330 by using a processor or a central processing unit (CPU).

[0157] Fig.14 is a block diagram of a base station according to one embodiment of the present disclosure.

[0158] refer to Fig.14 , the base station includes a transceiver 1410, a controller 1420, and a memory 1430. The controller 1420 may refer to a circuit, an application specific integrated circuit (ASIC), or at least one processor. The transceiver 1410, the controller 1420, and the memory 1430 are configured to execute the following steps: Figures 1 to 12 Or the operation of the base station described above. Although the transceiver 1410, the controller 1420, and the memory 1430 are shown as separate entities, they can be implemented as a single entity like a single chip. Alternatively, the transceiver 1410, the controller 1420, and the memory 1430 can be electrically connected or coupled to each other.

[0159] The transceiver 1410 may transmit and receive signals to and from other network entities (eg, terminals).

[0160] The controller 1420 may control the base station to perform functions according to one of the embodiments described above. For example, the controller 1420 controls the transceiver 1410 and / or the memory 1430 to transmit configuration information for 2-step random access to the terminal, and receives a 2-step random access preamble on a PRACH opportunity based on the configuration information.

[0161] In one embodiment, the operation of the base station can be implemented using a memory 1430 storing corresponding program codes. Specifically, the base station can be equipped with a memory 1430 to store program codes for implementing the desired operation. In order to perform the desired operation, the controller 1420 can read and execute the program code stored in the memory 1430 by using a processor or a central processing unit (CPU).

[0162] While the present disclosure has been shown and described with reference to various embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present disclosure as defined by the appended claims and their equivalents.

[0163] As described above, the embodiments disclosed in the specification and the drawings are only used to present specific examples to easily explain the content of the present disclosure and help understanding, but are not intended to limit the scope of the present disclosure. Therefore, in addition to the embodiments disclosed herein, the scope of the present disclosure should be analyzed to include all changes or modifications based on the technical concept of the present disclosure.

[0164] Although the present disclosure has been described with various embodiments, various changes and modifications may be suggested to one skilled in the art. The present disclosure is intended to encompass such changes and modifications as fall within the scope of the appended claims.

Claims

1. A method performed by a terminal in a wireless communication system, the method comprising: receiving, from a base station, a message including a first physical random access channel (PRACH) configuration index for a four-step random access; In case a 2-step random access is initiated and the message does not include a second PRACH configuration index for the 2-step random access, Identify a random access preamble of the 2-step random access based on the number N of synchronization signal blocks SSBs per PRACH opportunity of the 4-step random access and the number of contention-based preambles per SSB of the 2-step random access; Identifying a PRACH opportunity for the 2-step random access based on a first PRACH configuration index for the 4-step random access; and transmitting a message A (MSGA) including the random access preamble to a base station using the PRACH opportunity of the 2-step random access, Wherein, when the number N of SSBs for each PRACH opportunity of the 4-step random access is less than 1, the contention-based preamble of each SSB of the 2-step random access starts from a preamble index R, R is the number of contention-based preambles for each SSB of the 4-step random access, and Wherein, when the number N of SSBs of each PRACH opportunity of the 4-step random access is greater than or equal to 1, the contention-based preamble of each SSB of the 2-step random access is indexed from the preamble Starting with n, the SSB index, and is the total number of preamble codes of the four-step random access.

2. The method of claim 1, wherein: In case the message includes a second PRACH configuration index for 2-step random access: identifying a random access preamble for the 2-step random access based on the number of SSBs for each PRACH opportunity of the 2-step random access and the contention-based preamble for each SSB of the 2-step random access, and The second PRACH configuration index based on the 2-step random access identifies a PRACH opportunity for the 2-step random access.

3. The method of claim 2, wherein: In case the message includes a second PRACH configuration index for 2-step random access: In case the number of SSBs per PRACH opportunity of a 2-step random access is less than 1, the contention-based preamble for each SSB of the 2-step random access starts from preamble index 0, and In the case where the number of SSBs per PRACH opportunity for a 2-step random access is greater than or equal to 1, the contention-based preamble for each SSB of the 2-step random access is indexed from the preamble Starting with n, the SSB index, and is the total number of preamble codes of the 2-step random access.

4. The method of claim 1, wherein: The message comprises a system information block 1 (SIB1) or a radio resource control RRC reconfiguration message, and The first PRACH configuration index and the second PRACH configuration index are used for a specific uplink bandwidth part BWP.

5. A method performed by a base station in a wireless communication system, the method comprising: Transmitting a message to a terminal, the message including a first physical random access channel PRACH configuration index for four-step random access; as well as In the case of initiating a 2-step random access, receiving a 2-step random access message A (MSG A) from the terminal using a PRACH opportunity, the message A (MSG A) including a random access preamble of the 2-step random access, Wherein, in a case where the message does not include a second PRACH configuration index for 2-step random access, the random access preamble of the 2-step random access is based on the number N of synchronization signal blocks SSBs for each PRACH opportunity of the 4-step random access and the number of contention-based preambles for each SSB of the 2-step random access, Wherein, when the number N of SSBs for each PRACH opportunity of the 4-step random access is less than 1, the contention-based preamble of each SSB of the 2-step random access starts from a preamble index R, where R is the number of contention-based preambles for each SSB of the 4-step random access, Wherein, when the number N of SSBs of each PRACH opportunity of the 4-step random access is greater than or equal to 1, the contention-based preamble of each SSB of the 2-step random access is indexed from the preamble Starting with n, the SSB index, and is the total number of preambles in the 4-step random access, and The PRACH timing is based on the first PRACH configuration index of the 4-step random access.

6. The method of claim 5, wherein: In case the message includes a second PRACH configuration index for 2-step random access: The random access preamble of the 2-step random access is based on the number of SSBs of each PRACH opportunity of the 2-step random access and the contention-based preamble of each SSB of the 2-step random access, and The PRACH opportunity of the 2-step random access is based on the second PRACH configuration index of the 2-step random access.

7. The method of claim 6, wherein: In case the message includes a second PRACH configuration index for 2-step random access: In case the number of SSBs per PRACH opportunity of a 2-step random access is less than 1, the contention-based preamble for each SSB of the 2-step random access starts from preamble index 0, and In the case where the number of SSBs per PRACH opportunity for a 2-step random access is greater than or equal to 1, the contention-based preamble for each SSB of the 2-step random access is indexed from the preamble Starting with n, the SSB index, and is the total number of preamble codes of the 2-step random access.

8. The method of claim 5, wherein: The message comprises a system information block 1 (SIB1) or a radio resource control RRC reconfiguration message, and The first PRACH configuration index and the second PRACH configuration index are used for a specific uplink bandwidth part BWP.

9. A terminal in a wireless communication system, the terminal comprising: Transceiver; as well as A controller is coupled to the transceiver and is configured to: receiving a message including a first physical random access channel PRACH configuration index for 4-step random access from a base station, In case a 2-step random access is initiated and the message does not include a second PRACH configuration index for the 2-step random access, identifying a random access preamble for the 2-step random access based on a number N of synchronization signal blocks SSBs for each PRACH opportunity of the 4-step random access and a number of contention-based preambles for each SSB of the 2-step random access, identifying a PRACH opportunity for the 2-step random access based on a first PRACH configuration index for the 4-step random access, and transmitting a message A (MSGA) including the random access preamble to a base station using the PRACH opportunity of the 2-step random access, Wherein, when the number N of SSBs for each PRACH opportunity of the 4-step random access is less than 1, the contention-based preamble of each SSB of the 2-step random access starts from a preamble index R, R is the number of contention-based preambles for each SSB of the 4-step random access, and Wherein, when the number N of SSBs of each PRACH opportunity of the 4-step random access is greater than or equal to 1, the contention-based preamble of each SSB of the 2-step random access is indexed from the preamble Starting with n, the SSB index, and is the total number of preamble codes of the four-step random access.

10. The terminal according to claim 9, wherein: In case the message includes a second PRACH configuration index for 2-step random access: identifying a random access preamble for the 2-step random access based on the number of SSBs for each PRACH opportunity of the 2-step random access and the contention-based preamble for each SSB of the 2-step random access, and The second PRACH configuration index based on the 2-step random access identifies a PRACH opportunity for the 2-step random access.

11. The terminal according to claim 10, wherein: In case the message includes a second PRACH configuration index for 2-step random access: In case the number of SSBs per PRACH opportunity of a 2-step random access is less than 1, the contention-based preamble for each SSB of the 2-step random access starts from preamble index 0, and In the case where the number of SSBs per PRACH opportunity for a 2-step random access is greater than or equal to 1, the contention-based preamble for each SSB of the 2-step random access is indexed from the preamble Starting with n, the SSB index, and is the total number of preamble codes of the 2-step random access.

12. The terminal according to claim 9, wherein: The message comprises a system information block 1 (SIB1) or a radio resource control RRC reconfiguration message, and The first PRACH configuration index and the second PRACH configuration index are used for a specific uplink bandwidth part BWP.

13. A base station in a wireless communication system, the base station comprising: Transceiver; as well as A controller is coupled to the transceiver and is configured to: transmitting a message to a terminal, the message comprising a first physical random access channel PRACH configuration index for 4-step random access, and In the case of initiating a 2-step random access, receiving a 2-step random access message A (MSG A) from the terminal using a PRACH opportunity, the message A (MSG A) including a random access preamble of the 2-step random access, Wherein, in a case where the message does not include a second PRACH configuration index for 2-step random access, the random access preamble of the 2-step random access is based on the number N of synchronization signal blocks SSBs for each PRACH opportunity of the 4-step random access and the number of contention-based preambles for each SSB of the 2-step random access, Wherein, when the number N of SSBs for each PRACH opportunity of the 4-step random access is less than 1, the contention-based preamble of each SSB of the 2-step random access starts from a preamble index R, where R is the number of contention-based preambles for each SSB of the 4-step random access, Wherein, when the number N of SSBs of each PRACH opportunity of the 4-step random access is greater than or equal to 1, the contention-based preamble of each SSB of the 2-step random access is indexed from the preamble Starting with n, the SSB index, and is the total number of preambles in the 4-step random access, and The PRACH timing is based on the first PRACH configuration index of the 4-step random access.

14. The base station according to claim 13, wherein: In case the message includes a second PRACH configuration index for 2-step random access: The random access preamble of the 2-step random access is based on the number of SSBs of each PRACH opportunity of the 2-step random access and the contention-based preamble of each SSB of the 2-step random access, and The PRACH opportunity of the 2-step random access is based on the second PRACH configuration index of the 2-step random access.

15. The base station according to claim 14, wherein: In case the message includes a second PRACH configuration index for 2-step random access: In case the number of SSBs per PRACH opportunity of a 2-step random access is less than 1, the contention-based preamble for each SSB of the 2-step random access starts from preamble index 0, and In the case where the number of SSBs per PRACH opportunity for a 2-step random access is greater than or equal to 1, the contention-based preamble for each SSB of the 2-step random access is indexed from the preamble Starting with n, the SSB index, and is the total number of preambles of the 2-step random access, The message includes a system information block 1 (SIB1) or a radio resource control RRC reconfiguration message, and The first PRACH configuration index and the second PRACH configuration index are used for a specific uplink bandwidth part BWP.

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